Summary: Increasing synchronization among neurons in an upstream brain region that sends information markedly improves the fidelity and processing of that information in downstream regions.
Source: Bar-Ilan University
In the early 20th century, researchers first began measuring brain activity using electrodes on the scalp. They discovered slow and fast rhythmic patterns of electrical activity—now commonly referred to as “brain waves.”
Since that discovery, brain waves have been intensively studied for their role in coordinating information flow between distinct brain regions. In healthy brains, changes in wave intensity and frequency accompany many cognitive functions, including memory formation and learning.
Alterations in wave patterns are also associated with neurological conditions. For example, Alzheimer’s disease often shows a pronounced drop in activity at specific frequencies, while epilepsy is linked to abrupt increases in activity at other frequencies. Autism and other disorders are likewise associated with atypical oscillatory activity.
Brain waves reflect synchronized firing of large groups of neurons. When many neurons fire together, the resulting increase in wave intensity is thought to represent coordinated activity that supports information transfer. But how exactly does synchronization improve information transmission and processing across brain regions?
A new study led by doctoral student Tal Dalal in the laboratory of Prof. Rafi Haddad at the Gonda Multidisciplinary Brain Research Center, Bar-Ilan University, directly addresses this question.
Published in Cell Reports, the study experimentally manipulated the level of synchronization in an upstream olfactory brain region and measured how those changes affected information flow and representation in a downstream area responsible for higher-level processing.
The research focused on the olfactory system, which naturally exhibits strong oscillatory activity. Within the olfactory bulb, a subset of inhibitory neurons—granule cells—plays a key role in generating synchronized γ (gamma) oscillations that shape the output of mitral and tufted cells (MTCs), the principal excitatory neurons that relay odor information forward.
To control synchronization, the team used optogenetics, a precise method that turns specific neurons on or off in response to light flashes. This allowed selective activation or suppression of the granule cells that induce synchrony, enabling the researchers to change synchronization independently from overall firing rates.
They designated the manipulated area as the “upstream” region—where initial odor processing and synchronization occur—and the downstream target as the piriform cortex, which integrates and refines odor representations for higher-order processing.
The main finding was clear: enhancing synchronization in the upstream region substantially improved the transfer and representation of odor information in downstream neurons. Increased γ-synchrony led to stronger, more reliable cortical responses and better discrimination of odor ensembles. In contrast, reducing synchronization impaired downstream odor representations.
An unexpected observation emerged: activating the synchrony-inducing granule cells actually lowered overall firing rates in the upstream region. One might expect reduced activity to degrade information transfer, yet the synchronized output more than compensated for this reduction and enhanced downstream processing.
Tal Dalal explains the effect with a simple analogy: synchronized neurons are like a large, organized demonstration in a public square—coordinated and powerful—whereas asynchronous neural activity resembles isolated individuals spread out across a city. The impact of coordinated activity is far greater than that of independent, scattered firing.
These results provide causal evidence that synchronization improves the reliability and power of information transmission between brain areas. When thousands of neurons align their activity, downstream regions receive clearer, less variable signals that improve processing, even if the total number of spikes is reduced.
This work may help explain why reduced synchrony and weakened oscillatory power are linked to cognitive decline in neurodegenerative conditions such as Alzheimer’s disease. Previous studies reported correlations between decreased synchrony and cognitive impairment; this study demonstrates a mechanistic pathway by which loss of synchrony can degrade information flow and thus contribute to deficits.
The findings also open potential therapeutic avenues. In principle, restoring proper synchrony through targeted stimulation of specific neuron types could improve information processing in affected brain networks. While the study used optogenetics in mice, the concept suggests future strategies to correct abnormal rhythms in human neurological disorders.
The study’s implications extend to understanding how coordinated network activity supports sensory processing and cognition, and why disruption of that coordination can lead to functional decline.
About this information processing research news
Author: Elana Oberlander
Source: Bar-Ilan University
Contact: Elana Oberlander – Bar-Ilan University
Image: The image is credited to Tal Dalal
Original Research: Open access. “Upstream synchronization enhances odor processing in downstream neurons” by Tal Dalal et al., Cell Reports.
Abstract
Upstream synchronization enhances odor processing in downstream neurons
Highlights
- Modulating granule cell activity separates MTC odor-evoked γ-synchrony from changes in firing rates.
- Increasing MTC γ-synchrony enhances piriform cortex odor responses despite a reduction in MTC spikes.
- Decreasing γ-synchrony degrades piriform cortex odor responses.
- Interactions between granule cells and MTCs are sufficient and necessary to enhance piriform cortex odor processing.
Summary
Gamma-band oscillatory activity is widespread across brain regions, and many studies have proposed that γ-synchrony enhances sensory information transfer. Direct causal evidence, however, has been scarce. In this study, the authors test that hypothesis in the mouse olfactory system. Local GABAergic granule cells in the olfactory bulb shape mitral/tufted cell output, and by optogenetically modulating granule cell activity the researchers dissociate MTC γ-synchronization from firing rate changes.
Recordings from downstream piriform cortex neurons show that enhancing MTC γ-synchronization increases cortical odor-evoked firing rates, reduces response variability, and improves ensemble odor representation. These benefits occur even though MTC firing rates fall. Conversely, reducing MTC γ-synchronization without altering firing rates degrades piriform cortex odor responses. These findings provide causal evidence that increased γ-synchronization enhances the transmission of sensory information between brain regions.