Effect of Diverse Temporal Recoding of Granule Cells on Pavlovian Eyeblink Conditioning in The Cerebellum

We consider the Pavlovian eyeblink conditioning (EBC) via repeated presentation of paired conditioned stimulus (tone) and unconditioned stimulus (airpuff), and investigate the effect of diverse temporal recoding of granule (GR) cells on the EBC in a cerebellar network by varying the connection probability pc from Golgi to GR cells. For an optimal value of , individual GR cells exhibit diverse spiking patterns which are well- or ill-matched with the unconditioned stimulus. Then, these diversely-recoded signals via parallel-fibers (PFs) from the GR cells are effectively depressed by the error-teaching signals via climbing fibers (CFs) from the inferior olive. Synaptic weights at well-matched PF-Purkinje cell (PC) synapses of active GR cells are strongly depressed via strong long-term depression (LTD), while practically no LTD occurs at ill-matched PF-PC synapses. This kind of “effective” depression at PF-PC synapses coordinates firings of PCs effectively, which then exert effective inhibitory coordination on cerebellar nucleus neuron [which evokes conditioned response (CR; eyeblink)]. When the learning trial passes a threshold, acquisition of CR begins. In this case, the timing degree of CR becomes good due to presence of ill-matched spiking group which plays a role of protection barrier for the timing. With further increase in the trial, strength of CR (corresponding to the amplitude of eyelid closure) increases due to strong LTD in the well-matched spiking group, while its timing degree decreases. In this way, the well- and the ill-matched spiking groups play their own roles for the strength and the timing of CR, respectively. Thus, the (overall) learning efficiency degree (taking into consideration both timing and strength of CR) for the CR increases with learning trial, and eventually it becomes saturated. By changing pc from , we also investigate the effect of diverse spiking patterns of GR cells on the EBC. Plots of both the diversity degree of spiking patterns of GR cells and the saturated learning efficiency degree of CR versus pc are found to form bell-shaped curves with peaks at , and they also have a strong correlation. Consequently, the more diverse in temporal recoding of GR cells, the more effective in motor learning for the Pavlovian EBC.