AAWSAP DIRD, Technological Approaches to Controlling External Devices, March 2010

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Developing complex neural networks on top of chips prior to implant.
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Development of chronic electrode materials such as biopolymers that may be
suitable for implant without an ex-vivo grown sheath.
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Creating a biological to biological interface upon implant.
This technology does still rely on proximal sensing and stimulation of action potentials,
but the neural tissue at the biological to physical interface is engineered rather than
native, thus providing the opportunity to develop an effective bridging network to
seamlessly integrate between the two systems. Development of such chronic implant
capability could make feasible the nondestructive addition of cerebellar pathways for
control activity that incorporates the huge potential of brain plasticity without adding
significant cognitive burden on the prefrontal cortex. This would effectively turn the
controlled device into part of the body as far as the brain is concerned.
IMPLANTABLE CHIPS, LADDERS AND ARRAYS
Research utilizing ECoG or neocortical ladder array technology is the state of the art in
neural communication. However, stimulating nerves or peripheral pathways in this
matter without damage to the receiving cells has proven difficult. Even in cochlear
arrays, normal functioning of the surrounding tissue is lost and only a fraction of the
quality of natural stimulation is available. Locating single neurons has also been
challenging, though new electrode designs are being developed. These devices will
continue to be useful for research applications such as better understanding of network
structure and network function in conjunction with fMRI. BMI application will continue in
the foreseeable future to be limited to instances where closed-loop with visual or other
traditional sensory feedback is sufficient. Until new electrode designs develop a robust
method of two-way communication with single neurons, they will not be the dominant
BMI technology for use in normal, healthy individuals.
Conclusions
The gamut of modern technologies that connect neural systems to physical systems has
been surveyed, with attention to the underlying physiological signals. Many examples
have been presented of studies illustrating the different research paths under way. Two
of these technologies show the most promise of near term and long term successful
high-bandwidth integration of brain and external systems.
In the near term, noninvasive electrical sensors that primarily rely on EMG signals, but
also include those weaker signals directly from neuronal firing, are expected to
dominate real-world applications. The decoding of these signals from just a handful of
dry sensors can produce a large combination of on-off and variable strength control
commands that should surpass the information capability of traditional electro­
mechanical interfaces in the next 5 years. This technology is limited, however, by the
number of available EMG sites and the required coherent firing of very large numbers of
neurons. To surpass these limitations, technologies capable of connections to individual
neurons on a large scale will be necessary.
In the far term, an invasive approach to establish high-bandwidth duplex
communication networks, 5-20 bits/second, using interfaces with single neurons
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