Project: Research project

Project Details


Responsiveness for a given concentration of sucrose is influenced by both
the absolute and relative stimulus properties of the tastant. If there
is no opportunity for comparison between two disparate concentrations of
sucrose, a rat will respond to the absolute stimulus properties of each
tastant by generating more licks for a high than for a low concentration
of sucrose. This is referred to as a concentration effect. If, on the
other hand, the rat is given the opportunity for comparison, licking
behavior also will be influenced by relative stimulus properties. That
is, intake of the low concentration will be suppressed and, intake of the
high concentration enhanced, relative to non-comparison conditions. This
exaggerated response, resulting from the immediate comparison of two
different concentrations of sucrose, is referred to as a Simultaneous
Contrast Effect. Simultaneous Contrast is the behavioral expression of
the most basic form of comparison examined in the gustatory system. It
is believed to primarily reflect sensory processes, rather than the more
complex long-term memory or associative processes thought to mediate the
two other forms of consummatory contrast. While both the absolute and
relative stimulus properties of a tastant contribute to ingestion,
scientific investigation has focused almost exclusively on absolute
stimulus properties. No attempt has been made to directly evaluate the
neural mechanisms that mediate processing of the relative stimulus
properties of a tastant. Some evidence suggests that a normal
concentration-response function for sucrose reflects both absolute and
relative stimulus properties and that the isolated brainstem is both
necessary, and sufficient, to support this behavior. Thus, it seems
logical to begin the evaluation of the neural mechanisms mediating
responsiveness to the relative stimulus properties of a tastant (i.e.,
Simultaneous Contrast Effects) at the level of the first and second
gustatory relays in the brainstem. The present experiments are designed
(1) to examine the behavioral expression of Simultaneous Contrast Effects
in rats using an automated gustometer, (2) to evaluate the contribution
of the first and the second central gustatory relay in Simultaneous
Contrast in the gustometer using lesion techniques and, (30 to ascertain
the extent to which the brainstem may, in and of itself, be sufficient
for the occurrence of contrast by using a decerebrate preparation.
Effective start/end date12/1/9311/30/95


  • National Institute on Deafness and Other Communication Disorders
  • National Institute on Deafness and Other Communication Disorders


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