Psychological dependence
Psychological dependence is a cognitive disorder that involves emotional–motivational withdrawal symptoms, e.g. anxiety and anhedonia, upon cessation of prolonged drug abuse or certain repetitive behaviours. It develops through frequent exposure to a psychoactive substance or behaviour, though behavioural dependence is less talked about. The specific mechanism involves a neuronal counter-adaption, which could be mediated through changes in neurotransmittor activity or altered receptor expression. Withdrawal symptoms can be attenuated by environmental enrichment and physical activity. Psychological dependence is not to be confused with physical dependence, which induces physical withdrawal symptoms upon discontinuation of use. However they are  not mutually exclusive. Symptoms. Symptoms of psychological dependence include: Development. Psychological dependence is caused by consistent and frequent exposure to a drug or behavioural activity. It is often associated with effects of drug use, but it can also be caused by behavioural activity e.g. pornography. The mechanism that generates dependence involves a neuronal counter-adaption, which is localized to areas of the brain responsible for a drug's positive reinforcement. This adaption occurs as a change in neurotransmitter activity or in receptor expression. 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 was either placed in an 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.