Sensory-Based Motor Differences

According to a leading paper on the topic, sensory processing differences can be categorized into three basic patterns or subtypes:

1. Sensory Modulation Differences, including sensory over-responsivity, sensory under-responsivity, and sensory seeking/craving.
2. Sensory Discrimination Differences
3. Sensory-Based Motor Differences

My post entitled What is Sensory Processing? defines Sensory Modulation Differences and Sensory Discrimination Differences. This is a follow-up post about the third subtype: Sensory-Based Motor Differences.

Simply put, some motor coordination difficulties are due, at least in part, to faulty sensory processing. There are two sub-types of Sensory-Based Motor Differences: Postural Differences and Praxis Differences.

Postural Differences

To understand Postural Differences, it’s important to first understand postural control. The terms for postural function vary somewhat among professionals and in the literature. Most experts agree, though, that there are two main functions of the postural control system:

1. To keep you upright against gravity and help you maintain your balance, for which I prefer the term postural stability. This can be further broken down into static and dynamic functions. Static posture (meaning still, unchanging) is when you are holding a position against gravity without moving, and dynamic posture (meaning ever-changing) is how you keep your balance while moving.
2. To keep the rest of your body still so you can use a part of the body to push, pull, reach and/or use force to complete a task. For this function, I like the term postural regulation. To conserve energy and increase the accuracy and precision of your movements, you must stabilize parts of your body and use isolated movements to carry out actions.

Postural control is a lot more complex than just standing and sitting up straight, which is what many equate with “good” posture. In addition to keeping us in good alignment, research has shown postural control actually prepares the body to move, which is referred to as anticipatory or feedforward postural adjustments. Postural control also contributes to your body schema or internal map of where you and all your body parts are in relationship to gravity. This is crucial for maintaining joint and muscle alignment as well as determining your center of gravity. Additionally, reflexive postural reactions help you recover when you are bumped, jostled, or otherwise knocked off balance. And, perhaps most complex of all, motor coordination relies on the combination of good posture and movement.

Postural skills are largely subconscious, meaning you probably do not pay much attention to them. However, you rely heavily on your posture to complete every day tasks such as brushing your teeth or typing at a computer. Holding yourself up against gravity and coordinating your movements actually requires integration of multiple sensory systems. The sensory systems that contribute most to posture include your: proprioceptive (muscles and joints), vestibular (equilibrium and balance), tactile (touch), and visual (sight) systems.

So, what qualifies a posture pattern as a sensory-based motor difference (or disorder, if you prefer)? Just like all sensory differences (or disorders), a sensory-based posture difference is caused by brain wiring differences that are developmental (present from birth). Therefore, poor posture due to injury, disease, poor physical fitness, or health problems would not be considered primarily a sensory-based condition (although sensory conditions can be secondary to an injury or neurological illness).

Symptoms of a postural difference (or disorder) may include:

• Chronic muscle tension in the neck, shoulders, and back
• Unusually loose or tight muscles at rest
• Decreased control of movements (i.e., clumsiness, poor body awareness)
• Core muscle imbalance, resulting in rounded, slouched, or uneven posture
• Slow reflexes/reactions when knocked off balance (for example, you may not be able to catch yourself when tripping or falling)
• Inefficient or excessive/extraneous movements (such as motor overflow) resulting in fatigue

Praxis Differences

Motor praxis is perhaps even more complex than postural control. In sensory integration theory, the term “praxis” encompasses all of the processes involved in performing skilled movements. Briefly stated, praxis includes:

• Ideation–coming up with ideas; problem-solving; using the imagination to “mime” actions without objects (for example, pretending to brush your teeth without an actual toothbrush)
• Planning–deciding what to do
• Sequencing–logically ordering actions from “Where should I start?” to “How I know I’m finished”
• Execution–carrying out your plan of action
• Feedback–reflecting on how well a plan of action worked (as well as feedforward, which is how well a plan of action is working in the moment)

When a professional is assessing praxis abilities, some of the areas that may be examined are:

• Constructional praxis–building or copying configurations of materials or shapes from a model or instructions
• Oral motor praxis–coordinating the muscles of the mouth and jaw for speech production and facial expressions
• Imitation of movements–watching a demonstration of a complex movement or a series of motions before doing the same movement/motions
• Motor patterns–sustaining repetitive movement patterns (such as a rhythmic clapping pattern)

When praxis is optimal, it has three main functions:

1. Coming up with ideas, making plans, thinking of ways to get organized, and problem-solving for actions you will take in the future. This includes reflecting on recent experiences and processing what you thought went well (and what you wish had happened differently). These processes happen in the top and front area of the brain, primarily in the frontal lobe of the cerebral cortex.
2. Monitoring your performance in the moment to sustain actions, or make adjustments to improve your accuracy or speed. This process combines cortical functions throughout the cerebral cortex as well as more automatic or reflexive functions that occur in the subcortical region of the brain.
3. Completing motor tasks automatically, often using the same pattern of movements without much thought. For example, you may shower or fix breakfast the same way every day without making any decisions about what action to take next. You just “go through the motions.” This automaticity of movements saves a lot of mental energy, which frees up energy for your brain to use on newer, more interesting functions. This process occurs at the base of the brain in the subcortical region and is more a result of good praxis than an actual function of praxis.

When praxis skills are not fully functional, one or more of the above processes are impaired. Depending on the severity, impairment in praxis is called praxis differences or dyspraxia. The literal definition of dyspraxia is “bad” or “difficult” action. Some people use the term dyspraxia interchangeably with, or prefer other terms, such as apraxia (which is literally defined as “without” action), developmental coordination disorder, or motor planning problems. In the United States, occupational therapists commonly use the terms praxis differences or dyspraxia as an umbrella term for developmental praxis problems and apraxia is reserved for praxis challenges brought on by illness or injury.

Praxis abilities are based on the sensory processing functions of modulation and discrimination of inputs, the cortical functions of planning and sequencing, as well as the cerebellar functions of sequencing and rhythmicity. Praxis differences, as categorized under sensory-based motor differences, are developmental in nature (as in developmental coordination disorder), and not caused by illness or injury (such as a head injury or stroke). Again, in the United States, rehabilitation professionals tend to prefer the term apraxia for praxis challenges brought on by illness or injury.

Some symptoms of praxis differences (dyspraxia) are:

• Poor coordination, especially for complex tasks involving multiple body parts
• Difficulty learning complex motor skills, such as driving a car
• Struggling to come up with ideas or becoming distressed when answering simple open-ended questions, like, “What do you want to eat tonight?”
• Difficulty with multi-tasking
• Having trouble following multi-step instructions
• Always doing things “the hard way” or in an illogical or inefficient way
• Having trouble planning ahead
• Difficulty managing time
• Poor organization
• Being overly rigid with plans and routines

As you can see, sensory-based motor differences can be quite complex and affect many different aspects of daily life. Currently, best practice for addressing posture and praxis challenges is to work on bottom-up (body- and sensory-based) strategies in combination with top-down (cognitive) strategies to manage symptoms and improve quality of life.