Motor cortex

The motor cortex is the region of the brain responsible for planning, initiating and controlling voluntary movement. It occupies a strip of the frontal lobe known as the precentral gyrus, running from the top of the brain down towards the ear on each side. Each hemisphere controls the opposite side of the body: the right motor cortex controls movement of the left arm, leg and face, and vice versa. The motor cortex works in close coordination with adjacent areas including the premotor and supplementary motor cortices, which are involved in planning sequences of movement, and with the cerebellum and basal ganglia, which refine and coordinate output.

The representation of the body across the motor cortex is mapped in a distorted way that reflects the precision required for different body parts, a concept visualised as the cortical homunculus. Areas controlling the hands and face take up a disproportionately large amount of motor cortex, reflecting the fine motor control needed for tasks such as writing, speech and manual manipulation. Areas controlling the trunk and legs are smaller by comparison, though still critically important for posture and walking.

After cardiac arrest, hypoxic-ischaemic brain injury can affect the motor cortex, producing weakness or paralysis (hemiplegia or monoplegia) on the contralateral side of the body. The watershed zones between major cerebral arteries, which are particularly vulnerable to global hypoperfusion, sometimes include motor cortex territories. Survivors may also experience more subtle difficulties with fine motor control, coordination or speed of movement, even without obvious weakness.

Physiotherapy and occupational therapy form the cornerstone of motor rehabilitation following brain injury. Neuroplasticity, the brain’s capacity to reorganise and form new connections, allows for significant recovery of motor function over months and years in many patients, particularly with intensive repetitive task practice. Early referral to neurorehabilitation services and setting realistic but ambitious rehabilitation goals are both important.