NEURONAL-ACTIVITY IN HUMAN LATERAL TEMPORAL CORTEX DURING SERIAL RETRIEVAL FROM SHORT-TERM-MEMORY

Neuronal activity was recorded extracellularly from 20 populations in the lateral cortex of the left anterior temporal lobe of 11 patients u ndergoing awake craniotomy for epilepsy, during an input-distraction-r etrieval measure of recent verbal memory that also included two later successive retrievals of the same information after additional distrac ting tasks. Changes in activity were determined for each 1 sec epoch i n three major comparisons: (I)the same visual cues used for naming an input to recent memory, naming without a memory component, and a spati al matching task; (2) memory input (MI), distraction (S), and initial cued retrieval(R1) from memory, where object naming was the input to m emory and naming of other objects the distracters; (3) initial retriev al (R1) and the two subsequent serial retrievals of the same informati on (R2, R3). Control comparisons were also made with serial naming and viewing of blank slides, and repeated naming of the same objects. In comparison 1, 13 of the 20 populations showed consistently increased a ctivity during memory input(''memory units''); two others showed chang es during language measures. In comparison 2, a significant proportion of all 20 populations, and the 13 memory units considered alone showe d increased activity in initial epochs of MI and pi, confirming earlie r findings of increased lateral temporal neuronal activity at memory e ntry and initial retrieval. In comparison 3, a significant proportion of the memory units showed increased activity in early epochs of R1 an d decreased activity in late epochs of R3. This decrease in population s with increased activity at R1 was also evident when R1 was compared to R2 or R2 to R3. Control comparisons showed no evidence of general h abituation or decline in activity. Increased neuronal activity occurs in many left temporal neocortical neurons with input and the initial r etrieval of an item from recent verbal memory, and the activity fades rapidly with repeated retrievals.