Amygdala involvement in human avoidance, escape and approach behavior Page: 6
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Schlund and Cataldo Page 6
each amygdala (r's ranging from +.81-+.95). Collectively, results highlight that within-subject
responses were relatively similar to avoidance, escape and approach cues but between-subjects
differences in response magnitude were present.
The primary aim of the present investigation was to examine amygdala reactivity to threatening
cr cues even when avoidance responding consistently prevented contact with an upcoming
aversive event. Our secondary aim examined reported amygdala contributions to escape from
a proximal aversive event and to approach maintained by reinforcement. The inclusion of these
conditions provided a novel opportunity to compare amygdala responses under a range of
aversive and appetitive conditions to determine if it serves a broader role as a 'behavioral
relevance' detector (Ousdal et al., 2008; Paton et al., 2006; Sander et al 2003; Schoenbaum et
C_. al., 2003). A number of novel observations emerged from this investigation, helping to
elucidate amygdala contributions to avoidance, escape and approach and gain insight into
individual differences in amygdala reactivity.
One significant finding that emerged from this investigation was observation of bilateral
amygdala activation to threatening avoidance and escape cues relative to a neutral baseline
cue. This occurred under conditions where aversive money loss was routinely avoided during
neuroimaging. Moreover, avoidance and escape behaviors were well learned through extensive
Zpretraining, thus activation cannot be attributed to acquisition of Pavlovian cue-outcome or
Ioperant response-outcome contingencies. Findings highlighting amygdala activation to
avoidance and escape cues in humans establishes an important link between the amygdala and
learned avoidance suggested by prior studies on human avoidance (Mobbs, 2009), mood
Disorders characterized by avoidance behavior (Etkin and Wager, 2007) and studies involving
0 escape behavior (Gold et al., 1976; Herdade et al., 2006). Results showing amygdala
involvement in supporting avoidance in adults is also consistent with results of our prior
investigation on avoidance that highlighted amygdala involvement in supporting avoidance in
youths (ages 9-13 years) (Schlund et al, 2010). Overall, our findings suggest the amygdala
c may function as one important neural mechanism within the framework of two-factor theories
--. of avoidance which propose threatening fear-conditioned cues motivate avoidance and removal
of threatening cues and fear-reduction negatively reinforce avoidance (Cain and LeDoux,
2008; Miller, 1948). At a broader level, it is also worthy to note that cues prompting avoidance,
escape and approach behavior recruited a similar fronto-striatal-parietal network. Our findings
implicating a role for the striatum in avoidance replicates previous findings obtained with
humans (Jensen et al, 2003; Kim et al., 2006; Mobbs et al., 2009) and extends the role of the
striatum to also include escape behavior.
Z Two additional findings of significance emerged from our within-subject analyses of amygdala
I responses. First, the magnitude of activation to avoidance, escape and approach cues was
generally similar within-subjects. The second notable finding was the presence of considerable
between-subject variability in the magnitude of amygdala activation. A clear subset of subjects
c showed little or no activation while another subset of subjects exhibited marked activation
=r across conditions. The variability observed does not appear to stem from poor experimental
" control by programmed contingencies as behavioral performances across subjects were optimal
Sand stable. On the one hand, the reduced level of activation observed in some subjects is
consistent with evidence from nonhuman investigations that suggest learned avoidance is not
dependent upon the amygdala (Andrzejewski, et al., 2005; Lehmann et al., 2000; Poremba and
"-,. Gabriel, 1997, 1999; Roozendaal et al., 1993) and human neuroimaging investigations that
have not observed amygdala activation (Jensen et al, 2003). Reduced activation may reflect
attenuation of conditioned fear or perceived threat, which may subside once avoidance is
Learned because the avoidance cue predicts the absence of the aversive event (Lovibond et al.,
Neuroimage. Author manuscript; available in PMC 2011 November 1.
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Schlund, Michael W. & Cataldo, Michael F. Amygdala involvement in human avoidance, escape and approach behavior, article, November 1, 2010; [Amsterdam, Netherlands]. (digital.library.unt.edu/ark:/67531/metadc77178/m1/6/: accessed September 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT College of Public Affairs and Community Service.