Biomedical engineering

Bionic rats at Polytechnique

This fall, the Polystim laboratory at École Polytechnique, affiliated with the Université de Montréal, is commencing in vivo trials of its visual cortex stimulator in rats. Combining computer technology and microelectronics, this engineering gem—the size of a pinhead—may give vision to the blind.

Now fully set up in the new Pierre Lassonde Building at École Polytechnique, Mohamad Sawan, founder and director of the Polystim neurotechnology laboratory, holds between his fingers the fruit of six years of work: a two millimetre square matrix and 16 perfectly aligned microelectrodes. “This matrix is connected to a computer module that controls the signals as well as another wireless control. This fully implantable unit is very flexible: several of them can be interconnected and dispersed according to cerebral convolutions. This is advanced electronics,” states Prof. Sawan.

This stimulator can send information directly to the visual cortex in the brain without going through the eye and optical nerve. In fact, a camera replaces the eye and transmits the visual signal via an external image processing unit to the microelectrodes.

A dozen members at Polystim are preparing to test the device. “This fall, we will use rats to test the activation of phosphenes and to make sure that the electronic module functions properly. This is a crucial step for us,” explains Prof. Sawan.

A phosphene is a relatively intense point of light that enters the visual field. Its position in space must correspond to its position in the visual field. But, how does one detect if a rat sees a point of light? “Going on the principle that a rat immersed in a pool of water will look for a way out, we will indicate its exit path by stimulating its cortex accordingly,” explains Prof. Sawan. If the blind rat finds the exit according to the activation of phosphenes, the principle will be validated.

According to the same principle, during a clinical trial conducted at the National Institute of Health in the United States in the mid-1990s, a blind patient was able to recognize the characters formed using a matrix of 38 thin wires inserted in his visual cortex. “Introducing an image into the brain is no simple matter. Furthermore, how do you introduce it in such as way that the cortex interprets it correctly? None of this is very well documented at this point,” states Prof. Sawan, who calls his research experimental. That’s why another team at the Polystim laboratory is working on recording activity in the cortex in order to obtain a detailed electroencephalogram. This involves the opposition of simulation, but with a seeing subject. “We are curious to see what happens when information enters the visual cortex. For example, what stimulation pattern is generated when a subject is put in a dark room and a light is turned on?”

While knowledge is still patchy and there is insufficient data to understand how the brain processes visual signals, the engineer still hopes to be able to perfect a functional system that can be used in humans by 2010. “In the medical field, we talk in terms of 15 to 20 years before putting a product on the market. It takes a lot of motivation to get there. One doesn’t embark on this kind of project hoping to be able to solve problems from one day to the next, particularly when dealing with vision and the brain, with its 10 billion neurons!” Last July, the École Polytechnique de Montréal hosted the 10th Conference of the International Functional and Electrical Stimulation Society. Chaired by Mohamad Sawan, the event brought together some 200 bioengineers, clinicians and therapists to discuss advances in technomedicine.