Decision making in patients with spinal cord damage: afferent feedback and the somatic marker hypothesis.
Damasio has proposed an influential model of human decision making - the somatic marker hypothesis (Damasio AR. Descates' Error. London: Papermac/Macmillan, 1994), where he argues that somatic feedback to the brain influences decision making in man. It is proposed that when choosing between options that differ in relative risk, a somatic marker (e.g. a 'gut feeling') feeds back to the brain and influences cognitive appraisal. In the present study patients who had suffered a complete tetraplegia at the level of the sixth cervical vertebra were compared with matched healthy control subjects. As the spinal injury group have reduced somatic/peripheral feedback via the spinal cord, it was predicted, based on the somatic marker hypothesis, that they may demonstrate riskier behaviour than controls. All subjects completed the Iowa Gambling Task, a computerised card playing game where the player is instructed to try and win as much money as possible over 100 selections from one of four decks. The rules are not disclosed in advance, and the player gradually 'learns' that two of the decks are 'high risk' and lead to significant financial losses. Healthy individuals have previously been shown to learn to avoid the risky decks, whereas patients with medial frontal lobe damage (Bechara A, Damasio AR, Damasio H, Anderson SW. Insensitivity to future consequences following damage to human prefrontal cortex. Cognition 1994;50:7-15) and those with peripheral neuropathy (Bechara A, Tranel D, Wilson J, Heberlein AS, Ross M, Damasio AR, 1998. Impaired decision-making in peripheral neuropathy. Society for Neuroscience Abstracts 24:1176) select an excessive number from the risky decks, and consequently lose money. In the present study there were no significant differences between the spinal sectioned and healthy control groups in either card selection strategy or net financial outcome. This result suggests that in terms of the somatic marker hypothesis, feedback to the brain from the periphery via the cranial vagus and other nerves and the hormonal route may be equally or more influential than afferent feedback transmitted via the spinal cord.