• Neuroscientists illuminate how brain cel

    From ScienceDaily@1:317/3 to All on Tue Nov 16 21:30:38 2021
    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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