![Ventromedial prefrontal cortex](https://upload.wikimedia.org/wikipedia/commons/c/c8/Ventromedial_prefrontal_cortex.png)
The somatic marker hypothesis, formulated by
Antonio Damasio
Antonio Damasio ( pt, António Damásio) is a Portuguese-American neuroscientist. He is currently the David Dornsife Chair in Neuroscience, as well as Professor of Psychology, Philosophy, and Neurology, at the University of Southern California, ...
and associated researchers, proposes that
emotion
Emotions are mental states brought on by neurophysiological changes, variously associated with thoughts, feelings, behavioral responses, and a degree of pleasure or displeasure. There is currently no scientific consensus on a definition. ...
al processes guide (or bias)
behavior
Behavior (American English) or behaviour (British English) is the range of actions and mannerisms made by individuals, organisms, systems or artificial entities in some environment. These systems can include other systems or organisms as wel ...
, particularly decision-making.
[ '' Descartes' Error'']
"Somatic markers" are feelings in the body that are associated with emotions, such as the association of rapid heartbeat with
anxiety
Anxiety is an emotion which is characterized by an unpleasant state of inner turmoil and includes feelings of dread over anticipated events. Anxiety is different than fear in that the former is defined as the anticipation of a future threat wh ...
or of
nausea
Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the ...
with
disgust
Disgust (Middle French: ''desgouster'', from Latin ''gustus'', "taste") is an emotional response of rejection or revulsion to something potentially contagious or something considered offensive, distasteful, or unpleasant. In ''The Expression o ...
. According to the hypothesis, somatic markers strongly influence subsequent decision-making. Within the brain, somatic markers are thought to be processed in the
ventromedial prefrontal cortex
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 r ...
(VMPFC) and the
amygdala
The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain's cerebrum in complex verteb ...
. The hypothesis has been tested in experiments using the
Iowa gambling task
The Iowa gambling task (IGT) is a psychological task thought to simulate real-life decision making.
It was introduced by Antoine Bechara, Antonio Damasio, Hanna Damasio and Steven Anderson, then researchers at the University of Iowa. It has been ...
.
Background
In
economic theory
Economics () is the social science that studies the production, distribution, and consumption of goods and services.
Economics focuses on the behaviour and interactions of economic agents and how economies work. Microeconomics analyzes ...
, human decision-making is often modeled as being devoid of emotions, involving only logical reasoning based on
cost-benefit calculations. In contrast, the somatic marker hypothesis proposes that emotions play a critical role in the ability to make fast, rational decisions in complex and uncertain situations.
[
Patients with frontal lobe damage, such as ]Phineas Gage
Phineas P. Gage (18231860) was an American railroad construction foreman known for his improbable survival of an accident in which a large iron rod was driven completely through his head, destroying much of his brain's left frontal lobe, and ...
, provided the first evidence that the frontal lobes were associated with decision-making. Frontal lobe damage, particularly to the ventromedial prefrontal cortex
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 r ...
(vmPFC), results in impaired abilities to organize and plan behavior and learn from previous mistakes, without affecting intellect in terms of working memory
Working memory is a cognitive system with a limited capacity that can hold information temporarily. It is important for reasoning and the guidance of decision-making and behavior. Working memory is often used synonymously with short-term memory, ...
, attention
Attention is the behavioral and cognitive process of selectively concentrating on a discrete aspect of information, whether considered subjective or objective, while ignoring other perceivable information. William James (1890) wrote that "Atte ...
, and language comprehension and expression.
vmPFC patients also have difficulty expressing and experiencing appropriate emotions. This led Antonio Damasio to hypothesize that decision-making deficits following vmPFC damage result from the inability to use emotions to help guide future behavior based on past experiences. Consequently, vmPFC damage forces those affected to rely on slow and laborious cost-benefit analyses for every given choice situation.
Antonio Damasio
Antonio Damasio ( pt, António Damásio) is a Portuguese-American
Portuguese Americans ( pt, português-americanos), also known as Luso-Americans (''luso-americanos''), are citizens and residents of the United States who are connected to the country of Portugal by birth, ancestry, or citizenship.
Americans and ...
neuroscientist
A neuroscientist (or neurobiologist) is a scientist who has specialised knowledge in neuroscience, a branch of biology that deals with the physiology, biochemistry, psychology, anatomy and molecular biology of neurons, Biological neural network, n ...
. He is currently the David Dornsife Professor of Neuroscience, Psychology and Philosophy at the University of Southern California
The University of Southern California (USC, SC, or Southern Cal) is a Private university, private research university in Los Angeles, California, United States. Founded in 1880 by Robert M. Widney, it is the oldest private research university in C ...
and an adjunct professor at the Salk Institute
The Salk Institute for Biological Studies is a scientific research institute located in the La Jolla community of San Diego, California, U.S. The independent, non-profit institute was founded in 1960 by Jonas Salk, the developer of the polio vacci ...
. Damasio heads the Brain and Creativity Institute
Brain and Creativity Institute (BCI) is a research unit of the College of Letters, Arts and Sciences at the University of Southern California, which aims to "gather new knowledge about the human emotions, decision-making, memory, and communication ...
, and has authored several books: his most recent work, ''Self Comes to Mind: Constructing the Conscious Brain'' (2010), explores the relationship between the brain and consciousness. Damasio's research in neuroscience has shown that emotions play a central role in social cognition and decision-making.
Hypothesis
When individuals make decisions, they must assess the incentive
In general, incentives are anything that persuade a person to alter their behaviour. It is emphasised that incentives matter by the basic law of economists and the laws of behaviour, which state that higher incentives amount to greater levels of ...
value of the choices available to them, using cognitive
Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...
and emotional processes. When the individuals face complex and conflicting choices, they may be unable to decide using only cognitive processes, which may become overloaded. Emotions, consequently, are hypothesized to guide decision-making.
Emotions, as defined by Damasio, are changes in both body and brain states in response to stimuli.[ Physiological changes (such as ]muscle tone
In physiology, medicine, and anatomy, muscle tone (residual muscle tension or tonus) is the continuous and passive partial muscle contraction, contraction of the muscles, or the muscle's resistance to passive stretch during resting state.O’Sull ...
, heart rate
Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excr ...
, endocrine activity, posture
Posture or posturing may refer to:
Medicine
* Human position
** Abnormal posturing, in neurotrauma
** Spinal posture
** List of human positions
* Posturography Posturography is the technique used to quantify postural control in upright stance in ...
, facial expression
A facial expression is one or more motions or positions of the muscles beneath the skin of the face. According to one set of controversial theories, these movements convey the emotional state of an individual to observers. Facial expressions are a ...
, and so forth) occur in the body and are relayed to the brain where they are transformed into an emotion that tells the individual something about the stimulus that they have encountered. Over time, emotions and their corresponding bodily changes, which are called "somatic markers", become associated with particular situations and their past outcomes.
When making subsequent decisions, these somatic markers and their evoked emotions are consciously or unconsciously associated with their past outcomes, and influence decision-making in favor of some behaviors instead of others.[ For instance, when a somatic marker associated with a positive outcome is perceived, the person may feel happy and thereby motivated to pursue that behavior. When a somatic marker associated with the negative outcome is perceived, the person may feel sad, which acts as an internal alarm to warn the individual to avoid that course of action. These situation-specific somatic states based on, and reinforced by, past experiences help to guide behavior in favor of more advantageous choices, and therefore are adaptive.
According to the hypothesis, two distinct pathways reactivate somatic marker responses. In the first pathway, emotion can be evoked by changes in the body that are projected to the brain – called the "body loop". For instance, encountering a feared object like a snake may initiate the ]fight-or-flight
The fight-or-flight or the fight-flight-or-freeze response (also called hyperarousal or the acute stress response) is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to survival. It was first des ...
response and cause fear. In the second pathway, cognitive representations of the emotions (imagining an unpleasant situation "as if" you were in that particular situation) can be activated in the brain without being directly elicited by a sensory stimulus – called the " as-if body loop". Thus, the brain can anticipate expected bodily changes, which allows the individual to respond faster to external stimuli without waiting for an event to actually occur. The amygdala and VMPFC (a subsection of the orbitomedial prefrontal cortex or OMPFC) are essential components of this hypothesized mechanism, and therefore damage to either structure will disrupt decision-making.
Experimental evidence
In an effort to produce a simple neuropsychological tool that would assess deficits in emotional processing, decision-making, and social skills
A social skill is any competence facilitating interaction and communication with others where social rules and relations are created, communicated, and changed in verbal and nonverbal ways. The process of learning these skills is called social ...
of OMPFC-lesion
A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals.
Types
There is no designated classifi ...
ed individuals, Bechara and collaborators created the Iowa gambling task
The Iowa gambling task (IGT) is a psychological task thought to simulate real-life decision making.
It was introduced by Antoine Bechara, Antonio Damasio, Hanna Damasio and Steven Anderson, then researchers at the University of Iowa. It has been ...
. The task measures a form of emotion-based learning. Studies using the gambling task have found deficits in various neurological (such as amygdala
The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain's cerebrum in complex verteb ...
and OMPFC lesions) and psychiatric populations (such as schizophrenia
Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations (typically hearing voices), delusions, and disorganized thinking. Other symptoms include social withdra ...
, mania
Mania, also known as manic syndrome, is a mental and behavioral disorder defined as a state of abnormally elevated arousal, affect, and energy level, or "a state of heightened overall activation with enhanced affective expression together wit ...
, and drug abuse
Substance abuse, also known as drug abuse, is the use of a drug in amounts or by methods which are harmful to the individual or others. It is a form of substance-related disorder. Differing definitions of drug abuse are used in public health, ...
rs).
The Iowa gambling task is a computerized test in which participants are presented with four decks of cards from which they repeatedly choose. Each deck contains various amounts of rewards of either $50 or $100, and occasional losses that are greater in the decks with higher rewards. The participants do not know where the penalty cards are located, and are told to pick cards that will maximize their winnings. The most profitable strategy turns out to be to choose cards only from the small reward/small penalty decks, because although the reward is smaller, the penalty is proportionally much smaller than in the high reward/high penalty decks. Over the course of a session, most healthy participants come to adopt the profitable low-penalty deck strategy. Participants with brain damage, however, are unable to determine the better deck to choose from, and continue to choose from the high reward/high penalty decks.
Since the Iowa gambling task measures participants' quickness in "developing anticipatory emotional responses to guide advantageous choices", it is helpful in testing the somatic marker hypothesis. According to the hypothesis, somatic markers give rise to anticipation of the emotional consequences of a decision being made. Consequently, persons who perform well on the task are thought to be aware of the penalty cards and of the negative emotions associated with drawing such cards, and to realize which deck is less likely to yield a penalty.
This experiment has been used to analyze the impairments of people with damage to the ventromedial prefrontal cortex, which has been known to affect neural signaling of prospective rewards or punishments. Such persons perform less well on the task.[ ]Functional magnetic resonance imaging
Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area o ...
(fMRI) has been used to analyze the brain during the Iowa gambling task. The brain regions that were activated during the Iowa gambling task were also the ones hypothesized to be triggered by somatic markers during decision-making.
Evolutionary significance
Damasio has posited that the ability of humans to perform abstract thinking quickly and efficiently coincides with both the development of the ventromedial (VM) cortex and with the use of somatic markers to guide human behavior during evolution. Patients with damage to the VM cortices are more likely to engage in behaviors that negatively impact personal relationships in the distant future, but they never engage in actions that would lead to immediate harm to themselves or others.[ The evolution of the prefrontal cortex was associated with the ability to represent events that may occur in the future.]
Application to risky behavior
The somatic marker hypothesis has been applied to trying to understand risky behaviors, such as risky sexual behavior
Risky sexual behavior is the description of the activity that will increase the probability that a person engaging in sexual activity with another person infected with a sexually transmitted infection will be infected or become pregnant, or make ...
and drug addiction.
According to the hypothesis, riskier sexual behaviors are more exhilarating and pleasurable, and therefore they are more likely to stimulate repetitive engagement in such behaviors. When this idea was tested in individuals who were infected with HIV
The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune ...
and were substance dependent, differences were found between persons who scored well in the Iowa gambling test, and those who scored poorly. The high scorers showed a correlation between the amount of distress they reported having over their HIV status, and their acceptance of risk during sexual behavior – the greater the distress, the greater the risk that these people would take. The low scorers, on the other hand, showed no such correlation. These results were interpreted as indicating that persons with intact decision-making abilities are better able to rely on past emotional experiences when weighing risks, than are persons who are deficient in such abilities, and that acceptance of risk serves to ameliorate emotional distress.
Drug abusers are thought to ignore the negative consequences of addiction while seeking drugs. According to the somatic marker hypothesis, such abusers are impaired in their ability to recall and consider past unpleasant experiences when weighing whether to consider drug seeking behaviors. Researchers analyzed the neuroendocrine
Neuroendocrine cells are cells that receive neuronal input (through neurotransmitters released by nerve cells or neurosecretory cells) and, as a consequence of this input, release messenger molecules ( hormones) into the blood. In this way they b ...
responses of substance-dependent individuals and healthy individuals after being shown pleasant or unpleasant images. In response to unpleasant images, drug users showed decreased levels of several neuroendocrine markers, including norepinephrine
Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter. The name "noradrenaline" (from Latin '' ad'', ...
, cortisol
Cortisol is a steroid hormone, in the glucocorticoid class of hormones. When used as a medication, it is known as hydrocortisone.
It is produced in many animals, mainly by the ''zona fasciculata'' of the adrenal cortex in the adrenal gland ...
, and adrenocorticotropic hormone
Adrenocorticotropic hormone (ACTH; also adrenocorticotropin, corticotropin) is a polypeptide tropic hormone produced by and secreted by the anterior pituitary gland. It is also used as a medication and diagnostic agent. ACTH is an important c ...
. Addicts showed lesser responses to both pleasant and unpleasant images, suggesting that they may have a diminished emotional response. Neuroimaging
Neuroimaging is the use of quantitative (computational) techniques to study the structure and function of the central nervous system, developed as an objective way of scientifically studying the healthy human brain in a non-invasive manner. Incre ...
studies utilizing fMRI indicate that drug-related stimuli have the ability to activate brain regions involved in emotional evaluation and reward processing. When shown a film of people smoking cocaine
Cocaine (from , from , ultimately from Quechuan languages, Quechua: ''kúka'') is a central nervous system (CNS) stimulant mainly recreational drug use, used recreationally for its euphoria, euphoric effects. It is primarily obtained from t ...
, cocaine users showed greater activation of the anterior cingulate cortex
In the human brain, the anterior cingulate cortex (ACC) is the frontal part of the cingulate cortex that resembles a "collar" surrounding the frontal part of the corpus callosum. It consists of Brodmann areas 24, 32, and 33.
It is involved ...
, the right inferior parietal lobe
The parietal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus.
The parietal lobe integrates sensory informa ...
, and the caudate nucleus
The caudate nucleus is one of the structures that make up the corpus striatum, which is a component of the basal ganglia in the human brain. While the caudate nucleus has long been associated with motor processes due to its role in Parkinson's di ...
than did non-users. Conversely, the cocaine users showed lesser activation when viewing a sex film than did non-users.
Criticism
Some researchers believe that the use of somatic markers (i.e., afferent feedback) would be a very inefficient method of influencing behavior. Damasio's notion of the ''as-if'' experience dependent feedback route, whereby bodily responses are re-represented utilizing the somatosensory cortex (postcentral gyrus
In neuroanatomy, the postcentral gyrus is a prominent gyrus in the lateral parietal lobe of the human brain. It is the location of the primary somatosensory cortex, the main sensory receptive area for the somatosensory system, sense of touch. Lik ...
), also proposes an inefficient method of affecting explicit behavior. Rolls (1999) stated that; "it would be very inefficient and noisy to place in the execution route a peripheral response, and transducers to attempt to measure that peripheral response, itself a notoriously difficult procedure" (p. 73). Reinforcement association located in the orbitofrontal cortex and amygdala, where the incentive value of stimuli is decoded, is sufficient to elicit emotion-based learning and to affect behavior via, for example, the orbitofrontal-striatal pathway. This process can occur via implicit or explicit processes.
The somatic marker hypothesis represents a model of how feedback from the body may contribute to both advantageous and disadvantageous decision-making in situations of complexity and uncertainty. Much of its supporting data comes from data taken from the Iowa gambling task. While the Iowa gambling task has proven to be an ecologically valid measure of decision-making impairment, there exist three assumptions that need to hold true.
First, the claim that it assesses implicit learning as the reward/punishment design is inconsistent with data showing accurate knowledge of the task possibilities and that mechanisms such as working-memory appear to have a strong influence. Second, the claim that this knowledge occurs through preventive marker signals is not supported by competing explanations of the psychophysiology generated profile. Lastly, the claim that the impairment is due to a 'myopia for the future' is undermined by more plausible psychological mechanisms explaining deficits on the tasks such as reversal learning, risk-taking, and working-memory deficits. There may also be more variability in control performance than previously thought, thus complicating the interpretation of the findings.
Furthermore, although the somatic marker hypothesis has accurately identified many of the brain regions involved in decision-making, emotion, and body-state representation, it has failed to clearly demonstrate how these processes interact at a psychological and evolutionary level. There are many experiments that could be implemented to further test the somatic marker hypothesis. One way would be to develop variants of the Iowa gambling task that control some of the methodological issues and interpretation ambiguities generated. It may be a good idea to include removing the reversal learning confound, which would make the task more difficult to consciously comprehend. Additionally, causal tests of the somatic marker hypothesis could be practiced more insistently in a greater range of populations with altered peripheral feedback, like on patients with facial paralysis.
In conclusion, the somatic marker hypothesis needs to be tested in more experiments. Until a wider range of empirical approaches are employed in order to test the somatic marker hypothesis, it appears that the framework is simply an intriguing idea that is in need of some better supporting evidence. Despite these issues, the somatic marker hypothesis and the Iowa gambling task reestablish the notion that emotion has the potential to be a benefit as well as a problem during the decision-making process in humans.
References
External links
*
{{DEFAULTSORT:Somatic Marker Hypothesis
Neuropsychology
Behavior
Emotion
Hypotheses
Somatic psychology