Finger Posture and Finger Load are Perceived Independently

Abstract

The ability to track the time-varying postures of our hands and the forces they exert plays a key role in our ability to dexterously interact with objects. However, how precisely and accurately we sense hand kinematics and kinetics has not been completely characterized. Furthermore, the dominant source of information about hand postures stems from muscle spindles, whose responses can also signal isometric force and are modulated by fusimotor input. As such, one might expect that changing the state of the muscles – for example, by applying a load – would influence perceived finger posture. To address these questions, we measure the acuity of human hand proprioception, investigate the interplay between kinematic and kinetic signals, and determine the extent to which actively and passively achieved postures are perceived differently. We find that angle and torque perception are highly precise; that loads imposed on the finger do not affect perceived joint angle; that joint angle does not affect perceived load; and that hand postures are perceived similarly whether they are achieved actively or passively. The independence of finger posture and load perception contrasts with their interdependence in the upper arm, likely reflecting the special functional importance of the hand.

Force, angle, and velocity parameters of finger movements are reflected in corticospinal excitability

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“…In both situations, the vibration disrupts the natural stimulation of the Ia afferents, resulting in inaccurate perception of the posture of the stimulated effector [53]. Muscle spindle afferents also monitor applied load (force against the limb) [56]. Unlike in the elbow joint, where applied load and muscle stretch interact to produce a proprioceptive percept of limb position, these inputs are processed independently in the fingers [56].…”

“…Muscle spindle afferents also monitor applied load (force against the limb) [56]. Unlike in the elbow joint, where applied load and muscle stretch interact to produce a proprioceptive percept of limb position, these inputs are processed independently in the fingers [56]. Therefore, vibration of the finger flexors may affect perception of finger posture, force against the fingers, or both, so the effects may not be specific to proprioception as it is in studies of other joints.…”