Use of progressive fixed-ratio procedures in the assessment of intracranial reinforcement.

Six rats with electrodes chronically implanted in septal or hypothalamic sites were tested for intracranial reinforcement on a progressive fixed-ratio schedule. Two variations of this schedule were also examined and compared. Functions relating the highest level of stable fixed-ratio responding to a wide range of stimulus currents were, unlike those derived from continuous reinforcement rates, monotonic at all stimulation sites tested. One of the procedures described, in particular, is quite sensitive to intracranial reinforcement parameters, provides a reliable technique for within-session assays of these parameters, and successfully avoids many problems commonly encountered with administration of central stimulation on a continuous reinforcement schedule.