Previous research has shown that repeated drug treatments can be regarded as conditioning processes. Sleep disorders are especially of interest to be investigated under the perspective of conditioning with drugs, since sleep quality can be defined both in terms of subjective ratings (self-rated sleep quality parameters) and objective measures (via polysomnographic assessment PSG; e.g., total sleep time, sleep onset, sleep architecture). By using two different drugs (zolpidem, amitriptyline) that modulate sleep differentially, the investigators intend to implement a conditioning paradigm in sleep disorders dissociating conditioning effects on subjective and objective sleep parameters. Both drugs should affect objective and subjective sleep parameters positively, while only amitriptyline should modulate the objectively assessed sleep architecture by REM-suppression (latency of REM-sleep onset, percentage of REM-sleep).Patients with mild to moderate insomnia will undergo a classical conditioning paradigm with one of two study medications: amitriptyline or zolpidem. After an acquisition period and a wash-out period, conditioned sleep changes are assessed in an evocation trial. During a second treatment phase of 7 days, patients receive different doses of amitriptyline (between 0mg and 50mg per night) or zolpidem (between 0mg and 5mg per night) to evaluate alternative dosing regimens in the pharmacotherapy of mild to moderate Insomnia.