Archive for ‘Neuroscience’

November 19, 2011

Overactive Neurons May Tangle the Senses… But There’s More to It

Synesthesia is pretty interesting. In the most common form certain colors are perceived when particular associated letters or numerals are seen (even if they are not actually colored themselves). Other more unusual forms may (for example) associate colors with the performance of certain types of swimming strokes, or involve seeing two distinct colors at the same time.

When this happens, it’s as though some wires are crossed in the brain. Research just published suggests that an effect consistent with that idea and somewhat but not entirely like it is actually happening. It seems to occur in people in whom some of their perceptual neurons are too easily excitable. Consequently, higher levels in the perceptual system register more stimuli than are actually present, as the brain attempts to make sense of the inconsistent lower level data.

The research considered the commmon type of synesthesia – grapheme-color synesthesia – where colors are associated with particular letters and numbers.

Synaesthesia sends visual cortex crazy

Terhune and colleagues, stimulated the visual cortex of six grapheme-colour synaesthetes by applying a magnetic coil to the scalp to produce a weak magnetic field.

They found non-synaesthetes required three times greater magnetic stimulation to their visual cortex than synaesthetes in order to experience phosphenes, transient flashes of light or other visual disturbances.

Terhune says the study is the first to show that synaesthesia is linked to hyperexcitability in the area of the brain known as the visual cortex.

“One of the really interesting things about this study is the difference in the level of excitability [between synaesthetes and non-synaesthetes] is so great,” says Terhune.

But there must be more to synesthesia than hyperactive neurons.

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November 9, 2011

Retrotransposons may influence brain activity

Retrotransposons (known informally as “jumping genes”) are like viruses that are permanently encoded in a genome. They are genetic elements that can cause additional copies of themselves to be added to the genome. Because of this ability, they make up a large part of the noncoding (“junk”) DNA in a genome. About 42% of human DNA is active or inactive retrotransposons. In other mammals the percentage may be even higher. Even more of our genomes may represent traces of retrotransposon activity in the distant past.

As far as biologists can tell, retrotransposons generally serve no useful purpose. They exist, like parasites, simply because they can. However, the view that they have no use may need to be revised in light of new research. On the other hand, retrotransposon activity that isn’t adequately suppressed may be responsible for neurological diseases from dementia to Parkinson’s to schizophrenia, and perhaps cancer too.

Determination of whether human retrotransposons are beneficial or detrimental is yet to be made. All that’s now been shown, in the new research, is that retrotransposons are active in brain tissue, especially in parts of the brain responsible for learning and memory – specifically the hippocampus and the caudate nucleus.

“Jumping Genes” May Influence Brain Activity

Mobile DNA molecules that jump from one location in the genome to another may contribute to neurological diseases and could have subtle influences on normal brain function and behavior, according to a study published October 30 in Nature. …

Researchers from the Roslin Institute in Edinburgh, Scotland, have now comprehensively mapped retrotransposon insertion sites in the genomes of normal human brain cells for the first time.

They used state-of-the-art DNA sequencing technology to screen for retrotransposons in tissue samples taken postmortem from three individuals who were healthy when alive and had no neurological disease or signs of abnormality in their brain tissue. Focusing on two brain regions—the hippocampus and caudate nucleus—they identified nearly 25,000 different sites for the three main retrotransposon families.

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November 5, 2011

Hippocampus plays bigger memory role than previously thought

Psychologists and neuroscientists, in their research into how memory works, distinguish several different types of memory. At the highest level, there’s declarative memory (facts, knowledge, experiences) and procedural memory (skills). Declarative memory can be further divided into episodic memory (personal experiences) and semantic memory (facts about the world).

Two processes are considered to be aspects of episodic memory: recollection and familiarity. Recollection is the ability to recall specific details about an experience or event. Familiarity is the less specific sense that one has had an experience, but without being able to recall specific details. People who read a lot are well acquainted with this distinction, usually to their frustration and annoyance. One may be sure of having read somewhere about a certain piece of information or situation in a novel – but without any clue as to when or where, which makes it pretty difficult to go back to the source in order to check one’s memory and fill in the details.

Neuroscientists have considered several questions about this issue. Are the two processes basically the same, differing only in strength of recall? Are different parts of the brain associated with these two processes? Two papers just published deal with these issues and indicates that when the subjective feeling of confidence in the memory is high (“strength”) the hippocampus is significantly involved in both processes.

Hippocampus Plays Bigger Memory Role Than Previously Thought

Prevailing research posits that recollection and familiarity memories involve different regions in the brain’s medial temporal lobe: the hippocampus for recollection, the adjacent perirhinal cortex for familiarity.

“But given the connectivity in that part of the human brain, that separation seemed too clean, too neat,” said Squire, a leading expert on the neurological bases of memory. “The idea of distinct functions was unlikely.”

Recollection-based memories are typically associated with higher confidence and accuracy than familiarity-based decisions. Accordingly, in the past, comparisons between recollection and familiarity have also involved a comparison between strong memories and weak memories. So the question is how the brain accomplishes recollection and familiarity when the effect of memory strength is taken off the table.

Larry Squire, a prominent figure in memory research, has published a number of other studies on this subject (References). In one of the two new papers, Squire and his colleagues conclude

The Hippocampus Supports Both Recollection and Familiarity When Memories Are Strong

As in earlier studies, recollected items had higher accuracy and confidence than familiar items, and hippocampal activity was higher for recollected items than for familiar items. Furthermore, hippocampal activity was similar for familiar items, misses, and correct rejections. When the accuracy and confidence of recollected and familiar items were matched, the findings were dramatically different. Hippocampal activity was now similar for recollected and familiar items. Importantly, hippocampal activity was also greater for familiar items than for misses or correct rejections (as well as for recollected items vs misses or correct rejections). Our findings suggest that the hippocampus supports both recollection and familiarity when memories are strong.

Further reading:

Medial Temporal Lobe Function and Recognition Memory: A Novel Approach to Separating the Contribution of Recollection and Familiarity

September 27, 2011

Brain wiring continues

Well, that’s a relief! To suppose that brain development more or less stops at the end of adolescence implies all that happens afterwards is just adding data. Surely there’s more to things like prudence, levelheadedness, and understanding of others than just added data.

Brain wiring continues – University of Alberta

It has been a long-held belief in medical communities that the human brain stopped developing in adolescence. But now there is evidence when examining the development of wiring in some parts of the brain this is not in fact the case, thanks to medical research conducted in the Department of Biomedical Engineering by researcher Christian Beaulieu, an Alberta Innovates – Health Solutions scientist, and by his PhD student at the time, Catherine Lebel. Lebel recently moved to the United States to work at UCLA, where she is a post-doctoral fellow working with an expert in brain-imaging research.

“This is the first long-range study, using a type of imaging that looks at brain wiring, to show that in the white matter there are still structural changes happening during young adulthood,” says Lebel. “The white matter is the wiring of the brain; it connects different regions to facilitate cognitive abilities. So the connections are strengthening as we age in young adulthood.”

Further reading:

Longitudinal Development of Human Brain Wiring Continues from Childhood into Adulthood

September 8, 2011

Premature baby brains can’t tell pain from touch

Premature baby brains can’t tell pain from touch – New Scientist

Premature babies up to the age of 35 weeks had bursts of activity across the whole brain in response to both pain and touch, but a change happened around 35 weeks. Between 35 to 37 weeks – just before a fetus would normally be born – the brain seemed to become able to tell the two stimuli apart. The responses to both pain and touch now took place in specific areas on the front, back and sides of the brain, but the signal was much stronger for pain.

Further reading:

A Shift in Sensory Processing that Enables the Developing Human Brain to Discriminate Touch from Pain

September 8, 2011

Scientists Probe Connection Between Sight and Touch

Scientists Probe Connection Between Sight and Touch – USC News

USC scientists have discovered that as you look at an object, your brain not only processes what the object looks like, but remembers what it feels like to touch it as well. This connection is so strong that a computer examining data coming only from the part of your brain that processes touch can predict which object at which you are actually looking.

Building on previous work demonstrating a comparable link between the visual and auditory sectors of the brain, Antonio and Hanna Damasio’s research group at the USC Dornsife Brain and Creativity Institute used magnetic resonance brain scans and specially programmed computers to explore how memory and the senses interact.

Further reading:

Seeing Touch Is Correlated with Content-Specific Activity in Primary Somatosensory Cortex

September 5, 2011

New Map Shows Where Tastes are Coded in the Brain: How Does the Brain Know What the Tongue Knows?

New Map Shows Where Tastes are Coded in the Brain: How Does the Brain Know What the Tongue Knows? – HHMI News

Each taste, from sweet to salty, is sensed by a unique set of neurons in the brains of mice, new research reveals. The findings demonstrate that neurons that respond to specific tastes are arranged discretely in what the scientists call a “gustotopic map.” This is the first map that shows how taste is represented in the mammalian brain.

September 4, 2011

Neuroscience vs philosophy: Taking aim at free will

Neuroscience vs philosophy: Taking aim at free will – Nature News

Philosophers start with a conclusion – that free will must exist, because, well, it just must, or else the consequences for personal and social life would be too terrible. And from this they find ingenious ways to criticize scientific experiments that clearly cast significant doubt on the whole idea of “free will”.

Meanwhile, as scientific techniques continue to improve, the scientific evidence against “free will” continues to grow. “Free will” seems to be an idea continually being driven into the realm of once cherished notions like élan vital and phlogiston.

As humans, we like to think that our decisions are under our conscious control — that we have free will. Philosophers have debated that concept for centuries, and now Haynes and other experimental neuroscientists are raising a new challenge. They argue that consciousness of a decision may be a mere biochemical afterthought, with no influence whatsoever on a person’s actions. According to this logic, they say, free will is an illusion. “We feel we choose, but we don’t,” says Patrick Haggard, a neuroscientist at University College London.

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September 1, 2011

Localizing language in the brain

Localizing language in the brain – MIT News Office

The contentious issue is whether there are areas of the brain that are exclusively “for” certain higher-level functions. The issue is known as “modularity”. Are there high-level functions that are handled by specific subsystems, rather than more general-purpose brain tissue?

New study pinpoints areas of the brain used exclusively for language, providing a partial answer to a longstanding debate in cognitive science.

September 1, 2011

Word association: Study matches brain scans with complex thought

Word association: Study matches brain scans with complex thought – ScienceBlog.com.

In an effort to understand what happens in the brain when a person reads or considers such abstract ideas as love or justice, Princeton researchers have for the first time matched images of brain activity with categories of words related to the concepts a person is thinking about. The results could lead to a better understanding of how people consider meaning and context when reading or thinking.