Preferential involvement by nucleus accumbens shell in mediating probabilistic learning and reversal shifts

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Decision Making

Background:

• The nucleus accumbens (NAc) is crucial for reward processing and flexible behavior.
• Its subregions, the NAc shell and core, have distinct roles in action selection and strategy shifting.
• Understanding their function in uncertain reward environments is key to explaining cognitive flexibility.

Purpose of the Study:

• To investigate the roles of the NAc shell and core in probabilistic reversal learning.
• To determine how these NAc subregions contribute to flexible response strategies under uncertain reward delivery.

Main Methods:

• Inactivation of the NAc shell and core in well-trained rats using an operant conditioning task.
• Repeatedly reversing reinforcement contingencies within a session to assess probabilistic reversal learning.
• Assessing performance on tasks with predictable and unpredictable reward schedules.

Main Results:

• NAc shell inactivation impaired reversal learning, reducing completed reversals and win-stay behavior, indicating a deficit in using probabilistic reward feedback.
• Shell inactivation also impaired performance on a predictable reversal task after initial association, suggesting a role in refining action selection.
• NAc core inactivation did not affect reversal performance but increased lever-approach latencies, suggesting a role in promoting reward-seeking behavior.

Conclusions:

• The NAc shell and core play distinct but complementary roles in reward seeking and cognitive flexibility under uncertainty.
• The NAc core facilitates approach to reward-associated stimuli.
• The NAc shell refines action selection based on the probability of reward delivery.