Who Needs Emotions? The Brain Meets the Robot

asic principles for emotional processing 89
Thalamus
CS
(tone)
Auditory Cortex
Behavior
Figure 4.2. The neural pathways involved in fear conditioning are well
characterized. When the conditioned stimulus (CS) is acoustic, the pathways
involve transmission to the lateral nucleus of the amygdala (LA) from
auditory processing areas in the thalamus and auditory cortex. LA, in turn,
projects to the central nucleus of the amygdala (CE), which controls the
expression of fear responses by way of projections to brain-stem areas
controlling the autonomic nervous system, the production of hormones, and
the appropriate behavior.
1997). Although some lesion studies have questioned the ability of the thalamic
pathway to mediate conditioning (Shi & Davis, 1999), recordings from
single neurons show that the cortical pathway conditions more slowly over
trials than the thalamic pathway (Quirk, Armony, & LeDoux, 1997), thus
indicating that the association between CS and US in the amygdala occurs
initially through the thalamic pathway. Recent functional magnetic resonance
imaging (fMRI) studies in humans have found that the amygdala shows
activity changes during conditioning that correlate with activity in the thalamus
but not the cortex (Morris, Ohman, & Dolan, 1999), further emphasizing
the importance of the direct thalamo-amygdala pathway.
In addition to expressing fear responses to the CS, rats exhibit these when
returned to the chamber in which the tone and shock were paired or a chamber
in which shocks occur alone. This is called “contextual fear conditioning,”
where context refers to the various visual and olfactory aspects of the chamber,
and requires both the amygdala and hippocampus, a brain structure
know to enable long-term memories (Kim & Fanselow, 1992; Phillips &
LeDoux, 1992; Maren, Aharonov, & Fanselow, 1997; Frankland et al.,
1998). Areas of the hippocampus project to B and AB in the amygdala
(Canteras & Swanson, 1992), and damage to these areas interferes with
contextual conditioning (Maren & Holt, 2000). Hippocampal projections
to B and AB thus seem to be involved in contextual conditioning (for a
LA
CE
Autonomic
system
Hormones