EXPERIMENTAL TENSOR MODELING OF HEAD SENSORIMOTOR SYSTEM

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Substantial preliminary studies, and now also experimental results obtained by independent scientists abroad, demonstrate that the tensor model of CNS function, developed by the PI over a decade can quantitatively predict how neuronal networks implement sensorimotor transformations. These testable predictions are based upon the geometrical arrangement of the vestibular sensors and muscle effectors. For the experimental testing of the theory a system is selected where the geometry is known. There are no restrictions on the complexity of this geometry, since the model to be constructed can deal with systems where the coordinate frame may be non-orthoganal and the number of muscles may well exceed the number of degrees of freedom. The choice is the general, non-orthogonal, overcomplete system of the vestibulocollic reflex (VCR) a closed-loop sensorimotor system that generates neck-muscle motor signals that position the head, controlled by vestibular sensory signals arising directly from head movements. The analogous retinocollic reflex (RCR) will be compared to the VCR. The Co-PI's contribution in the past and the future is instrumental to the experimental definition of the function of the VCR & RCR, both in muscular response to body rotations and as revealed by the signals in neuronal pathways involved. The procedures developed for studying responses of the multicomponent vestibular and neck-muscle apparatus to rotations in three dimensions, will serve as ideal means for testing predictions of a tensorial model of the VCR. This convergence of experimental and theoretical approaches provides a rare opportunity for a collaborative study of VCR & RCR. Funds requested will be directed towards further constructing and testing a tensorial model of VCR & RCR, based on quantitative measurements of semicircular canal and neck muscle geometry and to relating the tensor model to experimental data. The model will be designed, constructed, tested, and applied to specific further experimental paradigms, such as cerebellectomy. Experimental tests include comparing measurements of spatial properties, such as dependency on rotational-directions, of VCR & RCR signals. They will be recorded from neck muscles and brainstem neurons, and results related to predictions of the model both for intact and cerebellectomized preparation. Tensorial modeling already appears to be passing these tests and thus is expected to become applicable to gaining understanding of other sensorimotor CNS functions, eventually facilitating rehabilitation of impaired sensorimotor function.