A method and system to determine brain stiffness is disclosed. Upon comparison of the previously established process state, including the associated history information to the process state established after occurrence of the reset event on the basis of the newly gathered history information, it is decided whether or not a reset of the process controller has been necessary. A cooling medium is in fluid communication with the plenum. In a second embodiment, the peak energy in relation to a noise estimate for the localized portion of the correlation function is compared to a jammer threshold. This is further done in a simple, secure, and reliable way.