Input Output Processing


Input Output Processing

Jenn Pilotti


I had a version of the following conversation with two different clients last week: Client: “How should I be holding myself? Should I think about lifting through my ribs? Should I keep my left hip always back? Should I emphasize pressing down my right foot?” Me: “You should stand in a way that feels good. Give yourself permission to shift a little bit until you find a position that feels most comfortable for you, and if that becomes uncomfortable, shift again.”

Our behavior, which can also be thought of as motor output, is based on two factors:

  1. Sensory input, or information we receive from the somatic aspect of the peripheral nervous system

  2. Cognitive control, or our conscious interpretation or control of how we think we should behave.

These two ways of processing information are called bottom-up and top-down processing, respectively. Perception, or the way we interpret the experience, is based on both top-down and bottom-up processing. Even if it feels like one type of processing is more dominant than the other, our perception of our reality is based on both types of input.

A reminder about how the nervous system works…

Your brain and spinal cord make up your central nervous system. The central nervous system is responsible for coordinating behavior and transmitting signals to different areas of the body ( Our ability to slow down, think about how we are moving, and consciously try moving in a different way is the result of the central nervous system. So, too, is the rapid reaction of moving the hand away from a hot surface, a behavior that occurs so quickly it’s not consciously processed. The detection of the hot surface and resulting behavior of jerking the hand away is a spinal cord reflex. This happens fast in contrast to consciously thinking about how you are going to move. This happens at the level of the brain and results in slower movement.

The peripheral nervous system is everything else. It’s the part of the nervous system that information gathers about whether you’re hungry or full, standing on a level or flat surface, or whether the dog next door is barking. It’s also the part of the nervous system that carries out the response to the input. When you reach for the banana, send blood to your organs to aid with digestion, shift your weight to your left to create more balance, or cock your head in the direction of your neighbor’s house, that’s all happening at the level of the peripheral nervous system.

Your peripheral nervous system has two distinct branches: the autonomic nervous system and the somatic nervous system. It’s worthwhile to understand how these two aspects of the peripheral nervous system work if you want to more fully understand processing and movement. Let’s see if I can explain. The autonomic nervous system controls automatic bodily functions. Things like heart rate, blood vessel tone, and digestion are controlled by the autonomic nervous system.

The autonomic nervous system has three branches:

  1. The sympathetic nervous system (SNS)

  2. The parasympathetic nervous system (PNS)

  3. The enteric nervous system (ENS) (

The ENS can function independently; it can also be influenced by the SNS and PNS. It governs the function of the gastrointestinal tract. Another way to think of this is gut function is controlled by the ENS.

The SNS and PNS regulate arousal. If you are alert, guarded, and prepared for a stressful situation like presenting budget to your superiors or climbing a rock wall to escape a crumbling bridge, your SNS will be activated. Your breathing will be faster and more shallow, and your heart rate will be slightly elevated. You may have an increase in muscular tone and blood will be shunted away from your digestive organs out to the periphery in case you need to move quickly.

If, on the other hand, you sit in a hot tub for twenty minutes after a massage, your SNS will be down-regulated, which is a fancy way of saying less active. Your PNS will be up-regulated, which means your heart rate will be low, your respiration rate will be slow, and your muscles won’t feel tense. Blood will be directed towards your organs for digestion as opposed to towards your muscles.

Different aspects of the day require different amounts of SNS and PNS activity. They dance with each other. Sometimes the SNS leads, sometimes the PNS leads, creating a teeter totter type action. If one always leads, the teeter totter remains tipped towards the more dominant leader. This can create problems until the balance in the dance is restored and the teeter totter begins to tip the other way.

The somatic branch of the peripheral nervous system is the voluntary aspect of the peripheral nervous system. Unlike aspects of physiology that we can’t consciously control, like blood vessel tone and where the blood is being sent, the somatic nervous system is under conscious, voluntary control—if you decide to pick up a piece of paper from the floor, your somatic nervous system enables you to pick up the paper. Another way to think of this is the somatic nervous system encompasses the control of body movement via skeletal muscles. There are two branches:

  1. The sensory, or afferent, branch

  2. The motor, or efferent branch

If in the above example, you prepare to bend down to pick up the piece of paper but you are off balance and in a suboptimal position to pick up the piece of paper, the afferent branch of the somatic nervous system detects that information before you move through specialized neurons devoted to detecting internal forces on joints, muscles, and tendons. This information is your proprioception and, along with information from the vestibular and visual system, is responsible for maintaining balance and stability.

The afferent nervous system also detects sensation of touch, vibration, and/or pressure on the skin, as well as the sensation of sharp, cutting pain, like when you get a paper cut or slice your hand while chopping vegetables.

The way you shift so you feel more stable and the subsequent act of picking up the paper by bending over is output sent via the efferent, or motor aspect of the somatic nervous system. The way you move is based on the information from the afferent nervous system and ways you have successfully accomplished similar tasks in the past. Basically, your present state and your past experience determines your behavior, or how you move. All of this takes place in the motor cortex, three different areas of the frontal lobe of the brain which are responsible for the execution of movement.

When you don’t think about how you move and you just move, there is a heavy reliance on previously successful motor patterns to perform the desired task. In fact, coordination is largely a feedforward process—an internal action is established before sensory feedback is translated and folded into the way the movement is performed.

For instance, let’s say you bend over to pick up the piece of paper without thinking about it. You start to lose your balance because you haven’t adjusted for the slightly off kilter way you are standing. Before you fall over, you stand back up, change your position, and do it again. This time, you keep you balance and successfully pick up the piece of paper. The initial attempt at picking up the piece of paper was largely a bottom-up process using feedforward mechanisms that didn’t quite work. The sensory feedback regarding joint position and instability resulted in changing the motor output and leading to (hopefully) a successful outcome.

A common example of a feedforward response is anticipatory postural adjustments (APAs). When you are about to move your arm, the motor cortex coordinates movement to keep you stable by activating muscles near the spine, controlling your center of mass and allowing you to respond to the change in position so you remain upright. What happens when the feedforward response is delayed?

The center of mass probably won’t be controlled very well. You can see this in people who lift their arm and visibly shift the spine away from the arm. What would this mean?

It could mean lots of things, but from a movement professional’s point of view, it means that it would probably benefit the person to interrupt the bottom-up processing and consciously try and alter what happens when the arm moves through a combination of feeling the spine move away from the spine and trying to find ways to not move the spine. This can be done a number of ways, including with more feedback or support in the other limbs. The conscious awareness of not moving the spine is an example of using top-down processing to interrupt a habitual pattern.

Top-down processing, then, is a useful way to alter behavior and try on a different way of moving. Based on the information about the new movement, the motor cortex may adopt it because it’s more efficient or it may decide the “old” way of doing things is easier because it requires less muscular effort and it’s the way it’s been doing things for years, so why should the motor output change?

In our example of lifting the arm, if the person lacks overall strength and has a history of low back pain, providing alternative ways of moving that are more strength based is probably a worthwhile endeavor. Learning how to lift the arm without shifting the torso will initially feel like a lot of muscular work. If the person does basic strength training in addition to a regular practice of lifting the arm without shifting the torso, the sensation of work will decrease. Eventually, the person will no longer have to think about what the spine does when the arm lifts—the inherent stability will be automatic and the feedforward response will be altered to reflect the increase in options..

What happens if the person bears down and braces every time they lift their arm, attempting to achieve the “perfect” position for arm lifting? And what happens if the person thinks about this strategy, repeatedly, daily for months? Instead of allowing any self organization or bottom-up processing to occur, the person is interrupting the feed forward response. This constant, conscious interruption of moving prevents the person from using the innate intelligence of self-organization and results in not only a fixation on body sensation and position, but also a separation of the body and the self.When everything is predicated on top-down processing, you lose any sense of trust in your peripheral nervous system’s ability to gather information and produce an appropriate response.

Summary, or main points if TLDR:

This brings me all of the way back to the original example. What, then, do I suggest to the person who is consciously trying to change their position and make it “right?”

I tell the person to check in with position occasionally throughout the day. If things feel comfortable and supported, there is no reason to change anything. If, on the other, the feedback they are getting from their nervous system is that the position isn’t comfortable, I suggest they alter their position until they find one which is more comfortable. If the person is aware of their habits, that is usually the easiest place to start—is the right knee hyperextended? Try not hyperextending the right knee. Are the ribs flared forward and up and is the weight shifted forward? Try softening the ribs and shifting the weight back more in the heels. Does one foot feel like it has more weight than the other? Try shifting the weight.

Once a position is established that’s comfortable, I tell the person to let go of the conscious awareness of the body and return to what they were doing. Checking in once an hour or so to listen to what your body is telling you reminds you to shift and alter position; constantly trying to control position, on the other hand, will make you slightly crazy. (Or maybe more than slightly.)

There is a time and a place for controlling movement. Establishing awareness and being aware of your patterns and tendencies is a great way to introduce movement variability and find more ease and coordination of movement by finding alternate pathways for movement. To consciously hold yourself in a specific way, all day every day, interrupts bottom-up processing and creates a disconnect in the confidence of the mind/body connection—for there to truly be a connection, it much go both ways, with the body influencing the mind as much as the mind influences the body.

Another way to look at this is to ask yourself if there is a right way to move? I am going to argue no, there isn’t. There is simply the way that best serves you in the moment.

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