19 Nov 2020

Maintaining Balance

Maintaining balance is important, but the research on how our brain does that has become a neglected field. ESI’s Jean Laurens explains why it still makes sense to pay attention to a sensory system that we would miss the most once we’ve lost it.

Searching the term ‘vestibular system’ on PubMed, a database for scientific literature, returns about ten thousand hits. Searching for the term ‘visual system’ returns a tenfold of hits. Is the visual system ten times more interesting than the vestibular system?

Jean Laurens: As somebody who is doing research on the vestibular system, I would obviously answer no, but that doesn’t change the fact that the visual system receives a lot more attention. There are many reasons for this, but one of them surely is that we humans are very visual animals. Seeing is something we do very consciously. It dominates our experience. But plenty of people will not even know that there is a balance organ in the inner ear or maybe they will know, but never think about it. In fact, we generally only notice it when it doesn’t work as it should.

Does that mean we simply don’t research our sense of balance because we are less aware of it being important?

Jean Laurens: No. In the 1960s and 70s, with the first manned space flights and the so-called Space Race, the vestibular system was quite popular. In many respects it was a pioneering field for understanding sensory-motor control and since then we know a lot about its anatomy, physiology and neural dynamics. Some of the mathematical models developed in the field are just beautiful, and incredibly accurate at predicting motion sensation or neuronal responses. But since the late 1990’s there has been comparatively less novelty so the vestibular system has become a rather neglected sensory system in current neuroscientific research.

If you put it like this, it sounds a bit like everything relevant is known already. What are you researching when there’s no questions left?

Jean Laurens: In fact, there has been some fundamental innovation in the field in the last decades, but few people have appreciated them. In the past, most vestibular research has used laboratory settings where a subject is put in a rotating chair. We know more or less everything about how neurons in the brain react to rotating chairs, including during all sorts of weird motions! But unless we are on a fun fair this is not a probable scenario in real life. So people started to look at vestibular neurons in a more natural setting: when animals moved themselves instead of being moved. And they found that neurons didn’t react. Why? Because the vestibular system is a feedback system: when we move voluntarily, the brain literally knows what to expect. The vestibular system only monitors that everything goes as expected. Its importance really shows up on difficult terrains, like walking on mud and wet leaves, or when we slip, and the motor activity needs to be corrected. I think that it took a while for the vestibular research field to assimilate these new results. Yet, this concept of vestibular feedback is now understood and has made its way into mathematical models. And that is what I am focusing on because I think that this is opening a new avenue for neurophysiological research.

So rather than sticking to old paradigms, you are looking at the vestibular system in a more natural setting of self-motion of the body?

Jean Laurens: Yes, I am working at the intersection between two research fields. On the one hand I investigate spatial navigation, and on the other hand the vestibular system: in a nutshell all my research centers around the question how we are able to move from one place to another. Let’s say I go from my office down into the garden in the backyard. This sounds very simple, because it is easy for us to do, but in fact it is incredibly complicated for the brain. It requires the ability for spatial navigation and therefore the ability to perceive your own motion in space, and it requires postural control so you are not falling when you are walking down the stairs or stepping from the concrete onto the much softer grass. All this hard work is the job of the vestibular system. It is a great mixture also with respect to how different the fields are: The navigation field is young, it’s dynamic, there are new things happening every six months, because it is easy to discover something new when a field is young. Research in the vestibular system is moving slower and has become very sophisticated: In particular, there really has to be a lot of mathematics to conceptualize the experiments. But really, I love it!

In fact you are passionate enough about it, that you recently started a twitter series in which you explain basic concepts of the vestibular system. Now if we talked about the visual system there would be tons of these things out there. How is that for the vestibular system?

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Jean Laurens: There is some information about what happens if you move your head or get dizzy. But that’s where it stops. And I think that is part of the problem why people don’t see the value of this research anymore. Frankly, the vestibular community didn’t do a good job in explaining their findings outside the immediate field. On Twitter I am really trying to give an overview of the fundamental principles of self-motion sensation, and the most recent work I can recall to do something like this is from 1974. And if you look into the current neuroscience text-books, the vestibular system is just barely touched upon. It is sad that I have to say: ‘Hey, guys, the vestibular system is great. Go and read the review from seventy-four.’

Is there something neuroscientists in general could learn from the vestibular system?

Jean Laurens: Our sense of balance plays into many other sensory systems. For example there is a pretty well understood link between the visual system and the vestibular system that helps to stabilize gaze while moving about. But vestibular research could also be particularly inspiring for people who work on motor-control, because they involve similar questions of sensing and controlling the three-dimensional dynamics of body parts. For example: I want to lift a box and don’t know whether it’s full or empty, heavy or not. This is a motor-control problem that requires flexible adjustments like muscle tension, flexion and tension of different joints. The vestibular system is very similar to that but is more simple and tractable, with less variables to factor in. Best thing: we know the central neuronal pathways of the vestibular system, and we have the models describing them. So the vestibular system is a great model to understand motor-control in a wider context. I think it is a loss to the scientific community that there is so little awareness of it. We are overlooking knowledge that could help us to move research forward. I hope to be able to improve this.