As information flows through brain's heirarchy, higher regions use
higher frequency waves

Date:
September 8, 2020
Source:
Picower Institute at MIT
Summary:
To produce your thoughts and actions, your brain processes
information in a hierarchy of regions along its surface, or cortex,
ranging from "lower" areas that do basic parsing of incoming
sensations to "higher" executive regions that formulate your plans
for employing that newfound knowledge.

In a new study, neuroscientists seeking to explain how this
organization emerges report two broad trends: In each of three
distinct regions, information encoding or its inhibition was
associated with a similar tug of war between specific brain wave
frequency bands, and the higher a region's status in the hierarchy,
the higher the peak frequency of its waves in each of those bands.



FULL STORY ==========================================================================
To produce your thoughts and actions, your brain processes information
in a hierarchy of regions along its surface, or cortex, ranging from
"lower" areas that do basic parsing of incoming sensations to "higher" executive regions that formulate your plans for employing that newfound knowledge. In a new study, MIT neuroscientists seeking to explain how
this organization emerges report two broad trends: In each of three
distinct regions, information encoding or its inhibition was associated
with a similar tug of war between specific brain wave frequency bands,
and the higher a region's status in the hierarchy, the higher the peak frequency of its waves in each of those bands.


==========================================================================
By making and analyzing measurements of thousands of neurons and
surrounding electric fields in three cortical regions in animals, the
team's new study in the Journal of Cognitive Neuroscience provides a
unifying view of how brain waves, which are oscillating patterns of the activity of brain cells, may control the flow of information throughout
the cortex.

"When you look at prior studies you see examples of what we found in
many regions, but they are all found in different ways in different experiments," said Earl Miller, Picower Professor of Neuroscience in
The Picower Institute for Learning and Memory and senior author of the
study. "We wanted to obtain an overarching picture so that's what we
did. We addressed the question of what does this look like all over the cortex." Added co-first author Mikael Lundqvist of Stockholm University
and MIT: "Many, many studies have looked at how synchronized the phases
of a particular frequency are between cortical regions. It has become
a field by itself, because synchrony will impact the communication
between regions. But arguably even more important would be if regions communicate at different frequencies altogether. Here we find such a
systematic shift in preferred frequencies across regions. It may have
been suspected by piecing together earlier studies, but as far as I know
hasn't been shown directly before. It is a simple but potentially very fundamental observation." The paper's other first author is Picower
Institute postdoc Andre Bastos.

To make their observations the team gave animals the task of correctly distinguishing an image they had just seen -- a simple feat of visual
working memory. As the animals played the game, the scientists measured
the individual spiking activity of hundreds of neurons in each animal
in three regions at the bottom, middle and top of the task's cortical
hierarchy -- the visual cortex, the parietal cortex and the prefrontal
cortex. They simultaneously tracked the waves produced by this activity.



==========================================================================
In each region they found that when an image was either being encoded
(when it was first presented) or recalled (when working memory was
tested), the power of theta and gamma frequency bands of brain waves
would increase in bursts and power in alpha and beta bands would
decrease. When the information had to be held in mind, for instance in
the period between first sight and the test, theta and gamma power went
down and alpha and beta power went up in bursts.

This functional "push/pull" sequence between these frequency bands has
been shown in several individual regions, including the motor cortex,
Miller said, but not often simultaneously across multiple regions in
the course of the same task.

The researchers also observed that the bursts of theta and gamma power
were closely associated with neural spikes that encoded information about
the images. Alpha and beta power bursts, meanwhile, were anti-correlated
with that same spiking activity.

While this rule applied across all three regions, a key difference
was that each region employed a distinct peak within each frequency
band. While the visual cortex beta band, for instance, peaked at 11
Hz, parietal beta peaked at 15 Hz and prefrontal beta peaked at 19
Hz. Meanwhile visual cortex gamma occurred at 65 Hz, parietal gamma
topped at 72 Hz and prefrontal gamma at 80 Hz.

"As you move from the back of the brain to the front, all the frequencies
get a little higher," Miller said.

While both main trends in the study -- the inverse relationships between frequency bands and the systematic rise in peak frequencies within each
band - - were both consistently observed and statistically significant,
they only show associations with function, not causality. But the
researchers said they are consistent with a model in which alpha and
beta alternately inhibit, or release, gamma to control the encoding of information -- a form of top-down control of sensory activity.

Meanwhile, they hypothesize that the systematic increase in peak
frequencies up the hierarchy could serve multiple functions. For instance,
if waves in each frequency band carry information, then it higher
regions would sample at a faster frequency to provide more fine-grained sampling of the raw input coming from lower regions. Moreover, faster frequencies are more effective at entraining those same frequencies in
other regions, giving higher regions an effective way of controlling
activity in lower ones.

"The increased frequency in the oscillatory rhythms may help sculpt
information flow in the cortex," the authors wrote.


========================================================================== Story Source: Materials provided by Picower_Institute_at_MIT. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Mikael Lundqvist, Andre' M. Bastos, Earl K. Miller. Preservation and
Changes in Oscillatory Dynamics across the Cortical
Hierarchy. Journal of Cognitive Neuroscience, 2020; 32 (10):
2024 DOI: 10.1162/jocn_a_01600 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200908113326.htm

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