Neurophilosophy

Evolutionary origins of the nervous system

Fri, 03 Jul 2009 09:34:37 -0500

THE HUMAN BRAIN is a true marvel of nature. This jelly-like 1.5kg mass inside our skulls, containing hundreds of billions of cells which between them form something like a quadrillion connections, is responsible for our every action, emotion and thought. How did this remarkable and extraordinarily complex structure evolve? This question poses a huge challenge to researchers; brain evolution surely involved thousands of discrete, incremental steps, which occurred in the mists of deep time across hundreds of millions of years, and which we are unlikely to ever fully understand.

Nevertheless, a number of studies published in recent years have begun to shed some light on the evolutionary origins of the nervous system, and provide clues to some of the earliest stages in the evolution of the human brain. These clues come from the most unexpected of places - from sea sponges, which lack nervous systems altogether, and from the extant descendents of a primitive worm which lived some 600 million years ago.

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Brain mechanisms of hypnotic paralysis

Fri, 26 Jun 2009 08:37:24 -0500

THE TERM 'HYPNOSIS' was coined by the Scottish physician James Braid in his 1853 book Neurypnology. Braid defined hypnosis as "a peculiar condition of the nervous system, induced by a fixed and abstracted attention of the mental and visual eye". He argued that hypnosis was a form of "nervous sleep", and tried to distinguish his theory from that of the mesmerists, who believed that the effects of hypnosis were mediated by a vital force, or animal magnetism.

Because of mesmerism, and its association with stage entertainment and charlatanry, hypnosis was regarded with skepticism for much of its history. In recent years, though, it has come under the scrutiny of cognitive neuroscientists, and is now thought of as an altered state of consciousness - sometimes referred to as being trance-like - which is associated with increased suggestibility, enhanced imagery and reduced reality testing. We know that hypnosis can profoundly affect the mind and behaviour, so that thought processes and perceptions can be easily manipulated, but the underlying neural mechanisms are poorly understood.

According to a new study of the neural mechanisms of hypnosis-induced paralysis, Braid's definition was remarkably accurate. The study, published in the journal Neuron, demonstrates that hypnosis does indeed lead to increased activity in areas of the brain involved in attention, as well as in other areas involved in mental imagery and self-awareness. Hypnosis can therefore exert control over bodily movements by enhancing mental representations of the self (or self-imagery) and focusing attention on them.

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Mental time travel

Mon, 15 Jun 2009 12:10:20 -0500

Memory, Blake wrote, enables us to "traverse times and spaces far remote". It constitutes mental time travel, with which we can recollect, in vivid detail, events that took place many years ago. We have known, for the best part of a century, that memory is reconstructive rather than reproductive. That is, recollection involves piecing together specific details of the event, and mixing these with our own biases and beliefs. While not being completely accurate, our memories are, in most cases, reliable enough.

It is because of the reconstructive nature of memory that we are able to travel forward in time as well as back into the past. Research carried out in recent years has shown that imagining future events and recalling those that we have already experienced are dependent on the same core network of brain regions. It seems that both involve the same cognitive processes - when we look forward to something that might happen in the future, the brain generates a simulation of that event using fragments of memories of past events.

However, the evidence for this is indirect, and it is possible that what are thought to be simulations of future events are in fact merely memories of past events being "recast" into the future. But a new study, due to be published in the September issue of the journal Neuropsychologia, now confirms that these simulations are indeed novel constructions, and also shows that remembering actual experiences and imagining possible future events depend on distinct subsystems within the common core network.

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How we feel affects what we see

Mon, 08 Jun 2009 18:25:55 -0500

People who place an emphasis on positive things and are generally optimistic are sometimes said to "see the world through rose-tinted glasses". According to a new study by Canadian researchers, this is more than just an idiom. The study, which has just been published in the Journal of Neuroscience, provides the first direct evidence that the mood we are in affects the way we see things by modulating the activity of the visual cortex. Their findings show that putting on the proverbial rose-tinted glasses of a good mood is not so much about colour, but about the broadness of the view.

A number of behavioural studies have already shown that emotions can have an effect on perception. When, for example, observers are asked to selectively pay attention to a target at the centre of the visual field while ignoring surrounding "distractor" objects, the prior induction of a positive emotional state leads to more interference from the surrounding objects than does induction of a negative mood. Likewise, positive moods are associated with a tendency to perceive global components, and negative moods with the local components, of a visuospatial stimulus.

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Fernando Vicente

Sun, 31 May 2009 04:30:28 -0500

A beautiful and macabre combination of anatomy and portraiture by Spanish artist Fernando Vicente.

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Confabulatory hypermnesia, or severe false memory syndrome

Tue, 26 May 2009 17:56:59 -0500

What did you do on March 13th, 1985? People with hyperthymesia (which has been characterized only recently, and of which just a handful of cases have so far been reported) would likely provide a vivid account of what happened on that day. And if this particular date has personal significance for you - if, for example, it was your wedding day, or the birth date of one of your children - then you will probably remember it quite well. But for most of us, the answer to this question is likely to be "I don't know".

In the journal Cortex, researchers describe the case of a patient with severe memory loss who has a tendency to invent detailed and perfectly plausible false memories (confabulations) in response to questions to which most people would answer "I don't know", such as the one above. They have named this unusual condition confabulatory hypermnesia, and believe that theirs is the first study to document it.

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Decoding the brain's response to vocal emotions

Mon, 18 May 2009 16:49:20 -0500

The ability to interpret other peoples' emotions is vital for social interactions. We recognize emotions in others by observing their body language and facial expressions. The voice also betrays one's emotional state: words spoken in anger have a different rhythm, stress and intonation than those uttered with a sense of joy or relief. But how the emotional content of a voice is encoded in the brain was unclear.

Now though, Swiss researchers report that they have decoded the neural activity in the voice-sensitive regions of the brain, and demonstrate that this activity can be analyzed to predict which vocal emotion is being heard. The study, which is published in the journal Current Biology, is the first to show that different vocal emotions are encoded by distinct patterns of brain activity, and could lead to a better understanding of psychiatric disorders in which the ability to recognize the emotional information in voices is compromised.

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Music affects how we perceive facial expressions

Mon, 11 May 2009 12:15:07 -0500

Music can be thought of as a form of emotional communication, with which the performer conveys an emotional state to the listener. This "language" is remarkably powerful - it can evoke strong emotions, and make your heart race or send tingles down your spine. And it is universal - the emotional content of a piece of music can be understood by anyone, regardless of cultural background.

Are the emotions evoked by piece of music similar to, and can they influence, other emotional experiences? The answer to these questions is unclear. But a new study, which has just been published in Neuroscience Letters, provides both behavioural and physiological evidence that the emotions evoked by music can be transferred to the sense of vision, and can influence how the emotions in facial expressions are perceived.

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The universal grammar of birdsong is genetically encoded

Mon, 04 May 2009 20:49:58 -0500

Human cultural traits such as language, dress, religion and values are generally said to be passed from one generation to the next by social learning. And in animal species which have language, the same is true; male song birds, for example, learn the songs with which they serenade potential mates from older male relatives.

A new study, published online in the journal Nature, shows that the songs of isolated zebra finches evolve over multiple generations to resemble those of birds in natural colonies. These findings show that song learning in birds is not purely the product of nurture, but has a strong genetic basis, and suggest that bird song has a universal grammar, or an intrinsic structure which is present at birth.

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The waterfall illusion can be transferred between vision and touch

Tue, 14 Apr 2009 05:30:10 -0500

If you look at a waterfall for about 30 seconds, and then shift your gaze to a nearby stationary object, such as a rock or a tree, that object will seem to drift slowly upwards. This well known optical illusion demonstrates a phenomenon called the motion after-effect, which is thought to occur as a result of adaptation - the brain compensates for movement in one direction, causing us to momentarily perceive a stationary objects to be moving in the other.

Although illusory motion can also be induced in the sense of touch, the brain is thought to process visual and tactile motion separately. But now researchers from MIT have found that not only can moving visual stimuli induce a tactile motion after-effect, but also that moving tactile stimuli can induce a visual motion after-effect. The findings, which are published in Current Biology, show that the senses of vision and touch are closely linked, and that each can influence the other.

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New cells in the adult brain migrate long distances by crawling along blood vessels

Fri, 03 Apr 2009 13:15:47 -0500

The journey undertaken by newly generated neurons in the adult brain is like the cellular equivalent of the arduous upstream migration of salmon returning to the rivers in which they were hatched. Soon after they are born in the subventricular zone near the back of the brain, these cells migrate to the front-most tip of of the olfactory bulb. This is the furthest point from their birth place, and they traverse two-thirds of the length of the brain to get there.

The first leg of this epic journey - the departure of the newborn cells from the subventricular zone - involves some of the signalling cues that guide cell migrations during development of the brain. However, these signals alone are known to be insufficient, and until now the precise mechanisms governing this migration were unclear. But a new study by Canadian researchers shows that the cells travel such long distances by crawling along the capillaries in the olfactory bulb.

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MicroRNAs regulate adult neurogenesis

Wed, 01 Apr 2009 15:00:19 -0500

It is now well established that the adult mammalian brain contains stem cells which continue to generate new neurons throughout life. This discovery, and subsequent research, has transformed the way we think about the brain. It is, for example, known that physical and mental exercise can stimulate the growth of new nerve cells in a part of the brain which shrinks in Alzheimer's and depression, and so it is believed that such activities can reduce the risk of both conditions.

Despite all this, little is known about the mechanisms by which neural stem cells are directed to generate neurons. Now researchers from Columbia University Medical Center have found that neurogenesis in the adult mouse brain is regulated by microRNAs, the small nucleic acid molecules which are encoded in those parts of the genome that were often referred to as "junk" DNA.

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Voluntary amputation and extra phantom limbs

Fri, 27 Mar 2009 19:01:17 -0500

If someone told you that they wanted to have a perfectly good leg amputated, or that they have three arms, when they clearly do not, you would probably be inclined to think that they are mentally disturbed. Psychiatrists, too, considered such conditions to be psychological in origin. Voluntary amputation, for example, was regarded as a fetish, perhaps arising because an amputee's stump resembles a phallus, whereas imaginary extra limbs were likely to be dismissed as the products of delusions or hallucinations.

However, these bizarre conditions - named body integrity identity disorder (BIID) and supernumerary phantom limb, respectively - are now widely believed to have a neurological basis. Two forthcoming studies confirm this, by providing strong evidence that both conditions occur as a result of abnormal activity in a part of the brain which is known to be involved in constructing a mental representation of the body, or body image.

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Optogenetics controls brain signalling and sheds light on Parkinson's therapy

Tue, 24 Mar 2009 06:50:04 -0500

Optogenetics is a recently developed technique based on a group of light-sensitive proteins called channelrhodopsins, which which were isolated recently from various species of micro-organism. Although relatively new, this technique has already proven to be extremely powerful, because channelrhodopsins can be targeted to specific cells, so that their activity can be controlled by light, on a millisecond-by-millisecond timescale.

A group of researchers from Stanford University now report a new addition to the optogenetic toolkit, and demonstrate that it can be used to precisely control biochemical signalling pathways in the mouse brain and to manipulate complex reward-related behaviour. They have also used the existing channelrhodopsins to probe the neural circuitry implicated in Parkinson's Disease and thus gain a better understanding of why deep brain stimulation is effective in treating the disease.

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How we perceive others influences our sense of touch

Fri, 20 Mar 2009 19:17:16 -0500

The way we perceive other people has a big influence on how we interact with them. For example, attractive people are more likely to be perceived as talented than less attractive people, and this so-called "halo effect" is often reflected in our behaviour towards them. Similarly, we tend to favour people perceived to be like us over people who are perceived to be different ("in-group bias").

It turns out that the way we perceive others can also influence our own sense of touch. In a new study published in the open access journal PLoS One, researchers from the University of Bologna report that looking at photos of faces being touched strongly enhances the perception of touch on the observer's face when the photos are of people who belong the same ethnic or political group.

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