Dendritic orientation of thalamocortical projection neurons in the ventrobasal complex of macaques.

This study describes the orientation of dendritic arbors from intracellularly labeled thalamocortical projection (TCP) neurons of Macaca fascicularis or Macaca mulatta. All neurons were located in the ventrobasal complex and responded to non-noxious stimuli. Each neuron was composed of dendrites that varied considerably in size and each dendrite tended to occupy a particular region of the perisomatic space with minimal overlap with other dendrites. Quantitative and qualitative analysis of the dendritic arbors of the labeled neurons showed they had an asymmetric distribution so that some regions of the perisomatic space contained more of the dendritic tree than others. Eleven of the thirteen reconstructed neurons had a larger percentage of the dendritic tree projecting into the medial portion of the perisomatic space. These results show that the dendritic arbors of macaque TCP neurons are not organized in a radially symmetric pattern as previously described and the asymmetric distribution of dendrites may be related to synaptic input.