| The neuroanatomical analyses of archicortical and neocortical developmental abnormalities in Down's syndrome were reviewed. Both conventional and spectral EEG studies of Down's syndrome were reviewed. For the study, thirty Down's Syndrome children and young adults, aged 9 months to 26 years, were paired with age-matched normal children and young adults. Eyes-open and eyes-closed EEG were recorded from nineteen scalp sites of the International 10/20 system. The following bipolar spectral EEG variables were compared for the two groups: relative power, interhemispheric amplitude asymmetries, and total power. Monopolar coherence was also compared and to aid in topographic analysis, was grouped into five anatomical categories: anterior-to-posterior, posterior-to-anterior, posterior temporal, anterior temporal, and interhemispheric.; Results show that relative power discriminated the two groups, but the head circumference covariate significantly reduced this difference. Total power was consistently greater in Down's, as expected. Amplitude asymmetries only weakly discriminated the groups. Coherence was the strongest discriminator, and strongly and consistently showed the greatest differences from normals were in the left hemisphere. In addition, it also indicated the posterior cortical regions differ more from normal than do the anterior regions. Among normals, the left hemisphere is known to have the greatest cellular differentiation and the posterior regions have the highest cell packing densities. The consistently higher coherence among the Down's syndrome individuals indicates a diminished functional differentiation in cortico-cortical connections, particularly in the left hemisphere and posterior regions. A differentiation hypothesis is proposed to explain the differences between Down's and normals' neocortex indicated by this topographic pattern of EEG findings. |
