222 Self and the Phenomenon of Life
b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity “9x6”Fig. 10.5. Diagram showing the circuitry of three neurons involved in Aplysia gill
retraction. Differences between habituation, sensitization and classical conditioning are
shown. Under the baseline condition, when the siphon is lightly touched, the gill retracts
weakly. On repeated touching, the response becomes weaker and weaker, until it ceases
(habituation). If the tail is shocked, causing a strong retraction of the gill, subsequent
touching of the siphon alone produces a strong retraction (sensitization). To establish
classical conditioning, the animal must be trained by being subjected to paired stim-
ulation of light touch (conditioned stimulus or CS) and electric shock (unconditioned
stimulus or US), with touch preceding shock by a short internal. The unconditioned
response (UR) of gill retraction reacting to shock becomes a conditioned response (CR)
when, at the end of training, the conditioned stimulus (light touch) alone elicits strong
gill retraction.[See Note 11: Squire & Kandel.]
“axon-dendritic” synapse between A on B. The modulatory function of
C on A leads to the increased release of glutamate from A. The differ-
ence between sensitization and classical conditioning lies in the relation
between the two stimuli (touch and shock). The former is non-associative
and non-specific, as in a situation where any harmless noise will startle