Nav: Home

Dyslexia linked to shorter memory trace of previous stimuli

January 24, 2017

Researchers have provided new insight into the brain mechanisms underlying a condition that causes reading and writing difficulties.

Humans have a type of long-term memory (called 'implicit memory') that means we respond less to stimuli as they are repeated over time, in a process called neural adaptation. But the new research suggests that dyslexics recover faster than non-dyslexics from their responses to stimuli such as sounds and written words, leading to their perceptual and reading difficulties. The discovery could pave the way for earlier diagnosis and intervention of the condition.

Dyslexia is a common learning difficulty that affects one in every 10 to 20 people in the UK alone, impacting their ability to read and spell words but not affecting their general intelligence. Researchers from the Hebrew University of Jerusalem, led by Professor Merav Ahissar of the Psychology Department and The Edmond & Lily Safra Center for Brain Sciences, decided to carry out a number of experiments with dyslexics and non-dyslexics to shine new light on the mechanisms behind this condition.

"While dyslexics are mainly diagnosed according to their reading difficulty, they also differ from non-dyslexics in performing simple perceptual tasks, such as tone-frequency discrimination," says first author Sagi Jaffe-Dax.

"Our lab previously found that this is due to 'poor anchoring', where dyslexics have an inefficient integration of information from recent stimuli, collected as implicit memory. This memory typically forms 'anchors' that provide specific predictions that clarify noisy stimuli, and we wanted to see why this is not the case in dyslexics," says Ahissar.

In the current study, the team gave 60 native Hebrew speakers, including 30 dyslexics and 30 non-dyslexics, frequency discrimination and oral reading tasks. During the frequency-discrimination task, participants were asked to compare two tones in each trial. All participants' responses were affected, or biased, by implicit memory of previous stimuli. Both groups were affected in similar ways by very recent stimuli, but dyslexics were less affected by earlier stimuli.

"This suggests that implicit memory decays faster among dyslexics," says Jaffe-Dax. "We decided to test this hypothesis by increasing the length of time between consecutive stimuli and measuring how it affects behavioral biases and neural responses from the auditory cortex, a section of the brain that processes sound.

"Participants with dyslexia showed a faster decay of implicit memory on both measures. This also affected their oral reading rate, which decreased faster as a result of the time interval between reading the same nonword - a group of letters that looks or sounds like a word - numerous times."

The team concludes that dyslexics' faster recovery from stimuli can account for their longer reading times, as it causes less reliable predictions for both simple and complex stimuli.

Co-author Orr Frenkel explains: "The formation of adequate predictions is crucial for becoming an expert in general, and an expert reader in particular. Achieving this depends on matching printed words with predictions based on previous encounters with related words, but such predictions are less accurate in dyslexics.

"However, while shorter implicit memory means they are unable to yield efficient predictions, it may be advantageous with unexpected stimuli, such as novel events in a sequence of predictable, familiar events. Further studies will be needed if we are to establish whether this is indeed the case."
-end-
Reference

The paper 'Dyslexics' faster decay of implicit memory for sounds and words is manifested in their shorter neural adaptation' can be freely accessed online at http://dx.doi.org/10.7554/eLife.20557. Contents, including text, figures, and data, are free to reuse under a CC BY 4.0 license.

Media contacts

Emily Packer, eLife
e.packer@elifesciences.org
+44 1223 855373

Avivit Delgoshen, The Hebrew University of Jerusalem
avivit.delgoshen@mail.huji.ac.il
+972 2 5881641

About eLife

eLife is a unique collaboration between the funders and practitioners of research to improve the way important research is selected, presented, and shared. eLife publishes outstanding works across the life sciences and biomedicine -- from basic biological research to applied, translational, and clinical studies. All papers are selected by active scientists in the research community. Decisions and responses are agreed by the reviewers and consolidated by the Reviewing Editor into a single, clear set of instructions for authors, removing the need for laborious cycles of revision and allowing authors to publish their findings quickly. eLife is supported by the Howard Hughes Medical Institute, the Max Planck Society, and the Wellcome Trust. Learn more at elifesciences.org.

eLife

Related Brain Articles:

Scientists predict the areas of the brain to stimulate transitions between different brain states
Using a computer model of the brain, Gustavo Deco, director of the Center for Brain and Cognition, and Josephine Cruzat, a member of his team, together with a group of international collaborators, have developed an innovative method published in Proceedings of the National Academy of Sciences on Sept.
BRAIN Initiative tool may transform how scientists study brain structure and function
Researchers have developed a high-tech support system that can keep a large mammalian brain from rapidly decomposing in the hours after death, enabling study of certain molecular and cellular functions.
Wiring diagram of the brain provides a clearer picture of brain scan data
In a study published today in the journal BRAIN, neuroscientists led by Michael D.
Blue Brain Project releases first-ever digital 3D brain cell atlas
The Blue Brain Cell Atlas is like ''going from hand-drawn maps to Google Earth'' -- providing previously unavailable information on major cell types, numbers and positions in all 737 brain regions.
Landmark study reveals no benefit to costly and risky brain cooling after brain injury
A landmark study, led by Monash University researchers, has definitively found that the practice of cooling the body and brain in patients who have recently received a severe traumatic brain injury, has no impact on the patient's long-term outcome.
More Brain News and Brain Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#537 Science Journalism, Hold the Hype
Everyone's seen a piece of science getting over-exaggerated in the media. Most people would be quick to blame journalists and big media for getting in wrong. In many cases, you'd be right. But there's other sources of hype in science journalism. and one of them can be found in the humble, and little-known press release. We're talking with Chris Chambers about doing science about science journalism, and where the hype creeps in. Related links: The association between exaggeration in health related science news and academic press releases: retrospective observational study Claims of causality in health news: a randomised trial This...