Download - Nucleus Accumbens
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The Nucleus Accumbens
Martina Cupova and Julia Matejcek
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Location in the Brain• Midbrain, at the top
of the brainstem.• Works in tandem
with the other centers involved in pleasure.– Ventral tagmental
area– Prefrontal cortex
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Function• Part of the reward circuit.• Two neurotransmitters:
– dopamine (desire)– seretonin (satiety and
inhibition)• Maintains motivation.• Controls feeding, sexual,
reward, stress-related, and drug self-administration behaviours.
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A study by James Oldes• Aim – to determine how rats would respond to
the opportunity of stimulating their pleasure centers by pressing a lever.
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Procedure
• Oldes implanted electrodes in the brains of the rats.
• They received an electrical shock to their nucleus accumbens each time they pressed a lever.
• In some conditions, an electrified grid was placed between the rat and the lever.
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Results and Findings
• The rats became addicted to the rush of pushing the lever.
• They preferred it to eating and drinking – some of the rats even starved themselves.
• Many even ran across the electrified grid to reach the lever.
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A study by Axmacher et al.
• Aim: to determine whether activation of the nucleus accumbens precedes the formation of memories of surprising events.
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Procedure• Implanted electrodes in the nucleus accumbens
and hippocampus of participants.• Showed participants a picture of a face on a red
background for a few seconds and then switched the picture to a house on a green background.
• Used an electroencephalogram (EEG) to put together the overall pattern of brain activity while this was happening.
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Results and Findings• Switching the stimulus activated the
hippocampus, the nucleus accumbens, and then the hippocampus again.
• This brain pattern provides a way to consistently predict memory formation.
• The nucleus accumbens is involved in processing not only rewards, but also novel information.– May influence further processing by the
hippocampus.
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Schaepfer et al.
• Aim: try to treat severely depressed patients who had not responded to alternative treatments using deep brain stimulation.
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Procedure
• Implanted the electrodes in the nucleus accumbens of the patients.
• Turned on the stimulator to send electrical signals to that part of the brain.
• Turned the stimulator on and off over a period of weeks and tracked development of symptoms by questionnaires.
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Results and Findings• Most patients reported positive effects
instantaneously – they had newfound motivation.
• Most patients improved only in the short-term – they had instant results that did not last.
• Deep brain stimulation of the nucleus accumbens did not treat depression in the long term.
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What happens when the nucleus accumbens is dysfunctional?
• Depression – the nucleus accumbens is the centerpiece of the rewards circuit so when it is dysfunctional, motivation and satisfaction can be impaired.
• ADHD – motivation is impaired.
• Drug addiction – unusually high levels of dopamine in the nucleus accumbens.
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Works CitedCrane, J., & Hannibal, J. (2009). Psychology: Course Companion. Oxford:
Oxford University Press.
Dubuc, B. (2002, September). The Pleasure Centres Affected by Drugs. In The
Brain from Top to Bottom. Retrieved from http://thebrain.mcgill.ca/
Fernandez-Espejo, E. (2000, May). How does the Nucleus Accumbens
Function? In Pub Med [biomedical data base]. Retrieved from
http://www.ncbi.nlm.nih.gov/ pubmed
Harmon, K. (2010, February 24). Surprised? How the Brain Records Memories
of the Unexpected. In The Scientific American. Retrieved from
http://www.scientificamerican.com
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Works Cited cont.New Way To Fight Cocaine Addiction Discovered. (2009, April 2). Science Daily.
Retrieved from University of California - Irvine website:
http://www.sciencedaily.com
Scientists Discover Alterations in Brain’s Reward System Related to Attention-
Deficit/ hyperactivity Disorder. (n.d.). Science Daily. Retrieved from
Universitat Autònoma de Barcelona website: http://www.sciencedaily.com
Singer, E. (2007, April 26). Brain Electrodes Help Treat Depression. In Technology
Review. Retrieved from Massachusetts Institute of Technology website:
http://technologyreview.com
Surprise! Neural Mechanism May Underlie an Enhanced Memory for the
Unexpected. (2010, February 25). Science Daily.