Cognitive reserve refers to differences in the way people's brains are made up with some people's brains having a denser network of links between brain cells and a higher processing efficiency than others. This difference in brain capacity can be measured, very roughly, by IQ tests and there is evidence to show that a higher IQ is linked to a lower risk of mental-health problems. A study of 1,037 people born between 1972 and 1973 in Dunedin, New Zealand measured their IQ at 7,9 and 11 and assessed them for mental-health problems at 18, 21, 26 and 32. The researchers found that a lower childhood IQ was associated with an increased risk of developing schizophrenia, depression and anxiety and people with lower childhood IQs tended to have more persistent mental-health problems. Higher childhood IQ was associated with an increased risk of mania in adulthood.
Koenen, Karestan C. ... [et al] - Childhood IQ and adult mental disorders: a test of the cognitive reserve hypothesis American Journal of Psychiatry January 2009, 166(1), 50-57