The rate of learning measured at a single synapse.

On the reformulation of inhibition in Hull's system.

“…Tentative evidence for this opinion is found in the experiments on spinal conditioning, which, however, are not yet entirely beyond dispute as examples of true conditioning. Nevertheless, for what it is worth, Shurrager and Shurrager (1946) have reported that both conditioning and extinction, measured at a single synapse in a spinal preparation, become faster with successive periods of conditioning and extinction. Hull (1952, p. 114) also pointed out that the delay CR (the "inhibition of delay" being due to &/«) is eliminated by certain drugs, for example, caffeine and benzedrine.…”

A search for 'spinal conditioning' and for evidence that it can become a reflex.

“…Briefly the following observations have been made. The CR ,is generally restricted to a very small group of muscle fibres, said to be one motor unit (15). .…”

Some Neurological Correlates of Behavior.

“…It is doubtful that the normal functional interneuronic relationship is ever limited to two at a time, although such may be obtained in special researches (cf. Shurrager and Shurrager, 1946). It is more likely that thousands of cells fire in all sorts of possible relationships.…”