Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Periventricular heterotopia ?
    ### Response:
    Periventricular heterotopia is a condition in which the nerve cells (neurons) do not migrate properly during the early development of the fetal brain from about the 6th week to the 24th week of pregnancy. Affected people typically develop recurrent seizures (epilepsy) beginning in mid-adolescence.
    