Cerebellar structure and function: making sense of parallel fibers.

Many parts of the brain have to cooperate in a finely tuned way in order to generate coordinated motor output. Parameters of these cooperations are adjusted during early childhood development and years of motor learning later in life. The cerebellum plays a special role in the concert of these brain structures. With the unusual geometrical arrangement of its neuronal elements, especially of parallel fibers and Purkinje cells the cerebellum is a selective and sensitive detector of a specific class of spatio-temporal activity patterns in the mossy fiber system: sequences of excitatory input which 'move' along the direction of parallel fibers at about 0.5 m/s, i.e. the speed of spike conductance in parallel fibers. Precise spatio-temporal neuronal activity patterns have been shown to occur in two major sources of afference to the cerebellum, the neocortex and the sensory feedback system. Based on our own experimental work and the above-mentioned findings we suggest that the cerebellum detects specific spatio-temporal activity patterns which trigger learned cerebellar output related to motor control and which contributes to the control of precise timing of muscle contraction. Copyright 2002 Elsevier Science B.V.