Biomedical Engineering Reference
In-Depth Information
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Figure 6.7
Microfabricated electrode arrays for brain prostheses.
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(Reprinted with the kind permission of Nature Publishing Group.)
new field known as 'cybernics' that incorporates technological and mechanical
elements from the areas of mechanics, bionics, electronics and robotics.
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In order to detect signals originating in the brain, the structure depicted in
Figure 6.8 suggests a way to overcome di
culties related to the signal intensity
evanescence in time by using electrodes that sense the location of the strongest
neuronal signal and consequently move towards that location. The whole
device is mounted on the skull and employs piezoelectric micromotors to four
electrodes, independently of each other, in one micron increments. In order to
prevent damage to the neurons, the device has a collision avoidance capability
that restricts the movement when the voltage rises rapidly indicating there is
danger of puncturing a neuron. Such implants can decode motor signals in rats
and intention signals in monkeys, and can be fitted onto paralyzed individuals
allowing them to control a computer cursor and navigate the web.
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6.4 Replacing Damaged Brain Components
Scientists not only hope to stimulate brain activity with electronic devices, but
also to replace damaged parts of the brain in individuals who suffer from
epilepsy or Alzheimer's disease and those with brain damage due to strokes.
There are deep ethical concerns that surround the use of devices that mimic
brain activity. These concerns are motivated by the potential effects of such a
device on memory, mood, awareness and consciousness, all of which contribute
to an individual's fundamental identity. Although further research is required
to investigate whether or not brain implants could influence an individual's
personality, high level cognitive brain signals can be decoded with implants. Of
course the precise mechanism through which the brain encodes information
remains elusive. Accordingly, the only strategy open at this point is a low level
of functional mimicry. For example, slices of animal brain can be stimulated
with electrical signals millions of times over until a pattern of inputs and
outputs can be established. Then the information from various slices can be
functionally assembled together, resulting in a mathematical model of a specific
part of the brain. It sounds deeply mechanistic and reductionistic in character,
