Mossy fibers in the cerebellar hemisphere show delay activity in a delayed response task

To examine whether mossy fibers (MFs) in the cerebellar hemisphere show delay activity, we recorded MF activity during a wrist movement task with a random instructed delay period in two monkeys. Among 155 task-related MFs, 70 MFs (45%) demonstrated significant delay activity. Those MFs were widely distributed in the cerebellar hemisphere. Some of the activities were evoked by instruction cue presentation, whereas other activity started in anticipation of the upcoming go signal. For most MFs, the delay activities showed directional tuning. These patterns of the activity were in common with those of neurons in the cerebral motor cortices.