IMPROVING SPATIAL AND TEMPORAL RESOLUTION IN EVOKED EEG RESPONSES USING SURFACE LAPLACIANS

Spline generated surface Laplacian temporal wave forms are presented a s a method to improve both spatial and temporal resolution of evoked E EG responses. Middle latency and the N1 components of the auditory evo ked response were used to compare potential-based methods with surface Laplacian methods in the time domain. Results indicate that surface L aplacians provide better estimates of underlying cortical activity tha n do potential wave forms. Spatial discrimination among electrode site s was markedly better with surface Laplacian than with potential wave forms. Differences in the number and latencies of peaks, and their top ographic distributions, were observed for surface Laplacian, particula rly during the time period encompassing the middle latency responses. Focal activities were observed in surface Laplacian wave forms and top ographic maps which were in agreement with previous findings from audi tory evoked response studies. Methodological issues surrounding the ap plication of spline methods to the time domain are also discussed. Sur face Laplacian methods in the time domain appear to provide an improve d way for studying evoked EEG responses by increasing temporal and spa tial resolution of component characteristics.