Tuesday, June 10, 2008
Recognizing relatives is also helpful for avoiding inbreeding.
Until recently, the ability to recognize kin has been attributed exclusively to animals. But last year, Susan Dudley, at McMaster University in Hamilton, Ontario, reported on the “secret social life” of the American sea rocket, a dune-dwelling plant with little purple flowers, found on the beaches of the Great Lakes.
Dr. Dudley and her graduate student Amanda File found that sea rockets grow more roots when they share a pot with strangers than when they are potted with relatives.
By growing more roots, plants increase their competitive ability underground. Plants with more roots are better at soaking up water and nutrients.
So sea rockets purposely leave more space in the pot for their relatives, giving them a better chance to access water and nutrients. But when a stranger is nearby, they have no inhibitions about hogging all the resources.
Sea rockets seem to recognize their neighbors based on some cue in the roots, since plants potted individually do not change their root-growing behavior when non-relatives are placed in nearby pots.
Since Dr. Dudley published her findings, kin recognition has been demonstrated in several other plant species.
Plants have several different ways of sensing their neighbors. They can detect changes in light, caused by absorption of particular wavelengths by neighboring plants. They can also detect chemicals released by other plants into the soil or air.
One parasitic weed, the dodder, which thrives on nutrients extracted from other plants, actually grows towards its victims, a behavior startlingly similar to hunting.
Plants may be more aware of their surroundings than we’d like to admit. Scientists have known for 100 years that plants send electrical signals from one part of the plant to another. But nobody knows what these signals are for.
Sensory plant biology has blossomed into a hot topic, with a deep rift separating scientists who believe that plants have some sort of sensory-nervous system, and those who maintain that intelligence is limited to animals.
Attributing intelligent or planned behavior to plants may seem a stretch, but maybe plants are smarter than we think. We just haven’t noticed, because they move orders of magnitude slower than we do.
(photo from Harold Davis on flickr.com)
Sunday, June 8, 2008
As with most of biology’s wonders, we take our coordination for granted. We see something we want; we reach out and grab it. Even if the desired object is moving, like a glass of champagne on the tray of a passing waiter. How do our brains do it?
Our brains analyze the visual target (the approaching glass), make an estimate of its velocity, and send a signal to the arm and hand to reach out and grasp. The grasping has to be timed precisely, and the hand has to open the right amount. We use a different grasping motion for a wine glass than for a beer mug.
Amazingly, scientists now know enough about these brain signals to tap into them and use them to control artificial limbs.
A team of scientists headed by Andrew Schwartz at the
The monkeys were first trained to control the prosthetic arm using a joystick. The arm had 6 degrees of freedom; three at the shoulder, one at the elbow, and one at the hand.
Once they got the feel for the arm, the monkeys were implanted with electrode arrays situated on the part of the brain that controls arm and hand movement. The prosthetic arm was hooked up to the monkey and controlled by the signals recorded from the electrodes.
After several weeks of training, the monkeys were able to grasp bits of food held out to them by a researcher, and put the food into their mouths. The monkeys’ arms were restrained to keep them from grabbing the food with their own hands.
The monkeys got very comfortable eating with the prosthetic limb. They even licked their prosthetic fingers when bits of marshmallow stuck to them. There are some nice videos of the monkeys in action here.
Prosthetics which are controlled by nerve signals already exist for humans, but they intercept the nerve signals at the shoulder. They’re great for patients with amputated arms, and they’ve made remarkable progress, allowing users to grasp objects and move individual fingers.
Brain-computer interfaces exist for patients with locked-in syndrome, which is a syndrome in which patients are awake and aware, but cannot move or communicate. Generally, these interfaces allow patients to move a cursor on a computer screen, and thus communicate with the outside world.
Tapping brain signals to control prosthetic limbs will someday help paralyzed patients to regain movement.