Short- and long-term summation characteristics of electrical self-stimulation reward

Using a Y-maze preference test paradigm, we examined the characteristics of the neural networks that integrate trains of rewarding stimulation pulses. Rats compared the rewarding effectiveness of various durations of a test reinforcement to those of 3 durations of a standard reinforcement. By changing the duration of the standard reinforcement while keeping the pulse frequency constant, we varied the stimulation magnitude to which the test reinforcement was being compared. This enabled us to examine the relationships between stimulation parameters both within a constant stimulation magnitude and across different stimulation magnitudes. The data were inconsistent with a simple integrating system with a single decay time constant such as is usually assumed. They can most parsimoniously be accounted for by two systems having quite widely differing time constants. The time constant of the first integrator is ca. 450 ms, whereas that of a second integrator is ca. 6.5 s.