Phase-Based Control of the Central Pattern Generator for Locomotion

We have previously shown that the lamprey's central pattern generator (CPG) for locomotion can be manipulated by applying electrical stimuli to the spinal cord at precise phases within the CPG cycle. Here we demonstrate how these so-called phase dependent responses (PDR) can be used to repeatably and reliably manipulate individual parameters of locomotion in the lamprey. In particular, we show that: (1) the PDR for an arbitrary stimulus prescribes the phases at which to stimulate in order to effect specific modifications of the locomotor output; (2) ipsilateral and contralateral burst lengths can be controlled separately; and (3) the responses predicted by a single-cycle PDR plot remain stable over many cycles of stimulation. All of these properties suggest that phase-dependent stimulation may be an effective means of controlling the CPG in a future spinal locomotion neuroprosthesis.