Person:

LeBlanc, Jocelyn J.

Extensive experience-dependent refinement of cortical circuits is restricted to critical periods of plasticity early in life. The timing of these critical periods is tightly regulated by the relative levels of excitatory and inhibitory (E/I) neurotransmission during development. Genetic disruption of synaptic proteins that normally maintain E/I balance can result in severe behavioral dysfunction in neurodevelopmental disorders like autism, but the mechanisms are unclear. We propose that abnormal critical periods of sensory circuit refinement could represent a key link between E/I imbalance and the cognitive and behavioral problems in autism.

Background: Duplication and deletion of the chromosomal region 16p11.2 cause a broad range of impairments, including intellectual disability, language disorders, and sensory symptoms. However, it is unclear how changes in 16p11.2 dosage affect cortical circuitry during development. The aim of this study was to investigate whether the visual evoked potential (VEP) could be used as a noninvasive quantitative measure of cortical processing in children with 16p11.2 copy number variation. Methods: Pattern-reversal VEPs were successfully recorded in 19 deletion carriers, 9 duplication carriers, and 13 typically developing children between the ages of 3 and 14 years. The stimulus was a black and white checkerboard (60’) that reversed contrast at 2 Hz. VEP responses were extracted from continuous EEG recorded using a high-density elasticized electrode net. Results: Quantitative analysis of the VEP waveform revealed that, relative to controls, deletion carriers displayed increased amplitude and duplication carriers displayed diminished amplitude. Latencies of the VEP waveform components were unaffected by 16p11.2 status. P1 amplitude did not correlate with age, IQ, or head circumference. Conclusions: The results of this study suggest that recording VEP is a useful method to assay cortical processing in children with 16p11.2 copy number variation. There is a gene dosage-dependent effect on P1 amplitude that merits further investigation. The VEP is directly translatable to animal models, offering a promising way to probe the neurobiological mechanisms underlying cortical dysfunction in this developmental disorder.