Complex sentence: Amongst his writings is the description of an experiment designed to measure the effect of video games on human brain activity and he claims that the experiment demonstrates the existence of an "Adverse effect that video games have on the human brain".
Split into simpler sentences: Amongst his writings is the description of an experiment designed to measure the effect of video games on human brain activity. He claims that the experiment demonstrates the existence of an "Adverse effect that video games have on the human brain".