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Abstinent chronic crack‐cocaine and crackcocaine/alcohol abusers evidence normal hippocampal volumes on MRI despite persistent cognitive impairments

We measured hippocampal volumes and cognitive functioning in crack‐cocaine and crack‐cocaine/alcoholdependent subjects (abstinent approximately 10–12 weeks) compared to age‐matched controls. Cognitive function was evaluated using the computerized MicroCog Assessment of Cognitive Functioning (which includes tests of explicit, declarative memory subserved by the hippocampus). The hippocampal volumes were quantified on T1‐weighted MRIs and were expressed as a proportion of intracranial vault volume. Both subjects and controls showed the larger right versus left hippocampal volume expected in normal anatomy, but we found no differences in hippocampal volume between any of the groups. However, both abstinent cocaine‐dependent subjects and abstinent cocaine/alcohol‐dependent subjects showed persistent cognitive impairments, including deficits in explicit memory. Our results suggest that either: (1) the hippocampus is resistant to structural volume loss in young and middle‐aged cocaine or cocaine/alcohol‐dependent subjects, (2) the hippocampal volume loss suffered by young and middle‐aged cocaine or cocaine/alcohol‐dependent subjects resolves after approximately 3 months of abstinence, or (3) hippocampal atrophy is obscured by the process of gliosis. Further, the cognitive impairments persisting in these abstinent cocaine and cocaine/alcohol‐dependent samples may (1) be unrelated to hippocampal function or (2) be associated with abnormal hippocampal function that is not reflected in MRI measures of overall hippocampal atrophy.