The HumanNervous System

In the first season of the blog, we have spent considerable time covering the brain and nervous system to lay down the foundations for discussing the mind and consciousness. Let’s pause and reflect on what so-called neurological disorders can tell us, and further consider what that even means, to have a neurological disorder. To be neurodivergent.

I used to carry around a dogeared copy of Oliver Sacks’ book, The Man Who Mistook His Wife for A Hat and Other Clinical Tails. I read aloud from it in lectures given to medical students, college students, as well as middle and high school students. The stories are appealing and pique interest in how the nervous system works. These case studies highlight that the brain works on multiple independent channels or streams. These streams can be considered as brain modules. A patient can lose their awareness of their body, or of one of their limbs, or lose the ability to recognize faces. Individual functional modules or streams can be lost, and the rest of the brain keeps on chugging along. Oliver Sacks says that neurology’s favorite word is ‘deficit’, denotating an impairment, shortcoming, or insufficiency of neurological function.

Let’s talk about the use of the words ‘deficit’, ‘disorder’, and ‘disease’ when looking at dysfunction of the nervous system, notably the brain. The Diagnostic and Statistical Manual of Mental Disorders, 5^th Edition (DSMV) and the International Classification of Diseases and Health Related Problems, Volume 11 (ICD-11) use these words to describe psychological, neurological, and behavioral conditions in children and adults.

 We tend to think of disorders as constellations of behaviors that are not normal and that are difficult to link to a cause, while diseases are a collection of body symptoms that have an evident cause. We know this is not true. Genetic, environmental, and cognitive factors interact in human behavior and in human diseases and disorders. Sometimes a disease has an evident, singular cause, but not always. Many modern diseases arise from the very thing that allowed us to evolve and survive – living together in social groups.

We tend to think of a deficit as a loss of something, as in a visual deficit. As we have seen in earlier blog posts, visual deficits do not affect all aspects of vision. For example, in damage to one side of the optic stream or the visual cortex, the patient has no awareness of the complete contralateral visual field. An entire part of the visual field can be missing, but the brain uses what is available to create a visual awareness. As another example, in Attention Deficit Hyperactive Disorder (ADHD), a person has presumably lost some function of attention, not the entire attentional system.

These diagnoses indicate a deviation from normality, from normal function, and the need to return to that normal function. We have a statistical concept of normality and abnormality. For most measures you can think of, from IQ to weight, most of the population, over 60%, is within one standard deviation from the mean. 95% are within two standard deviations of the mean. We are more alike than different on most things.

A statistical or quantitative approach to normality gives us numbers that indicate deviation from the group. We need a more qualitative perspective on normality. What does the healthy individual look like? What qualities indicate health? Can a person be healthy and not typical? Let’s look at the neurobiology of some examples of brain dysfunction and consider what this tells us about consciousness.

Autism spectrum disorder (ASD), a neurological developmental disorder, gives us a good opportunity to explore these ideas. I am not an expert on ASD, but I have professionally studied and researched the topic. My purpose here is to think about what we can learn about consciousness from thinking about neurological disorders. For many, referring to someone as being “on the autism spectrum” suggests that someone could be more autistic or less autistic, a linear spectrum. While a person diagnosed with ASD may have some brain function that is a deviation from normal that results in behavioral difficulties, for example in the size and connectivity of brain structures, the other parts of their brain work “normally”. If we think of the autism spectrum as multidimensional, with each dimension representing a type of neurological process, we can avoid this linear view of deficits, and avoid placing people on a sliding scale from neurodivergent to neurotypical.

Consider some of the neurological processes (modules) we have discussed and how we have tried to tie them to brain structures and connectivity between those structures. For example, we tend to think of executive control and motor function as frontal lobe processing, language as temporal lobe processing, and somatosensory processing in the parietal lobe.

Perception is the binding together our sensory processes into an awareness of the objects in our environment. An attentional network (brain module) ties together the visual, auditory, and olfactory cortical processing, producing our conscious awareness. Each of these modules represents a dimension. An individual diagnosed with a neurodivergent disorder has difficulties in certain aspects of everyday life related to one of those dimensions or modules, while the rest of their nervous system functions normally. Each person with autism would have a different constellation of traits in that multidimensional space. That constellation is affected by the environment as well, such that a person with typical language skills and neurodivergent sensory filters could have language difficulties in a distracting environment.

This same linear sliding scale is often applied to other disorders as well, including attention deficit hyperactive disorder (ADHD), schizophrenia, and depression. As we have seen, individuals with damage to neurological structures, streams, or modules, still have an intact consciousness.

A patient with a neurological condition, from a disorder, a disease, or injury, is a normal person with a dysfunction of some aspect of brain activity. They don’t have a set of neurological deficits. They can have a set of behavioral or cognitive difficulties caused by their brain, by a damaged stream, structure, or module. It may seem like semantics, but these semantics can bleed into our treatment, both medically and socially of those we label as behaviorally and neurally divergent. Studies of stigma associated with autism document decreases in well-being and a variety of negative consequences resulting from experiences of stigma. When we know better, we should do better.

What does this tell us about the nervous system and consciousness? We know that brain operates on multiple streams of input and output. These streams are integrated in association cortex, and the streams and modules are connected in networks. These networks are only active during certain behaviors, and quiet in others, for example, in perception and attention. People with autism and with attentional deficit disorder, have been shown to have different patterns of activation of these networks compared to neuronormal individuals. The default mode network we discussed in the Sleep and Dreams post, is an example of a network used differentially by people with autism and attention deficit disorder than people without those diagnoses. The default mode network becomes active when people are offline, not focused on the outside world, for example when your mind wanders, or you daydream about your next vacation.

People with these diagnoses do not have less of some attribute; they don’t have a deficit in the common use of the word. We would not expect them to have a deficit in their conscious phenomenology. Looking at these diagnostic spectrums as multidimensional, rather than linear, improves the evaluation and treatment of individuals diagnosed with disorders. Looking at attention, perception, the mind and consciousness as multidimensional, looking at the functioning of the brain as multidimensional, gives us tools and language to understand ourselves. It brings the study of mind and consciousness into the realm of science.

That science has progressed to the point of building working models that mimic the workings of the mind and brain. Artificial intelligence and artificial life are a part of our daily lives. AI is good at pattern recognition and decision making, and now very good at producing generative grammar and language. These were once considered unique traits of humans, the goalpost for determining if species communication was truly language with semantics, syntax, and the ability to produce an infinite number of meaningful expressions. In the next post, we will look closer at artificial intelligence, and how the math of the brain is reflected in the algorithms used in machine learning and intelligence.