Poster D6, Friday, August 17, 4:45 – 6:30 pm, Room 2000AB

Ageing does not affect excitability of articulatory motor cortex during speech perception

Helen E Nuttall1,2, Gwijde Maegherman2, Patti Adank2;1Lancaster University, UK, 2University College London, UK

It has become increasingly evident that motor areas for speech production activate during speech perception. Such motor activation has been proposed to assist perception of speech, particularly in challenging listening environments. Recent reports suggest that upregulation of activity in motor areas may compensate for impaired speech perception in older adults. However, it is not known how ageing affects the recruitment of articulatory motor cortex during speech perception, in optimal or sub-optimal listening conditions. The aim of the present study was to determine the effect of ageing on the excitability of articulatory motor cortex when listening to speech in quiet, and in varying levels of background noise. We hypothesised that if older adults demonstrate greater recruitment of articulatory motor cortex, then excitability of articulatory motor cortex would be enhanced when listening to speech in challenging conditions, relative to excitability measured in younger adults (H1). If older and younger adults equally recruit articulatory motor cortex, then excitability of articulatory motor cortex would be equivalent (H2). We tested these hypotheses by applying single-pulse Transcranial Magnetic Stimulation (TMS) to the lip area of left M1 to elicit Motor Evoked Potentials (MEPs) to index excitability of articulatory motor cortex. The M1 hand area was also tested as a control site. TMS was applied while subjects listened to clear speech syllables, syllables presented in +10 dB signal-noise-ratio (SNR), 0 dB SNR, and -10 dB SNR. Subjects completed a syllable identification task throughout MEP recording to assess speech perception ability. Twenty younger adult subjects (aged 18-25), and twenty older adult subjects (aged 65-80) participated in this study. Results showed a significant effect of background noise level on the syllable identification task (F(3,114) = 7.40, p < 0.001), as well as an interaction between age group and task (F(3,114) = 5.30, p = 0.002). This was driven by a significant effect of noise on the older group’s ability to perform the syllable task (F(3,57) = 9.57, p < .001), that was not present for the younger group (F(3,57), = 0.36, p = 0.78). Specifically, the older adults were significantly less accurate in the 0 dB SNR condition compared to the younger adults (F(1,38) = 4.54, p = 0.04). There was also a significant effect of background noise level on lip MEPs (F(3,114) = 3.92, p = 0.01). Planned contrasts confirmed that there was a significant reduction in MEP excitability when listening to speech in the 0 dB SNR condition compared to clear speech (F(1,38) = 8.45, p = 0.006). There was no interaction between age group and lip MEPs (F(3,114) = 1.37, p = 0.255). There was no effect of background noise on control hand MEPs (F(3,108) = .89, p = .45). These data indicate that speech-induced facilitation in articulatory motor cortex is suppressed when listening to speech in noise at 0 dB SNR, but this effect is not modulated by ageing (H2). These findings suggest that activity in articulatory motor cortex may be modulated by listening effort, and not background noise level, as previously thought.

Topic Area: Speech Motor Control and Sensorimotor Integration

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