Causal contributions of human frontal eye fields to distinct aspects of decision formation

Several theories propose that perceptual decision making depends on the gradual accumulation of information that provides evidence in favour of one of the choice-options. The outcome of this temporally extended integration process is thought to be categorized into the ‘winning’ and ‘losing’ choice-options for action. Neural correlates of corresponding decision formation processes have been observed in various frontal and parietal brain areas, among them the frontal eye-fields (FEF). However, the specific functional role of the FEFs is debated. Recent studies in humans and rodents provide conflicting accounts, proposing that the FEF either accumulate the choice-relevant information or categorize the outcome of such evidence integration into discrete actions. Here, we used transcranial magnetic stimulation (TMS) on humans to interfere with either left or right FEF activity during different timepoints of perceptual decision-formation. Stimulation of either FEF affected performance only when delivered during information integration but not during subsequent categorical choice. However, the patterns of behavioural changes suggest that the left-FEF contributes to general evidence integration, whereas right-FEF may direct spatial attention to the contralateral hemifield. Taken together, our results indicate an FEF involvement in evidence accumulation but not categorization, and suggest hemispheric lateralization for this function in the human brain

Causal contributions of human frontal eye fields to distinct aspects of decision formation

Several theories propose that perceptual decision making depends on the gradual accumulation of information that provides evidence in favour of one of the choice-options. The outcome of this temporally extended integration process is thought to be categorized into the ‘winning’ and ‘losing’ choice-options for action. Neural correlates of corresponding decision formation processes have been observed in various frontal and parietal brain areas, among them the frontal eye-fields (FEF). However, the specific functional role of the FEFs is debated. Recent studies in humans and rodents provide conflicting accounts, proposing that the FEF either accumulate the choice-relevant information or categorize the outcome of such evidence integration into discrete actions. Here, we used transcranial magnetic stimulation (TMS) on humans to interfere with either left or right FEF activity during different timepoints of perceptual decision-formation. Stimulation of either FEF affected performance only when delivered during information integration but not during subsequent categorical choice. However, the patterns of behavioural changes suggest that the left-FEF contributes to general evidence integration, whereas right-FEF may direct spatial attention to the contralateral hemifield. Taken together, our results indicate an FEF involvement in evidence accumulation but not categorization, and suggest hemispheric lateralization for this function in the human brain.ISSN:2045-232

Shining new light on dark percepts: visual sensations induced by TMS

Phosphenes induced by transcranial magnetic stimulation (TMS) are sensations of light, whereas a missing region in the visual field induced by TMS is generally referred to as a scotoma. It is believed that phosphenes are caused by neural excitation, while scotomas are due to neural inhibition. In light of the recent literature it might, however, be surmised that both phenomena are the result of neural noise injected into the cortex by TMS and that the likelihood of perceiving the two kinds of percepts depends on the state of the cortex at the time of stimulation. In the present study, TMS was applied over the left occipital cortex under different background conditions (Experiments 1-2) and using different TMS intensities (Experiment 3). Behavioral responses indicate the visual system processes luminance in a standardized manner, as lighter percepts were reacted to faster than darker percepts; this effect, however, did not extend to percept size. Our results suggest that phenomenological characteristics of artificial visual percepts are in line with the proposed effects of TMS as the induction of random neural noise interfering with the neural dynamics (the state of the cortex) at the time of stimulation