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 elimin ated by regional anesthesia of the working arm, indicating the importa nce of afferent neural input. The purpose of this study was to determi ne the specific type of afferent input required for this cerebral acti vation. The rCBF was measured at +5.0 and +9.0 cm above the orbitomeat al (OM) plane in 13 subjects during 1) rest; 2) dynamic left-hand cont ractions; 3) postcontraction ischemia (metaboreceptor afferents); and 4) biceps brachii tendon vibration (muscle spindles). The rCBF increas ed only during dynamic band contraction; contralateral MS1 (OM + 9) by 15% to 64 +/- 8.6 ml . 100 g(-1). min(-1) (P < 0.05); supplementary m otor 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 sugges t that the rCBF increase during dynamic hand contraction does not requ ire neural input from muscle spindles or metabolically sensitive nerve fibers, although the involvement of mechanoreceptors (group III or Ib ) cannot be excluded.