Fast Adapting Mechanoreceptors are Important for Force Control in Precision Grip but not for Sensorimotor Memory

Sensory feedback from cutaneous mechanoreceptors in the fingertips is important in effective object manipulation, allowing appropriate scaling of grip and load forces during precision grip. However the role of mechanoreceptor subtypes in these tasks remains incompletely understood. To address this issue, psychophysical tasks which may specifically assess function of type I rapidly adapting (RAI) and slowly adapting (SAI) mechanoreceptors were used with object manipulation experiments to examine the regulation of grip force control in an experimental model of graded reduction in tactile sensitivity (healthy volunteers wearing two layers of latex gloves). With gloves, tactile sensitivity decreased significantly from 1.9 ± 0.4μm to 12.3 ± 2.2μm in the Bumps task assessing function of RAI afferents, but not in a grating orientation task assessing SAI afferents (1.6±0.1mm to 1.8±0.2mm). Six axis force/torque sensors measured peak grip (PGF) and load forces (PLF) generated by the fingertips during a grip-lift task. With gloves there was a significant increase of PGF (14±6%), PLF (17±5%) and grip and load force rates (26±8%; 20±8%). A variable weight series task was used to examine sensorimotor memory. There was a 20% increase in PGF when the lift of a light object was preceded by a heavy relative to a light object. This relationship was not significantly altered when lifting with gloves, suggesting that the addition of gloves did not change sensorimotor memory effects. We conclude that RAI fibres may be important for the online force scaling but not for the build-up of a sensorimotor memory