Ricci, M. 1 , Mohamed, A. 2 , Savage, G. 1 & Miller, L. 2, 3
1 ARC Centre of Excellence in Cognition and its Disorders, Macquarie University, Sydney, Australia
2 Institute of Clinical Neurosciences, Royal Prince Alfred Hospital, Sydney, Australia
3 ARC Centre of Excellence in Cognition and its Disorders, University of Sydney, Australia
Associations between contextual details define our episodic memories. The hippocampus has been proposed to be especially important in associative learning, but not much research has investigated its role in retention of associations versus the retention of individual details. We set out first to determine whether the hippocampus is particularly important to the learning of associations between faces and two types of elements: factual versus contextual. Second, we looked at how focal epilepsy and existence of a hippocampal lesion affect retention of associations versus individual details over delays of 30 minutes, 24 hours and 4 days. We enrolled 21 patients with temporal lobe epilepsy (12 with and 9 without hippocampal lesions), 11 patients with extra-temporal epilepsy (ETE) and 29 control subjects. The patients underwent simultaneous ambulatory EEG. Regression analyses indicated that hippocampal lesions and depression resulted in deficient learning and retention of associations (irrespective of element type). Higher levels of depression also had a negative impact on retention of individual factual details, whereas a hippocampal lesion and seizures during the delay interval were associated with impaired memory for individual contextual details. We conclude that the hippocampus is involved in binding associations and also in learning and retention of individual contextual items.