Brain-Machine Interface ( BMI )

Thursday, July 16, 2009 |

Brain-Machine Interface ( BMI ) - an inside look

The Majority of motor function in our body r driven by electrical currents originating in the brain motor cortex & conducted through the spinal cord & peripheral nerves to yhe muscles, where the electrical impluse is converted to motion by the contraction & retraction of specific muscles. for eg, to bend the arm at the elbow joint , the biceps muscles contraction & the triceps relaxes. This seemingly simple movement. The neurons, following a cognitive decision to bend the arm, generate an electric impluse through the peripheral nerves, causing the correct muscles to contract or relax.

The term used for neuronal activity is "action potential". Action potential occurs when an electric impluse shoots through the long shaft of the neuron called the Axon. Each neuron has one axon but is connected to many other neurons through chemical connections called synapses & can influence other neurons or b influenced itself by the activity of adjacent neurons , creating an extremely complex network of neural cells.

BMIs can b divided into 2 main group : noninvasive & invasive.

Noninvasive BMIs

Noninvasive BMIs rely on reading the brains activity without actually piercing the brain surface. The EEG is one of the earliest noninvasive BMIs , measuring the combined activity of massive groups of brain neurons through voltage difference b/w diff. parts of the brain. The EEG is performed by placing approx. 20 electrodes on the scalp; these electrodes r connected by wires to an amplier , through which the signal is converted to a digital reading , which can then b filtered by a computer to remove any artifical interfernce. Once connected to the EEG, the subject can b show diff. stimuli & brain electrical patterns in response to the stimuli can b studied.

EEGs have many shortcomings, due to much overlapping of electrical activity in the brain as well as electrical artifacts. To achieve better resolution , electrodes can b inserted b/w the skull & brain , without piercing the brain tissuse & can allegedly achieve a higher resolution of brain activity.

Invasive BMIs

While noninvasive BMIs achieve a vague picture of a subjects intention & state of mind by reading the activity of massive groups of neurons, invasive BMIs r able to read the activity at a much higher resolution , up to the activity of a single neuron.

The main challenge in creating a BMI is deciphering the firing "code" & converting it to a meaningful movement. An electrode inserted into the appropriate region of the brain cortex can measure the voltage of many adjacent cells & with the use of electronic filters, it can isolate the voltage of a single cell. It is then potentially possible to determine the "preffered direction" of a certain cell in a humans brain by measuring the firing rate as the subject moves his or her hand in diff. directions. The preffered direction of a cell is the direction the hand is moving when the firing rate of that cell is at its highest. In clinical trials involing monkeys, the problem with this type of reading was it varied greatly from trial to trial , even though the movement executed was virtually identical.

The Future of BMI

One of the next chalenges in the field of BMI prosthetics is making them feel like normal limbs. A normal limb has a sense of touch & proprioception , the process by which sensory feedback to the brain transmits the location & position of the body muscles, allowing us to b aware of the arms position without having to look. This is accomplished by an array of receptors in the muscles & joints , as well as mechanical receptors in the skin , that enable us to kown when we r touching an object . The next generation of the prosthetic arms will hv proprioception & feeling , generating feedback pulses to the brain or the nerve ending that will result in their bearers hv an almost natural feel to their bionic limb.

BMI technologies r not only confined to prosthetic & paralyzed limbs. In the future , BMIs may allow blind people to see using an artifical picture capturing device, much like a camera. several methods for visual prothetics hv already been used sucessfully with patients. These methods use a computer chip implanted on the retina that is fed by a miniature camera on a patients glasses. The chip stimulates the optic nerves , transmitting a picture to the brain. Devices used today allow patients to see vague shapes or distinguish light from dark but future devices, such as the cortical visual prosthesis.

BMI - Brain Machine Inteface has a very Bright Future , it will fill colours & joy in many Lifes.
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