Measuring Human Capabilities An Agenda for Basic Research on the Assessment of Individual and Group Performance Potential for Military Accession (2015) / Chapter Skim
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Appendix D: Neural Signals and Measurement Technologies
Appendix D: Neural Signals and Measurement Technologies
Pages 247-258
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From page 247... ...
Direct Neural Signals In these bio-electric networks, ions of sodium, potassium, and chlorine move through the cell membranes perpendicular to the propagation of the action potential down the axon. This electrical signaling allows information to be transmitted faster than ions could flow down the axon.
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From page 248... ...
Action potentials have durations of 1-10 msec. Input signals can result in transmission of multiple action potentials, and thus the frequency and number of neuronal firings do vary with the input.
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From page 249... ...
signal requires the coherent firing of tens of thousands of neurons, while electrical detection of a single neuronal firing requires that a measurement probe be placed proximal to the neuron of interest, such that the probe is closer to that neuron than to any adjacent neuron. Obviously this requires opening or mechanical penetration of the skull, and that is outside the parameters of application for widespread assessment.
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The hemodynamic response, by changing the net ratio of oxyhemoglobin to deoxyhemoglobin in the local venous structure, thus changes the local magnetic susceptibility and local infrared resonance spectra around focused brain activity. This complex chain reaction is called the Blood Oxygen Level Dependent (BOLD)
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The two direct-measure technologies are EEG, which detects mainly surface currents from relative voltage changes at or just below the scalp, and MEG, which detects nearscalp magnetic fields associated with neural pathway current throughout the brain, but mainly near-surface parallel and perpendicular current flow. The remaining two technologies are indirect measures that monitor the BOLD response either through rapid successions of whole brain MRI scans (using fMRI)
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From page 252... ...
Current EEG technologies are fast enough to capture signals of interest, making it a viable measure for research on performance as well as for use in direct selections. For example, if future technology such as phased array high impedance antennae makes localization of multiple person unobtrusive EEG recording possible, the measurements are unlikely to be any more precise than the current capabilities of an EEG via scalp electrodes.
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From page 253... ...
pulse near the resonant frequency of hydrogen protons, 42.6 MHz/tesla or 128 MHz at 3 tesla, knocks the spins perpendicular to the external field, and their relaxation back to ground state releases RF energy in patterns that can be reconstructed to show both the composition and distribution of any hydrogen-rich material. The resonant frequency is a direct function of the local magnetic field, defined by the Larmor relation: w = g B, where w is the frequency of precession, B is the local magnetic field, and g is a constant of the material (42.6 MHz/tesla for bare protons, as mentioned above)
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From page 254... ...
A series of fast scan sequences, typically collecting an entire brain volume at a resolution of 3 mm3 in 2 seconds, that are calibrated to optimize detection of the BOLD signal will show the dynamics of brain functioning under the specific internal or applied conditions at the time of scan; this is known as a functional MRI, or simply fMRI.8 The major advantages of fMRI are unmatched three-dimensional spatial resolution compared 7 Frequency detection sensitivities in MRI are very good, and "substantial" here means about 3 parts per million. The frequency shifts caused by imaging gradients range in the parts per thousand.
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From page 255... ...
. It is thought that such future devices, as well as those that might alter the atomic nuclei observed by MRI to nuclei of sodium, calcium, potassium or another element with a nonzero magnetic moment, could be operated by minimally trained technicians, the way Army medics are trained to operate medical imaging equipment for limited applications, or research assistants are trained to acquire EEG data from subjects in a sleep center.
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Advanced image analysis can perform facial recognition based on naturalistic video captures, and automated eye monitoring can calculate SBR (Jiang et al., 2013)
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. Mi crotesla MRI with a superconducting quantum interference device.
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From page 258... ...
. Intrinsic signal changes accompanying sensory stimulation: Functional brain mapping with magnetic resonance imaging.
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