- Montreal Neurological Institute, Montreal, PQ, Canada. 
Address correspondence and reprint requests to Dr. Bernard Brais, 6150 avenue du Boisé, Apt A6, Montréal, PQ, Canada, H3S 2V2.
Presented in part at the 43rd annual meeting of the American Academy of Neurology, Boston, MA, April 1991. This paper was awarded the Lawrence C. McHenry Award of the American Academy of Neurology, April 25, 1991.
Received April 23, 1991. Accepted for publication in final form August 12, 1991.