Presentation
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Single-Unit Recordings of Broca’s Area Indicate a More Cognitive Role than Speech Production
Poster E5 in Poster Session E, Thursday, October 26, 10:15 am - 12:00 pm CEST, Espace Vieux-Port
Erin Kunz1, Francis Willett2, Chaofei Fan1, Alisa Levin1, Darrel Deo1, Foram Kamdar1, Donald Avansino2, Leigh Hochberg3, Krishna Shenoy1,2, Jaimie Henderson1; 1Stanford University, 2Howard Hughes Medical Institute, 3Massachusetts General Hospital,Harvard Medical School; Brown University;VA RR&D Ctr. for Neurorestoration and Neurotechnology, Providence, RI
Broca’s area, located in the dominant inferior frontal gyrus (IFG), has long been thought to play a key role in the translation of thought into articulatory motor plans. However, its exact role in speech articulation is under debate [1-6]. In contrast to imaging-based localization of function, neurosurgical studies have increasingly cast doubt on the area’s role in articulatory control, as many patients with focal stroke or surgical resection of Broca’s area have failed to exhibit Broca’s aphasia [7-9]. Recent stimulation studies have shown that stimulation of IFG sites that induce errors in specific “speech” tasks also induce errors in non-speech behaviors, including music production as well as halting manual movements [10-11]. Neural recordings with a higher temporal and spatial resolution than neuroimaging studies may help to clarify the exact function of this area and its role in the cortical language network. Recent studies looking at direct cortical recordings using electrocorticography (ECoG) have shown that IFG is not active during overt speech production, implicating it instead in pre-articulatory lexical, grammatical or phonological processing [12-13]. Here we present data from the first IFG recordings from chronically-implanted intracortical microelectrode arrays during a variety of speech, language and other cognitive tasks. Our results align with previous ECoG studies revealing no discernible activity during overt speech production or motor planning, and implicate this region in having a more significant “domain-general” function [14-15]. A research participant with anarthria due to amyotrophic lateral sclerosis had two 64-channel recording arrays placed in dominant IFG (Brodmann’s area 44) and two in ventral precentral gyrus (area 6v). Most tasks included in this study were conducted in an instructed-delay paradigm: each trial was cued with sequences of displayed text or audio recordings during one or more ‘cue’ periods followed by a ‘go’ period, during which the participant attempted to vocalize the desired response or perform the desired action. We collected recordings during tasks spanning the space of overt speech production; semantic, lexical, phonological and prosodic processing; orofacial and limb movements; working memory; arithmetic; audio and musical processing; and multi-task combinations. While IFG recordings during overt speech production (repetition of single words and sentences, object naming) showed increased modulation from rest during cue presentation, they showed little to no cue-specific modulation that would indicate a direct role in speech production. By contrast, a wide variety of other tasks did evoke cue-specific modulation, such as rhythm repetition, arithmetic, spelling, and auditory working memory. Additionally, a task in which different cognitive operations (e.g. semantic analogy, grammatical manipulation, or repetition) resulted in the same set of spoken answer words showed stronger modulation differences by operation than by answer. Similarly, analyses of tasks that could be sub-divided by operations such as prosody (exclamatory, questioning, statement) and spelling (forwards vs. backwards) showed stronger decodability by operation than by word to which an operation was being applied. Further data collection and analysis will aim to elucidate a unifying role that IFG may play in this diverse set of cognitive tasks.
Topic Areas: Language Production, Speech Motor Control