On the directionality of classically-conditioned glycemic responses.

Rats were administered either exogenous insulin or glucose as the unconditioned stimulus paired with a distinctive stimulus complex. Following several such pairings, the administration of a saline (test) solution to the animal in that environment produced, in both cases, a reduction in blood-glucose levels (hypoglycemia) as compared to control animals who received saline injections throughout. We suggest that, contrary to previous researchers' assumptions, direct changes in blood glucose levels immediately following the administration of either glucose or insulin should not be treated as the unconditioned response. The response of the CNS to the glucose or insulin, and not the immediate effect of increases or decreases in blood glucose levels, must be considered. Our reanalysis suggests, then, that in the case of glucose conditioning the conditioned response produces hypoglycemia which is in the same direction as that of the unconditioned response. In the case of insulin conditioning, the unconditioned response has not been well identified and consequently the conditioned response may be in the same or opposite direction to that of the UR.