SPINAL REFLEX ORGANIZATION IN EARLY DEVELOPMENT - ELECTROPHYSIOLOGICAL MEASURES AND PROPOSED MOTOR PATHWAYS

The delay in developmental milestones in cerebral palsy (CP) is presum ed to result from a nonprogressive insult to the developing central ne rvous system (CNS). In CP, the site(s), type, duration, and magnitude of CNS insult(s) may never be defined, and a single focus of damage ma y not be revealed by standard brain imaging methods. The neurological examination (i.e., assessment of reflexes, tone, and motor coordinatio n) generally does not define the insult with precision, nor can it pre dict the delays in motor skill development. The CNS damage may only be suspected from the medical history during the prenatal or perinatal p eriod; confirmation of CNS insult may be deferred until the child miss es developmental milestones in the first few months or years of life. In CP, patterns of motor incoordination and delay emerge gradually ove r time during development. While the original CNS injury is presumed t o be a nonprogressive insult to higher motor centers (e.g., cerebral m otor cortex), the damage probably causes significant modulation of fun ctional neural connections during maturation of the brain and spinal c ord. Such aberrant communication in motor pathways may be caused by, o r result in, motor incoordination. In turn, repetition of uncoordinate d movements may reinforce aberrant neural connections with, or at, the spinal cord. In this paper, we review neural responses to stimulation of sensory and motor systems and compare data for healthy neonates an d children, and children and adults with CP. Age-related differences a re identified in measured onset latencies of responses, computed centr al conduction delays, and relative levels of excitatory drive. Differe nces in muscle responses are shown among subject groups for myotatic r eflex activation of agonist, antagonist, and more distant limb muscles . From these data, inferences have been made that, in CP, impairments in CNS circuitry may include descending corticospinal pathways and/or spinal reflex pathways (e.g., ''reciprocal excitation''). Data from a number of investigators support the theory that changes in spinal refl ex pathways are likely to play a fundamental role in the development o f motor control. (C) 1997 Wiley-Liss, Inc.