Abstract
Despite decades of research, the neural mechanisms of spatial working memory remain poorly understood. Although the dorsal hippocampus is known to be critical for memory-guided behavior, experimental evidence suggests that spatial working memory depends not only on the hippocampus itself, but also on the circuit comprised of the hippocampus and the medial prefrontal cortex (mPFC). Disruption of hippocampal-mPFC interactions may result in failed transfer of spatial and contextual information processed by the hippocampus to the circuitry in mPFC responsible for decision making and goal-directed behavior. Oscillatory synchrony between the hippocampus and mPFC has been shown to increase in tasks with high spatial working memory demand. However, the mechanisms and circuitry supporting hippocampal-mPFC interactions during these tasks is unknown. The midline thalamic nucleus reuniens (RE) is reciprocally connected to both the hippocampus and the mPFC and has been shown to be critical for a variety of working memory tasks. Therefore, it is likely that hippocampal-mPFC oscillatory synchrony is modulated by RE activity. This article will review the anatomical connections between the hippocampus, mPFC and RE along with the behavioral studies that have investigated the effects of RE disruption on working memory task performance. The article will conclude with suggestions for future directions aimed at identifying the specific role of the RE in regulating functional interactions between the hippocampus and the PFC and investigating the degree to which these interactions contribute to spatial working memory.
Highlights
Working memory refers to the holding of mind of task-relevant information for use in goaldirected behavior (Baddeley, 1986)
The individual contributions of each component of this circuit will be described, followed by a description of the anatomical connectivity between these structures, evidence for functional interactions within the circuit during working memory performance, and future directions in the effort to discover the mechanisms within this circuit that give rise to our ability to use working memory
In an effort to examine the involvement of RE/rhomboid nuclei (RH) in a task that requires both hippocampal and medial prefrontal cortex (mPFC) function, Hembrook and Mair (2011) performed RE/RH lesions and examined performance in a radial arm maze task, which had been previously shown to depend on both hippocampus and mPFC (McDonald and White, 1993; Mair et al, 1998; Porter et al, 2000)
Summary
Working memory refers to the holding of mind of task-relevant information for use in goaldirected behavior (Baddeley, 1986). Delay tasks are used to assess working memory in a variety of species. For these tasks, a cue must be held in memory over a temporal gap before an appropriate response can be emitted. Many attempts have been made to discover the neural circuitry responsible for working memory, there are still many unanswered questions about how the brain accomplishes this important and remarkable phenomenon. The individual contributions of each component of this circuit will be described, followed by a description of the anatomical connectivity between these structures, evidence for functional interactions within the circuit during working memory performance, and future directions in the effort to discover the mechanisms within this circuit that give rise to our ability to use working memory
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