The medial accessory nucleus of Bechterew: a cell group within the anatomical limits of the rostral oculomotor complex receives a direct prefrontal projection in the monkey.

The medial accessory nucleus of Bechterew, a vertically oriented cell group in the rostral lateral oculomotor nucleus (OMN), contiguous dorsally with the nucleus of Darkschewitsch (ND) and ventrally with the parvocellular red nucleus, is separated from the interstitial nucleus of Cajal (IC) by a small paraoculomotor fascicle (POF) that forms the anatomical limits of the OMN. Horseradish peroxidase (HRP) gel implants in the prearcuate frontal cortex dorsal to the caudal third of the principal sulcus in the monkey resulted in an anterogradely labeled bilateral projection to this paraoculomotor cell group. The functional role of this largely overlooked nucleus is yet to be determined. However, the failure to retrogradely label following HRP injections involving both the extraocular muscles and ciliary ganglion suggests that it cannot be classified as belonging to either the somatic or the visceral cell column at the present time. We suggest that, like IC and ND, it probably contributes to the POF of the medial longitudinal fasciculus and may be involved in internuclear connections. There is little doubt that it has been involved inadvertently in studies of oculomotor connections.