(IMAGE) Paul Scherrer Institute Caption Researchers in the PSI Center for Life Sciences are working to enable medical intervention at the cellular level using light-activated switches: Oliver Tejero and last author Ching-Ju Tsai, Gebhard Schertler and Matthew Rodrigues (left to right). Credit Paul Scherrer Institute PSI/Mahir Dzambegovic Usage Restrictions PSI provides image and/or video material free of charge for media coverage of the content of the above text. Use of this material for other purposes is not permitted. This also includes the transfer of the image and video material into databases as well as sale by third parties. 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.