Healthy adult volunteers, whose levels of serotonin activity had been lowered, rated couples in photos as being less intimate and less romantic than volunteers with normal serotonin activity.
The approach involved giving amino acid drinks to two groups of volunteers in order to manipulate blood concentrations of the amino acid tryptophan, which is a vital ingredient in the synthesis of serotonin. One group received drinks that contained tryptophan. The other group received drinks that did not contain tryptophan. They were then asked to make judgments about sets of photographs of couples. Differences in the judgments made by the two groups reflected changes in their serotonin activity. [...]
The results raise the possibility that lower serotonin activity in people with depression and other psychiatric conditions could contribute to changes in the way they perceive personal relationships, or even in their ability to maintain positive personal relationships.
“Although this is only a small study, the same patterns may well extend to the way we perceive our own relationships,” said Professor Rogers. (via.)
The contrasts between disbelief and belief showed increased signal in the anterior insula, a region involved in the sensation of taste, the perception of pain, and the feeling of disgust, indicating that “false propositions might actually disgust us,” the authors state. “Our results appear to make sense of the emotional tone of disbelief, placing it on a continuum with other modes of stimulus appraisal and rejection,” they add.
Uncertainty evoked a positive signal in the anterior cingulate cortex (ACC) and a decreased signal in the caudate, a region of the basal ganglia, which plays a role in motor action. Noting that both belief and disbelief showed an increased signal in the caudate compared to uncertainty, the authors suggest that the basal ganglia may play a role in mediating the cognitive and behavioral differences between decision and indecision.
The study raises the possibility that the differences between belief, disbelief and uncertainty may one day be reliably distinguished by neuroimaging techniques. They conclude: “This would have obvious implications for the detection of deception, for the control of the placebo effect during the process of drug design, and for the study of any higher-cognitive phenomenon in which the differences between belief, disbelief, and uncertainty might be a relevant variable.” (via.)