The differential roles of right and left sides of the brain in memory formation

A series of transitions in chick memory formation, with sharp standard timi ngs, which were revealed by amnestic agents, coincide with a series of brie f windows of enhanced recall ('retrieval events'), repeating with periods o f 16 min (left hemisphere) and 25 min (right). Their timings were recently confirmed by: (1) the demonstration of a brief dip in recall 5 min after ea ch left hemisphere event in the period 0-100 min, (2) spontaneous use of th e eye providing direct input to the hemisphere undergoing an event, and (3) good performance in a delayed match-to-sample task after 100 min, only at times of near, or exact coincidence (400 min) with right and left events. T he exact coincidence is accompanied by a late episode of consolidation, as is a transition in memory formation in the zebra finch with precisely the s ame timing. Linkages between right and left versions of a single experience appear to be established as a result of near coincidences of events. The g reater involvement of the left hemisphere in initiating such interactions a ppears to be responsible for a wide range of asymmetries described for inte rocular transfer and unilateral insult. (C) 1999 Elsevier Science B.V. All rights reserved.