Can a nonresponsive patient with brainstem activity, possibly due to severe brain injuries or conditions such as stroke or traumatic brain injury, experience pain?

Can Nonresponsive Patients with Brainstem Activity Experience Pain?

Yes, nonresponsive patients with brainstem activity can likely experience nociception (the neural encoding of noxious stimuli), but whether they experience the subjective, conscious perception of pain depends critically on the integrity of their cortical structures and thalamocortical connections—not just brainstem function alone.

Critical Distinction: Nociception vs. Pain Experience

The International Association for the Study of Pain emphasizes that nociception and pain are fundamentally different phenomena 1, 2.

• Nociception refers to the neural process of encoding noxious stimuli and can occur without conscious pain perception 1, 2
• Pain requires intact cortical processing, functional connectivity between multiple brain regions (including somatosensory, insular, cingulate, and prefrontal cortices), and conscious awareness 1

What Brainstem Activity Alone Can Support

Patients with only brainstem function can demonstrate:

• Reflexive withdrawal responses to noxious stimuli through spinal reflex arcs, which do not require pain perception 1
• Autonomic responses (changes in heart rate, blood pressure, pupillary dilation) that reflect nociceptive processing but not necessarily conscious suffering 1, 2
• Brainstem-mediated nociceptive signaling through structures like the periaqueductal grey and rostroventral medulla 1

However, these responses do not confirm conscious pain experience 1.

Neuroanatomical Requirements for Pain Perception

For a patient to consciously experience pain (not just nociception), the following must be intact 1:

1. Thalamocortical connections that relay sensory information from the thalamus to the cortex (develop between 24-32 weeks gestation in fetal development, as a reference point) 1
2. Functional cortical structures including:
   • Primary and secondary somatosensory cortices (for sensory-discriminative aspects) 1
   • Insular cortex (for emotional/affective components) 1
   • Anterior cingulate cortex (for suffering and emotional processing) 1
   • Prefrontal cortex (for cognitive-evaluative aspects) 1
3. Intact connectivity between these regions forming the "dynamic pain connectome" 1

The classic example: lobotomy patients could describe the location and intensity of noxious stimuli but experienced no suffering because the prefrontal cortex was disconnected from other brain regions 1.

Clinical Assessment in Nonresponsive Patients

Assessment Tools for Different States of Consciousness

For nonresponsive patients, use structured assessment to determine the level of brain function 1, 3, 4:

• FOUR Score is superior to Glasgow Coma Scale for assessing brainstem function in nonresponsive patients, evaluating eye responses, motor responses, brainstem reflexes, and respiratory patterns 1, 3, 4
• Nociception Coma Scale-Revised (NCS-R) can assess nociceptive responses in patients with severe disorders of consciousness like vegetative state or minimally conscious state 1

Key Clinical Scenarios

Vegetative State/Unresponsive Wakefulness Syndrome:

• These patients show brainstem activity and sleep-wake cycles but lack cortical awareness 5
• Traditional teaching suggests they cannot experience pain, only nociception 5
• However, patients with cognitive motor dissociation (CMD)—who appear vegetative but show awareness on functional neuroimaging—likely can experience pain 5

Minimally Conscious State:

• These patients have partial preservation of cortical function and likely can experience some form of pain 1, 5

Practical Clinical Approach

When to Assume Pain Capacity Exists

Err on the side of assuming pain capacity is present when 1, 2:

1. Any evidence of cortical function exists beyond pure brainstem reflexes
2. The patient shows purposeful motor responses (even inconsistently)
3. Visual tracking or command-following is present (even intermittently)
4. Advanced neuroimaging suggests preserved thalamocortical connectivity

Pain Management Strategy

Provide appropriate analgesia for potentially painful procedures or conditions in all nonresponsive patients with brainstem activity 1, 2:

• Brain-injured patients in neurocritical care experience more significant pain than initially presumed 1
• Up to 70% of neurocritical care patients can self-report pain when able; the remainder require clinician-rated assessment 1
• Use the Behavioral Pain Scale (BPS) for clinician-rated pain assessment in nonresponsive patients 1

Important Caveats

• Sedation, opioids, and neuromuscular blockade confound all neurological assessments and must be accounted for 1, 3
• Autonomic responses and reflexive movements do not prove pain perception but should prompt consideration of analgesia 1, 2
• Current brain imaging cannot definitively determine if an individual patient is experiencing pain, as many brain activity patterns associated with pain are not specific to pain 1

Bottom Line for Clinical Practice

Treat nonresponsive patients with brainstem activity as if they may be capable of experiencing pain, particularly when:

• Cortical structures appear intact on imaging 1
• The patient shows any behavioral responses beyond pure brainstem reflexes 1, 3
• Potentially painful conditions or procedures are present 1, 2

The presence of brainstem activity alone is insufficient for pain experience, but the absence of behavioral responsiveness does not exclude the possibility of conscious pain perception, especially in cases of cognitive motor dissociation 5.