Relation of koniocellular layers of dorsal lateral geniculate to inferior pulvinar nuclei in common marmosets

<jats:title>Abstract</jats:title><jats:p>Traditionally, the dorsal lateral geniculate nucleus (<jats:styled-content style="fixed-case">LGN</jats:styled-content>) and the inferior pulvinar (IPul) nucleus are considered as anatomically and functionally distinct thalamic nuclei. However, in several primate species it has also been established that the koniocellular (K) layers of <jats:styled-content style="fixed-case">LGN</jats:styled-content> and parts of the <jats:styled-content style="fixed-case">IP</jats:styled-content>ul have a shared pattern of immunoreactivity for the calcium‐binding protein calbindin. These calbindin‐rich cells constitute a thalamic matrix system which is implicated in thalamocortical synchronisation. Further, the K layers and <jats:styled-content style="fixed-case">IP</jats:styled-content>ul are both involved in visual processing and have similar connections with retina and superior colliculus. Here, we confirmed the continuity between calbindin‐rich cells in <jats:styled-content style="fixed-case">LGN</jats:styled-content> K layers and the central lateral division of <jats:styled-content style="fixed-case">IP</jats:styled-content>ul (<jats:styled-content style="fixed-case">IP</jats:styled-content>ul<jats:styled-content style="fixed-case">CL</jats:styled-content>) in marmoset monkeys. By employing a high‐throughput neuronal tracing method, we found that both the K layers and <jats:styled-content style="fixed-case">IP</jats:styled-content>ul<jats:styled-content style="fixed-case">CL</jats:styled-content> form comparable patterns of connections with striate and extrastriate cortices; these connections are largely different to those of the parvocellular and magnocellular laminae of <jats:styled-content style="fixed-case">LGN</jats:styled-content>. Retrograde tracer‐labelled cells and anterograde tracer‐labelled axon terminals merged seamlessly from <jats:styled-content style="fixed-case">IP</jats:styled-content>ul<jats:styled-content style="fixed-case">CL</jats:styled-content> into <jats:styled-content style="fixed-case">LGN</jats:styled-content> K layers. These results support continuity between <jats:styled-content style="fixed-case">LGN</jats:styled-content> K layers and <jats:styled-content style="fixed-case">IP</jats:styled-content>ul<jats:styled-content style="fixed-case">CL</jats:styled-content>, providing an anatomical basis for functional congruity of this region of the dorsal thalamic matrix and calling into question the traditional segregation between <jats:styled-content style="fixed-case">LGN</jats:styled-content> and the inferior pulvinar nucleus.</jats:p>