Finding unravels nature of cognitive inflexibility in fragile X syndrome

January 22, 2018, New York University
Mice with the genetic defect that causes fragile X syndrome learn and remember normally, but show an inability to learn new information that contradicts what they initially learned, shows a new study by a team of neuroscientists. Credit: iStock/AlexLMX

Mice with the genetic defect that causes fragile X syndrome (FXS) learn and remember normally, but show an inability to learn new information that contradicts what they initially learned, shows a new study by a team of neuroscientists. FXS is the most common genetic cause of intellectual disability and autism.

"These findings suggest that neural circuits in FXS may be fundamentally intact but improperly tuned, which results in inflexibility in gaining certain types of knowledge," explains André Fenton, a professor in New York University's Center for Neural Science and the senior author of the paper, which appears in the journal PLOS Biology. "We now have a better understanding of a cognitive deficit that is characteristic of FXS—excessive recollection of the that was once accurate and an inability to process corrective material."

The study, co-authored with Dino Dvorak, a post-doctoral fellow in NYU's Center for Neural Science, focuses on the hippocampus. This part of the brain is crucial for , especially about space, which requires both encoding and remembering information.

However, because the same neurons are active in both encoding and remembering, it's unknown what neural events control whether hippocampal neurons are encoding current experience into memory or recollecting information from memory. This dynamic is one of the keys to better understanding FXS, which impairs use of memory in multiple ways.

To explore this, first the scientists had to uncover an electrophysiological "signature of recollection" in hippocampus—a mapping that pinpointed whether these neurons are encoding current experience into memory or recollecting information from memory.

This resulted in two primary findings.

Specifically, they found that encoding and recollection are the result of a neural "tug-of-war" between two distinctive types of rhythmic neural synaptic activity within the hippocampus. Notably, encoding occurs when fast rhythmic activity overwhelms slower rhythmic activity; by contrast, recollection occurs when the slower rhythm dominates the medium rhythm.

The second finding, which sheds new light on FXS, shows that FXS have an excessive amount of the slow rhythm.

FXS hippocampus neurons are normal, and, as a result, FXS mice can learn and remember in the ways other mice do. However, due to excessive dominance of the slow rhythm in FXS mice, these mice fail to learn new information that specifically contradicts what they initially learned—in other words, the neural tug-of-war is too often won by the slower rhythm, preventing normal adaptive flexibility of cognitive function.

"This cognitive behavioral inflexibility is characteristic of FXS and autism and now is explained by excessive recollection of the formerly correct but currently incorrect information that is stored in the hippocampus," Fenton observes.

Explore further: Fragile X finding shows normal neurons that interact poorly

More information: Dino Dvorak et al. Control of recollection by slow gamma dominating mid-frequency gamma in hippocampus CA1, PLOS Biology (2018). DOI: 10.1371/journal.pbio.2003354

Related Stories

Fragile X finding shows normal neurons that interact poorly

January 18, 2018
Neurons in mice afflicted with the genetic defect that causes Fragile X syndrome (FXS) appear similar to those in healthy mice, but these neurons fail to interact normally, resulting in the long-known cognitive impairments, ...

How your brain remembers what you had for dinner last night

January 17, 2018
Confirming earlier computational models, researchers at University of California San Diego and UC San Diego School of Medicine, with colleagues in Arizona and Louisiana, report that episodic memories are encoded in the hippocampus ...

Study expands understanding of how the brain encodes fear memory

May 15, 2017
Research published by scientists at the University of California, Riverside on "fear memory" could lead to the development of therapies that reduce the effects of post-traumatic stress disorder (PTSD).

RNG105/Caprin1 is essential for long-term memory formation

November 21, 2017
The research group of Associate Professor Nobuyuki Shiina of the National Institute for Basic Biology have revealed that the function of RNG105 (aka Caprin1) is essential for the formation of long-term memory.

Neurons in the brain tune into different frequencies for different spatial memory tasks

April 17, 2014
Your brain transmits information about your current location and memories of past locations over the same neural pathways using different frequencies of a rhythmic electrical activity called gamma waves, report neuroscientists ...

Neurons can be reprogrammed to switch the emotional association of a memory

October 24, 2014
Memories of experiences are encoded in the brain along with contextual and emotional information such as where the experience took place and whether it was positive or negative. This allows for the formation of memory associations ...

Recommended for you

How social isolation transforms the brain

May 17, 2018
Chronic social isolation has debilitating effects on mental health in mammals—for example, it is often associated with depression and post-traumatic stress disorder in humans. Now, a team of Caltech researchers has discovered ...

Researchers crowdsource brain mapping with gamers, discover six new neuron types

May 17, 2018
With the help of a quarter-million video game players, Princeton researchers have created and shared detailed maps of more than 1,000 neurons—and they're just getting started.

New study sheds light on brain's ability to orchestrate movement

May 17, 2018
To carry out any action, whether playing the piano or dancing the jitterbug, the brain must select and string together a series of small, discrete movements into a precise, continuous sequence.

Cannabidiol significantly reduces seizures in patients with severe form of epilepsy

May 17, 2018
Cannabidiol (CBD), a compound derived from the cannabis plant that does not produce a "high" and has been an increasing focus of medical research, was shown in a new large-scale, randomized, controlled trial to significantly ...

Learning music or speaking another language leads to more efficient brains

May 17, 2018
Whether you learn to play a musical instrument or speak another language, you're training your brain to be more efficient, suggests a Baycrest study.

Old drug provides promising new avenue for treatment of MND

May 17, 2018
An international study led by biochemists at the University of Liverpool has shown that the drug-molecule ebselen can correct many of the toxic characteristics of a protein that causes some cases of hereditary motor neurone ...

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.