ABSTRACT
Transcranial direct current stimulation (tDCS) has recently undergone a resurgence in popularity as a powerful tool to non-invasively manipulate brain activity. While tDCS has been used to alter functions tied to primary motor and visual cortices, its impact on extrastriate visual areas involved in visuo-spatial processing has not yet been examined. In the current study, we applied tDCS to the cat visuoparietal (VP) cortex and assayed performance in a paradigm designed to assess the capacity to detect, localize and orient to static targets appearing at different spatial eccentricities within the visual field. Real or sham cathodal tDCS was unilaterally applied to the VP cortex, and orienting performance was assessed during (online), immediately after (offline; Experiments 1 and 2), and 1 or 24 h after the end of the tDCS stimulation (Experiment 2). Performance was compared to baseline data collected immediately prior to stimulation. Real, but not sham, tDCS induced significant decreases in performance for static visual targets presented in the contrastimulated visual hemifield. The behavioral impact of tDCS was most apparent during the online and immediate offline periods. The tDCS effect decayed progressively over time and performance returned to baseline levels approximately 60 min after stimulation. These results are consistent with the effects of both invasive and non-invasive deactivation methods applied to the same brain region, and indicate that tDCS has the potential to modify neuronal activity in extrastriate visual regions and to sculpt brain activity and behavior in normal and neurologically impaired subjects.
