“The human language capacity is overlaid in sensorimotor systems that originally evolved to do things other than support language” – Philip Lieberman
According to Philip Lieberman, a scientist and recognized expert on the human brain and the evolution of speech, cognition and language, evidence from contemporary neuroscience indicates that our brains do not operate in a manner analogous to digital computers. 1 It has been shown conclusively that human brains do not consist of independent modules resembling an illustrated phrenology model. Early brain models based on the theory that “each gene controls something” such as math, morality, kindness, speech or language skills, that lock their consequences into predictable patterns of behavior have also been shown to be incorrect.
The Demise of Modularity
In 1861, Paul Broca published two famous case studies of patients who both had extreme difficulty articulating speech after brain damage that resulted from strokes. Post mortem examination revealed brain lesions in very similar cortical areas of the brain. Karl Wernicke 2 in 1874 studied a stroke patient who could not understand speech. Post mortem study revealed identifiable damage to a posterior temporal region of the brain’s cortex. In the tradition of phrenologic thinking, of the time those specific locales became identified as Broca’s and Wernicke’s areas and credited as the center of their specific aphasic dysfunctions.
Later neurological studies showed that patients often recovered function when the damage was limited to the cortical area, thus validating concepts of neural plasticity. When damage occurred at the basal ganglia, thalamus or other subcortical structures, recovery never occurred.
In Broca’s and Wernicke’s time autopsies did not require sectioning of the brain, and MRIs did not exist for another 100 years. Sectioning of the brain and the later technology of Diffusion Tensor Imaging 3 revealed that the neural circuits linking activity between cortical and basal ganglia control the language facility of humans. These newer technologies demonstrate that brain function is a coordinated combination of cortical and basal circuitry, rather than modularity. The concept of modularity has been proven incorrect as a model of how the brain functions.
Basics of Human Nervous System Function
The basic input element of the brain and nervous system is the neuron. A neuron consists of a cell body or soma, numerous branching processes called dendrites and a single axon. The neuron receives inputs via the dendrites from as many as thousands of other neurons. The output element of a neuron is the axon which transmits information to thousands of other neurons. Synapses are the interfaces that transmit interneuronal information from dendrite to axon. Synapses are the neural equivalent of the volume control of an audio amplifier. An electrical signal is transmitted across a synapse when a certain threshold is reached.
Neural circuits link local operations in our brains. The number of synapses determine the strength of the action potential. The more synapses the more abrupt the rise in electrical spike. The system is dynamic, enlisting additional neural resources as the task complexity increases.
A new born brain is a blank slate. It is analogous to a new factory owner who has yet to decide what is going to be manufactured. The first thing the brain has to learn is how to learn. A new born baby does not know what is important in their world. Everything matters and anything a baby senses via eyes, ears, nose or skin translates into brain impulses. As new skills are developed and become stronger, the faster and more reliable the neural routes become. Neural networks develop in baby’s competitively plastic machinery. At some point a selective control switch is formed, saving positive experiences and turning off negative ones. Baby’s brain, as it becomes more selective, controls its own self-development. Soft wiring via neural networks allows humans to adapt to a changing environment via behavioral or cognitive modifications, rather than by hard-wired genetic changes. The notion that humans have to mutate each time a significant advance is made, grossly underestimates their tremendous capacity for brain plasticity. 5
The circuits that regulate particular functions are not genetically specified. Motor control programs are formed as the individual learns to perform a given task. Trial and repetitions shape circuits such as speaking, writing, or riding a bicycle. Skills result from a dynamic distributed network that recruits additional neural resources in response to increasing task demands. There can be several to many neural paths to perform a task. Competent bicycle riders have at their command multiples or alternate motor control programs to coordinate all the fine skills necessary for competitive bike riding (motor equivalence).
The neural bases of human cognition evolved from primitive reptile brain cells (subcortical basal ganglia) that ultimately resulted in a complex coordination of function and thought via interconnecting neural circuits with cortical cells to produce speech, language and cognition; functions not developed in any species besides human beings. During embryonic development there are transcriptional factors, like “master genes” that play the role of coordinators, determining how other genes manifest themselves (cellular determination). Proteins bind to a particular DNA sequence and control the information they release to the RNA. Human beings have a particular gene foxp2human 6 that supercharges circuits conferring cognitive flexibility and creativity. Human basal ganglia have increased synaptic plasticity that enhances motor learning, associative learning and vocal control.
The human brain cortex is made up of six layers of neurons. The distribution of the various types of neurons varies in different locations. Regions of the brain are connected by synapses that coordinate activity between cortex and subcortical basal ganglia. Basal ganglia, our reptilian carry-overs, appear to be the switching mechanisms. The cortex is the storage area for learned concepts. The root of human creativity is cognitive flexibility.
Neural Network defines the complex operational system of the human brain. A neural network consists of a large number of neurons conducting impulses in a coordinated manner, structured and operating at different brain levels, each with its own sphere of influence.
Summary Of The Neural Network Literature On Speech
Neural networks are three dimensional, operating at all levels of the brain. Functional language systems are distributed over many parts of the brain. The location and distribution can be different in different individuals. Distributed neural networks are massively redundant. Similar operations are performed in parallel redundantly in different anatomical sites. The system is dynamic, enlisting additional neuronal resources as task complexity increases. Many new circuits are formed as humans learn to execute more skilled motor programs.
People’s brains differ as much as faces, feet, teeth, hearts, immunological responses. There is no single “phrenology map” in the human brain. Different functional systems exist at different places to achieve particular goals. Individual muscles are influenced by neurons in multiple, separate locations in the motor cortex. Human neural architecture that regulates a particular aspect of behavior is neither logical, parsimonious or predictable.
Branches linking multiple control sites link to control multiple muscles. Neuronal populations coordinate to control groups of muscles to carry out particular actions. The neuronal circuits that regulate particular muscles or specific movements are not genetically specified. A given neuroanatomical structure can support many circuits projecting to different assemblages. Human brains have at their disposal alternate motor control programs that coordinate different groups of muscles to produce a motor task. “Motor equivalence” is the term that refers to the ability of the human nervous system to accomplish the same goal using different muscles or different body parts.
Speaking and Breathing
Speech is so essential to our concept of intelligence that its possession is virtually equated with being human and it is unique to human beings. The shared foodway/airway is also unique to humans. It has three main functions breathing, swallowing and speech. The shared foodway/airway in human beings is an evolutionary change resulting from erect posture and bipedalism. 7
Language and speech are learned skills, not an instinct. Speech is a learning process similar to that by which a human learns to play a violin, hit a baseball, or binocular vision. There are “sensitive” or “critical” periods during which such skills can be more readily developed. Enhanced linguistic ability cannot be differentiated from enhanced cognitive ability and other complex motor activity such as bipodal locomotion.
The ability to audibly express ourselves in languages enables our ability to think. The production of speech by human beings involves performing complex acrobatic maneuvers with the tongue, lips and larynx, using brain control of some parts that do not exist in any other living species and some that derived from species as primitive as reptiles. Subcortical basal ganglia, base structures in the reptilian brain play a key role in human speech. In the middle 1800’s, Darwin knew that with evolution, parts adapted to particular functions in one species can change to take on completely different tasks in other species.
The neural bases of human cognition evolved from primitive reptile brain cells (subcortical basal ganglia) that ultimately resulted in a complex coordination of function via interconnecting neural circuits with cortical cells to produce speech, language and cognition; functions not developed in any species besides human beings. It is important to note that the evolutionary adaptations that had to occur to get big headed human babies to successfully emerge from the birth canal are the very same ones that resulted in the production of speech, namely: 8
- Change in position of foramen magnum from behind to under the skull
- Fontanelles in newborn skull
- Disappearance of snout
- Flat face
- Smaller chin
- Shorter oral cavity
- Changes in jaw function
- Repositioning of ears behind the jaws
- Ascent of the uvula and descent of the epiglottis
- Right angle bend in tongue
- Creating compliant, flexible airway-foodway
- Bigger brains
These same evolutionary changes that resulted in upright posture, bipodalism, big heads and larger brains to facilitate functional balance and speech, caused problems as well. To orchestrate their survival as a species humans have to survive with repositioned, reconditioned, rebuilt, redesigned, miniaturized and in many cases, head parts of inferior design for olfaction, mastication swallowing, hearing, breathing and conditioning of inspired air.
OSA occurs at the first moment of inhalation. Speech only occurs on exhalation. Complex brain planning is required to coordinate breathing with speaking when a person is awake. Depending on the length of the sentence and how loud it is being spoken, there is a programmed “hold back” function to distribute even air flow during the entire intended sentence. Before a word is uttered the brain programs the lung and diaphragm to maximally hold back the initial spring force of expelled air so it doesn’t instantly collapse like a released balloon. As the lung volume falls the air pressure out is regulated by the brain to achieve level speech volume to finish the intended sentence.
Human speech is an activity of five functional systems:
1. Supraglottal lungs (including diaphragm)
2. Larynx (tension of pharyngeal muscles)
3. Supralaryngeal airway (including glossopharyngeal tongue function)
4. Mouth (and tongue hypoglossal function)
5. Respiratory control center of the brain (Pre-BotC)
In the course of human evolution, the demands of speech, coordinating the actions of the tongue, neck, hyoid bone, and big head, combined with a long, open, non-intranerial larynx characterized by ascent of the uvula and descent of the epiglottis, have compromised our survival. Human tongues, reshaped to enhance the clarity of speech and swallowing, can become fatigued or malpositioned by other functional factors such as mouth breathing, and collapse on the airway, causing choking or sleep apnea.
OSA is a dysfunction/disease that involves the same five functional systems as speech. The voluntary respiratory control center of the human brain referred to as “PreBotC” 10, involves the same five functional systems. Sports performance involves the same five functional systems. “TMJ”, Tourette’s Syndrome, spasmotic dysphonia, torticollis, bruxism all involve operation of the same five functional systems. All neural principles regarding speech are also true for the above situations.
The Future: Neuroplasticity
In 2000 the Nobel Prize for medicine was awarded to Eric Kandel for demonstrating that as learning occurs, the connections among nerve cells increase. 11 Plasticity is ongoing throughout life and involves neurons, glial and vascular cells. The brain possesses the remarkable capacity to reorganize pathways, create new connections, and even new neurons. Synapses transfer information from one neuron to the next. Constant modification of synaptic patterns involves weighting the strength and number of neurons doing the signaling.
Understanding the fundamentals of the unique human neural network operating system is emerging science. The same neural networks via coordination between cortical, neocortical brain cells and “reptilian” basal ganglia operating cranial nerves, control sleep, breathing and speech. There are no lights, colors, smells or sounds inside the brain. There are patterns of electrical information, retinas, sense receptors, cochlea in the ears which are, in energy terms, transducers. What they do is translate one form of energy into another. Electrical patterns of energy in the brain cause it to sculpt itself neuroplastically.
Early childhood is a time of rapid brain growth. At birth, every neuron in the cerebral cortex has an estimated 2,500 synapses. By the age of three, this number has grown to 15,000 synapses per neuron. An average adult, however, has about 7,500. As humans gain new experiences and learn, some connections are strengthened while others are eliminated. By a process of “synaptic pruning” 12 the brain adapts to the constantly changing environment. Structural plasticity refers to the brain’s ability to change its physical structure as a result of learning.
Different neural structures linked together in virtually unpredictable, complex circuits make up the operating system for every act and thought that human beings perform. The new operative concept that the human brain is soft-wired, has great neuroplasticity and demonstrates motor equivalence, offers tremendous possibilities that alternative sciences such as the study of speech will generate new insights and solutions to old challenges such as better treatment of OSA. Functional plasticity refers to the capacity of the brain to move functions from a damaged area to other undamaged areas. People who have suffered a stroke with loss of speech and no damage to the subcortical basal ganglia, based on the brain’s functional neuroplasticity, and extensive training, can recover their speech capability.
OSA is a disease or dysfunction that usually occurs later in life. Trained opera singers rarely get apnea. Vocal training as an alternative treatment for OSA has been shown to be effective. Thirty thousand hours of practice may change one’s structural plasticity. Angela Cain 14, in the UK, reported reducing the AHI of OSA patients by teaching singing methods. Milo Puhan 15 reported in the British Medical Journal, December 2005, that didgeridoo training significantly reduced the AHI in a group of Swiss students with OSA. Research by Katia Guimares 16 in 2009, showed that oropharyneal exercises from traditional speech therapy techniques reduced the severity of OSA. These decreases in AHI with practice indicates with a high degree of certainty that OSA does not involve subcortical basal ganglia. Natural, non-invasive techniques of activating the human brain’s own transformative capacities for healing are being currently developed by such leaders in human brain plasticity as Norman Doidge 13 and Michael Merzenich. 5
OSA and speech share the same neuroplastic, non-modular control system. It is more than just ironic that Guimares 16, using speech therapy techniques, reduced OSA levels. The conclusion suggested by this discussion is a paradox, that the same non-intranarial airway whose collapse results in OSA, but also resulted in the gift of speech may also hold the key to more successful treatment methods for OSA, better designs for oral appliances or perhaps even a cure for OSA. OH
Oral Health welcomes this original article.
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- Konnicova, M. The man who couldn’t speak and how he revolutionized psychology. Scientifid American, Feb 8, 2013, https://blogs.scientificamerican.com/literally-psyched/the-man-who-couldnt- speakand-how-he-revolutionized-psychology/
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- Moses AJ, Kalliath ET, Pacini G, Evolution of the human oral airway and apnea. Dental Sleep Practice, Winter 2017, 32–38
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- Wikipedia, https://en.wikipedia.org/wiki/Pre-B%C3%B6tzinger_ complex
- Nobel Prize Award Ceremony Speech, 2000 https://www.nobelprize.org/nobel_prizes/medicine/laureates/2000/presentation-speech.html
- Chechik G, Meilijson I, Neuronal Regulation: A Mechanism For Synaptic Pruning During Brain Maturation. Neural Computation, 1998 1-23 http://www.robotics.stanford.edu/~gal/Papers/For_Aliza/chechik_nr_del.pdf
- Doidge N, The Brain’s Way of Healing. Viking Press, 2015
- Caine A, Developing Your Voice as Part of Your Treatment Plan.Positive Health, April 2007 24-28 https://www.voicegym.co.uk/
- Puhan M, Suarez, A, et.al. Didgeridoo playing as alternative treatment for obstructive sleep apnoea syndrome: randomized controlled study. BMJ 2006;332 (7536)266-270
- Guimares KC, Drager LF, et.al. Effects of oropharyngeal exercises of patients with moderate obstructive sleep apnea syndrome. Am J Crit Care Med 2009 v179 962-966
About the Author
Allen J. Moses, DDS is an Assistant Professor of Rush University Medical School’s Department of Sleep Disorders in Chicago, Illinois; a Diplomat of The American Academy of Dental Sleep Medicine; and a Diplomat of The American Academy of Cranial Facial Pain. He is the inventor of The Moses™ oral appliance for the treatment of snoring and sleep apnea.