Functional Neurology: Rewiring the Brain Without Drugs
For most of the twentieth century, neuroscience carried a grim assumption: the adult brain is fixed. You get what you get.
Functional Neurology: Rewiring the Brain Without Drugs
The Brain Is Not Hardwired
For most of the twentieth century, neuroscience carried a grim assumption: the adult brain is fixed. You get what you get. Neurons die, they don’t regenerate. Circuits set in childhood are permanent. Damage is irreversible. This belief shaped everything — from how we treated stroke to how we dismissed children with learning disabilities.
It was wrong.
The revolution began with Michael Merzenich at UCSF, whose experiments in the 1980s and 1990s demonstrated that the adult cortex is continuously remodeling itself based on input and experience. Merzenich mapped the somatosensory cortex of owl monkeys and showed that when a finger was amputated, the cortical territory that had served that finger was rapidly colonized by neighboring regions. The brain was not static. It was a living map, constantly redrawing its own borders based on demand.
Norman Doidge brought this science to the public with “The Brain That Changes Itself” (2007), documenting case after case of patients recovering functions that neurology had declared permanently lost — stroke patients regaining movement years later, blind people learning to “see” through their tongues, chronic pain patients rewiring their pain circuits. The book’s message was radical in its simplicity: the brain changes in response to what you do with it.
This is neuroplasticity. And it is the foundation of functional neurology.
What Is Functional Neurology?
Functional neurology — sometimes called chiropractic neurology — emerged from the work of Ted Carrick, a chiropractor who began integrating neurological assessment and rehabilitation into clinical practice in the 1970s and 1980s. Carrick founded the Carrick Institute for Graduate Studies, which now trains clinicians worldwide in the application of neuroplasticity-based therapies.
The core premise is deceptively simple: the nervous system operates on a use-it-or-lose-it principle. Neural pathways that receive adequate stimulation remain robust. Pathways that are understimulated weaken. Functional neurology identifies which specific pathways are weak — through detailed clinical examination — and then applies targeted, receptor-based stimulation to strengthen them.
This is not vague brain training. It is precise. A functional neurologist does not say “let’s do some brain exercises.” They say: “Your right cerebellar output is diminished, causing degraded postural control on the left side, impaired smooth pursuit eye movements to the right, and past-pointing on finger-to-nose testing. We will stimulate the right cerebellum through specific proprioceptive input, targeted eye movement exercises, and vestibular activation to rebuild that pathway.”
The specificity matters. The brain does not respond to general stimulation the way a muscle responds to general exercise. It responds to precise, patterned input through specific sensory receptors. The right stimulus, to the right pathway, at the right intensity, for the right duration.
The Functional Neurological Examination
The examination in functional neurology is remarkably detailed — often 60 to 90 minutes of observation, testing, and integration. It goes far beyond the standard neurological exam taught in medical school.
Cerebellar Assessment
The cerebellum — that densely packed structure at the base of the brain containing more neurons than the rest of the brain combined — is the master coordinator. It does not initiate movement; it refines it. It does not generate thoughts; it smooths them. Cerebellar dysfunction shows up as:
- Dysmetria: Overshooting or undershooting on finger-to-nose or heel-to-shin testing
- Dysdiadochokinesia: Impaired rapid alternating movements (flip the hand back and forth — a weak cerebellum makes this clumsy and irregular)
- Intention tremor: Tremor that worsens as the hand approaches a target
- Gait ataxia: Wide-based, unsteady walking
- Rebound phenomenon: Inability to check movement (push down on the patient’s arm, release suddenly — the arm overshoots upward)
Each cerebellar hemisphere controls the ipsilateral (same side) body. Right cerebellar weakness shows up in the right arm and leg.
Oculomotor Testing
The eyes are a window into the brainstem, cerebellum, frontal lobes, and parietal lobes simultaneously. Functional neurologists spend more time examining eye movements than perhaps any other clinicians.
Saccades — rapid, ballistic eye movements from one target to another. The frontal eye fields (prefrontal cortex) initiate voluntary saccades. The superior colliculus and brainstem paramedian pontine reticular formation execute them. A hypometric saccade (undershooting the target, requiring a corrective second jump) suggests cerebellar or brainstem dysfunction. Slowed saccades suggest brainstem pathology. Inaccurate anti-saccades (looking the wrong direction when asked to look opposite the target) suggest impaired frontal lobe inhibition — relevant in ADHD and TBI.
Smooth pursuits — the ability to track a slowly moving target. This requires the parieto-occipital cortex, vestibular nuclei, cerebellum (flocculus and paraflocculus), and brainstem. Jerky or broken pursuit — “cogwheel” tracking — indicates breakdown in the pursuit circuit. Each direction of pursuit is controlled by different brain regions, so directional asymmetries provide localizing information.
Optokinetic nystagmus (OPK) — the reflexive eye movement generated by watching a repeating visual pattern (like watching telephone poles from a moving car). OPK testing evaluates the integrity of the parietal cortex, brainstem, and cerebellar pathways. Asymmetric OPK responses indicate hemispheric or brainstem asymmetry.
Vestibulo-ocular reflex (VOR) — head rotation should produce equal and opposite eye movement to stabilize the visual image. VOR testing (head impulse test, rotational chair, video head impulse test — vHIT) evaluates the semicircular canals, vestibular nerve, vestibular nuclei, and their connections to the oculomotor system.
Vestibular Testing
Balance is not a single system — it is a three-legged stool: vision, proprioception (joint position sense), and the vestibular apparatus. Functional neurology assesses each leg independently and then evaluates how the brain integrates them.
Romberg testing (standing with feet together, eyes open then closed) isolates proprioception. Foam pad testing reduces proprioceptive input. Tandem walking (heel-to-toe) challenges the vestibulospinal system. Dynamic posturography (computerized or clinical) measures postural sway under varying conditions.
Cortical Function Mapping
Higher cortical functions are assessed through:
- Frontal lobe: Executive function, impulse control, working memory, verbal fluency, motor planning
- Parietal lobe: Spatial awareness, graphesthesia (recognizing numbers drawn on the skin), stereognosis (identifying objects by touch), two-point discrimination
- Temporal lobe: Auditory processing, memory, language comprehension (Wernicke’s area)
- Occipital lobe: Visual processing, pattern recognition, visual field integrity
Each finding is not treated as an isolated abnormality but as a data point in a functional map of the entire nervous system.
Hemispheric Asymmetry
One of the more controversial — and clinically productive — concepts in functional neurology is hemispheric asymmetry, particularly as developed by Robert Melillo in his work with children.
The two cerebral hemispheres are not identical. They have different functions, different neurochemistry, and different developmental timelines. The left hemisphere tends toward detail, language, sequential processing, and approach behavior. The right hemisphere tends toward gestalt perception, emotional processing, social awareness, body awareness, and withdrawal/avoidance behavior.
Melillo proposed that many developmental disorders — ADHD, autism spectrum, dyslexia, OCD, Tourette syndrome — represent not global brain dysfunction but functional disconnection between hemispheres, often driven by developmental immaturity of one hemisphere relative to the other. He called this “functional disconnection syndrome” and described specific patterns:
- Right hemisphere deficiency: Poor social skills, poor body awareness, poor coordination, weak immune regulation, emotional dysregulation — often presenting as autism spectrum or nonverbal learning disability
- Left hemisphere deficiency: Poor reading, writing, or language processing, poor fine motor control, poor sequential processing — often presenting as dyslexia or language-based learning disabilities
His Brain Balance Achievement Centers apply this framework through hemispheric-specific stimulation — sensory, motor, cognitive, and nutritional interventions targeted to the underdeveloped side. The approach remains debated in mainstream neurology, but the clinical outcomes reported by practitioners are difficult to dismiss entirely. Melillo’s “Disconnected Kids” (2009) laid out the framework for parents and clinicians.
The key insight, regardless of where one stands on Melillo’s specific model, is that the brain should be assessed for regional imbalances, not just global dysfunction. A brain that is strong on one side and weak on the other will not function well — not because anything is broken, but because the integration between hemispheres is insufficient.
Receptor-Based Therapies
The therapeutic approach in functional neurology is stimulus-specific. The nervous system has distinct receptor types — proprioceptors in joints, mechanoreceptors in skin, vestibular receptors in the inner ear, photoreceptors in the retina, chemoreceptors, baroreceptors. Each feeds into specific pathways and brain regions.
Proprioceptive stimulation: Joint manipulation (the chiropractic adjustment) generates a massive burst of proprioceptive input — type I and type II mechanoreceptors, Golgi tendon organs, muscle spindles. This is why Carrick began with chiropractic: the adjustment is not just about joint mobility. It is a neurological event. Specific adjustments to specific spinal segments (or extremities) can be used to drive input into specific spinal cord levels, which in turn feed specific brain regions.
Vestibular rehabilitation: Head positioning, rotational exercises, balance challenges — all calibrated to the specific canal or otolith organ that is underperforming. Unilateral vestibular stimulation (caloric testing, rotational chair) can drive input to a specific hemisphere through the vestibular nuclei.
Visual therapies: Saccade training, pursuit training, convergence exercises, prism lenses — each targets specific oculomotor circuits. A patient with weak left frontal eye field function might do rightward saccade training to fire that pathway.
Auditory stimulation: Filtered music, specific frequency ranges, dichotic listening exercises — can be used to stimulate temporal lobe function.
Olfactory stimulation: The olfactory nerve is the only cranial nerve with direct cortical input (no thalamic relay). Specific scents can activate the limbic system, hippocampus, and prefrontal cortex.
The dosing matters. Too little stimulation produces no change. Too much stimulation can exhaust a weakened pathway — a phenomenon called metabolic exhaustion — causing temporary worsening. The functional neurologist must find the therapeutic window: enough to drive plasticity, not so much that it overwhelms the system. Sessions are often short (15-30 minutes) with precise intensity. A patient might do three specific exercises for five minutes each, twice a day, and nothing more. Precision over volume.
Integration with Functional Medicine
Here is where functional neurology and functional medicine become inseparable. Neuroplasticity does not occur in a vacuum. The brain needs specific raw materials and metabolic conditions to rewire:
Inflammation blocks plasticity. Chronic systemic inflammation — from gut dysbiosis, food sensitivities, infections, or toxins — activates microglia and shifts the brain into a defensive mode that suppresses neuroplastic change. You cannot rehabilitate a brain that is on fire. The IFM approach of identifying and resolving inflammatory triggers is not optional — it is prerequisite.
Blood sugar dysregulation starves neurons. The brain consumes 20% of the body’s glucose despite being 2% of its mass. Insulin resistance in the brain (Type 3 diabetes) means neurons cannot access their primary fuel. Metabolic optimization — through diet, exercise, and targeted supplementation — provides the energy substrate for rewiring.
Sleep is when consolidation happens. Neuroplastic changes initiated during daytime training are consolidated during deep NREM sleep. Without adequate sleep, the rehabilitation gains are lost overnight.
Nutritional cofactors for neuroplasticity. Omega-3 DHA (membrane fluidity for new synaptic connections), magnesium L-threonate (synaptic density, MIT research), B vitamins (methylation and myelination), BDNF support (exercise, lion’s mane mushroom, curcumin), and adequate protein (amino acids for neurotransmitter synthesis) are all essential.
Gut health affects brain function directly. The vagus nerve carries information from the gut microbiome to the brainstem and limbic system. Dysbiosis alters neurotransmitter production (90% of serotonin is produced in the gut). Lipopolysaccharide (LPS) from gram-negative bacteria crosses a permeable gut barrier and activates brain inflammation. Functional neurology without gut healing is building a house on sand.
Conditions Addressed
Functional neurology has been applied to a wide range of neurological conditions:
Traumatic brain injury and concussion — perhaps the most compelling application. Post-concussion syndrome often reflects specific pathway dysfunction (vestibular, oculomotor, autonomic, cervicogenic) that can be identified and rehabilitated. Standard neurology offers “rest and time.” Functional neurology offers targeted rehabilitation.
Vertigo and dizziness — BPPV, vestibular neuritis, vestibular migraine, persistent postural-perceptual dizziness. Vestibular rehabilitation is evidence-based and widely accepted, but functional neurology brings a more granular assessment of which specific pathways are impaired.
Dysautonomia — POTS, orthostatic intolerance, vasovagal syncope. Autonomic regulation depends on brainstem nuclei (nucleus tractus solitarius, dorsal motor nucleus of the vagus, rostral ventrolateral medulla) that can be influenced through specific interventions — cold exposure, breathing exercises, vestibular input, vagal toning.
ADHD and learning disabilities — Melillo’s hemispheric model, Dianne Craft’s brain integration therapy, vision therapy for convergence insufficiency (which mimics ADHD symptoms), auditory processing training.
Movement disorders — Dystonia, essential tremor, and functional movement disorders often respond to targeted cerebellar and basal ganglia rehabilitation strategies. Parkinson’s-specific programs (LSVT BIG, PWR!) incorporate neuroplasticity principles.
Chronic pain — Central sensitization and pain neuroscience education combined with targeted desensitization protocols, graded motor imagery, and mirror therapy — all neuroplasticity-based interventions that change the brain’s pain processing rather than masking the output with medication.
The Philosophical Shift
Functional neurology represents a fundamental shift in how we think about the nervous system. Rather than asking “what is damaged?” it asks “what is underperforming, and can we train it?” Rather than labeling and medicating, it assesses and rehabilitates. Rather than waiting for the brain to heal passively, it actively drives the healing through targeted stimulation.
The brain is not a computer that is either working or broken. It is more like an orchestra — and functional neurology is the process of finding which instruments are out of tune, which musicians have stopped playing, and systematically bringing them back into harmony.
Combined with functional medicine’s ability to clear the metabolic barriers to neuroplasticity — inflammation, dysbiosis, nutritional deficiency, hormonal imbalance, toxic burden — the result is a comprehensive model of brain rehabilitation that neither discipline could achieve alone.
If the brain can change itself, what responsibility do we have to provide it the right conditions and the right inputs to change in the direction of healing?