Although the sensory system is very complex and its correct development is vital, this post is only able to provide a brief guide. I will however highlight the major problems, which children who suffer brain injury face in the developmental areas of vision, hearing and touch.
We take in information about our environment through our senses. This is something, which we cannot help but do. The amount of sensory information our brains are processing at any one moment is phenomenal. As I sit here typing for instance, I am aware of several sensory stimuli. Visually I see the computer keyboard, with the letters printed on the keys; I can see my hands, the desk, the computer screen and more. In my peripheral vision, I am aware of the window, my dog, the sofa and other items in the room. Auditorially (hearing), I can hear the kettle beginning to boil, I hear my fingers tapping on the keys of the keyboard and I hear my cat mewing. In terms of touch (tactility), I can feel the keys of the keyboard; feel the wooden floor beneath my feet etc. These are merely the things of which I am aware and these sensory stimuli are all being processed simultaneously, in a fraction of a second.
As an example of this processing, consider the complexity of my typing this text, which hopefully you are reading with enjoyment! The front part of my brain (the frontal cortex) is sending out messages to the motor parts of my brain (the motor cortex), which control my hands,
instructing it which keys on the keyboard I need to hit next in order for the written words on this page to make sense. The motor cortex then instructs the hands to move in order to hit those keys. Parts of the brain known as the basal ganglia and cerebellum then become involved in
order to attempt to execute the necessary movements of the hands in a fluent and accurate manner. When the movements have been executed, feedback signals are then sent back to the frontal cortex, via the ‘cerebellum’ and ‘basal ganglia’ to inform it how successful the hands
were at hitting the correct keys on the keyboard and whether the movements were accurate and fluent. If necessary, the frontal cortex then issues new instructions, to correct any errors.
In a healthy, uninjured brain, this grossly oversimplified description of events all takes place within a fraction of a second whilst the brain simultaneously takes care of many other complex tasks. It is a phenomenal feat.
Also, consider how the brain decodes the various sounds we call language and how it regulates its own attention. Imagine you are sitting in your lounge holding a conversation with a visiting friend. There you are, happily chatting away; - you are attending to your friend’s voice
so that your auditory system is able to process the constant stream of noise, which we call speech. Your brain is able to take this constant stream of sound, break it down into recognisable chunks and attribute meaning to it so that you understand what it is your friend is saying. At
the same time, your brain is tuning out extraneous sounds in the background, such as traffic passing outside your window, so that you are able to focus on the task at hand. Your brain does all of this and much more, (this again is actually a gross oversimplification), with the
minimum of effort, without you even being conscious of the processes involved.
Now consider a brain, which is not healthy; - a brain, which has suffered injury and try to imagine the chaos, which might ensue for a child whose sensory processing system has been impaired. Imagine this child’s ability to ‘tune out’ noises, which he does not wish to pay attention to, has been impaired. What havoc would that child experience?
I believe that the sensory problems, which are faced by brain-injured children can be assigned to five categories, which we shall discuss later. Fundamentally it seems to me that many brain-injured children experience difficulties in correctly modulating incoming sensory information, their sensory system processing incoming stimuli in a distorted manner.’ I have applied these theories (which are all supported by evidence), to differing patterns of brain-injury: - And there are many patterns of brain-injury to which they can be applied! A particular pattern rarely has absolute, identifiable boundaries and symptoms from another. There is often a great deal of ‘overlap’ in the symptoms which differing patterns of brain-injury display. Allow me to explain.
A good example is my proposition that cerebral palsy, autism and ADHD are not distinct separable conditions, but are a continuum; they are overlapping expressions of brain–injury and consequently it is possible to have some symptoms of autism, or ADHD within what is termed cerebral palsy. It is also possible to have some symptoms of cerebral palsy within what is known as autism or ADHD.
I can already hear the howls of indignation over the fact that I have referred to autism as brain-injury! Have you not seen all the recent evidence, they will say, which points to the cause of autism as being genetic? Yes, I have seen this evidence and I accept that some forms
of autism have genetic causes. However, I have seen too many children with brain-injuries, who display amongst their repertoire of symptoms, many autistic qualities. Thus, I cannot ignore the fact that some forms of autism also have environmental causes. In other words, they are produced by brain-injury. I am also aware that genes can only express themselves in the correct environmental conditions!
It was Delacato in the 1970’s, who first claimed that children suffer distortions of sensory processing, separating them into the categories of ‘hyper-sensory,’ hypo-sensory’ and white noise. I have managed to identify five categories of sensory difficulties, which children display,
(other researchers may find more!) and I see these as symptoms of a malfunctioning ‘tuning mechanism’ in the brain. This ‘tuning’ mechanism is the structure which enables us to ‘tune out’ background interference when we wish to selectively attend to something in particular; it also enables us to ‘tune in’ to another stimulus when we are attending to something completely different. It is the same mechanism of the brain, which allows us to listen to what our friend is saying to us, even when we are standing in the midst of heavy traffic on a busy road. It is this mechanism that allows us, even though we are in conversation in a crowded room, to hear our name being spoken by someone else across that room. It is this mechanism, which allows a mother to sleep though various loud, night-time noises such as her husband snoring, or an aeroplane passing overhead and yet the instant her new baby stirs, she is woken. It is a remarkable feature of the human brain and it seems to be the responsibility of three structures operating cooperatively; - these are the ascending reticular activating formation, the thalamus and the limbic system.
Having made such a bold claim, allow me to furnish you with the evidence to support it. The three structures just mentioned receive sensory information from the sense organs and relay the information to specific areas of the cortex. The thalamus in particular is responsible
for controlling the general excitability of the cortex (whether that excitability tunes the cortex up to be overexcited, tunes it down to be under excited, or tunes it inwardly to selectively attend to it’s own internal sensory world.) (Carlson, 2007). The performance of these neurological structures, or in the case of our children, their distorted performance seems to be at the root of the sensory problems our children face.
I would label the five categories of sensory distortion, which I have witnessed in brain-injured children as follows: -
1. Sensory over-amplification. The particular sensory modality, (vision, hearing, touch, etc) can become oversensitive to stimuli from the environment. It is my belief that in this case, the thalamus, limbic system and reticular formation, which are acting as the brain’s ‘tuning
system’ are malfunctioning and are not effectively regulating the level of incoming sensory stimuli. Indeed, in this case they would appear to be acting to over-excite the cortex, which would have the effect of amplifying the sensory stimuli. This could possibly cause the child to
overreact, or to withdraw into himself as a defensive strategy from a world, which in sensory terms is simply overwhelming.
2. Sensory under-amplification. The particular sensory modality can appear to become under sensitive to incoming stimuli from the environment. In this case, I believe the thalamus and other two brain structures, acting as the tuning system, are acting to under-excite the cortex, which is having the effect of appearing to dampen down incoming sensory stimuli. This could influence the child to act as though he cannot see, hear or feel; - he may be deficient in this way, in one or more sensory modalities.
3. Internally focussed sensory tuning. In this case, the particular sensory modality appears to be ‘inwardly tuned.’. In this case the three brain structures, acting as the brain’s tuning system are exciting the cortex to attend to sensory information of the sensory system’s own making, or from within the child’s own body. Consequently, the child may have difficulties perceiving the ‘outside’ sensory world through this haze of internal stimulation. We see this effect ourselves in the visual aura of a migraine, or when we have 'pins and needles.'
4. Wide spectrum tuning. In this case, the three neurological structures are exciting the cortex and attempting to tune its attention to many incoming stimuli simultaneously. They seem unable to filter out background noise, sights, etc in order to allow the child to focus on one aspect of the environment. For this child, the world is absolute chaos and again, he often withdraws into himself.
5. Narrow spectrum tuning. In this case, the neurological structures are only exciting the cortex selectively, allowing the cortex to attend to limited, isolated sensory stimuli. This child may often seem ‘over-focussed’ on one particular aspect of his environment. He can for instance, become intensely interested with a spinning top or the particular features of one toy and will not play with anything else, to the point of seeming obsession. For this child, it appears his sensory tuning system is focussed too narrowly and he cannot spread his attention to incorporate several features of his environment simultaneously.
Can these problems be addressed? Yes they can. As part of its programme for children with sensory processing issues, Snowdrop creates an individually tailored 'adapted sensory environment' for the child to encourage his sensory system to begin to process stimuli on a much more normal level. Are we experiencing success with children who have sensory processing problems? Yes we are.
Anyone requiring more information should contact firstname.lastname@example.org
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Mulleners, W. M., Chronicle, E. P., Palmer, J, E., Koehler, P. J., and Vredeveld, J. W. (2001), Suppression of perception in migraine: Evidence for reduced inhibition in the visual cortex, Neurology, January 23, 2001; 56(2): 178 - 183.
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