Project Details


It has been long established that the expression of a memory does not
necessarily reflect the underlying strength of the memory trace. In
particular, it is known that a conditioned response based on an
associative memory might reflect not only the associative "strength" of
the memory, but also such factors as the animal's motivation to respond,
competition between other cues present at the time of training or testing,
and whether the memory was stored in a form which is readily retrievable.
In the present series of experiments, we will examine several such
determinants of responding in a simple organism using an associative
learning task.

For nearly thirty years, a "simple systems" approach has dominated the
exploration of the neurophysiological mechanisms underlying memory
formation. For instance, using model systems such as habituation and
sensitization in Aplysia and associative eyeblink conditioning in the
rabbit, many of the biophysical and biochemical events which are critical
to memory formation have been elucidated, and in the case of vertebrate
models, an appreciation of the anatomical substrates of certain memories
has been achieved. While this approach has been quite successful, much of
what psychologists consider to be fundamental memory processes have
received relatively little attention. In the present proposal, several
general classes of experiments are planned, focusing on the Interaction
between training variables (i.e., number and distribution of training
trials) and the induction and subsequent retentIon of an associative
memory in Hermissenda. Many of these variables have been assessed at the
behavioral level in vertebrate species. For instance, it is well
established that retention is influenced by the number of initial training
trials, and the rate at which the successive trials are presented.
Moreover, it has been demonstrated that postconditioning exposure to
components of the initial learning event (e.g., the CS, the US, or the
training context) can either facilitate or retard subsequent responding
depending on such factors as the number of exposures to these stimuli, and
the strength of the original memory trace. Using Hermissenda we will
attempt to establish parameters by which facilitated reacquisition
following memory degradation may be observed, and to determined when post-
training cuing treatments (i.e., brief exposure to the CS, the US, or the
training context) are effective. These experiments, which are conceptually
based in the vertebrate learning literature, are to be undertaken in
Hermissenda for several reasons. First, given the capacity to condition
Hermissenda using in vitro techniques, it should be possible to examine
biophysical and biochemical properties of cells involved in memory
formation during each stage of memory processing. Second, associative
learning in Hermissenda occurs within a narrow range of parameters, and
depending on the number of training trials, the effective retention
interval can be as short as several minutes or as long as seven to ten
days. In total, these two features (capacity for neurophysiological
analysis during in vitro procedures and strict control of the capacity for
retention) provides a unique opportunity to study the neurophysiological
mechanisms underlying these simple psychological processes.
Effective start/end date1/1/9512/31/96


  • National Institute of Mental Health
  • National Institute of Mental Health


  • Animal Science and Zoology


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