P1vital CNS Experimental Medicine : EMOTION POTENTIATED STARTLE

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Antidepressants that inhibit the reuptake of serotonin (SSRIs) or noradrenaline are effective in the treatment of disorders such as depression and anxiety. Cognitive theories emphasize the importance of correcting negative biases of information processing in the non-pharmacological treatment of these disorders, but it is not known whether antidepressant drugs can directly modulate the neural processing of affective information.

Consequently, researchers in Oxford led by Prof Guy Goodwin have assessed the actions of repeated antidepressant administration on perception and memory for positive and negative emotional information in healthy volunteers.

Forty-two male and female volunteers were randomly assigned to 7 days of double-blind intervention with the SSRI citalopram (20 mg/day), the selective noradrenaline reuptake inhibitor reboxetine (8 mg/day), or placebo. On the final day, facial expression recognition, emotion- potentiated startle response, and memory for affect-laden words were assessed. Questionnaires monitoring mood, hostility, and anxiety were given before and after treatment. In the facial expression recognition task, citalopram and reboxetine reduced the identification of the negative facial expressions of anger and fear. Citalopram also abolished the increased startle response found in the context of negative affective images. Both antidepressants increased the relative recall of positive (versus negative) emotional material. These changes in emotional processing occurred in the absence of significant differences in ratings of mood and anxiety. However, reboxetine decreased subjective ratings of hostility and elevated energy. The effects of citalopram on the processing of fear are consistent with a role for the amygdala in SSRI action.

The amygdala plays a primary role in the enhanced startle response during fear, largely characterized in animal models, but supported by studies of patients with amygdala damage. Thus fear potentiated startle may provide an alternative method for assessing the action of novel antidepressants.