From Daydreams to Reality: Brain’s Alertness Mechanism Unlocked

Summary: Researchers discovered how the brain transitions from daydreaming to alertness through activity in the dentate gyrus, also contributing to memory formation. This mechanism serves as the brain’s method for realigning our cognitive focus to immediate realities and processing new information.

The study, which analyzed mouse models, found that dentate spikes in the hippocampus are crucial for this shift and for associating memories with sensory stimuli. These findings could lead to new insights into neuropsychiatric disorders and the development of targeted treatments.

Key Facts:

  1. The dentate gyrus is key for switching from daydreaming to alertness and forming associative memories.
  2. Dentate spikes occur during “offline” brain states, helping process new information and orient to the environment.
  3. This research offers potential new perspectives on conditions like ADHD, PTSD, epilepsy, and Alzheimer’s disease.

Source: Boston Children’s Hospital

When we daydream, we must be able to snap back to attention at a moment’s notice. Researchers at Boston Children’s Hospital uncovered how our brains can do things like react to a question when we’re daydreaming: firing activity in part of the brain called the dentate gyrus keeps us focused on what’s happening in our environment. And the team found that the same neural activity also helps with forming memories.

The findings were published in Nature on March 13, 2024.

This shows a man and a thought bubble.
This new knowledge about dentate spikes could open windows into some neuropsychiatric disorders. Credit: Neuroscience News

“We have found a brain mechanism for breaking up periods of mind wandering and realigning the ‘cognitive map’ back to reality,” says Jordan Farrell, PhD, an investigator in the F.M. Kirby Neurobiology Center and Rosamund Stone Zander Translational Neuroscience Center at Boston Children’s.

It’s known that during sleep or periods of daydreaming, our brains replay past events in a form of synchronized activity known as the “sharp-wave ripple.” This enables us to consolidate our memories.

Analyzing data from a mouse model, Farrell and colleagues from the laboratory of Ivan Soltesz, PhD, at Stanford University began exploring another, little-known neuronal activity pattern: synchronized spikes of firing in the dentate gyrus, part of the hippocampus.

These spikes, they found, occur when an “offline” brain is aroused. They may help us quickly process new information and orient ourselves to what’s happening in our environment.

But dentate spikes also seem to promote associative memory — in which a sensory stimulus (say, a series of loud beeps) is stored as a memory, so that we come to associate the noise with a smoke alarm going off and the possible need to evacuate.

Sharp-wave ripples and dentate spikes may have complementary roles, Farrell says. “The brain is toggling through these two states.”

This new knowledge about dentate spikes could open windows into some neuropsychiatric disorders. Perhaps dentate spikes affect attention and arousal in people with attention-deficit/hyperactivity disorder or post-traumatic stress disorder. Or maybe they are altered in Alzheimer’s disease, disrupting formation of new memories.

Farrell is most interested in epilepsy, which is marked by synchronized spikes of excessive neuron firing. He plans to investigate the role of dentate spikes by better understanding their basic mechanisms and then manipulating the neural networks that control dentate spikes in the brains of epileptic mice. He also hopes to extend the study to children with epilepsy, in collaboration with clinicians at Boston Children’s.

“In people with epilepsy, the synchronous activity during dentate spikes could tip the brain into a pathological state,” Farrell speculates. “The dentate spikes add an extra push to the system.”

About this alertness and neuroscience research news

Author: Gina Mantica
Source: Boston Children’s Hospital
Contact: Gina Mantica – Boston Children’s Hospital
Image: The image is credited to Neuroscience News

Original Research: Open access.
Neural and behavioural state switching during hippocampal dentate spikes” by  Jordan Farrell et al. Nature


Neural and behavioural state switching during hippocampal dentate spikes

Distinct brain and behavioural states are associated with organized neural population dynamics that are thought to serve specific cognitive functions.

Memory replay events, for example, occur during synchronous population events called sharp-wave ripples in the hippocampus while mice are in an ‘offline’ behavioural state, enabling cognitive mechanisms such as memory consolidation and planning.

But how does the brain re-engage with the external world during this behavioural state and permit access to current sensory information or promote new memory formation?

Here we found that the hippocampal dentate spike, an understudied population event that frequently occurs between sharp-wave ripples, may underlie such a mechanism.

We show that dentate spikes are associated with distinctly elevated brain-wide firing rates, primarily observed in higher order networks, and couple to brief periods of arousal. Hippocampal place coding during dentate spikes aligns to the mouse’s current spatial location, unlike the memory replay accompanying sharp-wave ripples.

Furthermore, inhibiting neural activity during dentate spikes disrupts associative memory formation. Thus, dentate spikes represent a distinct brain state and support memory during non-locomotor behaviour, extending the repertoire of cognitive processes beyond the classical offline functions.

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