Anterior thalamus deep brain stimulation at high current impairs memory in rats

Deep brain stimulation (DBS) of the anterior thalamic nucleus (AN), an important relay in the circuitry of memory, is currently being proposed as a treatment for epilepsy. Despite the encouraging results with the use of this therapy, potential benefits and adverse effects are yet to be determined. We show that AN stimulation at relatively high current disrupted the acquisition of contextual fear conditioning and impaired performance on a spatial alternating task in rats. This has not been observed at parameters generating a charge density that approximated the one used in clinical practice. At settings that impaired behavior, AN stimulation induced a functional depolarization block nearby the electrode, increased c-Fos expression in cerebral regions projecting to and receiving projections from the AN, and influenced hippocampal activity. This suggests that complex mechanisms might be involved in the effects of AN DBS, including a local target inactivation and the modulation of structures at a distance. Though translating data from animals to humans has to be considered with caution, our study underscores the need for carefully monitoring memory function while selecting stimulation parameters during the clinical evaluation of AN DBS.