Abstracts

Some investigators assert that medial temporal structures initially play a critical part in memory, but that a subsequent consolidation process results in the formation of remote cortical memories that no longer rely on this region (Scovile [amp] Milner, 1957; Squire [amp] Alvarez, 1995). However, others have proposed a multiple trace model of memory whereby medial temporal structures remain critical in the retrieval of remote memories indefinitely (Nadel [amp] Moscovitch, 1997). To test these theories, we examined recent and remote autobiographical memory during unilateral hemispheric anesthesia following intracarotid amobarbital injections. We reasoned that greater difficulty with recent than with remote recall following injections contralateral to known medial temporal damage (i.e., producing a temporary state of bilateral medial temporal dysfunction) would support a consolidation theory of memory. In contrast, comparable difficulty recalling recent and remote events would support a multiple trace theory. Following injections ipsilateral to known medial temporal damage, patients were expected to recall both recent and remote autobiographical events.
Sixteen temporal lobe epilepsy patients (11 left, 5 right) with unilateral medial temporal damage underwent intracarotid amobarbital testing both ipsilateral and contralateral to the hemisphere of suspected seizure onset. Two types of temporally distinct autobiographical memory questions were utilized: [quot]recent[quot] items, which assessed memory for events that occurred within the last five years (e.g., What memorable event occurred during your last vacation?), and [quot]remote[quot] items, which assessed memory for events that occurred more than five years ago (e.g., What memorable event occurred during grammar school?). Recent and remote autobiographical memory item scores for both ipsilateral and contralateral injections were compared via paired samples t-tests.
There was no significant difference between recent and remote autobiographical recall following ipsilateral injections. As expected, following injections contralateral to medial temporal damage, recall of recent events was poorer than memory for remote events (t = 2.33, p [lt].04).
These results support the consolidation theory of memory suggesting that medial temporal structures play only a temporary role in autobiographical memory retrieval, where as over time, memory retrieval is supported by structures outside the medial temporal region.
[Supported by: The Epilepsy Foundation through the generous support of the American Epilepsy Society.]