Psychological dependence

Psychological dependence is a cognitive disorder that involves emotional–motivational withdrawal symptoms – such as anxiety or anhedonia – upon cessation of prolonged drug abuse or certain repetitive behaviors. It develops through frequent exposure to certain psychoactive substances or behaviors, which leads to an individual requiring further exposure to avoid withdrawal symptoms, as a result of negative reinforcement. Neuronal counter-adaptation is believed to play a role in generating withdrawal symptoms, which could be mediated through changes in neurotransmitter activity or altered receptor expression. Environmental enrichment and physical activity can attenuate withdrawal symptoms.

Symptoms
Symptoms of psychological dependence include:


 * Anxiety
 * Panic attack
 * Dysphoria
 * Anhedonia
 * Craving
 * Stress

Development
Psychological dependence develops through consistent and frequent exposure to drug or behavioral activity. After sufficient exposure to a stimulus capable of inducing psychological dependence (e.g., drug use), an adaptive state develops and results in the onset of withdrawal symptoms that negatively affect cognition upon disengagement.

Psychostimulants, such as amphetamine or cocaine, are an example of a drug class where only emotional and motivational (i.e., cognitive) symptoms are observed in withdrawal, as opposed to somatic withdrawal in cases of physical dependence. Whilst psychological dependence is often associated with effects of drug use, a behavioral dependence-withdrawal syndrome is possible. For example, exercise dependence can develop in amateur and professional athletes whereby marked cognitive withdrawal symptoms - associated with depressive symptoms and increased anxiety - are experienced when abstaining from experience for two weeks or longer.

The mechanism that generates dependence involves a neuronal counter-adaptation, which is localized to areas of the brain responsible for a drug's positive reinforcement. This adaptation occurs as a change in neurotransmitter activity or in receptor expression.

Biomolecular mechanisms
Change in neurotransmitter activity

Studies have shown that in rats experiencing ethanol withdrawal, stimulant withdrawal or opioid withdrawal, the nucleus accumbens shows lower levels of serotonin and dopamine than controls. These decreases are associated with depression and anxiety.

In anatomically distinct areas of the rat brain, withdrawal is linked to lower levels of GABA and neuropeptide Y as well as higher levels of dynorphin, corticotropin-releasing factor, and norepinephrine; these fluctuations can contribute to psychological dependence.

Altered receptor expression

Changes in receptor expression have also been linked to various symptoms of drug withdrawal. For example, in a study of rats undergoing nicotine withdrawal there has been observed a down regulation of α6β2*n-icotinic acetylcholine receptors in the mesostriatal dopaminergic pathways.

Methods for reducing dependence
A study examined how rats experienced morphine withdrawal in different surroundings. The rats were either placed in a standard environment (SE) or in an enriched environment (EE). The study concluded that EE reduced depression and anxiety withdrawal symptoms.

Another study tested whether swimming exercises affected the intensity of perceivable psychological symptoms in rodents during morphine withdrawal. It concluded that the anxious and depressive states of the withdrawal were reduced in rats from the exercise group.

Distinction between psychological and physical dependence
The major differences between psychological dependence and physical dependence are the symptoms they cause. While symptoms of psychological dependence relate to emotional and motivational impairment, physical dependence entails somatic symptoms e.g. increased heart rate, sweating, tremor. The type of dependence experienced after chronic use varies between different substances (see table 1).

Although psychological dependence and physical dependence are distinct entities, they should not be characterized as mutually exclusive. Empirical studies have shown that cravings, which are traditionally associated with psychological dependence, involve a physiological element.