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Monday, April 23, 2012

Visuo-spatial difficulties and how they cause motor delay

You're standing in a field, crouched in position for a fly ball.  Crack!  You hear bat against ball.  Your attention sharpens, your eyes focus on the movement in the air, you run to position your body in its path, hold out your glove, anchor your body to absorb the force, make adjustments in your stance and position as it approaches and you catch it.  All of these actions, although simple to most, are nearly impossible for someone with Williams syndrome.  As mentioned in other sections of this blog, those with Williams syndrome have low tone so their muscle strength and response is slow, but that is only part of the equation of motor delay.  Many of the brain studies that were discussed in the speech section of this blog focus on the spatial difficulties that are prominent in Williams syndrome (WS).  This section of the blog focuses on how this spatial disability inhibits movements in ways separate from low tone.

So, what does visuo-spatial mean?

Many individuals with WS have a hard time interpreting where they are in space.  They also struggle with directional orientation, such as understanding right from left and mirror images.  Visuo-spatial difficulties mean a person would have a hard time judging their surroundings, primarily with visual information, in order to understand where they are in their environment.  For example, imagine yourself navigating down a busy staircase.  It is crowded with people and you must walk in a cramped space.  Now make that stairway spiral and you must move with a swift motion to keep in pace with the crowd.  What do you do?  You may run your finger tips along the stair railing as you move.  You keep your eyes down to the ground to evaluate where you will step.  You tense up the trunk of your body for stability.  All of these actions are your adaptations to that environment.  Your fingertips are gathering information about your position and balance.  Your eyes relay info to your brain about where it is safe to step and your core is in guard to stabilize your body.  These are all visuo-spatial skills. 

People constantly interpret a large amount of sensory information about their environment.  You use peripheral vision, cues from receptors in your muscles about your physical orientation (proprioreceptors), balance information from the inner ear (the vestibular apparatus) and visual cues about what is around you in space.  Those with WS seem to have difficulty coordinating this information.  They struggle when presented with situations where they need to make shifts in their space, such as changing their posture on a crowded bus to let someone walk by.  This body awareness issue along with their difficulties in motor planning, spatial cues and directional cues make it hard for them to do planning activities such as when it is appropriate to cross a busy street or the ability to judge the speed of oncoming traffic.  This is one reason many of them do not drive as an adult (along with anxiety issues- see a future blog post on this topic) 

The directional disability also contributes to reasons why many of the individuals have difficulty understanding left from right, even as an adult and they have some difficulties understanding mirror images.  This directional disability also contributes to handedness.  Most children establish whether they are right handed or left handed by the age of 4-6.  Individuals with WS often don't achieve this until the age range of 5-8.  Many studies suggest this is due to the brain disorganization.  Most with WS will alternate between a preferred hand, use one hand for household tasks, such as eating, and another for writing.  They may alternate the use of their hand when activities require them to cross over the body to complete a task, such as building a large block tower.  Most with WS become left handed. 

There are several theories on why those with WS have this visuo-spatial disability:
  • deletion of the LIM-kinase I gene.  There is research out there, although in its infancy, that the deletion of this gene is correlated with the visuo-spatial disability.  However, there are case studies of children missing this gene who do not display spatial delays, so evidence is inconclusive.
  • A disconnect in the dorsal stream nervous pathway
  • An atypical pattern of brain activity
It all has to do with the cellular pathways in the brain

Many of the researchers in brain studies are psychologists who study the brain function of children and adults with WS.  Their goal is to attempt to identify the areas of the brain that are medically classified as "dysfunctional" or have slower motor pathways.  Before getting into the brain studies, lets take a look at some basic brain anatomy that will help you picture why this "dysfunctional" classification is assigned.

Background on Neural pathways

The human brain is made up of many neurons, or nerve cells.  These cells have cell bodies that are unique in shape and extending from the main portion of the cell are processes or "arms", so to speak.  There are processes, called dendrites, that receive messages.  Sensory neurons sit outside the central nervous system and collect information from the environment using their dendrites.  These sensory neurons have endings called receptors that monitor the environment.  This message containing information about the environment is sent down a long process (or arm) called the axon to a second neuron in the central nervous system.  Neurons in the central nervous system, called association neurons, are located in the brain and spinal cord.  They function to process this sensory information- by interpreting what is happening around you and how the body should react to it.  Then, the association neuron will communicate a new message, send it down its axon to a motor neuron.  The axon releases a chemical (called a neurotransmitter) which travels across a gap and talks to the motor neuron.  This motor neuron then takes that message and tells the muscles how to move.




Inside the brain there are many of these "thinking" neurons.  Depending on where they are in the brain, they have different jobs.  Some areas of the brain receive visual information whereas a separate part receives auditory info, for example.  There are also areas that are for figuring out the sensory info and then a separate area for linking that info to a memory so you can label it or attach it to an emotion.  All of this takes quite a bit of coordination within the brain in order to take in information from multiple senses and combine it to create a scene of what is happening in your environment.

Neurons have jobs
There are special nerve tracts within the center portion of the brain that connect the all the sensory pathways so the brain can share the info.  These pathways are called white matter.  White matter is buried deep inside the brain and is the color white because of tiny cells that wrap themselves around the neurons, called myelin.  The myelin is a fatty layer that allows the message to move quickly down the axon.  It makes for very fast messages and is essentially a "highway" system of neurons that move info from one side of the brain to another. 



  
The outer surface of the brain, which sits around the outside of the white matter is called grey matter.  The grey matter creates what we called the "cerebral cortex".  This is where the "magic" happens.  The cortex is made up of unmyelinated neurons, or neurons that are "naked" without that fatty layer.  The messages are sent more slowly here.  In these regions, your brain decides what to do, problem solves and determines how you will behave.  It is well known that the higher IQ or the better "thinker" you are, the thicker this portion of the brain is.  The grey matter builds up in folds called gyri.  These ridges of the brain are the same on everyone, but they are thicker/thinner based on your genetics and how much you challenge yourself as a learner.  In between the gyri are shallow grooves called sulci. 



In the speech section of this blog, I mentioned that in brain studies, researchers have found that individuals with WS tend to have very thick gyri in areas that are strengths for them- particularly in the auditory region and language centers of the temporal lobe.  There are regions of the brain that have much thinner gyri.  These thinner areas of the occipital (visual) and parietal (sensory) lobes result in a visuo-spatial disability in those with WS.



Figure shows comparisons of gyri in controls (samples from the general public) versus gyri of individuals with WS.  Red areas indicate increases in gyri thickness and blue indicates smaller gyri.  Green shows areas that are comparable between the two groups. 


Streams- flow of information within the highway of the brain
The flow of sensory information that moves through the white matter in the brain can take a variety of different routes.  Two of the more important visual routes are the dorsal stream and the ventral stream. 



There is a section of grey matter in the back of the brain that makes up one gyrus in the parietal lobe.  This gyrus is smaller in the brain of someone with WS than in a typical person.  This section of the brain is involved in the dorsal visual stream.  In the dorsal visual stream, the brain uses visual information to interpret its surroundings, such as an obstacle, and determines how you will move around it.  This stream of information is very slow in an individual with WS due to the small amount of grey matter, making it more difficult for them to navigate.  Research has also shown that in individuals with WS, the brain often doesn't even use this stream when you'd expect it should.  In MRI's this area of the brain shows low activity during movement tasks.

The highlighted area on this picture shows the gyri that is abnormal in WS.  This disrupts the dorsal stream of visual information that is used to produce motor activities.

The ventral stream, in contrast is a strength for those with WS.  It involves information moving from the parietal lobe to the temporal lobe where the gyri are much thicker.  This stream of neural activity is used to recognize people using visual information and labeling.  In case studies, these streams can be tested fairly easily.  If you ask someone with WS to identify the a pathway through an obstacle course they could look at it and tell you where the midpoint of the path is (using the ventral stream) but if you ask them to walk it (which uses their dorsal stream) they would move very slowly and clumsily through the pathway.

Particular motor difficulties that are directly related to deficits in the dorsal stream and are seen in the majority (97%) of individuals with WS include:
  • poor dexterity
  • slow speed in movements with the arms and legs
  • inability to move in response to visual information
  • difficulty manipulating an object in the proper orientation to place it in a slot that is shape specific (such as a card in a slot or a block in a shape sorter) 
Problems with nervous pathways are a increasing area of study in WS research.  The nerve interactions between the frontal lobe and parietal lobe point toward behavioral difficulties that are very common in individuals with WS- including high distractability, inability to maintain prolonged attention to a task,  acting impulsively and having difficulty understanding global concepts (topics that are not concrete in thinking).  (Look for a future blog post on ADHD and behavioral profiles of individuals with WS.)


Making plans...
  
Another skill that is inhibited by dorsal stream dysfunction has to do with motor planning.  Motor planning means that the child would see what is in their environment (such as a ball flying at them through the air) have to think of how they want to respond (such as catch it), plan on what muscles need to be used to do so and where that ball will land in space and then relay the message to those muscles to complete the task.  Typically developing children will accomplish this task but many of those with WS often watch the ball as it hits them.  This disability in motor planning- often called apraxia, seems to be a difficulty in about 92% of individuals with WS.  This skill is even more difficult in certain situations such as bouncing the ball because they have to predict what direction it will land.  These tasks that require a person to use a familiar task and modify them to match the spatial information is very difficult for them.

The motor planning dysfunction will often delay their ability to throw and catch a ball.  Although most kids with WS will throw and catch a ball by the age of 6.5, they will likely have a lifelong inability to throw (51%) and catch (67%) in a coordinated fashion.  When throwing a ball, one must rotate their body, move their arm and often step forward with their leg.  Those with WS display an inability to do this at all ages.  They often will throw their arm but lack the body positioning and rotation in the upper body to make a decent throw.  The catching action is mainly due to the visuo-spatial tracking and motor planning required to predict where the ball will land and those skills needed to right the body and extend the arms quickly enough to catch the ball in time.  They simply process this information too slowly and inaccurately in order to accomplish the task.

Studies have shown that although visuo-spatial difficulties are an issue for nearly everyone with WS, there are tools that children can learn to help minimize this disability.  Case studies frequently note that those individuals who learned or utilized verbal cues were better able to navigate obstacle courses.  For example, if the person who is walking through the course studies it first and vocalizes a plan, then as they walk they talk about how to move their body, they move less awkwardly and accomplish the task with better timing.   It is also important to note that individuals that participated in these studies had varying degrees of difficulty.  Some were only slightly impaired in the task and others had higher difficulties with most having a moderate level of challenge.  Therefore, while spatial navigation is a disability for all individuals with WS, the magnitude of that disability lies on a spectrum and can be different for each individual.

Walk this way

Poor motor abilities in an individual with WS extend to many other issues that are rooted in the nervous system.  Individuals with WS, especially in the early years, have a very distinguishable gait, or walk, that is described as clumsy and uncoordinated.  There are a variety of reasons for this.

First, young children who are new to walking have ingrained protective reflexes that they use to maintain balance.  If they find themselves fighting gravity or on an uneven surface, they will right their head over their body, tighten their core and throw their arms outwards to steady their bodies and protect them from a fall.  Kids with WS seem to lack this reflex (I can personally attest that my daughter has fallen many times without ever extending her arms out to catch herself, leading to minor head injuries). 

The majority (between 60-80%) of children with WS have gross motor delays or unorganized motor skills and delays associated with climbing stairs, walking down stairs, running, jumping (especially off an elevated surface), transitioning from one variegated surface to another, walking on uneven terrain (such as grass or mulch/sand), skipping and running.  These delays or motor planning deficiencies are associated with balance issues.  Balance is related to the processing of sensory information by the nervous system.  Approximately 60% of those with WS have balance processing disorders and another 80% have trouble interpreting gravitational signals.


Those with WS have trouble navigating quickly through obstacles that require them to take longer than average strides.  They improve this skill when sensory cues are present such as lights to step in to determine stride length.  But even with sensory cues their walk is much slower than typical.  This indicates there may be some dysfunction within the cerebellum, which is the part of the brain that controls balance and coordination.  Other cerebellar studies have found that in WS, the neocerebellar lobules are enlarged.



  These are regions on the sides of the cerebellum that have major nervous pathways that communicate with the thalamus and the cerebral cortex.  The thalamus is the main area in the center of the brain that associates sensory information with memory.  Major nerve tracts link problem solving to memory to the cerebellum through this nerve tract. 



Scientists have linked this stream directly to motor coordination when learning a new motor skill.  It's used for following a series of steps used to follow a motor procedure, such as riding a bike.  It coordinates limb movements in order to achieve the desired action.  This area of the cerebellum is also heavily linked to an area of the brainstem called the superior colliculi.  This is a visual reflex area that helps coordinate the motor movements in the eyes.  Dysfunction in this can lead to poor muscle control in the eyes and can be another cause of strabismus (see the eyes section of this blog).  The neocerebellar area also helps to coordinate motor movements used to coordinate speech.



Besides brian studies, there are other reasons individuals with WS may have a harder time with motor activities. 
  • Tone- The ability for the nervous system to control muscle contractions in appropriate times; previously discussed in this blog (See the muscles section).
  • Sleep- sleep is a well known difficulty for up to 97% of individuals with WS which can further affect cognitive development and motor planning.
  • Vision- Although vision is not an issue for all children with WS, if a child has strabismis or crossing of the eyes sends conflicting information to the brain about the person's surroundings.  This can lead to increased delay in motor skills- particularly spatial understanding.  This is even more evident if the individual has lost vision in the weaker eye.  This causes the body to lose their depth perception.  Everything will appear flat and in 2 dimensions.  This will cause additional issues with motor development. (see the eye section of this blog)
 
Fine motor delays due to visuo-spatial disabilities

Spatial difficulties offer up difficulties in a variety of motor tasks.  Early in a child's life occupational skills will seem less serious than gross motor skills but as the child ages, their abilities will change and fine motor skills will become increasingly important as they gain independent living skills. 

Self help
Most children (80%) have delays in fine motor skills required for self help.  These can be related to directional disability (used to set a table, for example) but most are due to the visuo-spatial disability.  Through therapy, most of these skills can be mastered, but approximately 30% of adults still find difficulty in some skills such as tying shoes, buttoning clothing, etc. For example, many will have high difficulty using knife skills, such as those used to make a peanut butter sandwich.  They may have trouble grasping the knife, creating the motion to spread the butter, applying the proper amount of force and stabilizing the bread.  This takes motor planning and the ability to judge the environment of the bread and make small motor adjustments to have the proper movement.  Other self help skills such as writing, cooking, buttoning clothing, using a zipper and tying shoes are difficult for a person with WS due to the need to plan motor movements during these activities and have spatial awareness. One study found that, on average there is a 2 year delay in children with WS, aged 4-12, in both fine motor skills and gross motor skills that require visuo-spatial ability.

One major fine motor activity a child with WS will find difficulty in is the ability to manipulate objects in space, such as placing mail into a narrow slot.  This skill is processed by the dorsal stream in the parietal lobe of the cerebrum.  Other examples of difficult motor task include movement planning time.  In one case study, researchers had adults draw a line between two circles using a stylus.  When the shapes changed sizes, those with WS had significantly slower times completing the task.  This study linked difficulties with this task to the inability for those with WS to anticipate the movement of an object and plan their motor response to it.

Drawing

Most typical children will draw recognizable pictures of objects by the age of 5 or 6 whereas those with WS draw them closer to the age of 9 or 10.  This is due to the visuo-spatial delay.  They draw comparably, though, to peers with mental disabilities.  IQ and drawing ability do not match in WS indicating it is an area of disability.  It is also notable to say that they do eventually achieve the ability to do this task by adulthood.

This photo is from the study completed by Dr. Mervis et al. and it shows a drawing of a bicycle, completed by a 12 year old with WS.  All the components of the bike are present, but those with WS have a difficult time picturing how they are connected- a spatial skill.
Therapists have identified a strategy that help individuals with WS improve their ability to draw.  This should be used in OT sessions.  The increase in gains when using the face as a drawing tool stems to brain studies that show individuals with WS use their brain differently to interpret faces.  Typical adults will process facial recognition with the right side of their temporal lobe.  Those with WS use a much larger area of the brain and primarily use the left side of the brain to do this.  The study also had interesting evidence that those with WS use the same amount of processing to interpret the face of a picture of a person that is upright versus on that is flipped up side down.  In typical adults, there is a delay in processing the flipped images as the brain has to try and associate the image with what they'd look like right side up.  Those with WS use more brain activity looking at a face in any position than a typical person would and they use the same brain activity despite the picture orientation.


Ways to help improve their drawing skill is to allow them to draw motivating pictures- focus on drawing people, facial expressions, etc rather than shapes.  Kids showed greater gains when they had developmental interpretation therapy session to help them process how the picture should fit together.  They also improved with frequent practice.  Case studies show that in children, ages 4-6, who participate in the developmental interpretation sessions and practiced drawing people and houses showed significant gains in elaboration of the picture, increases in inclusion of objects, improved their ability to draw an object in its proper context (like a person in a house) and increased in the ability to combine features (all the parts of the picture connected in the proper ways such as heads were on necks and legs attached to bodies).  Improvement has also been shown to have the subject verbally express what they are drawing and how it should connect the lines.  When they talk through the process, the picture ends up more organized.

In the same study the kids were assessed again between the ages of 12-15.  After 6 years of growth, the ability to draw more organized pictures improved in all subjects of the study.  So, although the skill is delayed, it does improve with time.  In all age groups, the subjects were able to draw more organized pictures of people and flowers versus objects such as houses, bikes and animals. 

In conclusion

Visuo-spatial difficulties are an issue for all individuals with WS but with purposeful and educated therapists, there are skills and techniques that they can learn to help them overcome this obstacle and improve their self help and motor skills as they age.

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