Navigation Links
Aggression-related gene weakens brain's impulse control circuits

A version of a gene previously linked to impulsive violence appears to weaken brain circuits that regulate impulses, emotional memory and thinking in humans, researchers at the National Institutes of Health's (NIH) National Institute of Mental Health (NIMH) have found. Brain scans revealed that people with this version ?especially males ?tended to have relatively smaller emotion-related brain structures, a hyperactive alarm center and under-active impulse control circuitry. The study identifies neural mechanisms by which this gene likely contributes to risk for violent and impulsive behavior through effects on the developing brain.

NIMH intramural researchers Andreas Meyer-Lindenberg, M.D., Ph.D, Daniel Weinberger, M.D., and colleagues report on their magnetic resonance imaging (MRI) study online in the Proceedings of the National Academy of Sciences during the week of March 20, 2006.

"These new findings illustrate the breathtaking power of 'imaging genomics' to study the brain's workings in a way that helps us to understand the circuitry underlying diversity in human temperament," said NIH Director Elias A. Zerhouni, M.D., who conducted MRI studies earlier in his career.

"By itself, this gene is likely to contribute only a small amount of risk in interaction with other genetic and psychosocial influences; it won't make people violent," explained Meyer-Lindenberg. "But by studying its effects in a large sample of normal people, we were able to see how this gene variant biases the brain toward impulsive, aggressive behavior."

The gene is one of two common versions that code for the enzyme monoamine oxydase-A (MAO-A), which breaks down key mood-regulating chemical messengers, most notably serotonin. The previously identified violence-related, or L, version, contains a different number of repeating sequences in its genetic code than the other version (H), likely resulting in lower enzyme activity and hence higher levels of serotoni n. These, in turn, influence how the brain gets wired during development. The variations may have more impact on males because they have only one copy of this X-chromosomal gene, while females have two copies, one of which will be of the H variant in most cases.

Several previous studies had linked increased serotonin during development with violence and the L version of MAO-A. For example, a 2002 study* by NIMH-funded researchers discovered that the gene's effects depend on interactions with environmental hard knocks: men with L were more prone to impulsive violence, but only if they were abused as children. Meyer-Lindenberg and colleagues set out to discover how this works at the level of brain circuitry.

Using structural MRI in 97 subjects, they found that those with L showed reductions in gray matter (neurons and their connections) of about 8 percent in brain structures of a mood-regulating circuit (cingulate cortex, amygdala) among other areas. Volume of an area important for motivation and impulse regulation (orbital frontal cortex) was increased by 14 percent in men only. Although the reasons are unknown, this could reflect deficient pruning ?the withering of unused neuronal connections as the brain matures and becomes more efficient, speculates Meyer-Lindenberg.

The researchers then looked at effects on brain activity using functional MRI (fMRI) scans. While performing a task matching emotionally evocative pictures ?angry and fearful faces ?subjects with L showed higher activity in the fear hub (amygdala). At the same time, decreased activity was observed in higher brain areas that regulate the fear hub (cingulate, orbital frontal, and insular cortices) ?essentially the same circuit that was changed in volume.

While these changes were found in both men and women, two other experiments revealed gene-related changes in men only. In a task which required remembering emotionally negative information, men, but not women, with L had increased reactivity in the fear (amygdala) and memory (hippocampus) hubs. Men with L were also deficient during a task requiring them to inhibit a simple motor response; they failed to activate a part of the brain (cingulate cortex) important for inhibiting such behavioral impulses. This region was, conspicuously, the cortex area that was most reduced in volume.

The findings echo those of a 2005 NIMH study** showing how another serotonin-related gene variant shapes the same mood-regulating circuit. In this study also, the gene version that boosts serotonin levels resulted in impaired emotion-related lower brain structures, increased fear hub activation and a weaker response of its regulatory circuits. Yet, the effects of the L version of MAO-A were more extensive, perhaps reflecting the fact that it also impacts another key mood-regulating neurotransmitter, norepinephrine.

The weakened regulatory circuits in men with L are compounded by intrinsically weaker connections between the orbital frontal cortex and amygdala in all men, say the researchers.

"Heightened sensitivity in brain circuits important to cognitive inhibition and memory for negative emotional information may contribute to increased vulnerability of men with L exposed to abuse during childhood," suggested Weinberger. "Since only men showed gene effects in several of these circuits, this could lead to a situation where multiple brain control mechanisms are impaired and contribute to manifestly violent behavior, a kind of genetic double jeopardy."


'"/>

Source:NIH/National Institute of Mental Health


Related biology news :

1. NYU study reveals how brains immune system fights viral encephalitis
2. Deep sleep short-circuits brains grid of connectivity
3. Thinking the pain away? Study shows the brains painkillers may cause placebo effect
4. Endocannabinoids ?the brains cannabis ?demonstrate novel modes of action to stress
5. Animal models show that anabolic steroids flip the adolescent brains switch for aggression
6. Both alcoholism and chronic smoking can damage the brains prefrontal cortex
7. Tiny RNA molecules fine-tune the brains synapses
8. Oops! Researchers publish new findings on the brains response to costly mistakes
9. Flick of whiskers helps tease out brains shadow signaling system
10. The brains executive is an event planner
11. The brains motivation station
Post Your Comments:
*Name:
*Comment:
*Email:


(Date:4/17/2017)... MELBOURNE, Florida , April 17, 2017 ... security technology company, announces the filing of its 2016 Annual Report ... Securities and Exchange Commission. ... Report on Form 10-K is available in the Investor Relations section ... well as on the SEC,s website at http://www.sec.gov . ...
(Date:4/13/2017)... According to a new market research report "Consumer IAM Market ... Authorization), Service, Authentication Type, Deployment Mode, Vertical, and Region - Global Forecast ... from USD 14.30 Billion in 2017 to USD 31.75 Billion by 2022, ... ... MarketsandMarkets Logo ...
(Date:4/11/2017)... , Apr. 11, 2017 Research and ... Market 2017-2021" report to their offering. ... The global eye tracking market to grow at a ... report, Global Eye Tracking Market 2017-2021, has been prepared based on ... covers the market landscape and its growth prospects over the coming ...
Breaking Biology News(10 mins):
(Date:10/10/2017)... (PRWEB) , ... October 10, 2017 , ... San Diego-based ... of its corporate rebranding initiative announced today. The bold new look is part ... as the company moves into a significant growth period. , It will also expand ...
(Date:10/10/2017)... 10, 2017 International research firm Parks Associates announced ... at the TMA 2017 Annual Meeting , October 11 in ... residential home security market and how smart safety and security products impact ... Parks Associates: Smart Home ... "The residential security market has ...
(Date:10/9/2017)... , Oct. 9, 2017  BioTech Holdings announced ... by which its ProCell stem cell therapy prevents ... ischemia.  The Company, demonstrated that treatment with ProCell ... limbs saved as compared to standard bone marrow ... HGF resulted in reduction of therapeutic effect.  ...
(Date:10/9/2017)... ... October 09, 2017 , ... ... 5, 2017, in the medical journal, Epilepsia, Brain Sentinel’s SPEAC® System which ... video EEG, in detecting generalized tonic-clonic seizures (GTCS) using surface electromyography (sEMG). ...
Breaking Biology Technology: