Mechanisms regulating regional cerebral activation during dynamic handgrip in humans

Dynamic hand movement increases regional cerebral blood flow (rCBF) of the contralateral motor sensory cortex (MS1). This increase is eliminated by regional anesthesia of the working arm, indicating the importance of afferent neural input. The purpose of this study was to determine the specific type of afferent input required for this cerebral activation. The rCBF was measured at +5.0 and +9.0 cm above the orbitomeatal (OM) plane in 13 subjects during 1) rest; 2) dynamic left-hand contractions; 3) postcontraction ischemia (metaboreceptor afferents); and 4) biceps brachii tendon vibration (muscle spindles). The rCBF increased only during dynamic hand contraction; contralateral MS1 (OM +9) by 15% to 64 +/- 8.6 ml.100 g-1.min-1 (P < 0.05); supplementary motor area (OM +9) by 11% to 69 +/- 9.8 ml.100 g-1.min-1 (P < 0.05); and there were also bilateral increases at MS2 (OM +5) [by 16% to 64 +/- 8.6 ml.100 g-1.min-1 (P < 0.05)]. These findings suggest that the rCBF increase during dynamic hand contraction does not require neural input from muscle spindles or metabolically sensitive nerve fibers, although the involvement of mechanoreceptors (group III or Ib) cannot be excluded.