Serotonergic Function and Emotion-Related Processing

Much of the human research relevant to this idea has examined behavioral effects of serotonergic function experimentally, using acute tryptophan depletion to temporarily reduce serotonin. Tryptophan depletion has been shown to impair performance on cognitive tasks of executive processes such as reversal learning, memory, and attention tasks (Park et al., 1994; Riedel, Klaassen, Deutz, van Someren, & van Praag, 1999). Tryptophan depletion affects performance on behavioral and cognitive tasks that have emotional components. As an example, tryptophan depletion impairs the ability to inhibit responses to previously rewarded cues (Cools, Blackwell, et al., 2005; Park et al., 1994; Rogers et al., 2003). It is noteworthy that the strongest effect of tryptophan depletion found by Cools, Blackwell, et al. (2005) was among people who reported being highly impulsive. This pattern is consistent with the two-mode model.

A particular focus has been on how cognitive tasks that involve emotional stimuli are affected by tryptophan depletion. For example, in one study acute tryptophan depletion led female participants to show slower processing of happy words (but not sad ones) in an affective go/no-go task (F. C. Murphy, Smith, Cowen, Robbins, & Sahakian, 2002). This study also found impairment on the first round of a reversal task involving reward and punishment, but no impairment on a task without affective stimuli.

Tryptophan depletion generally does not affect mood per se among persons with no personal or family history of depression (Benkelfat, Ellenbogen, Dean, & Palmour, 1994; Park et al., 1994). However, the impairment in suppressing emotion-relevant stimuli suggests that tryptophan depletion might exaggerate mood change in response to a stressor. Consistent with that possibility, tryptophan depletion has led persons to report more sadness during exposure to uncontrollable stress (aversive noise), whereas the effect was only minor when the noise was controllable (Richell, Deakin, & Anderson, 2005).

Evidence for the role of serotonin in inhibition of responses to emotion-relevant stimuli has also emerged in one study of tryptophan supplements (which enhance serotonin availability). Women given tryptophan supplements for 14 days showed decreased recognition of disgusted faces and a diminished startle response to negative pictures, as well as an increase in the ability to recognize subtle facial expressions of happiness, compared with a control group (S. E. Murphy, Longhitano, Ayres, Cowen, & Harmer, 2006). The effect did not emerge for men.

Дата добавления: 2015-11-14