Jan 22, 2008 | 1
Jan 2, 2008
Welcome toWith 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.
Dec 26, 2007
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,
Dec 18, 2007
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
Dec 11, 2007
Dec 5, 2007
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."
Nov 26, 2007
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.
Nov 19, 2007 | 1
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).
Nov 13, 2007
Welcome towhere 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.
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.
Nov 6, 2007
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 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.)
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