SYNAESTHESIA is a neurological condition in which there is a merging of the senses, so that activity in one sensory modality elicits sensations in another. Although first described by Francis Galton in the 1880s, little was known about this condition until recently. A rennaissance in synaesthesia research began about a decade ago; since then, three previously unrecognized forms of the condition have been described, and hypotheses for how it arises have been put forward.
Two new studies now provide some insight into time-space synaesthesia, the least researched of all the forms of this fascinating condition. One is a case study of an individual whose time-space synaesthesia has an apparently unique characteristic. The second demonstrates that time-space synaesthetes are superior to non-synaesthetes in some cognitive abilities, and suggests that time-space synaesthesia may underly the savant-like abilities of people with hyperthymestic (or "super-memory") syndrome.
IMAGINE sitting in a noisy restaurant, across the table from a friend, having a conversation as you eat your meal. To communicate effectively in this situation, you have to extract the relevant information from the noise in the background, as well as from other voices. To do so, your brain somehow "tags" the predictable, repeating elements of the target signal, such as the pitch of your friend's voice, and segregates them from other signals in the surroundings, which fluctuate randomly.
The ability to focus on your friend's voice while excluding other noises is commonly referred to as the cocktail party effect. Although first described more than 50 years ago, the brain mechanisms involved are unknown. But a new study by researchers at Northwestern University now shows that activity in regions of the brainstem are modulated by specific characteristics of the speaker's voice, and that this modulation is impaired in children with dyslexia.
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.
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.
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.
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.
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.
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.
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.
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.
