Salivette cortisol swabs

Saliva samples for cortisol analysis were collected using Salivette® Cortisol swabs (Sarstedt AG & Co, Nümbrecht, Germany) and analyzed with a Cortisol Saliva Luminescence Immunoassay (IBL International, Hamburg, Germany) according to the manufacturers´ instructions. Saliva samples were obtained the day after the VEP experiment at three times: immediately after awakening in the morning, 30 min after the first collection, and at 12:30 PM. Participants were instructed to not brush teeth and to refrain from physical activity, nicotine, and caffeine before saliva collection and to not eat or drink the last 30 min before the samples were obtained. Saliva cortisol was averaged across the three collections. We also computed the cortisol awakening response (saliva cortisol 30 min post awakening minus cortisol at awakening), as a previous study found that the cortisol awakening response was associated with transcranial magnetic stimulation (TMS)-induced motor cortex plasticity^{44 (link)}. Complete cortisol data were missing for one control and two individuals with BD type II.

Each participant sampled saliva at home using Salivette^® Cortisol swabs (Sarstedt, Nümbrecht, Germany) once a day for three days in a row, right after waking up in the morning and before taking breakfast or brushing the teeth. They were asked to hold the swab in their mouth for three minutes, return it to its tube, and store in a refrigerator at 4–8 °C. After the third sampling, the participants delivered three tubes to the Institute for Medical Research and Occupational Health, Zagreb, Croatia. The tubes were immediately centrifuged at 425 g for 10 min and stored at −18 °C until analysis (for 3–73 days).