The chairman at OHSU is primarily a functional neurosurgeon. He did the first DBS in the U.S. and likely does more DBS than any other neurosurgeon in the country (two or three each week). He does many microvascular decompressions, epilepsy cases, vagal nerve stimulators, spinal cord stimulators, gangliolysis, rhizotomy, etc. But even he does not do only functional neurosurgery. He does a significant amount of spine and tumor and still takes trauma call. As chairman of a big academic department certainly works long hours.
It would be difficult to have a neurosurgery practice consisting only of functional work as it takes a long time to become proficient at these procedures. As they are not that common you would likely not learn enough in residency to do this alone and would likely require fellowship and then a while doing general neurosurgery before becoming proficient to do this and nothing else. On top of that, solo neurosurgery practices are fairly rare, and in a group you would be expected to cover call and trauma which means long hours and being available for emergencies. Even pure functional cases are risky procedures in which post op patients can have emergencies day or night that need to be dealt with.
No matter what you do in the field of neurosurgery there will always be times where you will be needed in the middle of the night and on weekends and holidays. It is not a 9 to 5 office-type practice even in functional neurosurgery. Any specialty can be a "lifestyle" specialty if you love what you do. Everybody is frustrated by missing special occasions or wishing you could sleep a bit more. But there is nothing more satisfying than spending 12 or 14 hours a day doing what you enjoy AND making a difference in people's lives.