Oldie:
Characterization of freezing of gait subtypes and the response of each to levodopa in Parkinson's disease. - 2003 - NCBI.
ncbi.nlm.nih.gov/pubmed/128...
521 cite Schaafsma 2003: Characterization of freezing of gait subtypes and the response of each to levodopa in Parkinson's disease.