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4035 Test 3 Study Guide (got 96%)

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PSYC 4035

Neurobiology of Addiction1Pleasure Centers in the BrainaIn the 1950s James Olds and Peter Milner accidentally discovered existence of Pleasure Centers in the BrainiRats were implanted with electrodes in certain brain structuresWhen they pressed a lever these sites would be electrically stimulatedMost rats found this selfstimulation so desirable that they would not stop to eat drink or rest but would press the lever until they were exhaustedThey would even cross electrified grids to reach the leveriiSelfstimulation only occurred in some parts of the subcortical brainOne of those was the nucleus accumbens NaC which is also known as the ventral striatumIn humans stimulation of the NaC may elicit smiling laughter pleasurable feelings etcEventually mapping showed that there was a neural reward circuit in the brain of humans and other animals that was responsible for these positive statesiiiNeural Reward Circuit1The pathway starts in one structure made up of dopamine neurons the ventral tegmental area of VTA2The VTA when activated as a result of a rewarding sensation releases dopamine onto the nucleus accumbens as well as the amygdala and the prefrontal cortex PFC3bDopamine Mediates PleasureiBefore 1990 almost all data suggested that dopamine signaled pleasure whether in response to drugs or any other reinforcing activityiiiiiEvidence that Dopamine Mediates Pleasure1In 1975 R Wise and R Yokel trained rats to press a lever for amphetamineAmphetamine causes dopamine to be released from the VTAThey then gave rats a chemical that blocked dopamine pimozideThe rate stopped pressing a lever that caused amphetamine to be injected into their veinsActually at first the rats pressed morefaster showing that they still were motivated and could move normallyBut pimozide seemed to block the rewarding aspects of the amphetamine2Dopamineblocking drugs will also blunt the reinforcing effect of food and hungry rats will stop running toward food
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