 22. The Approach System as a Component of Personality 497
strong conceptual resemblance to BAS, as -
sessed at 54 months of age, predicted exter -
nalizing behaviors assessed at 15 years.
Consistent with the self-  report findings, 
hypersensitivity of the mesolimbic dopami -
nergic reward system has been implicated in 
a range of externalizing syndromes (Baskin- 
Sommers & Foti, 2015). Of note, heightened 
activation of the NAcc during reward an -
ticipation has been shown to correlate with 
externalizing symptoms and alcohol depen -
dence (Bjork et al., 2010), psychopathy (Pu -
jara et al., 2014), and cannabis use (Nestor, 
Hester, & Garavan, 2010).
Overactive Approach Motivation and  Mania
In its initial incarnation, the BAS hypersen -
sitivity model of bipolar disorder emerged 
from the observation that the core symptoms 
of mania overlap considerably with the out -
puts of the BAS, such as increased activity 
and heightened high arousal positive affect 
(Depue & Iacono, 1989). Direct tests of the 
relationship between self-  reported BAS sen -
sitivity and mania have generally supported 
this model. Of import, BAS sensitivity is 
prospectively related to initial onset of bipo -
lar spectrum disorders (Alloy et al., 2012) 
and to the course and severity of manic 
symptoms over time (Alloy et al., 2008; B. 
Meyer, Johnson, & Winters, 2001).
These findings converge with evidence 
that willingness to set ambitious goals has 
itself been found to predict the onset of bi -
polar disorder in at-risk individuals (Alloy et 
al., 2012) and a more severe course of mania 
over time among those diagnosed with bipo -
lar I disorder (Johnson, Carver, et al., 2012; 
Tharp, Johnson, Sinclair, & Kumar, 2016). 
Among persons with bipolar disorder, goal 
attainment is often followed by unusually 
persistent elevations in positive affect (Farm -
er et al., 2006), large increases in energy and 
effort (Fulford, Johnson, Llabre, & Carver, 
2010), and higher levels of manic symptoms 
(Johnson et al., 2000, 2008).
These self-  report findings are comple -
mented by behavioral and neurophysiologi -
cal evidence of increased willingness to ex -
pend effort for reward (e.g., Harmon-  Jones 
et al., 2008; Hayden et al., 2008) higher 
spontaneous eye blink rate in anticipation 
of reward (a proxy for dopaminergic func -tion; Peckham & Johnson, 2015), and dif -
ferential activity in the ventral striatum and 
orbitofronal cortex in response to reward 
(see Nusslock, Young, & Damme, 2014, for 
a review). Taken together, self-  report and 
biobehavioral findings provide compelling 
support for the notion that hypersensitivity 
of BAS is involved in the etiology of mania 
and bipolar disorder, although it has recently 
been suggested that the BAS hypersensitiv -
ity model may be overly broad, in that only 
certain facets of the BAS are dysregulated in 
bipolar disorder (see Johnson, Carver, et al., 
2012).
Unanswered Questions 
and Future  Directions
This chapter has focused on the idea that 
there is a domain-  general system organized 
around approach incentives, as well as some 
of the implications that might follow from 
the incorporation of such a system in per -
sonality. Given that focus, much else has 
been left aside. Clearly, more is involved in 
personality than approach incentives. For 
the most part, we have disregarded another 
very obvious category of motivation—  the 
desire to avoid or escape from threats—  and 
the emotions, actions, and other outputs 
that follow from that category of motiva -
tion. There is also a growing body of work 
suggesting that even these two broad systems 
do not sufficiently capture the complexity of 
human self-  regulation. In particular, many 
have suggested the existence of a system of 
self- control that comes into play when the 
potential arises for conflict between short-
term and longer-  term desires, for example.
In Gray and McNaughton’s (1982) origi -
nal conception of the BAS in humans, they 
gave the trait variable that was linked to 
BAS function the label “impulsivity.” In 
retrospect, that may have not been the best 
choice of label. At first glance, impulsiv -
ity does seem to be tied to intense desires 
for particular outcomes. But impulsivity is 
a concept with a great deal of complexity, 
and many influences may lie behind a given 
impulsive action (e.g., Eysenck, 1987; John -
son, Carver & Joormann, 2008; Parker & 
Bagby, 1997; Torrubia et al., 2001). By at -
taching the term impulsivity  to BAS sensitiv -