Interactions between olfaction and the trigeminal system: what can be learned from olfactory loss

Area of Science:

• Neuroscience
• Sensory Systems Biology
• Otolaryngology

Background:

• The olfactory and trigeminal systems are closely interconnected, with most odorants stimulating the trigeminal nerve.
• Olfactory loss is associated with decreased trigeminal sensitivity, but the mechanisms are not fully understood.
• Previous research suggests olfactory loss differentially impacts trigeminal processing stages.

Purpose of the Study:

• To investigate adaptive and compensatory changes in trigeminal system processing in individuals with acquired anosmia (AA).
• To enhance understanding of the interactive processes between the olfactory and trigeminal sensory systems.

Main Methods:

• Assessed trigeminal function at different processing levels in subjects with AA.
• Measured electrophysiological responses, event-related potentials, and psychophysical measures to irritants.
• Monitored changes in trigeminal sensitivity over a 9-month period.

Main Results:

• Subjects with AA exhibited heightened peripheral electrophysiological responses to mucosal irritants compared to controls.
• Central trigeminal processing showed reduced event-related potentials and psychophysical responses in AA subjects.
• Trigeminal sensitivity increased in AA subjects over 9 months, with further enhancement in those recovering olfactory function.

Conclusions:

• Acquired anosmia triggers dynamic, mixed sensory adaptation and compensation mechanisms.
• Trigeminal activation is elevated peripherally in AA and amplified centrally when olfactory function is restored.
• These findings illuminate the intricate interplay between olfactory and trigeminal sensory systems.