A circuit model (IMAGE) Picower Institute at MIT Caption Schematic representing a model of how a key loop becomes overwhelmed by beta wave activity in Parkinson's disease. Fast spiking interneurons (FSI) fail to inhibit medium spiny neurons (MSN). When DBS is applied between the STN and the FSIs that breaks the cycle. Credit Image by Elie Adam. Usage Restrictions with credit License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.