Magnetoencephalography

If you visit this site often enough you will hear of mild traumatic brain injuries (mTBI). The "mild" part is a cruel misnomer that has very little to do with long term prognosis or the functional severity of the injuries to brain networks. A mild traumatic brain injury can be a long-term and quite debilitating issue for the affected individual who will often complain of continued headaches, dizziness, emotional problems, extreme anxiety, and difficulty with emotional regulation and interactions with other persons. While some head injuries do get better, many do not and continue to cause suffering indefinitely. Sadly, many of these injured humans continue to fail in life without really linking the blow to the head to their decline in functioning and mental deterioration. ER's miss the diagnosis with a staggering frequency.

The widely quoted dogma proclaims that the percentage of individuals who have permanent difficulties is approximately 15 %.  The basis for this conclusion is usually the absence of abnormalities on neuropsychological tests or imaging studies. Or a history of mental problems. More recent investigations have demonstrated that the headaches and other symptoms may continue in approximately 40% of those injured. Some investigators, wonder if any of these injured individuals ever achieve a complete recovery! 

Enter magnetoencephalography (MEG). Don't get too excited about it and make an appointment for your test right now. There are approximately 20 of these machines functioning in the United States. The technology is advancing and the price appears to be falling. Good news for us in private practice. Magnetoencephalography is a method of recording the electrical activity of the various deep lying of the brain through the surrounding skull, blood vessels and scalp. Just like a conventional MRI scan which can "see" through the bony vault and is not affected by the tissues surrounding the brain. This is quite similar to conventional electroencephalography (EEG) which uses scalp electrodes to record direct current fluctuations. But much more powerful. And note, this is not a static picture of the brain. This is here and now, simultaneous brain drama!

The various parts and networks of the brain communicate via brain cell oscillations at various frequencies. For example, the alpha frequency indicates that the brain is awake but basically resting. Delta waves, which are quite slow, often are seen in sleep. The fastest waves are in the gamma frequency range of 30-80 Hz (reps per second). A physicist at the VA San Diego health care system, Mingxiong Huang has attempted to characterize these waves in individuals with mild traumatic brain injury. Contrary to what is seen in normal individuals, brain-injured patients have dramatically increased activity in the gamma range in the prefrontal and posterior parietal cortex.

Dr. Huang, who has a joint appointment in the Department of Radiology, believes this uninvited gamma activity may reflect poorly functioning networks deep in the brain which could never declare themselves with more conventional studies such as MRI, angiograms, EEG, functional MRI or radionucleotide examinations. 

Not only did Dr. Huang find the gamma abnormalities, but he also found a marked decrease is in the spontaneous activity in the ventral medial prefrontal cortex which is a primary player in the mood and anxiety business. This area is strongly connected to the amygdala which is largely responsible for fear and depression.

These findings do not just represent laboratory curiosities. The researchers are identifying areas that will be accessible to neural modulation such as transcranial magnetic stimulation or transcranial direct current stimulation. Dr. Huang plans further investigations to confirm his findings and possibly to identify other areas for study and to guide relevant treatment modalities. Transcranial magnetic stimulation is likely to play a major role here!

Author
Dr. David Sudderth

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