Abstracts

Rationale: The cortical operations underlying human behavior are processed dynamically across both spatial and temporal dimensions. Current methods using electrocortical stimulation for cortical mapping in epilepsy patients are cumbersome, inefficient, and do not account for the majority of processes involved in behavior (e.g., attention, decision-making, and response preparation). Our aim was to develop an algorithm for the acquisition and processing of electrocorticographic signals to provide a continuously updated spatiotemporal representation of the regional and distributed cortical networks relevant for human behavior. Methods: Five patients with intractable epilepsy were implanted with subdural grid electrodes for seizure monitoring. A signal acquisition and analysis algorithm was implemented for continuous time-frequency analysis with event detection. We used three different behavioral tasks: 1) a phonological target detection task in which patients were presented with a sequence of syllables and instructed to press a button when a pre-specified target syllable was detected; 2) a visual fixation center-out motor reaching task in which patients were instructed to move a computer cursor; and 3) a word repetition task. Results: For each task, event-locked time-frequency analyses focused on the high-gamma frequency range of oscillations demonstrated a specific spatiotemporal pattern of cortical activation. For task 1, the sequence demonstrated concurrent regional sensory processing of speech syllables in posterior superior temporal gyrus (STG) and speech motor cortex, which transitioned to sequential task-dependent processing in prefrontal cortex (PFC), to the final motor response in the hand sensorimotor cortex. For task 2, cortical activation of frontal eye fields by eye movements to the target location were followed by activation of arm and hand sites. For task 3, hearing a word robustly activated posterior STG (Wernicke’s area), whereas saying a word activated Broca’s area and mouth motor sites. When accounting for the spatiotemporal dynamics of the primary somato-motor and -sensory sites of activation, we found both high sensitivity and specificity with electrocortical stimulation. Conclusions: Large-scale rapid parallel and serial processing in sensory, cognitive, and motor structures underlies goal-directed human behavior. Electrocorticographic spectral mapping is a promising method for rapidly and more completely mapping the cortical organization of human behavior in patients undergoing evaluation for resective epilepsy surgery.