TMS over the Human Frontal Eye Field Distorts Perceptual Stability across Eye Movements

摘要

We perceive a stable outside word despite the constant changes of visual input induced by our own eye movements. An internal monitoring of eye movements may contribute to the seemingly perfect maintenance of perceptual stability. The frontal eye field (FEF) represents a candidate area for the cortical integration of oculomotor monitoring signals: It receives information about an impending eye movement from the brainstem (Sommer and Wurtz, 2002) and exhibits predictive receptive field changes that could serve the trans-saccadic integration of visual space (Umeno and Goldberg, 1997; Sommer and Wurtz, 2006). However, what perceptual consequences may arise from altered remapping circuits within the FEF remains unclear. Here, we show that transcranial magnetic stimulation (TMS) over FEF distorts perceptual stability across eye movements. To assess trans-saccadic perceptual integration, we asked normal healthy subjects to report the direction of intra-saccadic stimulus displacements. The saccade target was switched off intra-saccadically and reappeared 250 ms later at a displaced position (Deubel et al., 1996). In a critical condition, we applied offline TMS in a continuous theta-burst stimulation (cTBS) protocol before subjects were tested in this task. The cTBS protocol has been shown to suppress cortical excitability for up to 30 min after stimulation when applied over primary motor cortex (Huang et al., 2005) or FEF (Nyffeler et al., 2006). We determined the perceptual thresholds for intra-saccadic displacement detection. Immediately after cTBS over the right FEF, subjects showed significantly elevated detection thresholds for leftward saccades (i.e., for saccades directed to the contralateral hemifield with respect to the stimulated FEF). Control stimulation over the vertex yielded no significant threshold differences compared to a baseline measure without prior stimulation. These findings indicate that the FEF is involved in the integration of oculomotor feedback signals that support visual stability across eye movements.