Different types of memory and epilepsy

This article discusses different types of brainwaves, and how they relate to epilepsy.

Our long-term memory is consolidated when we sleep. Short-term memory traces in the hippocampus, an area deep in the brain, are then relocated to more outer parts of the brain. An international team of neuroscientists, among who Mathilde Bonnefond and Til Ole Bergmann from the Donders Institute at Radboud Universiy, now shows how a three-step brain oscillation plays an important part in that process. Nature Neurosciences publishes the results on September 21st.

Bonnefond and Bergmann specialize in research on oscillations: waves of brain activity. 'Non-rapid eye movement (NREM) sleep is responsible for the memory consolidation during our sleep', Bonnefond explains. 'NREM is known for its very slow oscillations (SOs). Other types of oscillations are hidden inside these SOs. We discovered that three types of oscillations are nested inside each other in the hippocampus and have a joint function.'

Slow waves, spindles and ripples

Slow oscillations only happen about once per second (~0.75 Hz). In a specific time frame within these SOs, Bergmann, Bonnefond and their colleagues found clusters of oscillations of an intermediate speed: the so called spindles which happen about 15 times per second (12 -- 16 Hz). And within these spindles, they found clusters of superfast oscillations called ripples, which happen about 90 times per second (80 -- 100 Hz), and which reflect the local reactivation of the memory trace to be shuttled to the cortex.

To summarize: SOs contain spindles, which in their turn contain ripples. 'Earlier studies only coupled these oscillation types in pairs', Bonnefond explains. 'But now, we see that SOs, spindles and ripples are functionally coupled in the hippocampus. And we hypothesize that they provide fine-tuned temporal frames for the transfer of memory traces to the neocortex.'

Epilepsy

The group of researchers investigated the process in human epilepsy patients during natural sleep. Doctors were looking for the brain areas responsible for their epilepsy, and the current research was done at the same time: with special electrodes, the researchers recorded oscillations from inside the brain. Bonnefond: 'This was a great opportunity to investigate the hippocampus, since it's difficult to measure deep brain regions with classical electrophysiological techniques.'

The patients did not have to remember any specific information. 'You're consolidating memories every night, so we investigated the process in general. The next step would be to link these clustered oscillations to specific memories.'

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Study: Brain waves may help to determine autism severity

A recent study shows that the severity of autism may  be determined by brainwaves. This is a small study and not ready for prime-time.
JR

Measuring how quickly a child's brain processes sounds might help identify the severity of autism, according to a new study.

Observing children's brainwaves may also allow identification of autism earlier than is currently possible, the study authors reported.

"The finding that the brain's response to certain types of information is associated with autism severity is hugely promising," said senior researcher Sophie Molholm, an associate professor of pediatrics and neuroscience at Albert Einstein College of Medicine in New York City.

"A major goal of autism research is to develop measurements to diagnose the disorder as early as possible, and that can help to identify areas of weakness, and strength, so that treatments can be optimized," Molholm said. "Our work shows that measuring brain activity is a viable approach to achieving these goals."

The findings were published in the Sept. 22 online edition of the Journal of Autism and Developmental Disabilities.

Approximately one in 68 children has been diagnosed with an autism spectrum disorder, according to the U.S. Centers for Disease Control and Prevention. But the experience of autism for these children differs significantly in terms of their symptoms and impairments.

Molholm's past research found that among children with autism, the brain takes slightly longer -- measured only in milliseconds -- to process sounds, sights and other sensory information.

In this study, Molholm and her colleagues measured this processing speed in 43 children with autism, aged 6 to 17, using electroencephalograms, or EEG (brain wave) recordings. When the children were shown an image, played a tone or provided a tone and image at the same time, they pressed a button while the EEG recorded how quickly their brains registered the stimulus.

Then Molholm's team compared the children's visual, audio and audiovisual processing speeds to the severity of their symptoms. The researchers based their assessment of autism symptom severity on how great the children's social-communication difficulties were, how severe their repetitive behaviors were and how restricted their interests were.

The more severe the children's symptoms were, the study found, the slower the children processed sounds. There was also a connection between how slow children processed combined audiovisual stimuli and the severity of symptoms, but there was no difference in how quickly they processed the images by themselves, according to the study.

"As we develop EEG probes that measure areas of dysfunction, or even areas that individuals with autism are unusually good at, we should be able to use them as tools to help diagnose autism," Molholm said.

This study's particular finding on audio and audiovisual processing, however, would only apply to those with slower sensory processing. That may not necessarily include all individuals with autism spectrum disorders, she said.

In addition, the association seen in the study does not prove a cause-and-effect relationship.

One autism expert expressed optimism about the study, but noted it has some significant limitations.

"The finding is intriguing and may well open new areas of researching the problems those with autism spectrum disorders have in interacting with their environment," said Dr. Glen Elliott. He is a clinical professor of psychiatry at Stanford School of Medicine and chief psychiatrist and medical director of the Children's Health Council.

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"An objective measure of autism severity would, indeed, be a boon -- for example, allowing regional centers to set a cut-off of who does and does not qualify for services, even if they meet criteria for autism spectrum disorder," Elliott said.

Molholm said she plans to continue looking at ways that EEGs can be used to assess individuals with autism spectrum disorders.

The more precise these tools can become, then the more information they might be able to provide long before it's currently possible to diagnose autism based on behavior.

"We imagine that once developed, these will be used in conjunction with clinically based diagnostics, at least for the foreseeable future," Molholm said. "However, the hope is to get to the point where they can be used for very early diagnosis."

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