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The Nucleus Accumbens
Martina Cupova and Julia Matejcek
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
The Reward Circuit
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.
A study by James Oldes•Aim – to determine how rats would respond to
the opportunity of stimulating their pleasure
centers by pressing a lever.
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.
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.
A study by Axmacher et al.
•Aim: to determine
whether activation of the
nucleus accumbens
precedes the formation
of memories of
surprising events.
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.
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.
Schaepfer et al.
• Aim: try to treat severely depressed patients who had not responded to alternative treatments using deep brain stimulation.
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.
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.
Dysfunction
•Depression
•ADHD – motivation is impaired.
•Drug addiction – unusually high levels of
dopamine in the nucleus accumbens.
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
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.