Brooks N, Kupshik G, Wilson JTL, Galbraith SL & Ward RD (1987) A neuropsychological study of active amateur boxers. Journal of Neurology, Neurosurgery, and Psychiatry, 50 (8), pp. 997-1000. https://doi.org/10.1136/jnnp.50.8.997
Neuropsychological examinations were carried out on 29 amateur boxers and 19 controls matched for age, ethnicity, and education. There was no evidence of significantly impaired performance in the boxers. Within the boxing group, a variety of features of boxing history were examined as possible predictors of cognitive performance (such as number of knockouts, duration of boxing). No feature was a significant predictor of lower cognitive performance.
Journal of Neurology, Neurosurgery, and Psychiatry: Volume 50, Issue 8