Facilitation of the spinal H-reflex by auditory stimulation in dyslexic adults

Dyslexic subjects show a variety of mild sensory and motor deficits that have been assumed to reflect dysfunction of the large-diameter 'magnocells' in different parts of the brain. Hearing as a warning sense relies on rapidly-conducting fibers, and on the basis of the magnocellular deficit theory, we wondered whether auditory alerting would be weakened in dyslexic adults. We quantified the strength of sound-induced spinal facilitation in seven dyslexic and eight normal-reading adults by measuring the amplitudes of H-reflex, a monosynaptic spinal reflex, after loud binaural sounds. The audiospinal facilitation was of similar strength in dyslexic and control adults, indicating normal auditory alerting via cerebrospinal pathways. The slightly prolonged facilitation in dyslexics agrees with the dyslexics' general sluggishness of sensorimotor processing.