Obsessive-compulsive disorder (OCD) has a long history of speculations concerning its cause. This article reviews human functional neuroimaging studies of OCD, then presents data from a study in the nonhuman primate that concerns the localization of brain systems that may mediate the expression of OCD symptoms. We use these lines of evidence to argue that increased "neural tone" through a section of the behaviorally disinhibiting "direct" basal ganglia pathway, relative to tone in the behaviorally inhibiting or moderating "indirect" basal ganglia system, may mediate the expression of OCD symptoms. The limbic orbital prefrontal cortex, the involvement of which is highly implicated in OCD, may have a greater influence on neural tone in the direct pathway than in the indirect, whereas more dorsal neocortical prefrontal regions may have the opposite effects on these two basal ganglia subsystems. Effective OCD treatments may obtain their results by preferentially decreasing neural tone through the direct relative to the indirect basal ganglia system.

We report a novel radio autocorrelation search for extraterrestrial intelligence. For selected frequencies across the terrestrial microwave window (1-10 GHz), observations were conducted at the Allen Telescope Array to identify artificial non-sinusoidal periodic signals with radio bandwidths greater than 4 Hz, which are capable of carrying substantial messages with symbol rates from 4 to 106 Hz. Out of 243 observations, about half (101) were directed toward sources with known continuum flux >∼1 Jy over the sampled bandwidth (quasars, pulsars, supernova remnants, and masers), based on the hypothesis that they might harbor heretofore undiscovered natural or artificial repetitive, phase or frequency modulation. The rest of the observations were directed mostly toward exoplanet stars with no previously discovered continuum flux. No signals attributable to extraterrestrial technology were found in this study. We conclude that the maximum probability that future observations like the ones described here will reveal repetitively modulated emissions is less than 5% for continuum sources and exoplanets alike. The paper concludes by describing a new approach to expanding this survey to many more targets and much greater sensitivity using archived data from interferometers all over the world.