Cerebrum

The cerebrum is the largest part of the brain, filling most of the skull. Its outer layer of grey matter — the cerebral cortex — is where conscious thought, perception, memory and voluntary movement are organised. Beneath it, white matter connects regions within and between the two hemispheres. A deep groove separates the left and right hemispheres, each of which largely serves the opposite side of the body.

Key facts

The cerebrum makes up about four-fifths of the brain's weight.
Its cortex is only a few millimetres thick but contains most of its neurons.
Left and right sides specialise loosely — language is usually left-dominant.
The corpus callosum, some 200 million fibres, joins the hemispheres.
Deep grey-matter nuclei within it (such as the basal ganglia) refine movement.

What can go wrong

Damage to the cerebrum — from stroke, injury or tumour — produces effects related to the area involved: weakness, speech problems, visual loss or personality change. Diseases such as Alzheimer's affect the cortex progressively. Epilepsy arises from abnormal electrical activity in the cortex.

Related conditions

Stroke

Related procedures & tests

EEG (electroencephalogram)

Related symptoms

Frequently asked questions

What is the difference between grey and white matter?

Grey matter is rich in neuron cell bodies and does the computing — the cortex is grey matter. White matter is the wiring: bundles of insulated axons (myelin gives the white colour) carrying signals between regions.

Is it true we use only 10% of the brain?

No — that is a myth. Brain imaging shows virtually all of the cerebrum active over the course of a day, and damage to almost any area causes some deficit.

Educational information only. This atlas explains normal anatomy and describes conditions in general terms; it is not medical advice and does not replace assessment by a qualified clinician. If you have symptoms that worry you, seek medical care.