neurophilosophy

Neurophilosophy now hosted by The Guardian

neurophilosophy — Thu, 11 Aug 2011 07:15:08 +0000

Neurophilosophy now hosted by The Guardian

AFTER four years here at ScienceBlogs.com, Neurophilosophy is moving to a new home. As of today, it will be hosted by The Guardian.

During its time here, the blog has grown from strength to strength. It has received over 2.5 million page views, was featured regularly on the New York Times science page, and has been translated into about a dozen languages. It has also enabled me to earn a living as a freelance science writer for the past two years.

Thanks to everyone here at ScienceBlogs and especially to all my readers. I hope you'll continue reading. The URL for the new blog is: http://www.guardian.co.uk/science/neurophilosophy and the feed is here: http://www.guardian.co.uk/science/neurophilosophy/rss; and here's my first post, 'The illlusion of attention.'

neurophilosophy Thu, 08/11/2011 - 03:15

Human echolocation activates visual parts of the brain

neurophilosophy — Wed, 25 May 2011 15:00:00 +0000

Human echolocation activates visual parts of the brain

WE all know that bats and dolphins use echolocation to navigate, by producing high frequency bursts of clicks and interpreting the sound waves that bounce off objects in their surroundings. Less well known is that humans can also learn to echolocate. With enough training, people can use this ability to do extraordinary things. Teenager Ben Underwood, who died of cancer in 2009, was one of a small number of blind people to master it. As the clip below shows, he could use echolocation not only to navigate and avoid obstacles, but also to identify objects, rollerskate and even play video games.

Very little research has been done on human echolocation, and nothing is known about the underlying brain mechanisms. In the first study of its kind, Canadian researchers used functional magnetic resonance imaging (fMRI) to monitor the brain activity of two blind echolocation experts. Their findings, published today in the open access journal PLoS ONE, show that echolocation engages regions of the brain that normally process vision.

Psychologist Lore Thaler of the University of Western Ontario and her colleagues recruited two expert echolocators for the new study. One, a 43-year-old man referred to as EB, was born with retinoblastoma - a form of cancer that affects cells in the retina - and had both eyes removed at 13 months of age. The other, a 27-year-old man known as LB, lost his vision at the age of 14, following degeneration of the optic nerve, which carries visual information from the eye to the brain. Both have trained themselves to be expert echolocators. Both of them use click-based echolocation on a daily basis, to navigate their home cities and explore unfamiliar ones, go hiking or play basketball.

The researchers seated their participants in a sealed room, placed various objects in front of them, and asked them to produce echolocation clicks. As they did so, the sounds they produced - and the faint echoes - were recorded with high quality stereo equipment. They also asked the participants to do the same thing in an outdoor courtyard surrounded by buildings, and made more recordings. Some of these contained echoes produced by a tree, car or lamp-post, while others did not.

EB and LB could accurately determine the size, shape, position and movements of objects in both situations. Crucially, they could do the same from the sound recordings when they were played back later. EB, for example, could distinguish a 3Â° difference in the position of a pole in the sealed room, as well as from the pre-recorded sounds. LB, was slightly less accurate, distinguishing 9Â° differences in position of the pole while in the room, and 22Â° differences from the recordings.

Thaler and her colleagues then scanned the blind participants' brains, and those of two sighted controls of the same age and sex, while they listened to the pre-recorded sounds through earphones. They found that the recordings activated the auditory cortex, which process sounds, in all four participants. The sounds also activated parts of the visual cortex in the blind participants, but this activity was completely absent in the sighted controls. EB exhibited greater visual cortical activation than LB. This may reflect the fact that he is more experienced at using echolocation.

The researchers observed another difference when they compared the brain activity evoked by outdoor recordings with and without echoes. The recordings without echoes produced the same pattern of activity as those used in the first experiment. Remarkably, though, the recordings containing echoes activated the visual cortex in the blind participants, but not the auditory cortex.

Although it is somewhat limited by the small number of participants, this study suggest that EB and LB both use echolocation in a way that is very similar to vision. The exact role of the visual cortex in human echolocation is unclear, but Thaler and her colleagues suggest that it might be processing spatial information contained in the echolocation clicks.

The researchers are cautious in their interpretation of the findings. They note numerous studies which show that blindness can lead to extensive brain re-organization. Such changes can produce cross-modal activation, whereby sensations activate brain regions that would not normally process them. But the observation that the echoes in the outdoor recordings activated visual but not auditory cortices in the blind participants supports the researchers' conclusion.

The use of pre-recorded sounds overcomes a number of difficulties in scanning the brains of echolocating people, and could stimulate other neuroimaging experiments of the phenomenon. Future studies of blind echolocators may confirm these new findings, and comparisons with sighted people who have been trained to echolocate and blind non-echolocators with an increased sensitivity to echoes could provide further insights into the underlying neural mechanisms.

Related:

Thaler, L., et al. (2011). Neural Correlates of Natural Human Echolocation in Early and Late Blind Echolocation Experts. PLoS ONE 6 (5): e20162. doi: 10.1371/journal.pone.0020162

neurophilosophy Wed, 05/25/2011 - 11:00

A whiff of early brain evolution

neurophilosophy — Thu, 19 May 2011 12:00:00 +0000

A whiff of early brain evolution

Skull of Hadrocodium wui. (Image courtesy of Mark Klinger and Zhe-Xi Luo, Carnegie Museum of Natural History)

THE question of how mammals evolved their exceptionally large brains has intrigued researchers for years, and although many ideas have been put forward, none has provided a clear answer. Now a team of palaeontologists suggests that the mammalian brain evolved in three distinct stages, the first of which was driven by an improvement in the sense of smell. Their evidence, published in tomorrow's issue of Science, comes from two fossilized skulls, each measuring little more than 1cm in length.

Mammals emerged during, or just before, the early Jurassic period, some 200 million years ago. We know that the earliest mammals were small, nocturnal animals that fed on insects, but there is very little in the way of details about how their brains might have looked, because fossils are scant, consisting mostly of isolated jaws and teeth. A few skulls have been found but until now studying the brain involved damaging the fossils which, given their rarity, was out of the question.

Zhe-Xi Luo, curator and associate director for research and collections at the Carnegie Museum of Natural History, found one of these rare skulls, along with the rest of the fossilized skeleton, about 10 years ago in the Yunnan province of China. It belonged to a tiny weasel-like creature that lived about 190 million years ago. The animal probably weighed just 2 grams, but it's skull was conspicuously large relative to it's 3 cm-long body. Luo therefore named it Hadrocodium, meaning "big head".

Closer examination of the skull revealed several other features that are characteristic of mammals. The bones of the middle ear were separated from those of the lower jaw, suggesting that the animal had a well developed sense of hearing, and the lower jaw contained cone-shaped teeth similar to those of other early insectivorous mammals. Significantly, Hadrocodium is much older than all other known early mammals - it pushes the emergence of these mamalian features back by some 45 million years, and may have been the ancestor of all living mammals.

Having studied the external features of the Hadrocium skull for about a decade, Luo and his colleagues exploited recent advances in medical imaging techniques to look inside without damaging it.

Digital reconstruction of Hadrocodium brain. The olfactory bulbs are at the front of the brain. (Image courtesy of Matt Colbert, University of Texas, Austin.)

In the new study, they used high resolution computed X-ray tomography to scan the skull and generate an endocast of the cavities inside it (above). The cast closely approximates the size and shape of the brain, enabling the researchers to digitally reconstruct the organ. They did the same thing with the skull of another early mammal called Morganucodon, and then compared both endocasts with those of more than 12 other animal fossils and more than 200 living animal species. (All of the scans used in the study have been uploaded to the DigiMorph.org website.)

The digital reconstructions provide anatomical details of the brains once contained within the skulls, which in turn give us clues about how the animals might have behaved. One of the researchers' main observations was that the nasal cavities of Hadrocodium and Morganucodon are nearly 50% larger than those of the mammal-like reptiles called cynodonts. Furthermore, the olfactory bulbs are clearly delineated from the brain proper by a deep fissure. They also observed enlargement of the olfactory region of the brain, and of the somatosensory cortex, which processes touch information from the skin surface.

Thus, expansion of the olfactory bulb and olfactory and somatosensory cortices account for much of the increase in brain size as the mammals evolved from reptiles. This led the authors to suggest a sequence of evolutionary events that drove the early expansion of the mammalian brain.

They conclude that the initial expansion in brain size was driven by an improvement in the sense of smell. It was also driven by an increased sensitivity to touch from the pelt of soft fur that covered the early mammals' small bodies, and by improved motor co-ordination. And the jaw bone rearrangements that accompanied the subsequent emergence of different tooth types - canines and molars - freed up more space in the nasal cavity, allowing for further enlargement of the olfactory bulb.

neurophilosophy Thu, 05/19/2011 - 08:00

Sleepy brain waves predict dream recall

neurophilosophy — Tue, 10 May 2011 13:05:25 +0000

Sleepy brain waves predict dream recall

THE patterns of brain waves that occur during sleep can predict the likelihood that dreams will be successfully recalled upon waking up, according to a new study published in the Journal of Neuroscience. The research provides the first evidence of a 'signature' pattern of brain activity associated with dream recall. It also provides further insight into the brain mechanisms underlying dreaming, and into the relationship between our dreams and our memories.

Cristina Marzano of the Sleep Psychophysiology Laboratory at the University of Rome and her colleagues recruited 65 students, selected on the basis of their sleeping habits. All of them had a regular sleep 'routine', going to bed at around the same time, and sleeping for an average of seven-and-a-half hours, every night. For the study, the participants slept for two consecutive nights in a sound-proof, temperature-controlled room in the lab. They were left to sleep uninterrupted on the first night, so that they would get accustomed to the new surroundings.

On the second night, the researchers used electroencephalography (EEG) to measure the participants' brain waves while they slept, and woke them up during specific types of sleep. Sleep occurs in five distinct stages, each characterized by a distinct pattern of brain waves, and most dreaming occurs in the rapid eye movement (REM) stage. Some of the participants were woken up during REM sleep, as determined by their brain waves, while others were woken up during stage 2 sleep. Soon after being woken up, they were asked filled out a 'sleep and dream diary', giving details of whether or not they dreamt, how many dreams they had and, if they could remember, the contents of any dreams they had.

The researchers found that they could predict successful dream recall from the brain activity patterns recorded just before awakening. Of the participants woken up during REM sleep, those who exhibited more low frequency theta waves in the frontal lobes were more likely to remember their dreams than those who did not. Dream recall after waking from stage 2 sleep was associated with a reduction in higher frequency alpha waves recorded from the right temporal lobe. The predictions were most accurate when based on the recordings of activity that occurred about five minutes before awakening.

We know that the brain processes newly acquired information while we sleep, and although the function of dreaming is unknown, some researchers believe that it plays an important role in memory consolidation. Our dreams may be a manifestation of the brain activity associated with 'replaying' the day's events, so dream recall can be thought of as a form of episodic, or autobiographical, memory.

Indeed, previous studies have shown that brain waves in the frontal and temporal lobes can predict encoding and subsequent recall of episodic memories, and that they can even be used to distinguish between true and false memories. We also know that oscillatory activity in the frontal and temporal lobes plays an important role in memory formation, and that interactions between these two regions are necessary for long-term memory storage.

The new study shows that dreaming and dream recall appear to involve the same brain wave patterns as encoding and retrieval of episodic memories. This suggests that the brain mechanisms underlying memory encoding and retrieval during sleep are the same as those during waking hours.

Marzano, C., et al. (2011). Recalling and Forgetting Dreams: Theta and Alpha Oscillations during Sleep Predict Subsequent Dream Recall. J. Neurosci. 31: 6674-6683 DOI: 10.1523/JNEUROSCI.0412-11.2011.

neurophilosophy Tue, 05/10/2011 - 09:05

Categories

Brain and Behavior

US military planned using spy crows to find Osama bin Laden

neurophilosophy — Sun, 08 May 2011 09:20:37 +0000

US military planned using spy crows to find Osama bin Laden

THE United States military funded research into using networks of 'spy crows' to locate soldiers who are missing in action, and extended the work to see if the birds might be useful in helping them to find Osama bin Laden. The idea may seem far-fetched, but unlike some military research programs (such as the Stargate remote-viewing program) it is actually based on sound science.

It is well established that crows are highly intelligent. They are known to use tools in the wild, and have remarkably sophisticated tool-making abilities. In the lab, they can solve complex problems, such as using three tools in sequence to obtain food. Other members of the Corvid family have equally amazing cognitive skills. The Clark's nutcracker, for example, caches up to 100,000 nuts in dozens of different locations at the end of spring, and can find them all again up to nine months later, even if they are covered with snow. They have even evolved clever strategies to guard their caches - if, while storing nuts, they are aware of being watched, they will return some time later to retrieve the nuts and bury them again elsewhere.

The idea of using crows to find the world's most wanted man was based on the work of John Marzluff, a wildlife biologist at the University of Washington who has been studying crow behaviour for over 20 years. Working with a population of wild American crows on the university campus in Seattle, Marzluff and his colleagues noticed that birds which they had previously captured seemed to be wary of them and were harder to catch.

The researchers therefore decided to investigate the possibility that crows can recognize human faces, and devised a relatively experiment using rubber masks. They went out on campus and in the surrounding areas wearing either a 'caveman' mask or a Dick Cheney mask. Those who wore the caveman mask caught and banded between 7 and 15 crows on each excursion, but those who wore the Dick Cheney mask did not.

In the following months, they went out wearing the same masks, walking around the university campus in pre-determined routes without bothering the crows. They also recruited volunteers to do the same. The crows consistently harassed anyone they saw wearing the caveman mask, scolding them with loud squawks and even mobbing them.

This happened regardless of the size, sex or walking style of the person wearing the mask., and even when the mask was partly hidden under a hat or worn upside down. They were, however, indifferent to the neutral mask - when they saw both masks simultaneously, they would ignore the person wearing wearing it, and instead follow the person wearing the caveman mask and scold them aggressively.

Evidently, the birds had perceived the caveman mask as threatening during the initial part of the experiment, and had remembered it.

What's more, their memory of the mask was persistent - nearly three years later, they continued to attack anyone who wore it. Marzluff says that he has been scolded by far more birds than had been originally trapped, suggesting that they not only recognized the mask, but had transmitted the information to their offspring and to other birds in the flock.

Marzluff and his colleagues published their findings about a year ago in the journal Animal Behaviour. Not surprisingly, military funding for the research ended long before they had obtained any evidence that crows can recognize human faces, and it is unlikely that the bird played any part in finding bin Laden.

"So, they have a long term memory, very acute discrimination abilities, and if a group of crows knew bin Laden as an enemy, they would certainly indicate his presence when they next saw him," he says. "One of the experimental branches of research that was used to try to find him was to have crows or ravens of the local area trained to identify his face."

Related:

Marzluff, J., et al. (2010). Lasting recognition of threatening people by wild American crows. Anim. Behav. 79: 699-707. DOI: 10.1016/j.anbehav.2009.12.022

neurophilosophy Sun, 05/08/2011 - 05:20

Speed of illusory body movements alters the passage of time

neurophilosophy — Wed, 04 May 2011 06:50:32 +0000

Speed of illusory body movements alters the passage of time

YOUR brain has a remarkable ability to extract and process biological cues from the deluge of visual information. It is highly sensitive to the movements of living things, especially those of other people - so much so that it conjures the illusion of movement from a picture of a moving body. Although static, such pictures trigger dynamic representations of the body, 'motor images' containing information about movement kinematics and timing. Researchers at the Institute of Cognitive Neuroscience in London now show that biological motion is processed unconsciously, and that the speed of apparent motion alters the perception of time.

Play around with this point light display and you'll see that your brain has specialized mechanisms dedicated to recognizing and visually processing the human body and its movements. The demo shows that the brain is adept at inferring structure from motion, so that we readily perceive biological motion even when a minimum amount of information about the body is available. It also shows that the motions of the body contain information about sex, weight, emotional state and even some personality traits, and that we can extract this information effortlessly.

On the other hand, the brain also infers motion from structure. Static pictures produce the illusion of movement by activating regions of the visual cortex that are sensitive to motion. In studies of apparent motion, participants shown two static images showing the initial and final position experience seeing an intermediate position linking the two, as long as the interval between them is consistent with the duration of the movement. If, however, the interval between the initial and final positions is very short, they see an impossible movement linking the two.

Motion-from-structure studies suggest that our perceptions of biological motion contain information about the timing of motions, and that apparent motion is linked to the subjecive experience of passage of time. Guido Orgs and his colleagues set out to investigate this. They captured a small number of professionally choreographed dance moves on video and produced a series of static pictures of each one, representing the initial, intermediate and final position of the dancer.

The researchers manipulated the apparent movement paths in some of the sequences by changing the order of the pictures. In the 'short path' picture sequences (shown in the top half of the figure on the right), the intermediate posture of the movement was in the middle position. In the 'long path' sequences (bottom), it was placed at the end, so that it produced an apparent movement path that is about one and a half times longer than those in the short path sequences.

18 undergraduates were shown five of these picture sequences interspersed with sequences of control pictures consisting of the same pictures with all biological cues removed. During each of 240 trials, the participants viewed five body movement picture sequences and five control picture sequences, in random order on a computer screen. The pictures in each sequence were shown one after the other, for one-tenth of a second each, with an interval of between 50 and 300 thousandths of a second, which was varied randomly between trials.

The pictures were surrounded by a white rectangle, which remained visible for the same duration as the sequence in the trial. Participants were told that the rectangle would be displayed for varying durations, and asked to judge how long it stayed on the screen in each trial, by pressing keys to indicate whether the duration of the rectangle was relatively longer or shorter than the one in the previous trial.

If the participants' judgements were based on the apparent movement paths, we would expect them to perceive the rectangles presented with the long path sequences as being visible for longer. The sequences would produce a dilation of subjective time, because they would take longer to execute. But the opposite was found to be the case: the long path sequences were perceived to take less time than the short path sequences, showing that the subjective experience of the durations for which they were displayed had been compressed.

In a second experiment, the participants were shown the same picture sequences and asked to judge the velocity of the apparent movements. This time the apparent movements in the long path sequences were perceived as being faster than the apprent movements in the short path sequences. Analysis of the data revealed that the apparent speed of long path sequences was perceived on average to be one and a half times faster than that of the short path sequences.

Thus, manipulating the apparent movement paths produced directly proportional changes in the perceived speed of the movements and inversely proportional changes in time perception. That is, sequences implying the longer movement paths produced faster apparent movements and a compression of subjective time, whereas sequences implying the shorter paths produced slower apparent movements and dilated the sequence duration.

These effects were far more pronounced for sequences of body pictures than for the control sequences or for picture sequences of the body in upside-down postures, suggesting that the brain mechanisms involved are specific for realistic biomotion. And the finding that the body posture pictures affected time perception despite being unrelated to the tasks being performed shows that the brain extracts biomotion information implicitly and automatically.

The researchers suggest a possible 'top-down' mechanism whereby sequences of body posture pictures are automatically merged into a continuous, dynamic representation of movement, which includes information about the timing of the movements. The mechanism produces propotional changes in the apparent duration and speed of the movements, contracting time as the apparent movement path increases, and vice versa. Their findings further suggest that the mechanism only processes static biological images when they are in the correct configuration, but does not rely on conscious attempts to "see" them.

Related:

Orgs, G., et al. (2011). From Body Form to Biological Motion: The Apparent Velocity of Human Movement Biases Subjective Time. Psych. Sci. DOI: 10.1177/0956797611406446

Grosjean, M., et al. (2007). Fitts's Law Holds for Action Perception. Psych. Sci. 18: 95-99 [PDF]

Blake, R. & Schiffrar, M. (2007). Perception of human motion. Annu. Rev. Psychol. 58: 47-73 [PDF]

neurophilosophy Wed, 05/04/2011 - 02:50

Box jellyfish stable-eyes vision to hunt prey

neurophilosophy — Thu, 28 Apr 2011 10:00:30 +0000

Box jellyfish stable-eyes vision to hunt prey

Ernst Haeckel's Kunstformen der Natur (Artforms of Nature) was a landmark in biological illustration. Published in 1904, it was lavishly illustrated with 100 exquisitely detailed lithographic plates, including this one, showing nine different species of cubomedusae, or box jellyfish.

It has been known, since around the time that Haeckel's masterpiece was published, that box jellyfish have a unique visual system which is more sophisticated than that of other jellyfish species. They boast an impressive set of 24 eyes of four different types, which are clustered within bizarre sensory appendages that dangle from the cube-shaped umbrella. The known light-guided behaviours of these organisms are, however, relatively simple, so exactly why they possess such an elaborate array of eyes was somewhat puzzling.

A group of Scandinavian researchers working in the Carribean now report that one of the box jelly's eye types is highly specialized to peer up towards the water surface at all times, so that it can use terrestrial landmarks to navigate towards its prey.

Anders Garm and his colleagues have been conducting experiments on wild populations of Tripedalia cystophora, a box jelly that inhabits the mangrove lagoons near La Parguera in Puerto Rico. These organisms, which measure just 10mm in diameter, inhabit the shallow water near the edges of the lagoons, between the prop roots of the mangrove trees. Here, they stay close to the water surface, where their prey - small crustaceans called copepods - gather in large numbers in the shafts of light formed by gaps in the mangrove canopy above.

Like other box jellys, T. cystophora has 24 eyes contained within a club-shaped sensory apparatus called a rhopalium, one of which is suspended from each side of the cube-shaped umbrella by a flexible, muscular stalk. Each rhopalium contains a cluster of six eyes - one pair of slit eyes, one pair of pit eyes, one lower lens eye and one upper lens eye. The slit eyes and pit eyes are simple structures consisting of openings containing light-sensitive pigments. The lower and upper lens eyes are 'true' eyes which resemble those of cephalopods and vertebrates more closely than those of other jellyfish. They contain a spherical lens, iris, cornea, which together work like a camera to form an image onto photoreceptor cells in the retina.

Garm and his colleagues are interested in how eyes evolved, and how they are adapted to an animal's lifestyle and habitat. Several years ago, they showed that box jellys use vision to avoid obstacles that might damage their delicate bodies, and that this avoidance response differs between species - it is stronger in T. cystophora, which is usually surrounded by roots, than in Chiropsella bronzie, which lives in shallow water off the sandy beaches of Queensland, Australia, a habitat that contains few obstacles.

Garm's group had also observed that T. cystophora quickly swim back to the edge of the lagoon when moved away from it. This behaviour is essential for survival - they forage for food at the lagoon's edge, and risk starvation if they stray too far. The researchers speculated that they might use the upper lens eye to navigate toward the edge of the lagoon, and performed a series of behavioural experiments to test the idea.

They placed a clear tank with cylindrical walls and a flat bottom in the water under the mangrove canopy, and filled it with water so that it floated, with the walls extending several centimenters above the water surface. They then placed a group of jellyfish in the tank and slowly dragged it away from the lagoon's edge, and recorded the movements of the jellyfish with a video camera suspended beneath the tank.

Using a geometrical model they had developed previously, the researchers predicted how the resolution of the eye would limit the detection of the mangrove canopy. At 5m tall, the mangrove trees would be detected easily at distances of 4m, but detection would be more difficult at 8m, due to ripples on the water surface, and impossible at 12m. This is exactly what was found in the behavioural experiments.

The jellyfish were seen to swim along the edges of the tank, bumping into it constantly as it was moved. But rather than swimming randomly, they always swam in the direction of the nearest mangrove trees. This behaviour was most evident when the tank was between 2 and 4 meters away from the lagoon edge. The jellyfish could still detect the direction of the nearest trees from a distance of 8 meters, but swam randomly along the edge of the tank when it was 12 meters or more away.

The experimental tank sealed off the water surrounding the jellyfish inside it, so that they could not detect any chemical cues in their environment, or the mechanical forces that would normally generated by movement. Visibility in the lagoon is poor, and there are no recognizable underwater landmarks. And the finding that their navigational ability depends on distance rules out the possibility that they use cues from the sun. So the only remaining explanation is that they are using the upper lens eye to detect visual cues from the mangrove canopy, and use these cues to determine the direction of the nearest lagoon edge. This was confirmed by a further experiment, in which a white sheet was used to obscure the canopy - with the trees hidden from view, the jellyfish swam randomly.

Close-up video recordings of freely-swimming T. cystophora revealed that the upper lens eye is remarkably specialized for this behaviour. Each rhopalium contains a heavy crystal called a statolith, which is found at the end of the muscular stalk furthest from the body. These weigh down the rhopalia, causing the stalk to bend when the jellyfish changes the orientation of its body.

Consequently, the upper lens eyes remain in a strictly upright position, regardless of body orientation (above), and their visual fields point directly upwards, even when the jellyfish is completely upside-down. The lower lens eyes, on the other hand, which are thought to be be required for repulsion and attraction to underwater objects, always point downwards.

The researchers used their geometric model to investigate the optical properties of the upper lens eye, revealing another remarkable specialization. Water bends light waves entering it, causing the 180Â° visual field we are accustomed to be compressed. From beneath the surface, everything above is seen through a cone of light with a width of about 96Â°. According to the researchers' simulation, the visual field of the upper lens eyes has a width of between 95Â° and 100Â°. This further suggests that the upper lens eyes probably evolved for the sole purpose of detecting visual cues from above the water surface.

The use of terrestrial landmarks for navigation is an advanced visually-guided behaviour, and this is the first time that such behaviour has been observed in a jellyfish species. The box jelly nervous system is more highly developed than that of other jellyfish, but nevertheless lacks a brain, and consists of a nerve ring around the base of the umbrella. The findings therefore show that a centralized brain is not necessary for advanced behaviours.

Navigation is the only known purpose of the upper lens eyes; similarly, the purpose of the lower lens eyes is apparently restricted to detection of underwater objects. Eyes like these, which support a single visually-guided behaviour, represent an early stage in the evolution of visual systems, and are presumed to require less neural processing power than multi-purpose eyes such as ours.

The complex eye arrays may, therefore, be an evolutionary strategy for producing complex visually-guided behaviours in the absence of a brain, and could explain why the box jelly nervous system is more complex than that of other jellyfish species. It is, however, unclear how box jellys process visual information, and this is something that Garm's group is keen to explore.

Garm, A., et al. (2011). Box Jellyfish Use Terrestrial Visual Cues for Navigation. Curr. Biol. DOI: 10.1016/j.cub.2011.03.05

Garm, A., et al. (2007). Visually guided obstacle avoidance in the box jellyfish Tripedalia cystophora and Chiropsella bronzie. J. Exp. Biol. 210: 3616-3623 [PDF]

Nilsson, D. E., et al. (2005). Advanced optics in a jellyfish eye. Nature 435: 201-205 [PDF]

neurophilosophy Thu, 04/28/2011 - 06:00

Categories

Life Sciences

Gut bacteria may influence thoughts and behaviour

neurophilosophy — Fri, 25 Mar 2011 06:55:28 +0000

Gut bacteria may influence thoughts and behaviour

THE human gut contains a diverse community of bacteria which colonize the large intestine in the days following birth and vastly outnumber our own cells. These intestinal microflora constitute a virtual organ within an organ and influence many bodily functions. Among other things, they aid in the uptake and metabolism of nutrients, modulate the inflammatory response to infection, and protect the gut from other, harmful micro-organisms. A new study by researchers at McMaster University in Hamilton, Ontario now suggests that gut bacteria may also influence behaviour and cognitive processes such as memory by exerting an effect on gene activity during brain development.

Jane Foster and her colleagues compared the performance of germ-free mice, which lack gut bacteria, with normal animals on the elevated plus maze, which is used to test anxiety-like behaviours. This consists of a plus-shaped apparatus with two open and two closed arms, with an open roof and raised up off the floor. Ordinarily, mice will avoid open spaces to minimize the risk of being seen by predators, and spend far more time in the closed than in the open arms when placed in the elevated plus maze.

This is exactly what the researchers found when they placed the normal mice into the apparatus. The animals spent far more time in the closed arms of the maze and rarely ventured into the open ones. The germ-free mice, on the other hand, behaved quite differently - they entered the open arms more often, and continued to explore them throughout the duration of the test, spending significantly more time there than in the closed arms.

The researchers then examined the animals' brains, and found that these differences in behaviour were accompanied by alterations in the expression levels of several genes in the germ-free mice. Brain-derived neurotrophic factor (BDNF) was significantly up-regulated, and the 5HT1A serotonin receptor sub-type down-regulated, in the dentate gyrus of the hippocampus. The gene encoding the NR2B subunit of the NMDA receptor was also down-regulated in the amygdala.

All three genes have previously been implicated in emotion and anxiety-like behaviours. BDNF is a growth factor that is essential for proper brain development, and a recent study showed that deleting TrkB, the receptor to which it binds, alters the way in which newborn neurons integrate into hippocampal circuitry and increases anxiety-like behaviours in mice. Serotonin receptors, which are distributed widely throughout the brain, are well known to be involved in mood, and compounds that activate the 5HT1A subtype also produce anxiety-like behaviours.

The finding that the NR2B subunit of the NMDA receptor down-regulated in the amygdala is particularly interesting. NMDA receptors are composed of multiple subunits, but those made up of only NR2B subunits are known to be critical for the development and function of the amygdala, which has a well established role in fear and other emotions, and for learning and memory. Drugs that block these receptors have been shown to block the formation of fearful memories and to reduce the anxiety associated with alcohol withdrawal in rodents.

The idea of cross-talk between the brain and the gut is not new. For example, irritable bowel syndrome (IBS) is associated with psychiatric illness, and also involves changes in the composition of the bacterial population in the gut. But this is the first study to show that the absence of gut bacteria is associated with altered behaviour. Bacteria colonize the gut in the days following birth, during a sensitive period of brain development, and apparently influence behaviour by inducing changes in the expression of certain genes.

Exactly how gut bacteria might exert such influences is unclear, but they may do so via the autonomic branch of the peripheral nervous system, which controls functions such as digestion, breathing and heart rate. A better understanding of cross-talk within this so-called 'brain-gut axis' could lead to new approaches for dealing with the psychiatric symptoms that sometimes accompany gastrointestinal disorders such as IBS, and may also show that gut bacteria affect function of the mature brain.

Neufeld, K., et al. (2011). Reduced anxiety-like behavior and central neurochemical change in germ-free mice. Neurogastroenterol. Motil. 23 DOI: 10.1111/j.1365-2982.2010.01620.x

neurophilosophy Fri, 03/25/2011 - 02:55

Categories

Brain and Behavior

Looking into Ramachandran's broken mirror

neurophilosophy — Thu, 10 Mar 2011 04:20:18 +0000

Looking into Ramachandran's broken mirror

I visited Vilayanur S. Ramachandran's lab at the University of California, San Diego recently, and interviewed him and several members of his lab about their work. Rama and I talked, among other things, about the controversial broken mirror hypothesis, which he and others independently proposed in the early 1990s as an explanation for autism. I've written a short article about it for the Simons Foundation Autism Research Initiative (SFARI), and the transcript of that part of the interview is below. I also wrote an article summarizing the latest findings about the molecular genetics of autism, which were presented in a symposium held at the Society for Neuroscience annual meeting last November.

MC: Autism is an umbrella term referring to numerous conditions. Can the broken mirror hypothesis account for all of them?

Ramachandran: Autism is characterized by a specific subset of symptoms. There may be three or four that are lumped together, but by and large it is one syndrome, as good a syndrome as any in neurology. It's not like dyslexia, where there are half a dozen or a dozen types. With autism, people are debating whether high functioning and low functioning autistics should be lumped together or not. There's a tendency to group them together rather than saying they're distinct.

We have suggested that the mirror neuron system is deficient in autism, and there's mixed evidence of that, but most groups support our view. [Marco] Iaconobi's group at UCLA did a brain imaging study showing that the mirror neuron system is deficient, but others claim that it's normal. That may partly be based on the heterogeneity of autism. The mirror neuron system itself could be normal but its projections, or the regions it's projecting to, could be abnormal. It's still up in the air.

One of the things I say in my book [The Tell-Tale Brain] is that the mirror neuron system allows you to take an allocentric view of other peoples' actions, to view the intentions to their actions. It may even be turning inwards and looking at one's self from an allocentric perspective, so it may be partly contributing to self-awareness. In addition to an allocentric perceptual view, the same system then evolved into adopting an allocentric conceptual, or metaphorical, view - "I see your point of view". This could have been an evolutionary step from perception to conception, but we don't know exactly when than magic line was crossed.

MC: There's another hypothesis, which states that theory of mind is defective in autism. What are the similarities and differences between this and the broken mirror hypothesis? It seems to me that the two aren't necessarily mutually exclusive, because mirror neurons are likely to be involved in theory of mind.

Ramachandran: The broken mirror hypothesis and defective theory of mind are complementary. It's like saying genetics excludes DNA, or something. They complement each other. The broken mirror theory is the one we proposed. We also proposed in the same paper that the salience landscape is defective, due to a derangement of connections between the amygdala and other limbic structures. Normally you assign zero salience to that [points to coffee] - well, it's tasty, so I assign some salience to it - but not much salience to that [taps the table]. The brain is constructing a salience landscape, and in autism that gets messed up, for some reason. You get trivial things provoking a fight or flight response, so you get the autonomic storms that characterize autism.

MC: You did an early experiment showing mu wave suppression in one person with autism. Have you obtained any more evidence for the phenomenon since then?

Ramachandran: We repeated it on 25 or 30 autistic kids and got the same result, and others have found evidence supporting the idea. Mu wave suppression occurs when they perform an action, but not when they watch somebody else performing it. There are people, like Iacoboni, who used functional neuroimaging to show mu wave suppression. The salience landscape idea was proposed with Bill Hirstein, and we published that in Proceedings of the Royal Society about 10 years ago. It's also described in our broken mirror article in Scientific American.

MC: One recent study failed to find any evidence for the existence of mirror neurons in the human brain, and some say there's a lack of evidence that the human brain actually contains mirror neurons.

Ramachandran: That's nonsense. First of all, there's functional brain imaging data. Secondly, why would the monkeys and anthropoid apes have mirror neurons, only to suddenly disappear in humans? It doesn't make intuitive sense and empirically it's flawed.

On the other hand, what people have said is that there's a lot of media hype about the magical properties that have been attributed to mirror neurons. But just because there's hype, doesn't mean it's wrong. That's a stupid argument.

The third argument is that some of the properties attributed to mirror neurons are acquired through learning. Every time a monkey reaches and grabs a peanut, a motor neuron fires when it sees its hand reach out, creating a Hebbian link, and the same neuron fires when it watches a peanut being grabbed. The counter-argument there is, why is it that only 30% of the neurons are mirror neurons? If it's just Hebbian association, what happens to the other neurons? Why don't they learn? So there are some hardware constraints. Secondly, even if it is learnt, what's the big deal? If we're interested in knowing what the mechanism is, the question of nature versus nurture is orthogonal. The existence of stereoscopic neurons and their circuitry is what you want to understand. How the behaviour is learned, or acquired or can be modified is a separate issue.

There's also a strong anti-reductionist streak, with psychologists saying it's the same as theory of mind. That's an idiotic argument, it's like saying that if you know Mendellian genetics you don't need to understand DNA. Mirror neurons provide a mechanism for the theory of mind, not a substitute for the idea. They complement each other very nicely. So that criticism goes down the tube.

neurophilosophy Wed, 03/09/2011 - 23:20

Categories

Social Sciences

Artificial nerve grafts made from spider silk

neurophilosophy — Mon, 07 Mar 2011 08:05:08 +0000

Artificial nerve grafts made from spider silk

EVERY year, hundreds of thousands of people suffer from paralyzed limbs as a result of peripheral nerve injury. Recently, implantation of artificial nerve grafts has become the method of choice for repairing damaged peripheral nerves. Grafts can lead to some degree of functional recovery when a short segment of nerve is damaged. But they are of little use when it comes to regenerating nerves over distances greater than a few millimeters, and such injuries therefore often lead to permanent paralysis.

Now though, surgeons from Germany have made what could be a significant advance in nerve tissue engineering. They have developed artificial nerve grafts made from hollowed-out pig veins filled with spider silk fibres and, in a series of animal experiments, showed that the grafts can enhance the regeneration of peripheral nerves over distances of up to 6cm. Their findings have just been published in the open access journal PLoS One.

Peripheral nerves have a greater regenerative capacity than those in the central nervous system, but regenerating them properly is challenging. The individual nerve fibres must not only regrow into the damaged area, but also find their proper targets. Furthermore, the regenerated nerve will not function properly unless it is populated by Schwann cells, which produce myelin. This fatty tissue is essential for full recovery, as it wraps itself around the nerve fibres at regular intervals (a process called myelination), facilitating the conductance of nervous impulses along their length.

Conventionally, damaged peripheral nerves are treated either by suturing or by implantation of nerve grafts. The two ends of a severed nerve can be surgically re-attached to each other, as long as the nerve is not stretched in the process. This is not possible for gaps longer than about 5mm, in which case a short length of nerve from elsewhere in the patient's body can be grafted into the damaged area. But this often causes causes pain in the donor area, and it can be difficult to find a nerve segment that has the same diameter as the damaged nerve. Nerves can be obtained from another person, but they can be rejected by the recipient's immune system, so drugs that suppress the immune response are usually administered.

An alternative approach, which has emerged in the past ten years or so, is the use of artificial nerve grafts made from silicon or synthetic polymers such as polyethylene. These form scaffolds which bridge the gap in the damaged nerve and serve as conduits through which the nerve fibres can regrow. Artificial grafts can lead to some degree of functional recovery, but they can become toxic with time, or they can constrict the nerve.

These problems can potentially be overcome by using nerve grafts made from biodegradable materials. Five years ago, Peter Vogt and his colleagues in the Department of Plastic, Hand and Reconstructive Surgery at Hannover Medical School reported that Schwann cells readily ensheath spider silk fibres when grown on them, and that nerve grafts made of de-cellularized veins filled with spider silk can be maintained in culture for periods of up to a week. More recently, they showed that spider silk vein grafts can be used to regenerate 20mm gap in the sciatic nerve of rats, either alone or when supplemented with Schwann cells.

In the new study, Vogt's group dissected 6cm lengths from the small veins in pigs' legs, washed them and stripped away most of the endothelial cells from their inner walls. They then harvested dragline silk from the golden silk spider Nephila clavipes and pulled the silk through the de-cellularized veins, until it filled about one quarter of their diameter. Using adult sheep, the researchers removed a 6cm length of the tibial nerve in the leg. In one group of animals, the gap was bridged with the spider silk constructs; in another, the section of nerve that had been removed was replaced in reverse orientation.

Defects in the animals' gait became apparent immediately after the surgery - the hind limb was partially paralyzed and flexed abnormally. But within three weeks there was a significant improvement, with both groups of animals being able to stand properly. By four months, the animals could stand upright on both hind limbs, the hind limbs moved in co-ordination with one another during walking, and there was no obvious difference in strength between the operated and unoperated limbs.

Ten months after surgery, the sheep were killed and their regenerated nerves examined under the microscope. In both groups of animals, the severed nerve fibres had regrown into the nerve grafts to bridge the 6cm gap; Schwann cells had migrated into the grafts and wrapped themselves around the entire length of the regenerated nerves; and the sodium channels required for generating nerve impulses were distributed irregularly along the fibres. This shows that myelination had occurred properly, with the formation of Nodes of Ranvier, the regular gaps in the myelin sheath at which the sodium channels normally cluster. No trace of residual spider silk was detected in the experimental animals, and there was no sign of inflammation at the repair site, indicating that the silk fibres were absorbed subtly without adverse effects.

These findings could have important applications in reconstructive nerve surgery. This is the first time that a large animal model has been used to study nerve regeneration, and the study is the first in which a defect longer than 2cm in length has been successfully repaired. The spider silk constructs enhanced nerve regeneration at least as effectively as the sheeps' own nerves, and would be advantageous in the clinic, because transplanting large lengths of a patient's own nerves is unfeasible.

More work will be needed before the technique can be applied to humans. Meanwhile, the regeneration reported here could be further enhanced in a number of ways. The spider silk constructs could, for example, be loaded with substances such as Nerve Growth Factor, or they could be grafted together with Schwann cells, to speed up nerve regrowth. But ultimately, engineering fully functional peripheral nerves will probably require a combination of advanced microsurgery, transplantation of both cells and tissues, advances in materials science and, possibly, gene transfer for the effective delivery of growth factors.

Radtke, C. et al. (2011). Spider Silk Constructs Enhance Axonal Regeneration and Remyelination in Long Nerve Defects in Sheep. PLoS ONE, 6 (2) DOI: 10.1371/journal.pone.0016990.

neurophilosophy Mon, 03/07/2011 - 03:05

Categories

Medicine