Nucleus Accumbens

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.