Information and Control in Organ Systems

DESIGNERS of artificial internal organs face many difficult physical and physiological requirements. In order to correct for an organic malfunction, it is necessary for these prosthetic devices to carry out certain physicochemical operations under the control of both specific and not-so-specific signals that originate inside the body and/or in the outside world. This task calls for the establishment of adequate information-matching procedures. The devices must be prepared to deal with control signals in the form of spatiotemporal patterns of electrical, mechanical, or even chemical activity. Appropriate coding (including the necessary redundancy) must insure the transmission of the information-bearing elements, or ``distinctive features,'' of these paterns in the presence of various types of interference, or ``noise.'' In many instances, our knowledge of the control circuits for the various organs is still incomplete. Neuro-physiological research during the last decade has, for instance, focused on elucidating the role of the less specific ascending and descending pathways in the nervous system, in contrast with the better-known (``classical'') afferent pathways.
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Designers of artificial organs are thus often faced with specifications that lack some of the most important data. Another difficulty that stands in the way of establishing rational procedures for the design of artificial organs is our inability to agree upon the evaluation of the performance of a device that has multiple inputs and multiple outputs and that only too often fulfills multiple functions. Under such circumstances, it is not reasonable to hope for a simple, unambiguous figure of merit or of efficiency.