An invasive diagnostic test wherein a pressure sensitive probe is inserted through the skull in order to directly measure the intracranial pressure (high or low) and detect any intermittent abnormalities therein.  This probe sends data to a recording device and that data is analyzed by diagnosticians and physicians to correlate a patient’s symptoms with these readings.  ICP monitoring bolts provides a longer recording of intracranial pressures than that which can be achieved by a lumbar puncture (spinal tap), which only provides a measure of intracranial pressure at the time of the procedure.