The phrase "this isn't brain surgery'' is used for good reason. Neurosugery is definitely in my top 10 list of real hard things to do. Your brain is an extremely delicate mass off specialised tissue sealed in a tough, durable casing, and many functioning regions are deeply buried that are often impossible to reach without burrowing through other active regions. Even so, it has become apparent that affecting these deep regions, or nuclei, can be hugely beneficial when treating motor diseases like Parkinson's.
Frank M. Skidmore directs the Movement Disorders Center at the VA Medical Center, Florida. A neurologist by trade, he works as a clinician diagnosing neurological disease and referring patients to teams of surgeons. Many of his patients require deep brain stimulaters (DBS), electrodes inserted into the brain that deliver electrical impulses, rather like a pacemaker. They act to interrupt misfiring nuclei with the hope of alleviating symptoms, such as loss of motor control. Unfortunately, these nuclei are small and difficult to pin point making accurate imaging of the brain, particularly while a patient is on the operating table, highly desirable.
What makes locating nuclei so difficult? Everyone's brain is different to a degree so no universal structural map exists. Even if a perfect structural map did exist, certain nuclei are independent of structure and so must be found by determining a functional map. As a result, the boundaries between brain regions are extremely blurred. But it gets worse. Opening the brain case causes pressure changes, fluids start to drain and air rushes in, so the sponge like mass of the brains begins to droop, and it does so continuously throughout an operation. Your small target is constantly moving. Even sneezing can course your brain to shift!
The situation can be alleviated some what by using a combination of MRI scans prior to an operation and a stereotactic frame, a scaffold that bolts to the skull and provides a 3D co-ordinate system for navigation. But inaccuracies in placing a frame bring additional problems and MRI scans can only provide a rough guide, as when the patient is moved to an upright position the brain will again shift in addition to the changes that occur during surgery.
Surgeons do have one extra trick up their sleeves. Pulses of electrical activity can be recorded using an electrode and played back as sound during live surgery. As it happens, different parts of the brain produce distinct sounds, including the target nuclei, which in the case of Parkinson's sounds like rain on a tin roof. This can indicate to the surgeon, with reasonable reliability, as to when he has hit the correct spot. The problem is that the electrode will have to be re-inserted until it is been placed correctly. With each re-insertion damage is caused in the form of scaring that can have major consequences to a patients mental abilities. One patient, who suffered from hand spasms, lost his ability to form coherent sentences due to scaring of the speech centre of the brain, but surprisingly he didn't mind as he could once again indulge himself in his hobby of model ship building.
The ultimate goal would be to do away with this trail and error approach and succeed with a quick, single pass insertion. Pioneering surgeons are utilising mobile MRI scanners to provide live inter-operative imaging of the brain, but this poses many new problems. The machinery is sizable and complex. Special surgical equipment is required that wont be effected by the strong magnetic fields radiated by the scanner. Alternatively, a mobile CT (computerised tomography) scanner can be used but software for tracking brain deformations during surgery does not yet exist. Even so, a CT scan can only reveal structure and not function.
If the problem of imaging could be solved it would need to be combined with robotic surgical hands that a computer could guide in precise co-ordination with live images. Advances in robotic surgery are promising, but the lack of the technology needed to map brain function and structure during surgery limits its use to body parts less complex. Without detracting from the amazing feats that brain surgeons achieve today, there is still a long way to go if we are to be masters of our own minds.