Spatial navigation is a complex mental task which is strongly dependent upon memory. As we make our way around a new environment, we look for easily recognisable landmarks and try to remember how their locations are related in space, so that when we return to it we can negotiate our path.  We know that spatial representations are encoded in the medial temporal lobe, and numerous studies implicate the hippocampus in particular as being crucial for the formation of spatial memories. Information about the environment is believed to be encoded by large populations of neurons distributed…
One of the central dogmas of neuroscience, which persisted for much of the history of the discipline, was that the adult human brain is immalleable, and could not change itself once fully developed. However, we now know that this is not the case: rather than setting like clay placed into a mould, the brain remains pliable, like a piece of putty, so that each new experience makes a lasting impression upon it.     This phenomenon, referred to as synaptic (or neural) plasticity, involves reorganization of the connections between nerve cells, and is arguably the most important discovery in…
More than 100 years ago, Sigmund Freud, the father of psychoanalysis, proposed a mechanism called repression, whereby desires and impulses are actively pushed into the unconscious mind. For Freud, repression was a defence mechanism - the repressed memories are often traumatic in nature, but, although hidden, they continue to exert an effect on behaviour. Many of Freud's theories have long since been discredited, but they remain influential to this day. Repression in particular has proven to be extremely controversial. It has attracted much attention in the context of the many legal cases…
Nervous tissue is extremely fragile, and so is very well protected. The brain, which has a jelly-like consistency, is encased in the skull, and is surrounded by cerebrospinal fluid, which acts to cushion it against blows that might cause it to come into contact with the inside of its bony case. Likewise, the spinal cord is surrounded by the vertebrae, the series of bones which runs down from the base of the skull.   Being so soft, the brain and spinal cord decompose quickly. When an animal dies, the nervous system begins to disintegrate immediately, until the armour in which it was…
Despite occuring only rarely, amnesia (or memory loss) has featured often in Hollywood films for almost a century. By 1926, at least 10 silent films which used amnesia as a plot device had been made; more recent productions, such as 50 First Dates and Eternal Sunshine of the Spotless Mind, are therefore part of a well established tradition.   In a review published in the British Medical Journal in 2004, clinical neuropsychologist Sallie Baxendale of the Institute of Neurology in London points out that cinematic depictions of amnesia are consistenly inaccurate, and usually "bear no relation…
Alzheimer's Disease is the most common form of dementia, affecting more than 400,000 people in the U.K. and some 5.5 million in the U.S. The disease has a characteristic pathology, which often appears first in the hippocampus, and then spreads to other regions of the brain. This is accompanied by impairments in cognition, with cell death and loss of connections leading first to deficits in memory and spatial navigation, and then to global dysfunction.  The exact cause of Alzheimer's is not known, but a number genes have been implicated. One of these encodes a protein called amyloid precursor…
These gorgeous stipple-engraved plates come from The Anatomy of the Brain, Explained in a Series of Engravings, by Sir Charles Bell. The book was first published in 1802 and contained 12 plates, 11 of which were printed in colour; these come from an edition which appeared in 1823. In the introduction to the book, Bell wrote: In the Brain the appearance is so peculiar, and so little capable of illustration from other parts of the body, the surfaces are so soft, and so easily destroyed by rude dissection, and it is so difficult to follow an abstract description merely, that this part of…
Working memory refers to the process by which small amounts of information relevant to the task at hand are retained for short periods of time. For example, before cellular phones became so ubiquitous, calling someone usually involved first finding the number and then remembering it for a just few seconds by repeating it to oneself several times. Once the digits had been dialled, they are immediately forgotten. Very little is known about the neural mechanisms underlying working memory, but very recently some advances have been made. Last month, a group from the University of Texas Medical…
Bones have been big news recently, following the publication of two papers which document remarkable fossil finds. First, a group of palaeontologists led by Phil Gingerich of the University of Michigan described Maiacetus inuus, a primitive whale which lived in the water but gave birth on land, and which marks the transition between modern whales and their terrestrial ancestors. This was quickly followed by the report, from Jason Head's group at the University of Toronto, of Titanoboa cerrejonesis, a prehistoric snake which is estimated to have grown to 13 metres and to weigh more than a…
Most of us have experienced the vague feeling of knowing something without having any memory of learning it. This phenomenon is commonly known as a "gut feeling" or "intuition"; more accurately though, it is described as implicit or unconscious recognition memory, to reflect the fact that it arises from information that was not attended to, but which is processed, and can subsequently be retrieved, without ever entering into conscious awareness. According to a new study, our gut feelings can enhance the retrieval of explicitly encoded memories - those memories which we encode actively - and…
I have finally jumped on the bandwagon and started to use Twitter. I had avoided it because I couldn't understand why anyone would want to share the mundane details of their life with others, but am now beginning to see how it can be useful, and also to enjoy using it. If you too are using Twitter, why not follow me (my username is @mocost), and engage me in an interesting conversation, share a link, or even tell me - if you really feel that you must - what you had for breakfast? Below is a mosaic of 40 people who are following me already. */ Get your twitter mosaic here.
When Sir Francis Galton first described the "peculiar habit of mind" we now call synaesthesia, he noted that it often runs in families. Modern techniques have confirmed that the condition does indeed have a strong genetic component - more than 40% of synaesthetes have a first-degree relative - a parent, sibling or offspring - who also has synaesthesia, and families often contain multiple synaesthetes. Synaesthesia is known to affect females more than males, and although the female predominance of the condition is now known to have been exaggerated, the condition is presumed to be linked to…
During the first half of the twentieth century, the American psychologist Karl Lashley conducted a series of experiments in an attempt to identify the part of the brain in which memories are stored. In his now famous investigations, Lashley trained rats to find their way through a maze, then tried to erase the memory trace - what he called the "engram" - by making lesions in different parts of the neocortex. Lashley failed to find the engram - no matter where he made a lesion, his experimental animals were still able to find their way through the maze. As a result, he concluded that memories…
In his epic poem Visions of the Daughters of Albion, William Blake asks: "Where goest thou O thought? To what remote land is thy flight?" More than two centuries later, memory remains as one of the enduring mysteries of neuroscience, and despite decades of intensive research using modern techniques, we still have no answer to the questions posed by Blake. Traditionally, memory has been regarded as consisting of several distinct processes or storage systems. Short-term memory (sometimes referred to as working memory) stores information that is required for the task at hand, but is severely…
What sensory cues do we rely on during the perception of speech? Primarily, of course, speech perception involves auditory cues - we pay close attention to the sounds generated by the speaker. Less obviously, the brain also picks up subtle visual cues, such as the movements of the speakers mouth and lips; the importance of these can be demonstrated by the McGurk effect, an auditory illusion in which the visual cues accompanying spoken words can alter one's perception of what is being said.  Integration of these auditory and visual cues is essential for speech perception. But according to a…
Delusions are pathological beliefs which persist despite clear evidence that they are actually false. They can vary widely in content, but are always characterized by the absolute certainty with which they are held. Such beliefs reflect an abnormality of thought processes; they are often bizarre and completely unrelated to conventional cultural or religious belief systems, or to the level of intelligence of the person suffering from them. The delusions experienced by psychiatric patients are sometimes categorized according to their theme. For example, schizophrenics often suffer from…
The brains of vertebrates are asymmetrical, both structurally and functionally. This asymmetry is believed to increase the efficiency of information processing - one hemisphere  is specialized to perform certain functions, so the opposite is left free to perform others. In the human brain, for example, the left hemisphere is specialized for speech. This has been known since the 1860s, when the French physician Paul Broca noted that the aphasia (or inability to speak) which is a common symptom of stroke is associated with damage to a discrete region of the left frontal lobe. Very little is…
The unique capabilities of the human hand enable us to perform extremely fine movements, such as those needed to write or to thread a needle. The emergence of these capabilities was undoubtedly essential in human evolution: a combination of individually movable fingers, opposable thumbs and the ability to move the smallest finger and ring finger into the middle of the palm to meet the thumb gives us dexterity that is unparalleled in the animal kingdom. Last year, geneticists identified a stretch of DNA which has undergone rapid change in humans but not in chimps, our closest relatives, or in…
The Boston Globe has a cool infographic by Jonah Lehrer and Javier Zarracina, describing five simple ways in which sensory perception can be altered using everyday objects. These include the Ganzfeld procedure, a mild sensory deprivation technique which leads to visual or auditory hallucinations; the Pinocchio illusion,  in which one's nose is perceived as being incredibly long; and the rubber hand illusion, whereby one can be fooled into thinking that a fake hand is a part of one's own body.
The familiar buzzing sound made by a mosquito may be irritating to us humans, but it is an important mating signal. The sound, produced by the beats of the insect's wings, has a characteristic frequency called the "flight tone"; when produced by a female, it signals her presence to nearby males, thereby attracting potential mates. Attraction is not simply a matter of the male hearing and homing in on the female's flight tone. Females were long believed to be deaf, but two years ago, it was found that courting pairs interact acoustically to create a duet: both male and female modulate the…