Depth-of-processing effects on memory encoding after selective amygdalohippocampectomy

Deeper semantic processing improves memory encoding of words. Neuroimaging studies suggest, that left-hemispheric structures, especially the left inferior frontal cortex and the left hippocampus mediate this effect. Therefore, we tested, whether chronic left hippocampal damage in epilepsy patients after selective amygdalohippocampectomy (SAH) diminishes the depth-of-processing effect in an incidental learning task. 16 patients after left SAH, 17 after right SAH and 15 healthy control subjects elaborated on word classification tasks under a non-semantic and two different semantic conditions. Recognition memory for the words was subsequently tested. Although memory in left SAH patients profited less from deeper semantic processing in terms of an absolute increase in the number of recognized words, the relative level of memory impairment compared to the two other groups was identical under the non-semantic and the semantic conditions. The results indicate that chronic left hippocampal damage affects recognition memory largely independent of semantic processing.

Research highlights▶ Left hippocampectomy reduces memory gains by increased depth-of-processing. ▶ This reduction is proportional to overall memory performance. ▶ It is explained by learning deficits of left hippocampectomy patients. ▶ Left hippocampal damage affects memory largely independent of semantic processing.