Learning and Memory Mechanisms Involved in Compulsive Drug Use and Relapse - Drugs of Abuse: Neurological Reviews and Protocols - page 83

Cravings may be indications of cognitive confl ict rather than the “cause” of
relapse—which very often happens on just those occasions when no such
confl ict occurred.
Acting deliberately vs habitually is not an all-or-nothing distinction. An
accurate account of drug abuse will likely incorporate multiple levels of habits,
motivations, and cognitive control. Rather than relying on a wholly distinctive
pathophysiology, addiction can be seen as an extension or exaggeration of
our normal human diffi culties with controlling our behavior to conform with
long-term personal or societal goals.
Viewed perhaps simplistically, the failure of executive control might arise
either from specifi c, strong habits that are intrinsically “hard” to overcome, or
from a more general defi cit in executive function. In fact, both may be important,
particularly in certain subpopulations. Some neuropsychological tests of drug
abusers have found defi cits in PFC functions (92 , 93) . General problems with
self-control may account for why substance abuse has higher prevalence in
subjects with comorbid additional psychiatric conditions. Naturally occuring
individual variation in aspects of executive control such as impulsivity (94 , 95)
may also contribute to the poorly understood issue of why some people are more
vulnerable to drug addiction than others. But it is also important to understand
that an abstinent former drug abuser trying to avoid relapse may be effectively
bombarded by drug-related cues and contexts unless a drastic break is made with
former friends, locations, and so forth. Even a normal, functional mechanism
for inhibitory/supervisory control that was 99% effective would not prevent
relapse within a few months if faced with daily challenges.
Lumping most PFC processes together under the label of “executive control”
is obviously a crude approximation. Other areas may also contribute to execu-
tive processes, and within frontal cortex distinct subregions can subserve
distinct aspects of executive functioning (reviewed in 96 , 97 ). It is not clear
what neural processes are involved in normal “predecisions” to bring into
working memory the relevant features of competing behavioral options and
their likely outcomes. One can speculate that, for example, communication
between hippocampus and prefrontal cortical regions may provide essential
information about whether the current “episode” of experience is entirely
routine or requires more on-line monitoring. Emotional “alert” cues may
also be important for this process of engaging adaptive decision-making
(98) . This and other aspects of evaluative processing may rely especially on
orbitofrontal cortex (99 , 100) ,while response selection may be more dependent
on dorsolateral PFC (101) . The continuing development and application of
sophisticated neuropsychological tests in conjunction with neuroimaging