But when men and women have nicotine in their bodies, these brain activity differences practically disappear. Among both smokers and non-smokers on nicotine, during aggressive moments such as impulsive or hostile acts, there are virtually no differences in brain activity between the sexes -- illustrating how nicotine can impact brain function. Results of the study, conducted by Brain Imaging Center researchers supported by the UCI Transdisciplinary Tobacco Use Research Center, are published in the online edition of the International Journal of Neuropsychopharmacology, and will be available in print next month.
The researchers found during behavioral and brain-imaging tests on hostility and impulsive reaction that brain-metabolism activity -- which indicates when neurons are working -- was much higher in many brain areas of women than men. But when the test subjects were given nicotine, metabolic activity significantly declined in the women and slightly increased in men -- the original differences all but disappeared.
According to Dr. Steven Potkin, who along with neuroanatomist James Fallon led the study, these results shed light on two issues. First, brain activity areas involved in choice, attention, short-term memory, planning, mood, emotion and language are different in men and women -- differences exaggerated during moments of hostility or impulsiveness. In addition, the study provides new evidence that men's and women's brains respond differently to the same stimuli -- a result sure to fuel the ongoing debate over fundamental variations in brain function based on gender. Since these differences are present even in non-smokers, they appear to be inherent differences in brain metabolism and function between men and women.
The study also found that nicotine can be an "equalizer" of the sexes in brain activity, with nicotine reversing brain responses that would otherwise take place. Along with better understanding nicotine's grip on the brain, when it comes to smokers, this finding will enhance researchers' appreciation for the distinctions between the sexes.
"Gender differences regarding the effects of nicotine on brain function and metabolism have been largely unstudied and unidentified," Potkin said. "Understanding brain activity will provide new light into understanding smoking behavior. For instance, we already know that men and women smoke cigarettes with varying rates and reasons. We also know women take fewer and shorter puffs of cigarettes than men. Women also are less successful using the nicotine patch or gum therapies when trying to quit smoking."
To better understand how nicotine impacts brain activity, Potkin and Fallon tested the behavior of smokers and non-smokers when subjected to different tests. For example, during one experiment, researchers had participants play a "hostility" game -- a game that allowed the winner to choose the loudness of a noise blasted at the losing player, with the opponent then having an opportunity to retaliate. The researchers found among all participants, behavioral responses differed by gender, with men retaliating by cranking up the volume in a short blast, while women sustained the noise longer, which one of the researchers referred to as shouting for the men and nagging for the women. Differences in brain activity also was split by gender: Among men and women who smoked, while their behavior differed by gender, their brain activity was virtually identical following nicotine.
Similar findings resulted when testing impulsive responses.
Potkin conducted the research using brain-imaging technology. This study included 42 females and 77 males, 64 of whom were non-smokers. The 55 smokers smoked at least 10 cigarettes, but fewer than two packs, per day for at least one year. Thus, these brain metabolism findings apply to most smokers. Nicotine was administered by a patch.
Potkin, who holds the Robert R. Sprague Chair in Brain Imaging, is director of the Brain Imaging Center, and Fallon is a professor of neurobiology and anatomy. David Keator, James Mbogori and Derek Taylor in the UCI School of Medicine assisted with the study.
About the UCI Transdisciplinary Tobacco Use Research Center:
UCI TTURC is funded jointly by the National Institute of Drug Abuse and National Cancer Institute in partnership with the Robert Wood Johnson Foundation. The major research focus of the center is to identify key factors that underlie susceptibility to nicotine addiction in adolescents and young adults.
About the University of California, Irvine:
The University of California, Irvine is a top-ranked public university dedicated to research, scholarship and community service. Founded in 1965, UCI is among the fastest-growing University of California campuses, with more than 24,000 undergraduate and graduate students and about 1,400 faculty members. The second-largest employer in dynamic Orange County, UCI contributes an annual economic impact of $3 billion.
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