Inhibitory interactions between the visual and motor systems during optokinetic stimulation and simultaneous dynamic handgrip exercise
Inhibitory interactions between the visual and motor systems are robustly found during the transient stimulation of either system. However, it is unknown how such interactions operate if both systems are continuously and simultaneously activated. To test this, we engaged the visual-oculomotor system in 14 right-handers with a large moving striped pattern that elicits characteristic eye movement responses, the optokinetic nystagmus (OKN). We also engaged the motor system with dynamic handgrip exercise simultaneous to OKN. We hypothesised that central versus occipital EEG upper-alpha (10-12 Hz) synchronisation would reflect systems-level inhibition between visual and motor processes. Optokinetic responses were recorded with eye tracking, and gripping force measured with dynamometry. First, when exploring whether continuous visual activation inhibits motor activity, we found that OKN increased alpha synchronisation over central electrodes, in line with classic findings of motor downregulation to transient visual stimuli. We found further evidence for the visual inhibition of motor-cortical activity, by comparing between visual conditions: increasing visual input, from closed eyes, to eye opening, to visual stimulation, produced progressively greater motor synchronisation into the inhibitory upper-alpha band. Second, we tested for the opposite interaction, that is, effects of motor engagement over ongoing visual and oculomotor processes. Behaviourally, left hand-grip exercise accelerated the ongoing OKN, increasing slow phase velocity. Electrophysiologically, performing this repetitive motor task with either hand interfered the occipital alpha desynchronization that OKN normally induces on EEG. These results support that mutual visual and motor inhibitory interactions persist during their simultaneous engagement, and show their effects on eye movements. Key pointsO_LIIncreasing levels of visual activation produced increasingly stronger signs of cortical inhibition. C_LIO_LIHand motor activation interfered with visual cortical activation during visual stimulation. C_LIO_LIHand motor activation altered oculomotor responses. C_LIO_LIOngoing visual-motor interactions were reflected by the EEG alpha band. C_LIO_LIEEG can be reliably assessed during nystagmus. C_LI