Roles of sub-regions of the Ventromedial Nucleus of the Thalamus (VMT) in an Attentional task Open Access
Henry, Nicholai Anthony (2013)
Abstract
The ventromedial nucleus of the thalamus (VMT) is a longitudinally elongated nucleus of mostly medium to large, multipolar and rounded closely packed cells. Autoradiography studies examining thalamocortical outputs have shown that the medial VMT projects to medial prefrontal cortex, while the lateral VMT projects to lateral prefrontal cortex, sensorimotor. Unpublished work in the Neill lab has investigated the effects of transient VMT manipulation on the performance of rats in the 5-choice serial reaction time task (5-CSRTT). The study showed that injections of the GABA agonist muscimol in the center-to-medial VMT produced an increase in premature responding in the 5-CSRTT. However, inadvertently misplaced cannulae, in which muscimol was injected into the medial VMT of one hemisphere and the lateral VMT of the other, showed large increases in errors of omission. Additionally, the results of a few rats with injections into the more medial VMT, at volume of 0.5 µl, showed an increase in premature responding, while the same amount of drug, at the same site, increased errors of omission when administered in a volume of 1.0 µl. Based on the unpublished results, two hypotheses were formed: (1) injections of higher volumes of muscimol into the medial VMT will result in increased errors of omission, presumably due to diffusion to a nearby tissue, and (2) that the lateral VMT is this tissue. To investigate these claims, sub-regions of the VMT were transiently deactivated by the GABA agonist muscimol and activated by GABA antagonist picrotoxin. The results of this study are consistent with the proposed hypotheses and suggest that the medial VMT function is one of "behavioral inhibition," while the lateral VMT is related to motoric slowing or loss of motivational attention.
Table of Contents
TABLE OF CONTENTS
List of figures ......1
List of Tables ......2
Introduction .......3
Methods ............8
Results ............16
Discussion ........29
References ........34
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