Damasio’s Somatic Marker Hypothesis Originated from the observation of individuals who had sustained damage to the ventromedial prefrontal cortex. Normal intellectual function Normal Neuropsychological function Normal on tests sensitive to frontal lobe function However, severe impairment in personal and social decision making and conduct. Difficulty with planning in the immediate, and future. No longer able to make personally advantageous decisions Often sustain social, personal, economic losses

The only deficit that could be detected was one in which these individuals failed to display emotion in situations in which emotion would be normatively expected. This led Damasio to posit that these individuals manifest a deficit in reasoning that is secondary to deficits in emotional processing. Within Damasio’s theory, the concept of convergence zones is important (This concept is also important in LeDoux’s theory of emotional experience, which we will discuss in two weeks’ time). Convergence zones are areas in the brain in which inputs from geographically / anatomically / functionally disparate regions come together and are integrated. Keeps a record (in the form of a memory trace or predisposition) of regions that, when active simultaneously (as a set) define the characteristics of a particular complex situation. For example, information from primary sensory regions (including somatosensory cortex), secondary sensory regions, association cortices, the hippocampus, the amygdala, and other prefrontal regions.

The VMPFC is ideally situated to fulfill such a role given its extensive bi-directional connections with brain regions responsible for the processing of the characteristics of complex situations. Damasio believes that the VMPFC is the crucial structure for learning the association between the characteristics of certain complex situations and the emotional state (and thus the somatosensory pattern) that has predominantly been associated with that situation in an individual’s past (through learning). Note that this theory is fully compatible with the James-Lange theory of emotion in that the relevant feature of emotion is the perception of bodily changes (Damasio refers to these as ‘somatic’, and includes musculoskeletal, visceral, and internal milieu components of physiology). When a situation occurs again, the VMPFC can reactivate the somatosensory pattern of the relevant emotion. These represent the ‘gut feelings’ that we have when we encounter particular stimuli or situations.

This can occur in two ways: 1) Through a ‘body loop’ in which bodily changes actually occur, and the information is relayed back to the somatosensory cortex. 2) Through an ‘as if’ loop in which the information about the relevant somatosensory patterns are conveyed directly to the somatosensory cortex, and thus bypass the bodily route. Damasio believes that the establishment / experience of a somatosensory (feeling state) appropriate to particular situations (based on an individual’s learning history) help us to reason about what is the most appropriate / adaptive course of action by constraining the process of reasoning over multiple options and outcome scenarios. The constraint operates according to a mechanism of qualification in which results from somatosensory patterns are juxtaposed to the information about the situation that triggered that pattern, and thus ‘marks’ it as potentially favourable or harmful.

That is, as you consider an option-outcome scenario, the somatic changes that are elicited by the VMPFC mark the scenario as one that is good or bad, and help you to make your decision. This process can happen in either an overt manner (you actually feel the somatic changes), which serve as an ‘alarm function’ (which theories does this invoke?), or a covert manner in which the changes affect attention and working memory by biasing them towards certain option-outcome scenarios (which theory does this invoke?). Thus, the somatic changes triggered by the VMPFC help to constrain the ‘problem space’ by allowing us to reason among fewer option-outcome scenarios… this biases us away from particular scenarios and towards others, based on our previous experience with these situations, and the feelings that are engendered when we consider or experience them again.

Consequently, the problem space becomes manageable for cost-benefit analysis. In the absence of a somatic marker, all option-outcome scenarios are given equal weighting, and logical / rational analysis must operate over too many contingencies… consequently, and individual may become ‘lost in thought’, or may respond randomly or impulsively (which is exactly what is seen in VMPFC patients). This notion of constraining the problem space, and the instrumental role of emotion in reason is integral to another theory we have studied… Which one?

Neuroanatomical justification: the VMPFC receives projections from all relevant brain structures necessary to link the characteristics of complex situations to particular emotional states and somatosensory response patterns. Also, the VMPFC is the only frontal lobe structure to have access to autonomic control regions (amygdala, hypothalamus, and brain stem), in order to cause bodily changes through activation of the ANS and consequent changes in the viscera, and endocrine system. Why emotion? Certain classes of situations concerning personal and social matters are frequently linked to reward and punishment, and thus to approach and withdrawal related systems in the brain related to emotion.

Thus, in normal individuals, the experience of complex situations (formed and processed in a distributed manner as a collection of propositional facts) are accompanied by body states that represent the typical emotional response that has been associated with that situation in the individual’s learning history. The propositional facts are held in dispositional form in appropriate association cortex (I.e. memory), while the somatic state does not have to be stored, because it can be reconstituted. All that has to be stored are the linkages between situations and the somatic states that accompany them, and Damasio believes that this these linkages are held in dispositional form in the VMPFC. Thus, individuals with damage to the VMPFC cannot elicit somatic states appropriate to the particular scenario encountered or considered, and thus cannot use these to guide their information processing and decision making.

Evidence for Damasio’s hypothesis 1) Psychophysiological investigation of emotional arousal in patients with damage to the VMPFC. Measured SCR in normal controls, brain damaged controls, and patients with VMPFC damage when presented with neutral / abstract or emotionally charged visual images. All groups reliably elicited increased SCRs to startle and deep breathing. Normal and brain damaged control subjects showed SCRs to emotionally evocative stimuli, while VMPFC patients did not. Damasio suggests that these results support the contention that VMPFC patients cannot generate somatic markers to emotionally arousing stimluli.

Gambling Experiments: Patients with VMPFC damage continue to select cards from the decks that incur losses, while normal controls sample from all decks for a while, but then gradually begin playing more frequently from the good decks (net gain) than from the bad decks. This is analogous to VMPFC patients’ inability to decide upon an advantageous course of action, when contingencies / future outcomes are uncertain. It is not possible to cognize the ‘rules’ or contingencies for the decks, so subjects must rely on their intuition or ‘gut instinct’ of which decks to play from. Normal controls manifest a SCR just prior to selecting a card from a bad deck (but not from a good deck… ‘somatic marker’?), while patients with VMPFC damage do not.