Posts tagged neurons
Articles and news from the latest research reports.
Limits on Brain’s Ability to Perceive Multifeatured Objects
New research sheds light on how the brain encodes objects with multiple features, a fundamental task for the perceptual system. The study, published in Psychological Science, a journal of the Association for Psychological Science, suggests that we have limited ability to perceive mixed color-shape associations among objects that exist in several locations.
Research suggests that neurons that encode a certain feature — shape or color, for example — fire in synchrony with neurons that encode other features of the same object. Psychological scientists Liat Goldfarb of the University of Haifa and Anne Treisman of Princeton University hypothesized that if this neural-synchrony explanation were true, then synchrony would be impossible in situations in which the same features are paired differently in different objects.
Say, for example, a person sees a string of letters, “XOOX,” and the letters are printed in alternating colors, red and green. Both letter shape and letter color need to be encoded, but the associations between letter shape and letter color are mixed (i.e., the first X is red, while the second X is green), which should make neural synchrony impossible.
“The perceptual system can either know how many Xs there are or how many reds there are, but it cannot know both at the same time,” Goldfarb and Treisman explain.
The researchers investigated their hypothesis in two experiments, in which they presented participants with strings of green and red Xs and Os and asked them to compare the number of Xs with the number of red letters (i.e., more Xs, more reds, or the same).
Participants’ responses to unique color-shape associations were significantly faster and more accurate than were their responses to displays with mixed color-shape associations.
The results show that relevant color and shape dimensions could be synchronized when the pairings between color and shape were unique, but not when the pairings were mixed.
These findings demonstrate a new behavioral principle that governs object representation. When shapes are repeated in several locations and have mixed color-shape associations, they are hard to perceive.
This research expands on Anne Treisman’s groundbreaking research on feature integration in visual perception, which shows that humans can encode characteristics such as color, form, and orientation, even in the absence of spatial attention.
Treisman is one of 12 scientists who received the National Medal of Science at the White House on February 1, 2013. The National Medal of Science, along with the National Medal of Technology and Innovation, is the highest honor that the US government grants to scientists, engineers, and inventors.
Peering into living cells — without dye nor fluophore
In the world of microscopy, this advance is almost comparable to the leap from photography to live television. Two young EPFL researchers, Yann Cotte and Fatih Toy, have designed a device that combines holographic microscopy and computational image processing to observe living biological tissues at the nanoscale. Their research is being done under the supervision of Christian Depeursinge, head of the Microvision and Microdiagnostics Group in EPFL’s School of Engineering.
Using their setup, three-dimensional images of living cells can be obtained in just a few minutes – instantaneous operation is still in the works – at an incredibly precise resolution of less than 100 nanometers, 1000 times smaller than the diameter of a human hair. And because they’re able to do this without using contrast dyes or fluorescents, the experimental results don’t run the risk of being distorted by the presence of foreign substances.
Being able to capture a living cell from every angle like this lays the groundwork for a whole new field of investigation. “We can observe in real time the reaction of a cell that is subjected to any kind of stimulus,” explains Cotte. “This opens up all kinds of new opportunities, such as studying the effects of pharmaceutical substances at the scale of the individual cell, for example.”
Watching a neuron grow
This month in Nature Photonics the researchers demonstrate the potential of their method by developing, image by image, the film of a growing neuron and the birth of a synapse, caught over the course of an hour at a rate of one image per minute. This work, which was carried out in collaboration with the Neuroenergetics and cellular dynamics laboratory in EPFL’s Brain Mind Institute, directed by Pierre Magistretti, earned them an editorial in the prestigious journal. “Because we used a low-intensity laser, the influence of the light or heat on the cell is minimal,” continues Cotte. “Our technique thus allows us to observe a cell while still keeping it alive for a long period of time.”
As the laser scans the sample, numerous images extracted by holography are captured by a digital camera, assembled by a computer and “deconvoluted” in order to eliminate noise. To develop their algorithm, the young scientists designed and built a “calibration” system in the school’s clean rooms (CMI) using a thin layer of aluminum that they pierced with 70nm-diameter “nanoholes” spaced 70nm apart.
Finally, the assembled three-dimensional image of the cell, that looks as focused as a drawing in an encyclopedia, can be virtually “sliced” to expose its internal elements, such as the nucleus, genetic material and organelles.
Toy and Cotte, who have already obtained an EPFL Innogrant, have no intention of calling a halt to their research after such a promising beginning. In a company that’s in the process of being created and in collaboration with the startup Lyncée SA, they hope to develop a system that could deliver these kinds of observations in vivo, without the need for removing tissue, using portable devices. In parallel, they will continue to design laboratory material based on these principles. Even before its official launch, the start-up they’re creating has plenty of work to do - and plenty of ambition, as well.
In the brain, broken down ‘motors’ cause anxiety
When motors break down, getting where you want to go becomes a struggle. Problems arise in much the same way for critical brain receptors when the molecular motors they depend on fail to operate. Now, researchers reporting in Cell Reports, a Cell Press publication, on February 7, have shown these broken motors induce stress and anxiety in mice. The discovery may point the way to new kinds of drugs to treat anxiety and other disorders.
The study in mice focuses on one motor in particular, known as KIF13A, which, according to the new evidence, is responsible for ferrying serotonin receptors. Without proper transportation, those receptors fail to reach the surface of neurons and, as a result, animals show signs of heightened anxiety.
In addition to their implications for understanding anxiety, the findings also suggest that defective molecular motors may be a more common and underappreciated cause of disease.
"Most proteins are transported in vesicles or as protein complexes by molecular motors," said Nobutaka Hirokawa of the University of Tokyo. "As shown in this study, defective motors could cause many diseases."
Scientists know that serotonin and serotonin receptors are involved in anxiety, aggression, and mood. But not much is known about how those players get around within cells. When Hirokawa’s team discovered KIF13A at high levels in the brain, they wondered what it did.
The researchers discovered that mice lacking KIF13A show greater anxiety in both open-field and maze tests and suggest that this anxious behavior may stem from an underlying loss of serotonin receptor transport, which leads to a lower level of expression of those receptors in critical parts of the brain.
"Collectively, our results suggest a role for this molecular motor in anxiety control," the researchers wrote. Hirokawa says the search should now be on for anti-anxiety drug candidates aimed at restoring the brain’s serotonin receptor transport service.
Mechanism Prevents Alterations in Neuronal Production During Embryonic Development
ScienceDaily (June 26, 2012) — Scientists from the University of Barcelona (UB) in collaboration with a multidisciplinary team from the Spanish National Research Council (CSIC) has discovered a mechanism that prevents alterations in neurogenesis, the process of neuronal formation, during the development of the nervous system in vertebrates. The study, published in the journal Development, relates these distortions to the natural presence of a molecule that inhibits the neuronal formation at the regions adjacent to the tissue suitable for neurogenesis.
Left: altered neurogenic wavefront in the absence of Delta. Right: normal neurogenic wavefront. (Credit: Image courtesy of Universidad de Barcelona)
Through a theoretical and computational analysis of the retina, scientists have found that lateral inhibition, a process that regulates the generation of neurons in the central nervous system, undergoes alterations at the neurogenic wavefront (i.e. the edge between the regions that generate neurons and the adjacent areas, where neurogenesis has not yet begun).
"The study shows that the absence of the Delta molecule at the adjacent regions reduces the robustness of the neurogenic process, often resulting in an increased production of neurons or in the presence of morphological alterations of the wavefront. These alterations could be catastrophic for the proper development of the nervous system," explains José María Frade, researcher from the CSIC, at the Cajal Institute.
Lateral inhibition during embryonic development aims to control the amount of neurons that are formed. It consists in cells that inhibit other neighbouring cells, promoting neuronal differentiation. “Neuronal precursor cells expressing high levels of Delta induce inhibitory signals in neighbouring cells. These inhibitory signals reduce the capacity of these cells to express Delta itself and, in turn, facilitate the differentiation of the high Delta-expressing precursors. Thus, the massive generation of neurons is avoided and the orderly production of different types of neurons necessary for brain function is facilitated,” explains researcher from the CSIC Saúl Ares, who works at the Spanish National Biotechnology Centre.
Previous theoretical studies suggested that the lateral inhibition process can be altered at the neurogenic edges. “However, the importance of this inhibition process had not been appropriately acknowledged. Our study demonstrates the relevance of Delta expression ahead of the neurogenic wavefront, provides predictions and explains developmental alterations resulting from the absence of Delta. It also represents a breakthrough in the theoretical field because it formulates a front propagation mechanism based on self-regulatory mechanisms,” points out Marta Ibañes, researcher from the UB.
According to researchers, this study provides a new concept that will attract the attention of neurobiologists who work both in the development of the nervous system and in several pathologies derived from neuronal development.
Source: Science Daily