Classical conditioning of insulin effects in healthy humans

Objective: Classical conditioning of insulin effects was examined in health y humans using a placebo-controlled design. This study examined whether sub jects who experienced a conditioned stimulus (CS) paired with insulin in th e acquisition phase of a conditioning protocol would show a conditioned dec rease of blood glucose when receiving the CS with a placebo injection in th e test phase. Methods: Twenty healthy male students were assigned either to group 1, which received insulin (0.035 IU/kg IV), or to group 2, which rec eived IV saline on 4 consecutive days (acquisition). On day 5 (test), both groups were injected with saline. The CS was an olfactory stimulus. Blood g lucose, serum insulin, plasma glucagon, plasma catecholamines, serum cortis ol, and symptoms were repeatedly measured during each session. Results: In the test phase, group 1 reacted with a significantly larger decrease of blo od glucose after presentation of the CS than group 2. Within group 1, a lar ger conditioned blood glucose decrease was associated with features that en hance classical conditioning (ie, intensity of the unconditioned response a nd intensity of the CS). Furthermore, in group 1, there was an increase of baseline insulin from day 1 to day 5 and a tendency for insulin reduction a fter CS presentation. Groups also tended to differ in cortisol and neurogly copenic symptoms after CS presentation. Conclusions: Conditioned effects in blood glucose are in accordance with the predictions. As a result of the e xploratory analyses, our data also provide hints about conditioned changes in insulin, counterregulatory hormones, and symptoms.