Anterior cingulate cortex
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The anterior cingulate cortex, also known as Area 25, is a region that is located towards the front of the corpus callosum, in the medial frontal lobe. This region is involved in decision making and emotional regulation as well as vital to the regulation of physiological processes, such as blood pressure and heart rate. In particular, the key functions of the anterior cingulate cortex revolve around:
Anatomy and location
The anterior cingulate cortex is located towards the front of the cingulate cortex--a region that circles above the corpus callosum (Gabriel, Burhans, Talk, & Scalf, 2002). This region is connected to the prefrontal cortex and parietal cortex as well as both motor and visual systems. Furthermore, the anterior cingulate cortex is one of the four main subdivisions of the cingulate cortex. The other subdivisions are the posterior cingulate cortex, the mid cingulate cortex, and the retrosplenial anterior cingulate cortex.
The anterior cingulate cortex is sometimes divided into four regions, each of which seem to underpin a separate function (see Bush, Luu, & Posner, 2000). In particular, the anterior cingulate cortex includes:
Functions of the anterior cingulate cortex
Detection of errors
Many scholars have highlighted the role of this region in the detection of errors or shortfalls (Bush, Luu, & Posner, 2000). That is, this region seems to be especially active after individuals commit errors on a task.
Research indicates the anterior cingulate cortex can be active even when individuals are not aware of their errors (Luu & Pederson, 2004). Nevertheless, awareness might increase activation (Luu & Pederson, 2004). Specifically, when individuals are aware of their errors, the error-related negativity--an event related potential that is evoked during the commission of errors and generated by the anterior cingulate cortex--might be higher in amplitude.
Research on the error-related negativity provides the main source of evidence that perhaps the anterior cingulate cortex underpins the monitoring of errors. That is, this evoked potential is evoked only in response to errors (e.g., Falkenstein, Hohnsbein, Hoormann, & Blanke, 1991; Gehring, Goss, Coles, Meyer, & Donchin, 1993). These potentials can be evoked either from incorrect responses or after participants are informed a response was incorrect. Furthermore, several studies show this evoked potential is most likely generated by the anterior cingulate cortex (Herrmann, R?mmler, Ehlis, Heidrich, & Fallgatter, 2004; Holroyd, Dien, & Coles, 1998).
Nevertheless, such attempts to locate the source of these potentials are often uncertain. Indeed, Gehring and Knight (2000) showed that such potentials are diminished after damage to the lateral prefrontal cortex--not to the medial prefrontal cortex in which the anterior cingulate cortex is located.
Detection of conflicts
Nevertheless, the precise characterization of the anterior cingulate cortex in this role is still controversial. For example, rather than representing errors or shortfalls, the anterior cingulate cortex might be most active when conflicts between competing tendencies emerge (see Carter, Braver, Barch, Botvinick, Noll, & Cohen, 1998). In the study conducted by Carter et al. (1998), for example, participants had to respond only when a letter X followed an A. The anterior cingulate cortex was most active when similar, but different, sequences of letters appeared.
Many other studies have also provided evidence that conflicts can generate activation in the anterior cingulate cortex. In a study conducted by Botvinick, Nystrom, Fissell, Carter, and Cohen (1999), for example, participants completed a flanker task--a task in which, typically, three stimuli are presented simultaneously in a row. Participants are instructed to respond to the central stimulus and to disregard the distracters.
On some trials, the central stimulus and distracters are congruent, corresponding to the same response. On other trials, the central stimulus and distracters are incongruent, corresponding to different responses. In these instances, the distracters might partly evoke the inclination to enact an unsuitable response, and this tendency must be inhibited. The anterior cingulate cortex is especially activated during these incongruent trials, in which a conflict between competing response tendencies arises. Other regions, such as the dorsolateral prefrontal cortex, are then activated to redress the error or conflict.
Nevertheless, contrary to this purported role of the anterior cingulate cortex, damage to this region does not obliterate the capacity of individuals to monitor errors or conflicts (Baird, Dewar, B. Critchley, Gilbert, Dolan, & Cipolotti, 2006). Likewise, Critchley (2005), in a review of this literature, also argued that many executive functions, including the monitoring of errors and conflicts, seems to remain intact even after lesions in this region (for another perspective, see Rushworth, Behrens, Rudebeck, & Walton, 2007).
Reward based learning theory
In contrast to merely error or conflict detection, reward based learning theory argues the anterior cingulate cortex is involved in a more comprehensive set of processes in this domain. Apart from detecting errors, this region evaluates the magnitude of these shortfalls and then impinges on the selection of responses.
To demonstrate, in a study conducted by Bush, Vogt, Holmes, Dale, Greve, Jenike et al. (2002), participants could receive monetary rewards or losses for correct or incorrect responses. This region seems to be especially activated when individuals lose money on trials, indicating the magnitude or consequences of shortfalls affect activation of the anterior cingulate cortex--especially the dorsal and rostral areas. In other words, this region is especially activated when the costs of errors are elevated (see also Brown & Braver, 2005)
Polli, Barton, Cain, Thakkar, Rauch, and Manoach (2005) showed the activation of dorsal error might amplify effort following errors. That is, errors seem to correspond to subsequent activation of the dorsal areas of the anterior cingulate cortex. Activation of this region also then corresponded to fewer subsequent errors.
When the anterior cingulate cortex receives conflicting response tendencies, the region might determine which motor systems should be activated (Holroyd, Nieuwenhuis, Mars, & Coles, 2004). Specifically, the anterior cingulate cortex might bias the selection of responses to accommodate expectations of rewards and losses. Nevertheless, regions in the dorsolateral prefrontal cortex, not the anterior cingulate cortex, are especially involved in the implementation of adjustments (Garavan, Ross, Murphy, Roche, & Stein, 2002)
Many studies highlight the role of this region in various forms of emotional regulation and experience. Electrodes in this region have been shown to curb depression in some patients (Mayberg, Lozano, Voon, McNeely, Seminowicz, Hamani, et a., 2005). According to these authors, this region is conduit between the cognitive functions of the prefrontal cortex and the emotional experiences of medial temporal limbic systems. Reduced activation of this region might curb the possibility that negative emotions can overwhelm cognitive operations.
Indeed, as Compton, Robinson, Ode, Quandt, Fineman, and Carp (2008) highlight, emotional regulation might invoke the same mechanisms as the detection of, and adjustment to, errors. That is, emotional regulation also involves the detection of shortfalls from some optimal emotion and the need to implement changes to redress this deficiency. Accordingly, the anterior cingulate cortex might be involved in the detection of undesirable emotions and the dorsolateral prefrontal cortex might be involved in the implementation of behavioral adjustments.
Several lines of evidence vindicate this position. First, the anterior cingulate cortex and the dorsolateral prefrontal cortex are indeed involved in emotional regulation (see Beauregard, Levesque, & Bourgouin, 2001; Kalisch, Wiech, Critchley, Seymour, O'Doherty, Oakley et al., 2005; Ochsner, Ray, Cooper, Robertson, Chopra, Gabrieli, & Gross, 2004).
Similar many studies show that proficient performance on tasks that purportedly utilize the anterior cingulate cortex also correlate with manifestations of emotional wellbeing. The capacity to adjust performance after errors, for example, tends to coincide with emotional wellbeing (Robinson, 2007).
Likewise, Compton, Robinson, Ode, Quandt, Fineman, and Carp (2008) showed that improvement in performance after an error on the previous trial, which presumably involves the anterior cingulate cortex, corresponds to emotional regulation. Specifically, individuals who showed this improvement in performance reported diminished anxiety even on days that involved many stressful or demanding events. Individuals who did not show improvement in performance after errors reported amplified anxiety on stressful days.
Differences in the amplitude of error related negativity between incorrect and correct trials also coincided with emotional regulation. That is, in some individuals, the amplitude of error related negativity was especially pronounced on trials in which individuals committed errors. These individuals reported diminished anxiety even on days that involved many stressful or demanding events (see Compton, Robinson, Ode, Quandt, Fineman, & Carp, 2008).
The experience of sadness and anxiety
Some researchers argue that a part of the anterior cingulate cortex--the supracallosal region--might represent the experience of sadness. According to one meta-analysis, approximately 50% of the neuroimaging studies that have induced sadness have shown increased activation of this region (see Murphy, Nimmo-Smith, & Lawrence, 2003). In contrast, he posterior and dorsal cingulate cortex is often activated when individuals feel happy, as fMRI studies show (Habel, Klein, Kellermann, Shah, & Schneider, 2005).
Many other studies have shown that another region, called the medial prefrontal cortex, is activated when sadness is induced (Phan, Wager, Taylor, & Liberzon, 2002). Interestingly, the supracallosal anterior cingulate cortex and medial prefrontal cortex are closely connected and might represent a circuit that underpins sadness (Mauss & Robinson, 2009).
One complication to these studies needs to be recognized, as highlighted by Barrett (2006). Usually, to evoke sadness, participants must recall some disturbing event in the past. These recollections demand cognitive effort, which activates portions of the anterior cingulate cortex. Hence, the recollections themselves, and not only the experience of sadness, could also affect activation of the anterior cingulate cortex.
The anterior cingulate cortex partly underpins the experience of anxiety as well. To illustrate, when individuals are afflicted with lesions to the anterior cingulate cortex, autonomic reactivity, such as increases in heart rate after shocks, diminishes (Critchley, Mathias, Josephs, O'Doherty, Zanini, Dewar, et al., 2003). Furthermore, these lesions can curb variations in affect, without compromising the capacity to control cognitive processes (Critchley, Mathias, Josephs, O'Doherty, Zanini, Dewar, et al., 2003).
As outlined by Wegner, Wenzlaff, and Kozak (2004), the anterior cingulate cortex might underpin elements of ironic rebound. Specifically, a variety of studies have shown that unanticipated problems that arise when individuals strive to suppress particular thoughts, attitudes, beliefs, or emotions. In particular, these suppressed cognitions and feelings over resurface, even more intensely than before (Wegner, 1994).
The most accepted and promulgated explanation of these ironic rebound effects was formulated by Wegner, Schneider, Carter, and White (1987), often referred to as the two component model of cognitive control. This model assumes that two mechanisms, called the monitor and operator, underpin suppression. The monitor attempts to detect or identify thoughts, beliefs, attitudes, emotions, or impulses that need to be suppressed. The operator then inhibits these cognitions or feelings. According to Wegner, Wenzlaff, and Kozak (20040, the anterior cingulate cortex might underpin the operator, by facilitating the inhibition of unsuitable cognitions or emotions.
The monitor continues to operate, even without conscious effort. In contrast, the operator is terminated once effort or attention shifts to other activities. As a consequence, when individuals no longer strive to suppress some thought or emotion, only the monitor persists. Individuals become especially sensitive to memories, events, and feelings that are related to the thought or emotion that was suppressed--and this sensitivity underpins the ironic rebound effect.
The anterior cingulate cortex is involved in detecting and resolving conflicts. Ironic rebound effects also involve monitoring conflicts--between natural cognitions or emotions and the need to suppress these thoughts or feelings--and selecting a suitable response. Hence, the anterior cingulate cortex may be central to ironic rebound effects (Wyland & Forgas, 2007).
Source of hemisity
According to the concept of hemisity, the dominant executive systems, or the will of individuals, must reside in one hemisphere. That is, proponents of this perspective maintain that individuals cannot be governed by two conflicting agents. Thus, agency or will must ultimately be underpinned by one of the two hemispheres.
If this executive system is located in the left hemisphere, the perception of individuals is more dependent upon their goals, called top-down thinking, and more confined to specific details. In contrast, if this executive system is located in the right hemisphere, the perception of individuals is more sensitive to features in the environment as well as more focused on global patterns.
The anterior cingulate tends to be larger in one hemisphere than in the other hemisphere. According to Morton and Rafto (2010), the side in which the anterior cingulate is larger represents the side in which this agency or will is located. Morton and Rafto (2010) undertook a study that verifies this possibility.
In this study, MRI was utilized to ascertain the size of various parts of the anterior cingulate cortex in 149 participants. First, this method was used to ascertain whether the paracingulate sulcus is negligible or prominent on each side. Second, the thickness of the ventral gyri of the anterior cingulate cortex was also assessed.
In addition, a series of six tests, all purportedly measures of hemisity, were administered. In one test, syllables were presented to both ears; participants were asked to write the syllable they could decipher. In another test, participants bisected a series of horizontal lines. If participants heard the left sound or bisected lines towards the right, their executive system was assumed to reside in the left hemisphere and vice versa.
As hypothesized, when the paracingulate sulcus was larger one side, the ventral gyri of the anterior cingulate cortex tended to be thicker on the same side. Furthermore, if these portions of the anterior cingulate cortex were larger on one side, test of hemisity also demonstrated a preference to the same side.
Role in psychopathology
Dysfunction of the anterior cingulate cortex might be prevalent in patients diagnosed with schizophrenia. These patients are often unable to respond optimally when they need to inhibit competing responses from distracters. In addition, in these patients, the error-related negativity--an event related potential that is evoked during the commission of errors and generated by the anterior cingulate cortex--is abnormal (see Holroyd, Nieuwenhuis, Mars, & Coles, 2004; Luu & Pederson, 2004)
The anterior cingulate might also be implicated in obsessive compulsive disorder. As shown by Pittenger, Bloch, Wegner, Teitelbaum, Krystal, and Coric (2006), glutamate activity seems low in this region in patients with obsessive compulsive disorder. In contrast, glutamate activity is elevated in many other regions in these patients.
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Created by Dr Simon Moss on 21/01/2009