Transcranial magnetic stimulation of the left human frontal eye fields eliminates the cost of invalid endogenous cues

Humans are able to selectively attend to specific regions of space without moving their eyes. However, there is mounting evidence that these covert shifts of attention may employ many of the same brain regions involved when executing the eye movements. For example, functional magnetic resonance imaging (fMRI) studies show that the oculomotor region known as the frontal eye fields (FEF) are activated by the covert shifts of attention. However, it remains possible that the activations seen in these studies result from actively inhibiting eye movements rather than as a direct result of modulating perceptual processing. Here we provide direct evidence for the role of this region in endogenously driven spatial attention. We show that briefly disrupting the left FEFs with transcranial magnetic stimulation (TMS) eliminated the slow response times associated with the invalid strategic cues when the target appeared in the right visual field. At first glance, our findings appear incompatible with the results reported by Grosbras and Paus (Grosbras, M. -H., & Paus, T. (2002). Transcranial magnetic stimulation of the human frontal eye field: effects on visual perception and attention. Journal of Cognitive Neuroscience, 14(7), 1109--1120) and we suggest this is likely due to the design differences. Specifically, we disrupted the FEF at the time of cue onset, rather than target onset. Taken together with the findings of Grosbras and Paus, our findings suggest that the FEF plays an early role in the inhibition of perceptual information. Furthermore, our findings complement work by Ro et al. (Ro, T., Farne, F., & Chang, E. (2003). Inhibition of return and the frontal eye fields. Experimental Brain Research, 150, 290--296) who report that stimulation of the frontal eye fields disrupts the inhibitory consequences of reflexive attention shifts.