Reciprocal connections between the first and second somatosensory cortical areas and the caudate nucleus

On the projections from the neostriatum to the cerebral cortex: the "displaced" neurons

The entire dorsal and lateral cortex of one cerebral hemisphere of rats was infiltrated with different fluorescent tracers and the neostriatum was examined for labelled perikarya. In spite of the extensive infiltration of the cortex, such neurons were seen only sporadically in the ipsilateral neostriatum and almost only in the vicinity of the globus pallidus and the subcortical white matter. The size and shape of these neurons, and particularly their proximity to some cell groups which surround the neostriatum and project to the cerebral cortex, suggest that these neurons belong to the neighbouring structures such as the magnocellular nuclei of the basal forebrain, the claustrum and the VIb cortical layer.

Anatomical evidence for cortical projections from the striatum in the cat

Several anatomical and physiological studies have thus far failed to confirm the existence of striatocortical projections proposed in 1895 by Cajal. Evidence for such striatocortical projections was obtained in the present study using the horseradish peroxidase (HRP) tracing method. When 0.1-0.8 microliter of 30-50% HRP in saline was injected into different cortical regions in cats, HRP was transported to cells in different thalamic nuclei, striatum and the globus pallidus. Only large striatal cells, 30--60 micrometers in their long axes, contained HRP reaction product. After injection in area AI, the striatocortical cells were located in the dorsal parts of the middle third of putamen, where auditory cortical afferents are known to project, thereby suggesting reciprocal connections between the cerebral cortex and the striatum.