Neuropsychological effects of cerebellar tumor resection were evaluated in 19 children at the Department of Neurology, Massachusetts General Hospital, Boston, MA. Eleven had medulloblastoma, seven astrocytoma and one an ependymoma. Ages ranged from 3 years to 14 years (mean age, 8 years) at the time of tumor resection. Eight had received chemotherapy prior to neuropsychological testing, but none had received cranial irradiation or methotrexate. The time between surgery and neuropsychological testing ranged from 1 to 22 months (mean, 5 months). Executive function, including planning and sequencing, was impaired in 5 patients, expressive language in 7 (37%), visual-spatial function in 7 (37%), visual spatial memory in 5, and modulation of affect in 6. Fourteen (74%) had mild to marked impairment of fine motor coordination, sometimes independent of cognitive deficits. Dysregulation of affect was associated with lesions of the vermis. Age was a factor, the youngest being least likely to show cognitive deficits: of 9 who were under 7 years of age, only 3 (33%) showed deficits, whereas 8 (80%) of 10 older than 7 years had deficits. 
COMMENT. Acquired cerebellar lesions associated with cerebellar tumor resection in children may result in impairments of neurobehavioral function. The degree and type of dysfunction are correlated with age at the time of surgery and the site of the tumor resection. The cerebellum is important in cognitive and behavioral mechanisms.
Cerebellar site specific cognitive and behavioral deficits were demonstrated in a study of 26 children treated surgically for posterior fossa tumors at the Carlo Besta National Neurological Institute, Milan, Italy . Impairments of auditory sequential memory and language processing occurred with right cerebellar hemisphere tumors, whereas deficits in spatial and visual sequential memory were associated with left cerebellar tumors. Vermis lesions resulted in post-surgical mutism and behavioral disorders, including autism.
Cerebral white matter lesions and cognitive dysfunction. An MRI study in elderly subjects at the Erasmus University Medical School, Rotterdam, showed that the more severe periventricular white matter lesions affected speed of cognitive processes more than global cognitive and memory tasks. 
The genetic basis of cognition was reviewed from the Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, UK . Genetic approaches are limited to exploring neuronal function. Genetic mutations with a cognitive and behavioral phenotype are characterized by specific effects, but their delineation is difficult to determine in the mentally retarded. How a specific gene determines cognitive function is poorly understood.