 487
Over the past several decades, a large body 
of work has examined the idea that a broad, 
general-  purpose system manages motiva -
tion, affect, cognition, and behavior in re -
sponse to cues of incentive and reward. This 
system has been referred to as the approach 
system, behavioral activation system (BAS), 
behavioral engagement system, or behavior -
al facilitation system (e.g., Depue & Iacono, 
1989, Fowles, 1988; Gray, 1990). Personal -
ity, neural, animal conditioning, and psy -
chopharmacology models all differentiate 
one system that acts to foster the approach 
of incentive cues from another system that 
acts to avoid threats (Elliot, 2008).
The biological basis of the BAS has been 
characterized as involving dopaminergic cir -
cuits that project from the ventral tegmental 
area to the ventral striatum (including the 
nucleus accumbens [NAcc], bilateral puta -
men, and caudate), and into prefrontal re -
gions such as the medial orbitofrontal cor -
tex, ventromedial prefrontal cortex, and 
anterior cingulate cortex (Whitton, Tread -
way, & Pizzagalli, 2015). In particular, re -
search suggests that reward anticipation ac -tivates the NAcc (Knutson & Greer, 2008) 
and that activation of this region is particu -
larly related to willingness to work to obtain 
reward (Treadway, Buckholtz, Schwartz -
man, Lambert, & Zald, 2009).
We have found it useful to differentiate 
among inputs to, outputs of, and sensitivity 
of the BAS (see Johnson, Edge, Holmes, & 
Carver, 2012). Allergies provide a helpful 
metaphor for these distinctions: a personal 
allergy (sensitivity) to pollen (the input) 
guides the degree of symptoms (output) that 
a person might develop when exposed to 
pollen. In the case of BAS, inputs are cues of 
potential reward, ranging from laboratory 
stimuli to broader life events that suggest 
potential for goal attainment. The neurobio -
logical pathways implicated in this system 
guide differential levels of individual sensi -
tivity to those inputs. BAS outputs include 
interest in incentives, motor activity, energy, 
confidence, and pleasure in rewards. Hence, 
a person with a strong trait-like tendency to -
ward high BAS activity would be expected 
to show more energy, activation, eagerness, 
and confidence when given an opportunity CHAPTER 22
The Approach System as a Component 
of Personality
Sheri  L. Johnson  
Benjamin  A. Swerdlow  
Jennifer G. Pearlstein  
Manon  L. Ironside  
Charles  S. Carver