Brain regions, mapping and challenges
Homeostasis and response • The human nervous system
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Key concepts
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Identification of major brain regions
The cerebral cortex is the outer layer of the largest brain section (the cerebrum) and appears as the folded outer surface. The cerebellum is a smaller, rounded structure at the back and base of the brain. The medulla lies below the cerebellum at the brainstem and connects to the spinal cord. Diagrams label these three structures clearly for rapid identification.
Functions of the cerebral cortex, cerebellum and medulla
The cerebral cortex processes higher-level tasks: conscious thought, intelligence, memory and language processing; specialised cortical areas process vision, hearing, touch and voluntary movement. The cerebellum receives sensory and motor inputs to coordinate posture, balance and fine control of voluntary movements; damage produces uncoordinated movement. The medulla controls autonomic functions such as breathing and heart rate; disruption causes life-threatening loss of vital reflex control.
Mapping brain regions using patients with brain damage
Lesion studies infer function from loss of ability after local damage. Consistent deficits after damage to the same region indicate that the region contributes to that function. Historical examples identify speech production deficits following damage to frontal-lobe areas, providing evidence for localisation of language. Lesion evidence remains valuable because cause (loss of tissue) produces measurable change in behaviour or ability.
Electrical stimulation and MRI scanning for mapping
Direct electrical stimulation briefly activates or disrupts small cortical areas during surgery, causing predictable effects (movement, sensory change or speech disturbance) that reveal function of the stimulated site. Functional MRI (fMRI) measures brain activity by detecting blood-flow changes; increased blood flow in a cortical area during a task indicates involvement in that task. fMRI images show different regions active during vision, speech, movement and writing, supporting the idea of specialised regions.
Limitations and difficulties
Lesion studies are limited by variability in lesion size and location and by brain plasticity that can mask function loss. Electrical stimulation is invasive and restricted to clinical settings. MRI provides indirect measures of activity and has limited temporal resolution and spatial constraints. The brain’s complexity, delicate structure and ethical limits on invasive research make investigation and treatment difficult; these factors restrict experimental design and clinical intervention.
Key notes
Important points to keep in mind