Most people tend to reach reasonable decisions. For example, if they discover that eating some food always elicits problems, such as nausea, they will refrain from this food in the future. Nevertheless, some people do not seem to learn from previous experiences. They often choose courses of action that elicit unfavorable consequences. They sometimes even choose these actions when they know, on some logical level, these alternatives are unsuitable.
As Damasio (1994, 1999) has highlighted, this inability to learn from previous experiences sometimes reflects dysfunction in specific brain regions such as the amygdala and ventromedial prefrontal cortex. For example, in most individuals, when individuals are exposed to a significant event or object, like a reward or bully, the ventromedial prefrontal cortex will evoke an amalgam of the bodily sensations and feelings that similar experiences in the past had elicited. These bodily sensations and feelings them bias the thoughts and decisions of individuals. If the sensations and feelings, in general, are pleasant, individuals might be more likely to approach this event or object. If the sensations and feelings are unpleasant, individuals might be more likely to flee or avoid this event or object.
For example, suppose that a particular bully tends to elicit anxiety as well as increase the blood flow to the legs in someone. In the future, even thoughts about this person will elicit the same responses, although to a lesser extent. These responses will then deter individuals from visiting this person again.
When the ventromedial prefrontal cortex is damaged, the contemplation of some object or event will not evoke the corresponding bodily responses and feelings. Individuals might not then approach or avoid this object or event when applicable (see also Jameson, Hinson, & Whitney, 2004).
This model emerged from an examination of patients with bilateral lesions--that is, damage--to the ventromedial region near the front part of the brain, towards the midline. These patients demonstrated a specific profile of difficulties.
Specifically, many of their capacities remained intact (Eslinger and Damasio, 1985& Saver and Damasio, 1991). They could readily solve logical problems, for example. Their comprehension of language, attention, and working memory were generally intact (see working memory).
These individuals, however, did not perform effectively if the problems entailed risk and uncertainty. They did not shun alternatives that elicited negative consequences, as studies with the Iowa Gambling Task showed (see measures of risky decision making).
In daily life, these individuals also exhibit many problems. They can plan their work day very well, because this task demands predictions about which activities will be beneficial. Their finances often decline severely, as they select unsuitable alternatives. They cannot choose, establish, or maintain friendships effectively. They seldom express emotions. In short, their choices are often unsuitable--a deficiency they do not demonstrate before the injury.
According to Damasio (1994, 1996), the ventromedial prefrontal cortex, together with other regions, might rapidly integrate and weigh all the potential consequences of some alternative or event, indicating whether this option is suitable. When this circuit or region is damaged, participants cannot utilize this signal to guide their decisions. Instead, they need to consider these benefits and drawbacks with conscious deliberation, impeding the efficiency of decisions as well as overlooking many possible consequences of these alternatives.
Over time, with more precision in their instruments, researchers showed that impairments confined to a specific region of the ventromedial prefrontal cortex--the orbitofrontal cortex--is especially likely to compromise performance on this task (see Bechara, 2004). The studies in this article that examined the ventromedial prefrontal cortex actually tended to investigate the orbitofrontal cortex in particular.
To understand the somatic marker hypothesis, the precise definition of various terms need to be clarified. The key terms are emotion, somatic, body states, as-if body states, and somatic marker.
People often assume that an emotion is merely a subjective feeling, like a feeling of anger, happiness, or sadness. However, Damasio (1994, 1999, 2003) defined emotion more precisely. Specifically, each emotion corresponds to a specific cluster of changes in the body and brain. Each emotion is evoked by perceptions of some object or event--like a person with a frown--partly biased by thoughts or memories of similar events in the past.
Changes in the body, called somatic or body states, might include variations in facial expression, posture, hormones, heart rate, and muscle contractions. Anger, for example, might correspond to a scowl and increased blood flow to the upper body as well as many other physiological responses.
Changes in the brain correspond to the release of neurotransmitters, including dopamine, serotonin, noreadrenaline, and acetylcholine. These changes also include mental representations of the bodily changes, partly underpinned by the insular cortex. That is, these mental representation, called as-if body states, roughly code or classify the complex array of physiological changes. Each code or signal corresponds to a specific pattern or suite of bodily states. These mental representations elicit the subjective experience of a feeling. Anger, for example, might elicit a mental representation that signals that blood flow has increased to the upper body as well as other bodily states, corresponding to a feeling of rage, without coding every somatic change.
The bodily changes that underpin emotions can be evoked by two classes of objects and events: primary inducers and secondary inducers (Damasio, 1995). Primary inducers elicit pleasant or unpleasant states and range from snakes to the realization of a solution to a problem. In some instances, primary inducers are inherently pleasant or unpleasant, such as the smile of a parent. In other instances, individuals learn that a primary inducer is pleasant or unpleasant after a sequence of positive or negative experiences. Even objects or events that merely predict a pleasant or unpleasant consequence--like a frown, which predicts a hostile response--are primary inducers.
In contrast to primary inducers, secondary inducers are thoughts or memories of a primary inducer. When evoked, these thoughts or memories elicit the corresponding somatic states, such as increases in heart rate. The memory of a snake--rather than the actual observation of a snake--represents a secondary inducer.
Some objects or events represent both primary and secondary inducers. The picture of a sick baby might automatically elicit changes in the body and brain, corresponding to a primary inducer. However, this picture could also evoke thoughts in individuals about how their own children could experience this illness, corresponding to a secondary inducer.
Different regions mediate primary and secondary inducers. Primary inducers are primarily underpinned by the amygdala. When this region is damaged, the somatic response to emotional objects or events, like a snake, is limited: A sense of intensity or urgency dissipates.
In particular, the amygdala establishes associations between emotional objects or events--the primary inducers--and somatic responses. The emotional objects or events are processed unconsciously by circuits that include the thalamus or consciously by circuits that entail sensory and association regions of the cortex. The somatic responses are underpinned by the hypothalamus and autonomic brainstem nuclei, which underpin visceral responses, as well as the ventral striatum, periacqueductal gray, and other regions, which underpin facial expressions and overt movements. Hence, the amydala, in essence, connects and integrates these regions.
Secondary inducers are primarily underpinned by the ventromedial prefrontal cortex. When this region is damaged, somatic changes or subjective feelings--that is, as-if body states--in response to emotional memories are dampened. Specifically, over time, individuals learn that specific patterns of somatic or bodily states recur. They might learn that increased blood flow to the arms may sometimes correspond to decreased blood flow to the legs. These patterns are essentially represented as specific codes in various regions such as the insular cortex, cingulate cortices and other somatosensory regions.
Hence, thoughts about a specific emotional event, like a bully, will evoke these representations. These representations will then activate similar bodily responses as the original emotional event, but to a lesser extent. If the bully increased blood flow to the legs, memories of this bully may also increase blood flow to the legs but to a lesser extent.
The ventromedial prefrontal cortex, in essence, connects or couples the memories and thoughts with somatic states and subjective feelings. That is, the memories or thoughts of an emotional event are represented in association regions of the cortex and converge on the ventromedial prefrontal cortex. This region then affects the activation of structures that coordinate the somatic or bodily responses as well as structures, like the basal forebrain, brainstem, and insular, that represent the unconscious or conscious feelings that correspond to these somatic patterns. In essence, the ventromedial prefrontal cortex attempts to activate or simulate the somatic responses to emotional events from knowledge, thoughts, or memories of these episodes.
Initially, if the associations between some emotional event and the consequences are not strong, only unconscious regions, like the basal forebrain and brainstem, are activated by the ventromedial prefrontal cortex. If the associations between some emotional event and the consequences are more established, conscious regions, like the insular, are activated as well. Thus, initially at least, some of these somatic responses are not experienced consciously.
Lesions to systems that represent primary inducers compromise the development but not maintenance of secondary inducers. If the amygdala is damaged, for example, individuals will not experience intense negative states if hit by a bully. Therefore, in the future, thoughts about this bully will not evoke these negative states. The bully will not become a secondary inducer. However, bullies that had previously been represented as secondary inducers will continue to elicit unpleasant states, even after the amygdala is damaged.
Sometimes, individuals need to decide between two alternatives, such as whether to drive rapidly or not. In many of these instances, information about these events is received by the ventromedial prefrontal cortex. This region then transmits output to the hypothalamus, brainstem, and other structures that generate the corresponding somatic or bodily states, like increased blood flow to the arms. This somatic or bodily states then transmits information back to subcortical and cortical regions via the spinal cord, humoral signals, and vagus nerve (Bechara, 2002).
Specifically, these somatic states can affect activity and processing in four systems. First, these somatic states affect regions, like the insular or SII, that represent patterns of bodily changes and elicit feelings. Thus, the somatic states can refine the feelings that individuals experience.
Second, these somatic states also transfer information back to the amygdala and ventromedial prefrontal cortex. This loop can increase or decrease the threshold that needs to be exceeded to activate these somatic states in the future. For example, suppose the ventromedial prefrontal cortex activates a specific set of bodily responses that is then punished in some sense. A loop that increases the threshold that must be reached to activate these bodily responses in the future would be adaptive.
Third, and more importantly, the somatic states can influence activity in regions that are associated with working memory, such as the dorsolateral prefrontal cortex, and motor selection, such as the striatum, anterior cingulate, and supplementary motor area. Accordingly, these bodily states can bias which concepts are salient in working memory as well as which responses are preferred. This facet of the loop partly underpins the association between emotion and decision making.
In some contexts, output from the ventromedial prefrontal cortex is not strong enough to elicit observable physiological changes. Nevertheless, some secondary inducers may elicit changes in the neurotransmitters and brain regions but not in the body itself, called the as if body loop. That is, the ventromedial prefrontal cortex transmits information directly to the brain stem, representing unconscious representations of somatic patterns, and the insular, SII and SI regions, representing conscious representations of these somatic patterns. In this instance, the somatic states are, in essence, simulated rather than actually enacted in the body (Damasio, 1994, 1996& Damasio, Tranel, & Damasio, 1991).
According to Bechara and Damasio (2005), when uncertainty or ambiguity are pronounced, the as if loop is more influential than is the body loop. That is, if individuals have not been exposed to an event before, or cannot predict which event is likely to unfold, the as if loop is more likely to guide decisions. Both loops, however, bias decisions.
As Bechara and Damasio (2005) highlight, in general, emotions bias working memory and decisions to optimize behavior. That is, decisions can incorporate a vast array of previous experiences. In particular, a concatenation of pleasant and unpleasant responses and sensations shape decisions.
Nevertheless, in some settings, these emotions can be misleading. That is, emotions that are evoked by extraneous forces, such as drugs, might maladaptively bias decisions. In these instances, the emotions are not related to the task. Therefore, the emotions are not informative but bias decisions anyway. Emotions, if evoked by other stimuli, could thus compromise performance on the Iowa gambling task and other activities.
Evidence to support the somatic marker hypothesis has mainly been derived from the Iowa gambling task (see also measures of risky decision making) coupled with physiological indices. The Iowa Gambling Task is usually administered over computer (see Bechara, Damasio, Tranel, Damasio, 1997). Typically, four decks of cards are presented, face down, labeled A, B, C, and D, each comprising 40 cards. Participants begin with a specific amount of money, such as $1000. Usually, the money is not real, although sometimes small amount of real money are used instead. This amount is specified on the screen, sometimes above the decks.
The participants then select a card from any of the four decks. Usually, they merely click a mouse onto a specific deck. Each card can generate a reward, a penalty, or both. After a card is selected, this reward and penalty appears on the screen for several seconds. To illustrate, one card might generate a reward of $100, a penalty of $150, and thus a net loss of $50. Their overall amount would then shift from $1000 to $950.
Participants then repeat this process many times. The number of trials, however, is not usually specified. Nevertheless, 100 trials are often presented.
Unbeknownst to participants, the probability of a reward and penalty as well as the distribution of these rewards and penalties varies across the decks. That is, two of the decks, over time, are more likely to incur losses than are the other two decks. Specifically, the two disadvantageous decks, on average, might lose $25. The two advantageous decks, on average might gain $25.
Nevertheless, the losses that each deck incurs vary across trials and, therefore, is difficult to decipher at first. For one of the advantageous decks, each card generates a gain of $50, and one in two cards incurs a loss of $50. For the other advantageous deck, each card generates a gain of $50, and one in ten cards incurs a loss of $250. For one of the disadvantageous decks, each card generates a gain of $100, and one in ten cards incurs a loss of $1250. Finally, for the other disadvantageous decks, each card generates a gain of $100, and one in every two cards incurs losses that range from of $150 to $350, although variations to these schemes can be included.
Typically, at the outset, most participants will choose the disadvantageous decks, because the gains are higher. Over time, usually within the first 40 trials, participants learn to choose the advantageous decks. Nevertheless, participants with lesions in specific regions of the prefrontal cortex, such as the ventromedial regions (Bechara, Damasio, Tranel, & Anderson, 1994), as well as some substance abusers or offenders do not learn to choose the advantageous decks.
To show that somatic states and emotions guide decisions, measures such as skin conductance can be assessed while participants complete the Iowa gambling task. In some studies, the amygdala, the ventromedial prefrontal cortex, or neither of these regions have been damaged in participants (e.g., Bechara, Damasio, Damasio, & Lee, 1999).
In participants with no damage to these regions, skin conductance responses are evoked, representing physiological arousal, after they receive a reward or punishment. Furthermore, after experience with this task, these responses are evoked before participants select a card, especially from the risky, disadvantageous packs. These participants, therefore, seem to experience a somatic, and perhaps aversive, state as they contemplate these disadvantageous packs.
In contrast, in participants with damage to the ventromedial prefrontal cortex, the skin conductance responses are evoked, but to a lesser extent, after they receive a reward or punishment. Nevertheless, before they choose a pack, even after experience with the task, they do not exhibit these responses. Hence, these individuals do not experience a somatic state that could deter unsuitable choices. Finally, participants with damage to the amygdala do not even exhibit the skin conductance responses after they receive a reward or punishment.
Bechara, Damasio, Tranel, and Damasio (1997) showed that somatic states and feelings can affect decisions even when participants are not aware of the reasons or rationale of their decisions. In one variant of the Iowa gambling task, the game is interrupted midway, at various times, and participants are asked questions about their awareness or strategies.
In participants with no damage to either the amygdala or ventromedial prefrontal cortex, the skin conductance responses are evoked after these individuals begin to preferentially choose the advantageous decks but before they experience a conscious hunch or intuition about which deck is beneficial. When the ventromedial prefrontal cortex is damaged, participants do not exhibit these skin conductance responses at any time and never develop a hunch or intuition about which decks are advantageous. Interestingly, 50% of these individuals did eventually realize that two decks were disadvantageous but would continue to select these decks at the previous rate anyway. Conscious understanding , therefore, did not seem to translate into actual behavior: Knowledge and behavior are often dissociated. In short, when these regions are intact, the somatic states and feelings seem to bias decisions either towards some alternatives even without rational awareness or deliberation.
Conclusions derived from the effects of lesions have also been confirmed in PET studies. For example, in one study (Ernst et al., 2002), PET scans were administered while participants completed the Iowa Gambling Task or a control task, in which they merely selected cards in a specified order. The primary regions that were activated included the ventromedial prefrontal cortex as well as the anterior cingulate cortex, dorsolateral prefrontal cortex, insula, and adjacent inferior parietal cortex, especially on the right side. Besides the ventromedial prefrontal cortex, the other regions represent working memory as well as representations of somatic patterns.
In general, fMRI studies have uncovered a similar, but not identical, pattern of findings as PET studies. In one study, event related fMRI was administered while healthy participants completed the Iowa Gambling Task (e.g., Fukui, Murai, Fukuyama, Hayashi, & Hanakawa, 2005). While contemplating their decisions, activation of the anterior cingulate and the neighboring medial frontal gyrus were activated--regions close, but superior, to the ventromedial prefrontal cortex.
More convincingly, Northoff et al. (2006) showed that activation of the ventromedial prefrontal cortex did correlate with performance on certain trials. Specifically, if activation of this region was especially active on trials in which the outcome was unexpected, performance on the Iowa Gambling Task improved rapidly. Presumably, this region enables individuals to learn from trials that diverge from their previous expectations.
Nevertheless, research shows that other regions of the prefrontal cortex might also be related to performance on the Iowa Gambling Task. In one study, conducted by MacPherson, Phillips, Della Sala, and Cantagallo (2008), performance on this task was impaired in individuals with damage to the prefrontal cortex relative to healthy control participants. Nevertheless, no difference was discovered between the individuals with damage to the ventromedial prefrontal cortex and individuals with damage to other regions of the prefrontal cortex. The number of participants with damage to other regions of the prefrontal cortex, however, was only 6.
As Maia and McClelland (2004) showed, if participants are probed more forcefully, they seem to concede more awareness of which decks are better, significantly earlier than previously assumed. Nevertheless, Persaud et al. (2007) showed that such questions could encourage participants to reconstruct a strategy they did not actually apply consciously while they completed the decision. That is, when participants are asked these probing questions, they are more willing to wage money on their beliefs about the task. Hence, the questions themselves seem to affect, rather than merely gauge, the beliefs of individuals.
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