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Abstract: Objective: The objective of this study was to investigate the effects of a simulated peripheral median nerve lesion on precision pinch movement by the thumb and index finger. Methods: A median neuropathy was created by blocking the median nerve at the wrist using an anesthetic. The subjects (n =5) were asked to perform pulp-to-pulp precision pinch movements before and after the nerve block. Digit motion data was obtained with a marker-based motion analysis system. Results: The radial offset of the thumb tip, as defined by the minimum distance of the thumb tip to the flexion-extension plane of the index finger, showed an increase of 11.2mm after the nerve block. For the thumb, the nerve block caused a decrease in the range of motion at the metacarpophalangeal (MCP) joint, and a compensatory increase in the range of motion at the interphalangeal (IP) joint. The range of motion ratio (MCP:IP) changed from 1:4.8 (pre-block) to 1:1.0 (post-block). The maximum flexion angle at the MCP joint increased from 18.8° (pre-block) to 33.7° (post-block), and maximum flexion angle at the IP joint decreased from 42.6° (pre-block) to 18.8° (post-block). For the index finger, the nerve block caused a decrease in the range of motion at the MCP joint, and compensatory increases in the ranges of motion at the proximal and distal interphalangeal (PIP and DIP) joints. The range of motion ratio (MCP:PIP:DIP) changed from 1:1.1:0.7 (pre-block) to 1:2.4:1.8 (post-block). The maximum flexion angle at the MCP joint decreased from 56.8° (pre-block) to 34.6° (post-block), and the maximum flexion angle at the PIP joint increased from 51.2° (pre-block) to 76.0° (post-block), but the change at the DIP joint was insignificant. Conclusions: The median nerve block caused remarkable degradation of the pinch performance as quantified by an inaccurate pulp-to-pulp contact of the thumb to the index finger and an alteration of joint motion of the digits. Significance: Many fine manual tasks require accurate pulp-to-pulp positioning of the thumb to the index finger. Within the hand, the median nerve is critical to the fine sensorimotor function due to the motor supply and the sensory endings to the thumb and index finger. People with median neuropathies (for example, carpal tunnel syndrome) experience clumsiness while performing simple manual tasks. The current approach to the examination of precision pinch movement may be utilized to quantify the apparent hand clumsiness observed in individuals with peripheral neuropathy such as carpal tunnel syndrome. [Copyright &y& Elsevier]

Objective: The main purpose of this study was to investigate changes in finger interaction after stroke with strongly unilateral motor effects. Effects of age on finger interaction were also analyzed.Methods: Sixteen stroke subjects and 16 control subjects produced maximal voluntary contractions with different finger combinations by one hand and by two hands simultaneously. Individual finger forces were measured. In multi-finger tasks, force deficit (FD) was quantified as the difference between the peak finger forces in single-finger tasks and in multi-finger tasks, while enslaving (ENSL) was quantified as forces produced by fingers that were not required to produce force.Results: In stroke subjects, the peak forces produced by the fingers of the impaired hand (IH) were about 36% less than those produced by the unimpaired hand. Stroke resulted in higher ENSL and decreased FD in the IH, particularly when the index and middle fingers produced force together, while aging led to higher FD and no change in ENSL. Two-hand tasks were accompanied by an additional drop in the force of individual fingers, i.e. bilateral deficit (BD). No changes in BD were observed with age or after stroke.Conclusions: We conclude that IH function in persons after stroke is accompanied not only by a general loss of finger force but also by changes in indices of multi-finger interaction. The contrast between the significantly changed indices of one-hand multi-finger interaction and unchanged BD implies that cortical neurons mediating interhemispheric inhibition are relatively spared in unilateral stroke.Significance: The study shows that stroke leads to changes not only in finger force but also in finger interaction. The conclusion on relatively spared interhemispheric projections is potentially important for therapy of hand function in stroke survivors. [Copyright &y& Elsevier]

Objective: We used transcranial magnetic stimulation (TMS) to investigate interactions among neuromuscular complexes involved in force production by individual fingers of a hand during single- and multi-finger tasks.Methods: Subjects were asked to press with the fingertips at various levels of force using different finger combinations. TMS was applied over the M1 cortical hand area during constant force production. TMS-induced increments in fingertip forces were analyzed, as well as motor evoked potentials (MEPs) in flexor digitorum superficialis.Results: Both MEP size and individual force increments had inverted U-shaped dependences on the background force (peak responses were seen at about 50% of the maximal force). Similar relationships were obtained when subjects were asked to produce different forces with the same finger combination or the same total force with different finger combinations. The relationships were similar when the force was produced by explicitly instructed fingers or by other fingers of the hand. Effects of TMS on the force of a finger showed a strong dependence on the background force produced by this finger and minimal or no dependence on forces produced by other fingers of the hand.Conclusions: Overall, TMS applied over M1 revealed little interaction among fingers. This supports the notion of digit-specific compartments in multi-digit extrinsic muscles of the hand and suggests that these compartments possess a high degree of physiological independence. [Copyright &y& Elsevier]