How the Autonomic Nervous System Responds to Pain

How the Autonomic Nervous System Responds to Pain

By David Hennessy, Clinical Psychologist

Pain is not simply a signal from injured tissues. Contemporary psychological and neuroscientific research consistently shows that pain reflects how the nervous system evaluates safety, threat, and capacity in a given moment. The autonomic nervous system (ANS) plays a central role in shaping this experience across people, contexts, and pain presentations.

Understanding pain through this lens can reduce confusion, fear, and self-blame, while opening more realistic pathways for support.

Pain as a Protective Nervous System Response

Pain arises when the brain integrates sensory input with contextual information such as past experience, emotional state, perceived threat, and environmental cues. Importantly, pain is now understood as a protective output of the nervous system, rather than a direct measure of tissue damage (1,2).

This perspective helps explain why pain can persist after tissues have healed, fluctuate with stress or fatigue, and vary significantly between individuals with similar injuries.

The Sympathetic Nervous System – Mobilisation and Defence

When pain is interpreted as threatening, the sympathetic branch of the ANS becomes more active. This system prepares the body for action and protection and often involves increased heart rate and blood pressure, muscle tension or guarding, heightened vigilance, and reduced digestion and restorative activity.

In acute situations, this response is adaptive and protective. However, evidence indicates that persistent sympathetic activation is associated with increased pain sensitivity, reduced movement confidence, and poorer outcomes in many chronic pain conditions (3,4).

The Parasympathetic Nervous System – Regulation and Recovery

The parasympathetic system, particularly via vagal pathways, supports regulation once the nervous system perceives sufficient safety. Research links parasympathetic activity with slower heart rate and steadier breathing, reduced muscle tone, improved digestion and sleep, and greater emotional and cognitive flexibility.

When pain is persistent, reduced access to parasympathetic regulation is best understood as a state-dependent nervous system pattern, not a failure of motivation or coping (5,6).

Freeze and Shutdown Responses

If pain is intense, prolonged, or associated with helplessness, the autonomic nervous system may shift into a freeze or shutdown response. This can involve emotional or bodily numbness, low energy or collapse, and slowed thinking or reduced emotional responsiveness.

These responses are well documented in both pain and trauma research and are considered biologically protective when escape or active coping feels unavailable (7).

Chronic Pain and Autonomic Sensitisation

A substantial body of research shows that chronic pain is often associated with central and autonomic sensitisation, where the nervous system becomes more efficient at detecting and amplifying threat (2,8).

As a result, pain may continue without ongoing tissue injury, smaller triggers can produce stronger responses, and symptoms may fluctuate day to day. This does not mean pain is imagined. Rather, it reflects learned neurobiological patterns shaped by experience, stress, and context.

Psychology and Pain Management

Psychology can be effective in pain management as part of a multidisciplinary approach. Australian clinical guidelines emphasise that persistent pain is best addressed through coordinated care involving medical, physical, and psychological interventions working together.

From this perspective, psychology does not aim to deny or minimise pain. Instead, it focuses on helping people understand their pain, reduce nervous system threat, improve emotional regulation, restore movement confidence, and increase engagement in meaningful life activities. These contributions are most effective when integrated with broader healthcare rather than used in isolation.

This approach is particularly relevant in conditions where nervous system dysregulation plays a central role, including functional neurological disorder (FND). You can read more about this in our article on psychology and functional neurological disorder.

A trauma-informed framework, explored further in our article on trauma-informed therapy, also helps contextualise pain responses as adaptive rather than pathological.

A Grounded and Hopeful Perspective

Across populations and conditions, the autonomic nervous system shows capacity for change. Evidence supports approaches that focus on education, pacing, graded re-engagement, emotional regulation, and restoring a sense of safety in the body (1,3,6).

Change is typically gradual and non-linear. Progress often involves increased nervous system flexibility rather than the complete elimination of pain.

Frequently Asked Questions

Can pain exist without tissue damage?
Yes. Pain reflects the nervous system’s assessment of threat and protection, not just tissue state. Pain can persist after tissues have healed due to nervous system sensitisation.

Is chronic pain psychological?
No. Chronic pain involves real neurobiological processes. Psychological factors influence pain, but they do not invalidate its physical reality.

How does psychology help with pain?
Psychology can help by addressing nervous system threat, stress responses, fear of movement, emotional regulation, and pain-related beliefs, particularly when integrated with medical and physical care.

Why does stress make pain worse?
Stress increases sympathetic nervous system activity, which heightens sensitivity and reduces the body’s capacity for regulation and recovery.

Can the autonomic nervous system calm down again?
Yes. With appropriate support, education, and pacing, the nervous system often becomes more flexible and less threat-focused over time.

References

1. Melzack, R. (1999). From the gate to the neuromatrix. Pain, 82(Suppl 1), S121–S126. https://doi.org/10.1016/S0304-3959(99)00145-1
2. Craig, A. D. (2009). How do you feel – now? The anterior insula and human awareness. Nature Reviews Neuroscience, 10(1), 59–70. https://doi.org/10.1038/nrn2555
3. McEwen, B. S. (2007). Physiology and neurobiology of stress and adaptation. Physiological Reviews, 87(3), 873–904. https://doi.org/10.1152/physrev.00041.2006
4. Villemure, C., & Bushnell, M. C. (2019). Cognitive modulation of pain. Nature Reviews Neuroscience, 20(6), 346–357. https://doi.org/10.1038/s41583-019-0122-6
5. Thayer, J. F., & Lane, R. D. (2009). Claude Bernard and the heart–brain connection. Neuroscience & Biobehavioral Reviews, 33(2), 81–88. https://doi.org/10.1016/j.neubiorev.2008.08.004
6. Kozlowska, K., et al. (2015). Stress, distress, and body symptoms. Harvard Review of Psychiatry, 23(4), 263–275. https://doi.org/10.1097/HRP.0000000000000066
7. Woolf, C. J. (2011). Central sensitization. Pain, 152(Suppl 3), S2–S15. https://doi.org/10.1016/j.pain.2010.09.030
8. Australian Pain Society. (2010). Pain in Australia: A national pain strategy.

Enquiries and Appointments

If pain is impacting your quality of life, you are welcome to enquire about appointments via Hennessy Clinical Psychology.