Optimal stimuli for detection of intracortical currents, applied to striate cortex of awake macaque monkeys

Macaque monkeys were trained to indicate the presence of electrical stimulation of perifoveal striate cortex via movable microelectrodes or fixed wire electrodes. In several series of experiments, the waveform and laminar position of stimulation were varied while measuring the minimal current needed for reliable detection. The optimal stimulus waveform was found to consist of rectangular, cathodal, current pulses of 200 μs duration applied in trains of 100 at 100 pulses/s. Using microelectrodes, minimum detection thresholds as low as 1 μA were often obtained when such stimuli were applied to layers 3 or 5, but less often when applied to other layers