Hippocampal lesions and trace conditioning in the rabbit

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Learning and Memory

Background:

• Trace conditioning is a form of associative learning that requires a temporal gap between the conditional stimulus (CS) and the unconditional stimulus (US).
• The hippocampus is implicated in various forms of learning and memory, particularly those involving temporal sequencing and contextual information.

Purpose of the Study:

• To investigate the role of the dorsal hippocampus and fimbria-fornix in trace conditioning of the nictitating membrane response (NMR) in rabbits.
• To determine if hippocampal lesions impair or alter the acquisition and expression of trace-conditioned responses.

Main Methods:

• Rabbits with lesions of the dorsal hippocampus and fimbria-fornix underwent trace conditioning using a white noise CS and an electrical shock US.
• The number, amplitude, and latency of conditional responses (CRs) were measured and compared between lesioned and control subjects.

Main Results:

• Hippocampus-lesioned rabbits showed similar numbers and amplitudes of CRs compared to control subjects.
• A slight, but statistically significant, reduction in CR latency was observed in hippocampus-lesioned subjects at certain stages of conditioning.

Conclusions:

• The dorsal hippocampus and fimbria-fornix are not essential for the basic acquisition and performance of trace-conditioned nictitating membrane responses.
• The hippocampus may play a modulatory role in the timing of conditioned responses during trace conditioning.