Adaptation to capsaicin within and across days

Area of Science:

• Sensory science
• Neuroscience
• Pharmacology

Background:

• Capsaicin, the active component in chili peppers, elicits a burning sensation through activation of the transient receptor potential vanilloid 1 (TRPV1) channel.
• Sensory adaptation, a decrease in response to a constant stimulus, is a common phenomenon in sensory systems.

Purpose of the Study:

• To investigate the time-course of capsaicin-induced oral burn and explore sensory adaptation over repeated exposures.
• To model the adaptation process using mathematical analysis.

Main Methods:

• Subjects were exposed to 100 ppm capsaicin on the tongue on Day 1 and Day 5.
• Between Day 1 and Day 5, subjects consumed hard candy containing capsaicin on Days 2-4.
• The time-course of the burn sensation was recorded, and data were fitted to a mathematical model.

Main Results:

• On Day 1, capsaicin burn intensity did not show rapid adaptation, plateauing after approximately 16 minutes or rising monotonically for 34 minutes.
• By Day 5, the perceived intensity of the capsaicin burn was significantly reduced compared to Day 1.
• Mathematical modeling indicated that adaptation across days was primarily due to changes in the gains of three underlying neural processes.

Conclusions:

• Repeated, intermittent exposure to capsaicin leads to significant oral sensory adaptation.
• The observed cross-day adaptation can be explained by modifications in the gain of specific neural pathways involved in processing the capsaicin stimulus.
• These findings contribute to understanding the mechanisms of sensory adaptation and the neurophysiology of taste and chemesthesis.