Behavioral activation of human hippocampal EEG: Relationship to recent memory

Resting regional brain activity correlates of verbal learning deficit in major depressive disorder

Memory deficits are reported in major depressive disorder (MDD). Prefrontal cortical and mesiotemporal cortical (MTC)/subcortical regions are involved in the Buschke Selective Reminding Task (SRT), a verbal list-learning task. To determine whether depression-related changes in resting brain metabolism explain (in part) the deficits in SRT performance found in MDD, statistical correlation maps were calculated between SRT total recall score (TR) and relative regional cerebral metabolic rate for glucose (rCMRglu), measured by [¹⁸F]-flourodeoxyglucose (FDG) positron emission tomography (PET), in unmedicated, depressed MDD patients (N = 29). Subsequently, to explore hypothesized loss of top-down control in MDD, we compared the correlations between rCMRglu of SRT-relevant regions of the dorsolateral prefrontal cortex (dlPFC) and amygdala in a larger cohort of MDD (N = 60; 29 inclusive) versus healthy controls (HC) (N = 43). SRT performance of patients is on average 0.5 standard deviation below published normative mean. TR and rCMRglu positively correlate in bilateral dorsomedial PFC, dlPFC, dorsal anterior cingulate; negatively correlate in bilateral MTC/subcortical regions, and cerebellum. rCMRglu in dlPFC correlates negatively with that in amygdala in HC but not in MDD. Depression-related changes present in FDG-PET measured resting brain activity may be in part responsible for memory deficit found in MDD.

Intraoperative thermal inactivation of the hippocampus in an effort to prevent global amnesia after temporal lobectomy

In an effort to assess the risk of amnesia after anterior temporal lobectomy (ATL), we conducted localized thermal inactivation (cooling) of the hippocampus with memory testing. Thirty-three ATL patients whose preoperative evaluation suggested risk for postoperative amnesia underwent hippocampal cooling. Cooling consisted of inserting a catheter in the temporal horn and irrigating it with an iced solution until a stable hippocampal temperature of approximately 20 degrees C was reached. Memory was assessed before and after cooling. In 12 of the 33 patients, memory testing was either aborted or suggested poor contralateral support, and the hippocampus was resected in 2 of these patients. The remaining 21 patients showed evidence of contralateral memory support, and the hippocampus was resected in 18. No patient became amnestic. These results suggest that intraoperative hippocampal cooling may be useful in selected cases. However, even among many patients who could cooperate with testing, discomfort, sedation, attentional deficits, confusion, and anxiety made test interpretation difficult.