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A new and seemingly-promising treatment for depression and other neurological maladies has been the topic of much speculation and debate though seldom discussed outside of academic circles.
Long-accepted medical wisdom says that neurons are irreplaceable, and that, after childhood, the fundamental structure of the brain becomes immutable. This means that once nerves are destroyed, they cannot regenerate. Lost limbs and other appendages can sometimes be reattached successfully by surgery, but nerves cannot. This certainty may be considered premature, however, as the latest research in the science of neuroregeneration seems to suggest that reversing neural damage may soon become a possibility.
According to the Journal of Biomedical Materials Research, every year an average of 90,000 people are adversely affected by nervous system injuries, spinal cord injuries alone accounting for nearly 10,000. The critical factor for restoring function, learning, and memory to damaged neurons is neuroplasticity.
Neuroplasticity, or brain plasticity, is an “umbrella term that encompasses both synaptic plasticity and non-synaptic plasticity—it refers to changes in neural pathways and synapses due to changes in behavior, environment, neural processes, thinking, emotions, as well as changes resulting from bodily injury.”
Michael C Ridding of the University of Adelaide defines neuroplasticity as the “reorganization of brain connectivity through experience”.
Neuroplasticity is the critical factor that determines how well the learning, memory, motor performance, and other nervous system functions can recover following brain injury or neural damage. Without neuroplasticity, the lost functions and the nerves that provide them cannot regenerate. What is lost can not be regained. The widespread belief is that this plasticity departs with childhood; many similar beliefs about the irreversible changes associated with the physiology of aging have been challenged in recent years as well.
There is ample evidence to support these findings. Pennsylvania State University researchers have recently discovered that dendrites, the nerve cell components that transmit information between separate nerve cells, have the capacity to regrow following injury .
Discoveries regarding the benefits of using weak electric currents to stimulate increases in neural function are not a recent phenomenon. Studies confirming neuronal responses in rats were done as early as the 1960s, which seemed to suggest that minute applications of electrical current in these animals precede alterations in neuronal activity lasting up to several hours.
Researchers at the University Medical Center, Hamburg, Germany (F. C. Hummel) discovered in recent studies with animals that direct epidural stimulation of the motor cortex elicits improvements in motor function.
Another form of non-invasive magnetic stimulation, called Transcranial Magnetic Stimulation (TMS) has been the subject of numerous recent studies measuring its effectiveness in treating depression. TMS affects the level of neuroplasticity in the brain. It was found that the application of high-frequency current applied to fully-conscious rats led to increased neuroplasticity, while applying current to anesthetized animals reduced their neuroplasticity.
After years of numerous studies, the consensus among researchers is that TMS may restore neuroplasticity that was lost as a result of long-term depression or brain injury. Depression has been shown to result in, as well as be the result of, changes in synaptic efficacy. Neurotransmitters – the chemicals which carry information between nerve receptors – have been shown to be critical in causing depression. TMS, it has been suggested, works on the bioelectrical circuitry underlying the biochemical processes between neurons in the brain.
In 2013 the FDA approved the Neurostar TMS System, a device that administers non-invasive magnetic stimulation. This device was specifically designed to treat major depressive disorder.
It’s too soon, however, to draw any definite conclusions about this new form of treatment and its possible long-term benefits, although thus far, transcranial magnetic stimulation and direct electrical stimulation have led to improvements of 10% to 30% in the motor-performance skills of test subjects.
It appears that the time interval between sessions is a key factor, but the ideal interval and ideal current strength have yet to be determined. According to FDA studies, the device is safe and effective (though under what circumstances they do not specifically mention).
On the flip side, a new study at Oxford University, published in the Journal of Neuroscience, states that brain stimulation has different effects on different people. In one study, researchers had test subjects solve math problems, while a control group received no current whatsoever. The study revealed that the subjects who received brain stimulation performed their task better, and subjects suffering from anxiety during the tests were better able to control their anxiety. In a separate study, however, when an arrow was placed alongside a body of text and students were asked where the arrow was pointing, those undergoing brain stimulation performed poorly, and the stimulus was deemed a possible distraction. (A control group receiving no stimulation performed better.)
What to make of this? Nick Davis of Swansea University suggests that this technology is still in the early stages of development, and is not yet meant to be mass marketed because it doesn’t take into account individual variations in responses. How a person responds to brain stimulation is important in making the determination regarding effectiveness. . On the other hand, as the FDA suggests, its potential drawbacks are minor, and if used wisely and in moderation at consistently-spaced intervals, the gains may exceed the risks.
At this moment in time, through non-invasive brain stimulation, we are on the cusp of major advances in the treatment of mood disorders and impairment arising from brain damage caused by ischemic infarct and head trauma. As with any ground-breaking treatment in the early stages, the exact mechanism behind it is not yet fully understood.
What conclusion can we draw from all of this? While manufacturers and health experts alike support the mass marketing of such a promising device, it is best not to use them too readily without first seeking out the contraindications and considering the possible deleterious effects. While those who stand to benefit most from this new technology are sure to find its potential tempting, they should proceed cautiously. We would do well to remember that some vaccines touted as miracle cures for disease were later found to have seriously detrimental effects on long-term health.
On a positive note, brain stimulation is – as the name suggests – non-invasive. Chemical alterations in the brain are not induced by the injection of synthetic fluids, chemicals, or other forms of invasive treatment. Electrical currents, on the other hand, are the basis of neuronal activity, and the idea of altering its workings in the brain, though new, is one that shows great promise for future therapies, whatever forms they may take.
 Alvaro Pascual-Leone and Timothy Wagner Center for Noninvasive Brain Stimulation, Harvard Medical School, Department of Neurology, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA
Kevin Naruse is the Science & Technology correspondent for Painted Brain News