Fig. 4.

Diagram of different ICSS session types. The open rectangle indicates the time line of an ICSS session, and vertical markers indicate division of the session into “trials” or “components” with varying stimulation parameters. Open/closed arrows indicate delivery of noncontingent/contingent stimulation, respectively. In free-operant sessions, stimulation parameters are constant throughout the session. Sessions can begin with noncontingent stimulation, followed by a period during which the subject can earn contingent stimulation under the prevailing schedule of reinforcement. In discrete-trial sessions, stimulation parameters can be adjusted during each trial within a session. Noncontingent stimulation is typically administered at the beginning of each trial, and subjects can then respond for one contingent stimulation during the trial. In hybrid sessions, stimulation parameters are adjusted across components that usually begin with noncontingent stimulation. Subjects can then earn multiple contingent stimulations by responding under the prevailing schedule of reinforcement.