What nTMS can do

So far, we have signified a tool and how the underlying mechanisms works, in, for instance, motor mapping. In pre-surgical language mapping, this mechanism is useful as well. The idea is that we would like to find the language areas before surgery in order to shorten the period that the patient is awake during surgery. Notice that for parts of the surgery, the patient has to be awake, because sub cortical areas cannot be reached by navigated TMS. Our aim is to find areas crucial for word selection, grammar, and meaning for both nouns and verbs. Our verb task tests the ability to retrieve a verb and to inflect it.

In this way, we can test meaning, word retrieval, and grammar, although at a very basic level. So far, it’s the best thing we can do in four seconds. The task is very similar to the one we use intraoperatively with direct electrical stimulation. The patient has to complete the sentence. The man– with walks. Of course, we should be very much aware that regions for verb retrieval and for inflection can be impaired, but those for nouns may be spared. So a combination of a verb and a noun test is necessary. In English, object naming in sentence context is a simple task. But in German or French, it’s more complex, because it requires accurate choice of the articles.

Using these tests enables us to locate areas important for noun and verb production. Let’s have a look at how this is done in detail. We want to be certain that objects are known to the patient. So we ask him to name the pictures preoperatively. [GERMAN:] That is a fist.

Then, in the second phase, we use those pictures that the patient was able to name and have him name them again. Now the areas that may be involved will be stimulated with TMS while the patient names the picture.

[GERMAN:] That is a haan [SIC] If errors occur, this particular area is important for that particular task. It is a so-called positive language area. This area should not be dissected. We have an example here. In the pre-name test, our patient names the picture correctly. Then, with simulation on certain areas where we can very precisely target a certain spot, the following error occurs.

We can mark this area as language positive. After checking all relevant spots with navigated TMS, we end it with a language map. And this map can be used in the OR. If we compare language maps of patients to those of non brain damaged individuals, we might see big differences. This is due to the spreading tumour that caused language functions to shift. We can also conclude from this that data of healthy participants are insufficient to localise language areas. But that we need to perform an individually tailored mapping per patient. We need to stress again that only part of the language mapping can be done with navigated TMS.

So far, it does not replace intraoperative language mapping, because it is still an experimental, yet very promising method. Improving navigated TMS mapping is part of a project done by the Idea Lab consortium, in which University of Groningen, the University Medical Centre Groningen, eemagine, and ANT Neuro cooperate. Currently, we are working on a project in which we compare direct cortical stimulation to navigated TMS, and evaluate if the two methods identify the same areas for nouns and verbs. If that’s achieved, the overall goal is reached. Navigated TMS can be used to identify cortical language areas preoperatively. This would make surgery less stressful, not only for the patient, but also for the neurosurgeon, the neuroanaesthesiologist, the neurophysiologist, the clinical linguist.

Basically, everybody involved in the procedure.