That fringe feeling we get that we should be wary, suspicion, rises into consciousness from time to time – but where does it come from?

A recent item in ScienceDaily (here) reports on a paper by Bhatt, Lohrenz, Camerer and Montague, Distinct contributions of the amygdala and parahippocampal gyrus to suspicion in a repeated bargaining game. They separate two types of suspicion.

“We found a strong correlation between the amygdala and a baseline level of distrust, which may be based on a person’s beliefs about the trustworthiness of other people in general, his or her emotional state, and the situation at hand. What surprised us, though, is that when other people’s behavior aroused suspicion, the parahippocampal gyrus lit up, acting like an inborn lie detector.”

One way to think of this is that there is a default level of wariness set by the amygdala. It is on a spectrum from being trusting as a default to being suspicious as a default for each individual and would also change with the danger of the situation and the day to day level of confidence of the individual. The parahippocampal gyrus on the other hand reacts to the probability that a particular person is untrustworthy.

So, the fringe feeling of wariness comes from the amygdala but the attribute of untrustworthiness associated with a specific individual comes from the parahippocampal gyrus.

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