Marc Verha
Sat, Jun-30-07, 06:16
Resolving Head Rotation for Human Bipedalism RC Fitzpatrick,
JE Butler & BL Day 2006 Current Biology
Alignment of the body to the gravitational vertical is
considered to be the key to human bipedalism. However, changes
to the semicircular canals during human evolution [1-3]
suggest that the sense of head rotation that they provide is
important for modern human bipedal locomotion. When walking,
the canals signal a mix of head rotations associated with path
turns, balance perturbations, and other body movements. It is
uncertain how the brain uses this information. Here, we show
dual roles for the semicircular canals in balance control and
navigation control. We electrically evoke a head-fixed virtual
rotation signal from semicircular canal nerves [4-6] as
subjects walk in the dark with their head held in different
orientations. Depending on head orientation, we can either
steer walking by 'remote control' or produce balance
disturbances. This shows that the brain resolves the canal
signal according to head posture into Earth-referenced
orthogonal components and uses rotations in vertical planes to
control balance and rotations in the horizontal plane to
navigate. Because the semicircular canals are concerned with
movement rather than detecting vertical alignment, this result
shows the importance of movement control and agility rather
than precise vertical alignment of the body for human
bipedalism.
JE Butler & BL Day 2006 Current Biology
Alignment of the body to the gravitational vertical is
considered to be the key to human bipedalism. However, changes
to the semicircular canals during human evolution [1-3]
suggest that the sense of head rotation that they provide is
important for modern human bipedal locomotion. When walking,
the canals signal a mix of head rotations associated with path
turns, balance perturbations, and other body movements. It is
uncertain how the brain uses this information. Here, we show
dual roles for the semicircular canals in balance control and
navigation control. We electrically evoke a head-fixed virtual
rotation signal from semicircular canal nerves [4-6] as
subjects walk in the dark with their head held in different
orientations. Depending on head orientation, we can either
steer walking by 'remote control' or produce balance
disturbances. This shows that the brain resolves the canal
signal according to head posture into Earth-referenced
orthogonal components and uses rotations in vertical planes to
control balance and rotations in the horizontal plane to
navigate. Because the semicircular canals are concerned with
movement rather than detecting vertical alignment, this result
shows the importance of movement control and agility rather
than precise vertical alignment of the body for human
bipedalism.