The effect of interstimulus interval change on cortical potentials in paired somatosensory stimuli

Aim: Discrimination of consecutive sensory stimuli is imperative for proper sensory perception and behavioral response. Somatosensory evoked potential responses from the primary sensory cortex with dual stimulation at different interstimulus intervals were analyzed.In addition, capsaicin which is a painful stimulant evaluated contribution to this process. Method: Under urethan anesthesia, the stimulation of the median nerve from the anterior paw of the rats in the control group (n=8) and the baseline somatosensory evoked potential changes with glass electrodes from the primary somatosensory cortex were recorded with paired stimuli at 35, 50, 80, 140 and 500 msec intervals. The latency, duration, amplitude, second response amplitude/first response amplitude fob sensory gating of each response, and the early and late components of both responses were analyzed in different frequency bands. In another rat group (n=8), 20 micrograms of capsaicin was given subcutaneously to the anterior paw, and the same analyzes were performed by repeating the study. Results: As the interstimulus interval increased, the amplitude of the second response, the ratio of the second response amplitude/first response amplitude, the second response time increased and the second response latency decreased statistically. It was found that capsaicin increased the second response time and first response amplitude, decreased the second response amplitude/first response amplitude ratio, and decreased the first response latency. The fact that the area of early high- frequency oscillations (150-400 Hz) in the 2nd response was significantly lower at 35 ms ISI indicates the role of the thalamocortical pathways in the second response at low ISI intervals of early HFO changes.