NeuroRelay

Antonio Damasio (Professor of Neuroscience Director, Brain and Creativity Institute, author of Descartes’ Error: Emotion, Reason, and the Human Brain) defines the somatic marker hypothesis as being a mechanism by which emotional processes can bias behavior, particularly decision-making. The somatic marker hypothesis proposes there is an important connection between emotion and feeling and decision making. So a defect in emotion causes an impaired decision making.When we make decisions, we must assess the value of the choices available to us, using cognitive and emotional processes. When we face complex and conflicting choices, we may be unable to decide using only cognitive processes, which may become overloaded and unable to help us decide. In these cases, somatic markers can help us decide. Somatic markers are associations between reinforcing stimuli that induce an associated physiological affective state. Within the brain, somatic markers are thought to be processed in the ventromedial prefrontal cortex (VMPFC; a subsection of the orbitomedial PFC). These somatic marker associations can reoccur during decision-making and bias our cognitive processing. When we have to make complex and uncertain decisions, the somatic markers created by the relevant stimuli are summed to produce a net somatic state. This overall state biases our decision of how to act. This influence on our decision-making process may occur unconsciously, via the brainstem and ventral striatum, or consciously, engaging higher cortical cognitive processing. Damasio proposes that somatic markers direct attention towards more advantageous options, simplifying the decision process.

Antonio Damasio

There are decisions which don’t require conscious thought (getting hungry, avoiding a falling object) and others which do (decisions in social groups and engineering design) but they all rest on the same mechanism. In those that require conscious thought, complexities and uncertainty loom so large that reliable predictions are not easy to come by.

Acquisition of somatic markers is performed in the pre-frontal cortices (they receive signals from all other sensory regions in which images are formed, they receive signals from several bio-regulatory sectors of the brain, they themselves represent categorisations of the situations in which the organism has been involved and they are ideally suited to deciding and reasoning because they are directly connected to every avenue of motor and chemical response available).

Emotions, as defined by Damasio, are changes in both body and brain states in response to different stimuli. Physiological changes (e.g., muscle tone, heart rate, endocrine release, posture, facial expression, etc.) 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 change(s) become associated with particular situations and their past outcomes.

When making decisions in the future, these physiological signals (or ‘somatic markers’) and its evoked emotion are consciously or unconsciously associated with their past outcomes and bias decision-making towards certain behaviors while avoiding others. For instance, when a somatic marker associated with a positive outcome is perceived, the person may feel happy and motivate the individual to pursue that behavior. When a somatic marker associated with the negative outcome is perceived, the person may feel sad and act as an internal alarm to warn the individual to avoid a 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 the 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 response and cause fear. In the second pathway, cognitive representations of the emotions can be activated in the brain without being directly elicited by a physiological response—called the “as-if body loop”. For instance, imagining an encounter with a snake would initiate a similar flight-or-fight response “as-if” you were in that particular situation (albeit perhaps a much weaker one). In other words, 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.

Testing the Somatic Marker Hypothesis. It was found that patients with frontal lobe damage could generate a skin conductance response to “startle” as could “normal” patients. However, frontal damage patients did not generate any skin conductance response to “disturbing” pictures. One of the patients observed that he knew the pictures should be disturbing but that he was not disturbed – he knew but did not feel.
In gambling experiments, the frontal lobe damaged patients continued to choose the high gain / high risk option and continued to loose as a result while normals tended towards the low risk / low gain option to receive a net gain. This combined with the inverted version of the game demonstrated that frontal lobe damage patients were not merely insensitive to punishment but had developed myopia for the future.
Further experiments combining the gambling games and the skin conductance responses. Both normal and frontal lobe damage patients generated a skin conductance response as each punishment and reward was issued. The normal subjects developed (acquired) an increasing skin conductance response immediately prior to selecting from the high risk option while frontal lobe damage patients showed no acquired anticipatory response whatsoever.

References:

• Bechara, A. (2003). Risky business: Emotion, decision-making and addiction. Journal of Gambling Studies, 19, 23-51.
• Bechara, A., Damasio, A.R. (2005). The somatic marker hypothesis: A neural theory of economic decision. Games and Economic Behavior 52: 336–372.
• Bechara, A., Damasio, A.R., Damasio, H. & Anderson, S.W. (1994). Insensitivity to future consequences following damage to human prefrontal cortex. Cognition, 50, 7–12.
• Bechara, A., Tranel, D., Damasio, H., & Damasio, A.R. (1996). Failure to respond autonomically to anticipated future outcomes following damage to prefrontal cortex. Cerebral Cortex, 6 (2), 215-225.
• Damasio, A. (1991). Somatic Markers and the Guidance of Behavior. New York: Oxford University Press. pp. 217–299.
• Damasio, A.R. (1994). Descartes’ Error: emotion, reason, and the human brain. New York: Grosset/Putnam.
• Damasio, A.R. (1996) The Somatic marker hypothesis and the possible functions of the prefrontal cortex
• Damasio, A.R. (1999). The feeling of what happens. New York: Harcourt-Brace & Company.
• Damasio, A.R., Tranel, D. & Damasio, H. (1991). Somatic markers and the guidance of behaviour: theory and preliminary testing
• Bechara, A., Damasio, A.R., Damasio. (2000). Emotion, Decision Making and the Orbitofrontal Cortex. Cerebral Cortex, 10: 295-307