FIG. 10.
Simplified schematic of the flow of neural signals involved in generating coordinated eye-head movements. Two partially independent pathways provide input signals. A head-movement command (Hc) provides one drive to the neck muscles (pathway 1), but the functional importance of this pathway during gaze shifts has yet to be determined. A desired gaze-displacement command (ΔGd) contributes to producing the saccadic eye and head components of the gaze shift. One possibility (pathway 2) is that ΔGd is dissociated into separate eye and head commands before the burst generator (BG), which in turn provides a drive to only the extraocular motoneurons (MNe). Thus no subset of the ΔGd drive to the neck muscles is gated by the OPNs. Another scenario (pathway 3) is that the separation of ΔGd into separate eye and head pathways occurs after the burst generator elements. Note that pathways 2 and 3 need not be mutually exclusive. MNn, neck motoneurons.