Cortical projections of the thalamic mediodorsal nucleus in the rabbit.

The cortical projection of the thalamic mediodorsal nuclear complex (MD) in the rabbit was mapped retrograde horseradish peroxidase and anterograde tritiated proline techniques. The projection field occupied the entire medial wall rostral to a mid corpus callosal level, wrapped around the frontal pole onto the lateral convexity and tailed off caudally on the dorsal bank of the rhinal sulcus. The projection of the lateral approximately one-half of MD, the half which does not receive olfactory input, was confined to medial cortex supply all but the most rostral region. This projection field of lateral MD was precisely organized in two dimensions with the most lateral part projecting most caudally and the most dorsal part projecting most ventrally. A representation for the third, anterior-posterior (A-P), dimension was not evident since any cortical point within the field was supplied by a cylinder of cells extending the entire A-P extent of lateral MD. The medial half of MD, which does receive olfactory input, projected to the remaining rostral medical cortex, the lateral convexity and rhinal sulcal region. The inverse dorsoventral relationship was partially preserved and on overlapping A-P gradient was present with sulcal projections originating more caudally in medial MD and the rostral medial projection originating more rostrally.