40 HZ. power functions in MBI and normal children during performance of behavioral tasks



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The electrical activity in 3 frequency bands in the 'arousal spectrum' was studied in the right parietal-occipital area of 10 male learning disordered (MBI) children (age, M=10.26, SD=1.31; IQ, M=98.00, SD=7.51) and 10 normal grade level (NGL) children (age, M=10.19, SD=0.74; IQ, M=98.40, SD=6.05) during three behavioral tasks. Visual (V), Verbal-Visual (VV), and Verbal-Auditory (VA), and a Rest Control. Continuous (moving-window) power spectral functions were computed with an analog computer for 31.5, 40, and 50 Hz. bands and for a 70 Hz. band which was used as an indicator of the degree to which muscle potentials were contributing to the power functions. After discarding data believed to be affected by muscle potentials on the basis of a criterion value from the 70 Hz. power function, the 'area under the curve' of the power spectral functions was measured with a planimeter during each stimulus to response interval of the test situation and during consecutive 10-sec. intervals in Rest Control. Power/sec was then calculated. These measures were subjected to digital analysis in which a statistical control was applied to remove power from each function to the extent of the correlation of each power function with the 70 Hz. 'muscle indicator' function. The results were: 1. The MBI group made significantly more errors than the NGL group on VV and VA tasks, while there was no significant difference in performance of the two groups on V tasks. 2. Mean power/sec in the 40 Hz. band was higher during VV tasks compared to VA tasks and Rest Control in the NGL group, but not in the MBI group. Mean power/sec in the 31.5 and 50 Hz. bands did not differ significantly between VV, VA, and Rest Control for either the NGL or the MBI group. 3. Mean power/sec was higher in the NGL group than in the MBI group in the 40 Hz. band during VV tasks. No such difference in absolute power values between the two groups was observed either in the 31.5 and 50 Hz. bands or during VA and Rest Control. 4. Power/sec was higher during VV tasks than during Rest Control in more trials in the 40 Hz. band than in 31.5 and 50 Hz. bands in the NGL group, but not in the MBI group. There was no significant difference between frequencies in number of trials showing greater power during VA tasks than during Rest Control for either the NGL or MBI group. These results were interpreted within the framework of the hypothesis of the 40 Hz. rhythm as a 'consolidation rhythm' with the learning disability child's problem conceptualized as a possible failure in the generation of the 'consolidation rhythm.' Implications of these results for the diagnosis and treatment of learning disability children were discussed. It was suggested that researchers might try to facilitate the generation of the 40 Hz. rhythm in the brain either by chemotherapy or by operant conditioning of this rhythm, as in recent alpha conditioning studies. The problem of muscle potentials in the study of brain potentials at frequencies 30 Hz. and above was discussed and practical solutions to the problem were offered.