Mammillary body lesions and restricted subicular output lesions produce long-lasting DRL performance impairments in...

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Cognitive Neuroscience

Background:

• The differential reinforcement of low rates (DRL) task assesses inhibitory control and timing.
• The mammillary bodies (MB) and related pathways are implicated in learning and memory, but their specific role in DRL is not fully understood.

Purpose of the Study:

• To investigate the role of mammillary bodies (MB) and their connections, including the subiculum, in differential reinforcement of low rates (DRL) performance in rats.

Main Methods:

• Rats underwent electrolytic lesions of the mammillary bodies (MB), transection of descending columns of the fornix (DCF), or transection of subicular projections to the ventral striatum (SC).
• Lesioned and sham-operated rats were tested on DRL tasks with different reinforcement schedules (DRL-18 and DRL-36).
• Timing behavior and retention of DRL-36 were assessed post-lesion.

Main Results:

• MB lesions significantly impaired DRL-18 efficiency, while DCF and SC lesions showed non-significant impairments.
• DRL-36 efficiency was significantly impaired in all lesion groups (MB, DCF, SC), with unique timing patterns observed in the SC group.
• Rats with MB lesions showed impaired retention of DRL-36, but this impairment was less severe than with immediate postoperative training.

Conclusions:

• Subicular output is crucial for normal DRL performance.
• Subicular projections to the MB and ventral striatum play independent roles in DRL.
• The functional relationship between the subiculum and MB explains why MB lesions mimic hippocampal lesion effects in DRL tasks.