P214 Noninvasive manipulation of fronto-parietal synchrony improves conscious visual perception in humans

Abstract

Question Correlational evidence in monkeys has reported increased synchrony of high-beta (22–34 Hz) cortical oscillations between frontal and parietal attentional regions during visual tasks engaging an endogenous capture of attention (Buschmann and Miller, Science, 2007). However, these results lack causality. We aim to demonstrate that this frequency specific intrahemispheric synchronization is causally linked to the modulation of visual performance. Methods We recorded EEG signals in human participants ( n = 14) who performed a conscious visual detection task while we manipulated cortical high-beta rhythms with brief rhythmic (30 Hz, 4 pulses) or random bursts of rhythmic Transcranial Magnetic Stimulation (rTMS) delivered to the right Frontal Eye Field (FEF). Participants had to report (yes/no) if he had seen the target (an individually titrated low contrast gabor at 50% detection levels) and if ‘yes’, where it had appeared (left/right of the fixation cross). Individual perceptual sensitivity (d ′ ) was determined using signal detection theory. From the EEG signal, a classical measure of phase-synchrony (evaluating the stability of the phase-relationship between 2 signals) was calculated between the electrode closest to the TMS coil position (FC2) and all other scalp electrodes. To rule-out artificial enhancement of synchrony between pairs of neighbouring scalp electrodes, zero-phase synchronization was not considered. Results We report, in the rhythmic TMS condition (compared to the random TMS control), an increase of inter-regional synchronization in the high-beta band (25–35 Hz) between the area stimulated (right FEF) and a group of parietal electrodes, as well as an increase of local inter-trial coherence in the same frequency band over parietal electrodes. Behaviorally, conscious visual detection was improved for left visual targets (contralateral to the stimulation) in the rhythmic but not random TMS condition. Conclusion Our results show that human high-beta inter-regional synchrony can be manipulated non-invasively and that high-beta oscillatory activity across the right dorsal fronto-parietal attention network causally contributes to the facilitation of conscious visual detection, suggesting potential applications of rhythmic non-invasive brain stimulation for the restoration of impaired visual behaviors. Download high-res image (1MB) Download full-size image