Who Needs Emotions? The Brain Meets the Robot

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processing circuits to sensory, cognitive, motor, and other systems is likely
to be similar across emotion categories. Some progress has also been made
in understanding emotions other than fear, as will be discussed below.
The neural system underlying fear has been studied especially in the
context of the behavioral paradigm called “fear conditioning” (Blanchard,
Blanchard, & Fial, 1970; Davis, 1992; Kapp, Whalen, Supple, & Pascoe, 1992;
LeDoux, 1996, 2000; Fanselow & LeDoux, 1999). In this work, the fear
system has been treated as a set of processing circuits that detect and respond
to danger, rather than as a mechanism through which subjective states of
fear are experienced. Measurable correlates of fear include blood pressure
changes, freezing responses, and release of pituitary–adrenal stress hormones.
Through such measurements, fear is operationalized, or made experimentally
tractable. Some limbic areas turn out to be involved in the fear system,
but the exact brain areas and the nature of their involvement would never
have been predicted by the limbic system theory. This operationalization of
emotion may also lead to interesting work in robotics. The understanding of
the processing circuits that detect and respond to danger can be used to design
new types of sensor, effector, and controlling device that together would
make up an “operationally fearful” autonomous robot. The general question
of the role of fear and its complex interactions with cognition and with other
emotional circuits can then be addressed explicitly in the fully controlled
and measurable environment of the robot and can potentially give insight
into the role of fear in humans and other animals.
Before describing research on fear in detail, several other approaches to
the study of emotion and the brain that will not be discussed further should
be mentioned. One involves stimulus–reward association learning (Aggleton
& Mishkin, 1986; Everitt & Robbins, 1992; Gaffan, 1992; Ono & Nishijo,
1992; Rolls, 1998), another involves the role of septo–hippocampal circuits
in anxiety (Gray, 1982), and still another involves distinct hypothalamic and
brain-stem circuits for several different emotions (Panksepp, 1998; Siegel,
Roeling, Gregg, & Kruk 1999).
What Is Fear Conditioning?
Since Pavlov (1927), it has been known that an initially neutral stimulus (a
conditioned stimulus, or CS) can acquire affective properties upon repeated
temporal pairings with a biologically significant event (the unconditioned
stimulus, or US). As the CS–US relation is learned, innate physiological and
behavioral responses come under the control of the CS (Fig. 4.1). For example,
if a rat is given a tone CS followed by an electric shock US, after a few tone–
shock pairings (one is often sufficient), defensive responses (responses that typi-