Taste in chimpanzees. III: Labeled-line coding in sweet taste

Area of Science:

• Neuroscience
• Sensory Biology
• Taste Perception

Background:

• The mechanism of taste coding in the peripheral nervous system is not fully understood.
• Two main theories, 'across-fiber pattern' and 'labeled line', propose different coding strategies.
• Previous research identified chimpanzee taste fibers clustering by taste quality (sweet, bitter, salt).

Purpose of the Study:

• To investigate whether specific taste fibers exclusively represent a single taste quality.
• To test the 'labeled line' theory's requirement that blocking a specific nerve line affects only one taste.
• To examine the role of the S-cluster (sweet-responsive) in sweet taste perception using chemical modulators.

Main Methods:

• Electrophysiological recordings from chimpanzee chorda tympani taste fibers.
• Application of gymnemic acids to block sweet taste responses.
• Application of miraculin to induce sweetness in response to sour stimuli.
• Analysis of fiber responses before and after chemical treatments.

Main Results:

• Gymnemic acids abolished responses to sweeteners in the S-cluster without affecting Q- (bitter) or N- (salt) clusters.
• Miraculin induced responses to acids in S-cluster fibers, which were previously unresponsive to acids.
• Gymnemic acids blocked both sweetener- and acid-induced responses in the S-cluster after miraculin treatment.

Conclusions:

• The results strongly support the 'labeled line' theory for sweet taste perception.
• Activity within the S-cluster of taste fibers is directly linked to the perception of sweet taste quality.
• Chimpanzee S-cluster fibers function as a labeled line, specifically signaling sweetness.