A self in the mirror: mirror neurons, self-referential processing, and substance use disorders.

Mirror neurons in the Rhesus monkey and the mirror neuron system (MNS) in the human brain respond to actions that are executed by self and observed in another animal or person (i.e., imitated). The status of the MNS in humans is unclear, with some positive and some negative findings using electroencephalography and functional neuroimaging. We suggest that the fronto-parietal MNS may be disparate nodes or modules of a (poorly understood) self-referential processing system that is important in drug abuse and addiction. We then discuss some theories of the etiology of these disorders that emphasize the self. A modular approach to human brain organization and function (as opposed to strict localizationist or extreme globalist models) may resolve some issues surrounding the MNS and drug abuse.

Are "physiological" and "psychological" addiction really different? well, no! ... um, er, yes?

The distinction often made between psychological and physiological addiction is a form of mind-body dualism. Therefore, it is a false distinction. However, this does not imply that behavioral and autonomic symptoms of addiction have the same brain substrates. In fact, they likely do not, although there is some overlap.

The habitual brain: an "adapted habit" theory of substance use disorders.

Behavioral habits are essential to human and animal life. We consider the many ways that habits - which are normally adaptive - can be expressed as drug use behavior and addiction. Although habit theories of substance use disorders have been proposed (e.g., Tiffany, 1990), the behavioral science and underlying neurobiology of habit development, maintenance, and change is only now being studied. We first define "adapted habit." We then propose that the etiology of an adapted habit represents the combination of: (a) initial "capture" of a habit, (b) development of behavioral action schemata, and (c) an overlay of cognitive expectancies concerning aspects of the habit. This combination conspires to make an intractable adapted habit such as substance abuse and addiction. Many intractable habits change, including substance use disorders such as cigarette smoking. As part of a science of habits, we need a real understanding of how to change habits to avoid or minimize harm.

Biological stress response terminology: Integrating the concepts of adaptive response and preconditioning stress within a hormetic dose-response framework.

Many biological subdisciplines that regularly assess dose-response relationships have identified an evolutionarily conserved process in which a low dose of a stressful stimulus activates an adaptive response that increases the resistance of the cell or organism to a moderate to severe level of stress. Due to a lack of frequent interaction among scientists in these many areas, there has emerged a broad range of terms that describe such dose-response relationships. This situation has become problematic because the different terms describe a family of similar biological responses (e.g., adaptive response, preconditioning, hormesis), adversely affecting interdisciplinary communication, and possibly even obscuring generalizable features and central biological concepts. With support from scientists in a broad range of disciplines, this article offers a set of recommendations we believe can achieve greater conceptual harmony in dose-response terminology, as well as better understanding and communication across the broad spectrum of biological disciplines.

Sensitization as a mechanism for multiple chemical sensitivity: relationship to evolutionary theory.

Multiple chemical sensitivity (MCS) is a disorder in humans attributed to prior chemical exposure. Sensitization is an amplification of neuronal responsiveness that elicits increased behavioral responding to stimuli, and occurs in a recently developed rat model of MCS. Rats were exposed to repeated formaldehyde (Form) and their response in three behavioral tests, including locomotor activity after a cocaine challenge, conditioned fear, and behavioral avoidance of Form, was assessed. In all three tests, rats demonstrated sensitized behaviors, implicating amplified responding within specific limbic brain regions. Evolutionary theory in the context of MCS specifies how the behavioral strategies of those with MCS are consistent with the notion that their self-perceived sense of survival and reproductive fitness may be threatened by chemical exposures. This behavior may be mediated by the same limbic brain regions that become sensitized after repeated chemical exposure in animals.

The self-perceived survival ability and reproductive fitness (SPFit) theory of substance use disorders.

A new theory of substance use disorders is proposed-the SPFit theory-that is based on evolutionary biology and adaptive systems. Self-perceived survival ability and reproductive fitness (SPFit) is proposed as a human psychobiological construct that prioritizes and organizes (i.e. motivates) behavior, but is highly vulnerable to temporary, artificial activation by drugs of abuse. Autoshaping/sign-tracking/feature positive phenomena are proposed to underlie the development of craving and expectations about drugs as the individual learns that abused drugs will easily and reliably inflate SPFit. The cortico-mesolimbic dopamine system and its modulating interconnections are viewed as the biological substrate of SPFit; it is proposed to be a survival and reproductive motivation system rather than a reward center or reward pathway. Finally, the concept of modularity of mind is applied to the SPFit construct. Although considerable empirical data are consistent with the theory, new research is needed to test specific hypotheses derived from SPFit theory.