Dr. Sulzer and his colleagues hypothesize that cortex overgrowth in early development, a possible cause of autism, can result from defects in the tuberous sclerosis pathway, which normally keeps neuronal growth under control. In a healthy individual, the tuberous sclerosis pathway promotes macroautophagy, a normal process by which cells break themselves down to restrict their growth. Sulzer and colleagues believe mutations in the tuberous sclerosis genes disrupt the macroautophagy pathway in neurons, allowing them to grow out of control in the brain. The researchers plan to study macroautophagy in experimental mice with inactivated tuberous sclerosis genes. From a biochemical perspective, they will ascertain whether dysregulation of mTOR — a protein that inhibits macroautophagy but is normally kept in check by the tuberous sclerosis proteins — results in overgrowth of neurons in the mice. The researchers also plan to assess whether the mutant mice have different levels of neuronal activity in the cortex than do healthy mice. Finally, the researchers plan to test whether the drug rapamycin, which inhibits the mTOR protein, can reestablish normal levels of macroautophagy in the mutant mice.