But new work at the University of Wisconsin-Madison is now starting to clear up some of the mystery. Writing in the journal Biological Psychiatry, UW-Madison researchers report that ADHD drugs primarily target the prefrontal cortex (PFC), a region of the brain that is associated with attention, decision-making and an individual's expression of personality.
The finding could prove invaluable in the search for new ADHD treatments, and comes amidst deep public concern over the widespread abuse of existing ADHD medicines.
"There's been a lot of concern over giving a potentially addictive drug to a child [with ADHD]," says lead author Craig Berridge, a UW-Madison professor of psychology. "But in order to come up with a better drug we must first know what the existing drugs do."
A behavioral disorder that afflicts both children and adults, ADHD is marked by hyperactivity, impulsivity and an inability to concentrate. The National Institute of Mental Health estimates that 2 million children in the U.S. suffer from the condition, with between 30 to 70 percent of them continuing to exhibit symptoms in their adult years.
Despite public anxiety over the treatment of a behavioral condition with pharmacological drugs, doctors have continued to prescribe meds like Adderall, Ritalin and Dexedrine because - quite simply - they work better than anything else.
ADHD drugs fall into a class of medications known as stimulants. ADHD stimulants boost levels of two neurotransmitters, or chemical messengers in the brain, known as dopamine and norepinephrine. Dopamine is thought to play a role in memory formation and the onset of addictive behaviors, while norepinephrine has been linked with arousal and attentiveness.
Berridge notes that scientists have learned little about how ADHD drugs work because past studies have primarily examined the effects of the medicines at high doses. High-dose stimulants can cause dramatic spikes in neurotransmitter levels in the brain, which can in turn impair attention and heighten the risk of developing addiction.
"It is surprising that no one was looking at low-dose [ADHD] drugs because we know that the drugs are most effective only at low doses," says Berridge. "So we asked the natural question: what are these drugs doing at clinically relevant doses?"
To answer that question, Berridge and his team monitored neurotransmitter levels in three different brain regions thought to be targeted by ADHD drugs: the PFC and two smaller brain areas known as the accumbens which has been linked with processing "rewards," and the medial septum, which has been implicated in arousal and movement.
Working with rats, the researchers conducted laboratory and behavioral tests to ensure that animal drug doses were functionally equivalent to doses prescribed in humans. Then, using a type of brain probe - a process known as microdialysis - the UW-Madison team measured concentrations of dopamine and norepinephrine in the three different brain areas, both in the presence and absence of low-dose ADHD stimulants.
Under the influence of ADHD drugs, dopamine and norepinephrine levels increased in the rats' PFC. Levels in the accumbens and medial septum, however, remained much the same, the scientists found.
"Our work provides pretty important information on the importance of targeting the PFC when treating ADHD," says Berridge, "In particular it tells us that if we want to produce new ADHD drugs, we need to target [neurotransmitter] transmission in the PFC."
In the future, Berridge and his colleagues plan to look deeper within the PFC to gain more detailed insights into how ADHD meds act on nerves to enhance cognitive ability.
Other researchers who contributed to the study include UW-Madison co-authors David Devilbiss, Matthew Andrzejewski, Ann Kelley, Brooke Schmeichel, Christina Hamilton and Robert Spencer, and Yale Medical School researcher Amy Arnsten.
Craig Berridge | EurekAlert!
Smart Data Transformation – Surfing the Big Wave
02.12.2016 | Fraunhofer-Institut für Angewandte Informationstechnik FIT
Climate change could outpace EPA Lake Champlain protections
18.11.2016 | University of Vermont
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy