Posted by twinleaf on December 9, 2009, at 9:21:47
In reply to rTMS, posted by morganator on December 7, 2009, at 16:14:55
I think I can add a bit about how it works. The treatments are given to the left frontal area, and, as Scott says, although the electromagnetic current does pass through the skull, it doesn't go very far into the brain- about one to two cm. only. So. it initially affects the left prefrontal area only. It does"perk up" neurons there. This can be important, as blood-flow studies in depression usually show underactivity of the whole left prefrontal cortex. As this is the more hopeful, problem-solving area of the brain, activating it, so that it becomes more equal to the right pre-frontal cortex, which tends to contain our pre-conscious and unconscious memories of past social stressors- abuse, neglect, failures and losses- can result in a much less depressed or hopeless state of mind.
And it does more. Connections between the prefrontal areas and the limbic system are very numerous, so messages get sent from the neurons in the prefrontal areas to those in the hippocampus and nearby structures. In major depression, work done at the German Primate Center and elsewhere has shown that severe social stressors result in an overactive HPA axis, with excessive production of cortisol and glutamate in the brain. This stops the formation of new cells in the hippocampus (and elsewhere). We are supposed to produce several thousand new neurons in the hippocampus every day throughout life, When this stops happening because of the toxic effects of high levels of stress hormones, the hippocampus becomes smaller than normal, and individual cells appear shrunken and damaged. rTMS has the effect, indirectly, of lowering the levels of stress hormones, causing the individual neurons to regain a more healthy appearance, and allowing neurogenesis to begin again.
The depression model used in studying this is the social-stressor model, which would be comparable to the type of depression in humans caused by childhood abuse, neglect, loss, etc. However in bipolar depression, which at times appears to be less closely related to social stressors, and more closely related to hereditary factors, it has also been used successfully.
ECT has essentially the same beneficial effects as TMS does, but it is an "overkill", with quite a high risk of impairments in memory and cognition. TMS does not carry these risks. I think it is always worth trying it first. If it doesn't work, there is the possibility of considering ECT next.
poster:twinleaf
thread:928451
URL: http://www.dr-bob.org/babble/20091206/msgs/928613.html