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 worked in a delayed matching-to-sample visual memory task. The brief electrical stimulation was used as a probe to determine when, around the 20 or 50 ms sample presentation, the disruption was most severe. 2. Stimulation within about 200 ms of the sample image onset severely perturbed the animals' ability subsequently to recognize that image. Identical stimulation at other times did not. 3. Thus, the processing during 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.