Date of Award

Fall 2011

Project Type

Dissertation

Program or Major

Psychology

Degree Name

Doctor of Philosophy

First Advisor

Robert Mair

Abstract

Spatial working memory is the ability to encode and temporarily store information for future retrieval to guide behavioral responses. Two areas of the brain that are important for this process are prefrontal cortex (PFC) and hippocampus. The hippocampus has strong connections to medial PFC, however there are no direct return projections from medial PFC to hippocampus. The reuniens (Re) and rhomboid (Rh) nuclei of ventral midline thalamus have anatomical connections with PFC and hippocampus. This dissertation sought to provide behavioral evidence for the role of the ventral midline thalamic nuclei in spatial working memory. Four experiments were conducted in rats using different methods to elucidate the role of Re and Rh nuclei in memory. Experiment 1 temporarily inactivated Re and Rh with pharmacological manipulations. Experiment 2 used permanent excitotoxic lesions to selectively damage Re or Rh nuclei. Experiment 3 used similar lesions on areas surrounding Re and Rh to rule out any potential contributions of these areas and Experiment 4 used event-related deep brain stimulation in Re and Rh to distinguish when during the memory process these nuclei are important. Results revealed impairments for the Re and Rh nuclei on different behavioral measures of spatial working memory that depend on the proper functioning of PFC and/or hippocampus. Temporal specificity was found for the storage and retrieval stages of the delayed nonmatching to position measure (DNMTP) of spatial working memory. These findings provide evidence that the ventral midline thalamic nuclei play an important role in spatial working memory, specifically for the communication of information across memory delays to guide memory responses.

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