Summary: New research reveals that individual neurons in the hippocampus can respond to both slow and fast brain waves at the same time by switching between different firing modes. This process, called interleaved resonance, allows brain cells to encode complex information by using bursts for slower theta waves and single spikes for faster gamma waves.
These findings offer a deeper understanding of how the brain organizes thoughts related to navigation and memory. The discovery may have far-reaching implications for neurological conditions like Alzheimer’s, epilepsy, and schizophrenia.
Key Facts:
- Dual Coding Mechanism: Neurons can simultaneously respond to both theta and gamma waves using distinct firing modes.
- Flexible Firing: Cells switch between bursts and single spikes based on internal ion currents and timing.
- Clinical Implications: Disruption of this tuning system may underlie cognitive deficits in neurological diseases.
Source: FAU
The brain is constantly mapping the external world like a GPS, even when we don’t know about it. This activity comes in the form of tiny electrical signals sents between neurons — specialized cells that communicate with one another to help us think, move, remember and feel.
These signals often follow rhythmic patterns known as brain waves, such as slower theta waves and faster gamma waves, which help organize how the brain processes information.
Understanding how individual neurons respond to these rhythms is key to unlocking how the brain functions related to navigation in real time – and how it may be affected in disease.
A new study by Florida Atlantic University and collaborators from Erasmus Medical Center, Rotterdam, Netherlands, and the University of Amsterdam, Netherlands, has uncovered a surprising ability of brain cells in the hippocampus to process and encode and respond to information from multiple brain rhythms at once.
The research, published in PLOS Computational Biology, reveals how a single neuron can switch between firing single spikes and rapid bursts depending on both its internal properties and the brain’s ongoing electrical activity – a phenomenon the researchers have termed “interleaved resonance.”
This discovery offers a new understanding of how the brain organizes thoughts for navigation, memories and behaviors and may have important implications for neurological conditions that are implicated to spatial memory and learning such as epilepsy, Alzheimer’s disease and schizophrenia.
The study focused on CA1 pyramidal neurons – a type of brain cell critical for memory formation and spatial navigation – how we figure out where we are and how to get from one place to another. These cells communicate by firing electrical impulses, either as isolated single spikes or as rapid bursts.
Each firing mode carries different types of information and is associated with specific behavioral contexts. Until now, the factors that determine when and how these neurons switch between modes were poorly understood.
Using advanced computational modeling and cutting-edge voltage imaging of real brain activity, the researchers demonstrated that neurons can respond to both theta (slow) and gamma (fast) brain wave inputs at the same time – but in different ways.
The result is a form of double-coding, where a neuron uses bursts to resonate with theta waves and single spikes to resonate with gamma waves – both simultaneously embedded in the same electrical signal.
“Our models show that a single neuron can behave like a multi-band radio, tuning in to different frequencies and changing its behavior accordingly,” said Rodrigo Pena, Ph.D., senior author, an assistant professor of biological sciences, within FAU’s Charles E. Schmidt College of Science on the John D. MacArthur Campus in Jupiter, and a member of the FAU Stiles-Nicholson Brain Institute.
“It’s a much more flexible and powerful system than we previously imagined.”
The team found that this behavior is influenced by the neuron’s internal settings – specifically, the levels of three ion-driven currents: persistent sodium, delayed rectifier potassium and hyperpolarization-activated current.
By adjusting these internal conductances, neurons can shift their resonance preferences between theta and gamma waves, and between burst and single-spike firing.
Additionally, neurons were more likely to fire bursts after long silent periods, introducing a time-dependent element to how information is encoded.
“This ability to ‘double code’ offers a new perspective on how the brain efficiently organizes and transfers information and could have broad implications for neurological conditions where brain rhythms are disrupted,” said Pena.
“If neurons are misfiring or unable to switch between single spikes and bursts appropriately, it could interfere with how memories are formed or how attention is directed. If we understand how neurons naturally adjust to different brain rhythms, then we can start to think about how to restore that flexibility in conditions where it’s lost.”
The findings also shed light on long-standing questions in neuroscience, including how spatial memory is formed in the hippocampus, and underscore the complexity and adaptability of the brain.
Previous research showed that theta and gamma rhythms influence when and how neurons fire as an animal moves through space.
This new work shows that neurons are not locked into one firing mode but can dynamically shift their response depending on both external input and their internal electrical environment.
In other words, a single neuron isn’t limited to sending just one type of signal – it can carry multiple layers of information depending on the context.
“The brain’s building blocks are far more dynamic than once thought,” said Pena.
“A neuron can simultaneously follow different brain rhythms, adjusting its firing patterns to match the needs of the moment.
“This discovery not only advances our understanding of how the brain works but could one day help guide treatments aimed at restoring healthy neural function when things go wrong.”
Study co-authors are César C. Ceballos, Ph.D., first author and a postdoctoral fellow, FAU Charles E. Schmidt College of Science; Nourdin Chadly, Ph.D., Erasmus Medical Center and University of Amsterdam; and Erik Lowet, Ph.D., an assistant professor, Neuroscience Department, Erasmus Medical Center.
About this neuroscience research news
Author: Gisele Galoustian
Source: FAU
Contact: Gisele Galoustian – FAU
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Interleaved single and bursting spiking resonance in neurons” by Rodrigo Pena et al. PLOS Computational Biology
Abstract
Interleaved single and bursting spiking resonance in neurons
Under in vivo conditions, CA1 pyramidal cells from the hippocampus display transitions from single spikes to bursts.
It is believed that subthreshold hyperpolarization and depolarization, also known as down and up-states, play a pivotal role in these transitions.
Nevertheless, a central impediment to correlating suprathreshold (spiking) and subthreshold activity has been the technical difficulties associated this type of recordings, even with widely used calcium imaging or multielectrode recordings.
Recent work using voltage imaging with genetically encoded voltage indicators has been able to correlate spiking patterns with subthreshold activity in a variety of CA1 neurons, and recent computational models have been able to capture these transitions.
In this work, we used a computational model of a CA1 pyramidal cell to investigate the role of intrinsic conductances and oscillatory patterns in generating down and up-states and their modulation in the transition from single spiking to bursting.
Specifically, we observed the emergence of distinct spiking resonances between these two spiking modes that share the same voltage traces in the presence of theta or gamma oscillatory inputs, a phenomenon we call interleaved single and bursting spiking resonance.
We noticed that these resonances do not necessarily overlap in frequency or amplitude, underscoring their relevance for providing flexibility to neural processing.
We studied the conductance values of three current types that are thought to be critical for the bursting behavior: persistent sodium current (INaP) and its conductance GNaP, delayed rectifier potassium (IKDR) and its conductance GKDR, and hyperpolarization-activated current (Ih) and its conductance Gh.
We conclude that the intricate interplay of ionic currents significantly influences the neuronal firing patterns, transitioning from single to burst firing during sustained depolarization.
Specifically, the intermediate levels of GNaP and GKDR facilitate spiking resonance at gamma-frequency inputs.
The resonance characteristics vary between single and burst firing modes, each displaying distinct amplitudes and resonant frequencies.
Furthermore, low GNaP and high GKDR values lock bursting to theta frequencies, while high GNaP and low GKDR values lock single spiking to gamma frequencies.
Lastly, the duration of quiet intervals plays a crucial role in determining the likelihood of transitioning to either bursting or single spiking modes.
We confirmed that the same features were present in previously recorded in vivo voltage-imaging data.
Understanding these dynamics provides valuable insights into the fundamental mechanisms underlying neuronal excitability under in vivo conditions.
