New studies shed light on why quality sleep is so important to learning things, and why we forget things (it's often due to interference)

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http://www.eurekalert.org/pub_releases/2006-12/m-lds120506.php

Public release date: 5-Dec-2006

Contact: Hahn

thahn@...

49-622-148-6463

Max-Planck-Gesellschaft

Learning during sleep?

If I can't remember this morning where I put my car keys last night,

it's due to my memory failing me again. Scientists at the Max Planck

Institute for Medical Research in Heidelberg have been investigating

how memories might be consolidated. Their new study offers the

hitherto strongest proof that new information is transferred between

the hippocampus, the short term memory area, and the cerebral cortex

during sleep. According to their findings and contrary to previous

assumptions, the cerebral cortex actively controls this transfer. The

researchers developed a new technique for their investigations which

promises previously impossible insight into the largely

under-researched field of information processing in the brain (Nature

Neuroscience, November 2006).

The question of how the brain stores or discards memories still

remains largely unexplained. Many brain researchers regard the

consolidation theory as the best approach so far. This states that

fresh impressions are first stored as short-term memories in the

hippocampus. They are then said to move within hours or a few days -

usually during deep sleep - into the cerebral cortex where they enter

long-term memory. Investigations by Hahn, Mayank Mehta and the

Nobel Prize winner Bert Sakmann from the Max Planck Institute for

Medical Research in Heidelberg have now shed new light on the

mechanisms that create memory. According to their findings, the areas

of the brain work together, but possibly in a different way from that

previously assumed. " This is a technically sophisticated study which

could have considerable influence on our understanding of how nerve

cells interact during sleep consolidation, " confirmed Edvard Moser,

Director of the Centre for the Biology of Memory in Trondheim, Norway.

It has been difficult up to now to use experiments to examine the

brain processes that create memory. The scientists in Heidelberg

developed an innovative experimental approach especially for this

purpose. They succeeded in measuring the membrane potential of

individual interneurones (neurones that suppress the activity of the

hippocampus) in anaethetised mice. At the same time, they recorded the

field potential of thousands of nerve cells in the cerebral cortex.

This allowed them to link the behaviour of the individual nerve cells

with that of the cerebral cortex. The researchers discovered that the

interneurones they examined are active at almost the same time as the

field potential of the cerebral cortex. There was just a slight delay,

like an echo.

This was a surprising finding, because the interneurones suppress

those neurones in the hippocampus which are supposed to write

information to the cerebral cortex precisely during phases of high

activity. According to Mayank Mehta the result can be interpreted in

very different ways. " Either the mechanism contributes to memory

consolidation, or the information transfer from one part of the brain

to another during sleep does not proceed as we have previously

assumed. " The brain researchers now want to find out which of the

possible explanations applies.

In any case, the scientists can use their new experimental method to

investigate many other open questions in brain research. Hahn

emphasised: " Putting the behaviour of a single neuron in the context

of wider-scale patterns of activity promises to yield completely new

insights into the principles according to which our brain is

organised. "

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Original work:

Hahn, Bert Sakmann & Mayank R. Mehta Phase-locking of

hippocampal interneurons' membrane potential to neocortical up-down

states Nature Neuroscience, November (2006)

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http://www.eurekalert.org/pub_releases/2006-12/uow-ccr120406.php

Public release date: 4-Dec-2006

Contact: Brad Postle

postle@...

608-262-4330

University of Wisconsin-Madison

Controlling confusion -- Researchers make insight into memory, forgetting

MADISON -- Why do we forget? Do memories decay on their own, or are

they harmed by interference from similar memories? Using a technique

called " transcranial magnetic stimulation " (TMS), brain researchers at

the University of Wisconsin-Madison may have found the answer.

Although the notion of decay makes sense, Brad Postle, assistant

professor of psychology at UW-Madison, says it may be inaccurate.

" Psychologists have known for decades that the intuitive notion of

decay is probably less of a factor in forgetting than is

interference, " he says. Interference occurs, he says, when " other

remembered information disrupts, competes with or confuses the

information that you want to remember. "

Interference is always present, Postle says, but we don't always notice it.

" An obvious case is like yesterday, when a friend was telling me his

cell phone number but actually gave me his home phone number, " he

says. Another scenario is equally familiar: we get most details of the

story right, but misidentify the source. Or we remember that the

quotation comes from Shakespeare, but we name the wrong play.

" Interference is also often to blame, " says Postle, " in cases when we

simply can't remember something. "

If blocking interference is so important to a good memory, where - and

how - does that blocking occur " In a study published in the

Proceedings of the National Academy of Sciences on the week of Dec. 4,

2006, Postle - together with Guilio Tononi of the UW-Madison School of

Medicine and Public Health, and Eva Federoes, a researcher in the

UW-Madison department of psychology - studied how part of the brain's

prefrontal cortex can reduce the disruptive effects of interference.

The prefrontal cortex is responsible for complex thought.

From brain scans, scientists already knew that the sub-region under

study, called the inferior frontal gyrus, or IFG, is active when

volunteers take memory tests while confronting interference. But was

the IFG essential to controlling interference, or was it just

contributing more brain horsepower to complex memory tasks " To answer

that question, the researchers temporarily disrupted the IFG using

TMS, a noninvasive technique that shows potential for treating

depression and other disorders.

" TMS is a technique that allows the induction of a current in the

brain using a magnetic field that passes through the scalp and the

skull safely and painlessly, " says Tononi, a pioneer in refining the

technique for brain research. " TMS can be used to briefly 'scramble'

neural activity in the underlying brain area for a short time,

typically a second or so. This scrambling is fully reversible, and

after the pulsing, the targeted brain area becomes fully functional

again. "

Neuroscientists have traditionally identified the roles of particular

parts of the brain by studying people with brain injury. TMS allows

them to do a similar study on healthy volunteers, Tononi says.

" The great advantage for researchers, " he says, " is that one can test

whether a given brain area is causally involved in producing a given

behavior, but as soon as the current is turned off, the brain returns

to normal. "

In the current study, volunteers read a group of letters ( " F, B, P,

X " ), and were asked a few seconds later whether a particular letter

had appeared in the most recent group ( " Did you just see a 'Z' " " ). In

this type of test, having seen a " Z " in the string-before-last causes

interference that makes the task more difficult. The subjects take

longer to respond, and are more likely to incorrectly say " yes. "

The research set-up was designed to be a simplified version of many

everyday memory challenges, says Postle. Without a good sorting

mechanism, our brains would be utterly confused by the vast amount of

observations, ideas and memories that we have stored away. We might,

for example, dial the phone number of the friend we just called rather

than the one we intended to call.

In previous studies of interference, the IFG consistently lit up in

brain scans, showing that it does something when the memory tries to

deal with interference. But the IFG could simply be contributing some

type of generic processing power to the task, says Postle.

However, the new study proved that the IFG is essential to blocking

interference, he says, because accuracy plummeted when the IFG got a

brief jolt of magnetic stimulation at the exact moment when the

subject was confronting confusion.

Eventually, Postle hopes that locating the site of specific memory

operations in the brain may help the millions of people with declining

memories. " Understanding how the brain controls interference may be a

first step to helping people with memory problems, " he says.

The precise system used to target the magnetic pulse has many other

applications in neuroscience research and treatment, Tononi adds. " TMS

can be used not only to disrupt brain activity, but also to change it.

If applied repeatedly, TMS can strengthen certain circuits that have

become pathologically weak, " he says.

TMS is already being tested to treat severe depression, one of the

most serious psychiatric illnesses. In studying this treatment, he

adds, " It is important to be able to target TMS exactly to the right

area for each individual brain, just as we did in this study. "

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