BREVITY OF PROCESSING IN A MNEMONIC TASK

1. A burst of from one to four current pulses of 0.2 ms at 100 Hz was administered bilaterally to medial temporal lobe areas while monkeys w orked in a delayed matching-to-sample visual memory task. The brief el ectrical stimulation was used as a probe to deter mine when, around th e 20 or 50 ms sample presentation, the disruption was most severe. 2. Stimulation within about 200 ms of the sample image onset severely per turbed the animals' ability subsequently to recognize that image. Iden tical stimulation at other times did not. 3. Thus, the processing duri ng encoding, that is accessible to the implanted medial temporal lobe electrodes, appears to occur only in a brief interval associated with receipt of the sensory input.