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.