Loving memory: Catching on to the slow gamma wave

New research into memory transmission may impact treatment of schizophrenia and Alzheimer’s

Gamma rhythms can be likened to the ocean’s waves advancing and receding. More surfers can catch the slower waves, just as more information can be saved on a slow gamma. Photograph: Getty Images

Gamma rhythms can be likened to the ocean’s waves advancing and receding. More surfers can catch the slower waves, just as more information can be saved on a slow gamma. Photograph: Getty Images

 

When it comes to memory retrieval, slow and steady wins the race. At least that is the finding from research at the University of Texas in Austin. Scientists have found a mechanism, which essentially compresses information needed for memory retrieval, imagination or planning and encodes it on a brain wave frequency that is separate from the one used for recording real-time experiences.

Featured in a recent edition of the journal Neuron, the findings are counter to what was previously believed about how memory is transmitted to and from the hippocampus.

Situated in the medial temporal lobe of the brain, the hippocampus is the centre of emotion, memory and the autonomic nervous system. It is crucial to the organisation of data, both for our short-term and long-term memories.

Like a conscientious editor, it brings all the memories gathered each day and tries to make something coherent out of it all. The hippocampus is assisted in this process by gamma rhythms – a type of brain wave that helps co-ordinate the activity of different brain cells acting together to carry out various functions.

Two types of gamma rhythms assist: low frequency (or slow) gamma and high frequency (or fast) gamma. It was widely understood that slow gamma rhythms carried less information than faster gamma, because there were fewer transmissions in any given cycle.

“The traditional viewpoint has been that one piece of information would be represented per gamma wave,” explains Laura Colgin, assistant professor of neuroscience, at the Centre for Learning and Memory at the University of Texas (UT), Austin.

From this it was assumed that faster gamma waves were getting more data to the hippocampus than their slower counterparts simply because they were working faster. Upon closer scrutiny, however, the scientists found the opposite. Slower gamma is able to carry several pieces of data per cycle while fast gamma can carry only one unit of information.

Surf’s up

“Think about a line of surfers at the beach,” says Colgin. “They’re all waiting to catch a wave but they’re coming in so fast, there’s room for only one surfer to catch each wave before it breaks.

“If the ocean swell reduces, the waves break more slowly so more surfers can catch the same wave. Because they come slowly, several surfers can surf a wave at the same time.

“Likewise, when the brain has an episode of slow gamma rhythms, a sequence of place cells should actually be coding a shorter path length within a certain amount of time. There are fewer slow gamma waves occurring within that time period, because it is at a lower frequency rhythm.” In short, units of information have more time to catch a ride on slow gamma.

“When the cell on the fast gamma cycle becomes active it may want to connect with another cell during earlier learning but there’s no time,” she says.

“There can only be that one piece of information represented in the cycle. “On the slower waves, however, the longer periods allow for cells to be more active. To put it another way, there is more time for a cell to activate another cell that it was aligned with earlier.”

Slow gamma mental compression is not dissimilar to the process of compressing files on a computer. However, like digital compression, when a previously compressed mental memory is replayed, the representation will likely have far less detail than the original source material.

Health implications

Colgin and the research team believe the findings could help explain why people with schizophrenia, who are experiencing disrupted gamma rhythms, have difficulty distinguishing between imagined and real experiences.

“Maybe they are transmitting their own imagined thoughts on the wrong frequency, the one usually reserved for things that are really happening.”

The UT research team has started follow-on research based on a mouse model with Alzheimer’s disease. “Very preliminary research has shown some disruptions in the selection of one type of gamma and not in the other that could possibly be significant,” says Colgin.

“At this point, it is just speculation, but perhaps the cells in the brain of someone with Alzheimer’s may not be co-ordinated in the same way during slow gamma frequency and this could possibly relate to why there is a problem with memory retrieval.”

The Irish Times Logo
Commenting on The Irish Times has changed. To comment you must now be an Irish Times subscriber.
SUBSCRIBE
GO BACK
Error Image
The account details entered are not currently associated with an Irish Times subscription. Please subscribe to sign in to comment.
Comment Sign In

Forgot password?
The Irish Times Logo
Thank you
You should receive instructions for resetting your password. When you have reset your password, you can Sign In.
The Irish Times Logo
Please choose a screen name. This name will appear beside any comments you post. Your screen name should follow the standards set out in our community standards.
Screen Name Selection

Hello

Please choose a screen name. This name will appear beside any comments you post. Your screen name should follow the standards set out in our community standards.

The Irish Times Logo
Commenting on The Irish Times has changed. To comment you must now be an Irish Times subscriber.
SUBSCRIBE
Forgot Password
Please enter your email address so we can send you a link to reset your password.

Sign In

Your Comments
We reserve the right to remove any content at any time from this Community, including without limitation if it violates the Community Standards. We ask that you report content that you in good faith believe violates the above rules by clicking the Flag link next to the offending comment or by filling out this form. New comments are only accepted for 3 days from the date of publication.