Temporal characteristics of electrical self-stimulation reward: fatigue rather than adaptation

Using a Y-maze preference test paradigm, we examined the temporal characteristics of the neural network subserving self-stimulation reward. Rats were given a choice between two pulse trains of stimulation, which varied in duration and pulse frequency. The results showed that increasing the pulse frequency decreases the duration at which the rewarding effectiveness of brain stimulation reaches an asymptote. The data also indicated that when prolonged stimulation is delivered at a high pulse frequency, the initial pulses contribute the most to the rewarding effect. Later pulses are affected by the reduced ability of the neurons or synapses to transmit signals along the neural network due to fatigue. The data are explained in terms of an improved model of summation involving more than one integrator and fatigue.