Neurophilosophy

The illusion of time: Perceiving the effect before the cause

Fri, 06 Nov 2009 12:50:39 -0500

A novel temporal illusion, in which the cause of an event is perceived to occur after the event itself, provides some insight into the brain mechanisms underlying conscious perception. The illusion, described in the journal Current Biology by a team of researchers from France, suggests that the unconscious representation of a visual object is processed for around one tenth of a second before it enters conscious awareness.

Chien-Te Wu and his colleagues at the Brain and Cognition Research Centre in Toulouse used a visual phenomenon called motion-induced blindness, in which a constantly rotating background causes prominent and motionless visual stimuli to disappear and reappear, as demonstrated in the video below. Fixate on the flashing green spot in the centre, and you'll notice that the surrounding yellow spots begin to disappear and reappear after about ten seconds. Then replay the clip and focus on any of the yellow spots; you'll see that it is a visual disappearance illusion. Exactly how it works is unclear; according to one hypothesis it is due to the properties of neurons in area V1 of the visual cortex.

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Phantom limbs can contort into impossible configurations

Wed, 28 Oct 2009 13:37:49 -0500

FOLLOWING the surgical removal of a body part, amputees often report sensations which seem to originate from the missing limb. This is thought to occur because the brain's model of the body (referred to as the body image) still contains a representation of the limb, and this leads to the experience that the missing limb is still attached to their body. Occasionally, amputees say that they cannot move their phantom limbs - they are perceived to be frozen in space, apparently because they cannot be seen.

Yet, research shows that the body image is malleable and easily manipulated. And according to a new paper published in the Proceedings of the National Academy of Sciences, phantom limbs can be altered by internal brain mechanisms alone. The study shows that some amputees can make their phantom limbs defy the anatomical constraints of the physical body, using visual imagery to make them perform movements which could not possibly be performed by a real limb.

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A pictorial history of neurotechniques

Wed, 21 Oct 2009 16:20:42 -0500

THE latest issue of Technology Review contains a photo essay by yours truly, called Time Travel Through the Brain, in which I look at how techniques used to investigate the brain have evolved during the 100 year history of modern neuroscience. The essay begins with a drawing by the great Spanish neuroanatomist Santiago Ramón y Cajal, who used the staining method discovered by Camillo Golgi to establish that nervous tissue is composed of cells, then goes on to describe more recent methods such as fibre tracing, Brainbow and various types of microscopy.

This image from the piece graced the cover of the Journal of Neuroscience back in April. It's a rotary shadow electron micrograph showing the cytoskeleton of a hippocampal neuron, by Bernd Knöll of the University of Tübingen and Jürgen Berger and Heinz Schwarz of the Max Planck Institute for Developmental Biology. The technique involves freezing the specimen under high pressure in liquid nitrogen, then fracturing it with a blade in an ultra-cooled vacuum chamber to strip off the membrane. During fracture, the specimen stage rotates; as it does so, platinum and carbon are deposited onto it from a pair of electrodes, to produce a metallic three-dimensional replica of the cell interior.

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Lasers used to write false memories onto the fruit fly brain

Tue, 20 Oct 2009 11:55:15 -0500

THE humble fruit fly (Drosophila melanogaster) has the ability to learn and remember, and to make predictions about the outcome of its behaviours on the basis of past experience. Compared to a human brain, that of the fruit fly is relatively simple, containing approximately 250,000 cells. Even so, little is known about the anatomical basis of memory formation. The neural circuitry underlying memories in these insects has now been dissected. In an elegant new study published in the journal Cell, researchers from the University of Oxford show that aversive memories are dependent on a tiny cluster of neurons, and also demonstrate that such memories can be implanted in the fruit fly's brain by using light to manipulate the cells' activity.

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Mice navigate a virtual reality environment

Sun, 18 Oct 2009 19:30:38 -0500

USING an inventive new method in which mice run through a virtual reality environment based on the video game Quake, researchers from Princeton University have made the first direct measurements of the cellular activity associated with spatial navigation. The method will allow for investigations of the neural circuitry underlying navigation, and to a better understanding of how spatial information is encoded at the cellular level.

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Surgery on conscious patients reveals sequence and timing of language processing

Fri, 16 Oct 2009 15:50:18 -0500

THINKING of and saying a word is something that most of us do effortlessly many times a day. This involves a number of steps - we must select the appropriate word, decide on the proper tense, and also pronounce it correctly. The neural computations underlying these tasks are highly complex, and whether the brain performs them all at the same time, or one after the other, has been a subject of debate.

This debate has now apparently been settled, by a team of American researchers who had the rare opportunity to investigate language processing in conscious epileptic patients undergoing surgery. In today's issue of the journal Science, the researchers report that the brain processes lexical, grammatical and phonological information in a well defined sequence that lasts less than half a second, and that a single language centre known as Broca's Area is involved in all these tasks.

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Kicking performance affects perception of goal size

Mon, 12 Oct 2009 13:50:09 -0500

ATHLETES who are on a winning streak often claim that they perceive their targets to be bigger than they actually are. After a run of birdies, for example, golfers sometimes say that the cup appeared to be the size of a bucket, and baseball players who have a hit a few home runs say that the ball is the size of a grapefruit. Conversely, targets are often reported to be smaller than they actually are by athletes who are performing badly.

Research carried out in the past 5 years suggests that these are more than just anecdotes, and that performance in sports can actually affect perception. A new study by psychologists at Purdue University now lends more weight to this, by providing evidence that success rate in American football field goals affects how the size of the goal posts is perceived.

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Alzheimer's fish go head to head in the Nikon Small World Competition

Fri, 09 Oct 2009 12:40:41 -0500

THIS image by Dominik Paquet of Ludwig-Maximilians-Universität in Munich is one of the winners of the 2009 Nikon Small World Photomicrography competition. It's a confocal fluoresence microscopy image of zebrafish larvae expressing a mutant form of human Tau protein, which forms the neurofibrillary tangles that are a pathological hallmark of Alzheimer's Disease. The work is described in this recent paper.

Below are two more images from the competition.

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The virtual body illusion and immersive Second Life avatars

Thu, 08 Oct 2009 16:00:32 -0500

SECOND LIFE is an online "virtual world" which enables users to create a customised avatar, or digital persona, with which they can interact with each other. It has become incredibly popular since its launch just over 6 years ago, with millions of "residents" now using it regularly to meet others, socialize and even to have virtual sex. Second Life is now filled with virtual communities and institutions - it has businesses and universities, and its own virtual economy.

Now, imagine a futuristic version of Second Life, in which avatars can transfer sensations to the bodies of their users. Such a scenario may seem far-fetched, but a team of European researchers has just taken us one step closer it. They demonstrate a perceptual illusion in which a computer-generated virtual body can be made to feel like one's real body, so that one can feel sensations from it and respond to it as if it were real.

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Visual analgesia: Seeing the body reduces pain

Wed, 07 Oct 2009 12:20:06 -0500

VISION is now well known to modulate the senses of touch and pain. Various studies have shown that looking at oneself being touched can enhance tactile acuity, so that one can discriminate between two pinpoints which would otherwise feel like a single sensation. And last year, researchers from the University of Oxford showed that using binoculars to make a limb look larger or smaller than it actually is can respectively enhance and diminish painful sensations.

These phenomena occur because the brain fuses stimuli from different sensory systems to generate a coherent experience of bodily sensations. The precise mechanisms are unknown, and it is also unclear whether these effects depend upon specific visual stimuli. But according to a new study from University College London, the general "context" of vison is enough to modulate pain. In the current issue of the Journal of Neuroscience, they report that merely looking at one's hand can affect the perception of laser-induced pain, and how it is processed in the cerebral cortex. Together with earlier work, these findings point to a simple method for managing acute pain.

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Circadian and social cues regulate sodium channel trafficking in electric fish

Fri, 02 Oct 2009 10:15:07 -0500

SEVERAL hundred species of fish have evolved the ability to generate electric fields, which they use to navigate, communicate and home in on prey. But this ability comes at a cost - the electric field is generated continuously throughout life, so consumes a great deal of energy, and it can also attract predators which are sensitive to it. Electrogenic fish species therefore utilize various strategies to save energy and to minimize the likelihood of being detected. Some generate irregular pulses of electrical discharges whose rate can be modulated; others can also modulate the strength of the electric field.

The cellular and molecular mechanisms underlying one of these behavioural adaptations are now revealed in a beautiful study published in the open access journal PLoS Biology. It shows that in one species of electric fish, circadian cues and social encounters regulate the movements of proteins called voltage-gated sodium channels - which are crucial for generating the electric field - in cells of the electric organ. At night, low light levels and social interactions drive the insertion of sodium channels into the cell membranes, leading to a dramatic increase in the strength of the electric field.

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Flight of the remote-controlled cyborg beetle

Wed, 23 Sep 2009 15:55:37 -0500

REMOTE-CONTROLLED insects may sound like the stuff of science fiction, but they have already been under development for some time now. In 2006, for example, the Defense Advanced Research Projects Agency (DARPA, the Pentagon's research and development branch) launched the Hybrid Insect Micro-Electro-Mechanical Systems program, whose ultimate aim is to turn insects into unmanned aerial vehicles.

Such projects provide proof of principle, but have met with limited success. Until now, that is. In the open access journal Frontiers in Integrative Neuroscience, a team of electrical engineers led by Hirotaka Sato of the University of California, Berkeley, report the development of an implantable radio-controlled neural stimulating device, with which they demonstrate, for the very first time, the accurate control of flight in freely flying insects.

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Vegetative and minimally conscious patients can learn

Mon, 21 Sep 2009 13:20:55 -0500

THE vegetative and minimally conscious states are examples of what are referred to as disorders of consciousness. Patients in these conditions are more or less oblivious to goings-on in their surroundings - they exhibit few, if any, signs of conscious awareness, and are usually unable to communicate in any way. It is, therefore, extremely difficult to establish what these patients are experiencing, and the consciousness disorders are among the least understood, and most commonly diagnosed, conditions in medicine.

Although technologies such as functional neuorimaging have enabled clinicians to gain some insight into these conditions, proper assessment and diagnosis of patients are still major challenges, and there are big ethical questions regarding how they should be treated. However, researchers from the University of Cambridge have made what could be a significant advance.

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The social thermometer: Temperature affects how we perceive relationships

Sat, 19 Sep 2009 10:50:24 -0500

LANGUAGE contains many sayings which link our feelings and behaviour towards others to temperature. We might, for example, hold "warm feelings" for somebody, and extend them a "warm welcome", while giving somebody else "the cold shoulder" or "an icy stare". Why is that we have so many metaphors which relate temperature to social distance? According to George Lakoff, a professor of cognitive science and linguistics at the University of California, Berkeley, we judge others on the basis of warmth because abstract concepts, such as affection, are firmly grounded in bodily sensations.

There is evidence for Lakoff's hypothesis, which shows that these sayings are more than just metaphors. Last year, a study by psychologists from the University of Toronto showed that participants who recalled an experience in which they felt socially excluded gave lower estimates of room temperature than participants who recalled a social inclusion experience. Hans Ijzerman and Gün R. Semin of Utrecht University now show that the opposite is also true. In a paper published in Psychological Science, they report that temperature affects the perception of social relations and the language used to describe them.

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A dual-use fluorescent calcium sensor virus

Thu, 17 Sep 2009 15:54:40 -0500

A paper by researchers from Princeton University, just published in the open access journal PLoS One, describes a new virus-based technique for probing the connections between neurons while simultaneously monitoring their activity in live animals. Various methods are available for studying the activity of neurons and how they are connected to one another, but examining the co-ordinated activity of multiple nerve cells in neural circuits has, until now, posed a big challenge, because none of them can monitor both activity and connectivity at the same time.

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