Many individuals with Parkinson's syndrome have an intellectual impairment which is large enough to be of both practical and theoretical significance. Forty patients with moderate to severe parkinsonism were examined with the WAIS before and after 5 to 13 months treatment with 4 to 8 gm of levodopa (L-dopa) daily. Approximately half of them improved the equivalent of 10 IQ points or more. The greatest improvement occurred on the function on which they were the most impaired prior to treatment, namely, perceptual organization. Patients with lower pretreatment IQs improved more than those with higher IQs. There was little or no relationship between physical or affective improvement and intellectual improvement.
Loranger AW, Lee JE, McDowell F. Levodopa Treatment of Parkinson's SyndromeImproved Intellectual Functioning. Arch Gen Psychiatry. 1972;26(2):163–168. doi:10.1001/archpsyc.1972.01750200067014
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