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Clarification of the cortical mechanisms underlying auditory sensory gating may advance our understanding of brain dysfunctions associated with schizophrenia. To this end, data from 9 epilepsy patients who participated in an auditory paired-click paradigm during pre-surgical evaluation and had grids of electrodes covering temporal and frontal lobe were analyzed. A distributed source localization approach was applied to intracranial P50 response and Gating Difference Wave obtained by subtracting the response to second stimuli from the response to first stimuli.Source reconstruction of the P50 showed that the main generators of the response were localized at the temporal lobes. The analysis also suggested that the maximum neuronal activity contributing to the amplitude reduction at the P50 time range (phenomenon of auditory sensory gating) is localized at the frontal lobe.Present findings suggest that while the temporal lobe is the main generator of the P50 component, the frontal lobe seems to be a substantial contributor to the process of sensory gating as observed from scalp recordings.

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We examined the reliability of three traditional P50 auditory event-related potential indices under paired-click conditions: (a) the conditioning response (C), (b) the testing response (T), and (c) the testing to conditioning suppression ratio (T/C). Three alternative indices, (a) the (C - T) difference, (b) the (C - T)/(C + T) adjusted difference, and (c) the (T - T') residualized difference, where T' is the regression of T on C, were also studied. The N100 wave was used as a generalizability check. Although C and T amplitudes were reliably measured by traditional means, the T/C suppression ratio was not. For psychometric reasons that are described, the reliability of the suppression ratio is undermined principally by the correlation between C and T. The C - T difference score is a promising alternative to the unreliable T/C suppression ratio. Theoretical consequences of changed metrics are discussed.

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