A hypothesis of the operation of cerebellar circuits involved in axial and limb movements

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Gilbert, Mike (2020). A hypothesis of the operation of cerebellar circuits involved in axial and limb movements. University of Birmingham. Ph.D.

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Abstract

For most brain regions the only realistic approach to theory is a top down, systems view because the evidence is too sparse to ‘join the dots’. For a number of reasons the cerebellum is probably the best-suited large brain structure to take a different, evidence-based approach. That is the approach here, combining evidence of anatomy, electrophysiology, molecular biology and behavioural conditioning studies with mathematical and computational modelling, to build a model of the way the cerebellum derives output from input. Modelling is used to test predictions and to generate hypothetical data not available with current experimental techniques, which feed back into the model. This allows modelled behaviour of different parts of the circuit to be tested against evidence of other parts. The focus is on circuits involved in control of axial and limb movements, although parts of an explanation are likely to be portable to other circuits (because cerebellar circuit wiring is modular). An important part of the proposals is that the functions of pattern recognition and output coding are separate. It is a function of recoding in the granular layer to turn input variables into independent (and fewer) internal variables. Independence means they can be used in different functions without mutual interference of the execution of those functions with each other. Pattern recognition determines which circuits have output and when, but does not code output. Instead, the response to a known pattern following training is permissive, creating a time window in which output cells are controlled ad hoc by internally generated information about movement. Recoding in the granular layer, as well as having a long-suspected role in pattern detection, also has a role in control of output rates, by turning (what is from a cerebellar view) an arbitrary range and frequency distribution of input rates into a narrow range of granule cell rates with a fixed bandwidth and a frequency distribution with a fixed shape, so that the only functional variable of internal signals traffic at the scale of input to a Purkinje cell is the adjustable range.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):