Issue 95 / September - October 2013
Jacobs J. et al. Direct recordings of grid-like neuronal activity in human spatial navigation. Nature Neuroscience, 2013
The Brain‚Äôs GPS
Do you happen to have a poor sense of direction? Do you often find yourself holding a map upside-down? Well, now you can blame your grid cells. Using direct human brain recordings, researchers have identified a novel type of cell in the brain that helps people keep track of their relative location while navigating through an unfamiliar environment. Scientists got this rare opportunity to identify these unique cells while they studied brain recordings of epilepsy patients via electrodes implanted deep inside their brains. These cells have been called "grid cells" because they are activated in a triangular grid pattern. The "grid cell" is distinct among brain cells because its activation represents multiple spatial locations, which allows the brain to keep track of navigational cues, such as how far you are from a starting point or your last turn. This type of navigation is called path integration. During brain recordings, 14 study participants were asked to play a video game where they ride a virtual bicycle to navigate from one point to another to retrieve objects and then recall how to get back to the places where they found the objects. While participants were playing the game, researchers examined the relation between navigation and the corresponding activity of individual neurons. Results were striking: each grid cell responded at multiple spatial locations that were arranged in the shape of a grid suggesting that the navigation information is principally encoded in our brains through this triangular grid pattern. Without grid cells, humans would frequently get lost or have to navigate based solely on landmarks. Differences in how well the grid cells work could potentially explain why some people have a better sense of direction than others. In addition, grid cells are located in the entorhinal cortex which is a critical component of human memory. The entorhinal cortex is also the first brain region affected in Alzheimer‚Äôs disease. Thus, understanding how grid cells work could potentially help us to understand why people with Alzheimer‚Äôs frequently become disoriented as well as to develop new strategies to improve brain function in the affected individuals.
Philippe N. et al. Pandoraviruses: amoeba viruses with genomes up to 2.5 Mb reaching that of parasitic eukaryotes. Science, 2013 Jul 19
Giant viruses open Pandora‚Äôs box
On a fairly ordinary day, two French biologists were analyzing water samples collected off the coast of Chile. What they saw under the microscope was quite amazing: a previously unidentified organism, about the size of a bacterial cell, appeared as a large dark spot. Astonishingly, these new organisms seemed to be infecting and killing the amoeba in the water. Later, another group of researchers found a similar organism in a pond in Australia. Both groups soon realized that they discovered a type of ‚Äúgiant‚ÄĚ virus which is at least twice as big as the largest known viruses. The biggest virus discovered so far was called Mimiviruses, with a size of 700 nanometers and carrying more than 1000 genes. The newly discovered viruses are called Pandoraviruses, which are 1 micrometer long and 0.5 micrometers across. Pandoraviruses are visible under a light microscope and contain more than 2500 genes. A viral genome consisting of 2500 genes is extremely large compared to known viruses, such as the Influenza or HIV, which only contain 10 genes or less. More importantly, 93% of the genes did not resemble any known lineage in the natural world, suggesting Pandoraviruses are not related to any known virus family and may represent a new life form. These findings generated new perspectives about how scientists see viruses. It raised the possibility that there might be many different kinds of giant viruses out there to be discovered. Some biological features in these giant viruses could easily blur the line between life forms and viruses, which are considered to be non-living. Although Pandoraviruses do not infect human cells, there might be other giant viruses out there that could infect human cells. There are still a lot of human diseases known to have an infectious component but for which no infectious agent has been identified yet. This study will definitely encourage people to actively look for the role of giant viruses in some diseases.
Haigh A. et al. How well do you see what you hear? The acuity of visual-to-auditory sensory substitution. Frontiers in Psychology, 2013 Jun 18
See through the Ears
Scientists have created a revolutionary device for the blind that allows them see the world through their ears. The device ‚ÄúvOICe‚ÄĚ trains the brain to invoke mental images of what they are hearing around them. The first test trial of vOICe has been performed on blindfolded sighted people. The participants took a standard eye test where they were asked to view the letter E turned in four directions and in various sizes. The best visual acuity is considered 20/20 (distance in feet/size of the E) and the majority of participants were able to achieve the best performance possible, nearly 20/400 sight. This is an impressive result when compared to an alternative stem-cell based sight restoration technique, which only yielded 20/800 visual acuity. In addition, the affordable and non-invasive nature of vOICe would offer a unique option. But, how might this work in practice? One can imagine that visually-impaired people would wear a discreet head-mounted camera such as Google Glass and receive wireless audio information through mini earbuds. As the person turns to look in various directions, the device scans images and correlates those with soundscapes, then the person‚Äôs brain would momentarily translate those into mental images of the objects ‚ÄĒ like braille for the ears. These sensory substitution devices could potentially be employed in combination with other alternative invasive techniques to train the brain to see again, or even to see for the first time.