Walking while holding a conversation and writing a letter whilst thinking about its content: we perform many actions without even thinking about them. This is possible due to the cerebellum. It regulates the automation of our movements and as a result the cerebrum can perform other tasks. However, how the cerebellum performs this task is not clear. Dutch researcher Angelique Pijpers reconstructed a part of cerebellar functioning in rats and investigated how it mediates in the control of hind limb muscles. Such research might in future provide a better understanding of how the elderly move.
Pijpers and her colleagues investigated which processes took place inside and outside of the cerebellum: how does it channel information and process this into a signal to the muscles? Subsequently they investigated which parts of the cerebellum are involved in regulating the activity of a single muscle. Furthermore, they examined the consequences of inactivation of one or more parts of the cerebellum on the functioning of this muscle.
Nerve cells in the cerebellum receive two types of signals. Through the climbing fibres, signals from a specific structure in the brain stem are transmitted to Purkinje cells located in the cerebellar cortex. Mossy fibres transmit signals from various parts of the central nervous system to the granule cells of the cerebellar cortex.
Pijpers reconstructed the modular anatomy of the cerebellum by injecting small quantities of traceable substances. This allowed mapping of different 'stations' of the information pathway. The reconstruction revealed that the cerebellum is organised into a number of modules or connections aligned in parallel. Up until now it had been thought that the climbing fibre and mossy fibre systems were organised in completely different manners. However, according to Pijpers they also exhibit similarities.
By injecting a viral tracer agent in various muscles, the researcher traced the cerebellar modules involved in the control of a single muscle. She then inactivated one of the modules by injecting a neurotoxin. The rat's ability to walk was scarcely altered but there was a strong decrease in its ability to respond quickly to obstacles in a reflexive manner. This revealed that specific modules of the cerebellum mainly regulate reflex functions during walking and match these to the situation.
Consequences for the elderly
Pijpers' research opens up new possibilities for further research into the role of the cerebellum in the control of movements. Results from follow-up studies could be important for research into how the elderly move. For example, the increased risk of falls in the elderly is often associated with physical limitations. According to Pijpers this could also be a linked to cerebellar functioning, since certain parts of the cerebellum appear to decrease as we get older.
Angelique Pijpers' research was funded by NWO.
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