Memory traces in spinal cord.

The complexity and inaccessibility of the vertebrate CNS impede the localization and description of memory traces and the definition of the processes that create them. Recent work has shown that the spinal stretch reflex (SSR), which is produced by a monosynaptic two-neuron pathway, can be operantly conditioned, and that memory traces responsible for this behavioral change reside in the spinal cord. The probable locations are the terminal of the Ia affernt neuron on the motoneuron and/or the motoneuron itself. Because it modifies a simple well-defined and accessible pathway, SSR conditioning may be a valuable experimental model for studying vertebrate memory.