Prepulse modulation of somatosensory evoked potentials

Prepulse modulation (PPM) studies are mostly related to brain stem reflexes and prepulse modulation of cortical responses are less. Observation of prepulse inhibition of brain stem reflexes in healthy subjects suggests that this cycle is an auto-protective inhibitory circuit. In this study; We aimed to investigate PPM in the primary sensory cortex with conventional median- Somatosensorial Evoked Potentials (SEP) that can be found in each center and to investigate the presence of a possible inhibitory circuit. 14 healthy volunteers were included in the study. In the first step, median-SEP recordings were performed by test electrical stimulation over the median mixed nerve of the right wrist. In the second step, prepulse stimuli (PP) at the sensory treshold were given with the same site (right hand median digital nerve, ulnar digital nerve, and posterior tibial mixed nerve) and opposite side hand (left hand median digital nerve). PPM-SEP recorded over the left primary sensory cortex. PP stimuli were given at seven intersitimulus intervals (10, 20, 30, 40, 100, 150 and 500 ms) in each region. Median Test-SEP and PPM-SEP responses were compared; PP stimuli from the same side caused a significant decrease in the amplitude of N20-P25 and N20 waves, but no significant difference was observed with opposite stimuli. PP stimuli from the same side with the test stimulation caused prepulse inhibition, whereas the stimuli from the other side did not change. Although our findings did not support a PPM in the primary somatosensory cortex, as in brain stem reflexes, it was suggested that prepulse stimuli given from the same side could lead to inhibition by another mechanism within the cortex.