Generators of the intracranial P50 response in auditory sensory gating

Abstract

Clarification of the cortical mechanisms underlying auditory sensory gating may advance our understanding of brain dysfunctions associated with schizophrenia. To this end, data from nine 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 the intracranial P50 response and the Gating Difference Wave obtained by subtracting the response to the second stimuli from the response to the first stimuli. Source reconstruction of the P50 showed that the main generators of the response were localized in the temporal lobes. The analysis also suggested that the maximum neuronal activity contributing to the amplitude reduction in 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.

Figures

Figure.1

Schematic illustration of the LORETA source localization approach. a.) individual MRI image with intracranial electrodes; b.) position of intracranial electrodes derived from the MRI in 3-dimensional virtual space; c.) segmentation of the cortical surface derived from MRI; d.) grid electrodes superimposed on 3-dimentional reconstruction of individual cortex; e.) Evoked Potentials (EP) recorded from grid electrodes; f.) topographical map of recorded EP superimposed on reconstructed cortex; g) LORETA solutions superimposed on the anatomical cortical reconstruction for an individual brain.

Figure.2

Illustration of EP morphology and GDW waveforms for each individual patient recorded at one of the most prominent electrode.

Figure.3

Results of data analyses for five patients who had grid of electrodes placed over the RIGHT hemisphere. Left panel: voltage grid distribution at the latency of P50 response to the first stimulus. Right panel: corresponding voltage grid distribution at the peak latency of Gating Difference Wave.

Figure.4

Left panel: LORETA results for the P50 source localization. Right panel: Localization results for the Gating Difference Wave source, also calculated with LORETA.

Figure.5

Results of data analyses for five patients who had grid of electrodes placed over the LEFT hemisphere. Left panel: voltage grid distribution at the latency of P50 response to the first stimulus. Right panel: corresponding voltage grid distribution at the peak latency of Gating Difference Wave.

Figure.6

Left panel: LORETA results for the P50 source localization. Right panel: Localization results for the Gating Difference Wave source, also calculated with LORETA