Transcranial magnetic stimulation of macaque frontal eye fields decreases saccadic reaction time
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Transcranial magnetic stimulation (TMS) is increasingly used to perturb targeted human brain sites non-invasively, to test for causal effects on performance of cognitive tasks. TMS might also be used in non-human primates to complement invasive work and compare with human studies. Here, we targeted the frontal eye fields (FEF) in two macaques with a continuous theta-burst (cTBS) protocol, testing the impact on visually guided saccades. After unilateral cTBS over the FEF in either hemisphere, a small (mean 7 ms) but highly consistent decrease in saccadic reaction times (RTs) was observed. Lower latencies arose for saccades both contra- and ipsilateral to the stimulated FEF after cTBS. These results provide the first demonstration that TMS can be used to affect saccadic behavior in non-human primates. The unexpectedly bilateral impact on RTs may reflect an impact on ‘fixation’ neurons in the FEF and/or transcallosal modulation of both FEFs induced by unilateral cTBS. In either case, this study demonstrates a clear behavioral effect induced by TMS in awake behaving monkeys performing a cognitive task. This opens new opportunities for investigating the causal roles of targeted brain areas in behavior, for measuring physiological consequences of TMS in the primate brain, and ultimately for human–monkey comparisons.
KeywordsFrontal eye field Macaque Saccades Theta burst TMS
The authors are indebted to A. Coeman, C. Fransen, M. Depaep, W. Depuydt, M. Deforche, P. Kayenbergh, G. Meulemans, C. Van Eupen, S. Verstraeten for help with the experiments. The work was supported by Human Frontiers Science Program (HFSPO RGP7/2007), Medical Foundation Queen Elisabeth (2008-10), Inter University Attraction Pole6/29, Program Financing 2010-15, Fonds voor Wetenschappelijk onderzoek, VLaanderen (FWO) G.0622.08; FWO G.0593.09, National Science Foundation BCS-0745436 and European Union (EU) grant (FP7 HEALTH-F2-2008-200728), BrainSynch. JD is a Royal Society Anniversary Research Professor. AG has an Aspirant fellowship of FWO-Flanders.
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