Abstracts

Rationale: Traditionally, the functional role of Broca’s area has been linked to speech production, as its injury causes a language deficit called expressive aphasia. Latest evidence demonstrates that Broca's area also plays a significant role in semantics, most likely by integrating reciprocal interactions with temporal and frontal regions, and formulating an appropriate articulatory code to be executed to corresponding articulatory gestures in the motor cortex (Flinker et al., 2015). In this study, we show that Broca’s area coordinates information flow across large-scale cortical networks, and enriches the pattern of effective connectivity in complex tasks leading to speech production. Methods: Using direct cortical surface recordings of six neurosurgical patients, we studied causal interactions among brain networks during naming to spoken definition and naming of ambiguous images, as well as naming of unambiguous images (Cho-Hisamoto et al., 2015). The interactions were analyzed with the event-related causality (ERC) method, which is a multichannel extension of the Granger causality concept, stating that an observed time series x(t) causes another series y(t), if knowledge of x(t)'s past significantly improves prediction of y(t). ERC gives an estimate of changes in the intensity and direction of neural activity propagation between recording sites as a function of frequency. Results: ERC analysis of “guess what” tasks leading to speech production, i.e. naming to spoken definition and naming of ambiguous images, revealed complex patterns of causal interactions between sensory cortices (auditory or visual), Broca's and other frontal areas, and the executory motor cortex. While naming of unambiguous images resulted in fewer interactions between Broca's area and sensory (visual) as well as executory (motor) subnetworks. However, the pattern of interactions among visual cortex networks during naming of unambiguous images was richer and more intense than for ambiguous images. These effects were observed before response onset, suggesting an integratory role of Broca's area. Conclusions: - Broca’s area integrates information across large-scale networks involved in language processing, and engenders the strategy/plan to be executed by the motor cortex.- Complex processes leading to speech production result in complex patterns of neur Funding: Supported by: R01 NS091139/NS/NINDS NIH HHS (NEC)R01 NS064033/NS/NINDS NIH (EA)