Research ReportTolerance to repeated rewarding electrical stimulation of the insular cortex

- Stimulation of the insular cortex induces naloxone-related behavioral preferences.
- We used two groups of animals (and controls) with daily or alternate-day stimulation.
- Daily but not alternate-day stimulation induced a reduction in the place preference.
- This tolerance effect was reversed by increasing the stimulation current.

The insular cortex (IC) has been related to various reinforcing behavioral processes. This study examined the effect of electrical stimulation of the posterior agranular IC on concurrent place preferences. Two groups of animals and their respective controls underwent rewarding brain stimulation every day or on alternate days. While the rats stimulated every other day maintained their preference for the place associated with brain stimulation, those stimulated every day evidenced a reduction in their place preference, suggesting tolerance to the stimulation׳s rewarding effect. A 15% increase in the current intensity produced a recovery of the preferences of the daily-stimulated rats but had no effect on those stimulated on alternate days. These results are discussed in terms of the rewarding effects induced by different electrical and chemical rewarding agents.