Researchers provide first evidence for learning mechanism

Aug 24, 2006

Finally confirming a fact that remained unproven for more than 30 years, researchers at MIT's Picower Institute for Learning and Memory report in the Aug. 25 issue of Science that certain key connections among neurons get stronger when we learn.

"We show what everyone has always believed: LTP (long-term potentiation) is indeed induced in the hippocampus when learning occurs," said Mark F. Bear, Picower Professor of Neuroscience. "This is a big deal for neuroscientists because such evidence has been absent for the 30-plus years we have known about LTP."

The findings described in the Bear paper and in a second, separate paper in the same issue of Science "substantially advance the case for LTP as a neural mechanism for memory," wrote Tim Bliss of the MRC National Institute for Medical Research in the UK, Graham Collingridge of the University of Bristol, and Serge Laroche of the Universite Paris Sud in a commentary on the work.

LTP is an example of plasticity - the amazing ability of the brain to change in response to experience. LTP builds up synapses, or the connections between neurons, while its counterpart, long-term depression, or LTD, pares unused synapses.

Since LTP was discovered in the late 1960s, thousands of papers have been published based on the assumption that the phenomenon is an important learning and memory mechanism in the hippocampus, the memory center of the brain.

Researchers had found that electrical stimulation of neurons, mimicking the electrical impulses that zap around the brain when it responds to sensory input, strengthens the connections among synapses. The assumption was that LTP occurs in the hippocampus as a consequence of learning, but there had never been conclusive evidence that learning was directly tied to LTP.

The problems were threefold.

Many learning tasks require more than one repetition of an event, and slight differences in animals' rates of learning obscured the time-sensitive markers of LTP. Second, the synaptic changes that occur in hippocampus-based learning are few and far between, making them hard to detect. Third, it became apparent that learning could be stored through LTD as well as LTP.

Using techniques pioneered by MIT's Susumu Tonegawa, director of the Picower Institute, neuroscientists began to pinpoint exactly which genes and proteins are involved in learning.

This created a "big thicket of correlations, but it never proved causality," said Bear, who also holds an appointment in MIT's Department of Brain and Cognitive Sciences. "Our contribution was that we had learned enough about LTP and the traces it leaves in the brain to track changes in proteins. We asked whether learning induces the same subtle changes."

In the experiment, rats learned that if they darted into the darkened area of a two-chambered box, they received an unpleasant foot shock. The animals quickly learned to avoid the darkened chamber and stay in the brightly lit area.

The researchers used biochemical probes that "marked" synapses that had recently been modified by learning, as well as a technique that allowed them to eavesdrop on the synaptic transmissions in the rats' brains as they learned. Learning, they found, did indeed induce LTP among synapses in the hippocampus.

In addition to Bear, the study's authors are Jonathan R. Whitlock, affiliated with Brown University; research scientist Arnold J. Heynen and research affiliate Marshall G. Shuler, both at the Picower Institute.

Source: Massachusetts Institute of Technology

Explore further: Free the seed: OSSI nurtures growing plants without patent barriers

add to favorites email to friend print save as pdf

Related Stories

The Mechanisms of Memory

Mar 09, 2010

(PhysOrg.com) -- USC College's Michel Baudry and graduate student Sohila Zadran brought forty years of research to a pinnacle with their breakthroughs in the science of learning and memory.

To make memories, new neurons must erase older ones

Nov 12, 2009

Short-term memory may depend in a surprising way on the ability of newly formed neurons to erase older connections. That's the conclusion of a report in the November 13th issue of the journal Cell that provid ...

Calcium channels optimize learning

Sep 18, 2009

(PhysOrg.com) -- Researchers at the Friedrich Miescher Institute for Biomedical Research, Switzerland, have shown how calcium channels in the brain have a positive impact on learning. Their results have been ...

Star-shaped cells in the brain aid with learning

Sep 07, 2009

(PhysOrg.com) -- Every movement and every thought requires the passing of specific information between networks of nerve cells. To improve a skill or to learn something new entails more efficient or a greater ...

Recommended for you

Plants with dormant seeds give rise to more species

Apr 18, 2014

Seeds that sprout as soon as they're planted may be good news for a garden. But wild plants need to be more careful. In the wild, a plant whose seeds sprouted at the first warm spell or rainy day would risk disaster. More ...

Researchers successfully clone adult human stem cells

Apr 18, 2014

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

User comments : 0

More news stories

Biologists help solve fungi mysteries

(Phys.org) —A new genetic analysis revealing the previously unknown biodiversity and distribution of thousands of fungi in North America might also reveal a previously underappreciated contributor to climate ...

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.