Journal of Neuroscience, Vol 8, 3000-3010, Copyright © 1988 by Society for Neuroscience
Differential expression of pseudoconditioning and sensitization by siphon responses in Aplysia: novel response selection after training
MT Erickson and ET Walters
Department of Physiology and Cell Biology, University of Texas Medical School, Houston 77225.
Nonassociative training with a noxious unconditioned stimulus (US) applied
to the head or tail of freely moving Aplysia caused a qualitative change in
siphon responses to midbody test stimulation, so that the midbody test
responses came to resemble the unconditioned siphon response (UR) to the US
when tested 1 d after exposure to the US. Such a nonassociative, US-induced
transformation of test responses into responses resembling the UR has
traditionally been termed "pseudoconditioning." Short-term
pseudoconditioning was compared to sensitization and to habituation in a
reduced preparation that used a photocell to distinguish "head-type" siphon
responses from qualitatively different "tail-type" responses.
Transformation of test responses (pseudoconditioning) was observed only
when the type of preexisting alpha response to the midbody test stimulus
was different from the UR. Sensitization, defined as a US-induced
enhancement of the alpha response to the test stimulus, was observed when
the initial alpha response and the UR were of the same type. General
sensory facilitation was excluded as a critical mechanism for
pseudoconditioning by the observation that the same midbody test response
could be transformed to either a head-type or tail-type response, depending
on the site of the US, and by the observation that simply increasing the
intensity of the midbody test stimulus in the absence of a head or tail US
did not produce similar response transformations. These studies demonstrate
pseudoconditioning in a preparation amenable to analysis at the level of
identified neurons, and draw attention to a distinctive and widespread form
of behavioral modifiability that has been neglected by investigators of
learning.