Interactions between the prefrontal cortex and amygdala during delay discounting and reversal

Abstract

Interactions between the prefrontal cortex and amygdala are thought to be critical for reward anticipation. Alterations in reward anticipation that lead to an inability to wait for rewards or a diminished capacity to change behavior when doing so would be optimal are often termed impulsivity and compulsivity, respectively. Distinct regions of the prefrontal cortex may support decreased impulsivity through self-control and decreased compulsivity through flexibility. However, both self-control and flexibility appear to involve the amygdala. Using a delay discounting paradigm, the current investigation found that inactivation and disconnection of the medial prefrontal cortex and basolateral amygdala led rats to become more impulsive by affecting preference for smaller immediate over larger delayed rewards. Conversely, inactivation and disconnection of the orbitofrontal cortex and amygdala led rats to become more compulsive as demonstrated by an inability to flexibly reverse stimulus-reward relationships in an odor reversal task. The current findings support a double dissociation between orbitofrontal cortex-amygdala interactions for odor reversal and medial prefrontal cortex-amygdala interactions for delay discounting.

Figure 1

Representative histological plates showing locations of cannula tips in BLA (Left), OFC (middle), and mPFC (right). Histological plates adapted from (Paxinos & Watson, 2005).

Figure 2

Experimental apparatus used (a) for the delay discounting task in which subjects chose between two rewarded locations by entering the central alley of the T-maze. In one arm of the T-maze a low value food reward (LVR) was always freely available. In the opposite arm a high value food reward (HVR) was available. In order to obtain the HVR, subjects were required to wait in front of a gate for 15 s. (b) Subjects were also tested to evaluate whether they could readily discriminate between reward magnitudes. This was accomplished by allowing subjects to enter the central alley of the T-maze with both gates closed and waiting for 15 s to elapse prior to opening both gates simultaneously.

Figure 3

Shows saline (S) and muscimol (M) conditions for (a) the mean percentage of selecting the delayed high value reward (HVR) arm for bilateral OFC and BLA and (b) the mean time spent waiting in seconds for the delayed HVR arm for bilateral OFC and BLA.

Figure 4

Shows saline (S) and muscimol (M) conditions for (a) the mean percentage of selecting the delayed HVR arm for bilateral, ipsilateral (IPSI), and contralateral (CONTRA) mPFC and BLA and (b) mean time spent waiting in seconds for bilateral, IPSI, and CONTRA mPFC and BLA.

Figure 5

Shows saline (S) and muscimol (M) conditions for the mean percentage of selecting the HVR for bilateral mPFC and BLA during discrimination between reward magnitudes.

Figure 6

Experimental apparatus used for the odor reversal task in which subjects were trained to discriminate between two different odors to obtain a food reward. On the day following discrimination training, the contingency was reversed so that the originally rewarded odor was unrewarded and the originally unrewarded odor became rewarded. The location of the rewarded odor was pseudorandomly switched between the two adjacent locations.

Figure 7

Shows the mean number of trials to reach criterion during acquisition (ACQ) and reversal (REV) for saline-saline (S-S) and saline-muscimol (S-M) conditions across bilateral mPFC, BLA, and OFC groups and (b) the mean number of perseverative (PERSEV) and regressive (REGRESS) errors during reversal for bilateral mPFC, BLA, and OFC groups.

Figure 8

Shows (a) the mean number of errors to reach criterion during acquisition and reversal for ipsilateral (IPSI) and contralateral (CONTRA) OFC and BLA and (b) the mean number of perseverative (PERSEV) and regressive (REGRESS) errors during reversal for IPSI and CONTRA OFC and BLA.