4.5. Amygdala (AMG)
The AMG is an essential part of the mesolimbic circuitry; however, there
is limited information on the role the AMG plays in ST/GT behavior. It
does not appear to be essential for the initial attribution of incentive
salience to cues, but it may act to amplify incentive value once it has
been acquired, possibly through dense glutamatergic projections from the
amygdala to the NAcc (Britt et al. 2012; Stuber et al. 2011). In one
study, opioid stimulation of the central nucleus of the amygdala
enhanced the intensity of conditioned responses without changing the
target of approach, causing STs to show stronger sign-tracking and GTs
to show stronger goal-tracking (DiFeliceantonio and Berridge 2012). In
another study, lesions of the basolateral amygdala reduced the rate of
lever pressing in STs after extended training, and disconnection of the
basolateral amygdala and the NAcc produced deficits in both the
acquisition of sign-tracking and in the rate of responding in trials
when sign-tracking occurred (Chang et al. 2012b). In contrast, lesions
of the central nucleus of the amygdala had no effect on the acquisition
or expression of sign-tracking behavior (Chang et al. 2012a).
The amygdala is also involved in the ability of sleep deprivation to
enhance the motivational effects of food cues. In a recent human study,
a single night of sleep deprivation increased the subjective valuation
of food cues and caused a parallel increase in activity in the amygdala
and hypothalamus (Rihm et al. 2018). In another study, subjects that
experienced sleep debt in daily life demonstrated elevated amygdala
reactivity to food cues, which was reduced after optimal sleep
(Katsunuma et al. 2017). Therefore, the increased activity in the
amygdala that results from suboptimal sleep may act to amplify the
incentive motivation that is triggered by reward-paired cues, and
contribute to the heightened reward-seeking behavior that often follows
sleep deprivation.