Abstracts

Rationale: Broca's Area (BA) has been the focus of extensive research for its role in speech production. To gain new insight into its functional heterogeneity, we performed a combination of electrical brain stimulation (EBS) and electrocorticography (ECoG) on patients implanted with intracranial electrodes. Fusion of high resolution pre-op MR and post-op CT scans allowed us to precisely localize intracranial electrodes over different BA subregions in multiple subjects. Methods: We used EBS to deliver electrical pulses between two electrodes while the patient read or repeated given sentences. Additionally, we recorded ECoG signals during a task in which patients read numbers, number-words, or non-number words aloud. For each electrode in BA, we compared the ECoG responses with the effect of EBS on the patient's ability to produce language. Results: Our findings revealed that only a subset of stimulations within the anatomical boundaries of BA caused speech arrest, and only a subset of electrodes located within BA had broadband activity (i.e., 30-180 Hz) activity during speech production. The EBS and ECoG results were significantly correlated. Our findings also revealed a heterogeneous pattern of electrophysiological responses in various parts of BA during articulation of different classes of stimuli. While an increase in broadband gamma activity preceded speech onset in some but not all BA subregions, the power of this response was greatest during word production and lowest during number production in most of the active BA electrodes. Conclusions: These results suggest that 1) certain regions of BA are more essential for speech production than others; 2) there is significant overlap between EBS and ECoG data; and 3) distinct neural populations in BA may be semantically selective to the numerical vs. non-numerical content of speech.