Extinction refers to the inability to perceive one of two stimuli presented simultaneously, typically observed in patients with neurological deficits. The phenomenon is primarily assessed in neurology but also has definitions in neurophysiology and psychology:

1. Neurology: Failure to perceive one stimulus when two corresponding stimuli are applied simultaneously on opposite sides of the body.

2. Neurophysiology: Loss of excitability of a nerve, synapse, or nervous tissue in response to stimuli that were previously adequate.

3. Psychology: Disappearance of a conditioned reflex due to lack of reinforcement.

Pathophysiology

• Neurological extinction: Usually results from lesions of the parietal lobe, particularly the right hemisphere, which impairs spatial attention and sensory integration.

• Neurophysiological extinction: Occurs when synaptic transmission or neuronal excitability is compromised due to injury, metabolic dysfunction, or pharmacologic suppression.

• Psychological extinction: Based on classical conditioning principles, occurs when a conditioned stimulus is no longer paired with reinforcement, leading to gradual loss of the conditioned response.

Examination Technique (Neurological Extinction)

• Patient positioning: Have the patient seated or lying comfortably.

• Instruction: Ask the patient to close the eyes or focus on a point to prevent visual cues.

• Stimulation: Simultaneously touch or apply light pressure to corresponding areas on both sides of the body (e.g., both hands or both cheeks).

• Assessment: Ask the patient to report all areas being stimulated.

• Interpretation:

  • Positive extinction: The patient fails to detect one of the stimuli (usually the contralesional side).

  • Normal: Both stimuli are perceived accurately.

Clinical Utility

• Localization: Helps identify parietal lobe lesions, often due to stroke, traumatic brain injury, or tumors.

• Monitoring recovery: Can track improvement in sensory integration and attentional deficits.

• Adjunct to neurological examination: Often assessed alongside hemianesthesia, neglect, and visual field deficits.

Differential Diagnosis

Pediatric considerations

• Extinction testing is limited in young children due to difficulty following instructions.

• Behavioral observation can provide indirect assessment of sensory awareness.

Geriatric considerations

• More common in older adults with stroke or neurodegenerative disorders.

• May co-exist with neglect, confusion, or dementia.

Limitations

• Requires patient cooperation and attention.

• Subtle extinction may be missed without careful repeated testing.

• Should be interpreted alongside other neurological findings, imaging, and history.

Patient counseling

• Explain the test is part of neurological examination to assess sensory and attention functions.

• Reassure patients that failure to detect some stimuli may indicate brain injury or temporary impairment, not intentional neglect.

• Discuss rehabilitation strategies if extinction is detected, such as sensory retraining and occupational therapy.

Conclusion

Extinction is an important neurological sign of impaired sensory perception and attention, commonly due to parietal lobe lesions. Understanding and detecting extinction helps clinicians localize cortical dysfunction, monitor recovery, and guide rehabilitation strategies.

References

1. Halligan PW, Fink GR, Marshall JC, Vallar G. Spatial cognition: Evidence from visual neglect. Trends Cogn Sci. 2003;7(3):125–133.

2. Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science. 5th ed. New York: McGraw-Hill; 2013.

3. Ropper AH, Samuels MA, Klein JP. Adams and Victor’s Principles of Neurology. 11th ed. New York: McGraw-Hill; 2021.

4. Bouton ME. Learning and behavior: A contemporary synthesis. 3rd ed. Sunderland, MA: Sinauer Associates; 2016.