P 236. Causal contributions of right and left frontal oscillatory activity to visual performance probed with high-beta rhythmic and arrhythmic patterns of non-invasive stimulation

Abstract

Introduction Despite growing evidence of the fundamental role played by cerebral oscillations in neural signaling and processing, the region-and hemisphere-specific contributions of frontal brain oscillatory activity to human visual cognition remains to be causally explored. Objectives In the current study, we aimed to explore the effects of 30 Hz oscillation patterns induced by rhythmic rTMS on the right and left Frontal Eye Fields, a region involved in attentional spatial orienting, and analyzed the impact of such intervention on visual discrimination and detection performance. Material and methods In two separate populations of subjects, we applied 4 pulse real or sham TMS bursts either to the left or the right Frontal Eye Fields (FEF) to manipulate local oscillatory activity and study the impact of such on the visual detection and categorization of low-contrast near-threshold targets. During the task subjects were requested to fixate on a central cross and following the appearance of a Gabor in a peripheral location (right/left ) and perform two consecutive tasks in this order: First a force-choice visual discrimination to indicate the orientation of the gratings within the stimulus ( right/left ); Second, a visual detection task to report if they had seen the target and in case they did, where it did appear ( yes/no and right/left) . In separate experimental blocks, in order to control for the effects of frequency, we compared the impact of frequency specific rTMS patterns (rhythmic) at high-beta (30 Hz) frequency to non-frequency-specific (a-rhythmic) rTMS patterns, matched in duration and number of pulses on correlates of visual performance: reaction time and accuracy for discrimination and visual sensitivity (d’) for the detection task. Results Our interventions revealed hemisphere-specific modulations of frontal oscillatory activity on the visual detection task. More specifically, on the right FEF frequency-specific high-beta TMS bursts enhanced perceptual sensitivity (d’) as compared to sham bursts, whereas no visual performance effects derived from the use of non-frequency-specific patterns. On the left FEF, however, only the non-frequency-specific TMS pattern yielded significant perceptual sensitivity (d’) improvements, whereas no visual performance effects emerged from the use of frequency-specific high-beta bursts. No significant modulations were observed for the discrimination task with any of the TMS patterns employed in the experiment. Conclusions Our results provide causal evidence in favor of hemisphere-specific frontal contributions to the modulation of visual performance and suggests different but complementary oscillation based mechanisms for the right and the left FEF in such phenomena.