Weizmann creates artificial nerve networks

Metal electrodes will measure what goes on inside the brain in hopes of finding cures to blindness or epilepsy.

By JUDY SIEGEL-ITZKOVICH
neuron 88 (photo credit: )
neuron 88
(photo credit: )
Scientists have already hooked brains directly to computers using metal electrodes in the hope of measuring what goes on inside the brain and healing conditions such as blindness or epilepsy. In the future, the interface might be based on nerve cells grown for that purpose. In research featured on the cover of Nature Physics, Prof. Elisha Moses of the Weizmann Institute's physics of complex systems department and his former research students Drs. Ofer Feinerman and Assaf Rotem have taken the first step in this direction by creating circuits and logic gates made of live nerves grown in the lab. When neurons are grown in culture, they don't form complex "thinking" networks. Moses, Feinerman and Rotem wondered whether the physical structure of the nerve network could be designed to be more "brain-like." To simplify things, they grew a model nerve network in one dimension only - by getting the neurons to grow along a groove etched in a glass plate. The scientists found they could stimulate these cells using a magnetic field (as opposed to other systems of lab-grown neurons that only react to electricity). Experimenting further with the linear setup, the group found that varying the width of the neuron stripe affected how well it sends signals. Nerve cells in the brain are connected to great numbers of other cells through their long, thin extensions called axons, and must receive a minimum number of incoming signals before they fire one off. The researchers identified a threshold thickness, one that allowed the development of around 100 axons. Below this number, the chance of a response was iffy, while just a few over this number greatly raised the chance a signal would be passed on. The scientists then took two thin stripes of around 100 axons each and created a "logic gate" similar to one in a computer. Both of these "wires" were connected to a small number of nerve cells. When the cells received a signal along just one of the "wires," the outcome was uncertain; but a signal sent along both "wires" was assured of a response. This type of structure is known as an AND gate. The next structure the team created was slightly more complex: Triangles fashioned from the neuron stripes were lined up in a row - point to rib - in a way that forced the axons to develop and send signals in one direction only. Several of these segmented shapes were then attached together in a loop. The regular relay of signals around the circuit turned it into a sort of biological clock or pacemaker. Moses notes: "We have been able to enforce simplicity on an inherently complicated system. Now we can ask what nerve cells grown in culture need to be able to carry out complex calculations. "As we find answers, we get closer to understanding the conditions needed for creating a synthetic, many-neuron 'thinking' apparatus." RATING CLOTHING FOR WARMTH When buying a winter coat, shoppers can get a pretty good idea of what the garment looks like. Knowing how warm it will keep them, however, takes guesswork, especially if ordering over the Internet or from catalogues. US manufacturers and importers put temperature ratings on jackets, coveralls and other such products, says Prof. Elizabeth McCullough, a textile expert at Kansas State University and co-director of its Institute for Environmental Research. Manufacturers have different methods to determine those temperature ratings, she adds. "At Kansas State, we do most of the testing for manufacturers like The North Face and L.L. Bean, but everybody wants it done a different way," McCullough notes. "One may do the testing of a jacket worn over a lightweight ensemble, the other over a heavyweight ensemble. Other manufacturers may put a range of comfort based on the person's activity level." She is chairing a committee in the American Society for Testing and Materials to develop a standard formula for determining temperature ratings for cold-weather clothing. The goal is to let consumers compare one product to another. "What we're trying to do is to guide people in the purchasing process," McCullough says. "The other thing is to provide safety. We're trying to prevent people from getting hypothermia."