Claustral and amygdaloid afferents to the head of the caudate nucleus in macaque monkeys

A single dose of horseradish peroxidase polyacrylamide gel (10%, 1.0 microliter) was injected, after callosotomy, into the head of the caudate nucleus in six macaque monkeys. In addition to the previously reported structures sending fibers to the caudate nucleus, such as the cerebral cortex, substantia innominata, thalamus, hypothalamus, substantia nigra and brainstem, labeled cells were found abundantly in the rostral portion of the ipsilateral claustrum, and fewer labeled cells were dispersed in the ipsilateral external and extreme capsules. Many labeled cells were also present in the ipsilateral insular cortex throughout its rostrocaudal extent. Moreover, labeled cells were seen ipsilaterally in the basolateral, basomedial, accessory basal, and cortical nuclei of the amygdaloid complex.