Delving Into The Autistic Brain - Part 3

How does the brain make sense of what we see?

When we look at something light stimulates the receptors in the eyeball to transmit visual impulses along the optic nerve to the brain stem nuclei. These nuclei process the impulses by integrating them with vestibular, tactile and proprioceptive input, forming our basic awareness of everything around us.88

From the brain stem, visual signals travel through the thalamus to the occipital lobes of the cortex where they are decoded and sorted into different aspects of vision: line, shape, color, movement and distance or depth.89 From here signals are communicated back and forth to other cortical lobes through long association tracts. This interactive exchange, primarily between areas of the occipital (visual) and temporal (language) lobes, allows the brain to incorporate more precise visual details into the picture, giving meaning to what we see.

How much of an impact does the vestibular system have on our vision and hearing?

There is definitely something different about the way a child with autism views the world. Information from the eyes and/or ears is not interpreted by the autistic brain in a conventional manner. Autistic children who do not have an underlying vestibular dysfunction, or whose dysfunction is on the mild to moderate side, tend to have an easier time learning to do and doing most things. Certainly they have and easier time looking and listening, because the vestibular sense is an integral part of our vision and hearing.

The inner ear contains both auditory and vestibular receptors. One type of vestibular receptor, tiny crystals attached to neuron fibers, responds to the force of gravity. The second type, small fluid-filled tubes or canals arranged at varying angles, respond to movement. The combined input from these vestibular receptors, in conjunction with proprioceptive information, tells us where we are in space, whether we are moving or still, how fast we are going and in what direction.”90 This knowledge affords us a physical reference point for all that we see and hear.

Our vestibular sense serves to link our body senses to our distal senses. Our visual and auditory perception -- the meaning we assign to what we see and hear--can only be accurate and complete if every sensory processing system from the brain stem on up and every single synapse along the way is working smoothly. The bottom line is that in the brain, “almost everything influences almost everything else.”91 Our body senses give meaning to auditory and visual information, our vision helps us to make sense of what we hear, and our hearing helps give meaning to what we see. If any single sense is weak, but particularly our vestibular sense, that sense will negatively impact all our other senses.

What might account for the difficulty many autistic people have in sustaining eye gaze or visual attention?

If input from the eyes is not being properly integrated with input from the inner ears--or if the brain’s interpretation of that input is “off” -- making sense out of visual information would be a pretty confusing business. A person with vestibular processing problems might see an object moving in his line of vision, but without clear vestibular information he might not be certain whether the object, his head or his whole body was doing the moving.92

Also, if the vestibular nuclei are not responding efficiently to inner ear feedback and adjusting the eyes and neck to compensate for head and body movements, looking might well be off-putting. A person’s visual field might appear to vacillate rather than remaining steady and stable.

The difficulty many autistic children have in sustaining eye gaze might also be attributable to poor proprioception from the eyeball muscles. But the primary culprit is probably poor connections. If the nuclei in the occipital lobe responsible for directing the eyes to look are not in good communication with the brain stem nuclei, they cannot do their job effectively.

What might account for the difficulty many autistic people have in integrating distal information, and how might this contribute to their language impairment?

Donna Williams, a woman now coping successfully with autism, has spoken of her difficulties in processing more than one type of distal sensory input at a time. As a child she could listen or look, she said, but she couldn’t do both at the same time. This was probably because the sensations from her body and from gravity were not well enough organized to allow for the smooth integration of so much stimuli, all of which required the most sophisticated and comprehensive neurological processing. Indeed, exposure to too much auditory and visual information might well confuse or over-stimulate the mind of someone whose basic sensory systems are not functioning properly, causing her to use or at least favor one distal sense and tune out or tune down the other.

The inability to process auditory and visual information smoothly and simultaneously might also explain the difficulty many autistics have in putting thoughts into words. In their book, From Ritual to Repertoire, Arnold and Eileen Miller write:

“Distal systems permit children to rapidly and easily use their sound making buttressed by ocular-motor input... to act upon and thus relate to a broad range of stimulating objects and events. A natural consequence of this capacity is the enhanced polarity between the child’s sense of his or her own body and the external world... Without distal systems, autistic children are confined to a reality based only on what they experience directly with their body or on what is within arm’s reach. In this reality, objects and people tend to exist upon entering their proximal space and disappear upon leaving it.”93

Because their processing of distal information is incomplete, many autistic children might simply fail to grasp that the words they utter “can be directed toward and represent objects and events both near and far.”94 This failure to appreciate that words can be used to relay more than mundane and instrumental requests and observations might well factor into the inability of many autistic people to use language in a less literal and functional, more conventional manner.

Why do people with autism often favor their visual sense and is this over-reliance one sense healthy?

Because information among and between the cortical lobes is not being communicated efficiently or effectively in the autistic brain, one sense sometimes winds up predominating all perceptions. In autism, this stronger and clearer processing channel is often the visual one. One explanation for this might be that the neural tracks leading to the occipital lobe are better established in most autistic brains than the tracks leading to other lobes. In fact, many children with autism who are unable to talk are remarkably proficient at computer or video games. Like Tommy, the pinball wizard from the rock opera, their visual concentration is intense because they contrive to ‘tune out’ their weaker, more distorted or distracting auditory sense.

However, this over-reliance on one sense over another may be detrimentally impacting the already compromised processing systems of many autistic individuals. Only by using their eyes and ears together and striving to derive meaning from the whole of sensory experience will all the circuitry in their brains be engaged, all the synapses exercised, the neural connection machinery stimulated and challenged to function in as normal a manner as possible.

What is specialization or lateralization?

For clarity sake I have written of the cortex and cortical lobes singly, but in fact, the cortex and cerebrum are divided into two hemispheres. Most sensory and motor messages cross over in the brain stem, so that the left hemisphere ends up controlling the right side of the body, and the right hemisphere handles the processing for the left side of the body.

As the processing capabilities of the brain increase and academic abilities begin to manifest themselves, each hemisphere also becomes specialized by function, meaning that some inputs are processed better on the right side, while others are handled better on the left. In most right-handed people, the ability to use and understand language, to perform fine motor skills and engage in logical thinking is located in the left hemisphere, while the right hemisphere is more involved in emotion and insightful thinking and in processing complex visual and spatial input.95

How might the left hemisphere contribute to the language problems characteristic of autism?

On the face of things, if one were looking to track down specific cortical involvement in the pathology of autism, the most logical place to begin looking would be in the left hemisphere because of its tie-in to language. In fact, one might be inclined to zero in on three specific areas: Broca’s area, in the left frontal lobe, which deals with grammar and articulation; Wernicke's area, in the left temporal lobe, which covers sense and understanding; and the angular gyrus in the parietal lobe, which turns images into words.96

Damage to any or all of these crucial language regions could produce symptoms akin to the communication deficits of autism. Impairment to Broca’s region would leave a person able to understand words but unable to speak them with any fluency, while impairment in Wernicke’s area would produce speech that is fluent but virtually meaningless.97 Damage to the angular gyrus might result in problems with word retrieval.

But, tempting as it is to simply blame the communication impairment in autism on problems with or faulty connections to one or more of these specialized speech areas, if one looks more closely at the precise characteristics of autistic language development and use, it becomes clear that the pattern doesn’t really fit. This is not to say that the left side of the autistic brain is entirely blameless or that it is functioning smoothly. If this were the case then, at the very least, every autistic child would be able to speak.

In her writing on “Hemispheric Specialization,” Elizabeth Murray states that while “the right hemisphere is dependent on connecting fibers for both the learning and maintaining of skills... the left hemisphere is only dependent on connecting fibers for learning skills.”98 This explains why most children have a relatively easy time learning to talk after they have mastered their first word or two. Because neural interconnections to the left hemispheres of their brains have done their work efficiently since infancy, the basic language skill processing machinery is set in place early on so that the process of acquiring words and combining them into sentences becomes almost instinctive.

The problem with autistic brains may be that the language skill is not learned and localized early on. Inefficient synapses and circuitry cause a critical delay in the formation of the language processing machinery, so that using and understanding speech remains dependent upon the complicated and complete transmission of multiple inputs.

How might the right hemisphere contribute to the communication and social deficits of autism?

Although the lobes of each hemisphere do specialize, there is a constant flow of information between them so that neither hemisphere truly operates alone.99 For instance, while the left hemisphere is generally responsible for processing and producing language, the right hemisphere also plays a crucial role in processing the auditory input that contributes to speech. It handles the non-verbal aspects of communication, such as gestures and voice intonation and enables us to generate new ideas, to draw inferences and to organize and synthesize information.100 So, while a person with a right hemispheric dysfunction might still be able to talk, their speech would tend to have a flat, monotonous quality, and there would likely be little depth or organization to its content along with a heavy reliance on jargon or cliches. Such a person would rarely use gestures and would often miss inferences or the “hidden meanings” in what was said to him.101

Furthermore, because of their difficulty in drawing inferences and synthesizing information, individuals with processing problems in their right hemisphere would not fare well in novel social situations. It would be difficult for them to “read” the situation and come up with an appropriate “game plan.”102 Such individuals would also have problems with attention; they would tend to focus on details rather than grasping the main idea. They might be able to decode or read words, because reading is primarily a function of the left hemisphere, but they would have a difficult time comprehending or getting the gist of what they read.

All of the above deficits are characteristic of autism, so clearly the right hemisphere is just as involved in the pathology of autism as the left, if not more so. More likely, as I have suggested, the fault lies in the connections between the two. If and when the left hemisphere language processing machinery forms in the autistic brain, it forms in an atypical manner, a manner indicative of some malfunction in the right hemisphere. This explains the autistic propensity to interpret language as a gestalt, since the right hemisphere processes information in a simultaneous holistic or gestalt manner, while the left uses a sequential processing style.103 Perhaps because the right hemisphere is more intermodal, more dependent on a steady influx of integrated sensory input and feedback than the left, whatever connection deficits there are in the autistic brain affect the functioning of this side more severely, and this side negatively impacts the other.

104 Susan A. Greenfield, The Human Mind Explained, New York (1996) Henry Holt and Company, p. 139.

105 Susan A. Greenfield, The Human Mind Explained, p. 139.

106 Susan A. Greenfield, The Human Mind Explained, p. 137.

107 Elizabeth A. Murray et al., Sensory Integration: Theory and Practice, Philadelphia (1991) F.A. Davis Company, p. 185.

108 Susan A. Greenfield, The Human Mind Explained, New York (1996) Henry Holt and Company, p. 139.

109 Elizabeth A. Murray, “Hemispheric Specialization,” Sensory Integration: Theory and Practice, Philadelphia (1991) F.A. Davis Company, p. 180.

110 Elizabeth A. Murray, “Hemispheric Specialization,” Sensory Integration: Theory and Practice, p. 191

111 Elizabeth A. Murray, “Hemispheric Specialization,” Sensory Integration: Theory and Practice, p. 191.

112 Elizabeth A. Murray, “Hemispheric Specialization,” Sensory Integration: Theory and Practice, p. 180.

113 Anne G. Fisher,et al., Sensory Integration: Theory and Practice, Philadelphia (1991) F. A. Davis Company, p.181.

114 Margaret L. Bauman, “Microscopic Neuroanatomical Abnormalities in Autism,” (Department of Neurology, Boston City Hospital & MGH) Pediatrics (1991). Also, “Neuropathology of Infantile Autism,” Current Trends in Autism Conference (Oct. 1999).

115 Robert Schultz, Ph.D., “Neuroimaging Studies of Autism; Static to Functional,” Current Trends in Autism Conference (Oct. 1999).

116 Margaret L. Bauman, MD, “Neuropathology of Infantile Autism,” Current Trends in Autism Conference (Oct. 1999) Notes, p. 16.

117 Margaret L. Bauman, “Neuropathology of Infantile Autism,” Conference notes, p. 14

118 Margaret L. Bauman, MD, “Neurobiology of Autism,” Current Trends in Autism Conference notes p. 9.

119 Stephen M. Edelson, Ph.D., “Autism and the Limbic System, Center for the Study of Autism, Salem, Oregon. Internet Website.

120 Stephen M. Edelson, “Autism and the Limbic System.” Internet Website. Also, Margaret L. Bauman, “Neurobiology of Autism,” Current Trends in Autism Conference (Oct. 1999) Notes, p. 5.

121 Margaret L. Bauman, MD, “Neurobiology of Autism,” Conference notes, p. 5.

122 Susan A. Greenfield, The Human Mind Explained, New York (1996) Henry Holt and Company, p. 131.

123 Margaret L. Bauman, MD., “Neurobiology of Autism,” Current Trends in Autism Conference (Oct. 1999) Notes, p. 7.

124 Susan A. Greenfield, The Human Mind Explained, New York (1996) Henry Holt and Company, p. 131.

125 Susan A. Greenfield, The Human Mind Explained, p. 131.

126 Margaret L. Bauman, MD., “Neuobiology of Autism,” Current Trends in Autism Conference (Oct. 1999) Notes, p. 7.

127 Walter J. Freeman, “Chaos in the CNS: Theory and Practice.” (Internet website)

128 James L. McGaugh, Ph.D., Introduction to the Center for the Neurobiology of Learning and Memory, University of California, Irvine campus. Internet website.