Brain Anatomy Introduction: Structure & Function | Soton Brain Hub

Brodmann areas are specific regions of the cerebral cortex with distinct functions. Key areas include: Area 1, 2, 3 (somatosensory cortex), Area 4 (primary motor cortex), Area 6 (motor association), Area 8 (eye movement control), Area 9 (motivation), Area 10 (personality), Areas 17-19 (visual cortex), Area 21 (auditory cortex), Area 22 (Wernicke's area for language comprehension), Area 44-45 (Broca's area for speech production), and Area 38 (gustatory cortex). The motor and sensory homunculus maps show disproportionate representation of body parts requiring fine motor control (face, tongue, hands) versus those requiring less control (trunk, legs).

Korbinian Brodmann mapped 52 brain areas based on cytoarchitecture (cell arrangement), creating a map still used today. Area 17 is the primary visual cortex, area 18 is secondary visual cortex. Wilder Penfield mapped motor and sensory functions by stimulating awake patients during surgery, creating the homunculus. This revealed that body parts with more sensory receptors (hand, mouth) have disproportionately large representations. This mapping demonstrates how the brain represents the body and has clinical applications for understanding stroke effects and neurosurgical planning.

Brodmann's 52 areas map the cerebral cortex's functional organization. Primary areas include area 4 (motor cortex), areas 3, 1, 2 (somatosensory cortex), area 17 (visual cortex), and area 41 (auditory cortex). Association areas integrate sensory information for complex functions like spatial awareness and motor planning. The motor homunculus shows that body parts requiring complex movements (hands, tongue, face) have disproportionately large cortical representations, reflecting their importance for skilled motor control. This mapping demonstrates the relationship between body part complexity and neural representation.

Brodmann's areas map functional regions of the brain: primary somatosensory area (parietal lobe) contains a distorted sensory homunculus where body parts with more receptors (hands, lips) are larger; primary motor area (frontal lobe) contains a motor homunculus reflecting movement complexity; primary visual area (occipital lobe), primary auditory area (temporal lobe), and primary olfactory area (medial temporal lobe) process their respective senses. Broca's area (left frontal lobe) coordinates speech production. These areas were mapped through patient studies of brain damage effects.

The cerebral cortex has gyri (ridges) and sulci (grooves) that increase surface area. The central sulcus separates frontal from parietal lobes. The primary motor cortex (precentral gyrus) controls voluntary movements, while the primary sensory cortex (postcentral gyrus) processes sensory information. The occipital lobe contains the visual cortex, and the temporal lobe contains the auditory cortex. Broca's area controls speech production. Brodmann's areas map brain functions based on cellular structure variations, identifying approximately 100 regions. The homunculus is a distorted body map showing how body parts are represented: body parts requiring fine control (face, hands) occupy larger areas in the motor homunculus, while body parts with high sensitivity (lips, tongue) occupy larger areas in the sensory homunculus.

This lecture explains how occlusions in specific cerebral arteries produce characteristic stroke syndromes based on vascular territories: MCA syndrome causes contralateral hemiplegia, sensory loss, aphasia, and visual field deficits; ACA syndrome causes contralateral weakness/sensory loss with lower extremity predominance, urinary/fecal incontinence, and behavioral changes; ICA syndrome presents with combined MCA/ACA features plus potential amaurosis fugax; PCA syndrome causes contralateral homonymous hemianopia; and vertebrobasilar artery syndromes produce brainstem and cerebellar signs including Wallenberg syndrome. The lecture emphasizes connecting vascular anatomy to functional brain regions to interpret patterns of motor, sensory, visual, language, and cognitive impairments in both anterior and posterior circulation strokes.

Traumatic brain injuries (especially gunshot wounds) can cause severe cognitive impairments. The bullet's rotation can damage multiple neural pathways, creating complex syndromes. Localized injuries can produce widespread cognitive deficits because the brain's functional organization is distributed. Oliver Sacks' clinical case studies (like 'The Man Who Mistook His Wife for a Hat') provide detailed examples of how specific brain lesions produce characteristic syndromes, demonstrating the relationship between brain structure and function.

Alzheimer's disease typically begins with memory deterioration, forgetfulness, and personality changes, with depression often coexisting or appearing years before diagnosis. Patients lack awareness of their changes (anosognosia) and deny deficits. Diagnosis is clinical, supported by neuropsychological testing. Neuropathologically, Alzheimer's disease features structural damage including senile plaques, neurofibrillary tangles, neuronal loss, and inflammatory processes, along with loss of cholinergic neurons in the basal nucleus of Meynert. This results in reduced acetylcholine projections to the neocortex, particularly temporal lobes and frontal/parietal association areas.

Dr. Lewin, a neuropathologist, focused on brain injury. He found Anthony suffered one acute subdural hematoma, two acute and sub-acute subarachnoid hematoma, three diffuse subarachnoid hematoma, four cerebral edema and tonsillar herniation, five left anterior parasagittal frontal acute hemorrhagic infarction, six right parasagittal occipital acute hemorrhagic infarction, seven acute hypoxic ischemic encephalopathy, eight diffuse axonal injury, nine thrombosis of superior sagittal and superficial cerebral veins acute, and ten intraparenchymal hemorrhage.

Second semester covers brain pathologies including cerebrovascular disease (ischemic/hemorrhagic strokes), traumatic brain injury (open, closed, diffuse axonal injuries), brain tumors (space-occupying lesions allowing partial reorganization), and neuroinfections (meningitis, encephalitis). Cognitive processes include intelligence (Wechsler scales), executive function (Fuster, Stuss models), and cognitive aging. Neurodegenerative diseases include Alzheimer's, Lewy body dementia, Parkinson's disease dementia, and frontotemporal dementia. Recommended texts include Arango Lasprilla's 'Daño Cerebral' and Ardila's 'Neuropsicología Clínica'.

Neuroimaging uses imaging technology to noninvasively measure brain structure and function, with MRI being the primary modality that includes T1-weighted (dark fluid, white matter white, grey matter grey, used for volume and cortical thickness measurements), T2-weighted (inverted contrast, good for detecting bleeds), diffusion MRI (maps water movement to assess white matter organization using fractional anisotropy), functional MRI (measures BOLD signal to detect brain activity through blood oxygenation changes), and resting state fMRI (examines correlated activity patterns between brain regions, revealing networks like the default mode network associated with conditions like depression).

Neuroimaging serves diagnostic support, understanding disorders, treatment monitoring, and prognosis. Structural imaging shows anatomy (atrophies, tumors, malformations) using MRI sequences (T1, T2, FLAIR) and DTI (water movement revealing neural tracts). Functional imaging shows real-time brain activity using BOLD technique (blood oxygenation changes), PET (glucose metabolism with FDG), and MEG (magnetic signals from neural activity). High-field MRI (3+ Tesla) enables better functional imaging. These techniques demonstrate that psychical activity is material and magnetic.

Brain imaging primarily uses CT and MRI modalities, each with specific applications: CT head without contrast serves as the main screening exam for acute neurological emergencies like stroke, hemorrhage, and trauma; CTA and CTV evaluate cerebral vasculature with contrast; MRI offers superior soft tissue contrast with multiple sequences including T1/T2/FLAIR for structural assessment, diffusion imaging for stroke detection, and susceptibility-weighted imaging for blood products, while MRA provides non-invasive vascular imaging without radiation.

Neuroimaging modalities provide different methods for visualizing and measuring brain structure and function: QSM quantifies iron and calcium concentrations in brain tissue; ASL measures cerebral blood flow and can detect vascular changes in migraines; MRS analyzes metabolite levels (such as NAA for neuronal health, lactate for anaerobic metabolism) to assess tissue damage and recovery; PET uses radioactive tracers like FDG to measure metabolic activity and amyloid binding for Alzheimer's research; SPECT detects blood flow through gamma-ray imaging; CT identifies acute pathologies like hemorrhages and swelling; EEG measures electrical activity on the scalp to detect seizures; and MEG measures magnetic fields generated by brain electrical currents to study frequency-specific brain activity.

CT imaging measures tissue density, appearing as hypodensities (darker) or hyperdensities (brighter), making it ideal for acute stroke evaluation where speed and blood detection are critical; MRI uses magnetism to measure tissue intensity, providing superior detail for tumors, infections, and demyelinating diseases but requiring longer scan times and being contraindicated with metal implants. Key MRI sequences include T1 (anatomical, gray matter darker than white matter), T2 (gray matter brighter than white matter), FLAIR (nulls CSF to highlight periventricular pathology), DWI/ADC (detects acute ischemia through diffusion restriction), and gradient echo/SWI (detects blood products and microbleeds). Vessel imaging via CTA or MRA is essential for stroke workup to identify large vessel occlusions, aneurysms, or AVMs.