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Addiction changes brain structures and their functions

Addiction changes brain structures and their functions: Addictions’ Effect on the Cerebral Cortex

Addiction changes brain structures and their functions

Did you know that addiction changes brain structures and their functions all for the wrong reasons? What you smoke, drink or inject could affect your brain functions badly.

The brain as an organ is a single unit which is driving the whole body daily operations. It is composed of many different parts otherwise known as regions and structures. The brain’s main role is that of transmitting effective communications to various parts of the body. This communication system enables the various regions and structures to coordinate their activities well. Each of these regions and structures are independent and serves different purposes. One of the biggest enemies to these regions and structures is the problem of drug addiction. This condition can alter these regions and structures. Besides that, addictions can also alter the way brain regions function. Therefore in this article, we are going to discuss the regions and structures that are affected by the addictive process. It is therefore very important to appreciate that addiction changes brain structures and their functions in very many ways. And going forward, we will be relying on the expert opinions from doctor Dalal Akoury and her team of experts from AWAREmed Health and Wellness Resource Center in reviewing the brain’s role in some of the commonly observed problems associated with addiction including the following:

Addiction changes brain structures and their functions: Impaired Decision-making, Impulsivity, and Compulsivity

The cerebral cortex is the outer most layer of the brain. The cerebral cortex is further divided into four areas. These four areas are: the frontal lobe (or frontal cortex), parietal lobes (left and right), temporal lobes (left and right), and occipital lobes (left and right). Each area is associated with certain brain functions: One area of the frontal cortex is called the prefrontal cortex. It has a vital role in higher-order functions. These functions include language, spatial learning, conscious thought, judgment, and decision-making. The process of addiction can negatively affect this area and alter its functioning.

Addiction changes brain structures and their functions: The prefrontal cortex

This enables us to make rational, sound decisions. It also helps us to override impulsive urges. If acted upon, these impulses urges can cause us to act without thinking. This is usually not in our best interest. For instance, suppose I’ve had a bad day at work. I may have an impulsive urge to tell my boss exactly what I think of her. To act on this impulse is not in my best interest. Fortunately, my prefrontal cortex is functioning quite well. I still have my job!

Obviously, this ability to inhibit impulses is very helpful. It enables us to function well in society. It protects us from harm by allowing us to consider the consequences of our actions. However, when the pre-frontal cortex is not functioning correctly, the opposite occurs. Addiction causes changes to the prefrontal cortex. These changes account for two characteristics of addiction: impulsivity and compulsivity.

Impulsivity is the inclination to act upon sudden urges or desires without considering potential consequences. Sometimes people describe impulsivity as living in the present moment without regard to the future. On the other hand, compulsivity is a behavior that an individual feels driven to perform to relieve anxiety. Once a person performs the compulsive behavior, the anxiety goes away and restores comfort. Thus, the presence of these behavioral characteristics in addicted persons indicates that changes to the prefrontal cortex have occurred. Unfortunately, these changes also make the discontinuation of drug use more difficult.

When we talk of addiction changes brain structure and their functions, the message being delivered is that an addiction is a process that coordinates the transition from impulsive to compulsive behavior. Impulsivity occurs during the early stages of addiction. During this phase, people impulsively act on powerful urges to experience the pleasure of their addiction. Anxiety is not associated with the urges during these early stages. Instead, addiction reflects acting on impulsive desire to receive immediate pleasure from the drug or activity. People are not considering the future consequences.

Addiction changes brain structures and their functions: The shifting progress of addiction

As addiction progresses a shift begins to occur. At this point, the compulsive aspect of addiction takes hold. When this shift occurs, people are no longer pursuing their addiction solely for pleasure. The compulsions compel them to participate in their addiction to relieve anxious, uncomfortable feelings. These may arise at the mere thought of stopping the addiction for any reason (supply shortages, lack of opportunity, etc.). At this later compulsive stage, “pleasure” comes in the form of relief from these anxious, uncomfortable feelings. Thus, despite the negative consequences of addiction, the addictive behavior continues in a compulsive manner.

Another way to describe the pre-frontal cortex is to think of it as a braking system. The pre-frontal cortex acts as the brain’s brakes. It sends out signals to inhibit particular behaviors or actions. When addiction damages this brain area, it limits the brain’s ability to control other behavioral systems as well. Imagine how difficult it would be to operate a car without brakes. At this point, we might say the brain is “high-jacked” by the addiction. The prefrontal cortex also projects to other brain regions associated with addictive problems. These include the reward system; memory and emotion; and stress regulation centers of the brain. Therefore, damage to the prefrontal cortex may further interfere with the functioning of these other brain regions as well.

Although addiction damages the brain’s brakes (pre-frontal cortex) this is not to say there is a complete loss of control. We are not slaves to our biology. We have a tremendous amount of control over our actions.  This is true even when impulsive and compulsive forces are operating. This recognition is vitally important if someone wishes to recover from addiction. When a person consciously decides the costs of addiction outweigh its benefits, they become motivated and able stop. This allows them to actively counter the effects of addiction on the pre-frontal cortex and other brain regions. Therefore if this description suits your situation, then you are in the right path and calling doctor Akoury today will go a long way in helping you solve all the addiction problems you may be having.

Addiction changes brain structures and their functions: Addictions’ Effect on the Cerebral Cortex







Neuroplasticity In The Mesolimbic Dopamine System And Cocaine Addiction

Neuroplasticity In The Mesolimbic Dopamine System And Cocaine Addiction

Cocaine is the most addictive of all forms substance abuse. It is characterized by a high compulsion and relapse. Despite several years of clinical research, scientists are yet to find an effective medication. However some studies indicate the activity of neurons in the mesolimbic dopamine system, which comprises cells in the Ventral Tegmental Area (VTA) that develop into the medial and detour prefrontal cortex, amygdala, and accumbent, motivates cocaine reward thereby contributing to high compulsion.

Based on these research activities often called neuropharmacological studies, the addiction of cocaine is caused by neuroadaptations induced by the drug. This is so reportedly because of the learning, reward-related and memory processes of the mesolimbic dopamine systems’ circuitry where dopamine projections are developed.

Neuroadaptation Cause of Cocaine Compulsion

Neuroadaptations are understood to cause very high sensitivity to cocaine. They are also believed to cause hypersensitivity to cocaine-associated electrochemical signals such as irrational decision making and irregular cultured behaviors characterized by high insensitivity to dire consequences of addiction.           A major characteristics of cocaine addiction is its’s compulsive drug use despite adverse consequences and high rates of relapse during periods of abstinence. A current popular hypothesis is that compulsive cocaine use and cocaine relapse is due to drug-induced neuroadaptations in reward-related learning and memory processes, which cause hypersensitivity to cocaine-associated cues, impulsive decision making and abnormal habit-like learned behaviours that are insensitive to adverse consequences. Here, we review results from studies on the effect of cocaine exposure on selected signalling cascades, growth factors and physiological processes previously implicated in neuroplasticity underlying normal learning and memory. These include the extracellular signal-regulated kinase (ERK) signalling pathway, brain-derived neurotrophic factor (BDNF), glutamate transmission, and synaptic plasticity (primarily in the form of long-term potentiation and depression, LTP and LTD). We also discuss the degree to which these cocaine-induced neuroplasticity changes in the mesolimbic dopamine system mediate cocaine psychomotor sensitization and cocaine-seeking behaviours, as assessed in animal models of drug addiction. Finally, we speculate on how these factors may interact to initiate and sustain cocaine psychomotor sensitization and cocaine seeking.

mesolimbic dopamine system

The premise that cocaine has a neuroadaptation effect to the chemical composition of certain parts of the brain has motivated various studies on the part of cellular actions and signaling forces that altogether causes neuro-synaptic plasticity. Effects of long-term exposure to cocaine on signaling forces, growth elements, psychosocial and physiological processes of reward transmission initially linked to neuroplasticity as a cause of mental recovery are a substantial number. They include extracellular-controlled kinase, distortion of normal neuron pathways and other neurotrophic factors, neuro-synaptic plasticity, and glutamate factors.

Neuroplasticity in Mesolimbic Dopamine System  

Neuroplasticity is the brain’s ability to adjust to new environments or needs by developing new nerve cells throughout the body. It is the brain’s way of recovery. Neuroplasticity allows the cells to compensate for any injuries or diseases in the nerve system. It also allows the neurons reorganize themselves to perform new functions of the brain depending on changes in their working environment, also involves recovery from drug addiction such as that of cocaine.

Cocaine-induced neurochemical changes in glutamate transmissions and synaptic plasticity in the mesolimbic dopamine system facilitates cocaine psychomotor high sensitivity, compulsion, self-injection, and reinstatement, being interesting aspects of study in shedding light into cocaine addiction menace has been reviewed time and again.

Experimental Evidence of Neuroplasticity on Long-Term Exposure to Cocaine

A key consideration in the above reviews has been what experimental evidence are needed to derive a conclusion of the particular effects of long-term exposure to cocaine on neuroplasticity and how those effects facilitate the learned behavioral symptoms associated with that.

Given this objective, researchers made a strict condition that if so cocaine-induced neuroplasticity causes certain attributer learned behavior then a reversal of the physiological processes that led to that state should, therefore, guarantee a reduced exhibition of such behavior.

After further intense studies on the same, the condition is continuously being met. This has led to yet another attempt to evaluate the role of cocaine-induced neurochemical alterations in glutamate transmissions, synaptic plasticity in VTA, accumbens and amyglada in as earlier mentioned psychomotor hypersensitivity and compulsive behavioral characteristic of the drug.

Many of those studies found out repeated cocaine administration amplified the rate of activity of ERK in the development areas of the mesolimbic dopamine system, which includes the accumbens, amygdala and the prefrontal cortex of the brain.

ERK Phosphorylation in Mesolimbic Dopamine System

Triggers of increased ERK phosphorylation includes D1 dopamine receptors, (PKA) the dependent protein kinase and methyl-D-aspartic acid (NMDA). On the other hand it was observed triggers of reduced ERK phosphorylation include CREB the transcription factor, mitogen-and stress-activated protein kinase-1 (MSK-1), and immediate early genes Fos and Zif268.

Extracellular signal-controlled kinase activity and the subsequent ERK-mediated reduced gene transcription are crucial for increased cocaine-induced psych as a result of exposure to the drug. On the other hand increased cocaine-induced ERK activity in the mesolimbic dopamine system does not facilitate the development of psych after a considerable time of withdrawal. Injection of either SL327 or VTA therefore before cocaine administration lessens sensitized the drug-induced movement during experimental tests for expression of psychomotor sensitization if done some time after withdrawal.

mesolimbic dopamine system

Cocaine Psychomotor Sensitization

More recent reports indicated psychomotor cocaine sensitization after several weeks of withdrawal from the drug increased ERK2 activity. This was linked to increased acumen α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and the receptor’s (AMPAR’s) surface appearance. However, no increases in ERK2 activity nor AMPAR surface expressions were observed in the specimens that did not exhibit psychomotor cocaine sensitization even after repeated non-dependent cocaine exposure and after some time of withdrawal.

Acumen’s ERK rate of activity possibly serves two specific roles in facilitating rewarding effects of the psychostimulant in a CPP procedure. During CPP training, the accumben’s rate of activity mediates consolidation of the learned behavior between the drug’s unconditioned rewarding effects and the drug’s related context during the CPP testing, ERK movement mediates serious expression of cocaine’s other habituated responses.

Systemic SL327 inoculations before cocaine CPP training prevented cocaine-induced accumbens, ERK phosphorylation and the subsequent expression of cocaine CPP. PD98059 accumben injections are given either before or after CPP training sessions blocked subsequent amphetamine CPP expression.

The relevance of the above fascinating correlational findings of cocaine’s compulsive characteristic, its’ psychomotor sensitization, and the ERK phosphorylation in the mesolimbic dopamine system is, however, a subject for further scientific, clinical research. Please sign up for this year’s August Integrative Addiction Medicine Conference to learn more about the same. Click the following link to get your chance to participate in the event: http://www.integrativeaddiction2015.com.

Neuroplasticity In The Mesolimbic Dopamine System And Cocaine Addiction


The Prefrontal Cortex and It’s Executive Control In Addiction

Role of the prefrontal cortex and executive control in addiction

prefrontal cortexThe prefrontal cortex is the part of the brain that is the cerebral cortex, which covers the front part frontal lobe. PFC’s most typical psychological term for its functions is executive function. The prefrontal cortex has been associated with a person’s personality by more than one scientist. It is associated with decision making, planning complex cognitive behavior, expressing ones personality as well as controlling and moderating social behaviors. Decision making is a process that is carried out in the brain through the interaction of the prefrontal cortex and the subcortical regions involved in reward and motivation. As a result, it is common that failure in self-regulatory behavior, common in addicted subjects, could be dependent upon the alteration of the interactions between the prefrontal cortex and the subcortical regions.

The PFC has plays a great role in regulating and governing behavior. This function is achieved through a complex interaction of different areas within the prefrontal cortex together with the subcortical areas integrating cognitive and executive functions to produce the “optimal choice”. The result of this interaction can also result in dangerous decisions some of which are observed in drug addicts. The PFC functional abnormalities are very much attributed to the continued use of drugs or traumatic experiences. PFC plays a role in the onset and in the progression of psychiatric disorders associated with very poor decision making such as schizophrenia, attention deficit or the hyperactivity disorder, and depression all of which are very likely to be suffered by drug addicts after a prolonged period of drug and substance abuse.

Dopamine is a neurotransmitter that helps control the brains reward and pleasure areas as well as regulating movement and emotional responses. Dopamine enables us to not only see the reward but to also take actions to move towards them. Addictive drugs such as cocaine, marijuana and nicotine cause an excess of dopamine in the brain. According to scientific theories, dopamine is released in the brain when something very important happens, whether that is an expected reward or an accident. Since it is involved in learning, memory and motivation, the chemical dopamine helps us to store the important information we need to survive as well as to remember it in the future. Drugs however hijack that process sending five to ten times more dopamine surging through the nucleus accumbens and forcing the brains motivational and attention mechanisms to focus purely on the drug. The drug therefore becomes the most important thing in the world which leads to addiction.

Improved performance  in cognitive tasks requiring working memory and inhibition have been observed in people that carry variations in the catechol-O-methyltransferase (COMT) gene which degrade the catecholamine neurotransmitters dopamine, epinephrine, and norepinephrine. As a result, when the role of COMT is altered, there could be increased likelihood of making the drug addiction even stronger. Addiction is therefore as a result of a number of factors and the PFC circuitry contributes to the expression of several behaviors that are associated with it. A large number of addicted people do not seek treatment, mostly because they do not even recognize their condition as a disease that requires a medical attention. This condition is probably brought about by viewing the abused substance as an essential ingredient of their life regardless of the consequences of its use.

Imbalance between two separate but interacting neural systems can lead to addiction. These neural systems could be an immediate one that generates decision making, based on the impulsivity-related amygdala system for transmitting pain or pleasure of the immediate prospects and a reflective one, whose basis are for the signaling pain or pleasure of future prospects. The level of controlling behavior is challenged by the ability of cues associated with strengthening activities such as drug abuse, food or sex. Self-control efforts however involve increased activity in the regions of the PFC regulating emotions and cognition and reduced activity in the regions that are associated with reward processing and craving. PFC could be associated with long term outcomes whereas sub-cortical activity is associated with more immediate outcomes.

The PFC is also responsible for the decision to quit taking a certain drug after a period of addiction. Abstinence is a multiple component condition in which the lack of drug effects is highly associated with the inner struggle between the desire of the reward brought about by intake of the drug and the assessment of the consequences of that behavior in terms of money, social life and environmental involvement for example smoking marijuana. This will very fast lead to appearance of withdrawal syndrome that is characterized by depressed mood, irritability, mild cognitive deficits accompanied by other peripheral psychological symptoms as the PFC tries to adjust. Some addicts who struggle to go through the abstinence of a certain drug at times relapse to their old habits. This relapse can be categorized into three major types which are; drug induced relapse, reinstatement of self-administration behavior upon exposition to drug related cues and stress induced relapse. This is a major setback in the recovery of the addicts.

prefrontal cortex/

Research has shown that addicts of strong drugs such as marijuana or cocaine have more problems in their daily lives both physically as well as emotionally. Their health is also very much at risk as this drugs alter the working mechanism of the brain and especially the prefrontal cortex. They report lower life satisfaction, poorer mental and physical health, more relationship problems, and they also have less academic and career success compared to those who do not abuse drugs. Decision making becomes a problem for them and they tend to choose the easy way out which to them is the choice to keep using the drugs. Eventually, they could lose their mind all together as the brain function mechanism gets more and more accustomed to the drug effects.

Role of the prefrontal cortex and executive control in addiction



Neural circuits of preoccupation/ anticipation “craving” stage

Addiction and It Stages

Drug addiction is a slow developing disorder that is long lasting characterized mainly by the urge to seek and take the drug, loss of control in limiting intake and development of a negative emotional state of anxiety and irritability. When the drug is prevented, the user exhibits withdrawal symptoms. Drug addiction has been viewed as a condition that involves element of both impulsive and compulsive behavior that is brought about by the addiction circle. The circle is made up of three stages: the intoxication stage the negative or the withdrawal effect, and the anticipation stage/ preoccupation which is the craving stage.

The neural circuits of the brain affected

Study on human behavior has revealed discrete circuits that play a major role in binding a major stage of the addiction circle. The ventral tegmental area and ventral striatum is the main focal point for the intoxication stage. The extended amygdala plays the role in the withdrawal while the  orbitofrontal cortex–dorsal striatum, prefrontal cortex, basolateral amygdala, hippocampus, and insula are involved in craving and the cingulate gyrus, dorsolateral prefrontal, and inferior frontal cortices in disrupted inhibitory control which is the preoccupation/anticipation stage. Drug addiction therefore alters the normal functioning of the neural circuits which may begin with changes in the mesolimbic doper mine system and the process of neural adaptations from the ventral striatum to dorsal striatum of the frontal cortex and eventually deregulates the prefrontal cortex and extended amygdala.

neural circuits

Of late there have been studies aimed at understanding the genetic cellular and molecular mechanisms that mediate the transitions from once-in-a-while drug use to the loss of a person’s control of a drug abuse and to the final stage of a relapse even after trying to abstain. Drug addiction has aspects of both impulsivity and compulsivity disorders. Impulse control disorder is precisely an increased sense of tension before engaging in an impulsive act and a feeling relieved at the time of committing the act. They are categorized as the positive and strengthening mechanisms. On the other hand compulsive disorders are characterized by anxiety and stress before taking part in a compulsive redundant behavior and relieve from the stress by carrying out the compulsive behavior. The compulsive disorders are greatly associated with negative reinforcement’s mechanisms.

Impulsivity and compulsivity.

As the stage of addiction moves from one cycle to the other, the user moves from a stage of impulsivity to a stage of impulsivity and compulsivity. As a result, they are no longer positively reinforced by the drug but negatively influenced. These three stages of addiction are attributed to interacting with each other getting more intense and finally leading to the pathological stage called addiction.  The brain neural circuitry system is engaged at each stage of the addiction cycle and changes with increased intake of the drugs of abuse hence producing the disorder known as addiction. Since the brain responds to stimulus the entire system becomes oriented specifically toward drug related stimuli leading to an increased drive for seeking and taking drugs.

Executive dysfunction

Executive dysfunction is a range of cognitive, emotional and behavioral difficulties which occur after the frontal lobe of the brain is injured. The executive function include abilities such as: planning and organization, social behavior, controlling emotions, safe awareness among others. Drug abuse alters the normal functioning of the frontal lobe of the brain and leads to executive dysfunction. This leads to deficits in cognitive skills which involves thinking, personality and social behavior. Executive dysfunction also makes it difficult to solve problems and as a result drug addicts do not make accurate judgments or find solutions if things are going wrong. They are also irritable find it hard to concentrate lose their r memory and do not get enough sleep. It is very hard for people with this this problem to get along with others as they appear antisocial and can be misunderstood as depression lack of motivation, selfishness and aggression.

Future treatment targets.

neural circuitsGABA receptor substance that does not act as agonist or antagonist but affects the gamma-amino butyric acid receptor-ionophore complex. The GABA receptors play a role in almost every single activity of the brain. Ultimately glutamate and GABA do the information processing; they’re the ones that encode sensory inputs and thoughts (GABA directly modulates the effect of glutamate). There is the cognitive enhancement which requires the knowledge of cognition and what it involves. This cognitive enhancement could be aimed at improving short-term memory, improving information processing improving recall, or enhancing long-term potentiation. Each of this involves different circuits that involve multiple neurotransmitter systems.

Homeostatic resetters refers to the process of removal of toxic substances from the body of an individual through a process called detoxification in that at the end of the process the body returns to homeostasis after a long term use of an addictive substance.

CRF is brain stress systems that is engaged during the withdrawal/negative affect stage. This will reduce the dopamine activity and also help in restoring the frontal lobe of the brain. Therefore, the CRF increases in the effects that occur with sudden withdrawal from drugs and have motivational significance not only for the anxiety effects of acute withdrawal but also for the increased drug intake associated with dependence.

Glutamate modulators are used to reduce the habits of addiction by greatly improving the mood of the user and treating major depressive disorder. Glutamate is the most abundant excitatory neurotransmitter in the brain. There has been studies carried out which have shown altered glutamate levels in serum and cerebrospinal fluid from patients with mood disorders. Administering glutamate to this patients will therefore greatly improve their mood.

Neural Circuits Of Preoccupation/ Anticipation “Craving” Stage

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The Human Brain

The Human Brain – Human Operation Manager


The Human brain. Being the nerve center and regulator of all body functions, drugs must not be allowed to get into the brain

Have you ever considered how the brain works, the a mount of information being processed by this organ is huge and what is surprising is how orderly and efficient hey are being processed. Take for example one of the life practical example like driving a car. A lot of multi-tasking will be taking place like you position yourself well on the steering wheel, focused on the road and not sleeping, communicate with your feet, leg, hands and arms, knowing where the brakes are  among very many things like listening to the radio, talking to your passengers. Can you imagine the kind of speed involved in processing such an amount of data all at the same time! While you look at these tasks as simple either because of your driving experience it may not be so if you bring the nerve center in the picture. In fact all these you are able to do them because of the proper functionality of your brain and so how does the brain work all these efficiently and perfectly?

Different Brain Regions Contribute to the Regulation of Different Functions

Taking our example of driving as the bigger task, the brain will break it into smaller units like communicating, hearing, seeing etc. for them to be processed. A section of the brain will analyze movement of objects we see, the other part will be organizing the tasks in other words each part of the brain carry out specific task meaning that whenever a given task is to be done the right information is processed by that specific part of the brain. The other aspect of the brain is that in the event that a section of the brain is damaged then all the functions done by that section will not be done and that is why in an accident if the occipital lobe at the back of the brain is damaged then blindness occurs but other unaffected areas like seeing and movement continues to function normally because the job of seeing is highly compartmentalized, individuals who have lost one aspect of sight like the ability to see colors or to recognize faces, may still be able to do other visual tasks can you imagine being able to recognize people by hearing their voices but not being able to recognize them by their faces when you see them?

The advantage of this localization of function is when larger jobs are parceled out throughout the brain they all can be done at once. This decentralization of labor adds great speed to our ability to understand what is happening in the world around us, to analyze it, and then to generate appropriate responses. Dealing with information in this way is called parallel processing and it has been used by the computer scientists in the development of computers.

The human brain consists of several large regions, each of which is responsible for some of the activities necessary for life. These include the brainstem, cerebellum, limbic system, diencephalon, and cerebral cortex.

The brainstem is that part of the brain which connects the brain and spinal cord. This part of the brain is involved in coordinating many basic functions such as heart rate, breathing, eating, and sleeping.

The cerebellum coordinates the brain’s instructions for skilled repetitive movements and for keeping balance and posture.

The limbic system is involved in regulating emotions, motivations, and movement. It includes the amygdala and hippocampus, which is important for memory formation.

The diencephalon contains the thalamus and hypothalamus. The thalamus is involved in sensory perception and regulating movement. The hypothalamus is an important regulator of the pituitary gland, which directs the release of hormones throughout the body.

The cerebral cortex makes up the largest part of the brain mass and lies over and around most of the other brain structures. It is the part of the brain accountable for thinking, perceiving, and producing and understanding language. The cortex can be divided into areas that are involved in vision, hearing, touch, movement, smell, and thinking and reasoning.

Drugs on the Reward System in the Brain

The same ways specific areas of the brain control seeing and hearing, specific brain areas also control emotions, motivations, and movement. These functions are carried out by a part of the brain called the limbic system. The limbic system prevails on how we react to the world around us. Imagine a cool sunny day. You finish your work early and head to your favorite park for a leisurely walk with your dog. You are feeling so mellow that when the dog slobbers on your clean shirt, you merely scratch him behind the ears. Nonetheless on another day you have a completely different experience when you have to work late, traffic is up, and the dog runs away instead of coming to welcome you home. This time when the dog slobbers on you (after he finds his way home again) you shove him away and scold him.

The feelings you have in those two different situations are a result of your limbic system at work. The limbic system uses memories, information about how your body is working, and current sensory input to generate your emotional responses to current situations.

The limbic system is involved in many of our emotions and motivations, particularly those related to survival, such as fear and anger. The system is also involved in pleasurable activities necessary for survival, such as eating and sex. If something is pleasurable, or rewarding, you want to do it repeatedly. Pleasurable activities engage the reward circuit (or system), so the brain notes that something important is happening that needs to be remembered and repeated. The reward system includes several interconnected structures the ventral tegmental area (VTA), located at the top of the brain stem; the nucleus accumbens; and the prefrontal cortex). Neurons from the VTA relay messages to the nucleus accumbens and the prefrontal cortex. Information is also relayed back from the cortex to the nucleus accumbens and the VTA.

Most drugs of abuse activate the same VTA and nucleus accumbens neurons and that is why drugs produce pleasurable feelings to the drug user. And, because the feelings are pleasurable, the user wants to continue to experience the pleasure which they felt during previous drug use.

One of the reasons that drugs of abuse can exert such powerful control over our behavior is that they act directly on the more evolutionarily primitive brainstem and limbic structures, which can override the cortex in controlling our behavior.

The Human Brain – Human Operation Manager