Mechanisms of spinal learning

The Horridge Paradigm (Horridge, 1962) has been used to demonstrate that the lumbar spinal cord is capable of instrumental learning, even absent neural connections to the brain (Grau et al., 1998; Crown et al. 2001, 2002).  We are developing and validating a modified version of this model to study spinal learning in the adult mouse following complete spinal transection at the T7-T8 level.  We use a small video camera-based tracking system (CMUCam2, Carnegie Mellon University), controlled by custom-built software (LabVIEW, National Instruments, Inc.) to track foot position, and a constant-current stimulator (S88X, Grass Telefactor) to provide appropriate shock to the tibialis anterior (TA) muscle when the foot falls below a constant vertical threshold.  Shock intensity is calibrated based on the force generated by the paw dorsiflexors using a muscle lever (Aurora Scientific, Inc.).  Preliminary experiments have shown that intermediate-intensity shocks contingent on foot position can elicit a sustained flexion response over time , suggesting that the Horridge Paradigm can be successfully applied to the adult spinal mouse.  Furthermore, this technique will provide a simple, minimally-invasive method for eliciting and detecting learning.  The mouse model will be important for identifying mechanisms of instrumental learning and the specific neural circuitry where learning occurs in the spinal cord.