Increasing evidence has implicated the cerebellum in providing forward models of motor plants predicting the sensory consequences of actions. Assuming that cerebellar input to the cerebral cortex contributes to the cerebro-cortical processing by adding forward model signals, we would expect to fi nd projections emphasising motor and sensory cortical areas. However, this expectation is only partially met by studies of cerebello -cerebral connections. Here we show that by electrically stimulating the cerebellar output and imaging responses with functional magnetic resonance imaging, evoked blood oxygen level-dependant activity is observed not only in the classical cerebellar projection target, the primary motor cortex, but also in a number of additional areas in insular, parietal and occipital cortex, including sensory cortical representations. Further probing of the responses reveals a projection system that has been optimized to mediate fast and temporarily precise information. In conclusion, both the topography of the stimulation effects and its emphasis on temporal precision are in full accordance with the concept of cerebellar forward model information modulating cerebro-cortical processing.

No abstract

No abstract

A common view of the architecture of different brain regions is that, despite their heterogeneity, they have optimized their wiring schemes to make maximal use of space. Based on experimental findings, computational models have delineated how about two-thirds of the neuropil is filled out with dendrites and axons optimizing cable costs and conduction time while keeping the connectivity at the highest level. However, whether this assumption can be generalized to all brain regions has not yet been tested. Here we quantified and charted the components of the neuropil in the four deep cerebellar nuclei (DCN) of the rat's brain. We segmented and traced the neuropil stained with one of two antibodies, one antibody against dendritic microtubule-associated proteins (MAP2a,b) and the second against the Purkinje cell axons (PCP2). We compared fiber length density, average fiber diameter, and volume fraction within different components of the DCN in a random, systematic fashion. We observed differences in dendritic and axonal fiber length density, average fiber diameters, and volume fraction within the four different nuclei that make up the DCN. We observe a relative increase in the length density of dendrites and Purkinje cell axons in two of the DCN, namely, the posterior interposed nucleus and the lateral nucleus. Furthermore, the DCN have a surprisingly low volume fraction of their dendritic length density, which we propose is related to their special circuitry. In summary, our results show previously unappreciated functional adaptations among these nuclei.