© 1999 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999

4.9.5 Neural Macrosensing

The ability to detect individual neural cell electrical discharges noninvasively in many different ways (Section 4.8.6), coupled with the abilities (A) to recognize and identify specific desired target nerve cells (Section 8.5.2, Chapter 25) and (B) to pool data gathered independently by spatially separated nanodevices in real time (Section 7.3), offers the possibility of indirect neural macrosensing of complex environmental stimuli by eavesdropping on the body's own regular sensory signal traffic.

For example, facultatively mobile nanodevices may swim into the spiral artery of the ear and down through its bifurcations to reach the cochlear canal, then position themselves as neural monitors in the vicinity of the spiral nerve fibers and the nerves entering the epithelium of the organ of Corti (cochlear or auditory nerves) within the spiral ganglion (Figure 7.4). These monitors can detect, record, or rebroadcast to other nanodevices in the communications network all auditory neural traffic perceived by the human ear. Advanced speech recognition systems (Section 7.4.2.3) may permit recovery of spoken words and identification of individual speakers (including vocalizations by the user), recognition of background noises, reception and validation of cues or commands spoken directly to in vivo nanosystems by authorized medical personnel, and so forth. Since properly configured monitors can also modulate or stimulate nerve impulses (Sections 4.8.6 and 7.4.5.6), these devices may add audible signals to the audio traffic, thus may be employed as hearing aids (using feedback loops), real-time language translation mechanisms, continuous vocalization/audition recorders, voice-stress analyzers, or nanodevice-user communications links (Section 7.4).

Nanomonitors positioned at the afferent nerve endings emanating from hair cells located in the otolithic membrane of the utricle and saccule and in the cristae ampullaris of the semicircular canals allow medical nanodevices to directly record, amplify, attenuate, or modulate the body's own sensations of gravity, rotation, and acceleration, although kinesthetic sensory management might also be required for complete control. Motor neurons likewise can be monitored to keep track of limb motions and positions, or specific muscle activities, and even to exert control (Section 7.4.6.2). Neuron-resident nanorobots may detect auditory effects induced in the brain by pulsed microwaves from external sources.³⁴⁷³ Feline cochlear neurons sensitive to audible frequencies of >300 Hz respond to single microwave pulses at a threshold-specific absorption rate of 6-11 watts/kg-pulse,^3479,3480 while in humans the threshold for effect, which depends on energy per pulse, may be as low as ~0.02 joule/m²-pulse for people with low hearing threshold.³⁴⁸¹

Olfactory and gustatory sensory neural traffic similarly may be eavesdropped by nanosensory instruments (Section 7.4). Nerve taps in the medulla oblongata or at the phrenic nerve that drives the diaphragmatic muscles allow direct monitoring of respiratory activity. Pain signals may be recorded or modified as required, as can mechanical and temperature nerve impulses from other receptors located in the skin. Even psychological variables such as emotionality, vigilance, and mental workload may be directly monitored by measuring ANS activity in sympathetic efferent fibers outside of the brain.⁵¹²

The most complex and difficult challenge in neural macrosensing will be optic nerve taps. The retina is thoroughly vascularized, permitting ready access to both photoreceptor (rod, cone, bipolar and ganglion) and integrator (horizontal, amacrine, and centrifugal bipolar) neurons. However, the optic nerve bundle itself has ~10⁶ tightly bunched individual nerve fibers, a 10-100 MHz signal bandwidth, and significant natural data compression techniques which all must be untangled in real time. Developing algorithms capable of interpreting raw optical nerve traffic,^3018-3021 say, to recognize a specific human face or a specific scene in the vision field, would prove a significant research challenge. (Direct monitoring of photo-receptors or retinal membrane potentials and other techniques (Section 7.4.6.5) may simplify untangling of the signal compression.) Rapid visual field identification using artificial neural nets is also a subject of much current research interest. Eyeball rotations (e.g., via resident intradevice nanogyroscopes; Section 4.3.4.1), eyelid position, pupil aperture, and lens accommodation under ciliary muscle control must be monitored to supplement the vision field analysis.

Last updated on 17 February 2003