Cerebral dominance and spinal excitability in cognition of motor space

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We previously demonstrated that arm and finger positioning was undershot when the head was rotated in the same direction as the positioning movement and overshot when the head was rotated in the direction opposite to positioning movement. Such biasing effects were assumed to arise etiher from some reflex effects due to head rotation or cognitive distortion in spatial pereception and control of arm and finger positioning. We examined in this research project two likely sources of the response biasing effects in arm and finger positioning with 90ﾟ head rotation. (1) A reaction-time experiment with a CNV paradigm was conducted to test the effects of cerebral dominance for directing attention towards reaction time stimuli that were given within the contralateral hemispace. Result showed only small amplitudes in CNVs at both C3 and C4, with the absence of laterality effects. This indicates the subjects may not have directed their attention to contralateral hemispace in the simple reaction time task used in this experiment. We will further examine in the future project the aspext of subjects' attention, using a choice reaction time task to manipulate subiject's attention toward contralateral hemispace. (2) The soleus H-reflex was examined throgh the period of 14 seconds after completion of head rotation. The amplitude of soleus H-reflex increased up to about 150% of controlH-reflex (at rest) just after the completion of head rotation. This then gradually returned to control level with in 6 or 7 sec. The head rotation could therefore affect spinal motoneuronal excitability no longer than about 6 or 7 sec after head rotation. This implies that the spinal reflex effect due to head rotation is ruled out as a sourceof the response biasing effect appearing in arm and finger positioning with 90ﾟ head-rotation.