In many situations, input from the environment is sufficient to drive cognition in a bottom-up fashion resulting in the production of appropriate behavior. At other times, such prepotent responses are not contextually appropriate, and we must exert top-down control to shape cognition and achieve a desired behavior. The prefrontal cortex (PFC) is thought to enable top-down control by biasing processing in other brain regions towards contextually appropriate representations.1–3
Extensive evidence indicates that PFC-mediated cognitive control encompasses a wide range of specific operations.4–10
For example, upon hearing a phone ring, you must decide whether to (a) execute the motor actions involved in answering your phone, (b) resist the inappropriate urge to answer your friend's phone, (c) attempt to ignore the sound as an auditory distraction, or (d) quickly attempt to silence the cell phone in order to minimize your embarrassment at the talk you are attending.
The lateral PFC consists of multiple subregions that differ in their cytoarchitectonics and their patterns of connectivity with posterior cortical sites.5,10–13
Remarkable progress has been made in the last two decades toward understanding the function-to-structure mapping that constitutes lateral PFC's macroscopic functional organization.14-24
This body of research suggests that PFC is a heterogeneous structure with distinct subregions relating to specific cognitive control operations. Progress has also been made in understanding the broader principles of PFC organization, such as the possibility that PFC is hierarchically organized along its rostro-caudal axis, with higher-order goals encoded by more anterior regions and increasingly specific subgoals encoded as one moves posteriorly through PFC.18,25–34
Importantly, for present purposes, key advances have arisen from an extensive literature focused on the organization of left ventrolateral PFC (VLPFC), with extant data documenting functional distinctions between the anterior (area 47), mid- (area 45), and posterior (area 44) subregions of left VLPFC.21,22,34–40
By contrast, considerably less is known about the functional organization of right PFC, and, in particular, it remains largely unclear whether the specific subdivisions of right VLPFC are functionally distinct and, if so, how to characterize their underlying computations.
While right VLPFC function is not well understood, neuroimaging studies employing various cognitive tasks have implicated this region as a critical substrate of control. At present, two prominent theories feature right VLPFC as a key functional region. From one perspective, right VLPFC is thought to play a critical role in motor inhibition, where control is engaged to stop or override motor responses.41
Consistent with this view, neuroimaging studies of tasks thought to require motor inhibition typically reveal activation in right VLPFC, among other regions.42–44
In addition, patients with damage to the inferior extent of right PFC take longer to override a prepotent response compared to healthy adults or even patients with damage to other PFC subregions.45
Based on this evidence, Aron et al.41
argued that right VLPFC plays a critical role in motor inhibition.
Alternatively, Corbetta and Shulman46–47
have advanced the hypothesis that there are two distinct fronto-parietal networks involved in spatial attention, with right VLPFC being a component of a right-lateralized ventral attention network that governs reflexive reorienting. From this perspective, right lateral PFC, along with a region spanning right temporoparietal junction (TPJ) and the inferior parietal lobule, are engaged when abrupt onsets occur in the environment, suggesting that these regions are involved in re-orienting attention to perceptual events that occur outside the current focus of attention.a
While much of the research brought to bear in support of this theoretical framework has focused on activity within lateral parietal cortex, the performance of tasks thought to tap reflexive reorienting also typically gives rise to robust right lateral PFC activation. Nevertheless, the precise operations mediated by right VLPFC in response to abrupt onsets remain unclear.
The motor inhibition
and reflexive reorienting
frameworks have gained traction in the last decade, and have guided an explosion of functional imaging research.44,48–68
The prominence of these theories has also motivated reverse-inferences, wherein right VLPFC activation in a given task is attributed to either engagement of motor inhibition or attentional orienting processes. At present, however, it is unclear whether these two frameworks implicate the same or distinct subregions within right lateral PFC (), and, at a process level, it is unclear how these two frameworks relate to each other. One possibility is that the VLPFC activity observed during one set of tasks can be explained in terms of the other putative control mechanism. For example, recent data suggest that stopping tasks often confound motor inhibition with the need to orient to behaviorally relevant cues and that this orienting response may be what drives right VLPFC engagement when stopping is required.67–68
Alternatively, tasks designed to target reflexive reorienting might also involve some demands on motor inhibition. 69
Figure 1 Anatomical divisions within the ventrolateral prefrontal cortex (VLPFC). VLPFC, or inferior frontal gyrus, is bounded superiorly by the inferior frontal sulcus (green) and inferiorly by the lateral sulcus (blue). Cytoarchitectonic and connectivity patterns (more ...)
Here we examine the relationship between these two theories of right PFC function by performing a meta-analysis of the functional magnetic resonance imaging (fMRI) literatures on motor inhibition and reflexive reorienting. The goal is to determine whether distinct PFC subregions respond similarly or differently to these two different types of cognitive control tasks. The results are then considered within the context of the broader empirical literature, as many behavioral tasks beyond those in the meta-analysis, lead to the recruitment of right VLPFC. From the current findings and our review of the literature, we then provide initial conclusions about the nature of functional heterogeneity within right VLPFC, with the ultimate goal of sparking future empirical work that will test these emerging hypotheses about the role of right VLPFC in cognitive control.