Poster B66, Tuesday, August 20, 2019, 3:15 – 5:00 pm, Restaurant Hall
Population dynamics in Broca’s area during overt and covert speech
Philémon Roussel1,2, Florent Bocquelet1,2, Stéphan Chabardès3, Blaise Yvert1,2;1INSERM, 2Grenoble-Alpes University, 3Grenoble-Alpes University Hospital
While overt and covert speech have been shown to share overlapping neural substrates, the detailed ensemble dynamics of either form of speech production remain largely unknown. Indeed, the activity of single cortical neurons in speech-related structures have only been described in few particular situations. In particular, the activity of Broca’s area, a region of the inferior frontal gyrus of the dominant hemisphere playing a major role in speech production, has not yet been investigated at the ensemble level. Here, we investigated the intracortical population dynamics within the Broca’s area of a patient undergoing awake surgery and temporarily implanted with a Utah array in the pars triangularis of the left hemisphere. Neural activity was recorded while the subject performed a task driven by cues on a screen. Each trial of the task consisted in reading aloud a short sentence, repeating it aloud and finally repeating it covertly. Over the 96 microelectrodes of the array, 38 putative single units showing stable activity on 33 consecutive trials could be isolated using spike sorting. Their smoothed firing rates were then computed by applying Gaussian kernel convolution on the binned spike times. Trials were divided into annotated intervals belonging to 3 conditions: overt speech, covert speech and silence. Ten cells were found to be significantly modulated across these 3 conditions, two of them showing similar increased activity in overt and covert conditions compared to silence periods, while some others were specific to overt speech. A linear discriminant model was then trained to classify all time samples between the 3 conditions using a relevant set of time-shifted firing rates, selected by a greedy approach. We found that it was possible to classify all overt and covert speech time samples with more than 80% and 70% accuracy, respectively. These results suggest the existence of different global ensemble dynamics specific to either form of speech in Broca’s area, with a subset of units showing similar activity in both cases.
Themes: Speech Motor Control, Computational Approaches
Method: Electrophysiology (MEG/EEG/ECOG)