Abstracts

Event-related electrocorticographic gamma activity ([gt]30 Hz) has been demonstrated during word production in perisylvian language cortex, basal temporal cortex, and sensorimotor cortex. Word production is presumed to require dynamic interactions between these cortical regions. We hypothesized that these interactions would occur in gamma frequencies during picture naming and word repetition and that the pattern of interactions with sensorimotor cortex would depend on response modality (speech vs. sign language)., A newly introduced multichannel Event Related Causality (ERC) method was used to determine changes in the direction and intensity of EEG activity flow during consecutive short-time periods, in reference to baseline activity. Normalization of the ERC method enabled comparisons between tasks and subjects. Signals recorded during performance of language tasks were filtered using IIR and FIR filters to investigate their influence on the ERC results. Five sub-bands of 30-120 Hz gamma activity were distinguished on the basis of ERC analysis. ERC measures were examined and compared for spoken vs. signed picture naming, as well as for spoken word repetition., Event-related increases in interaction were observed between hand area of sensorimotor cortex and language-related cortices (perisylvian language cortex, basal temporal cortex) in low gamma frequencies (30-60 Hz) during picture naming with sign language responses. Similar interactions did not occur during spoken naming. The largest interactions between language cortices and mouth area of sensorimotor cortex were observed during spoken word repetition in high gamma frequencies (85-120 Hz). In low frequencies (0-30 Hz), ERC usually showed decreased interactions during both tasks. Comparison of ERC[apos]s calculated for signals filtered with IIR and FIR filters showed quantitative, not qualitative differences., Functional interactions occur between language and sensorimotor cortices during word production. The topographic patterns of interactions with sensorimotor cortex depend on response modality (speech vs. sign language). Dynamic cortical network interactions are reflected by event-related changes in the flow of gamma activity between and within areas known to be involved in language., (Supported by NINDS R01 NS40596.)