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Poster E57, Friday, November 10, 10:00 – 11:15 am, Harborview and Loch Raven Ballrooms

Combining TMS and EEG to measure electrophysiological responses to speech after suppression of primary motor cortex

Helen E Nuttall1, Barrie Usherwood1, Patti Adank2, Outi Tuomainen2;1Lancaster University, 2University College London

It has become increasingly evident that primary motor (M1) areas for speech production activate during speech perception. Such motor activation has been proposed to assist perception of speech in non-motor brain areas, such as auditory cortex. Connectivity between M1 and auditory cortex is not completely understood, and it is not known whether activity from M1 contributes to processing in non-motor speech areas. This preliminary pilot study aimed to develop methods to investigate if suppressing M1 activity using Transcranial Magnetic Stimulation (TMS) with either a biphasic or monophasic pulse shape, affects electrophysiological Auditory Event-Related Potentials (AERPs), recorded during perception of clear speech and speech in noise. We hypothesized that if M1 contributes to electrophysiological processing of speech from non-motor brain areas, then decreasing M1 activation will modulate AERPs during speech perception (H1). Conversely, if M1 does not contribute to electrophysiological processing of speech, then decreasing M1 activation will not affect AERPs (H2). We tested these hypotheses by applying repetitive-TMS to the lip area of left M1. TMS was applied at a frequency of 1 Hz to create a temporary virtual lesion in M1 lip area. To investigate the role of TMS pulse shape, half of the subjects had monophasic 1 Hz TMS, and the others had biphasic 1 Hz TMS. To measure electrophysiological processing of speech, we used electroencephalography to record AERPs (N100 and P200) to clear speech and speech in noise. Responses were analysed from Cz, which yielded the largest response. Nine normally-hearing adult subjects (aged 18-40; 4 males) participated in this pilot study. Results indicated that that TMS significantly increased the latency of the N100 component, independent of TMS pulse shape (F(1,7) = 5.6, p = 0.05). There was a trend towards an interaction between TMS and speech type on N100 latency (F(1,7) = 4.79, p = 0.065). Planned contrasts confirmed that there was a marginally significant increase in N100 latency to clear speech post-TMS (t(8) = -2.22, p = 0.057). There was no effect of TMS on N100 amplitude. For P200, there was no significant effect of TMS on latency. However, there was an interaction between TMS and TMS pulse shape on P200 amplitude (F(1,7) = 10.44, p = 0.014). Preliminary data suggest that biphasic TMS may reduce P200 amplitude, and monophasic TMS increase P200 amplitude. These data indicate that combining TMS and EEG is an informative design that has potential to clarify the effects of TMS on the underlying electrophysiology of indirectly connected brain areas, during speech perception. Further data will inform how AERPs are modulated by TMS.

Topic Area: Speech Motor Control and Sensorimotor Integration

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