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

This Defense Intelligence Reference Document was produced by the Defense Intelligence Agency's Defense Warning Office under the Advanced Aerospace Weapon System Applications program and dated 23 March 2010. It surveys noninvasive and invasive brain-machine interface technologies, including EEG, MEG, fMRI, NIRS and implanted electrode arrays, that could control external devices without limb-operated interfaces. It concludes that noninvasive electrical monitoring is the most promising near-term approach. For the long term it favors invasive single-neuron cortical connections.

From the source: Release of 2026-09-18 Incident: 3/23/10, Las Vegas, Nevada. Released with redactions. This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD surveys brain-machine interface technologies intended to allow users to control external devices without conventional manual controls, and it evaluates both noninvasive and invasive approaches for turning neural or related physiological signals into usable commands. The report reviews the underlying neural signals, distinguishes between open- and closed-loop control systems, and examines technologies including scalp-based electrical recording, magnetic and imaging-based methods, and implanted cortical interfaces, with particular attention to bandwidth, response time, signal quality, and practical usability. It concludes that, in the near term, the most practical systems are likely to be noninvasive electrical approaches that draw heavily on muscle and neural signals, while longer-term high-bandwidth control would likely require more advanced invasive interfaces capable of robust two-way communication with individual neurons. The document presents thought-based control of external devices as a research field with plausible assistive and specialized applications, while emphasizing that naturalistic, high-performance control remained constrained by major technical and physiological limits.

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Direct Neural Signals
The human nervous system has two classes of cells, neurons and glia. Based on all
research to date, it is believed that signals within the network of neurons constitute the
whole of information processing, with gl ial cells playing a purely supporting role. This
neural doctrine has dominated research in BMI until recently and still constitutes the
only major research path in direct technologies. Furthermore, all technologies directly
measuring human neuronal action rely on detecting or influencing electrical activity of
these cells; no current in situ research selectively affects neurotransmitter activity
between local cells for the purpose of information exchange . Therefore, the focus for
the foreseeable future will be on the electrical activity of neurons as the primary target
of BMI.
Neurons consist of four parts: axon, dendrites, cell body or soma, and pre-synaptic
terminals. Electrical information is transmitted to the neuron through the dendrites,
proceeds through the cell body, and leaves the cell through the axon at one or more
pre-synaptic terminals. Neurons have one axon and from one to tens of thousands of
dendrites.
Figure 1. Simplified Rendering of a Neuron. The arrows indicate t he direction in which signals are
conveyed . The single axon conducts signals away from the cell body, while the multiple dendrites receive
signals from the axons of other neurons. The nerve terminals end on the dendrites or cell body of other
neurons or on other cell types, such as muscle or gland cells. (Reference 1)
Chemical details of how the action potentials travel through the cell or are transmitted
across the synapse are not important to the current treatise, other than the distinction
that in these biologically based electrical networks, ions of sodium, potassium, and
chlorine move through the cell membranes perpendicular to the propagation of the
action potential down the axon. This allows information to be transmitted faster than
ions could flow down the axon. The propagation of information is sim il ar to a wave
traveling down a garden hose: quickly move one end of the hose back and forth with
sufficient force, and a wave will travel to the other end of the hose; however, any part
of the hose structure has only moved (nominally) perpendicular to the direction of wave
propagation. In a similar fashion, ions flow through channels across the axon's cell
membrane, changing the local membrane potential and thus propagating the electrical
signal down the axon.
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