The Somatic Marker Hypotheses, and what the Iowa Gambling Task does and does not show

Damasio’s Somatic Marker Hypothesis (SMH) is a prominent neuroscientific hypothesis about the mechanisms implementing decision-making. This paper argues that, since its inception, the SMH has not been clearly formulated. It is possible to identify at least two different hypotheses, which make different predictions: SMH-G, which claims that somatic states generally implement preferences and are needed to make a decision; and SMH-S, which specifically claims that somatic states assist decision-making by anticipating the long-term outcomes of available options. This paper also argues that neither hypothesis is adequately supported empirically; the task originally proposed to test SMH is not a good test for SMH-S, and its results do not support SMH-G either. In addition, it is not clear how SMH-G could be empirically invalidated, given its general formulation. Suggestions are made that could help provide evidence for SMH-S, and make SMH-G more specific.