That Neuroscience Guy - The Neuroscience of Hitting a Tennis Ball

Episode Date: December 11, 2022

Previously on the podcast, we talked about the neuroscience of grabbing an apple. While this is great for explaining movement when you're at home or in the office, what happens when the environment is a bit more intense? As it turns out, in high-paced sports your brain is working overtime to get your body moving. in today's episode of That Neuroscience Guy, we discuss the neuroscience behind complex motor control, like when we are hitting a tennis ball. 

Hi, my name is Olof Krig Olsson, and I'm a neuroscientist at the University of Victoria. And in my spare time, I'm that neuroscience guy. Welcome to the podcast. Are you into sports? Like, do you like to hit tennis balls or hit golf balls or shoot basketballs? On previous episodes of the podcast, you know, in season one, we talked about the neuroscience of grabbing an apple and what goes on in your brain when you grab an apple. And in season three, we talked about the neuroscience of walking and how it's not as simple as you think. Well, today we're going to talk about the neuroscience of hitting a tennis ball. Now this applies to basically any complex sports skill, which is

what I'm really talking about. So on today's podcast, the neuroscience of hitting a tennis ball. So I think I'd like you to do some homework first. Go back to season one and listen to the episode on grabbing an apple. And then go to season three and listen to the episode about walking. And it's a good background for what I'm going to talk about. And once you've done that, you know, then obviously I'm just going to keep talking. But I'd pause right here and go back and listen to those if you haven't yet. So let's talk about the neuroscience of hitting a tennis ball.

Let's say you're standing across the court from Serena Williams, and she's about to serve to you. And Serena serves. Well, as the balls come in across, the first thing that happens is the processing of sensory information that underlies all complex sports skills. And there's three sort of key parts of the brain that are involved here. We've talked about them all, but let's focus on them in a sporting context. Vision, as we talked about in season one is divided into two visual streams there's the

ventral visual stream which is vision for perception and the dorsal visual stream which is vision for action well the ventral visual stream is in the inferior temporal cortex and basically as serena hits the ball that's the visual stream that's going to identify that it's a ball and it's going to know what's going on. It's going to be processing the information about perception. Oh, the ball's being hit. Looks like the ball's coming this way. It's doing all those sort of conscious judgments, if you will. And that's a good way to think of the ventral visual stream. It's conscious vision. What's the dorsal stream doing? Well, again, if you think back to season one, it's computing the exact distance to the, if you think back to season one, it's

computing the exact distance to the ball, the exact distance to the net, the exact distance to Serena. And it's doing this subconsciously. While you perceptually might not have a very accurate estimate of those distances, your dorsal stream knows those distances down to the millimeter. Now, while your visual system is doing its thing, the somatosensory cortex or the primary sensory cortex is taking in somatosensory information. So remember, that's like the angle of the joints, which muscles are contracted, which muscles are relaxed. So basically the state of the body. So it knows exactly the positioning of the body. Now the prefrontal cortex kicks in. It comes up with the intention to move.

Heck, I need to hit the ball. And it's working in conjunction with the anterior cingulate cortex, which plays a pretty important role in action selection. So between the two brain regions, it's going to work to decide forehand or backhand. Should I move forwards or move back? And let's say you select forehand. So between the two brain regions, the prefrontal cortex and the anterior cingulate cortex, they quickly decide to select forehand given the sensory information that's coming in at the time. Now this is where two other key brain regions come in, the premotor

cortex and the supplementary motor area. Now, these are both movement planning regions, and I'll talk about them in the neuroscience bites that go along with this podcast episode. But the reality is these brain regions aren't perfectly well understood. At a high level, we know they're both involved in movement planning, and we know that they both play a crucial role here. Basically, the premotor cortex seems to play a role in guiding body movements, and it helps integrate sensory information, and it sort of seems to be more focused on muscles that are clones to the center of the body whereas the supplementary motor area seems to be involved in more complex movements so the extremely complex movements and working with coordination of the hands and more of the

periphery now with that being said there's a wealth of studies looking at these brain regions and what they do but for the purposes of these episodes let's think of this as movement planning and a different concept that we haven't really talked about. And that's the concept of a motor program. So what's a motor program? Well, a motor program is essentially two things. One, it's your memory for a sport skill. So every time you execute a sport skill, you keep a memory of that sports skill. This is how you're able to get better at sports. And those memories are called motor programs. So right now, if I asked you to brush your teeth,

you might have a motor program for brushing your teeth and you would execute it. And that's a little different than programming that entire movement from scratch. Now, the motor program has a couple of key components. The first one we call order of events. What that really means is the motor program is storing which muscles are used and the order they fire in. So let's fire muscle A, then muscle B, then muscle C, or maybe D and E at the same time.

So that's order of events. It also stores something called relative force. Now what this is is a bit complex, but essentially if I'm going to fire my biceps muscle and my triceps muscle, there's a relative force between them. So if I'm going to do two units of force in my biceps muscle, the relative force might specify I only need one unit of force in the triceps for this motor skill to work. And relative because it's a ratio. So if I do the movement skill twice as hard, I'd get four units of force in the biceps and two units of force in the triceps because I have to keep that two to one ratio intact. I could never get three units of force in the biceps and two

units of force in the triceps because two units of force in the triceps because that's breaking the relative force. And the motor command also stores, or the motor program also stores relative timing. If I fire the biceps muscle for 200 milliseconds, I fire the triceps muscle for 300 milliseconds. And that two to three ratio has to be maintained just the same as the relative force. So these three things, the order of events, the relative force, and the relative time are stored together as a motor program or a motor memory, if you will. Now at a deeper level than this, what neuroscientists have figured out is that we actually store a series of motor primitives.

So you're scratching your head saying, okay, I think I barely got motor program. What's a motor primitive? Well, a motor primitive is just a simple movement. So imagine contracting your biceps muscle. That's a motor primitive. Imagine taking a step forward. That's a motor primitive. And imagine rotating at the hips. That's a motor primitive. So what the motor program is doing isn't specifying individual muscles. Instead, it's grabbing these motor primitives and gluing them together in a specific order. I need primitive B, C, F, and G. And I need them to do this in this order and these amounts of time and with this amount of force. And that's what the premotor cortex

and the supplementary motor area are really doing. They're gluing together motor primitives to form this motor program that we're going to execute to move. Now, there's a lot going on at the same time. You know, say I want to hit the ball deep against Serena Williams. Well, I need to know how much force to use, and that's where schemas come in. What's a schema?

Well, a schema is our brain's relationship, say, between force and distance and force and time. And if the motor system says, hey, I want to hit the ball to the back of the tennis court, it uses the schema to figure out how much force is needed. And this all takes place in a part of the brain called the cerebellum. So the premotor cortex and the supplementary motor area essentially are reaching out to the cerebellum saying, hey, we need to go this far. And the cerebellum replies with, well, hey, here's how much force you need. Now, in reality, in modern versions of motor control,

we sort of talk more about forward and inverse models. This is why I asked you to review, because if you did, you would understand these things from the episode on grabbing an apple. But essentially, this is part of the inverse model, where we reach back and we say, hey, this is what we want to achieve. What force do we need? And another good point to make here is that the motor system doesn't operate in serial. It doesn't go step one, then step two, then step three, then step four, then step five. Instead, what it does is all of this is happening in parallel. So while the premotor cortex and the supplementary motor

area are reaching out to the cerebellum for that schema information, other things are happening, sensory information is coming in, parts of the premotor cortex and the supplementary motor area are working on other parts of the motor command. So all these brain regions are lighting up at the same time. And when all this comes together, we have what's called a motor command. So the motor program is turned into a motor command, and that motor command is sent to the primary motor cortex. And we've talked about that one a lot. Once the motor command gets to the primary motor cortex, the body moves because the neurons

in the primary motor cortex, when they fire, directly fire muscles. Now, of course, this thing is sent as a cascade, if you will. You can't send the entire tennis swing at the same time because that forearm, it would all be executed at the same time. And obviously, there's things you need to do in sequence. You might need to rotate and take a step, for instance, move your arm back, then move it forwards. So part of what the premotor cortex

and the supplementary motor area are doing is governing this process as well. It's another role they play, which is, hey, unleash this little bit, then unleash this little bit, then unleash this little bit. But at the end of the day, all of it comes together and you have a motor command or a motor skill which you execute. So first, sensory information coming in. Ventral visual stream for identification. Dorsal visual stream for where things are in space. Somatosensory cortex, state of the body. Where is my body and what position am I in?

Decisions made to move. Premotor cortex and supplementary motor area begin to generate that motor program. Reaching out to the cerebellum, the schema, if you will, to get force distance information. And then the motor command is executed. Now, as you're executing, you can tweak the motor command.

And again, we talked about that when we talked about grabbing an apple and that's what we call online control. And that's where those forward models come in. So that's a part of it too. And there's stages of learning well i'll talk about that on the next episode so i'll talk about how a motor command changes with practice and exactly how that all works and what changes occur in the brain as that's going on so there's the neuroscience of hitting a tennis ball i hope you enjoyed that my apologies that we're a little bit late with this episode.

It's the end of the semester. It's a bit of chaos. Matt and I are doing our best to stay on top of it. And we will get all of the episodes out just a couple of days gaps from time to time as we deal with the realities of daily life as a professor and a PhD student. On that note, don't forget our website,

thatneuroscienceguy.com. There's links to our Etsy store where we've got our t-shirts. We've got some other merch ideas for the new year. There's also links to Patreon. Thank you so much for those of us that are donating

and supporting the podcast. Remember, all of that money goes to graduate students in the Kregolson Lab and specifically right now, Matt, who's doing all the sound production. Remember, if you've got ideas, a lot of the episodes this season were episodes you requested. So follow me

on Twitter at that neuroscience guy, and you can DM me and I'll take in your ideas with Matt. We'll discuss them and see what we can do. And of course, thank you so much for listening. Please subscribe. And again, thank you. And I'll see you for a neuroscience bite in a little bit my name is oliv krigolson and i'm that neuroscience guy thank you so much for listening and i'll see you soon