 21. Emotion and Personality  465
cal pain, when apparently being excluded 
from a three-  person game (DeWall et al., 
2011). Individuals who rely more strongly 
on cognitive reappraisal as an emotion regu -
lation strategy show heightened prefrontal 
cortex activity and lower amygdala activity 
while looking at others’ facial expressions 
of negative emotion (e.g., Drabant, McRae, 
Manuck, Hariri, & Gross, 2009). Moreover, 
those who implement instructed reappraisal 
more effectively in the laboratory also show 
greater inverse connectivity between these 
two structures, consistent with more effi -
cient use of cognitive control to modulate 
emotional attention and response (e.g., Lee, 
Heller, Van Reekum, Nelson, & Davidson, 
2012).
Variations in brain activity have multiple 
causes, from inherited genes to differential 
experiences shaping development. A par -
ticularly well-  documented example of how 
tiny genetic variations can translate into 
meaningful differences in neural activity, 
and thence into a wide array of individual 
differences in emotional experience, is pro -
vided by research on the serotonin trans -
porter gene. In humans, the serotonin trans -
porter gene ( 5-HTT ) codes for a protein 
that supports reuptake of serotonin back 
into the presynaptic axon terminal after it 
is released, reducing the time that this neu -
rotransmitter can activate receptors on the 
other side. A particular stretch of this gene 
(5-HTTLPR ) comes in “long” and “short” 
forms: the long-form version is more effec -
tive at vacuuming serotonin from the syn -
aptic gap; the short-form is less so, allow -
ing serotonin to linger longer. Early research 
suggested that short allele carriers were 
more at risk for mood disorders; they tend to 
be slightly higher on neuroticism (Schinka, 
Busch, & Robichaux-  Keene, 2004), more 
prone to anxiety (Lesch et al., 1996), and 
at higher risk for depression (Ogilvie et al., 
1996). Subsequent studies helped uncover 
mediators of the gene–  emotion effects. For 
example, individuals carrying one or more 
short alleles show a stronger attentional bias 
toward threat stimuli than those with two 
long alleles (Osinsky et al., 2008; Pergamin- 
Hight, Bakermans-  Kranenburg, Van IJzen -
doorn, & Bar-Haim, 2012). This attentional 
bias may be accounted for by individual dif -
ferences in brain activation supporting the detection of threats; specifically, people with 
one or more copies of the short serotonin 
transporter allele show heightened amyg -
dala reactivity to threat stimuli as well (e.g., 
Hariri et al., 2002).
More recently, studies suggest not sim -
ply that the short form of the gene confers 
risk for negative emotion, but rather that it 
promotes heightened emotional reactivity 
in general, in a true person × environment 
interaction. Short allele carriers who have 
experienced unusually intense life stress are 
at heightened risk for depression, but this is 
not the case for those with less stressful lives 
(Caspi et al., 2003; for a meta-  analysis, see 
Karg, Burmeister, Shedden, & Sen, 2011). 
In some studies, short-  allele carriers show 
an attentional bias not only to threaten -
ing stimuli but also to positive ones, such 
as happy facial expressions (e.g., Beevers et 
al., 2011; Beevers, Wells, Ellis, & McGeary, 
2009) though some studies have failed 
to replicate the effect for positive stimuli 
(e.g., Perez-Edgar et al., 2010). Those with 
two short alleles have been found to show 
more intense visceral responses to film clips 
depicting others in distress (Gyurak et al., 
2013), more smiling in response to positive 
stimuli (Haase et al., 2015), and their mari -
tal satisfaction is more closely linked to the 
profiles of negative and positive emotional 
behavior displayed during conflict with the 
spouse (Haase et al., 2013). These studies 
suggest that those carrying the short form 
of the serotonin transporter may respond to 
the environment with higher-  amplitude af -
fect rather than having an overall negative 
bias, but the search for the exact nature and 
mechanisms of these effects goes on. Over -
all, although our understanding of the neu -
ral basis of emotion is still in its infancy, it 
has tremendous promise for illuminating the 
origins of individual difference in various as -
pects of emotional response.
Biases in  Bodily Awareness:  Interoception
As emotions unfold, the brain tracks and 
represents the body’s visceral responses: 
Shifts in cardiovascular profile, digestive ac -
tivity, blush, chills, tears, dry mouth, mus -
cle tension, and breathing are transformed 
through complex processes beginning in the 
body in response to subjective experiences 