Basic HTML Version
298
ALASTAIR DOBBIN ET AL.
learning and memory . . . and plays a key role in formation storage and
consolidation of contextual fear conditioning” (Davidson, Pizzagalli,
Nitschke, & Putnam, 2001, pp. 555–556).
3. The prefrontal maintains the representation of goals and the means to
achieve them” and will “facilitate the expression of task-appropriate
responses in the face of competition with potentially stronger alterna-
tives” (Davidson et al., 2001, pp. 547–548). Particularly of interest are the
closely linked dorso-lateral prefrontal cortex (DLPFC) and the ventro
medial prefrontal cortex (vmPFC), which includes the cingulate. The
DLPFC is closely associated with working memory, and is active during
active generative visualization, executive activity, speech representa-
tions, and abstract thought (Ranganath & D’Esposito, 2005). The vmPFC
is able to directly suppress the activity of the amygdala CeA by direct
glutamatergic (excitatory) synapses with the intercalated neurons in the
lateral amygdala, which are inhibitory of the CeA (Quirk, Likhtik, Pelle-
tier, & Pare, 2003); such suppression is well documented in humans by
fMRI (Gottfried & Dolan, 2004). The DLPFC has extensive links with the
vmPFC (Ongur & Price, 2000) and so can suppress the amygdala indi-
rectly (Delgado, Nearing, Ledoux, & Phelps, 2008).
Simple “extinction” of fear conditioning—diminution of fear activ-
ity freezing and withdrawal by presentation of the conditioned stimu-
lus (CS) without the unconditioned noxious stimulus (US)—is
modulated by the vmPFC “wiring in” an override circuit to the
amygdala (Gottfried & Dolan, 2004); if “extinction does not erase con-
ditioning, it must form a new memory (a CS-no US association) that
exists in parallel with conditioning memory and is able to inhibit
expression of the conditioned response” (Milad, Rauch, Pitman, &
Quirk, 2006, p. 62). In animals the vmPFC can be (a) stimulated by elec-
trical stimulation or (b) suppressed by chemical manipulation, result-
ing in reciprocal (a) suppression or (b) activation respectively of the
amygdala (Amat, Paul, Watkins, & Maier, 2008; Quirk et al., 2003)
among other affected areas. Maier and Seligman (1976) found that
early experience of behavioral control of an electrical shock prevented
later apathy (learned helplessness—the classic animal model for
depression) in similar situations by promoting successful seeking of
control in later situations, a kind of “immunization” against such help-
lessness (Williams & Maier, 1977). Stimulating the vmPFC had the
same immunizing effect (protecting from apathy); inhibiting vmPFC
reversed the protection (Amat et al.). Evidence from different fields of
research shows that the vmPFC, as well as being activated by simple
extinction, is activated by various thinking styles and cognitive tech-
niques, many of which involve the DLPFC, for instance, instruction to
reduce sadness by adopting a “detached observer” stance (Lévesquea
et al., 2003). Reappraisal simultaneously stimulates the vmPFC while
reducing the physiological sequelae of stress (Goldin et al., 2007).
Downloaded by [ ] at 04:44 26 March 2012