Abstracts

Rationale: Electrical cortical stimulation (ECS) mapping in epilepsy patients with semi-chronically implanted subdural electrodes classically involves eliciting an observable reaction or a subjective report of a percept in response to brief application of electrical current to a focal area of cortex. Most ECS mapping is conducted with just a few trials of manually delivered current, which can be slow and imprecise. Furthermore, this often results in ambiguous results, particularly in cortical areas where function is not well understood. Methods: To circumvent these limitations, we developed a method for computer-controlled delivery of defined electrical current to implanted intracranial electrodes. We used this setup to deliver repeated, reliable and precise levels of ECS across multiple trials. Each trial of ECS was time-locked to a computer-generated, two-alternative forced choice behavioral task, which enabled us to statistically verify a patient’s reports of an ECS-evoked percept and to quantitatively measure behavioral thresholds for detection of electrical stimulation. Results: We applied computer-controlled electrical stimulation to mapping of early and late visual cortex in 10 patients. In all cases, we were able to rapidly collect data from dozens of stimulation trials and objectively identify the cortical sites where ECS produced a detectable percept. Quantitative thresholds for detection of ECS at each electrode site were calculated by fitting the data collected across multiple trials to a sigmoid function, and were as low as 0.49 mA. Conclusions: Computer-controlled cortical stimulation is well suited for systematic and quantitative mapping of virtually any region of cerebral cortex. This method may be particularly useful for studying cortical regions that are not well characterized, and for verifying the presence of percepts elicited from stimulation of sensory or association cortex that are otherwise difficult to objectively confirm.