Serotonin-transporter polymorphism, early life events and emotional information processing

The serotonin transporter (5-HTT) is known to be the key regulator of
serotonergic neurotransmission, which in turn affects a wide range of behaviors
(Lesch et al, 2003). A common polymorphism in the linked promoter region of the
5-HTT gene results in variants that involve a homozygous short (ss) allele or a
long (ll) allele or a heterozygous (sl) allele. Individuals who carry one or
two copies of the s allele are found to have increased levels of extracellular
serotonin compared to those with two copies of the l allele, which may render
them vulnerable to depression (Heils et al., 1996; Lesch et al., 1996).
Recent research has tried to examine the association between the 5HTT
polymorphism and cognitive functioning. Hariri and colleagues (2002, 2005)
assessed neural activation in a relatively small number of s allele carriers
during perceptual processing of fearful and angry human facial expressions.
This simple perceptual task is known to reliably engage the amygdala (Hariri et
al., 2000), a brain region that is central to the neural circuitry mediating
emotional arousal and vigilance across species (Davis & Whalen, 2001). During
the task, s allele carriers exhibited nearly fivefold greater amygdala activity
than ll homozygotes. Using a facial emotion recognition task Marsh et al (2006)
found that effects of acute tryptophan depletion on the processing of
emotional expressions varies as a function of genotype at the 5-HTT. Depletion
impaired the recognition of fear in s carriers but not in ll homozygotes.

The aim of this study is to further investigate the relationship between
5-HTTLPR genotype and emotional processing. Recent literature suggests that s
allele carriers of the 5HTT have a greater risk of developing depression in
response to stressful life events (Caspi et al, 2003; Wilhelm et al, 2006). The
s allele may facilitate processing of negative emotional information, and this
association may be moderated by adverse life experiences. Further, it seems
likely that mood induction procedures can enable latent differences in
emotional processing to become manifest (Mannie et al.,2007; Beevers et al.,
2007); thus, a mood induction will be included in the study.

Correlational study.

Sequence:
-Psychiatric interview
-Questionnaires
-Inf proc test
-Sad mood induction
-Inf proc test

Burden: sad mood induction. Effects are small and short-lasting (few minutes).