How we should map

We have the habit to say in university that the brain is organised with one area corresponding to one function. So the so-called localisationism, and especially one the most famous area is the area of Broca, corresponding according to the classical book of neurology to the area of speech, or Wernicke’s area corresponding to the area of understanding. And finally, my goal today is to try to give you some argumentations in favour of the fact that this is totally untrue, and that brain is in fact organised in parallel networks with interactions allowing as we will see also some degrees of neuroplasticity, or re-organisation, so a dynamic brain.

And this is very important for brain surgeon, like me, for instance, allowing me to remove a big part of the brain invaded by a tumour, for instance, without any complications, without any permanent deficit, without any permanent aphasia, despite the fact that we’ve removed a so-called Broca’s area. So the goal is definitely to switch from localisationism to connect and make view of brain processes.

I have the habit to do awake surgery for now 20 years, and definitely to adapt the task during surgery, and to the quality of life of each patient. So that means that I will not take into consideration so much of the location of the tumour by itself, but the preservation of the quality of life. And not only movement, language, but also cognition and emotion because everything is related if we started to consider the brain as interactive networking brain. So that means in practice that I take time to better understand what means quality of life of my patients before surgery, and not only to avoid aphasia and hemiplagia of course, but to adapt to tasks according to their job, hobbies, lifestyle.

For instance, if you have a mathematician, then I can add to the classical movement and language tasks, calculation tasks. If you are a lawyer, we can adapt some judgement tasks. If you are a dancer, we can adapt also with spatial cognition tasks in order to avoid the neglect. Of course this is not directly language, but everything is related. But also syntactic processing, if you are a writer, for instance in France, I performed surgery with a removal of the so-called Broca’s area, the famous writer, and he wrote three books following surgery. And he hasn’t a problem.

So my goal is to say it’s not a problem to remove Broca’s area, but it could be a problem to remove a part of the right non-dominant hemisphere for according also to this localizationist view, claiming that some area, you can remove them without any problem. And in fact, it depends on the level of quality of life that you would like to preserve. Typically, the right frontal lobe could be very important in a right-handed patient for mentalising, for theory of mind, for social cognition. And then a patient could have a perfect score regarding language and cognition following surgery, but in fact not able to return to work because modification of the behaviour.

This is the reason why, yes, I will awake the patient in the so-called right non-dominant hemisphere in order to map emotional processing.

Yes, but I should explain a little bit more, maybe neuroplasticity and the fact that it’s not really an issue to leave a small amount of tumour of course in order to preserve the quality of life of the patient because I will be able to come back a few years after and to remove more brain invaded by the tumour, because in between, some mechanisms of neuroplasticity will appear in the same patient over time. And I am able to identify that the mapping is not exactly the same. And that I can remove more, but also because, as you said, of course, much more invasion of the cortical areas.

In other words, the goal is to understand that when I do a stimulation, I disconnect a whole network. So it’s a desynchronisation between different cortical epicentres connected by white matter tract. So if I cut the white matter tract, it will be the limitation of brain plasticity, the connectomic view of brain plasticity. And it’s not my view. It’s the fact that if you have deep stroke, as you know, the patient will not recover, at least just a little bit improvement, but not a total recovery.

But in this network, because you have redundancies, if you remove just a cortical part, and if the connectivity continues to be powerful, efficient by connecting the other areas, and especially in the contralateral hemisphere, then the patient will be able to compensate. And it’s very impressive to see that you can induce this plasticity following a first surgery thanks to a burst of postoperative rehabilitation.

The limitation is definitely the subcortical connectivity. Why? Because the white matter tract have some anatomical constraint. I mean, it’s a fan. So if you are at the level of the cortex, you will have the possibility to see many redundancies connected by your fibres. More you are going to the depth, speaking about connectionism, association fibres, projection fibres, then you have anatomical constraint within the brain. If you cut a part of the brain at this level, finally, you can remove a big part of the cortex, as I said, previously, but finally, so few fibres. Now, for the same value, if you cut at the level of the deep connectivity, most of the time, you will cut different highways, crossing roads.

And suddenly, you will disconnect 2/3 of the hemisphere, or maybe also the connectivity between both hemispheres. And certainly what will happen, of course, the neuroplasticity will say, I reached my limitation. I can not recover.

I have the habit to turn to my patients, in fact I’m doing more or less nothing. I’m just a catalysor. But if you have so good results, it’s because my patients are heroes. And this is probably also a bias in my recruitment because I have patients very motivated with a lot of energy. So that means that more and more I use this energy, not only to help them, because finally they’re able more or less to do the job by themselves. I’m just here in order to guide them, and to guide, maybe also sometimes, the brain, thanks to the mapping, but also the postoperative rehabilitation as we say it. But that’s it. Finally, I’m just an observer.

But they are more because now thanks to them, we can be connected to these truths. And they know that they are participating in the full picture, not only for them, and medicine, and surgery, but also for global neuroscience. And this is the reason why I have the habit to say that when I have an award, it’s thanks to you.