Extinction (neurology)

Extinction is a neurological disorder characterized by inability to recognize two simultaneous stimuli on opposite sides of the body, or proximally and distally, though either one can be sensed alone. For example, a person displaying tactile extinction could feel a thumbtack pressed into the forefinger on either side normally, but if two thumbtacks were applied simultaneously, one to each forefinger, the subject would only feel one.

Extinction is a subtle form of hemispatial neglect that is usually associated with lesions of the right parietal lobe. It is less common in lesions of the dominant (usually left) parietal lobe, possibly because the dominant hemisphere is more specialized for language than it is for visuospatial functions. More rarely, it can be seen in right frontal or subcortical lesions. Whatever the location, the extinction will manifest on the opposite side of the body.

It can take several forms including tactile, visual extinction and less commonly, auditory. In visual extinction, a person could see a blinking light in either the left or right visual field alone, but if lights blinked in both fields simultaneously, the subject would only see one(or at least see the light less efficiently). If the left-side light were the one neglected (or extinguished), the subject would presumably have a lesion on the right side of the brain.

Testing tactile, visual, or auditory extinction are useful tests of sensory hemispatial neglect. In clinical practice, extinction can be measured with double simultaneous stimulation, in which stimuli are randomly presented to the patient unilaterally and bilaterally (as well as proximally and distally for tactile) and the patient verbally communicates whether the stimulus is on the left side, right side, or both sides. In order for the results to be accurate, the examiner must first establish normal primary sensation by testing each side of the patient’s body alone, and the patient’s eyes must be closed for tactile and auditory testing.