Children with Nonverbal Learning Disabilities (NLD): Coherence Values in the Resting State May Reflect Hypofunctional Long Distance Connections in the Right Hemisphere

Abstract

EEG intrahemispheric coherences (HCohs) in the resting state in twenty-four 4 Hz frequency windows between 1 and 51 Hz were studied in 18 children with “nonverbal learning disorder” (NLD) and compared to a group of 18 children with “verbal learning disorder” (VLD). New facts were found in the NLD group. These concern hemispheric balance, expressed as left minus right (L-R) homologous HCohs. In the high frequencies (25–51 Hz) the number of long-distance HCohs, higher in the right hemisphere (RH), is lower than HCohs, which are higher in the left hemisphere (LH). A reversed interhemispheric asymmetry is seen for short distance HCohs in that band. These asymmetries are not found in the VLD group, and the tendency is even reversed. In the low frequencies (1–27 Hz) all higher HCohs are more numerous in the RH, irrespective of interelectrode distance (IED). In these bands there are no NLD-VLD group differences. In NLD there is a significant inverse relationship between IED and (L-R)HCoh values (LRDif) in the high frequencies; the larger the IED, the higher the LRDif. In the lower frequencies there is no such tendency. In the VLD group these relationships were absent. These preliminary results suggest long distance gamma band hypoconnectivity in the RH of NLD children, in line with the hypothesis of an RH long distance connectivity problem in NLD. This may explain the difficulties with intermodal perception (gestalt function). Finally, in the NLD group some gamma band interhemispheric (ICohs) over F7/F8 and T3/T4 were lower than in VLD children and some gamma band ICohs were higher in NLD compared to VLD over O1/O2. This is possibly connected with the cognitive differences subserved by these areas, i.e., language and the respectively visuospatial function.