Addiction to Altering States: Observable Tendencies Attributed to Learning and Neurology
The observable tendency of a person to repeat the use of drugs, and continue use in spite of possible or real negative consequences, can be partially explained by examining several learning theories and learning with respect to neurological associative strength, and more importantly, the rewards pathways in the brain. There have been numerous attempts and proposed theories aimed at explaining addiction – and motivation to consume drugs in general – in terms of positive and/or negative reinforcement, but they are not quite adequate as free-standing theories.
Many of the older psychological theories are based on observational data and, although the more recent ones speculate on neurological processes, they are only valid insofar as they may predict behavior. Some recent developments in neuropsychology provide evidence of physiological-type mechanisms, which illustrate and supplement explanations of observed behavior. A comprehensive approach to addiction, and drug use in general, should include the integration of learning theories and recent neurological discoveries and research. The following essay is a preliminary attempt to lay out some of the elements of a future comprehensive approach.
Criteria and connotation vary between cultures with respect to the use of alcohol and drugs as well as alcoholism and drug addiction. The question of who will become an addict and who may remain a non-addicted social user is not yet explained by science. The first time a person uses drugs is typically voluntary (not accounting for things such as peer pressure). Kauer (2004) writes that “when an unanticipated primary reward is presented, dopamine neurons increase their firing rate” (p. 448).
Thus, the first few uses may result in general good experiences – reinforcing the use of the drug – leaving the user with the belief that they can decide if and when to take the drug (National Institute on Drug Abuse, 2007). With extensive research showing the activation of the neural mechanisms involved in stimulus reinforcement and learning, it is logical and often posited explanation that drug use in general is a result of the rewarding effects of drugs.
One of the major approaches to learning, upon which many of the present theories rely, is the classical (Pavlovian) conditioning model in which a neutral stimulus (called the conditioned stimulus, or CS), comes to be associated with a non-neutral (response-inducing) stimulus, called the unconditioned stimulus (US). A US is called unconditioned because it induces a response through an innate mechanism; the natural response to a US is called an unconditioned response, or UR. Following multiple presentations of the two stimuli together (CS+US), the neutral stimulus comes to elicit the natural response to the US in absence of the US. At this point the response is called a conditioned response (CR).
The standard example of classical conditioning is ringing a bell (stimulus to be conditioned or CS) quickly followed by giving food (the US) to a dog. When food is put into a dog’s mouth, the natural response is salivation. Once the dogs salivate (UR) to the bell (CS) without the presentation of food (US), conditioning has occurred and salivation is now the conditioned response (CR). Conditioned responding is a very important aspect of the theories that address behavioral patterns in continued consumption of commonly abused drugs.
Direction, whether precise or not, is inherent in all aspects of motivated behavior. Domjan (2006) refers to this under the heading of “The Sequential Organization of Behavior,” (p. 34). Each type of behavior, whether feeding, mating, fighting, or otherwise, has a set of actions involved in its successful execution from beginning to finish. In viewing behavior as a means to an end, there are two classes of behavior to consider – starting behaviors and stopping behaviors. The former class of behavior is called “appetitive behavior,” and the latter is “consummatory behavior” (Domjan, 2006, p. 34). According to this construct, appetitive behaviors serve to put an organism near to or in contact with an important stimulus, while consummatory behaviors include the sequence of actions, either instinctive or learned, which lead to the successful engagement of the target stimulus (e.g. ingesting food) (Domjan, 2006).
Animal feeding behavior as described by Domjan (2006) is analogous to a drug user’s general using process. There are three modes – each with its own direction and in specific order – which are directed toward the goal of eating (or in the drug user’s case, getting high). The first two modes fall under the appetitive behavior category and are named “general search” and “focal search,” while the third mode falls under the “consummatory” category and is called the “food handling” mode (Domjan, 2006, p. 35). Because animals do not spend all of their time in this process, one must assume that there is some mechanism that acts as a call to action; something initiates the appetitive and consummatory behavior.
An important point to recognize with regards to motivated behavior, which is very pertinent to explaining drug addiction, is that neither humans nor animals are able to choose when they will experience the inevitable phenomenon of hunger (or craving). Rather, it is said that a homeostatic mechanism, expressed in both theoretical and scientific theories and research (Carlson, 2004; Domjan, 2006; McKim, 2006), operates in order to maintain the default state of an organism – the default state or optimum state is called the “set point” (Carlson, 2004; McKim, 2006).
Carlson (2004) defines homeostasis as the “process by which the body’s substances and characteristics (such as temperature and glucose level) are maintained at their optimal level” (p. 322). The example Carlson (2004) provides is that of an HVAC system. A person sets the desired temperature on a thermostat and the system does the rest; when the temperature drops above or below the set point, the deviation from the set point engages the system, which heats or cools to compensate for the disturbance. With such a mechanism in place, an upset of balance in an animal – due to either a lack or overabundance of a chemical – should produce some sort of automatic compensatory response to restore the set point.
McKim (2006) outlines the current model of the motivational control system as it pertains to maintenance of the set point. It is composed of three major systems: the learning and memory system, the reinforcement system, and the motor loop system (McKim, 2006). The purpose of the system is essentially to direct behavior of an animal towards maintenance of homeostasis; behavior effected may be easily observable, as is the case with movement, or it may be unobservable, as is the case with things like hormonal regulation. The systems’ subcomponents will be described piecemeal as they relate to the functions being discussed.
Homeostatic input is said to be received in the ventral tegmental area (VTA) and then sent to the nucleus accumbens (McKim, 2006, p. 112). The VTA is consistently mentioned with respect to motivation and reinforcement in myriad studies, including studies on drug consumption (Carlson, 2004; Due et al., 2002; Hyman et al., 2006; McKim, 2006; National Institute on Drug Abuse, 2007; Wrase et al., 2008). Regardless of its manifestation, the response from this mechanism is considered “compensatory” because it acts to compensate for the imbalance.
The homeostatic mechanism is responsible for cuing motivational stimuli such as hunger and thirst, which result from an imbalance in fluid and nutrients (McKim, 2006). With respect to drugs, the homeostatic mechanism can be easily observed in some of the characteristic symptoms appearing after cessation of opioid use; the acute effects of opioids include constipation, dilated pupils, vasodilatation (resulting in lowered blood pressure), analgesia, inhibition of nausea (except upon first use), lowered rate of breathing, and relaxation, among others. After intoxication, the homeostatic mechanism is clearly illustrated when vomiting, diarrhea, and leg spasms appear; the leg spasms led to the phrase “kicking the habit,” which is indicative of a common experience that supports the idea of a homeostatic mechanism (McKim, 2006, p. 273). These symptoms can “be stopped almost instantly, at any stage, by the administration of any of the opioid drugs” (McKim, p. 273).
According to the American Psychological Association (2000), meeting the criterion for withdrawal includes having either “the characteristic withdrawal syndrome for the substance…[and/or] the same (or a closely related) substance is taken to relieve or avoid withdrawal symptoms” (p. 197). The withdrawal symptoms are analogous to the natural state of hunger in that the imbalance works as a behavior-provoking stimulus; the behavior is directed towards restoring balance. This idea of behavior provocation ties back to the animal feeding behavior – which will now be called drug using behavior – touched upon earlier. The terms hunger and food will be used interchangeably with craving and drugs (Domjan, 2006).
When an addict experiences hunger, he enters the abovementioned general search mode. Characteristic of general search is seemingly directionless movement, the purpose of which is increasing the likelihood of entering the vicinity of a source of food (Domjan, 2006). McKim (2006) explains the neurology of this process saying that the nucleus accumbens actually inhibits motor activity by default; it is homeostatic imbalances that cause the VTA to stimulate dopamine release in the nucleus accumbens, which results in a decrease in inhibition of the motor system (p. 111).
Once random movement is permitted, the success of the general search mechanism relies heavily on classical conditioning; for the general search mode to be effective in resolving craving, an addict must have the ability to identify a possible source of drugs when such a source is present. In order to recognize a possible source of drugs, an addict must have had an experience where the imbalance – in this case craving – was corrected by consumption of drugs (restoration of homeostasis). Because hunger is a strong stimulus, the stimuli preceding alleviation of hunger readily gain stimulus salience (also called incentive salience), which is one of the most important factors contributing to behavioral direction and will be discussed shortly. Stimulus salience is increased by the VTA-controlled release of dopamine at its synapses. This connection is called the “mesolimbic dopamine system, and it appears to play an important role in reinforcement” (McKim, 2006, p. 111).
The learning and memory system of the motivation control system includes the hippocampus, amygdala, and cortex; it plays an important role in the ability to identify a source of drugs (Carlson, 2004; Due et al., 2002; Goldstein & Volkow, 2002; Hyman et al., 2006; Kauer, 2004; McKim, 2006; National Institute on Drug Abuse, 2007; Siegel & Ramos, 2002; Wrase, J., Makris, N., Braus, D. F., Mann, K., Smolka, M. N., Kennedy, D. N., Caviness, V. S., Hodge, S. M., Tang, L., Albaugh, M., Ziegler, D. A., Davis, O. C., Kissling, C., Schumann, G., Breiter, H. C., & Heinz, A., 2008). McKim (2006) writes that the hippocampus and amygdala are engaged for the memories of previous exposures to hunger and related situational outcomes. Wrase et al. (2008) state that “positive and negative values of cues modulate neural activity in the amygdala, and this modulation occurs fast enough to account for learning” (p. 1183). Neither the hippocampus nor the amygdala are directly connected to sensory information and therefore cannot directly identify sources of drugs; they must rely on their connections with the cortex (McKim, 2006).
An overwhelming amount of sensory information is constantly being received by the brain. There is something that determines which stimuli are attended to and which are ignored (Domjan, 2006). Salience is the term used to describe the importance of a stimulus; it can be considered as a kind of ranking system. As the level of salience of a stimulus goes up, the stimulus becomes more readily recognized over other stimuli (e.g. a hungry mouse will more readily notice cheese than the mouse trap under the cheese) (Domjan, 2006; McKim, 2006). The importance of noticing stimuli leads to the third part of the motivation control system and also to an interesting learning theory that congeals with the neurological mechanisms.
The motor loop subsystem includes the basal ganglia, thalamus, and cortex (McKim, 2006). The role of the thalamus in the motor loop is the reception and relaying of sensory input to the cortex. The cortex processes and sends incoming sensory information to the hippocampus (outside of the motor loop); information is also sent to the nucleus accumbens (also outside of the motor loop), which in turn stimulates, or maintains stimulation of, the basal ganglia for continued movements, which may be directed by the cortex. The fifth criterion for diagnosis of substance dependence is that “a great deal of time is spent in activities necessary to obtain the substance…use the substance…or recover from its effects” (American Psychological Association, 2000, p. 198). This criterion is indicative of a fair amount of time spent in the aforementioned general search mode.
In light of the present approach to addiction, an interesting review by Quickfall and Crockford (2006) reports findings that help explain the great deal of general searching activity. Several studies reported increased right frontal lobe and bilateral frontal lobe activity following THC administration. Consistent with other findings, one study reported that cerebral metabolic rates between 35 and 50 minutes after THC administration were elevated in cannabis-dependent and control subjects alike. However, they found that “only cannabis-dependent subjects had increased orbitofrontal cortex (and basal ganglia) activity” (Quickfall & Crockford, 2006, p. 325). These findings clearly depict the activity of the mechanism responsible for movement in general search; this implies that dependent users may have a modified (whether innate or drug-induced) motivation control system such that a homeostatic imbalance may be compelling them into general search.
When the homeostatic imbalance is encountered, the nucleus accumbens is activated and stimulates the basal ganglia, which effects movement. The thalamus receives sensory input and passes it to the cortex. Eventually the animal will run into something in the environment that resolves the imbalance and the sensory information present (or recently present) will gain salience as they will be associated – in the cortex, hippocampus, and amygdala – with the restoration of the set point (McKim, 2006).
If notice of stimuli were restricted to precise stimuli (e.g. a tree where food was found becomes the only recognizable source of food; other trees do not indicate possible sources of food) an animal would most likely have a difficult time locating food, water, or other resources to restore the set point. The stimulus generalization theory, therefore, should be briefly discussed in light of the association of approximate stimuli (e.g. environmental factors) with the restoration of the set point. It has been validated by many studies, that after a UR has been conditioned to a specific CS, the presentation of different stimuli will elicit the CR to the extent that the stimuli are like the original CS (Domjan, 2006). This theory lends itself to the suggestion that the cortex may sort information categorically, perhaps by similarities; such a function would support schema theory.
Although dating back to the ancient Greek philosophers, Kant is generally credited with the modern introduction of schema theory (McVee, Dunsmore, & Gavelek, 2005, p. 535). Schema theory essentially proposes a process in the mind in which information is put into “organizing structures that mediate how we see and interpret the world…a schema was a lens that both shaped and was shaped by experience” (McVee et al., p. 535). Approaching more modern cognitive studies examining schema, McVee et al. (2005) cite a report that “defined schemas as ‘data structures representing the generic concepts stored in memory. They exist for generalized concepts underlying objects, situations, events, sequences of events, actions, and sequences of actions’” (p. 536). Classical conditioning says stimuli predicting reinforcement will be noticed over other stimuli, and it follows from the schema theory that it is not an exact stimulus that is noticed, but rather the aspects of the stimulus are noticed.
Neurological and psychological studies have shown that salience is affected by the physiological state of an animal (e.g. hungry or not), intensity of a stimulus (e.g. a large versus small electric shock), previous experience (reinforcement or punishment) with a stimulus, and the mechanisms of habituation and sensitization (Carlson, 2004; Domjan, 2006; McKim, 2006).
Domjan (2006) reports the dual-process theory of habituation and sensitization as an assumption based on observable changes in behavior to different stimuli (p. 42). Over repeated exposures to a stimulus, habituation is characterized by diminished responding, while sensitization is characterized by increased responding. The theory assumes that the processes are not exclusive but rather, in competition with each other (Domjan, p. 42); there are underlying neurological activities controlling the processes, which are confirmed by Kauer (2004), who says that “nearly all drugs of abuse elicit behavioral sensitization, indicating an important common target in the brain” (p. 450).
The relationships between salience, habituation, and sensitization are important to understanding the motivational mechanisms leading to repeated drug use at behavioral and neurological levels; if a neutral stimulus becomes a strong indicator of another reinforcing stimulus, typically the sensitization process will be stronger than the habituation process and there will be a net increase in salience. However, if the neutral stimulus does not come to predict a reinforcing stimulus, then there will be a net decrease in salience, also known as habituation. The net decrease results in less responding to the stimulus. It follows from this that stimuli which frequently appear preceding drug use will have a net gain in salience; they come to indicate the presence of a reinforcing stimulus. This theory is supported by reams of behavioral and neurological research (Carlson, 2004; Domjan, 2006; McKim, 2006; Siegel & Ramos, 2002).
Assuming there are always homeostatic compensatory responses to the disturbance of the set point, instigated by introduction of a drug, the infrequent use of a substance would provoke the typically brief drug-specific compensatory responses, similar to a hangover from alcohol. Essentially this means that drugs are used on a recreational basis to the extent that their reinforcing effects outweigh any punishing effects. It is therefore interesting that a person should continue to take a drug in spite of negative consequences resulting from drug use.Continued on Next Page »