Box 1. Human brain–machine applications

From the following article:

Man, machine and in between

Jens Clausen

Nature 457, 1080-1081(26 February 2009)

doi:10.1038/4571080a

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Deep brain stimulation (DBS)

Electrical signals generated in a central computing unit (CCU) placed subcutaneously are sent to electrodes implanted deeply in the brain to stimulate specific structures, such as the subthalamic nucleus in patients with Parkinson's disease.

Research directions: DBS is being extended to earlier stages of Parkinson's disease and to some other neurological impairments, including epilepsy, minimally conscious states and psychiatric disorders.

Cochlear implants

Acoustic signals are recorded by an external microphone and sent to a CCU placed outside the skull (containing a speech processor and a radio transmitter) to generate electrical impulses. These are sent wirelessly to a receiver inside the skull and stimulate the auditory nerve at the internal neural interface — an electrode implanted into the cochlea in the inner ear.

Research directions: for those whose auditory nerve is damaged, similar devices implanted into acoustically relevant areas of the brainstem or the midbrain are being tested clinically.

Retinal implants

Visual signals are recorded through light-sensitive diodes that stimulate the remaining cells of the retina. Alternatively, external signals recorded by camera are sent to an implant directly interfaced with the optic nerve. Some visual prostheses bypass the retina and stimulate the visual cortex.

Research directions: external power sources may be needed to provide the electrical stimulation required by some of these implants. Technologies for providing this power are being investigated.

Brain–machine interface-based motor prostheses

Motor signals are recorded through electrodes implanted in the brain and sent to a CCU, which computes and generates signals to direct an artificial limb.

Research directions: animal experiments are becoming widespread. In experiments in patients with epilepsy, epicortical grid electrodes are placed on the surface of the brain to examine and improve decoding algorithms.

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