Hippocampal unit activity and delayed response in the monkey

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Primate Research

Background:

• The delayed response (DR) task is crucial for assessing cognitive functions like working memory.
• The hippocampus is a brain region implicated in memory and spatial navigation, but its specific role in DR tasks requires further elucidation.

Purpose of the Study:

• To investigate the role of hippocampal single unit activity during a delayed response task in Japanese monkeys.
• To classify and characterize neuronal firing patterns in the hippocampus related to different task events.

Main Methods:

• Single unit extracellular recordings were performed in the hippocampus of Japanese monkeys (Macaca fuscata, n=4).
• Monkeys were trained to perform a delayed response task.
• Neuronal discharge rates were analyzed in relation to task events, including cue presentation, delay period, and response.

Main Results:

• A total of 272 hippocampal units exhibited significant changes in firing rate during the DR task.
• These units were categorized into six groups: cue-light, cue- and choice-light, choice-light, response-related, reward-error, and delay units.
• Delay units constituted 43.4% of related units, showing preferential firing during the delay period, with some exhibiting spatial-dependent modulation.

Conclusions:

• The findings provide experimental evidence supporting the involvement of the hippocampus in the delayed response task.
• Hippocampal neuronal activity, particularly during the delay period, plays a significant role in the cognitive processes underlying DR task performance.