Neuroscientists illuminate how brain cells 'navigate' in the light and
dark
Brain mechanism identified that tracks angular head motion during
navigation

Date:
November 16, 2021
Source:
Sainsbury Wellcome Centre
Summary:
Researchers have discovered how individual and networks of cells
in an area of the brain called the retrosplenial cortex encode
this angular head motion in mice to enable navigation both during
the day and at night.



FULL STORY ==========================================================================
To navigate successfully in an environment, you need to continuously
track the speed and direction of your head, even in the dark. Researchers
at the Sainsbury Wellcome Centre at UCL have discovered how individual
and networks of cells in an area of the brain called the retrosplenial
cortex encode this angular head motion in mice to enable navigation both
during the day and at night.


========================================================================== "When you sit on a moving train, the world passes your window at the speed
of the motion of the carriage, but objects in the external world are also moving around relative to one another. One of the main aims of our lab
is to understand how the brain uses external and internal information to
tell the difference between allocentric and egocentric-based motion. This
paper is the first step in helping us understand whether individual
cells actually have access to both self-motion and, when available, the resultant external visual motion signals" said Troy Margrie, Associate
Director of the Sainsbury Wellcome Centre and corresponding author on
the paper.

In the study, published today in Neuron, the SWC researchers found that
the retrosplenial cortex uses vestibular signals to encode the speed
and direction of the head. However, when the lights are on, the coding
of head motion is significantly more accurate.

"When the lights are on, visual landmarks are available to better estimate
your own speed (at which your head is moving). If you can't very reliably encode your head turning speed, then you very quickly lose your sense
of direction.

This might explain why, particularly in novel environments, we become much worse at navigating once the lights are turned out," said Troy Margrie.

To understand how the brain enables navigation with and without visual
cues, the researchers recorded from neurons across all layers in the retrosplenial cortex as the animals were free to roam around a large
arena. This enabled the neuroscientists to identify neurons in the
brain called angular head velocity (AHV) cells, which track the speed
and direction of the head.

Sepiedeh Keshavarzi, Senior Research Fellow in the Margrie Lab, and lead
author on the paper, also then recorded from these same AHV neurons during head-fixed conditions to allow the removal of specific sensory/motor information. By comparing very precise angular head rotations in the
dark and in the presence of a visual cue (vertical gratings), with the
results of the freely-moving condition, Sepiedeh was able to determine
the while vestibular inputs alone can generate head angular velocity
signals, their sensitivity to head motion speed is vastly improved when
visual information is available.

"While it was already known that the retrosplenial cortex is involved in
the encoding of spatial orientation and self-motion guided navigation,
this study allowed us to look at integration at both a network and
cellular level. We showed that a single cell can see both kinds of
signals: vestibular and visual.

What was also critically important was the development of a behavioural
task that enabled us to determine that mice improve their estimation of
their own head angular speed when a visual cue is present. It's pretty compelling that both the coding of head motion and the mouse's estimates
of their motion speed both significantly improve when visual cues are available," commented Troy Margrie.

The next steps will be to explore the pathways that bring vestibular
and visual information to the retrosplenial cortex and where these
signals might be relayed to. We now know there is, for example, a strong feedback loop with primary visual cortex that also receives motor signals relating to running speed. Future experiments designed to isolate and manipulate specific types of neural activity will inform us as to how
the cortex disambiguates self-motion generated signals from allocentric
ones, a process that is critical to how we navigate through a complex
visual world.

This research was funded by the Sainsbury Wellcome Centre Core Grant from
the Gatsby Charity Foundation (GAT3361) and Wellcome Trust (090843/F/09/Z
and 214333/Z/18/Z).

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


========================================================================== Journal Reference:
1. Sepiedeh Keshavarzi, Edward F. Bracey, Richard A. Faville, Dario
Campagner, Adam L. Tyson, Stephen C. Lenzi, Tiago Branco, Troy W.

Margrie. Multisensory coding of angular head velocity
in the retrosplenial cortex. Neuron, 2021; DOI:
10.1016/j.neuron.2021.10.031 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211116111409.htm

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