Decision making in humans: the effect of manipulating the central noradrenergic system.

OBJECTIVES: Damasio has proposed an influential model of human decision making-the Somatic Marker Hypothesis (SMH), where he argues that somatic feedback to the brain influences decision making in humans. It is proposed that when choosing between options that differ in relative risk, a somatic marker (for example, a "gut feeling") feeds back to the brain and influences cognitive appraisal. This study tested the hypothesis that the noradrenergic system may play a part in this afferent feedback process. METHODS: Thirty healthy young adults were randomly allocated to receive placebo, 4 mg, or 8 mg reboxetine (a new selective noradrenergic reuptake inhibitor that acts to increase central noradrenergic activity). It is hypothesised that enhancement of central noradrenergic activity may amplify the effect of afferent feedback, and lead to altered decision making. All subjects completed the Iowa Gambling Task (IGT), 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. RESULTS: There were no significant differences between the three groups in gambling task performance. CONCLUSION: This result suggests that central noradrenergic activity may not be critically involved in the afferent feedback mechanism that is central to the somatic marker hypothesis.

Dissociation of affective modulation of recollective and perceptual experience following amygdala damage.

It has been suggested that similar neural mechanisms may underlie the affective modulation of both recollective and perceptual experience. A case is reported of a patient who has bilateral amygdala damage and marked impairment in the perception of emotion, particularly fear. The patient DR and 10 healthy control subjects (matched for school leaving age, intelligence quotient, and non-emotional memory performance) were shown a series of slides accompanied by an emotionally arousing narrative. One week later DR and the controls were given a surprise memory test for this material. In addition, they completed a verbal memory test using emotionally arousing stimuli. Both DR and the healthy control subjects showed a normative pattern of enhanced memory for emotional material. On the basis of these results and the previously demonstrated impairment of perception of emotion in this patient, it is concluded that different neural mechanisms may underlie affective modulation of recollective and perceptual experience.