Relative Power of Specific EEG Bands and Their Ratios during Neurofeedback Training in Children with Autism Spectrum Disorder

Abstract

Neurofeedback is a mode of treatment that is potentially useful for improving self-regulation skills in persons with autism spectrum disorder. We proposed that operant conditioning of EEG in neurofeedback mode can be accompanied by changes in the relative power of EEG bands. However, the details on the change of the relative power of EEG bands during neurofeedback training course in autism are not yet well explored. In this study, we analyzed the EEG recordings of children diagnosed with autism and enrolled in a prefrontal neurofeedback treatment course. The protocol used in this training was aimed at increasing the ability to focus attention, and the procedure represented the wide band EEG amplitude suppression training along with upregulation of the relative power of gamma activity. Quantitative EEG analysis was completed for each session of neurofeedback using wavelet transform to determine the relative power of gamma and theta/beta ratio, and further to detect the statistical changes within and between sessions. We found a linear decrease of theta/beta ratio and a liner increase of relative power of gamma activity over 18 weekly sessions of neurofeedback in 18 high functioning children with autism. The study indicates that neurofeedback is an effective method for altering EEG characteristics associated with the autism spectrum disorder. Also, it provides information about specific changes of EEG activities and details the correlation between changes of EEG and neurofeedback indexes during the course of neurofeedback. This pilot study contributes to the development of more effective approaches to EEG data analysis during prefrontal neurofeedback training in autism.

Keywords: EEG bands' ratios; autism spectrum disorder; electroencephalography; gamma activity; neurofeedback.

Figure 1

A schematic representation of the wavelet transformation and band-pass filtering applications utilized to filter raw EEG signal into the desired filtered signal to be used for relative power calculation of the EEG bands of interest. “^*” Means the process of “convolution”; “∑” means the process of “summation”; the three lines of “…” are the ellipsis points, which means in the similar fashion from “Coefficient #3” to “Coefficient #128.”

Figure 2

Linear regression of the relative power of Gamma band over 18 sessions of neurofeedback training in 18 children with ASD (R = 0.491, y = 0.022x + 1.45%, t = 2.25, p = 0.039).

Figure 3

Linear regression of the theta/low beta ratio over 18 sessions of neurofeedback training in 18 children with ASD (R = 0.666, y = −0.079x + 9.49, t = −3.57, p = 0.003).

Figure 4

Linear regression of the theta/high beta ratio over 18 sessions of neurofeedback training in 18 children with ASD [R = 0.708, y = −0.088x + 6.24, t₍₁₇₎ = −4.01, p = 0.001].

Figure 5

Linear regression of the “40-Hz centered Gamma” index over 18 sessions of training [R = 0.547, y = 0.165x + 42.37, t₍₁₇₎ = 2.61, p = 0.019].

Figure 6

Linear regression of the “Focused Attention” index during 20 min long neurofeedback session (mean for all subjects across all sessions [R = 0.576, y = 0.063x + 70.64 c.u., t₍₁₉₎ = 2.99, p = 0.008].

Figure 7

Correlation of the theta/beta with the “Focused Attention” index during 20 min of neurofeedback training (across all sessions, r = −0.70, p = 0.001).