Chronic microstimulation of cat auditory cortex effective to evoke detection behaviors.

The purpose of this study was to clarify stimulus pulse parameters effective to elicit behaviors of cats trained to detect electric pulse stimuli through chronically implanted electrodes in the primary auditory cortex. One or two pulse parameters were systematically shifted from the standard stimulus consisting of constant-current pulses of amplitude 80 μA, duration 0.2 ms, number of pulses 33, and rate 200 Hz (compatible with interpulse interval 5 ms). Interaction between the pulse amplitude and pulse duration was investigated: although the proportion of stimulus detection responses increased with increasing phase charge (pulse amplitude×pulse duration), a combination of relatively high amplitude during short pulse duration elicited a higher proportion of detection responses when phase charge was constant. Interaction between the number of pulses and interpulse intervals was investigated. We found that the proportion of detection responses is explained by the linear function of two factors, overall charge (phase charge×the number of pulses) and train duration: the proportion of detection responses increased with increasing overall charge and decreasing train duration. Interaction between pulse amplitude and the number of pulses was investigated. We again found that the proportion of detection responses is explained by the linear function of overall charge and train duration in the amplitude-number shift paradigm. Thus, the behavior performance (proportion of detection responses) is a linear time function of overall charge and train duration regardless of the stimulus paradigm. We believe that the findings will contribute to the development of auditory cortex implants for transfer of auditory information directly to the brain.