Alteration of delay and trace eyeblink conditioning in fibromyalgia patients

Classical conditioning processes are important for the generation and persistence of symptoms in psychosomatic disorders, such as the fibromyalgia syndrome (FMS). Pharmacologically induced hyper- and hypocortisolism were shown to affect trace but not delay classical eyeblink conditioning. As previous studies revealed a relative hypocortisolism in FMS patients, we hypothesized that FMS patients also show altered eyeblink conditioning.

FMS patients (n = 30) and healthy control subjects (n = 20) matched for gender and age were randomly assigned to a delay or trace eyeblink conditioning protocol, where conditioned eyeblink response probability was assessed by electromyogram. Morning cortisol levels, ratings of depression, anxiety as well as psychosomatic complaints, general symptomatology, and psychological distress were assessed.

As compared with healthy controls, FMS patients showed lower morning cortisol levels, corroborating previously described disturbances in neuroendocrine regulation of the hypothalamus-pituitary-adrenal axis in these patients. Trace eyeblink conditioning was facilitated in FMS patients, whereas delay eyeblink conditioning was reduced, and cortisol measures correlated significantly only with trace eyeblink conditioning.

We conclude that FMS patients characterized by decreased cortisol levels differ in classical trace eyeblink conditioning from healthy controls, suggesting that endocrine mechanisms affecting hippocampus-mediated forms of associative learning may play a role in the generation of symptoms in these patients.