Electrophysiology is a major tool in understanding how information is processed in the brain. This method allows us to dissect some of the complexity of the signals propagated from subcortical limbic structures to the hippocampal formation, to understand the importance of information processing that mediates memory formation and cognition. Electrophysiology testing is a functional, not anatomic, evaluation of the nerve. Ultrasound becomes a complementary examination because of its capacity to show the PN's internal structure and the surrounding anatomic structures. Ultrasound assessment of PN pathology correlates well with electrophysiology results, and when used together with electrophysiology, the sensitivity for diagnosing PN entrapment syndrome is better than electrophysiology alone.