EEG Photic Driving Interhemispheric Coherence Deficit In Childhood Autism

Background: In our previous research, it was shown that the EEG photic driving responses to the intermittent photic stimulation (IPS) reveal in autistic patients with relatively intact verbal functions and without severe or moderate mental retardation certain latent interhemispheric asymmetry not present in the spontaneous background EEG: 1) the right hemisphere driving “hyporeactivity”, detected by the reduced presence of driving spectral peaks in the different hemispheric regions and a reduced driving amplitude in the occipital area, predominantly at the fast alpha and beta IPS frequencies (Intern. J. Psychophysiol, 2009, 71: 177-183); and 2) the left hemisphere driving “hyperconnectivity” – augmented a number of high intrahemispheric coherent connections of likely compensatory nature (Clin. Neurophysiol., 2010, 121:145-152).

Objectives: Examination of the EEG photic driving interhemispheric coherence during IPS in autistic patients with relatively intact verbal and intellectual functions in order to enhance the likely latent alterations in the interhemispheric neural connectivity. 

Methods: Fourteen autistic boys, aged 6–14 years, free of drug treatment, with I.Q. 91.4 ± 22.8, and 19 normally developing boys were subject to IPS of 11 fixed frequencies of 3–24 Hz. In each subject, the number of interhemispheric coherent connections among the 20 highest coherent connections with maximum coefficients of coherence (CC) at the EEG frequencies corresponding to those of stimulation was evaluated. The CC values between homologous symmetrical EEG derivations of the two hemispheres were also estimated at the EEG frequencies of stimulation. 

Results: Among the 20 highest coherent connections, the number of interhemispheric ones in autistic patients proved to be significantly lower than in the control group. This difference was observed at the IPS frequencies of 4 and 12 Hz and at all the beta frequencies applied: 3.6±2.4 as against 6.4±1.7 connections for different frequencies. The CC values between various homologous derivations were also lower in the autistic patients. For example, for the IPS frequency of 21 Hz, this difference was significant in the parietal, central and posterior temporal areas where the CCs were 0.48±0.06 as against 0.62±0.08.

Conclusions: Coherence characteristics of the EEG photic driving reactions show latent potential deficit in the interhemispheric functional connectivity at high EEG frequencies not detectable in the spontaneous EEG of the resting state.