Episodic memory in depression: the unique contribution of the anterior caudate and hippocampus

Background. Learning and memory impairments in older adults with depression are linked to hippocampal atrophy. However, other subcortical regions may also be contributing to these deficits. We aimed to examine whether anterior caudate nucleus volume is significantly reduced in older adults with depression compared to controls; whether anterior caudate volume is associated with performance on tasks of episodic learning and memory, and if so, whether this association is independent of the effects of the hippocampus. Method. Eighty-four health-seeking participants meeting criteria for lifetime major depressive disorder (mean age = 64.2, S. D. = 9.1 years) and 27 never-depressed control participants (mean age = 63.9, S. D. = 8.0 years) underwent neuropsychological assessment including verbal episodic memory tests [Rey Auditory Verbal Learning Test and Logical Memory (WMS-III)]. Magnetic resonance imaging was conducted, from which subregions of the caudate nucleus were manually demarcated bilaterally and hippocampal volume was calculated using semi-automated methods. Results. Depressed subjects had smaller right anterior caudate (RAC) (t = 2.3, p = 0.026) and poorer memory compared to controls (t = 2.5, p < 0.001). For depressed subjects only, smaller RAC was associated with poorer verbal memory (r = 0.3, p = 0.003) and older age (r =-0.46, p < 0.001). Multivariable regression showed that the RAC and hippocampus volume uniquely accounted for 5% and 3% of the variance in memory, respectively (beta = 0.25, t = 2.16, p = 0.033; beta = 0.19, t = 1.71, p = 0.091). Conclusions. In older people with depression, the anterior caudate nucleus and the hippocampus play independent roles in mediating memory. While future studies examining this structure should include larger sample sizes and adjust for multiple comparisons, these findings support the critical role of the striatum in depression.