Abstract
Polygraph recordings depend on the integrity of the autonomic and central nervous systems. Neurological disorders can disrupt this relationship by altering the pathways that mediate cardiovascular, respiratory, and electrodermal responses. This article examines how neurological diseases, injuries, and neurophysiological dysfunctions affect the reliability and safety of polygraph examinations and provides examiner guidelines for case assessment and data interpretation.
1. Introduction
Polygraph instrumentation captures physiological manifestations of autonomic arousal—principally changes in heart rate, respiration, and skin conductance.
These responses are coordinated through a complex interaction between the central nervous system (CNS) and autonomic nervous system (ANS).
Neurological pathology can impair these control mechanisms, distort recorded tracings, or render the examinee unable to comprehend or participate meaningfully in the testing process.
Accurate polygraph evaluation therefore requires an understanding of how neurological and neurophysiological conditions influence autonomic reactivity and chart interpretation.
2. Autonomic Regulation and Neural Pathways
The hypothalamus, limbic system, and brainstem nuclei regulate sympathetic and parasympathetic outflow to the heart, lungs, and sweat glands.
Any structural lesion, neurochemical imbalance, or peripheral nerve damage affecting these circuits can cause abnormal physiological responses unrelated to cognitive stress or deception.
Polygraph measurements are thus valid only when these regulatory mechanisms are intact and responsive.
3. Central Nervous System Disorders
3.1 Epilepsy and Seizure Disorders
- Abnormal neuronal discharge may trigger uncontrolled autonomic changes during a test.
- Certain antiepileptic drugs (phenytoin, carbamazepine, valproate) depress sympathetic activity and flatten physiological tracings.
- Sensory overstimulation or anxiety can provoke seizures in photosensitive or stress-sensitive individuals.
Examiner protocol: Do not test subjects with poorly controlled epilepsy; obtain medical clearance for those stabilized on medication.
3.2 Stroke and Cerebrovascular Injury
- Ischemic or hemorrhagic strokes may cause asymmetrical sweating, impaired respiration coordination, or altered vascular tone.
- Cognitive deficits can reduce comprehension of test questions or impair memory recall during the pre-test interview.
Chart impact: Reduced or irregular electrodermal and cardio reactivity; potential artifacts due to spastic movements.
3.3 Traumatic Brain Injury (TBI)
Post-concussive and traumatic brain injuries often disrupt prefrontal and limbic circuits responsible for emotion regulation.
Symptoms include impulsivity, poor attention, and autonomic dysregulation (tachycardia, variable blood pressure).
Examiner consideration: Only proceed if cognitive functioning allows full understanding and voluntary consent. Document all neurological history in the case file.
3.4 Neurodegenerative Disorders
| Condition | Physiological Impact | Effect on Polygraph |
|---|---|---|
| Parkinson’s disease | Tremor, rigidity, reduced sweating | Artifacts and flat EDA |
| Multiple sclerosis (MS) | Demyelination of autonomic fibers | Inconsistent cardio/respiratory coupling |
| Alzheimer’s disease | Cognitive impairment, autonomic instability | Inability to understand or consent |
| ALS (Amyotrophic lateral sclerosis) | Respiratory muscle weakness | Distorted pneumograph tracing |
Ethical note: Individuals with progressive neurodegenerative conditions are generally considered unfit for testing once comprehension or autonomic control is impaired.
4. Peripheral Nervous System and Autonomic Neuropathy
Peripheral nerve disorders affecting sympathetic fibers lead to attenuated or absent electrodermal activity (EDA) and reduced vascular tone variability.
Common causes:
- Long-standing diabetes mellitus
- Guillain–Barré syndrome (post-infectious demyelination)
- Chronic alcohol abuse
- Toxic neuropathies (heavy metals, chemotherapy)
Result: A “flatline” EDA tracing that cannot be scored.
Polygraph examination under such conditions is scientifically invalid and must be aborted.
5. Functional and Neuropsychiatric Conditions
5.1 Psychogenic Nonepileptic Seizures (PNES)
Stress-induced motor or autonomic episodes may occur during emotionally charged testing.
Because PNES are psychogenic rather than epileptic, they do not produce reliable physiological baselines.
5.2 Conversion and Somatoform Disorders
Subjects may exhibit involuntary body movements or hyperventilation that mimic deception-related reactions but stem from unconscious psychological conflict.
Examiner strategy:
If atypical or inconsistent physiological responses are observed across charts, note potential conversion features and recommend psychological evaluation.
6. Neuropharmacology and Its Influence
| Drug Class | Example | Effect on Polygraph Tracings |
|---|---|---|
| Antiepileptics | Valproate, Carbamazepine | ↓ CNS excitability, blunted ANS response |
| Dopaminergic agents | Levodopa | Tremor artifacts, variable HR |
| Benzodiazepines | Diazepam, Lorazepam | ↓ anxiety, ↓ reactivity |
| Anticholinergics | Trihexyphenidyl | Reduced sweating, low EDA |
| SSRIs / SNRIs | Sertraline, Venlafaxine | Variable sympathetic modulation |
Medication must always be documented and considered in data interpretation. Testing may remain possible but with notation of reduced physiological amplitude.
7. Examiner Safety and Testing Environment
Subjects with known neurological conditions may experience fatigue, dizziness, or autonomic instability during extended testing.
Ensure:
- shorter chart durations,
- availability of medical assistance,
- avoidance of flickering lights or loud stimuli (especially in seizure-prone individuals).
If neurological symptoms arise mid-exam (vertigo, tremor, altered consciousness), testing must cease immediately.
8. Ethical and Legal Standards
- Competence and Consent: Examiners must verify cognitive capacity to provide informed consent.
- Medical Disclosure: Health data remain confidential under HIPAA/GDPR.
- APA Standards of Practice (2024) explicitly prohibit testing when neurological impairment may invalidate results.
- Duty of Care: The examiner’s first obligation is the examinee’s safety, not test completion.
9. Summary Table – Neurological Conditions
| Category | Typical Manifestation | Polygraph Implication | Examiner Action |
|---|---|---|---|
| Epilepsy | Seizure risk, medications | Blunted or erratic reactivity | Require medical clearance |
| Stroke / TBI | Cognitive & motor deficits | Unreliable or asymmetrical data | Evaluate comprehension |
| Parkinson’s / MS | Tremor, low EDA | Movement artifacts, low signal | Postpone or mark artifacts |
| Autonomic neuropathy | No sweating | EDA invalid | Do not test |
| Dementia | Cognitive impairment | Cannot consent | Contraindicated |
10. Conclusion
Neurological and neurophysiological disorders significantly influence polygraph validity by altering the nervous system’s ability to generate consistent autonomic responses.
Examiners must differentiate between physiological effects of pathology and those arising from deception-related arousal.
Comprehensive pre-test medical screening, awareness of medication influences, and adherence to ethical standards are indispensable to ensure both safety and scientific integrity.
References
- Kircher, J.C., & Raskin, D.C. (2017). Computerized Polygraph Techniques.
- Handler, M., & Nelson, R. (2013). APA Best Practices for Polygraph Examiners.
- Meijer, E., et al. (2019). Neurological Modulation of Autonomic Reactivity in Forensic Psychophysiology. J. Forensic Sci.
- American Polygraph Association (2024). Standards of Practice.
- ASTM E2031-17. Standard Practice for Examination of Physiological Responses to Psychological Stress.