Neural Control of Interlimb Oscillations I: Human Bimanual Coordination
Cohen, Michael A.
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How do humans and other animals accomplish coordinated movements? How are novel combinations of limb joints rapidly assembled into new behavioral units that rnove together in in-phase or anti-phase movement patterns during complex movement tasks? A neural central pattern generator (CPG) model simulates data from human bimanual coordination tasks. As in the data, anti-phase oscillations at low frequencies switch to in-phase oscillations at high frequencies, in-phase oscillation occur both at low and high frequencies, phase fluctuations occur at the anti-phase in-phase transition, a "seagull effect" of larger errors occurs at intermediate phases, and oscillations slip toward in-phase and anti-phase when driven at intermediate phases. These oscillations and bifurcations are emergent properties of the CPG model in response to volitional inputs. The CPC model is a version of the Ellias-Grossberg oscillator. Its neurons obey Hodgkin-Huxley type equations whose excitatory signals operate on a faster time scale than their inhibitory signals in a recurrent on-center off-surround anatomy. When an equal cornmand or GO signal activates both model channels the model CPC: can generate both in-phase and anti-phase oscillations at different GO amplitudes. Phase transitions frorn either in-phase to anti-phase oscillations, or from anti-phase to in- phase oscillations, can occur in different pararncter ranges, as the GO signal increases.