TMS in the management of aphasia. TMS is a safe and painless method to stimulate the human brain. TMS uses strong, brief magnetic impulses produced by a probe held over the head. These impulses carry a small electric current through the scalp that activates the brain underneath. When a single pulse is given the effect lasts for a few seconds. We can also give TMS in a repeated manner, called repetitive TMS (rTMS). rTMS can change the activation of the brain for much longer, sometimes for up to one hour. Different stimulation patterns can produce different results. For example, we can either increase or suppress the activation of the brain.
Speech is controlled by a number of areas which for the right handed people are located on the left side of the brain. TMS can access these areas. For example, when TMS is given over a particular "speech area", it can cause stuttering or even a brief speech arrest. Some investigators showed that when rTMS is given over another area, it can shorten the time we need to find a word.
A stroke can damage some or all of the "speech areas", resulting in problems with understanding or/and producing speech. These speech problems are generally referred to as aphasia. Aphasia improves with time in various degrees. We now believe that this improvement occurs because the surviving areas of brain around the damage become more active in order to try to make up for the loss. In that sense, if we increased the activation of these areas even more, we might achieve better recovery. rTMS given with an excitatory pattern could be one way to do that. However, this is just a theory that has not been tested so far.
However, a different approach has already been tested. There are scientific data suggesting that sometimes the "healthy side" is overactive after a stroke and this limits recovery of the stroke side. On these grounds, one might argue that rather than activating the stroke side one should try to suppress the "healthy" side. A research group in the United States used rTMS with an inhibitory pattern to do this in a small number of aphasic stroke patients. They found that after two weeks of daily stimulation the participants improved their ability to name pictures. It should be noted that these results are preliminary and need replication in larger numbers of participants. However, they suggest that rTMS may represent a novel method to improve current speech therapy strategies after stroke.
Dr Penelope Talelli
Institute of Neurology
Sobel Department of Motor Neuroscience
Tel 0207 8373611 ext 4468
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