Cerebellar versus stiffness control

The mechanical properties of the muscular actuators are important for dynamics (compensation of internal/external loads and disturbances) as well as for spatial cognition. Consider the so called λ-model (Feldman and Levin, (1995)). The key point, from the point of view of space representation, is that that the controlled variable has the same dimensions of the control variable. The proprioceptive space can be defined as a lower-dimensional manifold in the set of all possible configurations and can be represented in a distributed way in terms of a self-organising cortical map. Its dimensionality and geometry is coded into the pattern of lateral connections that are excitatory and recurrent. These connections can be adapted by means of unsupervised Hebbian learning within a (probably innate) behavioural strategy of circular reaction. The same strategy and unsupervised learning paradigm allow the emergence of an internal distributed representation of the exteroceptive space and the nonlinear mapping between the two spaces, exploiting a side-effect of circular reaction