Interactions between the chemical senses: trigeminal function in patients with olfactory loss

Area of Science:

• Neuroscience
• Sensory Science
• Ophthalmology

Background:

• The intranasal trigeminal nerve and olfactory system have intricate connections.
• Acquired olfactory loss is linked to diminished trigeminal sensitivity due to disrupted central nervous system (CNS) interactions.
• The orbitofrontal cortex and rostral insula are crucial for amplifying trigeminal input, a function impaired in olfactory loss.

Purpose of the Study:

• To investigate the impact of olfactory loss on trigeminal nerve sensitivity.
• To explore the role of central nervous system interactions in trigeminal-olfactory pathways.
• To examine potential adaptive mechanisms in trigeminal responsiveness in individuals with hyposmia or anosmia.

Main Methods:

• This study reviews existing evidence on the neuroanatomical and functional connections between the trigeminal and olfactory systems.
• It analyzes the consequences of olfactory dysfunction on trigeminal sensory perception.
• The research considers the involvement of specific brain regions like the orbitofrontal cortex and rostral insula.

Main Results:

• Acquired olfactory loss leads to reduced trigeminal sensitivity, attributed to the absence of crucial central nervous system interactions.
• The amplification of trigeminal input, normally facilitated by the orbitofrontal cortex and rostral insula, is significantly diminished in patients with olfactory loss.
• Conversely, peripheral adaptive mechanisms appear to enhance trigeminal responsiveness in individuals experiencing hyposmia or anosmia.

Conclusions:

• Olfactory system integrity is vital for maintaining normal trigeminal sensitivity through central nervous system pathways.
• While central processing of trigeminal input is compromised by olfactory loss, peripheral adaptations may partially compensate.
• Further research is warranted to fully elucidate the complex interplay between the trigeminal and olfactory systems and their implications for sensory processing.