Premorbid brain size is a determinant of functional reserve in abstinent crack-cocaine and crack-cocaine-alcohol-dependent adults

Studies of Alzheimer's disease patients show that individuals with larger p remorbid brains have a later onset of disease, or a lessened severity of co gnitive impairment, or both. This may be due to a "functional reserve" asso ciated with the greater number of neurons and synapses available in larger brains. We used magnetic resonance imaging and the MicroCog Assessment of C ognitive Functioning to examine the association between intracranial volume (premorbid brain size) and neuropsychological function in abstinent crack- cocaine and crack-cocaine-alcohol dependent individuals. There were no sign ificant differences between the crack-only and the crack-alcohol dependent participants in neuropsychological performance or in intracranial volume. T he abstinent cocaine-dependent individuals (both crack-only and crack-alcoh ol) were significantly impaired in many neuropsychological domains. Intracr anial volume accounted for a significant proportion of the variance in neur opsychological performance. This result is consistent with the finding in t he Alzheimer's literature that larger brains can maintain function to a gre ater degree, or for a longer period of time, in the face of cerebral diseas e or insult. Functional reserve may be a heretofore little recognized prote ctive mechanism of the brain that has consequences for the severity of expr ession of cerebral disease or insult throughout life.