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In a study published Wednesday in the journal NeuroReport, scientists Martha McClintock and Suma Jacob found differences in brain activity among women exposed to the male steroid androstadienone. The scientists used brain scans to track changes in vision, attention and emotion when androstadienone was released on a long-term, rather than short-term basis.
The steroid is used to make perfumes and colognes and is found in sweat, auxiliary hair, blood and semen. McClintock, an expert on "chemosignals" and pheromones, said the study indicates chemosignals may be more important than previously thought.
"The widespread neural effects of this compound open the possibility that other olfactory signals may also have a significant impact on the whole human brain, even in the absence of conscious detection as an odor," McClintock said.
McClintock noted the olfactory system is man's most primitive sense.
"Many people view olfaction as something that we've evolved beyond -- that humans don't have a good sense of smell and, therefore, it is relatively unimportant," she said. "What this demonstrates is that tiny amounts of chemical can have a profound and widespread effect on the brain."
Earlier research by McClintock and Jacob indicated androstadienone moderates a woman's mood, with even tiny amounts helping to maintain a positive attitude as long as two hours after completion of a tedious questionnaire.
"This study is the first to demonstrate the cumulative effects of a sustained unconscious chemosignal on neural function, let alone a human chemosignal," the researchers said. "The widespread neural effects of this compound open the possibility that other olfactory signals, whether biologically relevant or not, may also have a significant impact on the whole human brain, even in the absence of conscious detection as an odor."
For the study, the researchers told 10 women, ages 20 to 35, they were conducting a study related to the sense of smell but did not tell them anything about the steroid. They placed a small amount of androstadienone in propylene glycol and used a trace of clove oil to mask any possible odor.
The women were tested in separate sessions two days apart by swiping a sample of the clove-propylene glycol solution with androstadienone under the women's noses in one test and a sample of the same solution without the steroid in another.
McClintock said there was a wide range of responses among the test subjects. While some reacted extremely positively to the steroid, others reactive negatively. The reactions may indicate that virtually undetectable chemical signals may be the reason why people take an instant dislike or liking to each other.
"It's possible this is a social form of communication," she said. To reduce the influence of outside factors, each woman was placed at a computer and told to perform simple, non-stressful tasks as they received a glucose solution intravenously on each of the test days.
The women were then given PET scans to measure the amount of the glucose just used by their brains. The chart of brain activity produced highlighted the areas of the brain that became more engaged and those that became less active.
The scans showed not only were the sections involved in olfactory functions engaged, but also regions associated with attention, emotion and vision.
"Our strong effects in this area support the hypothesis that androstadienone modulates ongoing behavior, or, more specifically, processing the task at hand," McClintock said.
An alternative explanation, she said, is that the steroid plays a previously unknown role in processing visual information. "It suggests we should think about these things much more broadly than sex," she said. "They really may be social signals and affect how we react and work when we're doing things in social groups."
The steroid is used to make perfumes and colognes and is found in sweat, auxiliary hair, blood and semen. McClintock, an expert on "chemosignals" and pheromones, said the study indicates chemosignals may be more important than previously thought.
"The widespread neural effects of this compound open the possibility that other olfactory signals may also have a significant impact on the whole human brain, even in the absence of conscious detection as an odor," McClintock said.
McClintock noted the olfactory system is man's most primitive sense.
"Many people view olfaction as something that we've evolved beyond -- that humans don't have a good sense of smell and, therefore, it is relatively unimportant," she said. "What this demonstrates is that tiny amounts of chemical can have a profound and widespread effect on the brain."
Earlier research by McClintock and Jacob indicated androstadienone moderates a woman's mood, with even tiny amounts helping to maintain a positive attitude as long as two hours after completion of a tedious questionnaire.
"This study is the first to demonstrate the cumulative effects of a sustained unconscious chemosignal on neural function, let alone a human chemosignal," the researchers said. "The widespread neural effects of this compound open the possibility that other olfactory signals, whether biologically relevant or not, may also have a significant impact on the whole human brain, even in the absence of conscious detection as an odor."
For the study, the researchers told 10 women, ages 20 to 35, they were conducting a study related to the sense of smell but did not tell them anything about the steroid. They placed a small amount of androstadienone in propylene glycol and used a trace of clove oil to mask any possible odor.
The women were tested in separate sessions two days apart by swiping a sample of the clove-propylene glycol solution with androstadienone under the women's noses in one test and a sample of the same solution without the steroid in another.
McClintock said there was a wide range of responses among the test subjects. While some reacted extremely positively to the steroid, others reactive negatively. The reactions may indicate that virtually undetectable chemical signals may be the reason why people take an instant dislike or liking to each other.
"It's possible this is a social form of communication," she said. To reduce the influence of outside factors, each woman was placed at a computer and told to perform simple, non-stressful tasks as they received a glucose solution intravenously on each of the test days.
The women were then given PET scans to measure the amount of the glucose just used by their brains. The chart of brain activity produced highlighted the areas of the brain that became more engaged and those that became less active.
The scans showed not only were the sections involved in olfactory functions engaged, but also regions associated with attention, emotion and vision.
"Our strong effects in this area support the hypothesis that androstadienone modulates ongoing behavior, or, more specifically, processing the task at hand," McClintock said.
An alternative explanation, she said, is that the steroid plays a previously unknown role in processing visual information. "It suggests we should think about these things much more broadly than sex," she said. "They really may be social signals and affect how we react and work when we're doing things in social groups."
