Connections between the frontal eye field and pretectum in the monkey: an anterograde/retrograde study using HRP gel and TMB neurohistochemistry.

Horseradish peroxidase (HRP) gel implants in the frontal eye field (FEF) of macaque monkeys, processed with tetramethylbenzidine (TMB) neurohistochemistry and studied with darkfield microscopy, demonstrated bidirectional HRP labeling of the afferents and efferents of this cortical area. It was evident that among the entire scope of its inputs, the FEF received a prominent afferent projection from the nucleus of the optic tract (NOT, nucleus limitans) and the suprageniculate nucleus, and projected to a medial subdivision of NOT, sublentiform nucleus, nucleus of the pretectal area, nucleus of the posterior commissure, and the rostral periaqueductal gray. The direct afferent projections to FEF from NOT could provide a route for visual input to reach FEF via the pretectum without first going to the visual cortex. The efferents probably represent the pathway through which FEF influences pupillary dynamics known to accompany, or occur independently of, eye movements.