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Inactivation of the nucleus reuniens/rhomboid causes a delay-dependent impairment of spatial working memory
Dylan M Layfield1, Monica Patel1, Henry Hallock1
1Department of Psychological and Brain Sciences, University of Delaware, United States.
Abstract:
Inactivation of the rodent medial prefrontal cortex (mPFC) and hippocampus or disconnection of the hippocampus from the mPFC produces deficits in spatial working memory tasks. Previous studies have shown that delay length determines the extent to which mPFC and hippocampus functionally interact, with both structures being necessary for tasks with longer delays and either structure being sufficient for tasks with shorter delays. In addition, inactivation of the nucleus reuniens (Re)/rhomboid nucleus (Rh) of the thalamus, which has bidirectional connections with the mPFC and hippocampus, also produces deficits in these tasks. However, it is unknown how delay duration relates to the function of Re/Rh. If Re/Rh are critical in modulating mPFC-hippocampus interactions, inactivation of the RE/Rh should produce a delay-dependent impairment in spatial working memory performance. To investigate this question, groups of rats were trained on one of three different spatial working memory tasks: continuous alternation (CA), delayed alternation with a five-second delay (DA5), or with a thirty-second delay (DA30). The Re/Rh were inactivated with muscimol infusions prior to testing. The results demonstrate that inactivation of RE/Rh produces a deficit only on the two DA tasks, supporting the notion that the Re/Rh is a critical orchestrator of mPFC-HC interactions.
Insights
The nucleus reuniens (Re)/rhomboid nucleus (Rh) is crucial for spatial working memory. Inactivating the Re/Rh impairs performance on tasks with delays, highlighting its role in coordinating brain regions.
Area of Science:
- Neuroscience
- Cognitive Neuroscience
- Behavioral Neuroscience
Background:
- The medial prefrontal cortex (mPFC) and hippocampus are vital for spatial working memory.
- Their functional interaction is modulated by delay length, with both necessary for longer delays.
- The nucleus reuniens (Re)/rhomboid nucleus (Rh) of the thalamus connects these regions and is implicated in working memory.
Purpose of the Study:
- To investigate the role of the Re/Rh in spatial working memory, specifically how delay duration affects its function.
- To determine if Re/Rh inactivation causes delay-dependent impairments in spatial working memory.
- To assess if the Re/Rh acts as a critical modulator of mPFC-hippocampus interactions.
Main Methods:
- Rats were trained on three spatial working memory tasks: continuous alternation (CA), delayed alternation with a 5-second delay (DA5), and delayed alternation with a 30-second delay (DA30).
- The Re/Rh was inactivated using muscimol infusions prior to behavioral testing.
- Performance deficits were analyzed across the different delay conditions.
Main Results:
- Inactivation of the Re/Rh produced significant deficits in spatial working memory performance.
- These deficits were observed specifically in the delayed alternation tasks (DA5 and DA30), not in the continuous alternation task (CA).
- This suggests a delay-dependent role for the Re/Rh in spatial working memory.
Conclusions:
- The Re/Rh plays a critical role in mediating spatial working memory, particularly when temporal delays are involved.
- These findings support the hypothesis that the Re/Rh is a key orchestrator of communication between the mPFC and hippocampus.
- The Re/Rh's function is essential for tasks requiring the maintenance of information over extended periods.
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