Common inhibitory mechanism in human inferior prefrontal cortex revealed by event-related functional MRI

Inhibition of an ongoing reaction tendency for adaptation to changing envir onments is a major function of the human prefrontal cortex. This function h as been investigated frequently using the go/no-go task and set-shifting ta sks such as the Wisconsin Card Sorting Test (WCST), Studies in humans and m onkeys suggest the involvement of the dorsolateral prefrontal cortex in the two task paradigms. However, it remains unknown where in the dorsolateral prefrontal cortex this function is localized, whether a common inhibitory m echanism is used in these task paradigms and how this inhibitory function a cts on two different targets, i,e, the go response in the go/no-go task and the cognitive set in the WCST. In the go/no-go task of this study, subject s were instructed to either respond (go trial) or not respond (no-go trial) , depending on the cue stimulus presented. The signals of functional MRT (f MRI) related to the inhibitory function should be transient by nature. Thus , we used the temporal resolution of fMRI (event-related fMRI) by which tra nsient signals in go and no-go trials can be analysed separately and compar ed with each other, We found a focus that showed transient no-go dominant a ctivity in the posterior part of the inferior frontal sulcus in the right h emisphere, This was true irrespective of whether the subjects used their ri ght or left hands. These results suggest that the transient activation in t he right inferior prefrontal area is related to the neural mechanism underl ying the response inhibition function, Furthermore, this area was found to be overlapped spatially with the area that was activated transiently during cognitive set shifting in the WCST The transient signals in the go/no-go t ask peaked 5s after the transient expression of the inhibitory function, an d the transient signals in the WCST peaked 7s after the transient expressio n, reflecting different durations of neuronal activity in the two inhibitor y task paradigms, These results imply that the right inferior prefrontal ar ea is commonly involved in the inhibition of different targets, i,e, the go response during performance of the go/no-go task and the cognitive set dur ing performance of the WCST.