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Classical conditioning of the gill-withdrawal reflex in Aplysia. (Adapted, with permission, from Hawkins et al. 1983.)
A. The siphon is stimulated by a light touch and the tail is shocked, but the two stimuli are not paired in time. The tail shock excites facilitatory interneurons
that form synapses on the presynaptic terminals of sensory neurons innervating the mantle shelf and siphon. This is the mechanism of sensitization. 1.
The pattern of unpaired stimulation during training. 2. Under these conditions the size of the motor neuron EPSP is only weakly facilitated by the tail shock.
In this example the EPSP actually decreases slightly despite the tail shock because repeated unpaired stimulation of the siphon leads to synaptic
depression. Source: Cellular Mechanisms of Implicit Memory Storage and the Biological Basis of Individuality, Principles of Neural Science, Fifth Editon
B. The tail shock
is paired
of Jessell
the siphon.
1. The siphon
touched (conditioned
stimulus orofCS)
immediately
priorEditon;
to shocking
the tail
Citation:
Kandelwith
ER, stimulation
Schwartz JH,
TM, Siegelbaum
SA,isHudspeth
AJ, Mack S. Principles
Neural
Science, Fifth
2012 Available
(unconditioned stimulus
or
US).
As
a
result,
the
siphon
sensory
neurons
are
primed
to
be
more
responsive
to
input
from
the
facilitatory
interneurons
in the
at: http://mhmedical.com/ Accessed: May 05, 2017
unconditioned
pathway.
This
is
the
mechanism
of
classical
conditioning;
it
both
amplifies
the
response
of
the
conditioned
pathway
and
restricts
the
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amplification to that pathway. 2. Recordings of EPSPs in an identified motor neuron produced by the siphon sensory neurons before training and one hour