Brain pleasure centers

To consider how drug treatment might succeed in reducing drug use, one must first look at what happens when someone becomes addicted to a drug. Starting in the 1950s, experimenters observed that animals that were allowed to control the stimulation of pleasure centers in the brain would continue to do so until they collapsed from exhaustion. The pleasure centers are a vital... 

The neurons activated by amphetamines are dense in the pleasure center of the brain and the depletion of the stores sets up a demand for progressively higher doses to achieve the same high, and accounts for the sometimes profound depression, or crash, that follows a drug binge. 

Cocaine is a local anesthetic with a peripheral sympathomimetic action that results from inhibition of transmitter reuptake at noradrenergic synapses (see Chapter 6 Introduction to Autonomic Pharmacology). It readily enters the central nervous system and produces an amphetamine-like effect that is shorter lasting and more intense. The major action of cocaine in the central nervous system is to inhibit dopamine reuptake into neurons in the "pleasure centers" of the brain. These properties and the fact that it can be smoked, "snorted" into the nose, or injected for rapid onset of... 

Amphetamines not only improve vigilance and accuracy in performing tasks, but they also improve the individual s attitude about doing work, especially when the required tasks are repetitive and boring. The euphoria does not last, however, and is followed by an intense mental depression and fatigue as the amphetamines deplete the neuronal stores of dopamine in the limbic system, the pleasure center of the brain (see Chapter 3). 

The drug bupropion, sold as Wellbutrin SR and Zyban, is a prescription-only antidepressant that has been successfully used to help smokers quit. It targets the pleasure centers of the brain. Again, talk with your doctor about possibly getting a prescription to help you cope with the emotional components of quitting. 

One of the most dramatic forms of instrumental conditioning can be demonstrated after electrodes are implanted in the pleasure centers of the brain of an experimental animal. If a lever switch is now connected to an electrical device that stimulates this pleasure area, the animal will learn to press the lever. Indeed, it will learn to press it as continuously as possible. Animals have been known to work their paws raw pressing the lever, ignoring food and water beside them in spite of their hunger and thirst, ignoring a sexually receptive mate. Direct stimulation of pleasure centers in the brain can be very reinforcing ... 

Simulations of reality, whether realistic or not, can also trigger emotions that in turn affect the brain s pleasure centers. We can become conditioned to distort our simulations of reality in ways that make us feel good. Since apparent unpleasant feelings often have a hidden secondary gain of feeling good underneath, as was discovered in studies of psychopathology, simulations of reality that seem to make us suffer may have a hidden payoff, a point we shall explore later. 

It requires denying the pleasure center in the brain those good feelings it has come to crave. Giving up drugs means giving up pleasure. 

Computer-brain interfaces can work two ways. Cochlear implants have been developed to detect sound with an external microphone and relay the electrical signal to electrode arrays that directly stimulate inner ear nerve fibers. A visual prosthesis promises to similarly help the blind by applying electrical signals from a camera to an array of microelectrodes implanted into the visual cortex of the brain. Electrical signals from the brain can be used to control prosthetic limbs, computer software, or robots. Electrodes implanted into the pleasure centers of the brains of rats have been used to train rats to respond to investigators commands. 

Ikemoto S. and Panksepp J. The role of nucleus accumbens dopamine in motivated behavior a unifying interpretation with special reference to reward-seeking. Brain. Res. Rev. 1999 31 6-41. lacques S. Brain stimulation reward pleasure centers after twenty five years. Neurosurgery 1999 5 277-283. 

Olds, J. (1956). Pleasure centers in the brain. Scientific American, October 1956. Reprinted in Coopersmith, S. (ed.). Frontiers of Psychological Research (1966), pp. 54—59. San Francisco W.H. Freeman and Company. 

As a stimulant, nicotine increases the level of adrenaline in the blood, which increases the heart rate and blood pressure. Nicotine is addictive because it activates pleasure centers in the brain. Coniine, which is obtained from hemlock, is extremely toxic. 

It is a central nervous system stimulant, preventing reuptake of neurotransmitters like dopamine (see pl69), serotonin (p451), and noradrenaline (p9). This impacts on the pleasure center of the brain, explaining its stimulant effects. It is also a sodium-channel blocker, which causes its anesthetic effects, because it interferes with the transmission of nerve impulses. 

Jacques S. Brain stimulation reward pleasure centers after twenty five years. Neurosurgery 1999 5 277-283. 

Figure 2.3 Many drugs of abuse act on the brain s reward center, which is illustrated above. The drugs cause neurons in the ventral tegmental area to release dopamine. The dopamine, in turn, initiates a chain of events that results in feelings of enjoyment and pleasure.

These natural reward centers have developed over the course of evolution to reinforce useful behaviors (e.g., pleasure, sexual satisfaction, eating, and drinking). It is believed that drugs such as cocaine and amphetamine directly stimulate these centers, while opiates free the pathways from inhibitory control. Nicotine, on the other hand, reaches the brain in as little as 10-20 seconds, where it stimulates nicotine receptors to cause dopaminergic neurons to release large quantities of dopamine. After a few hours, dopamine levels decline, causing withdrawal symptoms to readily appear (e.g., anxiety, irritability, and inattentiveness). When cigarette smokers say they need a smoke to steady their nerves, what they really mean is that they have to contend with nicotine withdrawal. 

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