Left and right hemisphere memory traces: their formation and fate. Evidence from events during memory formation in...

In the domestic chick, different versions of a particular learning experience are elaborated by right and left hemispheres (left: selection of cues allowing selection of appropriate response; right: elaboration of relatively complete and unselected record). During memory formation, further processing of the traces is associated with a series of brief points of trace reactivation, which recur with differing periodicity in association with the two hemispheres (16 min: left; 25 min: right). As a result there is a series of near coincidences, which allow interaction between the two traces. The first, at 48-50 min, is associated with such marked changes in what is available to recall that it has been identified as the onset of long-term memory. The period is shown here to begin with a left hemisphere event, which overlaps with a right hemisphere event, beginning at 50 min, in a way that helps to explain why the interaction that occurs at this time is predominantly one in which the left hemisphere accesses right hemisphere material. It is argued that the main change during hemispheric interaction is the establishment of linkages between different trace ''fragments''.