Myelinated axons of granular cells that run horizontally near the surface of the cerebellar cortex and perpendicular to the dendritic fields of Purkinje cells, and that make excitatory (glutamate) axodendritic synapses on spines of the distal dendrites of Purkinje cells, as well as those of basket, Golgi type II and stellate inhibitory interneurons – at least all those cells within a radius of a few millimetres. Cerebellar long-term depression (LTD) occurs when parallel fibers and climbing fibers are activated synchronously and repetitively. Thus, these fibers (or the granule cells from which they originate) can change their firing properties as a consequence of information that has been received previously. In other words, they can ‘learn’. Parallel fibers are seemingly also involved in another type of neural plasticity, namely, long-term potentiation.
See Basket cell, Cerebellar cortex, Cerebellum (anatomy), Glutumate (or glutamate), Golgi type II cell, Granule cells, Long-term depression (LTD), Long-term potentiation (LTP), Molecular layer, Plasticity (neural), Purkinje cells, Stellate cells