Monday, August 24, 2009

HUMAN MIND: SOUND AND VISION WIRED THROUGH SAME 'BLACK BOX'

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Sounds and images share a similar neural code in the human brain, according to a new Canadian study. In the online edition of the Proceedings of the National Academy of Sciences (PNAS), scientists from the Université de Montréal and the Montreal Neurological Institute at McGill University explain how the same neural code in the brain allows people to distinguish between different types of sounds, such as speech and music, or different images.

Participants were recruited to undergo functional magnetic resonance imaging (FMRI), a non-invasive form of brain mapping used to determine how the brain recognizes different characteristics in musical instruments, words from conversations or environmental sounds. Subjects underwent an exhaustive three hours of FMRI exams to provide precise information about how the brain reacts when different sounds are played.

"It turns out that the brain uses the same strategy to encode sounds than it uses to encode different images," explains lead author Marc Schönwiesner, a Université de Montréal psychology professor. "This may make it easier for people to combine sounds and images that belong to the same object, such as the dribbling of a basketball."

The next step for the researchers is to determine exactly how the brain distinguishes between rock drum beats to the strings of a symphony or from a French conversation to an English one. "Our goal is to disentangle exactly how the brain extracts these different types of sounds. This is a step may eventually let us reconstruct a song that a person has heard from according to the activity pattern in their brain," explains Dr. Schönwiesner, who is also a member of the International Laboratory for Brain, Music and Sound Research (BRAMS), a joint Université de Montréal and McGill University think-tank on music and the mind.

As scientists advance in decoding brain activation patterns, says Dr. Schönwiesner, mind-boggling applications can be envisaged. "If researchers can reconstruct a song a person has heard according to an fMRI reading, we're not far off to being able to record brain patterns during sleep and reconstruct dreams," he predicts. "That would be really cool, although this possibility is decades of research away."

(Photo: Marc Schönwiesner, Université de Montréal)

Université de Montréal

NO EXPERIENCE REQUIRED: CATEGORY-SPECIFIC BRAIN ORGANIZATION IN SIGHTED AND BLIND HUMANS

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A new study finds a surprising similarity in the way neural circuits linked to vision process information in both sighted individuals and those who have been blind since birth. The research, published by Cell Press in the August 13th issue of the journal Neuron, reveals that category-specific localized activation of a critical part of the visual cortex does not require any prior visual experience and provides fascinating and valuable insight into the evolutionary history of the human brain.

The ability to recognize visually presented objects relies on a critical neural pathway called the ventral stream. Previous imaging studies of the human brain have demonstrated that the sight of nonliving objects, such as tools and houses, activates different regions within the ventral stream than the sight of living things, such as animals and faces. It is not known whether category-specific neural responses in the ventral stream depend on visual experience.

One way to answer this question is to explore whether category-specific activation of the ventral stream is observed in adults who have been blind since birth. Although previous research with blind humans has shown that tactile exploration of objects or imagery of object shape based on sound activates the ventral stream, it is not clear whether stimuli from different conceptual domains activate localized regions within the ventral stream.

"In particular, it is unknown whether individuals who are blind since birth will show differential responses in medial regions of the ventral stream when thinking about nonliving things," says lead study author, Dr. Bradford Mahon, who is currently at the Department of Brain and Cognitive Sciences at the University of Rochester. "Similarly, it is unknown whether, in the absence of visual experience, stimuli corresponding to living things will lead to differential responses in regions that show the same category preference in sighted individuals."

Dr. Mahon and colleagues at the Center for Mind/Brain Sciences (CIMeC) at the University of Trento, Italy, and Harvard University designed a study to test whether the medial-to-lateral organization of the ventral stream, reflecting preferences for nonliving-to-living stimuli, respectively, was present in individuals with no sight experience. Sighted and blind individuals performed a size judgment task where groups of words all belonging to the same category (nonliving or living) were presented and subjects were asked to think about the size of the first item and compare it to subsequent items. All of the individuals kept their eyes closed during the task.

"Using functional magnetic resonance imaging, we found that the same regions of the ventral stream that show category preferences for nonliving stimuli and animals in sighted adults, show the same category preferences in adults who are blind since birth," explains senior study author Dr. Alfonso Caramazza from the CIMeC and Harvard University. "Our findings suggest that the organization of the ventral stream innately anticipates the different types of computations that must be carried out over objects from different conceptual domains."

Perhaps the most exciting possibility suggested by this research is that the functional organization of the human brain is strongly constrained by innate factors. The researchers discuss a theory in their article proposing that significant parts of the human brain are innately structured around a few domains of knowledge that were critical in humans' evolutionary history, such as animals, conspecifics, and perhaps tools.

Cell Press

THE MIND'S EYE SCANS LIKE A SPOTLIGHT

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You're meeting a friend in a crowded cafeteria. Do your eyes scan the room like a roving spotlight, moving from face to face, or do you take in the whole scene, hoping that your friend's face will pop out at you? And what, for that matter, determines how fast you can scan the room?

Researchers at MIT's Picower Institute for Learning and Memory say you are more likely to scan the room, jumping from face to face as you search for your friend. In addition, the timing of these jumps appears to be determined by waves of activity in the brain that act as a clock. The study, which appears in the Aug. 13 issue of the journal Neuron, sheds new light on a long-standing debate among neuroscientists over how the visual system picks out an object of interest in a complex scene.

In the study, monkeys were given the task of searching for one particular tilted, colored bar among a field of bars on a computer screen. By monitoring the activity of neurons in three of the animals' brain regions, researchers found that the monkeys spontaneously shifted their attention in a sequence, like a moving spotlight that jumped from location to location.

What's more, the study showed that brain waves act as a kind of built-in clock that provides a framework for shifting attention from one location to the next. The work could have implications for understanding or treating attention deficit disorder or even potentially speeding up the rate of cognition in the brain.

"For many years, neuroscientists have been debating competing theories on whether humans and animals spontaneously search elements of a visual scene in a serial or parallel manner," said lead author Earl K. Miller, the Picower Professor of Neuroscience. "Ours is the first study based on direct evidence of neurophysiological activity."

Activity in the brain comes and goes in waves, cycling between high and low activity states. Researchers have been recording brain waves for more than 100 years and although they think they play roles in working memory, decision-making and communication among brain regions, no one is sure of their exact role in brain function. This work suggests a new role for brain waves — one in which they are directly involved in the brain's processing.

Picower Institute postdoctoral associate and co-author Timothy J. Buschman found that the spotlight of the mind's eye shifted focus at 25 times a second and that this process of switching was regulated by brain waves. "This is one of the first examples of how brain waves play a specific role in cognitive computations," Buschman said.

"Attention regulates the flood of sensory information pouring into the brain into a manageable stream. In particular, a lot of different areas of the brain are involved in vision. If they all competed at once, it would be chaos," Miller said. "Brain waves may provide the clock that tells the brain when to shift its attention from one stimulus to another. Oscillating brain waves may provide a way for several regions across the brain to be on the same page at the same time — very similar to the way computers use an internal clock to synchronize the many different components inside."

The researchers' next step is to expand their search for brain wave function beyond the visual. They hope to discover whether brain waves are specific to visual function or act as a "general clock" for the brain.

The researchers have found that in the experiment with the monkeys, the speed at which the animals searched was related to the speed of their brain waves. When the clock ticked faster, the animals "thought" faster. This implies that it may be possible to change the speed of cognition if researchers can learn to artificially manipulate brain waves. In separate studies outside MIT, researchers are looking at the correlation between the brain waves' "clock speed" in humans and the speed at which subjects shift attention from one task to another.

(Photo: Donna Coveney)

Massachusetts Institute of Technology

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