Grey matter

Grey matter (or gray matter) is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and both unmyelinated axons and myelinated axons), glial cells (astroglia and oligodendrocytes) and capillaries. Grey matter contains neural cell bodies, in contrast to white matter, which does not and mostly contains myelinated axon tracts. The color difference arises mainly from the whiteness of myelin. In living tissue, grey matter actually has a grey-brown color, which comes from capillary blood vessels and neuronal cell bodies.

Function
Grey matter is made up of neuronal cell bodies. The grey matter includes regions of the brain involved in muscle control, sensory perception such as seeing and hearing, memory, emotions, and speech.

Distribution
Grey matter is distributed at the surface of the cerebral hemispheres (cerebral cortex) and of the cerebellum (cerebellar cortex), as well as in the depths of the cerebrum (thalamus; hypothalamus; subthalamus, basal ganglia - putamen, globus pallidus, nucleus accumbens; septal nuclei), cerebellar (deep cerebellar nuclei - dentate nucleus, globose nucleus, emboliform nucleus, fastigial nucleus), brainstem (substantia nigra, red nucleus, olivary nuclei, cranial nerve nuclei) and spinal grey matter (anterior horn, lateral horn, posterior horn).

Volume and cognition in elderly people
Significant positive correlations have been found between gray matter volume in elderly persons and measures of semantic and short-term memory. No significant correlations with white matter volume were found. These results suggest that individual variability in specific cognitive functions that are relatively well preserved with aging is accounted for by the variability of gray matter volume in healthy elderly subjects.

Volume associated with bipolar disorder
Some structural differences in gray matter may be associated with psychiatric disorders. There was no difference in whole-brain gray matter volume between patients with bipolar I disorder and healthy controls. Subjects with bipolar I disorder had smaller volumes in the left inferior parietal lobule, right superior temporal gyrus, right middle frontal gyrus, and left caudate. Only the volume of the right middle frontal gyrus was correlated with duration of illness and the number of episodes in patients.

Effects of smoking
Older smokers lose grey matter and cognitive function at a greater rate than non-smokers. Chronic smokers who quit during the study lost fewer brain cells and retained better intellectual function than those who continued to smoke.