Orofacial fine motor control impairments in congenital spasticity: evidence against hypertonus-related performance deficits.

Motor impairments in the fine force control of lips, tongue, and jaw were measured in subjects with congenital spasticity. Because these orofacial motor systems are not uniformly endowed with muscle spindles and monosynaptic reflexes, quantification of these motor impairments addresses the question of whether stretch reflex hypertonus is a positive or negative sign. The results indicated that hyperactive muscle spindle-based monosynaptic reflexes are not a causal factor in these voluntary orofacial motor impairments. These data also indicated that motor impairments were disproportionately greater at finer levels of isometric force control. These fine control measures appear useful as a quantitative index of general voluntary motor deficit.