The 40-Hz event related response in general learning disabled, specific arithmetic disabled, and normal children

The present study extends to a learning disabled population the findings of Galambos and his colleagues of the apparent resonance of the 40-Hz event-related response at stimulus repetition rates of 40/sec and at subharmonics of this frequency. The learning disabled subtypes of reading disabled and arithmetic disabled as well as age/intelligence matched control children were assessed with the auditory 40-Hz event-related procedure. The amplitude of the waveform was analyzed at rates of 40/sec and 20/sec. with and without contralateral distraction stimulus, and to left and right ears. The finding of no significant difference between the 40-Hz ERPs recorded in the left and right hemispheres of reading disabled and arithmetic disabled children suggests that this response is independent of the 40/EEG activity found by Sheer and his colleagues to be suppressed in learning disabled children. However, the findings of increased amplitude in the arithmetic disabled does support the frontal lobe modulatory component of the focused arousal model. Of greater theoretical importance is the logical extension of the present findings to support the cognitive processing model of Goldberg and Costa and the nonverbal learning disabled syndrome proposed by Rourke.