BRIEF RETENTION DEFICITS ASSOCIATED WITH CYCLICALLY RECURRING LEFT-HEMISPHERE EVENTS

In the chick, brief episodes of enhanced recall (''retrieval events'') recur approximately every 25 min in recall via the right hemisphere, and every 16 min in recall via the left. These events coincide with, a nd probably cause, the numerous transitions between memory phases desc ribed in the chick.; The most important of these is the transition to long-term memory, which is sometimes held to occur in chicks at about 50 min after learning, a transition picked out as unique by a Variety of effects of amnesia-inducing agents, and by a brief impairment (''di p'') in recall at 55 min. We used a single trial passive avoidance tas k, involving bead pecking, to show that in chicks using only one eye, such dips occur not only at 55 min (in right-eyed chicks only) but als o after each of the subsequent series of left hemisphere events (in le ft-eyed chicks only). Dips in recall appear to result when processes t hat are initiated by left hemisphere retrieval events result in hemisp heric interaction, with one hemisphere (which can be either left or ri ght) holding an inadequate trace (e.g., as a result of monocular train ing). Recall tests under such conditions may involve both the adequate and the inadequate trace, so that performance is impaired. Copyright (C) 1996 Elsevier Science Inc.