(Fig. 1: Humans have the ability to accurately estimate the speed of moving objects under good light conditions, such as a bird on a clear day (left). On a cloudy day (right), however, the sensory information may be more ambiguous and invokes a specific cognitive mechanism—perceptual bias—that is hardwired into the visual cortex. Image credit: Justin Gardner, RIKEN Brain Science Institute)

An early link to motion perception

When viewing a scene with low contrast, such as in cloudy or low-light situations, humans tend to perceive objects to be moving slower or flickering faster than in reality. This less-than-faithful interpretation of the sensory environment is known as perceptual bias and is thought to be a mechanism that can help humans interpret vague motion information. Brett Vintch and Justin Gardner from the Laboratory for Human Systems Neuroscience at the RIKEN Brain Science Institute have now shown that perceptual bias is encoded within the visual cortex—the region of the brain where visual stimuli first arrive and begin to be processed.

Although humans have the ability to estimate the speed of easily visible, high-contrast stimuli quite accurately, the speed of less-visible, low-contrast stimuli is harder to judge and is invariably underestimated. Speed perception is thought to be closely associated with the middle temporal zone of the visual cortex, but measurements have so far been unable to confirm this link.

Vintch and Gardner set out to resolve the link between cortical response and perception by conducting functional magnetic resonance imaging experiments on test subjects exposed to a series of low- and high-contrast images either moving across the screen at different speeds or flickering at different rates.

The researchers found that different speeds of motion in visual stimulus evoked different patterns of activity in the visual cortex. So systematic was the observed pattern of activity that Vintch and Gardner were able to predict the motion speed or flicker frequency of what the observer was viewing simply by examining the measured brain responses. Using these predictions, they found that when the test subjects viewed scenes with low contrast, the patterns of activity shifted to match what the observer was perceiving rather than what was actually physically present. 

The findings indicate that human perceptual bias about the movement of low-contrast stimuli originates from a shift in the response of neuronal populations in the parts of the brain that first start to process images. This early visual processing, which is hardwired into the visual cortex, may help humans make sense of ambiguous or vague visual information, such as moving or flickering scenes under low-contrast conditions (Fig. 1).

“Multiple aspects of human thought, such as sensory inference, language, cognition and reasoning, involve cognitive guesswork. We hope that our study of this very simple form of guessing by the nervous system will have implications for other high-level processes in the human brain,” explains Gardner.

Fruit flies, fighter jets use similar nimble tactics when under attack

When startled by predators, tiny fruit flies respond like fighter jets – employing screaming-fast banked turns to evade attacks.

Researchers at the University of Washington used an array of high-speed video cameras operating at 7,500 frames a second to capture the wing and body motion of flies after they encountered a looming image of an approaching predator.

“Although they have been described as swimming through the air, tiny flies actually roll their bodies just like aircraft in a banked turn to maneuver away from impending threats,” said Michael Dickinson, UW professor of biology and co-author of a paper on the findings in the April 11 issue of Science. “We discovered that fruit flies alter course in less than one one-hundredth of a second, 50 times faster than we blink our eyes, and which is faster than we ever imagined.”

In the midst of a banked turn, the flies can roll on their sides 90 degrees or more, almost flying upside down at times, said Florian Muijres, a UW postdoctoral researcher and lead author of the paper.

“These flies normally flap their wings 200 times a second and, in almost a single wing beat, the animal can reorient its body to generate a force away from the threatening stimulus and then continues to accelerate,” he said.

The fruit flies, a species called Drosophila hydei that are about the size of a sesame seed, rely on a fast visual system to detect approaching predators.

“The brain of the fly performs a very sophisticated calculation, in a very short amount of time, to determine where the danger lies and exactly how to bank for the best escape, doing something different if the threat is to the side, straight ahead or behind,” Dickinson said.

“How can such a small brain generate so many remarkable behaviors? A fly with a brain the size of a salt grain has the behavioral repertoire nearly as complex as a much larger animal such as a mouse. That’s a super interesting problem from an engineering perspective,” Dickinson said.

The researchers synchronized three high-speed cameras each able to capture 7,500 frames per second, or 40 frames per wing beat. The cameras were focused on a small region in the middle of a cylindrical flight arena where 40 to 50 fruit flies flitted about. When a fly passed through the intersection of two laser beams at the exact center of the arena, it triggered an expanding shadow that caused the fly to take evasive action to avoid a collision or being eaten.

With the camera shutters opening and closing every one thirty-thousandth of a second, the researchers needed to flood the space with very bright light, Muijres said. Because flies rely on their vision and would be blinded by regular light, the arena was ringed with very bright infrared lights to overcome the problem. Neither humans nor fruit flies register infrared light.

How the fly’s brain and muscles control these remarkably fast and accurate evasive maneuvers is the next thing researchers would like to investigate, Dickinson said.

Faster eye responses in Chinese people not down to culture

New research from University of Liverpool scientists has cast doubt on the theory that neurological behaviour is a product of culture in people of Chinese origin.

Scientists tested three groups – students from mainland China, British people with Chinese parents and white British people – to see how quickly their eyes reacted to dots appearing in the periphery of their vision.

These rapid eye movements, known as saccades, were timed in all of the participants to see which of them were capable of making high numbers of express saccades – particularly fast responses which begin a tenth of a second after a target appears.

The findings, published in the journal PLoS One, revealed that similar numbers of the British Chinese and mainland Chinese participants made high numbers express saccades, with the white British participants made far fewer. Culturally the British Chinese participants were similar to their white British counterparts and different to the mainland Chinese students.

Therefore in terms of eye movement patterns, Chinese ethnicity was more of a factor than culture. This is contrary to several previous reports from other research groups which looked at behaviour in Asian and white participants and concluded that culture explained behavioural differences between groups.

Neurophysiologist, Dr Paul Knox, from the University’s Institute of Ageing and Chronic Disease, led the study. He said: “Examining saccades from different populations is revealing a lot about underlying brain mechanisms and how we think.

"Many scientists believe that the eye movement patterns you develop are due to where you live – the books you read and the influence of your family, peers and community – your culture."

"Our research has shown that this cannot be the case, at least for saccade behaviour. What this leaves is the way we’re made, perhaps our genetics. And this may have a bearing on the way the brains in different groups react to injuries and disease."

All of the participants completed questionnaires which evaluated their cultural values. They then wore a headset and looked at a plain white board on which lights appeared. The headset measured the time it took for participants’ eyes to react to the lights as they appeared in different places on the board.

Twenty-seven percent of Chinese participants responded with high proportions of express saccades, similar to 22% of the British Chinese, but many more than the 10% of white British participants.

Dr Knox concluded: “From a situation where 80% of our understanding of neuroscience was derived from tests on US psychology undergraduates, we’re now showing how the human brain is not just amazingly complex in general, but also highly variable across the human population.”

(Image credit)

Scientists discover a protein in nerves that determines which brain connections stay and which go

A newborn baby, for all its cooing cuddliness, is a data acquisition machine, absorbing information to finish honing the job of brain wiring that started before birth. This is true nowhere more so than the eyes, which start life peering at a blurry world and within months can make out a crisp, three-dimensional image of a mobile dangling overhead.

This process of refining the brain’s wiring involves cutting off some of the excess nerve connections we have at birth while strengthening connections we use all the time. Some estimates show that as many as half of the brain’s connections formed during development are clipped back as the final wiring takes shape.

Carla Shatz, the David Starr Jordan Director of Stanford Bio-X, and her team, including postdoctoral researcher Hanmi Lee and Bio-X Graduate Fellow Jaimie Adelson, recently found a protein that is essential for the brain to remove those excess connections. The team specifically showed a role for the protein in the developing visual system in mice, but the work appears to apply broadly across the developing brain. They published their findings online March 30 in the journal Nature.

Shatz said the discovery helps clear up something that has been a mystery to those who study brain development: How does the decision get made to eliminate some connections? It also settles a decade-long debate over whether the nervous system or the immune system is making those decisions. (Spoiler alert: It’s the nervous system.)

A single vision

"Vision is a challenging problem because you have two eyes and only one view of the world," said Shatz, who is the Sapp Family Provostial Professor and professor of biology and of neurobiology. "There’s a very beautiful set of wiring steps that makes sure the eyes are pointed at the same place and the two images get aligned."

Shatz said the rule of which connections the brain cuts back to create that single vision follows a simple mantra: “Fire together, wire together. Out of sync, lose your link.” Or rather, if early in life the left sides of both eyes see the same duck motif wallpaper, those neurons fire together and stay linked up. When the top of one eye and bottom of the other eye form a connection, the nerves fire out of sync, and the connection weakens and is eventually pruned back. Over time, the only connections that remain are between parts of the two eyes that are seeing the same thing.

The ability to detect which nerves fire out of sync and should therefore lose their link requires the protein Shatz’s team reported, which goes by the name of MHC Class I D, or D for short. This protein is one that is famous for its role in the immune system, but only in the past decade has Shatz’s team started building a case for D’s independent role in the brain.

Two camps, one protein

In 2000 Shatz first published work suggesting that a group of immune proteins called MHC in mice and HLA in people played a role in the developing nervous system. At the time, this caused a stir among immunologists, who were surprised to find their proteins showing up in the brain.

Lawrence Steinman, professor of neurology and neurological sciences and of pediatrics at Stanford School of Medicine, has followed Shatz’s work from the perspective of both a neurologist and immunologist. “One of the reasons that I think the research is so interesting is that it shows us that molecules thought to be the province of one group can be in another,” he said, adding, “It slowed the prevailing idea that people believed that some molecules were the domain of one camp.”

Shatz is in the privileged position of directing Stanford Bio-X, which includes faculty members and students from both immunology and the neurological sciences. She said being able to talk about her work and collaborate with this mix of colleagues has helped break down barriers in thinking about her unexpected findings.

After the initial discovery, Shatz went on to show that two of those MHC proteins – D and its sister protein K – seemed to be important in eliminating connections in the brain. Mice genetically engineered to lack both K and D had poorly functioning immune systems and also ended up with the visual system in a jumble, with unrelated parts of the two eyes forming connections. Without D and K the mice weren’t detecting which connections fired out of sync, so those connections didn’t lose their link.

After Shatz published that work, some immunologists argued that perhaps D and K were necessary for brain remodeling only because of their key function in the immune system. “They were saying that the immune system was telling the nervous system what to prune,” Shatz said.

It was a theory, but not one Shatz agreed with. Her feeling was that just because D and K were first found in the immune system didn’t mean they couldn’t have a unique role in the brain. “The nervous system has just as much right to these immune proteins as the immune system,” Shatz said. Her most recent work makes that point clear.

D on the brain

Shatz and her group worked with the mice that were lacking D and K everywhere, then used genetic engineering tricks to add D back, but only in the neurons. These mice still had poorly functioning immune systems, but had perfectly normal eye connections. In these mice, the nerves were able to determine which connections to cut and which to keep, even without the immune system.

Steinman said the work settles the issue of whether D is acting in the brain separate from its role in the immune system. “If Carla had studied MHC proteins before the immunologists, then we would consider them to be part of the nervous system. They clearly have major roles in both the nervous system and the immune system,” he said.

The group went on to show that the presence of D alters the composition of other proteins on the nerve cell surface that are in charge of receiving signals from other nerves. Her team thinks that it is this difference in how the nerve receives signals with or without D that makes the pruning process go awry.

Essentially, without D all nerve connections appear to be firing together and therefore they stay wired together.

Shatz says that in addition to explaining an important part of brain development, the work could also provide a new avenue for studying schizophrenia. Some studies have shown that people with mutations in the human genes related to D (called HLA genes) are more prone to the disease. Other studies have associated schizophrenia with improperly formed connections in the brain. Shatz suggests that this new role for D in the brain could mean that the pruning process has gone awry in schizophrenia. The group plans to explore this idea further, as well as to tease apart what D is doing to alter the composition of neurotransmitter receptors on the nerve cell surface.

Lining up our sights

Neurologists at LMU have studied the role of the vestibular system, which controls balance, in optimizing how we direct our gaze. The results could lead to more effective rehabilitation of patients with vestibular or cerebellar dysfunction.

When we shift the direction of our gaze, head and eye movements are normally highly coordinated with each other. Indeed, from the many possible combinations of speed and duration for such movements, the brain chooses the one that minimizes the error in reaching the intended line of sight. Dr. Nadine Lehnen, who heads a research group based at LMU’s Center for Vertigo and Balance Disorders, in collaboration with her colleague Dr. Murat Saglam and Professor Stefan Glasauer of the Center for Sensorimotor Diseases at LMU, have now published a paper in the latest issue of the journal of Brain which investigates the significance of the vestibular system for this optimization of motor coordination. The vestibular system in the brain is mainly responsible for the maintenance of balance and posture. The new work focused on subjects suffering from bilateral defects in the vestibular system (a complete vestibulopathy) or lesions in the cerebellum, which is functionally linked to it.

The authors of the new study had previously developed a mathematical model that enabled them to predict the horizontal movements of the head and eyes in response to the presentation of an off-center stimulus. “When subjected to repeated trials, healthy subjects are able to select the combination of eye and head movements that minimizes gaze shift variability,” says Glasauer. They unconsciously choose the set of movements associated with the least error in the endpoint. Moreover, they can do this even when wearing a helmet with weights attached, which alters the moment of inertia of the head.

Learning to find the endpoint

However, patients who show defects in the vestibular system or the cerebellum have greater difficulty in controlling the direction of gaze in response to changes in their environment. “It turns out that information relayed from the balance organs to the vestibular system is essential for the optimization of gaze shifts,” says Nadine Lehnen. Patients with complete bilateral vestibular loss are therefore unable to perform such shifts in the most efficient way. “In striking contrast, patients with cerebellar damage can, to a certain extent, learn to optimize certain parameters of head and eye movements, by adjusting the velocity of head movement, for instance,” says Glasauer.

"These results provide the first evidence that the vestibular system is critical for optimizing voluntary movements“, says Dr. Kathleen E. Cullen from McGill University in Montreal in a scientific commentary to the study appearing in the print issue of Brain. The new findings are of relevance for the rehabilitation of patients who have suffered damage to the cerebellum and patients with incomplete vestibulopathies. “We assume that gaze shift control in these patients can be enhanced by a rehabilitation training based on active head movements,” says Nadine Lehnen. Head movements provide the vestibular feedback which generates the sensorimotor error messages that underlie the ability to learn how to optimize the coordination of eye and head movements. Instead of trying to hold their heads steady, these patients should be encouraged to actively move their heads, when they shift their gaze.

The question if patients with partial vestibulopathy can optimize gaze shift behavior by engaging in active head movements is now under investigation. This work forms part of a rehabilitation study which is being carried out at the Center for Vertigo and Balance Disorders at Munich University Hospitals, and is financed by the Federal Ministry for Education and Research.

These Boosts Are Made For Walkin’: Study Reveals that Movement Kicks Visual System into Higher Gear

Whether you’re a Major League outfielder chasing down a hard-hit ball or a lesser mortal navigating a busy city sidewalk, it pays to keep a close watch on your surroundings when walking or running. Now, new research by UC San Francisco neuroscientists suggests that the body may get help in these fast-changing situations from a specialized brain circuit that causes visual system neurons to fire more strongly during locomotion.

There has been a great deal of research on changes among different brain states during sleep, but the new findings, reported in the March 13 issue of Cell, provide a compelling example of a change in state in the awake brain.

It has long been known that nerve cells in the visual system fire more strongly when we pay close attention to objects than when we view scenes more passively. But the new research, led by Yu Fu, PhD, a postdoctoral fellow in the UCSF lab of senior author Michael P. Stryker, PhD, the W.F. Ganong Professor of Physiology, breaks new ground, mapping out a visual system amplifier that is directly activated by walking or running.

Though this circuit has not yet been shown to exist in humans, Stryker is designing experiments to find out if it does. He said he would be surprised if his group did not identify a similar mechanism in people, since such systems have been found in fruit flies, and the mouse visual system has so far proved to be a good model of many aspects of human vision.

“The sense of touch only tells you about objects that are close, and the auditory system is generally not as sensitive as the visual system to the exact position of objects,” he said. “It seems that it would be generally useful to have vision – the sensory modality that tells you the most about things that are far away – work better as you’re moving through the world.”

Stryker said that the neural system identified in the new work may have evolved to conserve energy, by allowing the brain to operate at less than peak efficiency in less demanding behavioral situations. “When you don’t need your visual system to be in a high-gain state, your brain may use a lot less energy in responding,” said Stryker. “A change in gain when you’re moving is ideally what you’d like to see – the neuron is doing the same thing that it’s always doing, but it’s talking louder to the rest of the brain.”

In the new research, mice were allowed to walk or run freely on a Styrofoam ball suspended on an air cushion while the scientists used a technique known as two-photon imaging to monitor the activation of cells in the primary visual area of the brain, known as V1.

The researchers found that a subset of V1 neurons, those that contain a substance called vasoactive intestinal peptide (VIP), were robustly activated in a time-locked fashion purely by locomotion, even in darkness, while other V1 neurons remained largely silent.

The mice were presented with visual stimuli both while motionless and while moving, and measurements showed that walking could increase the response of V1 neurons by more than 30 percent. Moreover, V1 responses to these stimuli increased or declined in tandem with the activity of VIP neurons, and with the starting or stopping of walking by the mice.

To firmly establish that VIP neurons were responsible for these changes, the researchers used optogenetic techniques, inserting light-sensitive proteins exclusively into VIP neurons. Using light to stimulate just this population of cells, the team found that they could emulate the effects of locomotion – when VIP cells were activated, V1 cells responded more strongly to stimuli, regardless of whether the animals were moving. Conversely, when the researchers specifically targeted and disabled VIP cells, locomotion-induced increases in the response of other V1 cells were abolished.

Motion-Sensing Cells in the Eye Let the Brain ‘Know’ About Directional Changes

How do we “know” from the movements of speeding car in our field of view if it’s coming straight toward us or more likely to move to the right or left?

Scientists have long known that our perceptions of the outside world are processed in our cortex, the six-layered structure in the outer part of our brains. But how much of that processing actually happens in cortex? Do the eyes tell the brain a lot or a little about the content of the outside world and the objects moving within it?

In a detailed study of the neurons linking the eyes and brains of mice, biologists at UC San Diego discovered that the ability of our brains and those of other mammals to figure out and process in our brains directional movements is a result of the activation in the cortex of signals that originate from the direction-sensing cells in the retina of our eyes.

“Even though direction-sensing cells in the retina have been known about for half a century, what they actually do has been a mystery- mostly because no one knew how to follow their connections deep into the brain,” said Andrew Huberman, an assistant professor of neurobiology, neurosciences and ophthalmology at UC San Diego, who headed the research team, which also involved biologists at the Salk Institute for Biological Sciences. “Our study provides the first direct link between direction-sensing cells in the retina and the cortex and thereby raises the new idea that we ‘know’ which direction things are moving specifically because of the activation of these direction-selective retinal neurons.” The study, recently published online, will appear in the March 20 print issue of Nature.

The discovery of the link between direction-sensing cells in the retina and the cortex has a number of practical implications for neuroscientists who treat disabilities in motion processing, such as dysgraphia, a condition sometimes associated with dyslexia that affects direction-oriented skills.

“Understanding the cells and neural circuits involved in sensing directional motion may someday help us understand defects in motion processing, such as those involved dyslexia, and it may inform strategies to treat or even re-wire these circuits in response to injury or common neurodegenerative diseases, such as glaucoma or Alzheimer’s,” said Huberman.

He and his team discovered the link in mice by using new types of modified rabies viruses that were pioneered by Ed Callaway, a professor at the Salk Institute, and by imaging the activity of neurons deep in the brain during visual experience.

Learning to see better in life and baseball

With a little practice on a computer or iPad—25 minutes a day, 4 days a week, for 2 months—our brains can learn to see better, according to a study of University of California, Riverside baseball players reported in the Cell Press journal Current Biology on February 17. The new evidence also shows that a visual training program can sometimes make the difference between winning and losing.

The study is the first, as far as the researchers know, to show that perceptual learning can produce improvements in vision in normally seeing individuals.

"The demonstration that seven players reached 20/7.5 acuity—the ability to read text at three times the distance of a normal observer—is dramatic and required players to stand forty feet back from the eye chart in order to get a measurement of their vision," says Aaron Seitz of the University of California, Riverside. For reference, 20/20 is considered normal visual acuity.

In the training game, the players’ task was to find and select visual patterns modeled after stimuli to which neurons in the early visual cortex of the brain respond best, Seitz explains. As game play commenced, those patterns were made dimmer and dimmer, exercising the players’ vision as they searched.

"The goal of the program is to train the brain to better respond to the inputs that it gets from the eye," Seitz says. "As with most other aspects of our function, our potential is greater than our normative level of performance. When we go to the gym and exercise, we are able to increase our physical fitness; it’s the same thing with the brain. By exercising our mental processes we can promote our mental fitness."

After the 2 month training period, players reported “seeing the ball much better,” “greater peripheral vision,” “easy to see further,” “able to distinguish lower-contrasting things,” “eyes feel stronger, they don’t get tired as much,” and so on.

The players also showed greater-than-expected improvements in their game. They were less likely to strike out and got more runs. The researchers estimate that those gains in batting statistics may have given the team an additional four or five wins in the 2013 season.

The researchers are now extending their work to include different groups, including members of the Los Angeles and Riverside Police Departments and people with low vision due to cataracts, macular degeneration, or amblyopia. They will also apply the same principles to other aspects of cognition, including memory and attention.

It all comes down to one thing: “Understanding the rules of brain plasticity unlocks great potential for improvement of health and wellbeing,” Seitz says.