The electroencephalograms (EEGs) of 127 subjects with intellectual disability were analysed with regarding to their correlation to intellectual functions in order to further understand the relationships between EEG and intelligence. The EEG frequency spectrum was subdivided into 15, 2-Hz-wide bands and was recorded from electrodes F1, Fpz, Fp2, F7, F3, Fz, F4, F8, T3, C3, Cz, C4, T4, T5, P3, Pz, P4, T6, O1, Oz and O2. Patterns of acorrelation showed several similarities when compared to other analogous studies with normal subjects. However, the typical finding in the present study was a high number of correlations involving the frontal lobes, mainly the prefrontal portions, which is at variance with the patterns of normal subjects. Frontal lobes, especially the prefrontal regions, seem to be affected, regardless of its aetiology, in subjects with intellectual disability.

The electroencephalograms (EEGs) of 127 subjects with intellectual disability were analysed with regarding to their correlation to intellectual functions in order to further understand the relationships between EEG and intelligence. The EEG frequency spectrum was subdivided into 15, 2‐Hz‐wide bands and was recorded from electrodes F1, Fpz, Fp2, F7, F3, Fz, F4, F8, T3, C3, Cz, C4, T4, T5, P3, Pz, P4, T6, O1, Oz and O2. Patterns of acorrelation showed several similarities when compared to other analogous studies with normal subjects. However, the typical finding in the present study was a high number of correlations involving the frontal lobes, mainly the prefrontal portions, which is at variance with the patterns of normal subjects. Frontal lobes, especially the prefrontal regions, seem to be affected, regardless of its aetiology, in subjects with intellectual disability.

The systematic correlations, produced by the target stimulus in perceptual abilities tasks, with the N1a (frontal) and not with N1b (posterior), suggest that the visual perception process involves frontal participation. These correlations support the idea that the N1a and N1b are not equivalent. The relationship between frontal functions and early stages of visual perception is revised and discussed, as well as the frontal contribution with the neuropsychological tests used. A possible relationship between the frontal activity dysfunction in ID and perceptive problems is suggested. Perceptive alteration observed in persons with ID could indeed be because of altered sensory areas, but also to a failure in the frontal participation of perceptive processes conceived as elaborations inside reverberant circuits of perception-action.

The present study compared two group of subjects with intellectual disability. The 44 subjects in group 1 had equivalent verbal and performance IQs (67 and 64, respectively), while the 12 subjects in group 2 had an intellectual performance IQ which was > or = 10 points above their verbal performance IQ (80 and 65, respectively). The second group showed an alpha peak at a higher frequency and an evoked potential closer to normality. The decrease in the voltage of the P300 wave in group 1 was especially significant. The cognitive evoked potentials were also different between the two groups.