Scientifically, impulsivity can appear as a choice for a small but immediate reward over a larger one that requires some delay. Choosing between present and future rewards is a fundamental need in schooling, says Luis Populin, associate professor of neuroscience at University of Wisconsin-Madison.
"If you say to an impulsive child, 'Do your homework so you will get a good grade at the end of the quarter,' that has less appeal than 'Let's play baseball this afternoon instead of studying chemistry.'"
To study impulsive behavior, Populin and graduate student Abigail Zdrale Rajala selected two rhesus macaque monkeys with opposite behaviors. One was extremely calm, while the other was nervous, fidgety and impulsive. The monkeys were trained to stare at a dot on a screen and, when it went dark, to choose between two pictures placed to the side. Their choice of picture determined whether they got a small but immediate sip of water, or a larger sip, after a delay ranging up to 16 seconds.
As expected, the calm monkey, but not the impulsive one, quickly figured out that waiting would bring the sweeter result.
This willingness to take a smaller reward right away rather than a larger, delayed reward, called "temporal discounting," is a common feature of "combined type" ADHD, which specifically lists impulsivity among its diagnostic criteria, Populin says.
When the monkeys were given a dose of methylphenidate, the active ingredient of the common ADHD drug Ritalin, they chose the delayed reward more frequently. The impulsive monkey actually showed the same preference for delayed rewards as the unmedicated, calm monkey. However, identifiable differences in their performance mean that methylphenidate improved the condition, but did not eliminate it.
"There is no perfect animal model of ADHD," says Rajala, "but many studies are performed on rodents; this one was done in a non-human primate, which is much closer to humans." The Society for Neuroscience adjudged the paper valuable enough to support Rajala's travel to the conference in San Diego.
Methylphenidate changes the elimination of dopamine, a "reward" neurotransmitter that is elevated by drugs like cocaine and amphetamine. The result is that more dopamine remains in the brain, which is the most likely explanation for the altered reward processing in the medicated monkeys.
Some scientists have thought that temporal discounting in ADHD may result from cognitive processing, which relies on the highly evolved frontal cortex in the brain. The new results support an alternative, but less common, hypothesis: that temporal discounting is linked to the reward-processing mechanism, which is governed by more primitive parts of the brain.
By teasing apart one characteristic of ADHD, the study could help refine drug or behavioral treatments of a disability that has grown 16 percent more common just since 2007, Populin says.David Tenenbaum
Luis Populin | EurekAlert!
Drone vs. truck deliveries: Which create less carbon pollution?
31.05.2017 | University of Washington
New study: How does Europe become a leading player for software and IT services?
03.04.2017 | Fraunhofer-Institut für System- und Innovationsforschung (ISI)
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...
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...
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...
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...
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)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
27.06.2017 | Earth Sciences
27.06.2017 | Earth Sciences
27.06.2017 | Life Sciences