February 4, 2010
Category: Neuroscience
IF a rapid series of taps are applied first to your wrist and then to your elbow, you will experience a perceptual illusion, in which phantom sensations are felt along the skin connecting the two points that were actually touched. This feels as if a tiny rabbit is hopping along your skin from the wrist to the elbow, and is therefore referred to as the "cutaneous rabbit". The illusion indicates that our perceptions of sensory inputs do not enter conscious awareness until after the integration of events occuring within a certain time window, and that the sensory events taking place at a certain point can be influenced by future events.
A group of Japanese researchers now shows that this illusion is not just confined to the body. In a new study published today in the Journal of Neuroscience, they report that the cutaneous rabbit can easily be induced to "hop out" of the body, so that the illusory sensations are perceived to originate not from the body itself, but from external objects that interact with it.
Read on »
Posted by Mo at 1:35 PM • 9 Comments • 0 TrackBacks
January 27, 2010
Category: Neuroscience
HOW does the brain encode the spatial representations which enable us to successfully navigate our environment? Four decades of research has identified four cell types in the brains of mice and rats which are known to be involved in these processes: place cells, grid cells, head direction cells and, most recently, border cells. Although the functions of most of these cell types are well characterized in rodents, it remains unclear whether they are also found in humans. A new functional neuroimaging study, by researchers from University College London, published online in the journal Nature, now provides the first evidence for the existence of grid cells in the human brain.
Grid cells were discovered in 2005 by Edvard and May-Britt Moser of the Kavli Institute for Systems Neuroscience in Trondheim, Norway, using multi-electrode arrays chronically implanted into the hippocampus and surrounding regions of freely moving mice. Whereas place cells fire when the animal is in a unique, specified position in its environment, grid cells - which are located in the entorhinal cortex - increase their activity in multiple locations, firing periodically as the mouse traverses a space. When a grid cell's activity is correlated with the animal's position and trajectory, and then superimposed onto a map of the environment, it is found to define a repeating pattern of equilateral triangles which 'tiles' the space (panel b, below). Each cell is activated whenever the animal's position coincides with any vertex in this grid, but each has its own periodicity, and so 'tiles' the environment using a unique scale.
Read on »
Posted by Mo at 12:40 PM • 3 Comments • 0 TrackBacks
January 23, 2010
Category: Neuroscience
"WHEN a man sits with a pretty girl for an hour," said Albert Einstein, "it seems like a minute. But let him sit on a hot stove for a minute, and it's longer than any hour." Einstein was describing one of the most profound implications of his Theory of General Relativity - that the perception of time is subjective. This is something we all know from experience: time flies when we are enjoying ourselves, but seems to drag on when we are doing something tedious.
The subjective experience of time can also be manipulated experimentally. Visual stimuli which appear to be approaching are perceived to be longer in duration than when viewed as static or moving away. Similarly, participants presented with a stream of otherwise identical stimuli, but including one oddball, or "deviant", stimulus, tend to perceive the deviant stimulus as lasting longer than the others. The underlying neural mechanisms of this are unknown, but now the first neuroimaging study of this phenomenon implicates the involvement of brain structures which are thought to be required for cognitive control and subjective awareness.
Read on »
Posted by Mo at 10:40 AM • 11 Comments • 0 TrackBacks
January 21, 2010
Category: Neuroscience
OUR ability to use and manipulate numbers is integral to everyday life - we use them to label, rank, count and measure almost everything we encounter. It was long thought that numerical competence is dependent on language and, therefore, that numerosity is restricted to our species. Although the symbolic representation of numbers, using numerals and words, is indeed unique to humans, we now know that animals are also capable of manipulating numerical information.
One study published in 1998, for example, showed that rhesus monkeys can form spontaneous representations of small numbers and use them to choose containers with more pieces of fruit. More recently, it was found that monkeys can perform basic arithmetic on a par with college students. Now, German researchers report that not only do rhesus monkeys understand simple mathematical rules, but also that these rules are encoded by single neurons in the rhesus prefrontal.
Read on »
Posted by Mo at 11:50 AM • 7 Comments • 0 TrackBacks
January 13, 2010
Category: Neuroscience
VIEWING a stimulus for a prolonged period of time results in a bias in the perception of a stimulus viewed afterwards. For example, after looking at a moving stimulus for some time, a stationary stimulus that is viewed subsequently appears to drift in the opposite direction. These after-effects reveal to us the properties of our perceptual system. They occur because the neurons which are sensitive to the initial stimulus re-calibrate their responses; they adapt to compensate for the earlier enduring stimulus, and so can continue to encode current stimuli efficiently.
It was long thought that the properties of the initial (or adapting) stimulus have to be similar to those of the subsequent (or adapted) stimulus for any after-effect to occur. But a new study published this week in the journal Current Biology contradicts this assumption about perceptual adaptations, by showing that viewing photographs of headless bodies causes the brain to adapt to faces that are viewed afterwards.
Read on »
Posted by Mo at 11:40 AM • 3 Comments • 0 TrackBacks
January 9, 2010
Category: Psychology
WE tend to assume that we see our surroundings as they really are, and that our perception of reality is accurate. In fact, what we perceive is merely a neural representation of the world, the brain's best guess of its environment, based on a very limited amount of available information. This is perhaps best demonstrated by visual illusions, in which there is a mismatch between our perception of the stimulus and objective reality.
Even when looking at everyday objects, our perceptions can be deceiving. According to the New Look approach, first propounded in the 1940s by the influential cognitive psychologist Jerome Bruner, perception is largely a constructive process influenced by our needs and values. Recent research has provided some evidence for this: in 2006, psychologists Emily Balcetis and David Dunning, then at Cornell University, reported that an ambiguous figure tended to be interpreted according to the self-interest of the perceiver. They now show that the desirability of an object influences its perceived distance.
Read on »
Posted by Mo at 2:00 PM • 11 Comments • 0 TrackBacks
December 17, 2009
Category: Neuroscience
HOW do you react when you see somebody else in pain? Most of us can empathize with someone who has been injured or is sick - we can quite easily put ourselves "in their shoes" and understand, to some extent, what they are feeling. We can share their emotional experience, because observing their pain activates regions of the brain which are involved in processing the emotional aspects of pain.
But can seeing somebody else in pain actually cause pain in the observer? People with mirror-touch synaesthesia are known to experience touch sensations when they see others being touched, and this may also extend to pain in such individuals. There are also several anecdotal cases of patients who experience pain in the absence of noxious stimuli. And a new study by British psychologists now provides evidence that a significant minority of healthy people can also experience pain when seeing others' injuries.
Read on »
Posted by Mo at 4:54 PM • 13 Comments • 0 TrackBacks
December 15, 2009
Category: Neuroscience
MEMORY is one of the biggest enduring mysteries of modern neuroscience, and has perhaps been researched more intensively than any other aspect of brain function. The past few decades have yielded a great deal of knowledge about the cellular and molecular mechanisms of memory, and it is now widely believed that memories are formed as a result of biochemical changes which ultimately lead to the strengthening of connections between nerve cells.
It is, however, also clear that memories are not encoded at the level of single neurons. Instead, the memory trace is thought of as a flurry of electrical activity within a scattered population of cells. Yet, very little is known about how memories are encoded and retrieved by populations of cells. Using a new large-scale recording technique, researchers from the Medical College of Georgia have now directly observed, for the first time, the population-level activity associated with encoding and retrieval of memory traces.
Read on »
Posted by Mo at 6:05 PM • 3 Comments • 0 TrackBacks
December 13, 2009
Category: Neuroscience
IN February of this year, Jacopo Annese (above), a neuroanatomist and radiologist at the University of California, San Diego travelled to Boston to take delivery of a brain. For Annese, collecting brains is not unusual - he is, after all, director of UCSD's Brain Observatory, which will eventually become a comprehensive library of brains donated by people who had neurological conditions such as Alzheimer's Disease, as well as by healthy people of all ages. This time though, the brain he collected was very special: it belonged to the amnesic patient Henry Molaison, who for more than 50 years was known in the scientific literature, and to every neuroscience and psychology student, as H.M.
Read on »
Posted by Mo at 11:45 AM • 7 Comments • 0 TrackBacks
