No Evidence That Frontal Eye Field tDCS Affects Latency or Accuracy of Prosaccades

Abstract

Transcranial direct current stimulation (tDCS) may be used to directly affect neural activity from outside of the skull. However, its exact physiological mechanisms remain elusive, particularly when applied to new brain areas. The frontal eye field (FEF) has rarely been targeted with tDCS, even though it plays a crucial role in control of overt and covert spatial attention. Here, we investigate whether tDCS over the FEF can affect the latency and accuracy of saccadic eye movements. Twenty-six participants performed a prosaccade task in which they made eye movements to a sudden-onset eccentric visual target (lateral saccades). After each lateral saccade, they made an eye movement back to the center (center saccades). The task was administered before, during, and after anodal or cathodal tDCS over the FEF, in a randomized, double-blind, within-subject design. One previous study (Kanai et al., 2012) found that anodal tDCS over the FEF decreased the latency of saccades contralateral to the stimulated hemisphere. We did not find the same effect: neither anodal nor cathodal tDCS influenced the latency of lateral saccades. tDCS also did not affect accuracy of lateral saccades (saccade endpoint deviation and saccade endpoint variability). For center saccades, we found some differences between the anodal and cathodal sessions, but these were not consistent across analyses (latency, endpoint variability), or were already present before tDCS onset (endpoint deviation). We tried to improve on the design of Kanai et al. (2012) in several ways, including the tDCS duration and electrode montage, which could explain the discrepant results. Our findings add to a growing number of null results, which have sparked concerns that tDCS outcomes are highly variable. Future studies should aim to establish the boundary conditions for FEF-tDCS to be effective, in addition to increasing sample size and adding additional controls such as a sham condition. At present, we conclude that it is unclear whether eye movements or other aspects of spatial attention can be affected through tDCS of the frontal eye fields.

Abnormal Connectivity and Brain Structure in Patients With Visual Snow

“…The observed hyperconnectivity of the AG to and within the prefrontal cortex (LPFC) suggests that VS impairs the network integrity of higher cognitive areas such as the IFG, LPFC, and contralateral AG. The hyperconnectivity of the IFG, LPFC, FEF, and IFG could index interference with cognitive control (Cieslik et al, 2013) or with visual search functionality in patients with VS (Schall, 2002;Nelson et al, 2016;Reteig et al, 2018). The AG is involved in higher cognitive function, such as calculation and symbol processing (Price and Ansari, 2011), but it also computes action awareness representations (Farrer et al, 2008).…”

Saccades, attentional orienting and disengagement: the effects of anodal tDCS over right posterior parietal cortex (PPC) and frontal eye field (FEF)

“…However, the results are not conclusive: whereas Kanai et al [2012] found stimulation-and task-specific effects on saccades directed to the contralateral visual hemifield, Tseng et al [2018] observed that effects of anodal tDCS over the right FEF depended on the probability of target location and the individual level of performance. On the other hand, Reteig et al [2018] found no effects of either anodal or cathodal stimulation. With respect to spatial attention, most studies employed behavioral paradigms (without eye movements recording), mostly stimulating PPC [e.g., Sparing et al 2009;Bolognini et al 2010;Loftus and Nicholls, 2012] and only few targeted also frontal areas [Ball et al 2013;Roy et al 2015].…”

“…Although this approach proved to be valid on primary cortices [Nitsche and Paulus 2000], polarization of associative cortices yielded mixed findings with respect to excitatory/inhibitory influences on behavior. With regard to eye movements, some studies applied tDCS over the FEFs in pro-and anti-saccades tasks [Kanai et al 2012;Tseng et al 2018;Reteig et al 2018]. However, the results are not conclusive: whereas Kanai et al [2012] found stimulation-and task-specific effects on saccades directed to the contralateral visual hemifield, Tseng et al [2018] observed that effects of anodal tDCS over the right FEF depended on the probability of target location and the individual level of performance.…”

Placebo Brain Stimulation Affects Subjective but Not Neurocognitive Measures of Error Processing

“…Prior to each experimental stimulation block, participants received a short 1-min ramp-up 1-mA anodal stimulation with the tDCS electrodes resulting in a slightly tingling sensation at the skin. This sham stimulation protocal was based on similar stimulation protocols that are typically included as a control condition in the lab at the University of Amsterdam (Reteig et al 2018;Talsma et al 2017). Also, as the sham anodal stimulation was the same in both the enhancement and the Fig.…”