There was also found to be an increased grey matter volume in the right fusiform gyrus.

However, grey matter volume was reduced by up to 25% in the primary visual cortex.

No significant correlations with white matter volume were found.

There was no difference in whole-brain grey matter volume between patients with bipolar I disorder and healthy controls.

However, in the three-year study, both groups of breast cancer survivors were observed to have similar gray and white matter volumes.

Unlike schizophrenia, bipolar disorder has very little differences for gray matter volume.

"The magnitude of this decrease is equivalent to the gray matter volume lost in 10 to 20 years of normal aging," they wrote.

They found that the decrease in gray matter volume was directly linked to the length of time the patient had been in pain.

Overall white matter volume does not appear to decline with age, although there is variation between brain regions.

A proposed alternative way of measuring intelligence is by using grey matter or white matter volume in the brain as an indicator.