Sensory integration in the perception of movements at the human metacarpophalangeal joint

1. These experiments were designed to investigate illusions of movements of the fingers produced by combined feedback from muscle spindle receptors an d receptors located in different regions of the skin of the hand. 2. Vibration (100 Hz) applied in cyclic bursts (4 s 'on', 4 s 'off') over t he tendons of the finger extensors of the right wrist produced illusions of flexion-extension of the lingers. Cutaneous receptors were activated by lo cal skin stretch and electrical stimulation. Illusory movements at the meta carpophalangeal (MCP) joints were measured from voluntary matching movement s: made with the left hand. 3. Localised stretch of the dorsal skin over specific MCP joints altered vi bration-induced illusions in 8/10 subjects. For the group, this combined st imulation produced movement illusions at MCP joints under, adjacent to, and two joints an away from the stretched region of skin that were 176 +/- 33, 122 +/- 9 and 67 +/- 11% of the size of those from vibration alone, respec tively. Innocuous electrical stimulation over the same skin regions, but no t at the digit tips, also 'focused' the sensation of movement to the stimul ated digit. 4. Stretch of the dor sal skin and compression of the ventral skin around o ne MCP joint altered the vibration-induced illusions in all subjects. The i llusions became more focused, being 295 +/- 57, 116 +/- 18 and 65 +/- 7% of the corresponding vibration-induced illusions at MCP joints that were unde r, adjacent to, and two joints away from the stimulated regions of skin, re spectively. 5. These results show that feedback from cutaneous and muscle spindle recep tors is continuously integrated for the perception of finger movements. The contribution from the skin was not simply a general facilitation of sensat ions produced by muscle receptor s but, when the appropriate regions of ski n were stimulated, movement illusions were focused to the joint under the s timulated skin. One role for cutaneous feedback from the hand may be to hel p identify which finger joint is moving.