[Effect of local cooling of the neocortex on motor responses evoked by intracortical microstimulation in the rabbit]

Effects of local cooling of the neocortical zone around stimulating microelectrode upon thresholds of initiation of vibrissal motor responses to intracortical microstimulation were studied in alert rabbits. The thresholds increased from 10-50 mua to over 200 microA during the cooling of the deep cortical layers to 20 degrees C - the level of blocking the intracortical synaptic transmission within stimulated zone. A transient decrease of the thresholds of vibrissal responses initiation occurred in slow cooling (1 degree C per 1 min) within the temperature range from 30 degrees C to 25 degrees C on the cortical surface. The neuronal excitation evoked by means of low-threshold repetitive microstimulation seems to be due mainly to indirect transsynaptic ways. The same group of vibrissae, however, respond to stimulation currents about 100 microA as to low-threshold trains of stimuli, only the intensity of motor responses being enhanced. Thus, no involvement of long transcortical axons into excitation of cortical zone occurs with ordinary microstimulation which allows the mapping of motor representations in the neocortex without side-effects.