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Cerebrum

The cerebrum is the largest and uppermost part of the human brain, consisting of two hemispheres connected by the corpus callosum and responsible for higher cognitive processes, voluntary movement, sensory interpretation, and conscious awareness.^[1]^[2] It derives from the telencephalon during embryonic development and encompasses the cerebral cortex, subcortical structures like the basal ganglia, and white matter tracts that facilitate communication between regions.^[3]^[4] The cerebral cortex, the outer gray matter layer of the cerebrum, is highly folded into gyri and sulci to maximize surface area for processing complex information, and it is divided into four main lobes: the frontal lobe (involved in executive functions, decision-making, and motor control), the parietal lobe (processing sensory input like touch and spatial awareness), the temporal lobe (handling auditory information, language comprehension, and memory formation), and the occipital lobe (primarily responsible for visual processing).^[5]^[4] Beneath the cortex lies white matter composed of myelinated axons that transmit signals across the brain, while deeper structures such as the basal ganglia regulate motor control and the limbic system modulates emotions and motivation.^[4]^[6] Functionally, the cerebrum integrates sensory data from the body and environment, enabling learning, problem-solving, reasoning, judgment, and emotional responses; the left hemisphere typically dominates language and logical tasks, while the right excels in spatial and creative abilities, though both collaborate via interhemispheric connections.^[1]^[7] It oversees voluntary actions through the motor cortex and contributes to autonomic regulation indirectly, making it essential for human intelligence and behavior.^[6] Damage to specific cerebrum regions can lead to deficits like aphasia, hemiplegia, or memory impairment, underscoring its role in overall neurological health.^[7]

Anatomy

Lobes and hemispheres

The cerebrum is divided into two largely symmetrical cerebral hemispheres, the left and the right, separated by the deep longitudinal fissure that runs along the midline. These hemispheres are interconnected by the corpus callosum, a thick band of white matter composed of approximately 200 million axons that enables interhemispheric communication and integration of information.^[7] Each cerebral hemisphere is subdivided into four principal lobes, defined by major sulci and fissures: the frontal lobe occupies the anterior portion, the parietal lobe lies superior and posterior to the frontal lobe, the temporal lobe is positioned laterally and inferiorly, and the occipital lobe forms the most posterior region. The frontal lobe encompasses areas responsible for higher executive functions such as planning and decision-making; the parietal lobe integrates sensory information from various modalities; the temporal lobe processes auditory stimuli and contributes to memory formation; and the occipital lobe is primarily dedicated to visual processing.^[8]^[9] The convoluted surface of the cerebrum, known as the cerebral cortex, features alternating ridges called gyri and depressions termed sulci, which increase the surface area for neural processing within the confined skull. Notable sulci include the central sulcus, a prominent vertical groove that demarcates the frontal lobe anteriorly from the parietal lobe posteriorly, and the postcentral sulcus, which bounds the primary somatosensory cortex. Deeper clefts, or fissures, further define lobar boundaries; the longitudinal fissure separates the hemispheres, while the lateral fissure (Sylvian fissure) extends laterally from the midline to separate the temporal lobe from the frontal and parietal lobes above.^[9]^[10] The arterial blood supply to the cerebrum arises from the internal carotid arteries, which provide anterior circulation via the anterior and middle cerebral arteries, and from the vertebral arteries, which contribute to posterior circulation through the basilar artery and posterior cerebral arteries; these systems interconnect at the base of the brain via the circle of Willis, a polygonal anastomotic ring that offers redundancy against vascular occlusion.^[7]

Cerebral cortex

The cerebral cortex forms the outermost layer of gray matter enveloping the cerebrum, serving as the primary site for higher-order neural processing, including perception, decision-making, and executive functions.^[5] It is predominantly composed of the neocortex, a six-layered structure designated as layers I through VI, which exhibits a characteristic laminar organization. Layer I, the molecular layer, is sparsely populated with neurons and rich in dendrites and axons; layers II and III contain small pyramidal and non-pyramidal neurons involved in local and commissural connections; layer IV, the internal granular layer, receives major thalamic inputs; layer V, the internal pyramidal layer, houses large pyramidal neurons that project to subcortical structures; and layer VI provides feedback to the thalamus.^[11] Pyramidal neurons, the predominant excitatory cells in the cortex, are especially prominent in layers III and V, functioning as the main output neurons that relay processed information to other cortical regions, subcortical nuclei, and the spinal cord.^[12] To accommodate its extensive computational demands within the confined space of the skull, the cerebral cortex features a highly folded surface with gyri and sulci, resulting in a total unfolded surface area of approximately 2,500 cm²—roughly the size of a large pillowcase—while the cerebral cortex itself occupies a volume of approximately 700 cm³ (ranging from 600–800 cm³).^[13]^[14] This gyrification increases the cortical surface by 2-3 times compared to a smooth brain, enabling greater neuronal density and interconnectivity essential for complex cognition.^[9] The cortex is further subdivided into cytoarchitectonic regions based on variations in cellular organization, laminar thickness, and staining properties, as systematically mapped by Korbinian Brodmann in the early 20th century. For instance, Brodmann area 4 corresponds to the primary motor cortex, characterized by large pyramidal cells in layer V (Betz cells) for direct motor output, while area 17 represents the primary visual cortex, with a prominent layer IV rich in stellate cells for relaying retinal inputs.^[15]^[5] Functionally, the cerebral cortex is divided into primary sensory and motor areas, which handle basic processing of specific modalities, and association areas, which integrate information across modalities for advanced functions like planning and problem-solving. Primary areas, such as the motor cortex located in the precentral gyrus (Brodmann areas 4 and 6), directly control voluntary movements through somatotopic organization.^[16] In contrast, association areas, exemplified by the prefrontal cortex (Brodmann areas 9-12 and 46), orchestrate executive processes including working memory, decision-making, and behavioral inhibition by synthesizing inputs from multiple sensory and limbic regions.^[17]^[18] Supporting this neuronal architecture, glial cells—primarily astrocytes, oligodendrocytes, and microglia—outnumber neurons in the human cerebral cortex at a ratio of approximately 3:1, providing structural support, insulation via myelination, and metabolic regulation.^[19] These non-neuronal cells play a critical role in synaptic plasticity, modulating neurotransmitter release, clearing excess ions and transmitters from the synaptic cleft, and releasing gliotransmitters that influence long-term potentiation and depression, thereby facilitating learning and adaptive neural circuits.^[20]

Subcortical structures

The subcortical structures of the cerebrum encompass the white matter and deep gray matter nuclei located beneath the cerebral cortex, forming critical pathways and processing centers for neural communication. White matter primarily consists of myelinated axons that facilitate rapid signal transmission between cortical regions, subcortical nuclei, and other brain areas. Key tracts include the internal capsule, a compact bundle of projection fibers that carries motor and sensory information between the cerebral cortex and brainstem or spinal cord, passing between the thalamus and basal ganglia.^[21] Another prominent association tract is the arcuate fasciculus, which arches around the lateral ventricle to connect regions across different cerebral lobes, such as linking frontal and temporal areas to support language and cognitive integration.^[22] The basal ganglia represent a group of interconnected subcortical nuclei involved in modulating voluntary movement and other functions. These include the caudate nucleus and putamen, collectively known as the striatum, which receive excitatory inputs from the cerebral cortex and play a central role in selecting and initiating actions. The globus pallidus, divided into external and internal segments, processes striatal outputs through two opposing pathways: the direct pathway, which facilitates movement by disinhibiting thalamocortical circuits via inhibitory projections from the striatum to the internal globus pallidus, and the indirect pathway, which suppresses unwanted movements by involving additional inhibition through the external globus pallidus and subthalamic nucleus.^[23]^[24] Within the cerebrum, elements of the limbic system contribute to emotional and memory processing. The amygdala, an almond-shaped structure in the medial temporal lobe, evaluates emotional significance, particularly fear and reward, by integrating sensory inputs and projecting to the hypothalamus and prefrontal cortex. The hippocampus, located in the temporal lobe adjacent to the amygdala, is essential for forming declarative memories and spatial navigation, consolidating short-term experiences into long-term storage through connections with the entorhinal cortex.^[25] The lateral ventricles, fluid-filled cavities within the cerebrum, are bordered by subcortical gray matter structures that influence cerebrospinal fluid dynamics and neural support. The caudate nucleus forms the lateral wall of the ventricular body, while the hippocampus borders the temporal horn inferiorly; these interfaces allow gray matter to interact closely with ventricular spaces, aiding in nutrient distribution and waste clearance.^[5]^[26]

Development

Embryonic origins

The embryonic development of the cerebrum begins with the formation of the prosencephalon, or forebrain, as one of the three primary brain vesicles emerging from the neural tube around the fourth week of gestation.^[27] By the fifth week, the prosencephalon subdivides into the telencephalon, which serves as the precursor to the cerebral hemispheres, and the diencephalon, which gives rise to structures such as the thalamus and hypothalamus.^[27] This division marks the initial patterning of the forebrain, with the telencephalon expanding laterally to form the foundational structures of the cerebrum.^[8] Within the telencephalon, neural progenitor cells primarily proliferate in the ventricular zone, a pseudostratified epithelial layer lining the neural tube's lumen.^[28] This proliferation drives the evagination of the telencephalic walls, resulting in the outward bulging that establishes the bilateral cerebral hemispheres around weeks 5 to 6 of gestation.^[29] Key signaling molecules regulate these processes: Sonic hedgehog (SHH), secreted from the prechordal plate and ventral midline, patterns the ventral telencephalon by promoting the specification of progenitor subtypes and inhibiting dorsal fates.^[30] Meanwhile, fibroblast growth factors (FGFs), particularly FGF8 and FGF2 from the rostral forebrain, stimulate progenitor proliferation and expansion in the ventricular zone, contributing to the overall growth of the telencephalon.^[31] By the seventh week of gestation, the choroid plexus begins to form within the telencephalic vesicles, particularly in the lateral ventricles, through the invagination of vascularized ependymal cells that produce cerebrospinal fluid (CSF) to support the developing brain environment.^[32] This structure emerges as a critical component for nutrient transport and hydrodynamics during early cerebral expansion.^[33] Cortical folding initiates later in gestation, with the first gyri and sulci appearing around week 20, driven by tangential expansion of the cortical sheet relative to the underlying white matter, which generates mechanical forces leading to buckling.^[34] This process reflects the differential growth rates between neuronal layers, establishing the foundational sulcal patterns observed in the mature cerebrum.^[35]

Postnatal maturation

Following birth, the human cerebrum undergoes rapid growth, with total brain volume increasing approximately 2.3-fold within the first two years of life, primarily driven by synaptogenesis—the formation of new synapses—and dendritic arborization, which expands neuronal connections to support emerging cognitive abilities.^[36]^[37] This expansion is most pronounced in the cerebral cortex, where gray matter volume increases by over 100% in the first year alone, reflecting the proliferation of synaptic contacts that peak early in postnatal life.^[36] Myelination, the process of insulating axons with myelin sheaths to enhance neural transmission speed, follows a caudal-to-rostral and posterior-to-anterior sequence during postnatal development. It begins in the brainstem and cerebellum shortly after birth and progresses to the cerebral cortex, with subcortical structures like the basal ganglia myelinating earlier than association fibers in the cortex.^[38]^[39] Myelination in sensory and motor pathways completes by early childhood, but higher-order regions such as the prefrontal cortex continue maturing into adolescence, reaching near-adult levels around age 25, which supports the delayed development of executive functions.^[40] Synaptic pruning refines these initial overproductions by eliminating unused connections, enhancing neural efficiency. Synapse density in the cerebral cortex reaches its peak around ages 1–3 years, exceeding adult levels by 50% or more, before declining through selective elimination, with approximately 40% of synapses pruned by late adolescence, particularly in frontal regions.^[37]^[41] This process, guided by activity-dependent mechanisms, shapes circuit specificity and continues gradually into early adulthood. Critical periods of heightened plasticity are prominent in sensory areas during early postnatal stages, allowing environmental inputs to calibrate neural circuits. In the visual cortex, plasticity is maximal during infancy, when disruptions like monocular deprivation can permanently alter binocular vision if not addressed, underscoring the time-limited window for sensory refinement.^[42]^[43] Environmental experiences profoundly influence postnatal cerebral maturation, with enriched settings—such as those providing cognitive stimulation and social interaction—promoting hippocampal volume increases through upregulated brain-derived neurotrophic factor (BDNF) expression, which supports neurogenesis and synaptic plasticity.^[44]^[45] Higher socioeconomic environments, serving as proxies for such enrichment, correlate with larger hippocampal volumes in children, linking experiential factors to structural outcomes.^[44]

Functions

Sensory processing

The cerebrum plays a central role in processing sensory information from the external environment, integrating inputs relayed through thalamo-cortical loops to form coherent perceptions. These loops involve specific thalamic nuclei that act as gateways, relaying sensory signals from peripheral receptors to primary cortical areas while receiving modulatory feedback from higher cortical regions. For instance, the lateral geniculate nucleus (LGN) for vision and the ventral posterior nucleus (VP) for somatosensation transmit ascending information to the cortex, where it is refined through reciprocal connections that enable gating and enhancement of relevant signals. Prefrontal cortical inputs further modulate these loops by influencing attentional selection, amplifying neural responses to behaviorally salient stimuli and suppressing irrelevant ones, thereby shaping perceptual awareness.00582-7)^[46] Visual processing begins in the primary visual cortex (V1) of the occipital lobe, where neurons detect basic features such as edges and orientations, as demonstrated by seminal electrophysiological recordings in cats and monkeys. From V1, information diverges into two major streams: the dorsal pathway, projecting to the parietal lobe for spatial analysis and motion processing, and the ventral pathway, extending to the temporal lobe for object recognition and form identification. This segregation, first proposed based on lesion studies and anatomical tracing in primates, allows the cerebrum to parse complex visual scenes into "what" (identity) and "where" (location) components, with integration occurring in association areas for holistic scene understanding.^[47]^[48] Somatosensory processing occurs primarily in the postcentral gyrus of the parietal lobe, known as the primary somatosensory cortex (S1), which contains a somatotopic map called the sensory homunculus. This map, derived from intraoperative electrical stimulation in humans, represents the body surface in a distorted fashion, with disproportionately large areas for sensitive regions like the hands and face due to denser innervation. Beyond S1, parietal association areas integrate somatosensory data with spatial information from other modalities, contributing to body schema and environmental navigation by encoding object locations relative to the body. Auditory processing is handled in the primary auditory cortex (A1) located in Heschl's gyrus within the superior temporal lobe, featuring a tonotopic organization where neurons are arranged by preferred sound frequencies, mirroring the cochlea's structure. Functional imaging in humans has revealed mirror-symmetric low-to-high frequency gradients along Heschl's gyrus, enabling precise spectral analysis of sounds from low bass tones laterally to high pitches medially. This organization supports the decomposition of complex auditory scenes, such as distinguishing speech from background noise.00669-X) Multisensory integration in the cerebrum occurs prominently in the superior temporal sulcus (STS), where auditory, visual, and somatosensory inputs converge to bind cross-modal cues, enhancing perceptual accuracy. For example, during audiovisual speech perception, STS neurons respond more robustly to congruent lip movements and sounds than to unimodal stimuli, facilitating the McGurk effect where visual cues alter auditory perception. Neuroimaging and electrophysiological studies in humans confirm that this region resolves temporal and spatial discrepancies between modalities, crucial for everyday interactions like face-to-face communication.00241-5)

Motor control

The cerebrum plays a central role in the planning, initiation, and execution of voluntary movements through interconnected cortical and subcortical regions. The primary motor cortex (M1), located in the precentral gyrus of the frontal lobe, serves as the main output area for motor commands, exhibiting a somatotopic organization where different body parts are represented in a distorted map known as the motor homunculus.^[16] This organization allows precise control over contralateral body regions, with larger cortical areas devoted to fine motor skills like those in the hands and face compared to the trunk.^[49] Adjacent to M1, the premotor cortex and supplementary motor area (SMA) contribute to the preparation of complex movement sequences. The premotor cortex integrates sensory cues to guide externally triggered actions, while the SMA specializes in internally generated movements, such as those initiated without external stimuli, facilitating the sequencing and timing of multi-joint actions.^[50] These areas project to M1 to refine motor output before execution.^[51] Subcortical structures, particularly the basal ganglia, modulate motor control via cortico-basal ganglia-thalamo-cortical loops. The direct pathway, involving excitatory projections from the striatum to the internal globus pallidus and substantia nigra pars reticulata, disinhibits thalamocortical neurons to facilitate desired movements.^[23] In contrast, the indirect pathway, through inhibitory connections from the striatum to the external globus pallidus and subthalamic nucleus, suppresses unwanted movements by enhancing inhibition of the thalamus.^[23] These opposing circuits enable selective activation and suppression of motor programs. The cerebellum influences cerebral motor areas indirectly through pontine nuclei relays, providing feedback for movement coordination and error correction. Mossy fiber inputs from the pontine nuclei convey cortical motor signals to cerebellar Purkinje cells, which in turn project via the dentate nucleus and thalamus to modulate activity in M1 and premotor regions, ensuring smooth and accurate trajectories.^[52] This loop refines ongoing movements without direct sensory processing. Voluntary motor signals from the cerebral cortex descend primarily via the corticospinal tract, a pyramidal pathway originating in layer V pyramidal neurons of M1 and premotor areas. Approximately 90% of these fibers decussate at the medullary pyramids, forming the lateral corticospinal tract that innervates spinal motor neurons for skilled, fractionated movements of the limbs, particularly the distal musculature.^[53] The remaining uncrossed fibers form the anterior corticospinal tract for axial and proximal control.^[54]

Cognitive processes

The prefrontal cortex plays a central role in executive functions, including working memory and decision-making. The dorsolateral prefrontal cortex (dlPFC) is particularly involved in the active maintenance and manipulation of information in working memory, enabling tasks that require holding multiple items online for cognitive operations.^[55] Lesion studies and neuroimaging have demonstrated that dlPFC activation correlates with the resolution of cognitive conflicts and the selection of goal-directed actions during decision-making processes.^[56] In contrast, the orbitofrontal cortex (OFC) contributes to reward evaluation by encoding the subjective value of outcomes, facilitating adaptive choices based on anticipated reinforcements.^[57] Disruptions in OFC function impair the ability to integrate emotional and reward signals into decisions, as evidenced by altered valuation in economic choice paradigms.^[58] Language processing in the cerebrum relies on interconnected networks spanning frontal and temporal regions. Broca's area, located in the inferior frontal gyrus, is essential for speech production and the grammatical formulation of language output.^[59] Wernicke's area, situated in the posterior superior temporal gyrus, supports language comprehension by processing semantic content and integrating auditory inputs into meaningful representations.^[60] These areas are linked by the arcuate fasciculus, a white matter tract that enables the rapid transfer of phonological and syntactic information necessary for fluent repetition and discourse.^[61] Functional imaging studies confirm that damage to this pathway disrupts the coordination between production and comprehension, leading to conduction aphasia.^[59] Memory systems in the cerebrum are divided into declarative and procedural types, each supported by distinct subcortical structures. Declarative memory, encompassing episodic recollections of personal events and semantic knowledge of facts, depends on the hippocampus for encoding and retrieval.^[62] Episodic memory involves reconstructing context-specific experiences, while semantic memory stores generalized information independent of personal context, both reliant on hippocampal-medial temporal lobe circuits.^[63] Procedural memory, involving skill acquisition and habit formation such as motor sequences, is mediated by the basal ganglia through reinforcement-based learning loops.^[64] This system operates implicitly, without conscious awareness, contrasting with the explicit nature of declarative recall.^[65] Learning mechanisms underlying memory consolidation include long-term potentiation (LTP), a process of synaptic strengthening observed prominently in the hippocampus. LTP is induced by high-frequency stimulation and requires activation of NMDA receptors, which permit calcium influx to trigger intracellular signaling cascades that enhance AMPA receptor trafficking and synaptic efficacy.^[66] This NMDA-dependent LTP is considered a cellular correlate of learning, as it persists for extended periods and supports the formation of associative memories.30957-6) Experimental evidence from rodent models shows that blocking NMDA receptors prevents LTP and impairs spatial learning tasks.^[66] The default mode network (DMN) facilitates introspective cognitive processes during periods of low external demand. Comprising regions such as the medial prefrontal cortex and posterior cingulate cortex, the DMN activates during mind-wandering, self-referential thought, and autobiographical memory retrieval.^[67] This network's engagement supports internal mentation, allowing the integration of past experiences with future planning outside of focused attention.^[68] Functional connectivity analyses reveal that DMN coherence increases during rest, contrasting with task-positive networks, and its dysregulation is linked to altered introspection in psychiatric conditions.^[67]

Clinical aspects

Associated disorders

The cerebrum is implicated in numerous neurological disorders that disrupt its structure, function, and connectivity, leading to profound cognitive, motor, and behavioral impairments. These conditions often involve degenerative processes, vascular events, trauma, or aberrant neuronal activity, with symptoms manifesting as memory deficits, motor weaknesses, seizures, or psychotic episodes. Pathological changes primarily affect the cerebral cortex and subcortical regions, underscoring the cerebrum's vulnerability to both genetic and environmental insults. Alzheimer's disease, a progressive neurodegenerative disorder, is characterized by the accumulation of amyloid-beta plaques in the extracellular space and hyperphosphorylated tau protein forming neurofibrillary tangles within neurons, predominantly in the cerebral cortex and hippocampus. These pathological hallmarks lead to synaptic dysfunction, neuronal loss, and atrophy, resulting in severe memory impairment, disorientation, and eventual global cognitive decline. As of 2025 estimates, Alzheimer's disease affects approximately 35 million individuals worldwide, representing the leading cause of dementia and imposing a substantial global health burden.^[69] Stroke, a major cerebrovascular event affecting the cerebrum, occurs in two primary forms: ischemic stroke, caused by thrombotic or embolic occlusion of cerebral arteries that reduces blood flow and leads to infarction, and hemorrhagic stroke, resulting from rupture of weakened vessels causing bleeding into brain tissue. These disruptions produce focal neurological deficits depending on the affected arterial territory; for instance, occlusion of the middle cerebral artery (MCA) often results in contralateral hemiparesis, sensory loss, and aphasia due to ischemia in the frontal, parietal, and temporal lobes. Symptoms can emerge acutely, with rapid intervention critical to mitigate permanent cerebral damage. Traumatic brain injury (TBI) frequently involves the cerebrum through direct mechanical forces, leading to cortical contusions—bruising of the gray matter at impact sites—and diffuse axonal injury (DAI) in the underlying white matter tracts. Cortical contusions arise from coup-contrecoup mechanisms, where brain tissue impacts the skull, causing localized hemorrhage and edema, while DAI results from shearing forces that disrupt axonal integrity across widespread cerebral regions. These injuries impair cognitive processing, executive function, and motor coordination, with long-term consequences including chronic headaches, mood disorders, and increased risk of neurodegeneration. Epilepsy manifests in the cerebrum as recurrent seizures due to cortical hyperexcitability, where focal seizures often originate in the temporal lobe, involving abnormal synchronized neuronal firing that spreads to adjacent cortical areas. This hyperexcitability disrupts normal sensory, memory, and emotional processing, producing symptoms such as auras, automatisms, or impaired consciousness during episodes. Management typically involves antiepileptic drugs that modulate neuronal excitability by enhancing inhibitory neurotransmission or suppressing excitatory pathways, thereby reducing seizure frequency and cerebral network instability. Schizophrenia, a chronic psychiatric disorder, features dopaminergic dysregulation in the prefrontal cortex, where excessive dopamine signaling in mesolimbic pathways and hypoactivity in mesocortical projections contribute to positive symptoms like hallucinations and negative symptoms such as apathy. Genetic factors, including mutations in the DISC1 gene, exacerbate this dysregulation by altering neuronal migration, synaptic plasticity, and dopamine receptor function during cerebral development. These prefrontal alterations lead to impaired executive function, working memory deficits, and disorganized thinking, profoundly affecting social and occupational functioning.

Neuroimaging techniques

Magnetic resonance imaging (MRI) is a cornerstone technique for visualizing the cerebrum's structure and function non-invasively. Structural MRI employs T1-weighted and T2-weighted sequences to provide contrast between gray and white matter, with T1 images highlighting anatomical details like cortical thickness and T2 images aiding in the detection of edema or lesions. These sequences typically achieve isotropic resolutions around 1 mm, enabling detailed mapping of cerebral gyri and sulci.^[70] Functional MRI (fMRI) extends this capability by measuring blood oxygenation level-dependent (BOLD) signals to infer neuronal activation in the cerebrum. The BOLD contrast arises from changes in deoxyhemoglobin concentration during increased neural activity, which alters local magnetic susceptibility and T2*-weighted signal intensity.^[71] This method maps task-evoked or resting-state activity across cortical regions, such as language or motor areas, with spatial resolutions of 2-3 mm and temporal resolutions on the order of seconds.^[72] Positron emission tomography (PET) complements MRI by assessing cerebral metabolic activity, particularly through 18F-fluorodeoxyglucose (FDG) uptake, which reflects glucose utilization in the cerebrum. In Alzheimer's disease, FDG-PET reveals characteristic hypometabolism in temporoparietal regions, where reduced uptake quantifies neuronal dysfunction and aids early detection.^[73] Amyloid tracers like 18F-florbetapir further enhance specificity by visualizing beta-amyloid plaques associated with neurodegeneration.^[74] Electroencephalography (EEG) and magnetoencephalography (MEG) provide high temporal resolution for studying dynamic cortical activity in the cerebrum. EEG measures electrical potentials from synaptic currents with millisecond precision, capturing event-related potentials during cognitive tasks.^[75] MEG detects the magnetic fields generated by these currents, offering similar sub-millisecond temporal resolution and improved source localization for superficial cortical sources. Both are invaluable for epilepsy mapping, where they identify seizure onset zones in the temporal or frontal lobes with spatiotemporal accuracy.^[76]^[77] Diffusion tensor imaging (DTI), an advanced MRI variant, elucidates white matter organization in the cerebrum by modeling water diffusion along axonal tracts. It quantifies microstructural integrity using fractional anisotropy (FA), a scalar value between 0 and 1 that indicates directional coherence of diffusion, with higher FA reflecting healthier, more aligned fibers. In the corpus callosum, reduced FA values signal demyelination or axonal loss, as seen in conditions affecting interhemispheric connectivity.^[78] By 2025, neuroimaging of the cerebrum has advanced with ultra-high-field 7T MRI, which boosts signal-to-noise ratios for sub-millimeter resolutions and reveals laminar cortical layering, distinguishing superficial and deep layers in regions like the visual cortex.^[79] Additionally, artificial intelligence (AI) enhances segmentation through deep learning models, automating personalized mapping of cerebral structures with accuracies exceeding 95% and enabling patient-specific atlases from routine scans.^[80]

Comparative anatomy

In mammals

The cerebrum in mammals exhibits a conserved six-layered neocortical structure that has undergone varying degrees of expansion across species, enabling adaptations to diverse ecological niches. In rodents, such as mice and rats, the neocortex is typically lissencephalic, featuring a smooth surface that limits cortical folding but maintains efficient neural packing within a compact brain size.^[81] In contrast, carnivores like cats and dogs, as well as primates, display gyrencephalic brains with folded surfaces that significantly increase the cortical area without proportionally enlarging the overall brain volume, facilitating enhanced sensory and cognitive processing.^[82] This gyrification is linked to the expansion of progenitor cell pools in the subventricular zone during development, a mechanism observed in larger-brained mammals.^[83] Hemispheric asymmetry is a shared feature in mammalian cerebrum, manifesting in lateralized behaviors that parallel functional specializations. For instance, rats exhibit individual-level paw preferences, with approximately 84% showing a consistent bias for one paw in reaching tasks, though without a clear population-level directional asymmetry akin to human handedness.^[84] These asymmetries arise from differential gene expression and connectivity between hemispheres, influencing motor and spatial processing, and are evident in other mammals like mice and non-human primates.^[85] The basal ganglia, a subcortical component integral to the cerebrum's motor and learning functions, show remarkable conservation across mammals, with similar striatal circuits supporting habit formation and action selection. In mice, these circuits, involving direct and indirect pathways in the striatum, underpin motor learning tasks such as lever pressing, mirroring mechanisms in larger mammals.^[86] This homology makes rodent models, particularly mice, valuable for studying basal ganglia dysfunction, as their striatal dopamine modulation closely resembles that in humans and other species used in Parkinson's disease research.^[87] Olfactory processing dominates the cerebrum in many mammals adapted to scent-driven environments, with the piriform cortex serving as the primary olfactory area often enlarged relative to other regions. In dogs, a macrosmatic species, the piriform cortex is prominently expanded to handle the integration of vast olfactory inputs from an extensive receptor repertoire, supporting behaviors like tracking and social recognition.^[88] Conversely, in humans and other primates, this region is relatively reduced in size compared to the expanded neocortex, reflecting a shift toward visual and cognitive dominance.^[81] Cortical organization in mammals universally relies on a columnar architecture, where minicolumns form the basic functional units of the neocortex, each comprising approximately 80-100 neurons arranged radially to process specific sensory or motor features. This minicolumnar structure, first described in seminal electrophysiological studies, is conserved from rodents to primates, providing a modular framework for neural computation despite variations in overall brain size.^[89] Minicolumns integrate inputs vertically while enabling lateral interactions via hypercolumns, ensuring efficient information flow across mammalian species.^[90]

Evolutionary variations

The telencephalon in early vertebrates, such as fish, originated with the pallium serving as a non-laminar sensory integration center that lacks a true layered cortex.^[91] In teleost fishes, this pallium consists of nuclear masses rather than laminar structures, processing multimodal sensory inputs like visual, somatosensory, and gustatory information through pathways such as the preglomerular complex.^[91] These nuclear formations represent an ancestral configuration for higher-order sensory processing, predating the development of cortical lamination in later vertebrates.^[91] In reptiles, evolutionary advancements included the emergence of the dorsal ventricular ridge (DVR), a pallial structure interpreted as a proto-cortex homologous to components of the mammalian neocortex. The DVR receives thalamic inputs and supports visual processing, with subdivisions in species like the iguana (Iguana iguana) dedicated to retinotopic organization of visual fields.^[92] This nuclear-organized region marks a transitional step in telencephalic complexity, enabling more specialized sensory elaboration without the full laminar architecture seen in mammals.^[93] Birds exhibit pallial equivalents to mammalian cortical functions through the hyperpallium, which operates analogously to the association cortex despite its nuclear organization.^[94] The hyperpallium integrates higher cognitive processes, such as multimodal sensory association and spatial memory, mirroring neocortical capabilities in a non-layered format that evolved convergently from reptilian ancestors.^[94] This structure's cytoarchitectonic features, including semi-layered subdivisions, facilitate avian intelligence comparable to that of mammals.^[95] Among primates, the prefrontal cortex underwent significant expansion relative to early mammals, with great apes and humans showing derived increases in size and connectivity that support advanced executive functions.^[96] This expansion is particularly pronounced in hominins, correlating with the advent of systematic tool use around 2.5 million years ago in early Homo species.^[97] The encephalization quotient (EQ), a measure of relative brain size adjusted for body mass, highlights these evolutionary trends, with humans exhibiting an EQ of 7.4–7.8 and dolphins at 5.3, far exceeding the mammalian average and indicating pronounced telencephalic development for cognitive demands.^[98]

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Jun 8, 2024 · The primary function of the motor cortex is to send signals to direct the body's movement. The motor cortex is part of the frontal lobe and is anterior to the ...Missing: association examples
[15]
Motor Cortex (Section 3, Chapter 3) Neuroscience Online
The primary motor cortex, or M1, is located on the precentral gyrus and on the anterior paracentral lobule on the medial surface of the brain.
[16]
Neuroanatomy, Frontal Cortex - StatPearls - NCBI Bookshelf
Within the precentral gyrus and anterior to the primary motor cortex is the prefrontal cortex. The prefrontal cortex is known to be the higher-order association ...Missing: examples planning
[17]
Higher Cortical Functions: Association and Executive Processing ...
Higher-order integrative cortical areas, called association areas, intervene between the sensory inputs and motor outputs.Missing: precentral | Show results with:precentral
[18]
Equal numbers of neuronal and nonneuronal cells make the human ...
Apr 10, 2009 · The ratios between glial cells and neurons in the human brain structures are similar to those found in other primates, and their numbers of ...
[19]
Glia as sculptors of synaptic plasticity - PMC - PubMed Central
Glial cells are non-neuronal cells in the nervous system that are crucial for proper brain development and function. Three major classes of glia in the central ...
[20]
[PDF] Virtual in Vivo Interactive Dissection of White Matter Fasciculi in the ...
The internal capsule is composed of fibers running from the cerebral cortex to the midbrain nuclei, cerebellum, and spinal cord. (motor projections) and of ...
[21]
Stanford Fiber Tractography Lab - Major White Matter Tracts
The arcuate fasciculus (AF) is probably the most well-known association tract. It is so named because it forms an “arc” like trajectory.
[22]
Neuroanatomy, Basal Ganglia - StatPearls - NCBI Bookshelf
The “Direct pathway” is comprised of inhibitory projections from the caudate or putamen. Activity in the “Direct pathway” releases or “disinhibits” motor ...Introduction · Structure and Function
[23]
Basal Ganglia (Section 3, Chapter 4) Neuroscience Online
There are two distinct pathways that process signals through the basal ganglia: the direct pathway and the indirect pathway. These two pathways have opposite ...
[24]
Neuroanatomy, Limbic System - StatPearls - NCBI Bookshelf
The limbic system is an aggregation of brain structures that are generally located lateral to the thalamus, underneath the cerebral cortex, and above the ...Missing: cerebrum | Show results with:cerebrum
[25]
Diverse Thalamocortical Projection Motifs in the Mouse Ventral ...
Oct 23, 2024 · Thalamocortical pathways from the rodent ventral posterior (VP) thalamic complex to the somatosensory cerebral cortex areas are a key model in
[26]
lecture2024-06 | The Human Brain - Yale University
Thalamic nuclei. The Ventral Posterior part of the thalamus provides input to the somatosensory cortex. It is composed of two nuclei: Ventral posterior ...
[27]
[PDF] Harvard-Oxford Atlas 2.0 (HOA2.0) Manual for Segmentation of ...
The lateral border of each ventricle at this level is a gray matter structure called the caudate nucleus (yellow arrow) that bulges into the ventricle and ...Missing: cerebrum | Show results with:cerebrum
[28]
Embryology, Weeks 6-8 - StatPearls - NCBI Bookshelf
Oct 10, 2022 · The prosencephalon later develops into the diencephalon and telencephalon. The diencephalon gives rise to the thalami, hypothalamus, optic ...
[29]
The Basics of Brain Development - PMC - PubMed Central
The most anterior of these embryonic brain vesicles is called the “prosencephalon” which is the embryonic precursor of the forebrain. The middle vesicle is ...
[30]
The human brain at stage 16, including the initial evagination of the ...
The cerebral hemispheres grow rostrally and dorsally, thereby forming the beginning of the longitudinal fissure. Apart from the commissure of the superior ...
[31]
Sonic hedgehog signaling confers ventral telencephalic progenitors ...
Interneurons in the cerebral cortex regulate cortical functions through the actions of distinct subgroups that express parvalbumin, somatostatin or calretinin.Reduced Nkx2. 1 And... · Upregulation Of Shh... · Fig 5. Exogenous Shh...
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FGF signaling is strictly required to maintain early telencephalic ...
The FGF family of extracellular signaling factors has been proposed to play multiple roles in patterning the telencephalon, the precursor to the cerebrum.
[33]
Neuroanatomy, Choroid Plexus - StatPearls - NCBI Bookshelf - NIH
[3] Once the neural tube closes, the choroid plexus of the fourth ventricle is the first to appear around the ninth week of gestation, followed by the ...Introduction · Structure and Function · Embryology · Blood Supply and Lymphatics
[34]
Embryonic blood-cerebrospinal fluid barrier formation and function
Developing choroid plexuses are first detected at E7 in chicks, at E12.5–E13 in rats and mice, and during the seventh week of gestation in humans (Bellairs and ...
[35]
Mechanics of the Spatiotemporal Evolution of Sulcal Pits in the ...
Typically, cortical folding begins during the third trimester of gestation and continues to develop after birth. Initially, primary folds form between 20 and 25 ...
[36]
Dynamic patterns of cortical expansion during folding of the preterm ...
Mar 5, 2018 · During the third trimester of human brain development, the cerebral cortex undergoes dramatic surface expansion and folding.
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A Structural MRI Study of Human Brain Development from Birth to 2 ...
Brain development in the first 2 years after birth is extremely dynamic and likely plays an important role in neurodevelopmental disorders, including autism ...Missing: tripling | Show results with:tripling
[38]
Synaptic density in human frontal cortex — Developmental changes ...
Synaptic density increased during infancy, reaching a maximum at age 1–2 years which was about 50% above the adult mean.Missing: peak | Show results with:peak
[39]
Sequence of central nervous system myelination in human infancy. II ...
We found eight time-related patterns of CNS myelination during the first two postnatal years in autopsied infants.
[40]
Sequence of central nervous system myelination in human infancy. I ...
This study establishes the sequence of myelination in a population of autopsied infants from birth through the second postnatal year.
[41]
Maturation of the adolescent brain - PMC - PubMed Central
The development and maturation of the prefrontal cortex occurs primarily during adolescence and is fully accomplished at the age of 25 years. The development ...
[42]
Pruning recurrent neural networks replicates adolescent changes in ...
May 27, 2022 · Estimates suggest that up to 40% of excitatory synapses are pruned in prefrontal cortex, between the ages of 10 and 30 (13). Studies also ...
[43]
Critical periods of brain development - PubMed
Brain plasticity is maximal at specific time windows during early development known as critical periods (CPs), during which sensory experience is necessary.
[44]
Critical Periods in Vision Revisited | Annual Reviews
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[45]
Association between Income and the Hippocampus | PLOS One
May 4, 2011 · Children from lower income backgrounds had lower hippocampal gray matter density, a measure of volume. This finding is discussed in terms of ...
[46]
Brain-Derived Neurotrophic Factor: A Key Molecule for Memory in ...
Enriched environment (EE) has been shown to increase BDNF levels in the hippocampus ... increase in hippocampal volume following exercise (Erickson et al., 2011).
[47]
Functional organization of thalamocortical relays
Recent research, reviewed in this article, demonstrates complicated circuitry and a rich array of membrane properties underlying the thalamic relay.
[48]
[PDF] hubel-wiesel-1968.pdf - Center for Neural Science
Where the steps are discrete one can try to discover the shape and extent of the regions. In the visual cortex a number of variables remain unchanged, or at ...
[49]
[PDF] Analysis of Visual Behavior - Center for Neural Science
separate visual areas within prestriate cortex (Ungerleider and Mishkin ... the pathways through which visual information reaches these two cor- tical ...
[50]
Detailed somatotopy in primary motor and somatosensory cortex ...
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The Roles of the Cortical Motor Areas in Sequential Movements
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[52]
role of premotor cortex and the supplementary motor area in the ...
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[53]
Contralateral cortico-ponto-cerebellar pathways reconstruction in ...
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[54]
Spinal Reflexes and Descending Motor Pathways (Section 3 ...
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[55]
Corticospinal Tract Lesion - StatPearls - NCBI Bookshelf - NIH
The corticospinal tract controls primary motor activity for the somatic motor system and is a major pathway for voluntary movements. The lateral corticospinal ...
[56]
Dorsolateral Prefrontal Contributions to Human Working Memory
Our findings elucidate the architecture of working memory, providing key neuropsychological evidence for the necessity of dlPFC in the manipulation of verbal ...
[57]
The role of prefrontal cortex in cognitive control and executive function
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[58]
The orbitofrontal cortex: reward, emotion and depression - PMC
The orbitofrontal cortex in primates including humans is the key brain area in emotion, and in the representation of reward value and in non-reward, ...Missing: seminal | Show results with:seminal
[59]
The neural code of reward anticipation in human orbitofrontal cortex
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[60]
Neuroanatomy, Broca Area - StatPearls - NCBI Bookshelf - NIH
Patients will also lose the ability of repetition, as an intact Broca area, Wernicke's area, and arcuate fasciculus are required to repeat words or phrases.Missing: seminal | Show results with:seminal
[61]
The Neural Architecture of the Language Comprehension ... - Frontiers
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[62]
Functional Contributions of the Arcuate Fasciculus to Language ...
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[63]
Hippocampus | Neuroscience Journal | Wiley Online Library
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[64]
Episodic and declarative memory: role of the hippocampus - PubMed
The idea is that the hippocampus is necessary for remembering ongoing life's experiences (episodic memory), but not necessary for the acquisition of factual ...Missing: procedural basal ganglia
[65]
The role of the basal ganglia in learning and memory
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[66]
Procedural and Declarative Memory Brain Systems in ... - NIH
The aim of the current study was to examine microstructural differences in white matter relevant to procedural and declarative memory between adolescents/young ...Missing: seminal | Show results with:seminal
[67]
NMDA Receptor-Dependent Long-Term Potentiation and Long ...
Calcium influx through synaptic NMDA receptors triggers long-term potentiation (LTP) and long-term depression (LTD). AMPA receptors are redistributed to either ...Missing: seminal | Show results with:seminal
[68]
20 years of the default mode network: A review and synthesis
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[69]
The Brain's Default Network and its Adaptive Role in Internal ... - NIH
The human brain increases its activity across a set of midline and lateral cortical brain regions known as the “default network.”
[70]
Joint super-resolution and synthesis of 1 mm isotropic MP-RAGE ...
Most existing algorithms for automatic 3D morphometry of human brain MRI scans are designed for data with near-isotropic voxels at approximately 1 mm resolution ...
[71]
Brain magnetic resonance imaging with contrast dependent ... - PNAS
The results suggest that BOLD contrast can be used to provide in vivo real-time maps of blood oxygenation in the brain under normal physiological conditions.
[72]
Overview of Functional Magnetic Resonance Imaging - PMC - NIH
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[73]
Brain PET in the Diagnosis of Alzheimer's Disease - PMC - NIH
The characteristic spatial distribution of glucose metabolism on brain FDG-PET can help in differentiating AD from other causes of dementia such as ...
[74]
Brain FDG PET and the Diagnosis of Dementia | AJR
We review the role of brain FDG PET in the diagnosis of Alzheimer disease, frontotemporal dementia, dementia with Lewy bodies, and vascular dementia.
[75]
Electroencephalographic imaging of higher brain function - PMC - NIH
High temporal resolution is necessary to resolve the rapidly changing patterns of brain activity that underlie mental function. Electroencephalography (EEG) ...
[76]
Current and Emerging Potential of Magnetoencephalography in the ...
Jan 29, 2017 · Magnetoencephalography offers excellent temporal resolution in the range of sub-milliseconds and very good spatial resolution of few millimeters ...
[77]
Magnetoencephalography-based approaches to epilepsy ...
Jul 12, 2023 · Magnetoencephalography (MEG) is a non-invasive, high temporal and spatial resolution electrophysiological data that provides a valid basis ...
[78]
Diffusion Tensor Imaging, White Matter Lesions, the Corpus ...
DTI assessed fractional anisotropy in the genu and splenium of the corpus callosum. Conventional MRI was used to evaluate for brain infarcts and white ...
[79]
Next-generation MRI scanner designed for ultra-high-resolution ...
Nov 27, 2023 · We designed and built a next-generation 7 Tesla magnetic resonance imaging scanner to reach ultra-high resolution by implementing several advances in hardware.
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Artificial intelligence for brain neuroanatomical segmentation in ...
This literature review aims to synthesise current research on the application of artificial intelligence (AI) for the segmentation of brain neuroanatomical ...Missing: cerebrum | Show results with:cerebrum
[81]
Development and Evolution of the Human Neocortex - PMC
Evolution of the neocortex in mammals is considered to be a key advance that enabled higher cognitive function. However, neo-cortices of different mammalian ...
[82]
[PDF] 5 Evolution and Ontogenetic Development of Cortical Structures
Gyrencephalic nonprimate mammals, such as sheep, ferrets, and cats, also tend to have an expanded SVZ with significantly more bRGCs than lissencephalic mammals.
[83]
Genetic Mechanisms Underlying Cortical Evolution in Mammals - PMC
In this review I propose a journey through the evolutionary history of the cortex in mammals. From the appearance of the six-layered neocortex in an ancestor ...
[84]
Hemispheric asymmetries and brain size in mammals - PMC
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[85]
Asymmetry in the brain influenced the neurological deficits and ...
Dec 22, 2008 · Paw preference in rats is similar to human handedness, which may result from dominant hemisphere of rat brain.Missing: mammals analogous
[86]
Shaping Action Sequences in Basal Ganglia Circuits - PMC
Recent studies suggest that cortico-basal ganglia circuits are important for chunking isolated movements into precise and robust action sequences.
[87]
Basal Ganglia, Movement Disorders and Deep Brain Stimulation
In parkinsonism, the loss of striatal dopamine results in the emergence of oscillatory burst patterns of firing of basal ganglia output neurons, increased ...Missing: conservation mammals
[88]
Canine Olfaction: Physiology, Behavior, and Possibilities for ...
Aug 21, 2021 · Dogs have an extraordinary olfactory capability, which far exceeds that of humans. Dogs' sense of smell seems to be the main sense, ...Missing: enlarged | Show results with:enlarged
[89]
[PDF] Learning a Dictionary of Shape-Components in Visual Cortex
Apr 24, 2006 · ... cortical organi- zation is a well documented fact, e.g., ≈ 80 − 100 neurons in a general column [Mountcas- tle, 1957, 1997] and even 2.5 ...
[90]
The large numbers of minicolumns in the primary visual cortex of ...
Each radial minicolumn contained pyramidal neurons which formed a single bundle of apical dendrites and had a single bundle of descending myelinated axons.
[91]
Non-laminar cerebral cortex in teleost fishes? - PMC - PubMed Central
Instead of the laminar cortex, telencephalic nuclear masses seem to have evolved as the pallium in teleost fishes.
[92]
Visual subdivisions of the dorsal ventricular ridge of the iguana ...
Oct 10, 2002 · The dorsal ventricular ridge (DVR) of reptiles is one of two regions of the reptilian telencephalon that receives input from the dorsal ...Missing: proto- | Show results with:proto-
[93]
Evolution of pallium, hippocampus, and cortical cell types ... - Science
May 3, 2018 · For example, a six-layered neocortex exists only in mammals, and the dorsal ventricular ridge (DVR) is found only in birds and reptiles. The ...Missing: proto- | Show results with:proto-
[94]
A cortex-like canonical circuit in the avian forebrain - Science
Sep 25, 2020 · Despite the nuclear organization of the bird pallium, it has a cyto-architectonic organization that is reminiscent of the mammalian cortex.
[95]
Avian brains and a new understanding of vertebrate brain evolution
The avian hyperpallium has a unique organization that has so far been found only in birds69. This consists of semi-layered subdivisions, and might have evolved ...
[96]
Exceptional Evolutionary Expansion of Prefrontal Cortex in Great ...
Mar 6, 2017 · Great ape and human prefrontal expansion are evolutionarily derived features · Great apes and humans are specialized to favor executive cognitive ...
[97]
A natural history of the human mind: tracing evolutionary changes in ...
Specializations of the granular prefrontal cortex of primates ... The conditions for tool use in primates: implications for the evolution of material culture.
[98]
Neuronal factors determining high intelligence - PMC
Gorillas and chimpanzees have astonishingly low EQs (1.5–1.8 and 2.2–2.5, respectively), and the highest EQs are found in dolphins (5.3) and finally humans (7.4 ...