Researchers provide first evidence for learning mechanism

August 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: Running helps the brain counteract negative effect of stress, study finds

Related Stories

The chemistry of memory

November 24, 2017

Learning requires the chemical adaptation of individual synapses. Researchers have now revealed the impact of an RNA-binding protein that is intimately involved in this process on learning and memory formation and learning ...

Study offers clue to memory formation in the brain

July 7, 2017

While memory loss makes an engaging theme for a movie, in real life, learning and memory may be the most intriguing topics in brain science. How does the brain help us learn from our daily experience? Where is memory formed ...

Special protein helps maintain an efficient brain

May 18, 2009

(PhysOrg.com) -- The instruction manual for maintaining an efficient brain may soon include a section on synaptotagmin-IV (Syt-IV), a protein known to influence learning and memory, thanks to a study by UW-Madison researchers.

Recommended for you

Archaeologists find ancient necropolis in Egypt

February 24, 2018

Egypt's Antiquities Ministry announced on Saturday the discovery of an ancient necropolis near the Nile Valley city of Minya, south of Cairo, the latest discovery in an area known to house ancient catacombs from the Pharaonic ...

AI and 5G in focus at top mobile fair

February 24, 2018

Phone makers will seek to entice new buyers with better cameras and bigger screens at the world's biggest mobile fair starting Monday in Spain after a year of flat smartphone sales.

Walking crystals may lead to new field of crystal robotics

February 23, 2018

Researchers have demonstrated that tiny micrometer-sized crystals—just barely visible to the human eye—can "walk" inchworm-style across the slide of a microscope. Other crystals are capable of different modes of locomotion ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.