Background: In order to optimize outcomes of novel therapies for cerebellar ataxias (CAs),
it is desirable to start these therapies while declined functions are restorable: i.e. while the so-called
cerebellar reserve remains.
Objective: In this mini-review, we tried to define and discuss the cerebellar reserve from physiological
and morphological points of view.
Method: The cerebellar neuron circuitry is designed to generate spatiotemporally organized outputs, regardless
of the region. Therefore, the cerebellar reserve may be defined as a mechanism to restore its
proper input-output organization of the cerebellar neuron circuitry, when it is damaged. Then, the following
four components are essential for recruitment of the cerebellar reserve: operational local neuron circuitry;
proper combination of mossy fiber inputs to be integrated; climbing fiber inputs to instruct favorable
reorganization of the integration; deep cerebellar nuclei to generate reorganized outputs.
Results: We discussed three topics related to these resources, 1) principles of generating organized
cerebellar outputs, 2) redundant mossy fiber inputs to the cerebellum, 3) plasticity of the cerebellar
Conclusion: To make most of the cerebellar reserve, it is desirable to start any intervention as early as
possible when the cerebellar cell loss is minimal or even negligible. Therefore, an ideal future therapy
for degenerative cerebellar diseases should start before consuming the cerebellar reserve at all. In the
meantime, our real challenge is to establish a reliable method to identify the decrease in the cerebellar
reserve as early as possible.