GUSTATORY CODING IN THE CAT CHORDA TYMPANI FIBERS SENSITIVE AND INSENSITIVE TO WATER

Abstract

1. Impulse discharges in single chorda tympani fibers of the cat in response to gustatory and thermal stimulations of the tongue were recorded. Fibers were classified into water-sensitive and -insensitive ones; the magnitudes of responses to 0.5 M LiCl, NaCl, CaCl₂ and SrCl₂ were significantly greater in the latter than in the former.
2. The water response in water-sensitive fibers was depressed when a small amount of salts was added to water. The maximum depressing effects were compared among cations of Cl salts and the following order was obtained: Li⁺>Na⁺>Sr⁺⁺>K⁺>Mg⁺⁺>Ca⁺⁺>NH₄⁺. An approximately inverse order was obtained regarding the stimulating action of these cations on water-sensitive fibers.
3. Statistical calculations of the frequency of responses of chorda tympani fibers to single gustatory stimuli or combinations of stimuli were made, assuming that responsiveness to any one stimulus is independent of that to other stimuli. No evidence of relatively specific sensitivity to a particular stimulus or a particular combination of stimuli was obtained in the cat.
4. Across-fiber correlation coefficients between the degrees of response to a pair of stimuli were calculated. Highly significant correlations were found between HCl and cooling, LiCl and NaCl, CaCl₂ and SrCl₂, and KCl and either MgCl₂ or NH₄Cl.