The anterior cingulate cortex is a region of the brain that is activated by sensation, cognition, and emotion. It appears to play an important role in autonomic, affective, and cognitive behavior. Because of its position, the anterior cingulate is anatomically and functionally well positioned to integrate information across the physical, intellectual and emotional domains. Important in the stress reaction, the anterior cingulate region is activated during self-regulation of arousal through its connections with the cholinergic basal forebrain. The whole structure, but especially area 32, produces inhibitory inputs that decrease amygdala responsiveness and are helpful in mitigating the effects of fear and in preventing or at least delaying “amygdala hijacks.”
The normal functioning of the anterior cingulate area leads to a normal response to stressful events, which is a psychophysiological arousal or increased emotionality. The normality of the brain response to traumatic stimuli also serves to inhibit feelings of fear when there is no true threat. Any chemical or structural failure of activation in this area and/or decreased blood flow in the adjacent subcallosal gyrus can lead to an exaggerated response to stress, resulting in significantly higher emotionality and the inability to properly regulate fear. The latter condition provides the inducing cues in anxiety disorders, i.e. increased and persistent fearfulness that is not appropriate for the context.
What the Anterior Cingulate Does
Physically, stimulation of the anterior cingulate (especially in area 24) induces changes in blood pressure, heart rate, respiratory rate, pupillary dilation, skin conductance, thermoregulation, gastrointestinal motility, and changes in adrenal cortical hormone secretion (ACTH). Cognitively, the anterior cingulate cortex plays a leading role in learning new behaviors, whether as a conditioned response to predictors of painful stimuli, as an instrumental response to avoid such stimuli, or in response to reduced reward. Emotionally, the anterior cingulate (along with other structures in the limbic system) mediates emotional responses including fear, agitation, and euphoria, and verbal expression with affective content, such as sighs, cries, and screams.
Neuroimaging studies with powerful fMRI instruments show electrical activation in the rostral–ventral anterior cingulate cortex when individuals under study are asked to recall sad memories or view faces with sad expressions, when they are told to anticipate an upcoming painful electric shock, and when exposed to scenes or words with emotional content. It should come as no surprise that stress-induced activations in the amygdala and orbitofrontal cortex occur simultaneously with those in the anterior cingulate cortex.
Genes, Stress and the Anterior Cingulate
Genetic studies have conclusively demonstrated that the anterior cingulate cortex is highly sensitive to environmental stressors, either physical, psychological, or behavioral. Anoxia (lack of oxygen), maternal separation, amyloid protein expression, and drug abuse all induce hypometabolism, gliosis, and programmed cell death in the anterior cingulate cortex. After prolonged and continued exposure to stress, nerve cells in the anterior cingulate cortex are damaged and killed by excessive stimulation, a process called excitotoxicity.
When the Anterior Cingulate Malfunctions
Several psychiatric disorders are linked with abnormalities in the function of the anterior cingulate cortex. Significantly elevated neurochemical activity in this region of the brain has been observed in obsessive–compulsive disorder, tic disorder, and depression. A normal range of activity is restored with behavioral and pharmacological treatment of these disorders. Other psychiatric disorders that have been associated with abnormal functioning of the anterior cingulate cortex include attention deficit hyperactivity disorder (ADHD) and schizophrenia.