Differential effects of parafascicular electrical stimulation on active avoidance depending on the retention time, in rats

To evaluate whether electrical stimulation of the parafascicular nucleus of the thalamus can improve short-term (24 h) and/or long-term (11 days) retention of two-way active avoidance, rats were implanted with an electrode at this nucleus (experimental groups with stimulation in the parafascicular, and control groups without stimulation) or above it (other control groups without stimulation). After a single 30-trial acquisition session, experimental groups were submitted to a 20-min session of electrical stimulation. Results showed that parafascicular stimulation improved the 24-h retention of the task (number of avoidances made), increasing also the percentage of subjects that achieved a learning criterion and reducing the number of trials needed to reach it. In contrast, no differences among groups were found on the 11-day retention test. The present results agree with previous data showing a short-term effect of parafascicular stimulation on retention, and confirm its involvement in learning and memory modulation. These data are discussed in the context of the acceleration and strengthening of the memory by activation of arousal systems, and/or specific cortical-striatal systems. Copyright (C) 2000 Elsevier Science Inc.