An intrahemispheric columnar projection between two cortical multisensory convergence areas (inferior parietal lobule and prefrontal cortex): an anterograde study in macaque using HRP gel. 
Horseradish peroxidase (HRP) gel and tetramethylbenzidine neurohistochemistry were used successfully in demonstrating the columnar organization of an intrahemispheric projection from the inferior parietal lobule to the prefrontal cortex in the macaque monkey.  Following an HRP gel implant within the upper portion of the posterior (caudal) bank of the intraparietal sulcus, a prominent anterograde terminal projection field, consisting of alternate light and dark (300-500 microns) columns, was observed using low-power dark-field microscopy in the caudal third of the sulcus principalis cortex (area 46).  At higher magnification large numbers of small retrogradely-labeled pyramidal cells were present in layers III and V of the same cortex.  The regionally-specific projection, coupled with its discrete anatomical organization, lends support to the reputed functional/behavioral subsectors within the prefrontal cortex and its apparent capacity for spatial representation.