How Brain-computer Interfaces Work

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http://computer.howstuffworks.com/brain-computer-interface.htm Follow this article and make notes.

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The easiest and least invasive method is a set of electrodes -- a device known as an electroencephalograph (EEG) -- attached to the scalp. The electrodes can read brain signals. However, the skull blocks a lot of the electrical signal, and it distorts what does get through.

Another way to measure brain activity is with a Magnetic Resonance Image (MRI). An MRI machine is a massive, complicated device. It produces very high-resolution images of brain activity, but it can't be used as part of a permanent or semipermanent BCI. Researchers use it to get benchmarks for certain brain functions or to map where in the brain electrodes should be placed to measure a specific function. For example, if researchers are attempting to implant electrodes that will allow someone to control a robotic arm with their thoughts, they might first put the subject into an MRI and ask him or her to think about moving their actual arm. The MRI will show which area of the brain is active during arm movement, giving them a clearer target for electrode placement.

concept, known as cortical plasticity, means that the brain is able to adapt in amazing ways to new circumstances. Learning something new or partaking in novel activities forms new connections between neurons and reduces the onset of age-related neurological problems. If an adult suffers a brain injury, other parts of the brain are able to take over the functions of the damaged portion.

Why is this important for BCIs? It means that an adult can learn to operate with a BCI, their brain forming new connections and adapting to this new use of neurons. In situations where implants are used, it means that the brain can accommodate this seemingly foreign intrusion and develop new connections that will treat the implant as a part of the natural brain.

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Although we already understand the basic principles behind BCIs, they don't work perfectly. There are several reasons for this.

The brain is incredibly complex. To say that all thoughts or actions are the result of simple electric signals in the brain is a gross understatement. There are about 100 billion neurons in a human brain [source: Greenfield]. Each neuron is constantly sending and receiving signals through a complex web of connections. There are chemical processes involved as well, which EEGs can't pick up on. The signal is weak and prone to interference. EEGs measure tiny voltage potentials. Something as simple as the blinking eyelids of the subject can generate much stronger signals. Refinements in EEGs and implants will probably overcome this problem to some extent in the future, but for now, reading brain signals is like listening to a bad phone connection. There's lots of static. The equipment is less than portable. It's far better than it used to be -- early systems were hardwired to massive mainframe computers. But some BCIs still require a wired connection to the equipment, and those that are wireless require the subject to carry a computer that can weigh around 10 pounds. Like all technology, this will surely become lighter and more wireless in the future.