"As far as we can tell, this is the first time this type of behavior has been reported in cells that are part of a larger organism," says Peter T. Cummings, John R. Hall Professor of Chemical Engineering, who directed the study that is described in the March 10 issue of the Public Library of Science journal PLoS ONE.
The discovery was the unanticipated result of a study the Cummings group conducted to test the hypothesis that the freedom with which different cancer cells move - a concept called motility - could be correlated with their aggressiveness: That is, the faster a given type of cancer cell can move through the body the more aggressive it is.
"Our results refute that hypothesis—the correlation between motility and aggressiveness that we found among three different types of cancer cells was very weak," Cummings says. "In the process, however, we began noticing that the cell movements were unexpectedly complicated."
Then the researchers' interest was piqued by a paper that appeared in the February 2008 issue of the journal Nature titled, "Scaling laws of marine predator search behaviour." The paper contained an analysis of the movements of a variety of radio-tagged marine predators, including sharks, sea turtles and penguins. The authors found that the predators used a foraging strategy very close to a specialized random walk pattern, called a Lévy walk, an optimal method for searching complex landscapes. At the end of the paper's abstract they wrote, "...Lévy-like behaviour seems to be widespread among diverse organisms, from microbes to humans, as a 'rule' that evolved in response to patchy resource distributions."
This gave Cummings and his colleagues a new perspective on the cell movements that they were observing in the microscope. They adopted the basic assumption that when mammalian cells migrate they face problems, such as efficiently finding randomly distributed targets like nutrients and growth factors, that are analogous to those faced by single-celled organisms foraging for food.
With this perspective in mind, Alka Potdar, now a post-doctoral fellow at Case Western Reserve University and the Cleveland Clinic, cultured cells from three human mammary epithelial cell lines on two-dimensional plastic plates and tracked the cell motions for two-hour periods in a "random migration" environment free of any directional chemical signals. Epithelial cells are found throughout the body lining organs and covering external surfaces. They move relatively slowly, at about a micron per minute which corresponds to two thousandths of an inch per hour.
When Potdar carefully analyzed these cell movements, she found that they all followed the same pattern. However, it was not the Lévy walk that they expected, but a closely related search pattern called a bimodal correlated random walk (BCRW). This is a two-phase movement: a run phase in which the cell travels primarily in one direction and a re-orientation phase in which it stays in place and reorganizes itself internally to move in a new direction.
In subsequent studies, currently in press, the researchers have found that several other cell types (social amoeba, neutrophils, fibrosarcoma) also follow the same pattern in random migration conditions. They have also found that the cells continue to follow this same basic pattern when a directional chemical signal is added, but the length of their runs are varied and the range of directions they follow are narrowed giving them a net movement in the direction indicated by the signal.
thinkahol * on 19 Oct 11Brain, bodily awareness, and the emergence of a conscious self: these entities and their relations are explored by Germanphilosopher and cognitive scientist Metzinger. Extensively working with neuroscientists he has come to the conclusion that, in fact, there is no such thing as a "self" -- that a "self" is simply the content of a model created by our brain - part of a virtual reality we create for ourselves. But if the self is not "real," he asks, why and how did it evolve? How does the brain construct the self? In a series of fascinating virtual reality experiments, Metzinger and his colleagues have attempted to create so-called "out-of-body experiences" in the lab, in order to explore these questions. As a philosopher, he offers a discussion of many of the latest results in robotics, neuroscience, dream and meditation research, and argues that the brain is much more powerful than we have ever imagined. He shows us, for example, that we now have the first machines that have developed an inner image of their own body -- and actually use this model to create intelligent behavior. In addition, studies exploring the connections between phantom limbs and the brain have shown us that even people born without arms or legs sometimes experience a sensation that they do in fact have limbs that are not there. Experiments like the "rubber-hand illusion" demonstrate how we can experience a fake hand as part of our self and even feel a sensation of touch on the phantom hand form the basis and testing ground for the idea that what we have called the "self" in the past is just the content of a transparent self-model in our brains. Now, as new ways of manipulating the conscious mind-brain appear on the scene, it will soon become possible to alter our subjective reality in an unprecedented manner. The cultural consequences of this, Metzinger claims, may be immense: we will need a new approach to ethics, and we will be forced to think about ourselves in a fundamentally new way. At
