Running cockroaches start to recover from being shoved
sideways before their dawdling nervous system kicks in to tell their legs what
to do, researchers have found. These new insights on how biological systems
stabilise could one day help engineers design steadier robots and improve
doctors' understanding of human gait abnormalities.
In experiments, the roaches were able to maintain their
footing mechanically—using their momentum and the spring-like architecture of
their legs, rather than neurologically, relying on impulses sent from their
central nervous system to their muscles.
"The response time we observed is more than three times
longer than you'd expect," said Shai Revzen, an assistant professor of
electrical engineering and computer science, as well as ecology and
evolutionary biology, at the University of Michigan. Revzen is the lead author
of a paper on the findings published online in Biological Cybernetics. It will
appear in a forthcoming print edition.
"What we see is that the animals' nervous system is
working at a substantial delay," he said. "It could potentially act a
lot sooner, within about a thirtieth of a second, but instead, it kicks in
after about a step and a half or two steps—about a tenth of a second. For some
reason, the nervous system is waiting and seeing how it shapes out."
How the study was done
To arrive at their findings, the researchers sent 15
cockroaches (one-by-one, in 41 trials) running across a small bridge onto a
placemat-sized cart on wheels. The cart was attached to an elastic cord that
was pulled tight like a loaded slingshot and held in place with a strong magnet
on the other side. Once a roach was about a body length onto the cart, the
researchers released the magnet, sending the cart hurling sideways.
The force was equivalent to a sumo wrestler hitting a jogger
with a flying tackle, said Revzen, adding that cockroaches are much more stable
To gather detailed information about the roaches' gait, the
researchers utilized a technique Revzen developed several years ago called
kinematic phase analysis. It involves using a high-speed camera to constantly
measure the position of each of the insects' six feet as well as the ends of
its body. A computer program then merges the continuous data from all these
points into an accurate estimate of where the roach is in its gait cycle at all
The approach gives scientists a more detailed picture than
just measuring the timing of footfalls—a common metric used today to study
In kinematic phase analysis, the signals are converted into a
wave graph that illustrates the insect's movement pattern. The pattern only
changes when the nervous system kicks in. How do the researchers know this? In
a separate but similar experiment, they implanted electrodes into the legs of
seven cockroaches to measure nerve signals.
The nervous-system delay the researchers observed is
substantially longer than scientists expected, Revzen said. And it runs
contrary to assumptions in the robotics community, where computers stand in for
brains and the machines' movements are often guided by continuous feedback to
that computer from sensors on the robots' feet.
Implications of the
Revzen said the new findings might imply that the biological
brain, at least in cockroaches, adjusts the gait only at whole-step intervals
rather than at any point in a step. Periodic, rather than continuous, feedback
systems might lead to more stable (not to mention energy-efficient) walking
robots—whether they travel on two feet or six.
Robot makers often look to nature for inspiration. As
animals move through the world, they have to respond to unexpected disturbances
like rocky, uneven ground or damaged limbs. Revzen and his team believe that
patterns in how they move as they adjust could give away how their machinery
and neurology work together.
"The fundamental question is, 'What can you do with a
mechanical suspension versus one that requires electronic feedback?"
Revzen said. "The animals obviously have much better mechanical designs
than anything we know how to build. But if we could learn how they do it, we
might be able to reproduce it."
More than 70 percent of Earth's land surface isn't navigable
by wheeled or tracked vehicles, so legged robots could potentially bridge the
gap for ground-based operations like search and rescue and defence.
For human gait analysis, Revzen and colleagues said their
noninvasive, high-resolution kinematic phase approach could be valuable in the
"Falls are a primary cause for deterioration in the
elderly," Revzen said. "Anything we can do to understand gait
pathology and stabilization of gait is very valuable."
These experiments were conducted at the University of
California, Berkeley, before Revzen came to U-M. The work was funded by the
National Science Foundation.