The origin of projections from the posterior cingulate and retrosplenial cortices to the anterior, medial dorsal and laterodorsal thalamic nuclei of macaque monkeys

John P Aggleton,Nicholas F Wright,Seralynne D Vann,Richard C Saunders

doi:10.1111/ejn.12389

John P Aggleton, Nicholas F Wright + Show 2 more

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https://doi.org/10.1111/ejn.12389

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Abstract

Interactions between the posterior cingulate cortex (areas 23 and 31) and the retrosplenial cortex (areas 29 and 30) with the anterior, laterodorsal and dorsal medial thalamic nuclei are thought to support various aspects of cognition, including memory and spatial processing. To detail these interactions better, the present study used retrograde tracers to reveal the origins of the corticothalamic projections in two closely related monkey species (Macaca mulatta, Macaca fascicularis). The medial dorsal thalamic nucleus received only light cortical inputs, which predominantly arose from area 23. Efferents to the anterior medial thalamic nucleus also arose principally from area 23, but these projections proved more numerous than those to the medial dorsal nucleus and also involved additional inputs from areas 29 and 30. The anterior ventral and laterodorsal thalamic nuclei had similar sources of inputs from the posterior cingulate and retrosplenial cortices. For both nuclei, the densest projections arose from areas 29 and 30, with numbers of thalamic inputs often decreasing when going dorsal from area 23a to 23c and to area 31. In all cases, the corticothalamic projections almost always arose from the deepest cortical layer. The different profiles of inputs to the anterior medial and anterior ventral thalamic nuclei reinforce other anatomical and electrophysiological findings suggesting that these adjacent thalamic nuclei serve different, but complementary, functions supporting memory. While the lack of retrosplenial connections singled out the medial dorsal nucleus, the very similar connection patterns shown by the anterior ventral and laterodorsal nuclei point to common roles in cognition.

Highlights

Interest in the connections of the posterior cingulate and retrosplenial cortices with the anterior thalamic nuclei stems from electrophysiological and disconnection studies that indicate how these pathways might support learning and memory (Gabriel, 1993; Sutherland & Hoesing, 1993)
Retrograde tracers were placed into three thalamic sites, the anterior nuclei, the laterodorsal nucleus and the medial dorsal nucleus
In contrast to their medial temporal lobe inputs, the present study found clear similarities in the distribution of inputs to the anterior medial nucleus and medial dorsal nucleus, there were changes in density

Summary

Introduction

Interest in the connections of the posterior cingulate and retrosplenial cortices with the anterior thalamic nuclei stems from electrophysiological and disconnection studies that indicate how these pathways might support learning and memory (Gabriel, 1993; Sutherland & Hoesing, 1993). Projections from the posterior cingulate cortex (areas 23 and 31) and retrosplenial cortex (areas 29 and 30) terminate in the anterior thalamic nuclei, the medial dorsal thalamic nucleus, the laterodorsal nucleus and the medial pulvinar (Vogt et al, 1979, 1987; Baleydier & Mauguiere, 1980; Yeterian & Pandya, 1988; Morris et al, 1999; Shibata & Yukie, 2003, 2009; Hsu & Price, 2007) All of these studies have, relied on anterograde tracers. The sources of the projections from some posterior cingulate and retrosplenial sites have been inferred by comparing the results from overlapping, but different, cortical injections (e.g., Yeterian & Pandya, 1988)

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