Grey matter

Grey matter is a fundamental component of the central nervous system (CNS), comprising the neuronal cell bodies, dendrites, synapses, unmyelinated axons, neuropil, glial cells, and dense networks of capillaries. It is readily distinguished from white matter by its relatively sparse myelination: white matter consists largely of long-range, myelinated axons, while grey matter contains the processing centres that underpin neurological function. In living tissue grey matter appears light grey with pinkish or yellowish tones due to its vascularity and the presence of neuronal bodies.

Structural Organisation

Grey matter is distributed throughout the brain, cerebellum, brainstem, and spinal cord. In the cerebral hemispheres it forms the outer cerebral cortex, while also occurring in subcortical structures including the thalamus, hypothalamus, subthalamus, basal ganglia, septal nuclei, and the nucleus accumbens. In the cerebellum it forms the cerebellar cortex and surrounds deep nuclei such as the dentate, globose, emboliform, and fastigial nuclei. The brainstem contains grey matter in the cranial nerve nuclei, substantia nigra, red nucleus, and olivary bodies.
In the spinal cord, grey matter appears in a characteristic H-shaped or butterfly-shaped arrangement known as the grey column. This structure comprises:• Anterior grey column – containing motor neurons responsible for voluntary muscle movement.• Posterior grey column – containing sensory synapses receiving input on touch, vibration, and proprioception.• Lateral grey column – involved in autonomic functions.
The left and right sides of the spinal grey matter are connected by the grey commissure. Spinal grey matter is further divided into functional layers termed Rexed laminae, each defined by the distribution and function of neuronal populations.
Developmentally, grey matter volume typically increases throughout early childhood before declining from around the age of eight. Grey matter density, by contrast, continues to rise into early adulthood. Sex-related differences have been noted, with males commonly showing greater volume but lower density relative to females in comparable brain regions.

Functional Significance

Grey matter contains the majority of the CNS neuronal cell bodies and is responsible for information processing, synaptic integration, and neural computation. In the brain it underlies essential cognitive and motor functions, including:• Sensory perception (vision, hearing, touch)• Motor control• Language and speech• Memory formation and consolidation• Emotional regulation• Executive functions such as decision-making and self-control
In the spinal cord, grey matter mediates both sensory reception and motor output. Sensory neurons synapse in the posterior column before their signals ascend via tracts such as the dorsal column–medial lemniscus and spinothalamic pathways. Motor neurons in the anterior column receive signals descending from cortical pathways and relay them to muscles. The lateral column contributes to sympathetic autonomic regulation.

Clinical and Behavioural Associations

Variations in grey matter volume and density have been linked to environmental, behavioural, and physiological factors. High alcohol intake correlates with noticeable reductions in grey matter volume, while long-term cannabis use has been associated with reduced grey matter in regions such as the hippocampus, amygdala, medial temporal cortex, and prefrontal cortex, accompanied in some studies by increased cerebellar grey matter. Short-term cannabis exposure appears not to produce significant structural change.
Meditative practices have been reported to increase grey matter in several cortical regions, indicating neuroplastic adaptation. Video gaming has yielded mixed findings: prolonged action game use has been associated with reductions in hippocampal grey matter, whereas engagement with three-dimensional platform games appears to stimulate hippocampal growth.
Neurodevelopmental and hormonal transitions also influence grey matter. Men and women with similar intelligence scores may have differing proportions of grey and white matter in cortical areas linked to intellectual function. Pregnancy induces long-lasting reductions in grey matter volume in networks related to social cognition, with patterns comparable to those observed during adolescence.

Historical and Linguistic Background

The anatomical term substantia grisea derives from Latin and is used in contemporary terminology to denote grey matter. Although grisea is not attested in classical Latin, it stems from the French gris, meaning grey. Historically, alternative terms such as substantia cana and substantia cinerea have been employed. The former aligns with the classical Latin adjective canus, meaning greyish or whitish, while the latter derives from cinereus, meaning ash-coloured. These descriptors reflect the subtle variations in shade visible in preserved or living neural tissues.
Grey matter remains central to modern neuroscience as the locus of neural integration. Its structural complexity and capacity for plasticity underpin the myriad functions of the human nervous system.