An evolutionary analysis of psychoactive drug use needs to focus on the relationship between mental state and adaptive behavior. To analyze the complexity of such a relationship, it may be useful to classify mental states and behaviors into dichotomous categories: positive and negative. Pleasurable mental states and adaptive behaviors fall into the positive category; aversive mental states and maladaptive behaviors fall into the negative category.
Applying such a classification, there are four possible combinations (Table 1). Three of these combinations (#1, 3, 4) were common throughout our evolutionary history and are easily explained by the adaptive functions of emotions. Emotions have evolved to provide information about costs and benefits of past, present, and future behavior. The capacity to experience mental pleasure and mental pain helped the individual to pursue goals relevant to biological adaptation and to avoid maladaptive situations (Nesse Reference Nesse1990).
Table 1.
Possible combinations of mental states and adaptive behaviors
Combination # 1 reflects the strict association between mental pleasure and adaptive behavior. The neuroscientist Jaak Panksepp (Reference Panksepp1998) has succinctly expressed this concept with these words: “Pleasure is nature's way of telling the brain that it is experiencing stimuli that are useful.” Under natural conditions, brain reward systems were activated when (and only when) the individual was pursuing or achieving a goal relevant to biological adaptation. Conversely, under minimally adaptive circumstances, an individual experienced mental suffering (e.g., anxiety and depression) that functioned in part as a warning system that one's goal-seeking efforts were failing (combination #4) and in part as a motivational drive activating counter-strategies that were likely to redirect toward the achievement of adaptive goals (combination #3 as a transient state preceding return to combination #1) (McGuire & Troisi Reference McGuire and Troisi1998). Finally, the experience of a pleasurable mental state in absence of potential or actual fitness benefits (combination #2) was extremely rare if not impossible under natural conditions.
Psychoactive drug use substantially modifies the relationship between mental state and adaptive behavior. Each of the four possible combinations needs to be reanalyzed from a different perspective. Nesse and Berridge (Reference Nesse and Berridge1997) first described combination #2 in their “hijacking” hypothesis of psychoactive drug use. The hijacking hypothesis suggests that a key factor causing the maladaptive consequences of psychoactive drug use is the inhibition of the incentive systems that normally motivate the individual to explore and investigate the social environment in order to get natural rewards. Through the availability of drugs, the individual no longer needs to vigorously pursue courses of action to experience the entire range of positive emotions that may derive, for example, from the establishment of intimate relationships or the achievement of competitive success (Troisi Reference Troisi2001). Müller & Schumann (M&S) propose an alternative evolutionary model. Psychoactive drugs can be consumed in order to change the present mental state into a previously learned mental state, which then allows for better performance of other, previously established behaviors and better goal achievement. M&S apply their model to situations that include both combination #1 (e.g., enhancing pleasure during sexual behavior) and #3 (e.g., self-medication for mental distress facilitating transition to combination #1). Combination #4 is not contemplated by either evolutionary or conventional models: No one takes drugs to self-induce aversive mental states.
The hijacking and drug instrumentalization models predict opposite outcomes in terms of adaptive behavior and fitness benefits. This does not necessarily mean that the two models are incompatible. They could apply to different situations involving individuals with different neurobiological profiles and personality traits. Yet, the question remains: Which is the range of applicability of each model? M&S make a sharp distinction between non-addicted and addicted users and apply the hijacking model to the latter group only. Because the prevalence of addiction is relatively low, drug instrumentalization would apply to the majority of cases of psychoactive drug use. Such a conclusion is premature for two different reasons.
First, we do not have reliable data on the impact of psychoactive drug use on adaptive behavior. Most studies assessing the harmful potential of drug use limit their analysis to medical, psychiatric, and legal problems in addicted users. An evolutionary analysis requires a much wider focus. For example, the use of social network software is increasing sharply. In the next few decades, virtual reality is likely to progress to the point that users will be able to interact with virtual partners through the concomitant stimulation of all sensorial channels. In terms of medical and legal risks, virtual reality is a “clean” instrument for manipulating mental state. However, its potential capacity of alienating the individual from the natural sources of satisfaction and joy in the real world could have a major disrupting impact on social functioning.
Second, the use of psychoactive drugs to alleviate aversive mental states may have maladaptive consequences. Not all mental symptoms are the same: Many manifestations of psychological distress are sophisticated adaptations, and their suppression (the so-called symptomatic or palliative therapy) may lead to unfavorable outcomes (blocking the transition from combination #3 to combination #1.) For example, prospective studies (e.g., Mellman et al. Reference Mellman, Bustanmante, David and Fins2002) have shown that there may be an increased incidence of post-traumatic stress disorder in individuals treated with anxiolytics immediately after exposure to trauma. The deleterious effects of acute phase treatments are likely to be caused by their interference with the acute stress response, a set of physiological and psychological mechanisms that evolved to cope with traumatic events in the natural environment. In healthy volunteers, exposure to antidepressants increases the recognition of positive face emotions and decreases recognition of negative emotions (Harmer Reference Harmer2010). When given to individuals who are showing a physiological response to adverse circumstances, might antidepressants interfere with a correct reading of social interactions in everyday life?
If the impact of psychoactive drug use on adaptive behavior is a relevant issue (and probably it is not for most drug users and mental health practitioners), future studies inspired by evolutionary models should expand the scope of outcome assessment.
An evolutionary analysis of psychoactive drug use needs to focus on the relationship between mental state and adaptive behavior. To analyze the complexity of such a relationship, it may be useful to classify mental states and behaviors into dichotomous categories: positive and negative. Pleasurable mental states and adaptive behaviors fall into the positive category; aversive mental states and maladaptive behaviors fall into the negative category.
Applying such a classification, there are four possible combinations (Table 1). Three of these combinations (#1, 3, 4) were common throughout our evolutionary history and are easily explained by the adaptive functions of emotions. Emotions have evolved to provide information about costs and benefits of past, present, and future behavior. The capacity to experience mental pleasure and mental pain helped the individual to pursue goals relevant to biological adaptation and to avoid maladaptive situations (Nesse Reference Nesse1990).
Possible combinations of mental states and adaptive behaviors
Combination # 1 reflects the strict association between mental pleasure and adaptive behavior. The neuroscientist Jaak Panksepp (Reference Panksepp1998) has succinctly expressed this concept with these words: “Pleasure is nature's way of telling the brain that it is experiencing stimuli that are useful.” Under natural conditions, brain reward systems were activated when (and only when) the individual was pursuing or achieving a goal relevant to biological adaptation. Conversely, under minimally adaptive circumstances, an individual experienced mental suffering (e.g., anxiety and depression) that functioned in part as a warning system that one's goal-seeking efforts were failing (combination #4) and in part as a motivational drive activating counter-strategies that were likely to redirect toward the achievement of adaptive goals (combination #3 as a transient state preceding return to combination #1) (McGuire & Troisi Reference McGuire and Troisi1998). Finally, the experience of a pleasurable mental state in absence of potential or actual fitness benefits (combination #2) was extremely rare if not impossible under natural conditions.
Psychoactive drug use substantially modifies the relationship between mental state and adaptive behavior. Each of the four possible combinations needs to be reanalyzed from a different perspective. Nesse and Berridge (Reference Nesse and Berridge1997) first described combination #2 in their “hijacking” hypothesis of psychoactive drug use. The hijacking hypothesis suggests that a key factor causing the maladaptive consequences of psychoactive drug use is the inhibition of the incentive systems that normally motivate the individual to explore and investigate the social environment in order to get natural rewards. Through the availability of drugs, the individual no longer needs to vigorously pursue courses of action to experience the entire range of positive emotions that may derive, for example, from the establishment of intimate relationships or the achievement of competitive success (Troisi Reference Troisi2001). Müller & Schumann (M&S) propose an alternative evolutionary model. Psychoactive drugs can be consumed in order to change the present mental state into a previously learned mental state, which then allows for better performance of other, previously established behaviors and better goal achievement. M&S apply their model to situations that include both combination #1 (e.g., enhancing pleasure during sexual behavior) and #3 (e.g., self-medication for mental distress facilitating transition to combination #1). Combination #4 is not contemplated by either evolutionary or conventional models: No one takes drugs to self-induce aversive mental states.
The hijacking and drug instrumentalization models predict opposite outcomes in terms of adaptive behavior and fitness benefits. This does not necessarily mean that the two models are incompatible. They could apply to different situations involving individuals with different neurobiological profiles and personality traits. Yet, the question remains: Which is the range of applicability of each model? M&S make a sharp distinction between non-addicted and addicted users and apply the hijacking model to the latter group only. Because the prevalence of addiction is relatively low, drug instrumentalization would apply to the majority of cases of psychoactive drug use. Such a conclusion is premature for two different reasons.
First, we do not have reliable data on the impact of psychoactive drug use on adaptive behavior. Most studies assessing the harmful potential of drug use limit their analysis to medical, psychiatric, and legal problems in addicted users. An evolutionary analysis requires a much wider focus. For example, the use of social network software is increasing sharply. In the next few decades, virtual reality is likely to progress to the point that users will be able to interact with virtual partners through the concomitant stimulation of all sensorial channels. In terms of medical and legal risks, virtual reality is a “clean” instrument for manipulating mental state. However, its potential capacity of alienating the individual from the natural sources of satisfaction and joy in the real world could have a major disrupting impact on social functioning.
Second, the use of psychoactive drugs to alleviate aversive mental states may have maladaptive consequences. Not all mental symptoms are the same: Many manifestations of psychological distress are sophisticated adaptations, and their suppression (the so-called symptomatic or palliative therapy) may lead to unfavorable outcomes (blocking the transition from combination #3 to combination #1.) For example, prospective studies (e.g., Mellman et al. Reference Mellman, Bustanmante, David and Fins2002) have shown that there may be an increased incidence of post-traumatic stress disorder in individuals treated with anxiolytics immediately after exposure to trauma. The deleterious effects of acute phase treatments are likely to be caused by their interference with the acute stress response, a set of physiological and psychological mechanisms that evolved to cope with traumatic events in the natural environment. In healthy volunteers, exposure to antidepressants increases the recognition of positive face emotions and decreases recognition of negative emotions (Harmer Reference Harmer2010). When given to individuals who are showing a physiological response to adverse circumstances, might antidepressants interfere with a correct reading of social interactions in everyday life?
If the impact of psychoactive drug use on adaptive behavior is a relevant issue (and probably it is not for most drug users and mental health practitioners), future studies inspired by evolutionary models should expand the scope of outcome assessment.