Abstracts

Rationale: Human activities often involve hand-motor responses following external auditory-verbal commands. It has been believed that hand movements are predominantly driven by the contralateral primary sensorimotor cortex, whereas auditory-verbal information is processed in both superior temporal gyri often predominantly on the left side. It remains unknown whether cortical activation in the superior temporal gyrus during an auditory-motor task is affected by laterality of hand-motor responses. Here, event-related gamma-oscillations were intracranially recorded as quantitative measures of cortical activation; we determined how cortical structures were activated by auditory-cued movement using each hand. Methods: We studied 15 right-handed patients with a diagnosis of medically-uncontrolled focal seizures (age range: 6-18 years) who underwent chronic subdural electrocorticography (ECoG) as a part of presurgical evaluation. Five patients underwent the Wada test, which suggested left hemisphere dominance for speech in four patients and bilateral representation in the other. During ECoG recording, each subject completed two auditory-motor tasks (each task assigned to each side of hand). Subjects were instructed to press the button using the thumb when a pre-recorded verbal command saying “Press” was given and not to press the button when a command saying “Do not press” was given. ECoG amplitude modulations were evaluated to map sequential cortical activation elicited by the auditory motor tasks. Results: Regardless of the age of patient, location of seizure focus, or location of structural lesion, auditory-verbal stimuli elicited augmentation of gamma-oscillations in a posterior portion of the superior temporal gyrus, whereas hand-motor responses elicited gamma-augmentation in the pre- and post-central gyri. Neurostimulation of the site showing the largest event-related gamma-augmentation frequently elicited congruent clinical symptoms. The magnitudes of such gamma-augmentation in the superior temporal, pre-central and post-central gyri were significantly larger when the hand contralateral to the recorded hemisphere was used for motor responses, compared to when the ipsilateral hand was. Conclusions: Recording of event-related gamma-oscillations may delineate the cortical network involved in the auditory-motor tasks. The superior temporal gyrus in each hemisphere might play a greater pivotal role when the contralateral hand needs to be used for motor responses, compared to when the ipsilateral hand does. (Supported by NIH grants NS47550 & NS64033 to E. Asano)