Neuro-Electrophysiological Repetition Effects Are Associated with Age and Adaptative Skills in Infants
Intellectual disability is highly comorbid with autism. An important focus of neurodevelopmental research aims at identifying such disorders as early as possible in order to act favourably on development within the time window of highest brain plasticity. Habituation, the simplest form of learning, can be measured very early on behavioral paradigms. It has been shown to be moderately correlated with cognitive development (Bornstein & Sigman, 1986; Kavsek, 2013). The electrophysiological correlate of habituation, described as the repetition effect, has been shown to be associated with intellectual disability (Knoth et al., 2018) and sensorial hypersensitivity (Ethridge et al., 2016), traits that can be found in autism spectrum disorders. The repetition effect’s evolution with maturation and link with early behavioural development still need to be determined.
The purpose of our study is to investigate the relationship between EEG repetition effect and adaptive skills, an early surrogate of intellectual functioning, during the first year of life.
We recorded high density EEG in 49 healthy infants (19 females) age between 3 and 8 months at the CHU Sainte Justine hospital. The experimental design consisted of a sequence of three times the vowel A (AAA) presented 64 times. Auditory presentations were supported by visual images (faces pronouncing the syllables) in order to attract infant’s attention (Basirat, 2014). Adaptive skills were measured using the GAC score obtained through the parent form of the Adaptive Behavior Assessment System Second Edition (ABAS-II).
A time-frequency analysis was performed to investigate repetition effects associated with the three stimulus (A) repetitions. Statistical analysis was performed using a linear mixed model (LMM) approach. Changes in spectral power with regards to stimulus repetition were analysed in six frequency windows (FW) [3-5Hz; 5-10Hz; 10-20Hz; 20-30Hz; 40-61Hz; 80-120Hz] in the time window from 2 to 202ms post-stimulus and four regions of interest (ROI) [central, frontocentral, left frontal and right frontal]. Age, GAC score and sex were tested as potential predictors for the model.
Spectral power changes across repetitions were explained by age in the 40-60Hz FW [χ2(6, N=49) = 19.285, p<0.01] across all ROI. Specifically, older infants showed repetition enhancement in response to the third repetition. Furthermore, GAC score explained spectral power changes across repetitions in the 80-120Hz FW in the frontocentral region [χ2(2, N=49) = 8.07, p=0.017]. Higher GAC scores were associated with repetition enhancement at the second presentation of the stimulus.
Our results show modulation of the EEG repetition effect with maturation and adaptative skills. As expected, maturation and adaptive skills modulate higher frequency brain responses. Whereas brain signal is enhanced at the third repetition towards the end of the first year, increased brain signal is found at the second repetition in babies with higher GAC scores. A longitudinal follow-up of our sample will allow us to determine the predictive value of these markers in the early diagnostic of neurodevelopmental disorders.