Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Brain’s reward circuitry revealed in procrastinating primates

11.08.2004


Using a new molecular genetic technique, scientists have turned procrastinating primates into workaholics by temporarily suppressing a gene in a brain circuit involved in reward learning. Without the gene, the monkeys lost their sense of balance between reward and the work required to get it, say researchers at the NIH’s National Institute of Mental Health (NIMH).



"The gene makes a receptor for a key brain messenger chemical, dopamine," explained Barry Richmond, M.D., NIMH Laboratory of Neuropsychology. "The gene knockdown triggered a remarkable transformation in the simian work ethic. Like many of us, monkeys normally slack off initially in working toward a distant goal. They work more efficiently – make fewer errors – as they get closer to being rewarded. But without the dopamine receptor, they consistently stayed on-task and made few errors, because they could no longer learn to use visual cues to predict how their work was going to get them a reward."

Richmond, Zheng Liu, Ph.D., Edward Ginns, M.D., and colleagues, report on their findings in the August 17, 2004 Proceedings of the National Academy of Sciences, published online the week of August 9th.


Richmond’s team trained monkeys to release a lever when a spot on a computer screen turned from red to green. The animals knew they had performed the task correctly when the spot turned blue. A visual cue--a gray bar on the screen--got brighter as they progressed through a succession of trials required to get a juice treat. Though never punished, the monkeys couldn’t graduate to the next level until they had successfully completed the current trial.

As in a previous study using the same task, the monkeys made progressively fewer errors with each trial as the reward approached, with the fewest occurring during the rewarded trial. Previous studies had also traced the monkeys’ ability to associate the visual cues with the reward to the rhinal cortex, which is rich in dopamine. There was also reason to suspect that the dopamine D2 receptor in this area might be critical for reward learning. To find out, the researchers needed a way to temporarily knock it out of action.

Molecular geneticist Ginns, who recently moved from NIMH to the University of Massachusetts, adapted an approach originally used in mice. He fashioned an agent (DNA antisense expression construct) that, when injected directly into the rhinal cortex of four trained monkeys, spawned a kind of decoy molecule which tricked cells there into turning-off D2 expression for several weeks. This depleted the area of D2 receptors, impairing the monkeys’ reward learning. For a few months, the monkeys were unable to associate the visual cues with the workload – to learn how many trials needed to be completed to get the reward.

"The monkeys became extreme workaholics, as evidenced by a sustained low rate of errors in performing the experimental task, irrespective of how distant the reward might be," said Richmond. "This was conspicuously out-of-character for these animals. Like people, they tend to procrastinate when they know they will have to do more work before getting a reward."

To make sure that it was, indeed, the lack of D2 receptors that was causing the observed effect, the researchers played a similar recombinant decoy trick targeted at the gene that codes for receptors for another neurotransmitter abundant in the rhinal cortex: NMDA (N-methlD-aspartate). Three monkeys lacking the NMDA receptor in the rhinal cortex showed no impairment in reward learning, confirming that the D2 receptor is critical for learning that cues are related to reward prediction. The researchers also confirmed that the DNA treatments actually affected the targeted receptors by measuring receptor binding following the intervention in two other monkeys’ brains.

"This new technique permits researchers to, in effect, measure the effects of a long-term, yet reversible, lesion of a single molecular mechanism," said Richmond. "This could lead to important discoveries that impact public health. In this case, it’s worth noting that the ability to associate work with reward is disturbed in mental disorders, including schizophrenia, mood disorders and obsessive-compulsive disorder, so our finding of the pivotal role played by this gene and circuit may be of clinical interest," suggested Richmond.

"For example, people who are depressed often feel nothing is worth the work. People with OCD work incessantly; even when they get rewarded they feel they must repeat the task. In mania, people will work feverishly for rewards that aren’t worth the trouble to most of us."

Jules Asher | EurekAlert!
Further information:
http://www.nih.gov

More articles from Life Sciences:

nachricht For a chimpanzee, one good turn deserves another
27.06.2017 | Max-Planck-Institut für Mathematik in den Naturwissenschaften (MPIMIS)

nachricht New method to rapidly map the 'social networks' of proteins
27.06.2017 | Salk Institute

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Touch Displays WAY-AX and WAY-DX by WayCon

27.06.2017 | Power and Electrical Engineering

Drones that drive

27.06.2017 | Information Technology

Ultra-compact phase modulators based on graphene plasmons

27.06.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>