The Effect Of Fixation On Auditory Sensory Gating

BACKGROUND: Sensory gating is the ability of central nervous system to filter out incoming irrelevant sensory stimuli and it's an adaptation to protect the brain from being flooded with irrelevant inputs. Sensory gating is commonly indexed with auditory evoked potential P50. P50 suppression deficit is observed in schizophrenic patients, and this deficit reflects their poor sensory gating.In this research, we studied the effects of fixation on sensory gating. Besides, we designed tasks related with attentional factors to exclude the effect of attentional component of fixation on sensory gating. We used auditory evoked potential N100 to validate the existence of attentional factors in our tasks.METHODS: We used standard paired-click paradigm (PCP) to measure sensory gating. Since standard PCP does not control for eye movement and attentional factors, in addition to standard PCP, we used auditory PCP in three other different paradigms related with fixation and visual attention:(1) participants were asked to press a button when a grating appeared (passive go-nogo task); (2) participants were asked to fixate on a vertical grating during the whole task (grating double task); (3) participants were asked to fixate on a vertical grating during the whole task and press a button when the grating changed its orientation (grating go-nogo task). We acquired auditory evoked potentials through recording electroencephalograms (EEG) on healthy participants, and then we analyzed the P50 and N100 components in the four different paradigms.RESULTS: No significant difference of P50 gating ratio was observed in four different paradigms. In addition, N100 difference score was significantly larger in grating go-nogo task than that in passive double task. This result validated attentional factors in grating go-nogo task.CONCLUSIONS: Fixation has no effect on P50 sensory gating. This result suggests that P50 gating is not influenced by neural pathway of oculomotor control system or different visual inputs. Visual attention also has no effect on P50 sensory gating, suggesting that P50 is a preattentional process.