A unified framework for inhibitory control

Abstract

Inhibiting unwanted thoughts, actions and emotions figures centrally in daily life, and the prefrontal cortex (PFC) is widely viewed as a source of this inhibitory control. We argue that the function of the PFC is best understood in terms of representing and actively maintaining abstract information, such as goals, which produces two types of inhibitory effects on other brain regions. Inhibition of some subcortical regions takes a directed global form, with prefrontal regions providing contextual information relevant to when to inhibit all processing in a region. Inhibition within neocortical (and some subcortical) regions takes an indirect competitive form, with prefrontal regions providing excitation of goal-relevant options. These distinctions are crucial for understanding the mechanisms of inhibition and how they can be impaired or improved.

Figure 1. Prefrontal control over directed global and competitive inhibition

We argue that two distinct forms of inhibition – directed global vs. indirect competitive – can be understood within a unified framework that builds upon the well-accepted characterization of prefrontal areas as specialized for actively representing and maintaining abstract goal-related information, rather than for inhibition per se. While the specific type of content represented across each of the various prefrontal regions is still debated, we argue that inhibitory control arises as one downstream effect of these goal representations. Prefrontal cortex provides targeted global inhibition of some subcortical and archicortical regions (e.g., those related to fear, motor, and memory processing), and supports indirect competitive inhibition in neocortical and subcortical regions by enhancing relevant regions or representations (e.g., for processing colors), whose increased activity then causes reduced activation of competing areas or representations (e.g., for processing words or shapes). Targeted global inhibition thus leads to a global shutdown of associated regions, whereas competitive inhibition helps a winner to emerge from among a variety of competitors. To support basic survival processes (e.g., avoiding harm), subcortical regions are relatively “dumb” and inflexible, in the sense that they just turn on responses that can be adaptive (e.g. a fear response) but are physiologically and psychologically costly. Prefrontal regions support decisions about such responses, and globally inhibit subcortical circuitry and associated responses when the context indicates it is appropriate to do so (e.g., when stressors are controllable). Compared to subcortical processing systems, cortical processing systems are more flexible (changing more over the course of development and learning), and are less clearly linked to physiological and psychological benefits from being globally inhibited. These characteristics may explain why the prefrontal cortex excites the relevant cortical regions for a given goal rather than globally inhibiting irrelevant cortical regions. Regions whose activity is increased or enhanced are shown in green, while those whose activity is inhibited (globally or competitively) are shown in red; neocortical regions are labeled in ovals, while non-neocortical regions are labeled in rectangles.