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 timings, which were revealed by amnestic agents, coincide with a series of brief windows of enhanced recall ('retrieval events'), repeating with periods of 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 each left hemisphere event in the period 0-100 min, (2) spontaneous use of the 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. The exact coincidence is accompanied by a late episode of consolidation, as is a transition in memory formation in the zebra finch with precisely the same timing. Linkages between right and left versions of a single experience appear to be established as a result of near coincidences of events. The greater involvement of the left hemisphere in initiating such interactions appears to be responsible for a wide range of asymmetries described for interocular transfer and unilateral insult.