Executive control of the ACC

Posner et al. (2007), Posner and Rothbart (2007), and Bush, Luu & Posner (2000) have proposed that the anterior cingulate cortex, and specifically the anterior cingulate gyrus, is part of an executive attentional network, and that its main role is to regulate the processing of information from other networks, both in sensory and emotional modalities (Öschner & Gross, 2005).

The term cognitive control refers to a series of executive functions that serve to configure cognitive systems in order to perform a task, especially in situations involving effort or non-routine behavior (Botvinick et al., 2004).

How does this configuration occur? Some authors (Botvinick et al., 2004; Posner et al., 2004) have proposed a conflict monitoring hypothesis, in which conflict detection occurs in the task. When this detection occurs, the ACC sets in motion a series of strategic readjustments in cognitive control and response planning, with the aim of reducing the conflict on the next trial, and getting it right.

These results have been refined by Dosenbach et al. (2008). For their group, the ACC -and especially the dorsal ACC- seems to be a processing node that gains weight over prefrontal structures as a necessary structure to perform high-level cognitive tasks, especially when it is necessary to maintain a cognitive set, and to detect that this set is failing in the execution of a task.

To what extent does the Anterior Cingulate Cortex mediate this process?

Botvinick et al. (2004) state that conflict monitoring implies that if the ACC is involved in monitoring and evaluating the outcomes of an action, it could be that conflict is one of the outcomes to which the ACC is sensitive. This could be by detecting a reduction in reward, and also by detecting an increase in effort threshold, both functions that have been linked to the ACC.

Thus, the ACC would be responsible for establishing both parameters along with an estimate of the cost-benefit underlying the selection of a strategy or action. Monitoring would not be in charge of the selection of a cognitive strategy of resolution or an action plan, as we have seen, but of an evaluative control mechanism of the results that, in case they are not satisfactory, send information to other structures and nodes of the planning system -the frontoparietal network and the cerebellum- that are in charge of managing the error, establishing action strategies, and learning.

Fan, Hof, Guise, Fossella & Posner (2007), citing Strick and Picard (2001), establish a functional division during conflict processing, in which the:

– Rostral anterior cingulate cortex is involved in conflict processing.

– The posterior rostral cingulate cortex is involved in response selection, and the posterior cingulate cortex in response selection. And..

– the posterior cingulate cortex in movement execution.

For this group, the connections between this structure and others are effective, i.e., they exert a top-down control that redirects information: when conflict is detected in the rostral ACC, this information is directed to posterior areas of the cingulate cortex and areas of the frontal lobe (especially the supplementary motor cortex, premotor cortex and lateral prefrontal cortex) for response selection and execution.

Rostral CCA: an emotional control mechanism?

The rostral anterior cingulate cortex resolves the emotional conflict by suppressing the activity of the amygdala and its outgoing connections, leading to a weakening of the sympathetic autonomic responses. Therefore, we are talking about an emotional top-down phenomenon. To speak of inhibitory emotional control, we must make a distinction between conscious and non-conscious processes. Etkin et al. (2004) have already shown that there are differences in rostral ACC activity when stimuli are conscious and when they are not.

During unconscious processing of stimuli, subjects differed as they could not identify vigilance-related anxiety with a threatening context-related stimulus, and thus differed according to their individual anxiety level. The results also showed that once the subjects had recognized the potential threat, they responded in the same way and irrespective of the type of therapy they had received – i.e. having been successful they reduced their anxiety equally. In short, rostral ACC could exert conscious control of the initial nonconscious emotion produced by the amygdala, elucidating two stages of emotional processing.

The implication for attentional processing is obvious and important. In pathologies involving emotional processing, overactivation of the amygdala makes subjects more sensitive to interference, with high distractibility for psychiatric patients. This overactivation, moreover, correlates with a hypoactivation of the rostral ACC.

How does this emotional control mechanism relate to some clinical pathologies?

In depression, there is a hyperactivation of the medial prefrontal cortex and rostral ACC during self-referential processing of negative words. Rostral ACC activity presents the relationship between medial prefrontal cortex activity and symptom severity. In fact, the relationship between the medial prefrontal cortex, the amygdala, and the rostral ACC presented a correlation between self-referential processing and the processing of negative emotional information (Yoshimura et al., 2009).

In post-traumatic stress, they would show rostral ACC hypoactivity during trauma evocation and re-experiencing, and symptom severity is strongly correlated with rostral ACC hypoactivity. Similarly, in subjects with anxiety, there is a failure to suppress amygdala activity. Furthermore, during a situation perceived as strongly threatening, anxiety correlates negatively with rostral ACC activity, and positively with dorsal ACC, which could explain the state of hypervigilance.

Changes in activity would depend on the degree of perceived threat. And this perceived threat varies according to the anticipation of aversive stimuli. Indeed, Straube et al. (2008) also show in their study that there is a variation in the activity of the cingulate cortex that depends on the degree of perceived threat.

Attention-emotion continuum

It is in these phenomena where we can see how attention and emotion become one and the same phenomenon, excluding traditional dichotomies that are gradually being discarded. There is an attention-emotion continuum, and different degrees of control between the two. Intense emotion monopolizes attentional resources to the point of hypervigilance, or to the point of absolute distractibility with respect to relevant contextual stimuli. Thus, emotions can modulate attention by choosing one type of attentional focus over another, as for example interoceptive cues in subjects with hypochondria.

Or cognitive resources can exert control over emotions, allowing their control, or their reformulation (which is what happens in many therapies), for which they must recruit attentional resources focused on it, as for example in the checking of absurd arguments during depression, or during the cognitive reformulation of phobias.

Ultimately, the cingulate cortex is a “stepping stone” structure. It allows us to check our evolution as a species within our own brain: from the structures that make us equal to other animals (the limbic system), to the higher cognitive areas (neocortex); and how some structures influence the others.