Brain complexity: new techniques to explore it (Introduction)

by David Turell , Tuesday, February 02, 2016, 17:29 (3217 days ago) @ David Turell

Trying to understand the brain functions neuron by neuron is very difficult because so many neurons are tied up in a network with each activity:-http://www.scientificamerican.com/article/deciphering-the-language/-"There are close to 100 billion neurons in the human brain. Researchers know a lot about how these individual cells behave, primarily through “electrophysiology,” which involves sticking fine electrodes into cells to record their electrical activity. We also know a fair amount about the gross organization of the brain into partially specialized anatomical regions, thanks to whole-brain imaging technologies like functional magnetic resonance imaging (fMRI), which measure how blood oxygen levels change as regions that work harder demand more oxygen to fuel metabolism. We know little, however, about how the brain is organized into distributed “circuits” that underlie faculties like, memory or perception. And we know even less about how, or even if, cells are arranged into “local processors” that might act as components in such networks.-"We also lack knowledge regarding the “code” large numbers of cells use to communicate and interact. This is crucial, because mental phenomena likely emerge from the simultaneous activity of many thousands, or millions, of interacting neurons. In other words, neuroscientists have yet to decipher the “language” of the brain. “The first phase is learning what the brain's natural language is. If your resolution [in a hypothetical language detector] is too coarse, so you're averaging over paragraphs, or chapters, you can't hear individual words or discern letters,” says physicist Michael Roukes of the California Institute of Technology, one of the authors of the “Brain Activity Map” (BAM) paper published in 2012 in Neuron that inspired the BRAIN Initiative. “Once we have that, we could talk to the brain in complete sentences.”-***-"Today's state-of-the-art technology in the field is optical imaging, mainly using calcium indicators—fluorescent proteins introduced into cells via genetic tweaks, which emit light in response to the calcium level changes caused by neurons firing. These signals are recorded using special microscopes that produce light, as the indicators need to absorb photons in order to then emit these light particles. This can be combined with optogenetics, a technique that genetically modifies cells so they can be activated using light, allowing researchers to both observe and control neural activity.-***-"An alternative approach is being taken by a multidisciplinary collaboration of research groups, led by Roukes. Funded by a recent BRAIN grant, his team plans to combine optical methods with nanotechnology to produce nanoscale implants that are inserted into the brain but which interact with cells optically, at depths light can't otherwise reach. “With optical techniques where you're doing standoff sensing, as you go deeper, you lose resolution; the other paradigm is to implant things in the brain,” Roukes says. “Extremely narrow wires can be implanted slowly and tolerated, as long as you don't displace too much tissue.”-***-"One of the project's early aims is to record from every neuron in a one-millimeter3 volume of tissue. “We can't understand the entire brain in one fell swoop, we've got to find some pared-down problems,” Roukes says. “The question is: Can we identify some sort of regional processor in the brain that we could understand deeply in the next 10 years?” There are small structures in the cortex called “cortical columns” where internal connections are dense and outward connections are sparse, making them likely candidates for being local processors. In mice these are one millimeter wide, with a one-millimeter3 volume containing around 100,000 cells—in other words, an ideal early target for study.-***-"There are also indicators that report different types of activity—like other chemicals, neurotransmitters and even the actual physical force of moving parts of cells. “The brain is a complex chemical system and [the] techniques for optical interactions over large volumes would be applicable to many different indicators,” says Cohen, who mainly works on developing such tools."-Comment: Way beyond the fMRI gross looks that fascinated Romansh