LeDoux, Joseph E. Emotions: How Ive Looked for Them in the Brain."
Joseph E. LeDoux specializes
in the use of animal models for studying emotion. In Emotions: How Ive Looked
for Them in the Brain, LeDoux describes his work on fear conditioning in rats.
The rats are conditioned to associate a sound with a noxious stimulus. This
sound then elicits the behavioral responses accompanying the emotional
experience of fear: muscle tension, release of stress hormones, and so forth.
Note that LeDoux distinguishes between the behavioral system and subjective
feelings. It is the former, he argues, that should be seen as essential to
understanding the function of emotions.
LeDoux uses a variety of
techniques to relate fear behavior to specific circuits in the brain. First,
lesion studies (selective damage to parts of the brain) and brain imaging
techniques make it possible to locate the general regions involved. Next the
circuits activated in fear responses can be followed by injecting tracer substances
into those areas and recording the firing patterns of neurons in relation to
various emotional states under a variety of learning paradigms. In this way,
LeDoux has confirmed the crucial role of the amygdala, a distinctive cluster of
neurons found deep in the anterior temporal lobe of each hemisphere. Inputs to
the amygdala from sensory processes in the thalamus and cortex are key to
processing fear stimuli, while projections from the amygdala to brainstem areas
are involved in control of the behavioral, autonomic, and hormonal responses
that constitute fear behavior. LeDoux notes that a variety of other brain
systems are also involved in the various feeling states we term emotions in
humans; only empirical research will show whether his work on fear generalizes
to other emotions.
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