- Dr N Robertson, University of Cambridge, Neurology Unit, Addenbrooke’s Hospital, Hills Road, Cambridge CB2 2QQ, UK. Telephone 0044 1223 216751; fax 0044 1223 336941.
- Received 5 February 1998
- Revised 7 May 1998
- Accepted 15 May 1998
- Published online 1 November 1998.
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