by Susana Martinez-Conde, PhD
Director, Laboratory of Visual Neuroscience
Barrow Neurological institute
Phoenix, Arizona

Some camera work, some stroking, and next thing you know you're out of your own body.
Photo courtesy Henrik Ehrrson

Sir Arthur Conan Doyle, best known as the creator of the coolly analytical detective Sherlock Holmes, was paradoxically a firm believer in the paranormal. His obsession with the supernatural fueled much of his (non-Sherlockian) fiction. In his short story "How It Happened," the protagonist wakes from a car crash. He is shocked by the experience but relieved to find his old friend Stanley standing beside him. The protagonist's view of the wreck is partially obstructed, and so he does not identify the inert body on the road. He then remembers that Stanley, whom he has not seen for years, died long ago.


"˜Stanley!' I cried, and the words seemed to choke my throat "“ "˜Stanley, you are dead.'

He looked at me with the same old gentle, wistful smile.

"˜So are you,' he answered.

Similar accounts of out-of-body experiences -- in which a conscious person sees his or her own body from a location outside the physical body -- have been reported in clinical conditions that disturb brain function, such as near-death experiences, epileptic seizures, drug abuse, stroke, and certain psychiatric and neurological disorders. Last year, two research groups induced out-of-body experiences in healthy participants with virtual reality techniques. The experiments, described last August in studies by H. Henri Ehrsson and Olaf Blanke and colleagues in Science, demonstrate that out-of-body experiences, previously confined to the realms of psychiatry, fiction and the occult, occur when the normal processing of sensory information is disrupted. This research provides an important tool to understand how the feeling of self is generated by the brain. Sherlock would approve.

Meet your virtual doppelganger

The experiments were conducted by research teams in the UK (H. Henrik Ehrsson) and Switzerland (Bigna Lenggenhager, Tej Tadi, Thomas Metzinger and Olaf Blanke). The participants wore virtual reality goggles connected to video cameras that filmed the participants' backs. Thus each participant saw his or her own body from the back.

But this trick alone did not induce an out-of-body experience. (And a good thing too. Otherwise you might have an out-of-body experience every time you check out your own backside in the fitting room at the mall). To complete the illusion, the scientists used two plastic rods to stroke synchronously, for 1 or 2 minutes at a time, the participant's back and the back of the virtual body. Next, the participants were asked to complete a questionnaire to evaluate their subjective perception of the illusion. Amazingly, they reported feeling as if they were being behind their physical bodies and looking at them from this location. The illusion failed when the stroking was asynchronous.

The results demonstrated that there are two key components to the feeling of being located inside the body. First, visual information from the first-person perspective provides indirect information about the location of one's body in space. The second factor is the detection of correlated tactile and visual events on the (illusory) body. Such multisensory correlations, together with the first-person visual perspective, determine the perceived location of one's whole body -- even if the correlated tactile and visual events are constrained to a small part of the body.

Don't walk towards the light!

Meanwhile, down in Switzerland, Lenggenhager and colleagues wondered if, following an out-of-body experience, participants might misjudge the location of their own bodies in space. To test this idea, they blindfolded the participants immediately after the stroking, then passively displaced them to a different position in the room. Then they asked them to walk back to their original location. Participants did not accurately return to their initial position, however. Instead they drifted significantly towards the previous position of the virtual body, suggesting that they had (at least partially) assigned the location of their selves to the virtual body. Such drift was not significant in the asynchronous stroking condition.

In a second experiment, the authors examined whether the illusion might depend on cognitive knowledge about bodies, and whether the drift towards the virtual body might be due to a general motor bias that happened to overshoot the initial position. To address these possibilities, they either presented the participants with their virtual own body (as in the previous experiment), a virtual fake body, or a virtual non-corporeal object (an elongated block) during synchronous or asynchronous stroking. Asynchronous conditions produced no illusion or drift. Synchronous stroking induced the subjective illusion for both the virtual own body and the virtual fake body, but not for the virtual object. That is, participants self-identified with both virtual bodies (their own and the fake), but not with the object. Moreover, the blind-folded participants showed significant drift towards both virtual bodies, but not towards the object. These combined results showed that the drift towards the virtual body was not due to a general motor bias but to the out-of-body illusion itself. Also, out-of-body experiences depend on the participants' knowledge about bodies: a non-corporeal object will not induce an out-of-body experience, whereas a bodily representation will, even if the body is not the participant's own.

I feel your pain

To provide further objective evidence for the illusion, Ehrsson "hurt" the virtual body by hitting it with a hammer and registered the electrical resistance of the skin of the (real) participants at the same time. The participants' skin conductance response (used by psychologists to measure emotional arousal) was significantly greater in the synchronous stroking condition (that is, in the presence of an out-of-body experience) that in the asynchronous condition (that is, in the absence of an out-of-body experience). Thus during an out-of-body experience, the participants responded emotionally to the threat of the hammer as if they were located behind their physical bodies.

A full-blown out-of-body experience?

Although the healthy participants reported seeing themselves from behind and misjudged the location of their bodies, they did not have the feelings of overt disembodiment that are typical of "full-blown" out-of-body experiences, such as those found in some patients with temporal-parietal damage. Lenggenhager and colleagues therefore proposed that other mechanisms in addition to the correlation of visual-tactile information (for instance, the correlation of visual-vestibular information) may be necessary to generate more complete transfer of the self to an illusory body. The authors speculate that the neural mechanisms underlying the spatial unity of self and body, as well as the disruption of such unity, may lie at the brain's temporal-parietal junction.

The experiments described here open a new research venue to discern the brain mechanisms generating our feeling of self. They also provide a scientific and rational explanation for supposedly paranormal experiences such as the out-of-body illusion, showing that this previously puzzling phenomenon can be replicated in the lab by simple experimental manipulations.


Susan Martinez-Conde is the director of the Barrow Neurological Institute's Laboratory of Visual Neuroscience, where she studies the neural code and dynamics of visual perception.

Welcome to

Mind Matters

With the election season hard upon us and the spin machines working overtime, we thought it sensible to rerun a post from last year about a sort of spin machine recently discovered in the brain. Here, in a post first run last April 10, Susana Martinez-Conde examines the discovery of a bit of prejudicial pre-processing in a perception mechanism previously thought neutral. Think about it this election season before you decide to believe what you (think you) see.

Selective Vision The primary visual cortex (shown here in red) was long thought to passively record unfiltered information from the eyes. New findings suggests it's not quite so simple. Photo courtesy Wikipedia, via GNU Free Documentation License _________________________________________________________

Mind Matters - The First Year

We did not, alas, make it to the Prague Museum, which is pictured above. But with the end of both the calendar year and Mind Matters' first year it seems a good time to look a back and see where we have been since launching in January.

Memory and Learning

Looking back requires memory, and by chance that's where we started, with a post by memory researcher James Knierim reviewing what likely will prove the most influential single discovery we covered, that of grid cells in the mouse entorhinal cortex -- a system of neurons that appear to help track location and create context for memories. That discovery, wrote James Knierim,

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Greg Hickok Center for Cognitive Neuroscience University of California, Irvine

Mirror neurons are the rock stars of cognitive neuroscience. Discovered in the mid-1990s by Giacomo Rizzolatti and his colleagues at the University of Parma, these brain cells have been claimed to be the neural basis for a host of complex human behaviors including imitation, action understanding, language, empathy, and mind-reading "“ not psychic mind-reading, but our capacity to "get inside someone else's head" and imagine how they feel or what they might do. Meanwhile, dysfunction of the mirror neuron system has been linked to developmental disorders, such as autism. With that kind of explanatory range, it's no surprise that mirror neurons have headlined in all forms of news media. But is this rock star status deserved? Will mirror neurons have the star power longevity of Mick Jagger? Or are they just back up singers? The hidden mirror So what exactly are mirror neurons? While studying neurons in motor areas of the frontal lobe of the Rhesus monkey brain, Rizzolatti's team noticed that some cells were responsive not only when the monkey performed an action, such as grasping a raisin, but also when the monkey simply watched the experimenter perform the same action. It was as if these neurons were simulating, or mirroring, a perceived action in the motor system of the animal. This is a very interesting and important finding, showing that sensory and motor systems interact in the brain's cortex at the single cell level. But the interpretation of mirror neurons since then has extended well beyond sensory-motor interaction. For example, some have speculated that mirror neurons are the basis for our ability to understand the actions of others: because we know the consequences of our own actions, we can understand and anticipate the intended consequences of others' actions by activating similar neural networks in our own motor system. This concept was quickly generalized to more complex functions: because we speak, feel emotion, and have a sense of our own intentions, the theory goes, we can understand the speech of others, empathize, and "mind-read" intentions by mapping other people's behaviors onto our own mirror neuron system. What is really being reflected? Is the speculation that mirror neurons are responsible for "understanding" the behavior of others justified? Or are mirror neurons involved in less lofty, but nonetheless important, mental functions? A new study -- "Sensosirmotor Leaning Configures the Human Mirror System," from Current Biology (abstract or pdf download -- suggests the latter. Carolyn Catmur, Vincent Walsh, and Cecilia Heyes, researchers at University College London's Institute of Cognitive Science, stimulated the hand-related portions of motor cortex of human volunteers while they watched videos of hands performing movements of the index or little finger. Stimulation was accomplished using "transcranial magnetic stimulation" (or TMS), in which magnetic pulses are passed through the skull to induce brief electrical currents in the underlying brain tissue. TMS of motor cortex hand areas results in electrical neural impulses being transmitted to the hand itself, where these impulses can be measured by placing electrodes over the finger muscles. The researchers found that when a volunteer watched index finger movement, motor-cortex stimulation by TMS led to stronger electrical signals in the participant's own index finger compared to the pinky, and vice-versa when watching pinky finger movement. This is a mirror-neuron-like effect. Watching a video of index finger movement induces activation of the observer's own motor system controlling index finger movement. This naturally induced activity then sums with the TMS-induced activity to produce stronger than normal neural signals in the index finger muscles. The mirror neuron theorists would say that our "understanding" of this movement is a result of this heightened activation of our own motor system. But Catmur and colleagues went beyond this basic mirror neuron result. After their initial measurements, they trained the participants to make "counter-mirror" movements: that is, when you see the index finger move, move your own pinky finger, and vice-versa. After this training, the brain responses were reassessed -- and a reversal of the mirror effect was found: watching index-finger movement resulted in more electrical activity in the pinky, and watching pinky movement produced more activity in the index finger. The brain learned new sensory-motor associations, and it is these associations that underlie the mirror neuron-like effect. Fodder for, not parent of This is a very nice demonstration that mirror system-like activity is subject to sensory-motor learning, suggesting it is learned rather than hard-wired. But the real question for the mirror neuron theory of action understanding is what these newly trained volunteers "understand" about these movements. Since viewing index finger movement induces activity in the participants' pinky motor systems, do they now think they are viewing little finger movement? Of course not. They still understand that they are viewing index finger movement. Conclusion: mirror system activation is not necessarily correlated with "understanding" but rather with sensory-motor learning. This dissociation between mirror neuron-like activity and understanding comes as no real surprise. We know from decades (centuries even) of research involving patients with aphasia (language deficits resulting from brain damage, typically stroke) that it is possible to lose virtually all ability to articulate words while retaining the ability to understand the meaning of spoken words. Loss of the motor system controlling speech production, which contains the mirror system for speech, does not result in loss of the ability to understand the speech actions of others. It is also possible for the reverse situation to happen: in some patients with damage that spares the mirror system, the ability to repeat the speech of others may be intact (indicating intact sensory-motor associations), and yet they fail to understand the words. As in the study described above, mirror system function and action understanding dissociate. The implications are clear. The mirror neuron system is not the neural basis for action understanding. This is true for simple limb actions of the sort that led to the discovery of mirror neurons in the monkey, and it is true for the first complex human behavior that the mirror neuron theory was generalized to, namely speech. If the mirror neuron theory shatters for these behaviors, its generalization to abilities like empathy or "mind-reading" seems ridiculously overstated. This is not to say that a neural network supporting sensory-motor associations isn't important, or even that such associations are irrelevant to action understanding, language and the like. It seems quite likely that these higher-level systems make use of information derived from sensory-motor linkages. But that mirror neurons provide information that gets used by this high-level understanding does not mean that mirror neurons encode and produce this high-level understanding. You might be able to train a parrot to say "I can't get no satisfaction" -- but that doesn't mean he understands the message. Despite the hype to the contrary, mirror neurons are not the Mick Jagger of cognitive neuroscience. But there's no shame in singing backup. After all, who would want to sit through two hours of Mick singing a cappella? You need a whole band to make good music. The brain works the same way. Gregory Hickok is professor of cognitive neuroscience and the director of the Center for Cognitive Neuroscience at the University of California, Irvine. He blogs on the neural underpinnings of language at Talking Brains and contributes to a UC Irvine cog-sci group blog as well. -- Edited by David Dobbs at 12/18/2007 7:29 AM -- Edited by David Dobbs at 12/18/2007 10:07 AM -- Edited by David Dobbs at 12/18/2007 12:11 PM

by Robert Stickgold

Harvard Medical School



Most of us can remember at least one occasion on which we sat in class, half asleep, trying to pay attention and learn what we were being taught "“ to no avail. Why is this? What goes wrong when you try but fail to learn because you're "just too sleepy"? Well, I don't know about you, but for a group of 28 young adults, 18-30 years old, the answer now seems more clear. In a study published this February in Nature Neuroscience ("A deficit in the ability to form new human memories without sleep,") Seung-Schik Yoo, Matthew Walker, and their collaborators at Harvard Medical School looked at memory formation in young subjects with or without a night of sleep deprivation. To fully appreciate what they found, you'll need some background.

Sleep and memory consolidation

Over the last ten years, scientists have come to appreciate the complex relationships between sleep and memory. Not only does sleep prepare the brain for encoding new memories, sleep also provides an opportunity for the brain to consolidate and integrate recently learned information. Thus, sleep can make memories more stable, so that they are more resistant to interference and decay. For example, a night of sleep can make you better able to identify objects in your visual field where you studied them the night before, and it can make you faster and more accurate at typing a sequence of numbers that you practiced the night before (review by Stickgold: abstract or pdf download). But studies have also shown that sleep also can identify, extract, and store key features of memories, leaving a memory that is more useful the next day. Thus a night of sleep can increase the likelihood that you will discover a hidden shortcut for a mathematical procedure that you laboriously practiced the night before.

This wide range of benefits of post-training sleep suggests that such memory processing is a major function of sleep. But the findings I've described so far all concern the benefits of sleep on the formation and recollection of memories already formed. Another question is: How does sleep help you learn better the next day? Or, to put it another way, how does a lack of sleep affect your ability to form new memories?

Sleep and attention

For years scientists have known that sleep is necessary to focus attention on a task, whether you're trying to learn something or not. Specifically, sleep deprivation leads to reduced activation of attentional networks in the frontal and parietal lobes across a range of cognitive tasks. In addition, executive function tasks, thought to be mediated by prefrontal cortex, show greater deficits after a night of sleep deprivation than do other cognitive tasks, such as perceptual and memory tests. Such findings had led researchers to suspect that it is simply an inability to pay attention that causes the deficits in memory encoding following sleep deprivation.

Sleep and memory encoding

That diminished attention should account for the poor ability of sleep-deprived individuals to form new memories seems intuitively obvious. Yet animal studies have suggested that there's more to this poor memory formation than just attention problems. Studies in both humans and animals have found that a part of the brain known as the hippocampus is critical for forming new memories that we and animals can later recall. At the molecular level, this memory formation is thought to depend on a process known as long term potentiation, or LTP, which strengthens the connections between nerves cells in a manner that makes it easier for signals to pass between them, as must happen when memories are later recalled. LTP can be seen in slices of the hippocampus removed from rats and maintained in tissue culture. Studies of these rat hippocampal slices have shown that when you sleep-deprive a rat prior to removing and slicing its hippocampus, LTP is impaired in these slices. This clearly has nothing to do with the slice paying less attention; it has to do with hippocampal function. Which brings us to the study of Yoo, Walker, and their colleagues.

Using functional magnetic resonance imaging (fMRI), Yoo and colleagues monitored the brain activity in colleage-age subjects who had either slept normally the night before or slept not at all. They scanned these subjects' brains while the subjects went through 150 pictures of people, objects, landscapes, and more complex scenes, and classified each as an indoor or outdoor picture. Two days later, when both groups were well rested, they gave the subjects a surprise memory test. They showed them the same 150 pictures, mixed together with 75 new ones, and asked them to identify the pictures they remembered having seen before. Both groups did pretty well, but the sleep-deprived group forgot almost twice as many of the original pictures, 26 percent compared to only 14 percent for the well-rested group.

Sleep decreases stickyness

The researchers then went back to the fMRI recordings from the original training session and looked at what parts of the brain each group was using while studying the pictures. Although both groups seemed to show study-related activity in the same set of brain regions, the sleep-deprived subjects showed significantly less activity in the hippocampus; this was true even when Yoo looked only at the brain activity seen when individuals were studying pictures that they correctly recognized two days later. And even when the best performing sleep-deprived subjects were compared to the worst control subjects (whose performance matched that of the best sleep-deprived subjects), the sleep-deprived subjects still showed less hippocampal activation. In contrast, both groups activated attentional networks in the frontal and parietal lobes of the brain equally.

This somewhat heretical finding led the researchers to ask where brain activity was specifically correlated with hippocampal activation -- a question they hoped would reveal which region worked together with the hippocampus during memory formation. Now more differences showed up. Compared to the sleep-deprived subjects, the well-rested subjects showed stronger coupling between the hippocampi and other structures normally associated with episodic memory processing, including other areas in the medial temporal lobe. In contrast, the sleepy subjects showed tighter coupling with basic alertness networks in the brainstem and thalamus. Apparently, success in the sleepy subjects required activation of the hippocampus together with basic arousal circuits.

It may not be surprising that these sleepy subjects needed to crank up their arousal circuits along with their hippocampi. Yet it came as something of a surprise that they seemed to do so at the expense of other circuits that are normally involved in encoding new memories. This may further explain why sleepy subjects performed more poorly. Indeed, when activation patterns seen during successful encoding of pictures later remembered was compared to that seen during unsuccessful encoding, the same medial temporal lobe structures turned up during successful encoding for the well rested subjects but not for the sleepy ones. Despite adequate attention and extra effort at arousal, other crucial memory networks were not up to par.

None of this bodes well. As we become more and more sleep-deprived, replacing needed sleep with caffeine and bleary eyes, we can expect to see a concomitant slipping away of the ability to remember the very things we stayed up late trying to learn. You have to wonder whether it's worth it.

Robert Stickgold, an associate professor of psychiatry at Harvard Medical School, is also a researcher and clinician at the School's Division of Sleep Medicine, where -- when he's not sleeping -- he occasionally collaborates with researchers Yoo and Walker, who authored the study under review here.

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How Stereotypes Shape Performance

S. Alexander Haslam, Jessica Salvatore, and Thomas Kessler
University of Exeter, UK

Every sports fan has vivid memories of key occasions on which a favorite team or player has 'choked' under pressure. And every student who has ever taken a standardized test knows what that kind of pressure feels like. What makes for high-pressure situations, and how do they influence performance? In the last decade such issues have been explored by social psychologists researching the phenomenon of stereotype threat. Their work shows not only that pressure can compromise performance, but that this dynamic is more common among members of negatively stereotyped social groups.

Why? The classic demonstration of stereotype threat, in a 1995 paper by Claude Steele and Joshua Aronson, emerged from a series of studies in which high-achieving African American students at Stanford completed the Graduate Record Exam (GRE) under conditions where they thought either that the test was measuring intelligence or that it was not a test of ability at all. Intriguingly, these bright students did much worse when they considered it an intelligence test.. This, the researchers argued, was because "in situations where [a negative] stereotype is applicable, one is at risk of confirming it as a self-characterization, both to one's self and to others who know the stereotype."

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How Infants Predict Other People's Behavior

Valerie Kuhlmeier and Tania Tzelnic
Queen's University, Kingston, ON 

When it comes to watching the actions of others, we all have a little Nostradamus in us. When someone begins a physical action we can often "predict" the outcome before it occurs -- that is, our eyes move to the action's end point before the actor reaches it himself. In 2003, Randy Flanagan of Queen's University in Canada and Roland Johansson of Umea University in Sweden demonstrated this in an elegant way in a paper in the journal Nature.

Toward a Neurofunctional Definition of "Face-Blindness"
Alison M. Harris & Geoffrey K. Aguirre

University of Pennsylvania Philadelphia, PAIn 1947 Dr. Joachim Bodamer, a German neurologist, published a description of a 24-year-old patient who had come under his care in 1944 following a bullet wound to the head. Patient S, as Bodamer referred to him, had suffered damage to the areas of his brain associated with visual processing; as a result, he was completely blind for several weeks after his injury, and even as his sight gradually returned, he continued to have difficulties perceiving color and form.

Yet in addition to these impairments, which fit with other contemporary accounts of perceptual recovery, S displayed another striking deficit. As Bodamer wrote: "S recognised a face as such, i.e. as different from other things, but could not assign the face to its owner. He could identify all the features of a face, but all faces appeared equally "sober" and "tasteless" to him. Faces had no expression, no "meaning" for him. . . . He could distinguish men and women only by their hair or head covering and even then not always with certainty. Even S's own face, viewed in the mirror, evoked no spark of recognition: 'It could be that of another person, even that of a woman.'" (from Ellis & Florence, 1990, p. 86).

Welcome to

Mind Matters

where top researchers in neuroscience, psychology, and psychiatry explain and discuss the findings and theories driving their fields. Readers can join them. We hope you will.

This week:

The Green Space Cure 
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The Psychological Value of Biodiversity

Frank S. Muscara & Susan C. Saegert
City University of New York Graduate Center

As we chip away at and move away from the natural world, contact with it becomes more valuable: urban design now recognizes that access to green space is an important part of quality of life. A new study by Fuller, Irvine, Devine-Wright, Warren and Gaston ("Psychological Benefits of Greenspace Increase with Biodiversity," from Biology Letters - see abstract), suggests that not all green space is equal in this regard. Fuller and colleagues found that the more biologically diverse the green space, the higher its psychological value.

Welcome to Mind Matters
where top researchers in neuroscience, psychology, and psychiatry explain and discuss the findings and theories driving their fields. 
Readers can join them. We hope you will.
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This week Mind Matters visits not just a particular paper, but the massive annual meeting of the Society for Neuroscience -- 30,000+ neuroscientists, scores of major lectures, hundreds of symposia, thousands and thousands of symposia and minisymposia. Scientific American has three people here, and we haven't a prayer -- way too many things to attend. Sorting out what to do next poses severe challenges to mechanisms of time management, executive function, attentional control, sleep-cycle adjustment, shoe quality, and memory.In return you get exposed to stunning international diversity, an amazing variety of ideas and disciplines, and the occasional comic exchange that arises from the collision of all these things.

My favorite so far was a short conversation between two 30-ish neurobiologists. They were standing in front of their posters, which concerned arcane mechanisms of neurochemistry, and had just finished talking with someone who studied neuroethology -- a sort of crossroards between neuroscience, zoology, and evolution. After the two nascent neurobiochemists watched the neuroethologist walk away, one said to the other, "Neuroethology. What the hell is that?" After a pause the other one said, "Exactly." (For the answer, go here.)