Posts tagged brain response

Those vulnerable to alcoholism may experience an unusually large response in the brain’s reward-seeking pathway when they take a drink

Research from McGill University suggests that people who are vulnerable to developing alcoholism exhibit a distinctive brain response when drinking alcohol, according to a new study by Prof. Marco Leyton, of McGill University’s Department of Psychiatry. Compared to people at low risk for alcohol-use problems, those at high risk showed a greater dopamine response in a brain pathway that increases desire for rewards. These findings, published in the journal Alcoholism: Clinical & Experimental Research, could help shed light on why some people are more at risk of suffering from alcoholism and could mark an important step toward the development of treatment options.

“There is accumulating evidence that there are multiple pathways to alcoholism, each associated with a distinct set of personality traits and neurobiological features”, said Prof. Leyton, a researcher in the Mental Illness and Addiction axis at the Research Institute of the McGill University Health Centre (RI-MUHC). “These individual differences likely influence a wide range of behaviors, both positive and problematic. Our study suggests that a tendency to experience a large dopamine response when drinking alcohol might contribute to one (or more) of these pathways.”

For the study, researchers recruited 26 healthy social drinkers (18 men, 8 women), 18 to 30 years of age, from the Montreal area. The higher-risk subjects were then identified based on personality traits and having a lower intoxication response to alcohol (they did not feel as drunk despite having drunk the same amount). Finally, each participant underwent two positron emission tomography (PET) brain scan exams after drinking either juice or alcohol (about 3 drinks in 15 minutes).

“We found that people vulnerable to developing alcoholism experienced an unusually large brain dopamine response when they took a drink,” said Leyton. “This large response might energize reward-seeking behaviors and counteract the sedative effects of alcohol. Conversely, people who experience minimal dopamine release when they drink might find the sedative effects of alcohol especially pronounced.”

“Although preliminary, the results are compelling,” said Dr. Leyton. “A much larger body of research has identified a role for dopamine in reward-seeking behaviors in general. For example, in both laboratory animals and people, increased dopamine transmission seems to enhance the attractiveness of reward-related stimuli. This effect likely contributes to why having one drink increases the probability of getting a second one – the alcohol-induced dopamine response makes the second drink look all the more desirable. If some people are experiencing unusually large dopamine responses to alcohol, this might put them at risk.”

“People with loved ones struggling with alcoholism often want to know two things: How did they develop this problem? And what can be done to help? Our study helps us answer the first question by furthering our understanding of the causes of addictions. This is an important step toward developing treatments and preventing the disorder in others.”

(Source: newswise.com)

Controversy exists over what some mental health experts call “hypersexuality,” or sexual “addiction.” Namely, is it a mental disorder at all, or something else? It failed to make the cut in the recently updated Diagnostic and Statistical Manual of Mental Disorders, or DSM-5, considered the bible for diagnosing mental disorders. Yet sex addiction has been blamed for ruining relationships, lives and careers.

Now, for the first time, UCLA researchers have measured how the brain behaves in so-called hypersexual people who have problems regulating their viewing of sexual images. The study found that the brain response of these individuals to sexual images was not related in any way to the severity of their hypersexuality but was instead tied only to their level of sexual desire.

In other words, hypersexuality did not appear to explain brain differences in sexual response any more than simply having a high libido, said senior author Nicole Prause, a researcher in the department of psychiatry at the Semel Institute for Neuroscience and Human Behavior at UCLA.

"Potentially, this is an important finding," Prause said. "It is the first time scientists have studied the brain responses specifically of people who identify as having hypersexual problems."

The study appears in the current online edition of the journal Socioaffective Neuroscience and Psychology.

A diagnosis of hypersexuality or sexual addiction is typically associated with people who have sexual urges that feel out of control, who engage frequently in sexual behavior, who have suffered consequences such as divorce or economic ruin as a result of their behaviors, and who have a poor ability to reduce those behaviors.

But, said Prause and her colleagues, such symptoms are not necessarily representative of an addiction — in fact, non-pathological, high sexual desire could also explain this cluster of problems.

One way to tease out the difference is to measure the brain’s response to sexual-image stimuli in individuals who acknowledge having sexual problems. If they indeed suffer from hypersexuality, or sexual addiction, their brain response to visual sexual stimuli could be expected be higher, in much the same way that the brains of cocaine addicts have been shown to react to images of the drug in other studies.

The study involved 52 volunteers: 39 men and 13 women, ranging in age from 18 to 39, who reported having problems controlling their viewing of sexual images. They first filled out four questionnaires covering various topics, including sexual behaviors, sexual desire, sexual compulsions, and the possible negative cognitive and behavioral outcomes of sexual behavior. Participants had scores comparable to individuals seeking help for hypersexual problems.

While viewing the images, the volunteers were monitored using electroencephalography (EEG), a non-invasive technique that measures brain waves, the electrical activity generated by neurons when they communicate with each other. Specifically, the researchers measured event-related potentials, brain responses that are the direct result of a specific cognitive event.

"The volunteers were shown a set of photographs that were carefully chosen to evoke pleasant or unpleasant feelings," Prause said. "The pictures included images of dismembered bodies, people preparing food, people skiing — and, of course, sex. Some of the sexual images were romantic images, while others showed explicit intercourse between one man and one woman."

The researchers were most interested in the response of the brain about 300 milliseconds after each picture appeared, commonly called the “P300” response. This basic measure has been used in hundreds of neuroscience studies internationally, including studies of addiction and impulsivity, Prause said. The P300 response is higher when a person notices something new or especially interesting to them.

The researchers expected that P300 responses to the sexual images would correspond to a person’s sexual desire level, as shown in previous studies. But they further predicted that P300 responses would relate to measures of hypersexuality. That is, in those whose problem regulating their viewing of sexual images could be characterized as an “addiction,” the P300 reaction to sexual images could be expected to spike.

Instead, the researchers found that the P300 response was not related to hypersexual measurements at all; there were no spikes or decreases tied to the severity of participants’ hypersexuality. So while there has been much speculation about the effect of sexual addiction or hypersexuality in the brain, the study provided no evidence to support any difference, Prause said.

"The brain’s response to sexual pictures was not predicted by any of the three questionnaire measures of hypersexuality," she said. "Brain response was only related to the measure of sexual desire. In other words, hypersexuality does not appear to explain brain responses to sexual images any more than just having a high libido."

But debate continues over whether sex addiction is indeed an addiction. A study published in 2012 by Prause’s colleague Rory Reid, a UCLA assistant professor of psychiatry, supported the reliability of the proposed DSM-5 diagnostic criteria for hypersexual disorder. However, Prause notes, that study was not focused on the validity of sex addiction or impulsivity, and did not use any biophysiological data in the analysis.

"If our study can be replicated," she said, "these findings would represent a major challenge to existing theories of a sex ‘addiction.’ "

(Source: newsroom.ucla.edu)

Several human and animal studies have shown a relationship between a preference for highly sweet tastes and alcohol use disorders. Furthermore, the brain mechanisms of sweet-taste responses may share common neural pathways with responses to alcohol and other drugs. A new study using functional magnetic resonance imaging (fMRI) has found that recent drinking is related to the orbitofrontal-region brain response to an intensely sweet stimulus, a brain response that may serve as an important phenotype, or observable characteristic, of alcoholism risk.

Results will be published in the December 2013 issue of Alcoholism: Clinical & Experimental Research and are currently available at Early View.

"It has long-been known that animals bred to prefer alcohol also drink considerably greater quantities of sweetened water than do animals without this selective breeding for alcohol preference," explained David A. Kareken, deputy director of the Indiana Alcohol Research Center, a professor in the department of neurology at Indiana University School of Medicine, and corresponding author for the study. "More recently, it has become clear that animals bred to prefer the artificial sweetener, saccharin, also drink more alcohol. Although the data in humans are somewhat more variable, some studies do show that alcoholics, or even non-alcoholics with a family history of alcoholism, have a preference for unusually sweet tastes. Thus, while the precise reasons remain unclear, there does seem to be significant evidence suggesting some link between the rewarding properties of both sweet tastes and alcohol."

Kareken added that this is the first study to examine the extent to which regions of the brain’s reward system, as they respond to an intensely sweet taste, are related to human drinking patterns.

Kareken and his colleagues recruited 16 (12 males, 4 females) right-handed, non-treatment seeking, healthy volunteers with a mean age of 26 years from the community. All participants underwent a taste test using a range of sucrose concentrations, and their blood oxygen dependent (BOLD) activation was measured during an fMRI scan while receiving small squirts of either water or an intensely sweet mixture of sugar in water. All were asked about their drinking patterns.

"Our study was designed to determine which brain areas responded to sweet taste – as compared to plain water – and the extent to which these brain responses were related to subjects’ binge-drinking patterns, the number of alcoholic drinks subjects consumed per day when drinking," explained Kareken.

"In addition to ‘activating’ the brain’s gustatory or taste circuits, the sugared water also activated key elements of what neuroscientists consider to be part of the brain’s reward system, including the ventral striatum, amygdala, and parts of the orbitofrontal cortex – the inferior frontal lobe surface just above the eyes – that respond to ingested rewards," Kareken said. "We refer to these as ‘primary’ rewards, being distinct from secondary rewards, like money, which can be used to obtain primary rewards."

What the researchers found was that the response to this intensely sweet taste in the left orbitofrontal area correlated significantly with subjects’ drinking patterns.

"Specifically, the trend was such that those who drank more alcohol on drinking days had stronger left orbitofrontal responses to the intensely sweet water," said Kareken. "Subjects’ subjectively rated liking of the sweetened water also contributed to this relationship, so that both the brain response itself, as well as liking of the sugared water, collectively correlated with drinking behavior."

While previous human and animal research has noted this association between preferences for both sweet tastes and alcohol intoxication, Kareken believes that this is the first study to examine the human brain mechanism behind this association.

"While much more research needs to be done to truly understand the commonalities between sweet-liking and alcoholism, and while alcoholism itself is likely the product of several mechanisms, our findings may implicate a particular brain region that is more generally involved in coding for the value of ‘primary’ rewards such as pleasures," he said. "In a more practical sense, the findings are compelling evidence that the brain response to an intensely sweet taste may be used in future research to test for differences in the reward circuits of those at risk for alcoholism. This may be particularly useful since alcohol itself is not an easy drug to work with in this kind of human imaging, and since alcohol exposure is not ethically appropriate for use in all at-risk subjects, or in subjects trying to abstain from drinking."

(Source: eurekalert.org)