PWS is characterized by hypotonia, feeding difficulties, developmental delay and failure to thrive during infancy, and by an insatiable appetite (hyperphagia), rapid weight gain and obesity in early childhood.~Hyperphagia is one of the most prominent and debilitating features of PWS, and currently no pharmaceutical drug has been successful in decreasing appetite in such patients.~tDCS is a safe, noninvasive method whereby a weak electric current is directly transmitted into the brain via external electrodes connected to a 9-volt radio battery. It is based on decades-old observations that nerve cell firing can be altered by low amplitude direct current (DC). The researchers in this study believe that tDCS may have a positive impact on hyperphagia and weight.~In this study, the investigators intend to assess whether the effects tDCS differ between obese subjects, non-obese subjects, and subjects with Prader-Willi syndrome by measuring the amplitude and latency of eyeblink startle responses to a set of food- and non-food-related visual stimuli in all subjects, various hyperphagia questionnaires, and cognitive and behavioral assessments. It is hypothesized that as a group, subjects with Prader-Willi syndrome will demonstrate behavioral and psychometric evidence of abnormal food image processing, craving and associated behaviors relative to our control groups, and this group may receive potentially beneficial effects from tDCS sessions. Obese subjects are also predicted to have decreased hyperphagia and food cravings as a result of tDCS.
The purpose of this study is to determine the effects of transcranial direct current stimulation (tDCS) as it modifies hyperphagia in obese subjects, non-obese subjects, and subjects with Prader-Willi syndrome (PWS).