Ventromedial prefrontal cortex
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|Ventromedial prefrontal cortex|
Ventromedial prefrontal cortex shown on medial and ventral views of the brain, reflecting approximate location of damage in patients with decision making deficits.
Medial surface of the brain with Brodmann's areas numbered.
|Latin||Cortex praefrontalis ventromedialis|
|Anatomical terms of neuroanatomy|
The ventromedial prefrontal cortex (vmPFC) is a part of the prefrontal cortex in the mammalian brain. The ventral medial prefrontal is located in the frontal lobe at the bottom of the cerebral hemispheres and is implicated in the processing of risk and fear. It also plays a role in the inhibition of emotional responses, and in the process of decision making.
While the ventromedial prefrontal cortex does not have a universally agreed on demarcation, in most sources, it is equivalent to the ventromedial reward network of Ongur and Price. This network includes Brodmann area 10, Brodmann area 14, Brodmann area 25, and Brodmann area 32, as well as portions of Brodmann area 11, Brodmann area 12, and Brodmann area 13. However, not all sources agree on the boundaries of the area. Different researchers use the term ventromedial prefrontal cortex differently. Sometimes, the term is saved for the area above the medial orbitofrontal cortex, while at other times, 'ventromedial prefrontal cortex' is used to describe a broad area in the lower (ventral) central (medial) region of the prefrontal cortex, of which the medial orbitofrontal cortex constitutes the lowermost part. This latter, broader area, corresponds to the area damaged in patients with decision-making impairments investigated by António Damásio and colleagues (see diagram, and below).
To get a rough idea of where the ventromedial prefrontal cortex is, recall that the left and right hemispheres of the brain are separated [by the longitudinal cerebral fissure]. Now imagine you could take your hand and starting at the anterior brain (where your forehead is) insert it into this gap until you reached the insula (a structure that is beneath the frontal lobe). Your palm would be touching a part of the prefrontal cortex, which is in the front part of the brain and the lower part of your palm would be touching the ventral medial prefrontal cortex.
The ventromedial prefrontal cortex is connected to and receives input from the ventral tegmental area, amygdala, the temporal lobe, the olfactory system, and the dorsomedial thalamus. It, in turn, sends signals to many different brain regions including; The temporal lobe, amygdala, the lateral hypothalamus, the hippocampal formation, the cingulate cortex, and certain other regions of the prefrontal cortex. This huge network of connections affords the vmPFC the ability to receive and monitor large amounts of sensory data and to affect and influence a plethora of other brain regions, particularly the amygdala.
Functional differences between the orbitofrontal and ventromedial areas of the pre-frontal cortex have not yet been clearly established, although the areas of the ventromedial cortex superior to the orbitofrontal cortex are much less associated with social functions and more with pure emotion regulation. Research in developmental neuroscience also suggested that neural networks in the ventromedial prefrontal cortex are rapidly developing during adolescence and young adulthood supporting emotion regulation through the amygdala, being associated with a decrease in cortisol levels.
There are only a few reports of people with early-onset vmPFC (for instance, during childhood), but these individuals tend to have severe antisocial behavior and impaired moral judgment. Compared to individuals with damage later in life, their behavior pattern is similar but more severe.
Patients with bilateral lesions of the vmPFC develop severe impairments in personal and social decision-making even though most of their intellectual ability is preserved. For instance, they have difficulties in choosing between options with uncertain outcomes, whether the uncertainty is in the form of a risk or of an ambiguity. After their lesion, these patients have an impaired capacity to learn from their mistakes, making the same decisions again and again even though they lead to negative consequences. These patients choose alternatives that give immediate rewards, but seem to be blind to the future consequences of their actions. However, the underlying mechanisms of this behaviour are not yet fully understood.
Damage to the ventromedial prefrontal cortex (especially in the right hemisphere) has been connected with deficits in detecting irony, sarcasm, and deception. Subjects with damage in this area have been found to be more easily influenced by misleading advertising. This has been attributed to a disruption of a "false tagging mechanism" which provides doubt and skepticism of new beliefs.
People with damage to the ventromedial prefrontal cortex still retain the ability to consciously make moral judgments without error, but only in hypothetical situations presented to them. There is a gap in reasoning when applying the same moral principles to similar situations in their own lives. The result is that people make decisions that are inconsistent with their self professed moral values. People with early damage to the ventromedial prefrontal cortex are more likely to endorse self-serving actions that break moral rules or cause harm to others. This is especially true for patients whose damage occurred the earliest in life.
Regulation of emotion
Activation of the vmPFC is associated with successful suppression of emotional responses to a negative emotional signal. Patients with vmPFC lesions show defects both in emotional response and emotion regulation. Their emotional responsivity is generally diminished and they show markedly reduced social emotions such as compassion, shame and guilt. These are emotions that are closely associated with moral values. Patients also exhibit poorly regulated anger and frustration tolerance in certain circumstances.
Patients with focal lesions in the vmPFC show personality changes such as lack of empathy, irresponsibility, and poor decision making. These traits are similar to psychopathic personality traits.
The right half of the ventromedial prefrontal cortex was associated with regulating the interaction of cognition and affect in the production of empathic responses. Hedonic (pleasure) responses were also associations to orbitofrontal cortex activity level by Morten Kringelbach. This finding contributes findings suggesting ventromedial prefrontal cortex being associated with preference judgement, possibly assigning the ventromedial prefrontal cortex a key role in constructing one's self. Studies with PTSD also supported the idea that the ventromedial prefrontal cortex is an important component for reactivating past emotional associations and events, therefore essentially mediating pathogenesis of PTSD. Treatments geared to the activation of the ventromedial prefrontal cortex were therefore suggested for PTSD. The right half of the ventrolateral prefrontal cortex, being active during emotion regulation, was activated when participants were offered an unfair offer in a scenario. Specific deficits in reversal learning and decision-making have led to the hypothesis that the ventromedial prefrontal cortex is a major locus of dysfunction in the mild stages of the behavioural variant of frontotemporal dementia.
The capacity for mature defense mechanisms such as intellectualization, compensation, reaction formation, and isolation has been tied to proper functioning of the right ventromedial prefrontal cortex, while more primitive defense mechanisms such as projection, splitting, verbal denial, and fantasy have been found to rely on other regions, primarily in the left hemisphere .
Somatic marker hypothesis
One particularly notable theory of vmPFC function is the somatic marker hypothesis, accredited to António Damásio. By this hypothesis, the vmPFC has a central role in adapting somatic markers—emotional associations, or associations between mental objects and visceral (bodily) feedback—for use in natural decision making. This account also gives the vmPFC a role in moderating emotions and emotional reactions because whether the vmPFC decides the markers are positive or negative affects the appropriate response in a particular situation. However, a critical review of this hypothesis concluded that there is a need for additional empirical data to support the somatic marker theory.
Another role that the vmPFC plays is in the process of extinction, the gradual weakening and eventual cessation of a conditioned response. The specific role played by the vmPFC concerning extinction is not well understood, but it is believed that it plays a necessary role in the recall of extinction learning after a long period of time. Studies show that it aids in the consolidation of extinction learning. A separate study has implicated the correlation between the cortical thickness of the vmPFC and the degree of extinction memory. Patients with larger vmPFCs tended to have lower responses to the extinct conditioned stimulus, therefore suggesting a superior extinction memory. In general, the ventromedial prefrontal cortex plays a major role in the later stages of memory consolidation.
Ventromedial prefrontal cortex lesions were also associated with a deficit in processing gender specific social cues. One experiment tested the ability of patients with vmPFC lesions to categorize gender-specific names, attributes, and attitudes compared to patients with dorsolateral prefrontal cortex lesions and control subjects. Whereas the patients with dorsolateral prefrontal cortex lesions performed similarly to the control subjects on tests indicating gender stereotypes, patients with ventromedial prefrontal cortex lesions demonstrated impaired stereotypic social knowledge.
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