Distribution of mediodorsal thalamic nucleus afferents originating in the prefrontal association cortex of the dog.

The nediodorsal thalamic nucleus (MD) afferents originating in the prefrontal cortex (PFC) were studied in 14 dogs, using the method of retrograde horseradish peroxidase transport. Injections limited to small areas of MD indicated that projection between MD and PFC shows precise topography and reciprocity. However, the distribution of labeled neurons suggests a division of MD into two main segments related to the corresponding projection zones in the prefrontal cortex. The medioventral PFC zone is specifically related to the medial MD segment, while the dorsolateral PFC zone is related to its lateral segment. Transitional areas located on the lateral and medial surfaces were identified between the two main cortical zones. They are connected with both lateral and medial segments of MD.