Who Needs Emotions? The Brain Meets the Robot

92 brains
Is the Amygdala Necessary?
In spite of a wealth of data implicating the amygdala in fear conditioning, some
authors have suggested that the amygdala is not a site of US–CS association
or storage during fear conditioning (Cahill & McGaugh, 1998; McGaugh, 2000;
McGaugh & Izquierdo, 2000; McGaugh, McIntyre, & Power, 2002; McIntyre,
Power, Roozendaal, & McGaugh, 2003). They argue instead that the amygdala
modulates memories that are formed elsewhere. It is clear that there are
multiple memory systems in the brain (McDonald & White, 1993; Squire,
Knowlton, & Musen, 1993; Suzuki & Eichenbaum, 2000; Eichenbaum, 2001)
and that the amygdala does indeed modulate memories formed in other systems,
such as declarative or explicit memories formed through hippocampal
circuits or habit memories formed through striatal circuits (Packard, Cahill,
& McGaugh, 1994). However, evidence for a role of the amygdala in modulation
should not be confused with evidence against a role in US–CS association.
That the amygdala is indeed important for learning is suggested by studies
showing that inactivation of the amygdala during learning prevents learning
from taking place (Muller, Corodimas, Fridel, & LeDoux, 1997). Further, if
the inactivation occurs immediately after training, then there is no effect on
subsequent memory (Wilensky, Schafe, & LeDoux, 1999), showing that the
effects of pretraining treatment are on learning and not on processes that occur
after learning. Thus, in addition to storing implicit memories about dangerous
situations in its own circuits, the amygdala modulates the formation of explicit
memories in circuits of the hippocampus and related areas.
THE HUMAN AMYGDALA AND
COGNITIVE–EMOTIONAL INTERACTIONS
We now turn to studies on the roles of the human amygdala. Deficits in the
perception of the emotional meaning of faces, especially fearful faces, have
been found in humans with amygdala damage (Adolphs et al., 1996; Stone
et al., 2003). Similar results were reported for detection of the emotional
tone of voices (Scott et al., 1997). Further, damage to the amygdala (Bechara
et al., 1995) or areas of the temporal lobe including the amygdala (LaBar
et al., 1998) produced deficits in fear conditioning in humans. Also, damage
to the hippocampus in humans, as in rats, disrupts fear conditioning to
contextual cues (Anagnostaras, Gale, & Fanselow, 2001). Functional imaging
studies have shown that the amygdala is activated more strongly in the
presence of fearful and angry faces than happy ones (Breiter et al., 1996)
and that subliminal presentations of such stimuli lead to stronger activations
than freely seen stimuli (Whalen et al., 1998). Fear conditioning also leads