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

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

7.4.2.6 Neural Inmessaging

The most comprehensive inmessaging capability may be afforded by eavesdropping on selected neural sensory traffic (Section 4.9.5). Noninvasive monitoring of neuroelectric impulses (Section 4.8.6) by nanorobots stationed near afferent neurons can detect and interpret any sensory stimulus that can be consciously perceived by the patient. Virtually every inmessaging stimulus described elsewhere in Section 7.4.2 -- including finger-drumming, hand-signing, vocalized or olfactory signals, dermal heat sensations, scalp/eyebrow myopotentials, and the like -- may be indirectly detected by suitably positioned and configured neural monitors. For instance, finger-tapping generates electrical activity in a specific ~1 cm² patch of neurons in the primary motor cortex¹⁰⁹⁰ -- although nanorobots suitably positioned in the brachial plexus, or lower in the tree near critical junctions of the median nerve (above the digital, thumb, and palmar cutaneous branches) and the ulnar nerve (above the muscular, dorsal cutaneous, superficial palmar and deep palmar branches), may achieve more rapid and reliable monitoring of motor impulses. Neurons may fire at >100 Hz, so, ignoring significant electrical spike redundancy, inmessaging rates up to ~100 bits/sec per monitored neuron can in theory be achieved with this approach.

Nonsensory volitional neural inmessaging channels are also available to nanorobot monitors stationed in the brain. For example, by consciously recalling a specific series of numbers, letters, names, words, concepts, images, or events, a well-defined constellation of neural impulses of certain frequencies may be caused to pass repeatably through the same, say, (~200 micron)³ blocks of brain tissue for each recalled item. Brain tissue contains numerous "dominance columns" on approximately this scale which appear to represent functionally associated fiber bundles.^1036,1039 For example, 300-500 micron wide columns have been described in the striate and inferotemporal cortex of the macaque monkey;^742,1037 organized patterns of action potential waves have been observed via calcium imaging in rodents, measuring 100-300 microns wide in the retina and ~50 microns wide in the cortex.⁷⁷¹ An experiment using a context-recall memory task in monkeys suggested that an ensemble of as few as 16 motor cortical cells could perfectly classify (i.e., 100% accuracy) all the items in a sequence of five stimuli ;³¹⁸⁴ nanorobotic monitors stationed at those 16 cells could in theory discriminate all five-stimulus sequences.

Thus, without being able to understand any of the higher-order meanings of these signals (e.g., to "read human thoughts"), nanorobots detecting such reproducibly neurographically-localized impulse trains may pool their readings and interpret specific combinations of such localized trains as data or as command strings (a ~0.1-1 bit/sec channel) and then take appropriate action. Biofeedback monitors,¹⁶⁶¹ volitional scalp EEG multiband user interfaces, PET scanners and functional magnetic resonance imaging (fMRI) operate on a crudely analogous principle, but without the benefit of precise impulse localization that is made possible by molecular nanotechnology. In 1998, a glass cone electrode filled with neurotrophic factors (which encouraged neural ingrowth) was implanted in a patient's motor cortex; the patient learned to mentally operate the output signal as a binary switch.³⁰⁷⁴ Another system using cortical potentials achieved transfer rates of ~2 characters/min.³¹²¹

Last updated on 19 February 2003