There are plenty of studies that document grey matter thickening in certain brain areas as a result of meditation or exercise. However, it's often said that the extent of neurogenesis outside of the hippocampus is negligible. So can certain activities promote significant neurogenesis in the adult brain or can grey matter thickening be explained through other mechanisms (e.g. cell migration)?

An excerpt from Wikipedia article on grey matter:

Grey matter (or gray matter) is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and unmyelinated axons), glial cells (astrocytes and oligodendrocytes), synapses, and capillaries. Grey matter is distinguished from white matter in that it contains numerous cell bodies and relatively few myelinated axons, while white matter contains relatively few cell bodies and is composed chiefly of long-range myelinated axons.


Meditation-related increase in grey matter:

  1. https://pubmed.ncbi.nlm.nih.gov/27983555/
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3004979/

Grey matter increase in response to exercise:

  1. https://academic.oup.com/biomedgerontology/article/61/11/1166/630432

1 Answer 1


Except in three specific areas (olfactory bulb, dentate gyrus, SVZ) where neurogenesis continues to occur in adult organisms, it is virtually absent from everywhere else, including the cortex. However, there have been many reports that the grey matter of the cortex, i.e. the zone where cell bodies and their processes reside, can enlarge. Cortical expansion has been linked with changes in dendritic branching, neuronal soma size, synapse size, the number of dendritic spines, and the number of glial cells.

- Diamond MC, Krech D, Rosenzweig MR. The effects of an enriched environment on the histology of the rat cerebral cortex. J Comp Neurol. 1964;123(1):111 119.
- Diamond MC, Law F, Rhodes H, et al. Increases in cortical depth and glia numbers in rats subjected to enriched environment. J Comp Neurol. 1966;128(1):117 126.
- Diamond MC, Lindner B, Raymond A. Extensive cortical depth measurements and neuron size increases in the cortex of environmentally enriched rats. J Comp Neurol. 1967;131(3):357 364.
- Holloway RL. Dendritic branching: some preliminary results of training and complexity in rat visual cortex. Brain Res. 1966;2(4):393 396.
- Volkmar FR, Greenough WT. Rearing complexity affects branching of dendrites in the visual cortex of the rat. Science. 1972;176(4042):1445 1447.
- Greenough WT, Volkmar FR. Pattern of dendritic branching in occipital cortex of rats reared in complex environments. Exp Neurol. 1973;40(2):491 504.
- Uylings HB, Kuypers K, Diamond MC, Veltman WA. Effects of differential environments on plasticity of dendrites of cortical pyramidal neurons in adult rats. Exp Neurol. 1978;62(3):658 677.
- Mollgaard K, Diamond MC, Bennett EL, Rosenzweig MR, Lindner B. Quantitative synaptic changes with differential experience in rat brain. Int J Neurosci. 1971;2(3):113 127.
- West RW, Greenough WT. Effect of environmental complexity on cortical synapses of rats: preliminary results. Behav Biol. 1972;7(2):279 284.
- Altman J, Das GD. Autoradiographic examination of the effects of enriched environment on the rate of glial multiplication in the adult rat brain. Nature. 1964;204(4964):1161 1163.

  • $\begingroup$ So, do you think that neuronal migration from the SVZ is unlikely? $\endgroup$ Oct 11, 2021 at 14:11
  • $\begingroup$ I think you could adapt this answer slightly to make it more directly answer the OP's question about gray matter volume. That is, 1) cortical gray matter is not only cell bodies, a Ramon y Cajal drawing would be a good starting point, and 2) that no migration or new cell birth is necessary for gray matter to thicken. $\endgroup$
    – Bryan Krause
    Oct 11, 2021 at 15:21

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