Cortico-cortical evoked potentials and stimulation-elicited gamma activity preferentially propagate from lower- to higher-order visual areas.

OBJECTIVE: The lower-order visual cortex in the medial-occipital region is suggested to send feed-forward signals to the higher-order visual cortex including ventral-occipital-temporal and dorsal-occipital regions. We determined how stimulation-elicited cortical-signals propagate between lower- and higher-order visual cortices, and whether the magnitudes of stimulation-elicited cortical-signals recorded in the higher-order visual cortex differed from those recorded in the lower-order one. METHODS: We studied 10 patients with focal epilepsy who underwent extraoperative electrocorticography recording. Trains of 1-Hz stimuli with an intensity of 3 mA were delivered to an electrode pair within the medial-occipital region; then, cortico-cortical evoked-potential (CCEP) and stimulation-elicited gamma-activity at 80-150 Hz were measured in the ventral-occipital-temporal and dorsal-occipital regions. Likewise, CCEP and stimulation-elicited gamma-activity, driven by stimuli within the higher-order visual cortex, were measured in the lower-order visual cortex. RESULTS: CCEPs generated, via feed-forward propagations, in the higher-order visual cortex were significantly larger than those generated, via feed-back propagations, in the lower-order visual cortex. Stimulation of the lower-order visual cortex elicited augmentation of gamma-activity in the higher-order visual cortex after the preceding CCEP subsided. CONCLUSION: The propagation manners of stimulation-elicited cortical-signals differ between feed-forward and feed-back directions in the human occipital lobe. SIGNIFICANCE: : Such difference may need to be taken into consideration for future clinical application of CCEPs and stimulation-elicited gamma-augmentation in presurgical evaluation for epilepsy surgery.