Researchers have taken a major step toward that goal by designing a computer chip that mimics how the brain’s neurons adapt in response to new information. (Credit: MIT)

 

 

MIT Technology Review, Novenber 16, 2011  —  For decades, scientists have dreamed of building computer systems that could replicate the human brain’s talent for learning new tasks.

 

MIT researchers have now taken a major step toward that goal by designing a computer chip that mimics how the brain’s neurons adapt in response to new information. This phenomenon, known as plasticity, is believed to underlie many brain functions, including learning and memory.

 

With about 400 transistors, the silicon chip can simulate the activity of a single brain synapse — a connection between two neurons that allows information to flow from one to the other. The researchers anticipate this chip will help neuroscientists learn much more about how the brain works, and could also be used in neural prosthetic devices such as artificial retinas, says Chi-Sang Poon, a principal research scientist in the Harvard-MIT Division of Health Sciences and Technology.

 

Poon is the senior author of a paper describing the chip in the Proceedings of the National Academy of Sciences the week of Nov. 14. Guy Rachmuth, a former postdoc in Poon’s lab, is lead author of the paper. Other authors are Mark Bear, the Picower Professor of Neuroscience at MIT, and Harel Shouval of the University of Texas Medical School.

 

Modeling synapses

There are about 100 billion neurons in the brain, each of which forms synapses with many other neurons. A synapse is the gap between two neurons (known as the presynaptic and postsynaptic neurons). The presynaptic neuron releases neurotransmitters, such as glutamate and GABA, which bind to receptors on the postsynaptic cell membrane, activating ion channels. Opening and closing those channels changes the cell’s electrical potential. If the potential changes dramatically enough, the cell fires an electrical impulse called an action potential.

 

All of this synaptic activity depends on the ion channels, which control the flow of charged atoms such as sodium, potassium and calcium. Those channels are also key to two processes known as long-term potentiation (LTP) and long-term depression (LTD), which strengthen and weaken synapses, respectively.

 

The MIT researchers designed their computer chip so that the transistors could mimic the activity of different ion channels. While most chips operate in a binary, on/off mode, current flows through the transistors on the new brain chip in analog, not digital, fashion. A gradient of electrical potential drives current to flow through the transistors just as ions flow through ion channels in a cell.

“We can tweak the parameters of the circuit to match specific ion channels,” Poon says. “We now have a way to capture each and every ionic process that’s going on in a neuron.”

 

Previously, researchers had built circuits that could simulate the firing of an action potential, but not all of the circumstances that produce the potentials. “If you really want to mimic brain function realistically, you have to do more than just spiking. You have to capture the intracellular processes that are ion channel-based,” Poon says.

 

The new chip represents a “significant advance in the efforts to incorporate what we know about the biology of neurons and synaptic plasticity onto CMOS [complementary metal-oxide-semiconductor] chips,” says Dean Buonomano, a professor of neurobiology at the University of California at Los Angeles, adding that “the level of biological realism is impressive.

 

The MIT researchers plan to use their chip to build systems to model specific neural functions, such as the visual processing system. Such systems could be much faster than digital computers. Even on high-capacity computer systems, it takes hours or days to simulate a simple brain circuit. With the analog chip system, the simulation is even faster than the biological system itself.

 

Another potential application is building chips that can interface with biological systems. This could be useful in enabling communication between neural prosthetic devices such as artificial retinas and the brain. Further down the road, these chips could also become building blocks for artificial intelligence devices, Poon says.

 

Debate resolved

The MIT researchers have already used their chip to propose a resolution to a longstanding debate over how LTD occurs.

 

One theory holds that LTD and LTP depend on the frequency of action potentials stimulated in the postsynaptic cell, while a more recent theory suggests that they depend on the timing of the action potentials’ arrival at the synapse.

 

Both require the involvement of ion channels known as NMDA receptors, which detect postsynaptic activation. Recently, it has been theorized that both models could be unified if there were a second type of receptor involved in detecting that activity. One candidate for that second receptor is the endo-cannabinoid receptor.

 

Endo-cannabinoids, similar in structure to marijuana, are produced in the brain and are involved in many functions, including appetite, pain sensation and memory. Some neuroscientists had theorized that endo-cannabinoids produced in the postsynaptic cell are released into the synapse, where they activate presynaptic endo-cannabinoid receptors. If NMDA receptors are active at the same time, LTD occurs.

 

When the researchers included on their chip transistors that model endo-cannabinoid receptors, they were able to accurately simulate both LTD and LTP. Although previous experiments supported this theory, until now, “nobody had put all this together and demonstrated computationally that indeed this works, and this is how it works,” Poon says.

Woman reading in the small town of Brisighella, Italy, which is between Bologna and San Marino

 

 

LifeExtensionDailyNews, November 16, 2011 — Clerks at the Brunswick-Glynn County Library know Evelyn Connell well.

Like clockwork, the Brunswick resident stops by the library every other week, checking out as many books as she can carry. Last week, she signed out 14.

“I can really only carry about 12 or so in my bag, but I just stuff as many as possible in it anyway,” Connell said. “There is no limit on how many you can check out, so I take advantage of that, you’d say. I read at least six books a week.”

At 71, Connell is an active reader with a sharp mind. She is quick on her feet, clever and vivacious. She loves the TV trivia show “Jeopardy!” and usually knows most of the answers.

She can do several tasks at once and has a mind like a steel trap.

“Well, maybe I can’t remember things as much as I once could, but I think I’m hanging in there and doing well,” Connell said.

Her spryness and spunk are likely due to how active she keeps her brain, she speculates.

“I do think that the more active you keep your brain, the longer you hold on to those traits of brain power you have at a younger age,” Connell said.

Connell is not alone in that thinking. Overwhelming research has shown that older citizens who keep their minds sharp and active are more likely to retain a higher level of brain power as they age.

Keeping the brain active through exercises like reading regularly is vital to preventing memory loss and reduced brain function, said Janice Vickers, executive director of Alzheimer’s of Glynn/ Brunswick.

“There is no question that reading can maintain a healthy brain as you age,” Vickers said. “The saying is true: If you don’t use it, you lose it.”

An estimated 5.4 million Americans of all ages have Alzheimer’s disease, the most common form of dementia, according to the National Alzheimer’s Association. That’s one in eight older Americans.

Vickers said the disease, though prevalent in aging citizens, can be avoided or, at the very least, delayed. Working to prevent the condition at an earlier age is key to ensuring a quick mind like Connell’s, Vickers said.

That means flexing the brain as often as possible in a variety of ways.

Cracking a book or other printed work awakens many functions in the brain, including concentration, vision and comprehension, Vickers said.

Reading books, magazines and periodicals aren’t the only sources individuals can lean on for stimulating brain function. Doing research online, playing trivia games and even crossword puzzles have been shown as ways to produce more brain function and prevent dementia-related diseases, Vickers said.

Reading also can be a link to diagnosing early stages of memory loss. The ability to read can slip from some patients early in the process of developing the disease.

 

 

Photo Credit Flickr: Man reading in Spain

 

 

This is a common scene around various parts of New York City: elderly people, pretty much alone, sitting in a quiet corner somewhere to read a magazine or newspaper, while enjoying some pleasant weather. This photo was taken at Verdi Square, 72nd St. and Broadway, in Manhattan     Photo Credit Ed Yourdon