Laughter perception networks in brain different for mocking, joyful or ticklish laughter

A laugh may signal mockery, humor, joy or simply be a response to tickling, but each kind of laughter conveys a wealth of auditory and social information. These different kinds of laughter also spark different connections within the “laughter perception network” in the human brain depending on their context, according to research published May 8 in the open access journal PLOS ONE by Dirk Wildgruber and colleagues from the University of Tuebingen, Germany.

Laughter in animals is a form of social bonding based on a primordial reflex to tickling, but human laughter has come a long way from these playful roots. Though many people laugh when they’re tickled, ‘social laughter’ in humans can be used to communicate happiness, taunts or other conscious messages to peers. Here, researchers studied participants’ neural responses as they listened to three kinds of laughter: joy, taunt and tickling.

"Laughing at someone and laughing with someone leads to different social consequences," says Wildgruber. "Specific cerebral connectivity patterns during perception of these different types of laughter presumably reflect modulation of attentional mechanisms and processing resources.

The researchers found that brain regions sensitive to processing more complex social information were activated when people heard joyous or taunting laughter, but not when they heard the ‘tickling laughter’. However, ‘tickling laughter’ is more complex than the other types at the acoustic level, and consequently activated brain regions sensitive to this higher degree of acoustic complexity. These dynamic changes activated and connected different regions depending on the kind of laughter participants heard. Patterns of brain connectivity can impact cognitive function in health and disease. Though some previous research has examined how speech can influence these patterns, this study is among the first few to examine non-verbal vocal cues like laughter.

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Flies reveal that a sense of smell, like a melody, depends upon timing

The sense of smell remains a mystery in many respects. Fragrance companies, for instance, know it is crucial that chemical compounds in perfumes reach nostrils at different rates to create the desired sensory experience, but it is has been unclear why. Yale researchers decided to interrogate the common fruit fly for answers.

The team of Yale scientist Thierry Emonet, his postdoctoral associate Carlotta Martelli, and his colleague John Carlson systematically recorded both the stimulus reaching the fly and the responses of individual neurons over time. They found that the timing of neuronal response was independent of the concentration of the odor in the air, which in theory might help flies track fluctuating odor stimuli. However, the timing of neuronal response did depend on the identity of the odor.

Different odors elicited tiny delays in neural response. Such odor-dependent delays could be useful to the brain processing complex scents, say the scientists. The research also shows that specific interactions between odors and surfaces can affect the timing of the stimulus and therefore neural response.

Emonet says the findings suggest the world of smell is like music, in which chemical compounds of the scent act as notes and enable recognition of specific odors depending upon when they are played, or processed. For more information on the research, see the April 9 issue of the journal Neuroscience.

Your Brain on Big Bird: Sesame Street Helps to Reveal Patterns of Neural Development

Using brain scans of children and adults watching Sesame Street, cognitive scientists are learning how children’s brains change as they develop intellectual abilities like reading and math.

The novel use of brain imaging during everyday activities like watching TV, say the scientists, opens the door to studying other thought processes in naturalistic settings and may one day help to diagnose and treat learning disabilities.

Scientists are just beginning to use brain imaging to understand how humans process thought during real-life experiences. For example, researchers have compared scans of adults watching an entertaining movie to see if neural responses are similar across different individuals. “But this is the first study to use the method as a tool for understanding development,” says lead author Jessica Cantlon, an assistant professor in brain and cognitive sciences at the University of Rochester.

Eventually, that understanding may help pinpoint the cause when a child experiences difficulties mastering school work. “Psychologists have behavioral tests for trying to get the bottom of learning impairments, but these new imaging studies provide a totally independent source of information about children’s learning based on what’s happening in the brain,” says Cantlon.

The neuroimaging findings are detailed in a new study published Jan. 3 by the Public Library of Science’s open-access journal PLoS Biology, by Cantlon and her former research assistant Rosa Li, now a graduate student at Duke University.

Birdsong study pecks at theory that music is uniquely human

A bird listening to birdsong may experience some of the same emotions as a human listening to music, suggests a new study on white-throated sparrows, published in Frontiers of Evolutionary Neuroscience.

“We found that the same neural reward system is activated in female birds in the breeding state that are listening to male birdsong, and in people listening to music that they like,” says Sarah Earp, who led the research as an undergraduate at Emory University.

For male birds listening to another male’s song, it was a different story: They had an amygdala response that looks similar to that of people when they hear discordant, unpleasant music.

The study, co-authored by Emory neuroscientist Donna Maney, is the first to compare neural responses of listeners in the long-standing debate over whether birdsong is music.

“Scientists since the time of Darwin have wondered whether birdsong and music may serve similar purposes, or have the same evolutionary precursors,” Earp notes. “But most attempts to compare the two have focused on the qualities of the sound themselves, such as melody and rhythm.”

Earp reviewed studies that mapped human neural responses to music through brain imaging.

She also analyzed data from the Maney lab on white-throated sparrows. The lab maps brain responses in the birds by measuring Egr-1, part of a major biochemical pathway activated in cells that are responding to a stimulus.

The study used Egr-1 as a marker to map and quantify neural responses in the mesolimbic reward system in male and female white-throated sparrows listening to a male bird’s song. Some of the listening birds had been treated with hormones, to push them into the breeding state, while the control group had low levels of estradiol and testosterone.

During the non-breeding season, both sexes of sparrows use song to establish and maintain dominance in relationships. During the breeding season, however, a male singing to a female is almost certainly courting her, while a male singing to another male is challenging an interloper.

For the females in the breeding state every region of the mesolimbic reward pathway that has been reported to respond to music in humans, and that has a clear avian counterpart, responded to the male birdsong. Females in the non-breeding state, however, did not show a heightened response.

And the testosterone-treated males listening to another male sing showed an amygdala response, which may correlate to the amygdala response typical of humans listening to the kind of music used in the scary scenes of horror movies.

“The neural response to birdsong appears to depend on social context, which can be the case with humans as well,” Earp says. “Both birdsong and music elicit responses not only in brain regions associated directly with reward, but also in interconnected regions that are thought to regulate emotion. That suggests that they both may activate evolutionarily ancient mechanisms that are necessary for reproduction and survival.”

A major limitation of the study, Earp adds, is that many of the regions that respond to music in humans are cortical, and they do not have clear counterparts in birds. “Perhaps techniques will someday be developed to image neural responses in baleen whales, whose songs are both musical and learned, and whose brain anatomy is more easily compared with humans,” she says.

How Our Sense of Touch is a Lot Like the Way We Hear

Sliman Bensmaia, PhD, assistant professor of organismal biology and anatomy at the University of Chicago, studies the neural basis of tactile perception, or how our hands convey this information to the brain. In a new study published in the Journal of Neuroscience, he and his colleagues found that the timing and frequency of vibrations produced in the skin when you run your hands along a surface, like searching a wall for a light switch, play an important role in how we use our sense of touch to gather information about the objects and surfaces around us.

The sense of touch has traditionally been thought of in spatial terms, i.e. receptors in the skin are spread out across a grid of sorts, and when you touch something this grid of receptors transmits information about the surface to your brain. In their new study, Bensmaia, two former undergraduates, and a postdoctoral scholar in his lab—Matthew Best, Emily Mackevicius and Hannes Saal—found that the skin is also highly sensitive to vibrations, and that these vibrations produce corresponding oscillations in the afferents, or nerves, that carry information from the receptors to the brain. The precise timing and frequency of these neural responses convey specific messages about texture to the brain, much like the frequency of vibrations on the eardrum conveys information about sound.

Neurons communicate through electrical bits, similar to the digital ones and zeros used by computers. But, Bensmaia said, “One of the big questions in neuroscience is whether it’s just the number of bits that matters, or if the specific sequence of bits in time also plays a role. What we show in this paper is that the sequence of bits in time does matter, and in fact for some of the skin receptors, the timing matters with millisecond precision.”

Researchers have known for years that these afferents respond to skin vibrations, but they studied their responses using so-called sinusoidal waves, which are smooth, repetitive patterns. These perfectly uniform vibrations can be produced in a lab, but the kinds of vibrations produced in the skin by touching surfaces in the real world are messy and erratic.