[1] Columbia Univ, Neurol Inst, Dept Neurol, New York, NY 10032 USA
[2] Columbia Univ, Columbia Coll Phys & Surg, New York, NY 10032 USA
[3] Columbia Univ, Dept Neurol, Clin Motor Physiol Lab, New York, NY 10032 USA
[4] Columbia Univ, Dept Ophthalmol, New York, NY 10032 USA
[5] Mt Sinai Sch Med, Dept Neurol, New York, NY USA