. Earth Science News .

How the brain makes memories: Rhythmically!
by Staff Writers
Los Angeles CA (SPX) Oct 07, 2011

Contrary to what was previously assumed, Mehta and Kumar found that when it comes to stimulating synapses with naturally occurring spike patterns, stimulating the neurons at the highest frequencies was not the best way to increase synaptic strength.

The brain learns through changes in the strength of its synapses - the connections between neurons - in response to stimuli. Now, in a discovery that challenges conventional wisdom on the brain mechanisms of learning, UCLA neuro-physicists have found there is an optimal brain "rhythm," or frequency, for changing synaptic strength. And further, like stations on a radio dial, each synapse is tuned to a different optimal frequency for learning.

The findings, which provide a grand-unified theory of the mechanisms that underlie learning in the brain, may lead to possible new therapies for treating learning disabilities.

The study appears in the current issue of the journal Frontiers in Computational Neuroscience.

"Many people have learning and memory disorders, and beyond that group, most of us are not Einstein or Mozart," said Mayank R. Mehta, the paper's senior author and an associate professor in UCLA's departments of neurology, neurobiology, physics and astronomy. "Our work suggests that some problems with learning and memory are caused by synapses not being tuned to the right frequency."

A change in the strength of a synapse in response to stimuli - known as synaptic plasticity - is induced through so-called "spike trains," series of neural signals that occur with varying frequency and timing. Previous experiments demonstrated that stimulating neurons at a very high frequency (e.g., 100 spikes per second) strengthened the connecting synapse, while low-frequency stimulation (e.g., one spike per second) reduced synaptic strength.

These earlier experiments used hundreds of consecutive spikes in the very high-frequency range to induce plasticity. Yet when the brain is activated during real-life behavioral tasks, neurons fire only about 10 consecutive spikes, not several hundred. And they do so at a much lower frequency - typically in the 50 spikes-per-second range.

In other words, said Mehta, "spike frequency refers to how fast the spikes come. Ten spikes could be delivered at a frequency of 100 spikes a second or at a frequency of one spike per second."

Until now, researchers had been unable to conduct experiments that simulated more naturally occurring levels. But Mehta and co-author Arvind Kumar, a former postdoctoral fellow in his lab, were able to obtain these measurements for the first time using a sophisticated mathematical model they developed and validated with experimental data.

Contrary to what was previously assumed, Mehta and Kumar found that when it comes to stimulating synapses with naturally occurring spike patterns, stimulating the neurons at the highest frequencies was not the best way to increase synaptic strength.

When, for example, a synapse was stimulated with just 10 spikes at a frequency of 30 spikes per second, it induced a far greater increase in strength than stimulating that synapse with 10 spikes at 100 times per second.

"The expectation, based on previous studies, was that if you drove the synapse at a higher frequency, the effect on synaptic strengthening, or learning, would be at least as good as, if not better than, the naturally occurring lower frequency," Mehta said. "To our surprise, we found that beyond the optimal frequency, synaptic strengthening actually declined as the frequencies got higher."

The knowledge that a synapse has a preferred frequency for maximal learning led the researchers to compare optimal frequencies based on the location of the synapse on a neuron. Neurons are shaped like trees, with the nucleus being the base of the tree, the dendrites resembling the extensive branches and the synapses resembling the leaves on those branches.

When Mehta and Kumar compared synaptic learning based on where synapses were located on the dendritic branches, what they found was significant: The optimal frequency for inducing synaptic learning changed depending on where the synapse was located. The farther the synapse was from the neuron's cell body, the higher its optimal frequency.

"Incredibly, when it comes to learning, the neuron behaves like a giant antenna, with different branches of dendrites tuned to different frequencies for maximal learning," Mehta said.

The researchers found that not only does each synapse have a preferred frequency for achieving optimal learning, but for the best effect, the frequency needs to be perfectly rhythmic - timed at exact intervals. Even at the optimal frequency, if the rhythm was thrown off, synaptic learning was substantially diminished.

Their research also showed that once a synapse learns, its optimal frequency changes. In other words, if the optimal frequency for a naive synapse - one that has not learned anything yet - was, say, 30 spikes per second, after learning, that very same synapse would learn optimally at a lower frequency, say 24 spikes per second. Thus, learning itself changes the optimal frequency for a synapse.

This learning-induced "detuning" process has important implications for treating disorders related to forgetting, such as post-traumatic stress disorder, the researchers said.

Although much more research is needed, the findings raise the possibility that drugs could be developed to "retune" the brain rhythms of people with learning or memory disorders, or that many more of us could become Einstein or Mozart if the optimal brain rhythm was delivered to each synapse.

"We already know there are drugs and electrical stimuli that can alter brain rhythms," Mehta said. "Our findings suggest that we can use these tools to deliver the optimal brain rhythm to targeted connections to enhance learning."

The publication and related materials can be found here.

Related Links
University of California - Los Angeles
All About Human Beings and How We Got To Be Here

Get Our Free Newsletters Via Email
Buy Advertising Editorial Enquiries


. Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

Keeping track of reality
Cambridge UK (SPX) Oct 07, 2011
A structural variation in a part of the brain may explain why some people are better than others at distinguishing real events from those they might have imagined or been told about, researchers have found. The University of Cambridge scientists found that normal variation in a fold at the front of the brain called the paracingulate sulcus (or PCS) might explain why some people are better ... read more

The waste from the Japanese earthquake and tsunami

Japan nuclear plant worker dies

Nuclear contamination found beyond Japan no-go zone

New modelling results link natural resources and armed conflicts

A Race To Space Waste

Sensor Fusion Powers Next Generation of Smartphones and Tablets

Smartphone war pauses as world mourns Steve Jobs

Malaysians protest Australian rare earth plant

Reefs recovered faster after mass extinction than first thought

Doubts remain over global future of sharks

Space Observatory Provides Clues to Creation of Earth's Oceans

Chilean court overturns ban on giant Patagonia dam

Rising CO2 levels at end of Ice Age not tied to Pacific Ocean

Rising carbon dioxide levels at end of last ice age not tied to Pacific Ocean

Swiss warn of massive ice chunk breaking off glacier

Chinese target Arctic with Iceland land deal: experts

Floods drown Asia's rice bowl

Productivity of land plants may be greater than previously thought

Petition demands US label genetically engineered food

Micro-breweries take on local flavour in China

Philippine typhoon death toll reaches 82

Tenerife geology discovery is among 'world's best'

Indian Ocean tsunami alert system to be tested on Oct 12

Worst Cambodian floods in a decade kill 167

Food crisis looming in Sudan: UN agency

Kenya tries to contact French woman's abductors in Somalia

Berkeley Lab Tests Cookstoves for Haiti

Guyana opposition warns foreign bauxite firms

Alzheimer's might be transmissible in similar way as infectious prion diseases

Keeping track of reality

Merkel, rights groups hail Nobel nod to women

How the brain makes memories: Rhythmically!


The content herein, unless otherwise known to be public domain, are Copyright 1995-2011 - Space Media Network. AFP and UPI Wire Stories are copyright Agence France-Presse and United Press International. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement