FUNCTIONAL-STUDIES OF THE HUMAN CEREBELLUM WITH POSITRON EMISSION TOMOGRAPHY

New techniques of functional imaging with PET have resulted in improve d understanding of the organisation of the human brain at systems leve l. Many studies have concentrated on the organisation of the cerebral cortex, while the cerebellum has been subjected to less intensive inve stigations. In the motor system the contralateral cerebellum is intima tely related to the functions of the primary motor cortex. This has be en demonstrated in a number of studies involving simple and more compl ex motor activations. The relationship has also been demonstrated in p athology. The role of the cerebellum in the generation of tremor has b een the subject of some considerable study with the demonstration of f unctional relationships between the olivary nucleus and the cerebellum as well as between the cerebellum, thalamus and motor cortex in essen tial and parkinsonian tremor. The cerebellum is also involved in motor learning. Parts of the motor system exhibit physiological adaptation during the repeated performance of a simple motor task. The cerebellum , in particular, shows a decrease in regional blood flow with practice of a motor task despite a similar performance. A number of recent rep orts suggest that the cerebellum is also involved in cognitive functio ns and particularly language. Functional neuroimaging has not addresse d this problem explicitly; however, studies of severely depressed pati ents with cognitive impairments have shown an unexpected but interesti ng result in that impaired cognition but not the state of mind is asso ciated with increases in cerebellar activity. The reason for the pauci ty of systematic investigations of cerebellar function has been the li mited field of view, sensitivity and resolution of PET cameras. Recent advances mean that one can expect more informative studies in the nea r future.