Role of the Human Medial Frontal Cortex in Task Switching: A Combined fMRI and TMS Study

Abstract

of the human medial frontal cortex in task switching: a combined fMRI and TMS study. J Neurophysiol 87: 2577-2592, 2002; 10.1152/jn.00812.2001. We used event-related functional magnetic resonance imaging (fMRI) to measure brain activity when subjects were performing identical tasks in the context of either a task-set switch or a continuation of earlier performance. The context, i.e., switching or staying with the current task, influenced medial frontal cortical activation; the medial frontal cortex is transiently activated at the time that subjects switch from one way of performing a task to another. Two types of task-set-switching paradigms were investigated. In the response-switching (RS) paradigm, subjects switched between different rules for response selection and had to choose between competing responses. In the visual-switching (VS) paradigm, subjects switched between different rules for stimulus selection and had to choose between competing visual stimuli. The type of conflict, sensory (VS) or motor (RS), involved in switching was critical in determining medial frontal activation. Switching in the RS paradigm was associated with clear blood-oxygenation-level-dependent signal increases ("activations") in three medial frontal areas: the rostral cingulate zone, the caudal cingulate zone, and the presupplementary motor area (pre-SMA). Switching in the VS task was associated with definite activation in just one medial frontal area, a region on the border between the pre-SMA and the SMA. Subsequent to the fMRI session, we used MRI-guided frameless stereotaxic procedures and repetitive transcranial magnetic stimulation (rTMS) to test the importance of the medial frontal activations for task switching. Applying rTMS over the pre-SMA disrupted subsequent RS performance but only when it was applied in the context of a switch. This result shows, first, that the pre-SMA is essential for task switching and second that its essential role is transient and limited to just the time of behavioral switching. The results are consistent with a role for the pre-SMA in selecting between response sets at a superordinate level rather than in selecting individual responses. The effect of the rTMS was not simply due to the tactile and auditory artifacts associated with each pulse; rTMS over several control regions did not selectively disrupt switching. Applying rTMS over the SMA/pre-SMA area activated in the VS paradigm did not disrupt switching. This result, first, confirms the limited importance of the medial frontal cortex for sensory attentional switching. Second, the VS rTMS results suggest that just because an area is activated in two paradigms does not mean that it plays the same essential role in both cases.

Early attentional processes distinguish selective from global motor inhibitory control: An electrical neuroimaging study

“…The involvement of the pre-SMA in the selective but not the global inhibition condition corroborates previous functional neuroimaging studies on selective inhibition or on task switching involving initiating new movements after the interruption of ongoing movements (Dove et al, 2000;Rushworth et al, 2002). During selective inhibition trials, the SMA/pre-SMA would support the reshaping of excitatory motor pathway to enable the production of the new movement, a process including the inhibition of inappropriate ongoing movements as well as the selection and execution of new motor programs Isoda and Hikosaka, 2007;Mostofsky and Simmonds, 2008;Picton et al, 2007).…”

“…Dove et al, 2000;Rushworth et al, 2002), we hypothesize that this topographic modulation reflects differences in response selection and programming between the two inhibition conditions. Indeed, while the global inhibition required the suppression of all prepotent motor responses, the selective condition required a response of the Fig.…”

Internally generated and directly cued task sets: an investigation with fMRI

“…Therefore, we devised a new cue type which we refer to as transition cues (cf. Rushworth, Hadland, Paus, & Sipila, 2002). With this, we aimed to show neural correlates of the internal generation of task sets which requires a higher demand of endogenous control than directly cued task sets.…”

Persistent activity in the prefrontal cortex during working memory

“…For instance, stimulus factors, not motor behavior, are almost exclusively experimentally manipulated and inferences drawn are too almost exclusively framed in terms of memory for past perceptual events. Newer studies are beginning to emphasize processes further down stream in the perception-action cycle, such as response selection, motor preparatory set, and memoryguided actions [61][62][63][64][65]. For example, Pochon et al [66] reported DLPFC activation during the delay only when subjects mentally prepared for an upcoming memoryguided sequence of actions and not when they simply maintained the visuospatial information.…”