Abstracts

The cortical regions responsible for word production have been mapped with a variety of techniques, but the dynamic interactions between these cortical regions in real time have yet to be explored in depth. To investigate these interactions we recorded electrocorticographic (ECoG) signals while subjects spoke words in response to either visual or auditory stimuli, and we studied event-related gamma activity flows among different cortical regions. The short-time direct directed transfer function (SdDTF) is a new method for estimating causal interactions between different brain regions. SdDTF evaluates the direction and intensity of EEG activity flows during consecutive short-time epochs, for selected frequency bands. This multichannel approach enables comparisons of the strengths of relations between sites. ECoG signals recorded during two tasks, word repetition (auditory stimulus) and picture naming (visual stimulus), were analyzed. Event-related changes in cortical network interactions were studied with emphasis on 60-140 Hz (high gamma). Auditory word stimuli were associated with activity flows mainly between sites within superior temporal gyrus (STG) and from STG to inferior frontal gyrus (IFG) and to ventral sensorimotor cortex (vSMC); interactions between STG and basal temporal language area (BTLA) were also observed. In the interval between offset of the auditory word stimulus and onset of the verbal response, flows were observed predominantly from STG to IFG and BTLA. Flows between IFG, STG, and vSMC were also present. During picture naming the interval between onset of the stimulus and the verbal response was associated with many bidirectional interactions between IFG and STG, and between IFG, BTLA and vSMC. Spoken responses to both visual and auditory stimuli were associated with relatively fewer interactions, albeit involving all aforementioned sites. Cortical network interactions during word production predictably depend on stimulus modality. These interactions are reflected by changes in high-gamma activity flows between and within cortical regions commonly involved in language processing. (Supported by NINDS R01-NS41598.)