A question for neuroscientists: getting nowhere fast

Perhaps Shelley, Joseph, the Mungers, or one of the other “head honchos” skulking around these parts can help me with this one.
This afternoon I ran on a motorized treadmill for about an hour and fifteen minutes, something I rarely do. Immediately afterward I headed outside to put in another 15 minutes or so. As I headed down the street, I noticed the same thing I always do when going straight from the treadmill to a “land run” (or even a slow amble): I felt as though I were running on the moon (at least in terms of how I imagine this would feel), with the ground seeming to scroll beneath me at a rate discordant with my actual forward speed; it took a good four or five minutes for this odd sensation of being pushed along, along with the sensation of something akin to noinobtrusive vertigo, to dissipate.
I can understand at a vague intuitive level why flailing one’s limbs for over an hour in a manner consistent with forward movement, yet remaining stationary, would mess with one’s proprioception. But I’d be interested in the physiollogical specifics, which I assume are not especially complicated.

9 thoughts on “A question for neuroscientists: getting nowhere fast”

  1. Does that treadmill, like many I’ve seen, have a slight upward slope to its bed? If so, perhaps the sudden shift to more level ground provides an errant feeling of running downhill, with greater apparent speed.
    Of course, the visual cues and your breeze of passage probably also contribute to sensations of making greater progress.

  2. When running on a treadmill, I incline the belt to a 1% grade to compensate for the lack of air resistance inherent in outdoor running — this is what physiologists suggest on the basis of O2-consumption studies. That is, a 1% incline makes 7:00 per mile on the ‘mill equal to 7:00 per mile on level ground on a windless day. And the very beginning of the outdoor part of today’s run was in fact downhill. But even when I started up a hill two or three minutes in, the weird perceptions persisted.

  3. If I first run outside and then hit the treadmill, I find running in place exceptionally boring. Oh, wait — it always is!
    Actually, on the rare occasions I have done this, I haven’t noticed any difference in the treadmill portion (other than its being a little easier right from the start owing to my being “warmed up”).

  4. I think the brain adapts to the unchanging visual world as you run on the treadmill. As you begin your outdoor run the adaptation persists for a while and you get the feeling of covering a larger distance (measured visually) for the same amount of limb movement (proprioceptive cues). Eventually the visual system recalibrates.
    Try running with your eyes closed (without falling down and hurting yourself!) for about 15 min on the treadmill. I think this might be a nice experiment to measure timecourse of this adaptation. Alternatively you could focus your eyes at infinity (if there is a window in front of your treadmill).
    Obviously,, both these things might be pretty hard to acheive and might not work. Please don’t attempt them without being sure of your safety.

  5. I don’t know. But maybe you could explain to me why I have to start a run 10 times slower on the treadmill than on the roads? If I don’t, instant shinsplints!

  6. Basically, it happens because running on a treadmill causes a mismatch between what you see (standing still) and what you muscles and joints report to your brain (that your body is moving). Once adapted, when you get off and run for real, the optic flow caused by your movement appears speeded up, so you feel like you’re running faster. Its a great example of a visual-kinesthetic interaction, and illustrates the fact the vision dominates.
    You can reduce/abolish the aftereffect if you provide treadmill-runners with a movie screen that plays a movie with optic flow.

  7. I have a hard time believing that the effect is purely visual. However, the effect is most easily described by a similar effect that is purely visual. The visual cortex includes layers of neurons that respond to specific high-level stimuli. For example, there are neurons that fire when you see something moving leftward across your visual field. Other neurons fire when something moves rightward across your visual field. Still others fire when something moves approximately 30 degrees toward the left-bottom diagonal. And on and on… After firing for an extended period, any of those neurons can get fatigued, resulting in what is known as The Waterfall Effect, wherein all static things in your environment appear to move in the opposite direction of whatever you were just watching. Most people experience this after watching the credits scroll in a movie theater — when the lights come up, the entire theater appears to be moving downward.
    While I don’t know enough neurophysiology to be sure, I do know enough neurophysiology to say that it’s highly likely that the proprioceptive and vestibular centers in the brain probably have very similar layers of neurons. While running on a treadmill, you are triggering some neurons that sense one particular type of motion — the “staying still while running” motion. Running on solid ground triggers quite a different response, and the fatigue of the “staying still while running” neurons enhances the effect of the “moving while running” neurons.
    Or something like that.
    Or not.

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