Linking sight and movement
Researchers key in on finding that can help self-driving cars 'see'

Date:
August 14, 2020
Source:
Harvard University
Summary:
Researchers found that image-processing circuits in the primary
visual cortex not only are more active when animals move freely,
but that they receive signals from a movement-controlling region
of the brain that is independent from the region that processes
what the animal is looking at.



FULL STORY ==========================================================================
To get a better look at the world around them, animals constantly are
in motion. Primates and people use complex eye movements to focus their
vision (as humans do when reading, for instance); birds, insects, and
rodents do the same by moving their heads, and can even estimate distances
that way. Yet how these movements play out in the elaborate circuitry of neurons that the brain uses to "see" is largely unknown. And it could be
a potential problem area as scientists create artificial neural networks
that mimic how vision works in self-driving cars.


==========================================================================
To better understand the relationship between movement and vision,
a team of Harvard researchers looked at what happens in one of the
brain's primary regions for analyzing imagery when animals are free
to roam naturally. The results of the study, published Tuesday in the
journal Neuron, suggest that image-processing circuits in the primary
visual cortex not only are more active when animals move, but that they
receive signals from a movement-controlling region of the brain that is independent from the region that processes what the animal is looking
at. In fact, the researchers describe two sets of movement- related
patterns in the visual cortex that are based on head motion and whether
an animal is in the light or the dark.

The movement-related findings were unexpected, since vision tends to
be thought of as a feed-forward computation system in which visual
information enters through the retina and travels on neural circuits
that operate on a one-way path, processing the information piece by
piece. What the researchers saw here is more evidence that the visual
system has many more feedback components where information can travel
in opposite directions than had been thought.

These results offer a nuanced glimpse into how neural activity works
in a sensory region of the brain, and add to a growing body of research
that is rewriting the textbook model of vision in the brain.

"It was really surprising to see this type of [movement-related]
information in the visual cortex because traditionally people have
thought of the visual cortex as something that only processes images,"
said Grigori Guitchounts, a postdoctoral researcher in the Neurobiology Department at Harvard Medical School and the study's lead author. "It
was mysterious, at first, why this sensory region would have this representation of the specific types of movements the animal was making."
While the scientists weren't able to definitively say why this happens,
they believe it has to do with how the brain perceives what's around it.



==========================================================================
"The model explanation for this is that the brain somehow needs to
coordinate perception and action," Guitchounts said. "You need to
know when a sensory input is caused by your own action as opposed to
when it's caused by something out there in the world." For the study, Guitchounts teamed up with former Department of Molecular and Cellular
Biology Professor David Cox, alumnus Javier Masis, M.A. '15, Ph.D.

'18, and postdoctoral researcher Steffen B.E. Wolff. The work started in
2017 and wrapped up in 2019 while Guitchounts was a graduate researcher
in Cox's lab. A preprint version of the paper published in January.

The typical setup of past experiments on vision worked like this: Animals,
like mice or monkeys, were sedated, restrained so their heads were in
fixed positions, and then given visual stimuli, like photographs, so researchers could see which neurons in the brain reacted. The approach
was pioneered by Harvard scientists David H. Hubel and Torsten N. Wiesel
in the 1960s, and in 1981 they won a Nobel Prize in medicine for their
efforts. Many experiments since then have followed their model, but it
did not illuminate how movement affects the neurons that analyze.

Researchers in this latest experiment wanted to explore that, so they
watched 10 rats going about their days and nights. The scientists placed
each rat in an enclosure, which doubled as its home, and continuously
recorded their head movements. Using implanted electrodes, they measured
the brain activity in the primary visual cortex as the rats moved.

Half of the recordings were taken with the lights on. The other half were recorded in total darkness. The researchers wanted to compare what the
visual cortex was doing when there was visual input versus when there
wasn't. To be sure the room was pitch black, they taped shut any crevice
that could let in light, since rats have notoriously good vision at night.



==========================================================================
The data showed that on average, neurons in the rats' visual cortices
were more active when the animals moved than when they rested, even in
the dark. That caught the researchers off guard: In a pitch-black room,
there is no visual data to process. This meant that the activity was
coming from the motor cortex, not an external image.

The team also noticed that the neural patterns in the visual cortex that
were firing during movement differed in the dark and light, meaning they weren't directly connected. Some neurons that were ready to activate in
the dark were in a kind of sleep mode in the light.

Using a machine-learning algorithm, the researchers encoded both
patterns. That let them not only tell which way a rat was moving its head
by just looking at the neural activity in its visual cortex, but also
predict the movement several hundred milliseconds before the rat made it.

The researchers confirmed that the movement signals came from the motor
area of the brain by focusing on the secondary motor cortex. They
surgically destroyed it in several rats, then ran the experiments
again. The rats in which this area of the brain was lesioned no longer
gave off signals in the visual cortex.

However, the researchers were not able to determine if the signal
originates in the secondary motor cortex. It could be only where it
passes through, they said.

Furthermore, the scientists pointed out some limitations in their
findings. For instance, they only measured the movement of the head,
and did not measure eye movement. The study is also based on rodents,
which are nocturnal. Their visual systems share similarities with humans
and primates, but differ in complexity.

Still, the paper adds to new lines of research and the findings could potentially be applied to neural networks that control machine vision,
like those in autonomous vehicles.

"It's all to better understand how vision actually works," Guitchounts
said.

"Neuroscience is entering into a new era where we understand that
perception and action are intertwined loops. ... There's no action without perception and no perception without action. We have the technology
now to measure this." This work was supported by the Harvard Center
for Nanoscale Systems and the National Science Foundation Graduate
Research Fellowship.


========================================================================== Story Source: Materials provided by Harvard_University. Original written
by Juan Siliezar.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Grigori Guitchounts, Javier Masi's, Steffen B.E. Wolff, David Cox.

Encoding of 3D Head Orienting Movements in the Primary Visual
Cortex.

Neuron, 2020; DOI: 10.1016/j.neuron.2020.07.014 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200814123211.htm

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