An Evaluation of the Somatic Marker Hypothesis
Through the Lens of Emotion
Decision-making in moments of uncertainty may elicit an array of emotional responses. The somatic marker hypothesis posits that emotions are an integral part of decision-making. The theory centers on the premise that the sensations prompted by emotional events serve as a feedback mechanism in our decision-making processes regardless of whether we are consciously aware of them (Poppa & Bechara, 2018; Konstantinidis & Shanks, 2014). The somatic marker hypothesis provides explanations for a wide variety of behaviors including the advantageous processing of emotions in complex social circumstances (Beer, 2017), risk taking during gain and loss conditions (Wright & Rakow, 2017; Konstantinidis & Shanks, 2014) and emotion processing in opiate users (Biernacki et al., 2017).
Poppa and Bechara (2018) provide an updated neurophysiological framework for the dynamics of somatic states and how they influence decisions via afferent feedback. The authors recognize that although the ventromedial prefrontal cortex (VMPFC) and the mesial orbitofrontal cortex (OFC) are critical components of the neural network associated decision-making, an amalgamate of the peripheral nervous system and cortical and subcortical regions like the amygdala, somatosensory cortex and the insular cortex are also involved.
The somatic marker hypothesis holds the VMPFC as the center for linking complex situations and the associated bioregulatory processes or emotional states (Poppa & Bechara, 2018). Moreover, the VMPFC takes a lead role in reactivating somatic patterns that emerge out of confronting situations that are the same or similar to those previously encountered (Poppa & Bechara, 2018). This characteristic makes the VMPFC critical for learning adaptive ways for making decisions under uncertainty. Poppa and Bechara (2018) refer to this reactivation process as a ‘body-loop’ and they cite studies done on patients with focal brain damage to the VMPFC, amygdala and insula that show how altered autonomic responses illustrate the role of the body-loop in facilitating advantageous decision-making.
The processes behind the body-loop can be examined by answering the question of how somatic states are triggered and how they affect decision-making. The somatic marker hypothesis proposes that primary inducers (sensory stimuli that are innate or learned) and secondary inducers (sensory stimuli that are generated via recall) trigger somatic states (Poppa & Bechara, 2018). The amygdala has been associated with the former and the VMPFC with the latter (Poppa & Bechara, 2018). To answer the aforementioned question, Poppa and Bechara (2018) comment on the evidence suggesting that visceral processes are mediated by afferent the vagus nerve—a complex, autonomic, endocrine, and immune regulatory bridge between the body and the brain— which exerts its role in high-order cognition by altering neurotransmitters involved in learning and memory found in the brainstem. This insight also serves as a response to the recurrent criticism of the somatic marker hypothesis, which is that it falls short in explaining high-order cognitive processes. The complex interplay between somatic states and cognition explains how the body-loop described by the somatic marker hypothesis guides decision-making.
In order to measure how failure to react to somatic markers (e.g. increased heart rate and sweating) affects advantageous decision-making in patients with damage to the VMPFC, researchers created the Iowa Gambling Task (Wright & Rakow, 2017). This tasks consists of four decks of cards with two decks that tend to give positive net outcomes and two decks that tend to give negative net outcomes with higher immediate rewards that must be forgone in order to perform well on the task (Wright & Rakow, 2017). The somatic marker hypothesis explains that the intact somatic marker responses to high punishments in the bad decks seen in healthy participants enables them to perform well on the task (Wright & Rakow, 2017). The most common assessment of somatic markers manifested during the performance of the Iowa Gambling Task is skin conductance responses (Wright & Rakow, 2017). Because poor performance is seen in both healthy participants and patients with focal brain damage, the validity of Iowa Gambling Task is called into question.
As means to explore the applicability of the somatic marker hypothesis in other decision-making tasks, Wright and Rakow (2017) conducted a study where they examined performance on the Balloon Analogue Risk Task in conjunction with physiological responses (i.e. skin conductance). The Balloon Analogue Risk Task prompts participants to inflate a virtual balloon while being rewarded with money/points for each additional “pump” and punished with losing their rewards if the balloon bursts before they decided to collect their rewards (Wright & Rakow, 2017). The findings for this study suggest that there is little support for skin conductance guiding decision-making during the Balloon Analogue Risk Task. However, Wright and Rakow (2017) found that somatic states during trials that ended in a burst prompted greater skin conductance than trials where the participant decided to collect their rewards. The author concluded that there is distinctive physiological arousal when making decisions under uncertainty, but that this somatic states may not affect decision-making through the feedback mechanisms the somatic marker hypothesis puts forth.
Guided by the notion that somatic states may influence our decisions in moments of uncertainty beyond our awareness, Konstantinidis and Shanks (2014) examined how participants wager after partaking in the Iowa Gambling Task. The authors explain that one of the limitations of the Iowa Gambling Task is its failure to indicate at what stage participants learn the advantageous strategy and whether this piece of knowledge is accompanied by implicit signals that bias judgment. Furthermore, Konstantinidis and Shanks (2014) cite studies showing that conscious knowledge alone does not affect performance on the Iowa Gambling Task, studies that arrive at the conclusion that healthy participants decide advantageously before knowing the advantageous strategy, and studies that recognize the role of unconscious affective processes in decision-making scenarios like the Iowa Gambling Task.
Konstantinidis and Shanks (2014) assessed conscious knowledge in the Iowa Gambling Task by interjecting during the task and asking participants: “Tell me all you know about what is going in the game” and “Tell me how you feel about the game.” The authors also asked participants to place wagers on their earnings to examine their confidence on their decisions. Findings from this study show that acquired conscious knowledge—instead of the activation of implicit somatic states as proposed by the somatic marker hypothesis—is the main influence in decision strategies employed in the Iowa Gambling Task.
The original vision for the somatic marker hypothesis was to explain the severe impairments in decision-making in social and personal domains seen in patients with certain types of damage to prefrontal brain areas (Konstantinidis and Shanks, 2014). Beer (2017) comments on the applicability of the somatic marker hypothesis for explaining optimal decisions in social situations, which are guided by the way in which one processes emotional information elicited by the situation. She cites studies showing that patients that do not have afferent feedback of emotional arousal, as in the case of patients with spinal cord injuries, perform well on the Iowa Gambling Task. This is one of the reasons why research aiming to address the role of emotion in social cognition is relying less on the somatic marker hypothesis and more on the dual-process theories. The dual-process theories posit that two modes of reasoning (automatic and controlled) shape judgment and decision and facilitate the study of the neural underpinnings of emotion in social cognition (Beer, 2017).
Another application of the somatic marker hypothesis is in studying the decision-making processes involved in opiate use. The deficits in decision-making associated with opiate use suggest that substance users may experience abnormal somatic states involving reward and punishment (Biernacki et al., 2018).
Ultimately, the somatic marker hypothesis is not an all-encompassing theory for explaining the relationship between emotional states and decision-making, but it provides a reasonable paradigm for analyzing how somatic states influence the actions we take under uncertainty.