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Poster D77, Thursday, November 9, 6:15 – 7:30 pm, Harborview and Loch Raven Ballrooms

Speech encoding in the human subthalamic nucleus

Witold Lipski1, Ahmad Alhourani1, Tara Pirnia1, Peter Jones1, Christina Dastolfo-Hromack1, Leah Helou1, Susan Shaiman1, Michael Dickey1, Lori Holt1, Robert Turner1, Julie Fiez1, Mark Richardson1;1University of Pittsburgh

Speech production is disrupted in many neurological diseases that involve the basal ganglia. Notably, hypophonia and hypokinetic dysarthria (characterized by decreased motor gain) are prevalent in patients with Parkinson’s disease (PD). Deep brain stimulation (DBS) of the subthalamic nucleus (STN) produces predictable improvements in other motor symptoms of PD but does not result in consistent improvement in speech and can negatively impact language function. However, neurophysiological models of speech production typically do not account for the involvement of basal ganglia nuclei. To examine the role of the STN in speech production, we recorded STN neuron activity, STN local field potentials (LFP), and spoken acoustics while 14 PD subjects performed a speech task during awake, microelectrode recording-guided DBS surgery. On each trial, subjects were asked to read aloud a consonant-vowel-consonant syllable presented on a computer screen. Spike waveforms were sorted into single- and multi-unit recordings. LFP signals were bandpass filtered into canonical bands (delta 2-4Hz, theta 4-8Hz, alpha 8-12 Hz, beta 13-30Hz and gamma 50-90Hz). Power changes were calculated as a z-score relative to baseline, after applying a Hilbert transform to estimate signal amplitude and phase. First, we found evidence for the participation of STN neurons in speech production. Nearly half of the unit recordings (22 of 45; 13 subjects) showed either increases or decreases in firing rate when aligned to speech onset. STN LFP recordings also showed evidence for modulation related to speech production. Consistent with tracking the motor aspects of speech, we found an increase in gamma power in 13/14 subjects locked to the onset of speech, but not locked to cue presentation. In contrast, theta power increases were locked to cue presentation rather than speech onset (11/14 subjects), and this modulation was associated with an increase in inter-trial phase consistency (ITPC) (7/14 subjects), suggesting a role for theta-encoding in cognitive processing prior to speech onset. Likewise, we observed alpha and beta power decreases locked to cue presentation, but not to speech onset. In a subset of these recordings, we observed differences in both alpha and beta ITPC that were specific to whether the presented stimulus was a real word or a non-word. Lastly, we observed delta power and ITPC increases in relation to both cue presentation and speech onset (11/14 subjects), further suggesting that several types of speech-related information transfer occur within the STN. These results provide a foundation for developing a detailed model of basal ganglia participation in speech.

Topic Area: Speech Motor Control and Sensorimotor Integration

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