The present invention provides methods and systems for improving clinical trials of experimental therapies. The present invention uses minimally invasive, leadless implantable devices that facilitate long term monitoring of a physiological signal (e.g., neural signals) from a patient population which may provide an indication of the effect of the experimental therapy on the patient population. In preferred embodiments, neural signals are sampled from the patients in the patient population with an externally powered, leadless implanted device and are transmitted to an external device for further processing.