平特五不中

The brain鈥檚 quick interceptions help you navigate the world

When you are about to collide into something and manage to swerve away just in the nick of time, what exactly is happening in your brain? A new study from the Montreal Neurological Institute and Hospital 鈥� The Neuro, 平特五不中 shows how the brain processes visual information to figure out when something is moving towards you or when you are about to head into a collision. The study, published in the Proceedings of the National Academy of Sciences of the USA (PNAS), provides vital insight into our sense of vision and a greater understanding of the brain.

Researchers at The Neuro and the University of Maryland have figured out the mathematical calculations that specific neurons employ in order to inform us of our distance from an object and the 3D velocities of moving objects and surfaces relative to ourselves.聽 Highly specialized neurons located in the brain鈥檚 visual cortex, in an area known as MST, respond selectively to motion patterns such as expansion, rotation, and deformation. However, the computations underlying such selectivity were unknown until now.

Using mathematical models and sophisticated recording techniques, researchers have discovered how individual MST neurons function.聽 鈥淎rea MST is typical of high-level visual cortex, in that information about important aspects of vision can be seen in the firing patterns of single neurons. A classic example is a neuron that only fires when the subject is looking at the image of a particular face. This type of neuron has to gather information from other neurons that are selective to simpler features, like lines, colors, and textures, and combine these pieces of information in a fairly sophisticated way,鈥� says Dr. Christopher Pack, neuroscientist at The Neuro and senior author. 聽鈥淪imilarly, for motion detection, neurons have to combine input from many other neurons earlier in the visual pathway, in order to determine whether something is moving toward you or just drifting past.鈥澛� The brain鈥檚 visual pathway is made up of building blocks. For example, neurons in the retina respond to very simple stimuli, such as small spots of light. Further along the visual pathway, neurons respond to more complex stimulus such as straight lines, by combining inputs from neurons earlier on. Neurons further along respond to even more complex stimulus such as combinations of lines (angles), ultimately leading to neurons that can respond to, or recognize, faces and objects for example.

The research team found that a remarkably simple computation lies at the heart of this sophisticated neural selectivity: MST neurons appear to be capable of performing a multiplicative operation on their inputs. These inputs come from neurons one step earlier in the visual pathway, in a well-studied area known as MT. In other words, the inputs of MT neurons are multiplied in order to get the output of MST neurons. 聽This turns out to be remarkably similar to what has been observed in other brain areas and in other species, suggesting it may reflect a general strategy by which brains process sensory information. 鈥淥ne interesting aspect of the computation is that it appears to be about the same as what other people have found in flies and beetles, suggesting that evolution solved this problem once, at least a few hundred million years ago.鈥�

鈥淲e developed a new motion stimulus with a morphing pattern flow (e.g. dots on a screen that are expansive, swirl around, circle to the right, contract etc) and recorded MST neurons responding to these stimuli,鈥� says Patrick Mineault, 聽Ph.D. candidate at The Neuro and primary author on the study. 鈥淲e circumvented the issue of increasing complexities of calculations along the various steps of the visual pathway by incorporating known data from neurons just one step earlier in the pathway - area MT, which precedes MST. As we now had measurements of the output of the MST neurons from the study鈥檚 recordings, and already knew the input of MT neurons, we could calculate the math linking these two functions 鈥� and it turns out to be a multiplicative function.鈥� The mathematical models successfully account for the stimulus selectivity of some of the brain鈥檚 complex motion neurons - which are vitally important in helping navigate us through the world.聽

This work was supported by the Canadian Institutes of Health Research, Le Ministre du D茅veloppement 茅conomique, de l'Innovation et de l'Exportation du Qu茅bec , the National Science Foundation, the Fonds de recherche du Qu茅bec 鈥� Sant茅, and the聽 Fonds de recherche du Qu茅bec 鈥� Nature et technologies.

The Montreal Neurological Institute and Hospital聽:

The Montreal Neurological Institute and Hospital 鈥� The Neuro, is a unique academic medical centre dedicated to neuroscience. Founded in 1934 by the renowned Dr. Wilder Penfield, The Neuro is recognized internationally for integrating research, compassionate patient care and advanced training, all key to advances in science and medicine. The Neuro is a research and teaching institute of 平特五不中 and forms the basis for the Neuroscience Mission of the 平特五不中 Health Centre.聽 Neuro researchers are world leaders in cellular and molecular neuroscience, brain imaging, cognitive neuroscience and the study and treatment of epilepsy, multiple sclerosis and neuromuscular disorders. The Montreal Neurological Institute was named as one of the Seven Centres of Excellence in Budget 2007, which provided the MNI with $15 million in funding to support its research and commercialization activities related to neurological disease and neuroscience.