Rat head direction cell responses in zero-gravity parabolic flight
Title
Rat head direction cell responses in zero-gravity parabolic flight
Publication Type
Journal Article
Year of Publication
2004
Journal
J. Neurophysiol.
Volume
92
Pagination
2887-2997
MVL Report Number
04.10
Abstract
Astronauts working in zerogravity
(0-G) often experience visual reorientation illusions (VRIs).
For example, when floating upside down, they commonly misperceive
the spacecraft floor as a ceiling and have a reversed sense of direction.
Previous studies have identified a population of neurons in the rat’s
brain that discharge as a function of the rat’s head direction (HD) in
a gravitationally horizontal plane and is dependent on an intact
vestibular system. Our goal was to characterize HD cell discharge
under conditions of acute weightlessness. Seven HD cells in the
anterior dorsal thalamus were monitored from rats aboard an aircraft
in 0-G parabolic flight. Unrestrained rats locomoted in a clear plexiglas
rectangular chamber that had wire mesh covering the floor,
ceiling, and one wall. The chamber and surrounding visual environment
were relatively up-down symmetrical. Each HD cell was recorded
across forty 20-s episodes of 0-G. All HD cells maintained a
significant direction-specific discharge when the rat was on the chamber
floor during the 0-G and also during the hypergravity pull-out
periods. Three of five cells also showed direction-specific responses
on the wall in 1-G. In contrast, direction-specific discharge was
usually not maintained when the rat locomoted on the vertical wall or
ceiling in 0-G. The loss of direction-specific firing was accompanied
by an overall increase in background firing. However, while the rat
was on the ceiling, some cells showed occasional bursts of firing when
the rat’s head was oriented in directions that were flipped relative to
the long axis of symmetry of the chamber compared with the cell’s
preferred firing direction on the floor. This finding is consistent with
what might be expected if the rat had experienced a VRI. These
responses indicate that rats maintain a normal allocentric frame of
reference in 0-G and 1-G when on the floor, but may lose their sense
of directional heading when placed on a wall or ceiling during acute
exposures to 0-G.
(0-G) often experience visual reorientation illusions (VRIs).
For example, when floating upside down, they commonly misperceive
the spacecraft floor as a ceiling and have a reversed sense of direction.
Previous studies have identified a population of neurons in the rat’s
brain that discharge as a function of the rat’s head direction (HD) in
a gravitationally horizontal plane and is dependent on an intact
vestibular system. Our goal was to characterize HD cell discharge
under conditions of acute weightlessness. Seven HD cells in the
anterior dorsal thalamus were monitored from rats aboard an aircraft
in 0-G parabolic flight. Unrestrained rats locomoted in a clear plexiglas
rectangular chamber that had wire mesh covering the floor,
ceiling, and one wall. The chamber and surrounding visual environment
were relatively up-down symmetrical. Each HD cell was recorded
across forty 20-s episodes of 0-G. All HD cells maintained a
significant direction-specific discharge when the rat was on the chamber
floor during the 0-G and also during the hypergravity pull-out
periods. Three of five cells also showed direction-specific responses
on the wall in 1-G. In contrast, direction-specific discharge was
usually not maintained when the rat locomoted on the vertical wall or
ceiling in 0-G. The loss of direction-specific firing was accompanied
by an overall increase in background firing. However, while the rat
was on the ceiling, some cells showed occasional bursts of firing when
the rat’s head was oriented in directions that were flipped relative to
the long axis of symmetry of the chamber compared with the cell’s
preferred firing direction on the floor. This finding is consistent with
what might be expected if the rat had experienced a VRI. These
responses indicate that rats maintain a normal allocentric frame of
reference in 0-G and 1-G when on the floor, but may lose their sense
of directional heading when placed on a wall or ceiling during acute
exposures to 0-G.