A neural net model for escape learning

An escape learning situation is discussed in terms of a neural model in which a stimulus can result in a conditioned excitement and a specific conditioned response. By using the simplest relations between the strengths of conditioning and the number of reinforcements and by introducing a distribution of fluctuations occurring regularly in time, one can calculate the probabilities of various responses, as well as the various latencies, in successive trials. The results are in moderately satisfactory agreement with the data of R. L. Solomon and L. C. Wynne (Psychol. Monogr.,67, No. 4, 1953). Consequences of the model for various experimental situations are discussed. This research was supported in part by the United States Public Health Service Grant RCA GM K6 18,420 and in part by the United States Air Force through the Air Force Office of Scientific Research of the Air Research Development Command under Grant No. AF AFOSR 370-64.     

On visual adaptation: I. Photochemistry

Quantitative aspects of the photochemistry of visual adaptation are considered. A simplied model is given that fits data on changes of rhodopsin concentration during and following strong illumination. A variation on Wald’s compartment hypothesis is shown to fit the quasilinear dependence of log threshold upon pigment concentration. Finally, there is a brief review of pertinent data on cone pigments. This research was supported in part by the United States Air Force through the Air Force Office of Scientific Research of the Air Research Development Command under Contract No. AF(638)-414, and in part by the United States Public Health Service Training Grant 2G-833.     

On visual adaptation: II. The electroretinogram and the bipolar cells

First a model for theb-wave of the electroretinogram is given. The essential part of the model is the diffusion into the rod-bipolar synapse of a transmitter substance, followed by the induction of an inhibitor. Making use of this model, adaptation to an illumination too weak to cause of significant decrease in the concentration of visual pigment is interpreted as due to a decreased effectiveness of the rod impulse in exciting the bipolar cell. The disparity between threshold changes for very small test spots and for relatively large spots is explained simply, without invoking any additional physiological mechanisms. This research was supported in part by the United States Air Force through the Air Force Office of Scientific Research of the Air Research Development Command under Contract No. AF(638)-414 and in part by the United States Public Health Service Training Grant 2G-833.     

Electron microscopic observations on the reactional changes occurring in insect nerve fibers after transection

Summary An electron microscopic study of the interganglionic connectives of an orthopteran (Laplatacris dispar) demonstrated that a reaction starts in the sectioned fibers very soon after transection (30 minutes). This reaction is closely similar to that observed in sectioned nerves of vertebrates and consists in the appearance of microvesicles and the proliferation of mitochondria. Sectioned connectives were studied from 30 minutes to 88 hours after section. The reaction mentioned increases progressively during the indicated lapse of time.This research was supported by the United States Air Force under Contract No AF 49 (638) 585 and Grant Af 61-64, monitored by the Air Force Office of Scientific Research, Air Force Research Division of the Air Research and Development Command.     

A model for conditioning and the effect of spaced trials in learning

A mechanism is suggested in which a postulated substance can enter a synaptic region only during the simultaneous action of a conditioned and an unconditioned stimulus. If this substance remains and produces a physico-chemical change, then a consequence is that the degree of learning will depend on the spacing of conditioning trials and the time constant of the process will be related to the rate of diffusion or transport of the substance along the axon. This research was supported by the United States Air Force through the Air Force Office of Scientific Research of the Air Research Development Command under Contract No. AF 49(638)-414.     

On the interpretation of the effect of area on the critical flicker frequency

The effects of area and intensity on the critical flicker frequency, threshold, and reaction time are considered in terms of neural net theory. An attempt is made to develop a mechanism which can account for the phenomena associated with the empirically observed laws of Ricco, Granit, Talbot, and Ferry-Porter as well as observations on reaction time and threshold. A simple model gives results which are substantially in agreement with observation except for a few apparent discrepancies. Experimental procedures are suggested which can determine whether these are apparent or real. This research was supported by the United States Air Force through the Air Force Office of Scientific Research of the Air Research and Development Command under contract No. AF 18(600)-1454. Reproduction in whole or in part is permitted for any purpose of the United States Government.     

On the biophysics of vision

A photochemical system is considered which is similar to that of S. Hecht but which includes an intermediate substance between visual purple and visual white. This intermediate is assumed to change the embrane voltage of the photoreceptors. A simple model is presented from which one may calculate the frequency of the impulses resulting from the application of light. It is found that this physicochemicai model enables one to account for a considerable number of physiological phenomena of vision. Among these are the light and dark adaptation phenomena. By introducing a simple assumption regarding spatial interaction one can account for some psychological phenomena such as the effect of intensity, light-dark ratio, shape, and area on the critical flicker frequency. A number of other phenomena are discussed in terms of the model. This research was supported by the United States Air Force through the Air Force Office of Scientific Research of the Air Research and Development Command under Contract No. AF 18(600)-1454. Reproduction in whole or in part is permitted for any purpose of the United States Government.     

On some distribution functions for non-linear switching elements with finite dead time

Summary The output distribution function of a non-linear switching element with a Poissonian sequence of impulses at the input is calculated by a straightforward method. The dead time of the element is taken into account. Some limiting properties of this distribution and its mean value are studied.The present research has been sponsored in part by the Air Force Avionics Lab., Research and Technology Div., Wright-Patterson Air Force, Air Force System Command — U.S.A.F. — Government of United States of America, Contract no. AF 33(615)-2786.     

A mathematical interpretation of motor reactions to fixed and moving stimulation of the eye

The results of experiments performed by L.S. Stone and by R. W. Sperry on vision in salamanders are analyzed. A summary of Reichardt's theory, which originated in the researches of B. Hassenstein on insects, is given, and an application to salamanders is carried out. Introducing a simpler mathematical development based on the onefactor theory of excitation, the same formal results are obtained. A complete model, which includes those results and tries to fit the salamander behavior described by stone, is elaborated and translated into Boolean terms. As a complementary consideration, it is pointed out that the functional rigidity of the visuomotor system, deriving from a biological molecular hysteresis, could be framed in theneuro-affinity principle, the spatial expression of which would turn out to be abiological field. This research was supported by the United States Air Force through the Air Force Office of Scientific Research of the Air Research and Development Command under Contract No. AF 18(600)-1454. Reproduction in whole or in part is permitted for any purpose of the United States Government.     

Representation of modality in cutaneous sensibility

Morphologically identical nerve endings subserve more than one sensory modality. Two possible explanations are: such endings are functionally different, responding to one type of physical excitation only, or such endings are capable of responding to more than one type of physical stimulus, but central mechanisms discriminate between different stimuli. A simple network is described to illustrate how thermal receptors could discriminate between thermal and mechanical stimuli. This research was supported in part by the United States Air Force Office of Scientific Research of the Air Research and Development Command under contract No. AF 18(600)-1454. Reproduction in whole or in part is permitted for any purpose of the United States Government.     

Factors in visual acuity: I. Neural inhibition and the visual perception of contours

Interpretations of the mechanisms of perception of contours or of Mach bands have stressed either the role of various spatial derivatives of light intensity at the retina or the importance of various forms of inhibitory effects between neighboring retinal elements. Evidence is presented here in support of the latter type of interpretation. It is considered that the brightness contrast and perceived contours arise from neural elements, each of which is stimulated in proportion to the intensity of photo-receptor excitation at a point of the retina and inhibited in proportion to the mean intensity in some neighborhood of that point. The role of the spatial derivatives is best seen as a particular manifestation of the inhibitory mechanism. Predictions based upon this hypothesis appear to be consistent with experimentally observed evidence. This research was supported by the United States Air Force through the Air Force Office of Scientific Research of the Air Research and Development Command under Contract No. AF 18(600)-1454. Reproduction in while or in part is permitted for any purpose of the United States Government.     

On the reversibility of environmentally induced alterations in abstract biological systems

The environmentally induced alterations in structure of (M, ℜ) which were described previously (R. Rosen,Bull. Math. Biophysics,23, 165–171, 1961) are examined from the standpoint of determining under what circumstances they can be reversed by further environmental interactions. For simplicity we consider only the case of (M, ℜ)-systems possessing one “metabolic” and one “genetic” component. In the case of environmentally induced alteration of the “metabolic” component alone, a necessary and sufficient condition is given for the reversibility of the alteration. In the case of alteration of the “genetic” component, the situation becomes more complex; several partial results are given, but a full analysis is not available at this time. Some possible biological implications of this analysis are discussed. This research was supported by the United States Air Force through the Air Force Office of Scientific Research of the Air Research and Development Command, under Contract no. AF-49(638)-917 and Grant no. AF-AFOSR-9-63.     

Growth responses of barley seedling to simulated weightlessness induced by two-axis rotation

Summary A device used for simulated weightless studies is described and is called the Nogravatron. The Nogravatron apparatus produces simulated weight-lessness by rotating seedlings simultaneously at the rate of 0.25 rpm and 1.0 rpm in two axes perpendicular to each other. Atlas barley seedlings grown on the apparatus grew at rates different from that of stationary controls. Coleoptile elongation in rotated barley was not inhibited by light during the first 55 hours of rotation treatment whereas stationary controls were photoinhibited. After 55 hours the growth of rotated coleoptiles was inhibited by light. The coleoptiles did not show movements and were oriented along the longitudinal axis of the seed. Roots also did not show geotropic movements but the growth direction was affected by the proximity of other roots. Coleoptiles rotated in dark were significantly longer than stationary controls on the third and fourth day but not so on the fifth day and later. Coleoptiles rotated in light were about 35 percent longer than the stationary coleoptiles by the third day and maintained this significant difference to the end of the experiment.Supported in part by NASA Grant NsG 538-63 and by Air Force Office of Scientific Research Office of Aerospace Research, United States Air Force, Contract No. AF 49 (638)-1387.     

Contributions to the theory of active transport: II. The gate type non-carrier mechanism and generalizations concerning tracer flow,efficiency, and measurement of energy expenditure

The gate type non-carrier mechanism, an active transport model, is discussed. In this mechanism, the actively transported particle passes through the gate itself by means of a series of reorganizations of the active transport mechanism. The net rate of transport, the rate of transport in either direction, and the efficiency of this model are analyzed. It is shown that on the basis of these analyses alone, this mechanism cannot be distinguished from a carrier mechanism. Three generalizations which apply to many individual type active transport models are then discussed. These pertain to (1) the dependency of the flow in one direction on the cencentration of the particles on the opposite side of the membrane, (2) the possibility of very high efficiencies for these models independent of the rate of the active transport, and (3) the methods whereby the energy expended in the active transport may be experimentally found. This research was supported by the United States Air Force through the Air Force Office of Scientific Research of the Air Research and Development Command under contract No. AF 18(600)-1454. Reproduction in whole or in part is permitted for any purpose of the United States Government.     

Decision equation for binary systems. Application to neuronal behavior

Summary The exact mathematical treatment is given for a non linear equation describing the delayed yes-or-no response to a binary system to external stimulations, in some typical cases of interest. Comparison is made with neurophysiological data on the frequency rate of firings of stimulated neurons; the same equation, however, can be conceivably applied to a vast variety of phenomena. The procedures followed to solve the problems that arise in connection with this equation could be extended to more general types of non linear equations.The research reported in this document has been sponsored in part by the Air Force Office of Scientific Research under Contract no. AF EOAR 65-44 through the European Office of Aerospace Research, OAR, United States Air Force.     

Brain and physics of many-body problems

Summary On the basis of a recent physical theory of many-body problems developped in our Institute, a model of the brain is formulated, and it is shown how some of its typical features, such as learning and memory processes, find therein a natural and simple explanation. In the Appendix a short surview of the necessary mathematical formalism is finally given.A brief outline of the model presented in this paper was unformally given by one of the authors (L.M.R.) at the I.S.P. Neurosciences Research Program; Boulder Colorado, in July 1966.This work has been sponsored in part by: Air Force Avionics Lab., Research and Technology Div., Wright Patterson Air Force, Air Force System Commend-U.S.A.F.-Government of United States of America. Contract No. AF 33(615)-2786.     

Environmental objections to the PAVE PAWS radar system: a scientific review

As part of our continental defense system, the United States Air Force has operated a radar system, known generally by the label PAVE PAWS, off of Cape Cod, MA since 1978. Some populated areas in the vicinity of the system are subject to a low level of background radiofrequency radiation from the system, and local citizens' groups have expressed concern that this radiofrequency radiation may affect their health. These concerns have been fueled by presentations and letters by Dr. R. A. Albanese, an applied mathematician at the Air Force Research Laboratory, who has proposed standards by which that PAVE PAWS radiofrequency radiation which is incident on populations should be judged. I discuss those standards that are sufficiently well defined to be subject to analysis and show that they are not based on sound quantitative reasoning.     

A contribution to the study of diffusion of neutral particles through pores

Diffusion through a flat pore into a large open region is proportional to the linear dimension of the pore and not to its area. This was first explained by Brown and Escombe (1900) for a circular pore and is here generalized, by means of a dimensional argument, to include any type of regular opening. The problem is further generalized to include diffusion through pores of finite thickness, finite distance apart, and into finite regions. Since this problem cannot be solved exactly, an approximation method is introduced. Reasons for the credibility of the approximation are presented. It is then shown, by means of the approximation method, that the diffusive flow through a pore is equal to the total concentration difference divided by the resistance of the system. The resistance, in turn, is the sum of the resistances of all portions of the system, each of which is calculated. The result is compared with results which have been calculated exactly for limiting cases and found to agree very well. The results are then applied to a standard method of computing pore size in membranes, and it is shown that the correction factor is negligible. This research was supported by the United States Air Force through the Air Force Office of Scientific Research of the Air Research and Development Command under Contract No. AF 49(638)-414. Reproduction in whole or in part is permitted for any purpose of the United States Government.     

The derivation of D’Arcy Thompson’s theory of transformations from the theory of optimal design

It is shown informally that Cohn’s theory of Optimal Forms can be construed as a comparative theory, and that when this is done the celebrated theory of transformations of D’Arcy Thompson follows as a consequence. The implications of this type of theoretical foundation for the Thompson theory with regard to problems of comparative morphology are discussed, and some suggestions for the further implementation of the theory are described. This research was supported by the United States Air Force through the Air Force Office of Scientific Research of the Air Research and Development Command, under Contract No. AF 49(638)-917.     

Localization of monoaminergic neurons in the central nervous system of Astacus astacus Linné (Crustacea)

Summary The cellular localization of biogenic monoamines in crustaceans was studied by means of a highly specific and sensitive fluorescence method devised by Falck and Hillarp. It was found that neurons displaying specific fluorescence in the central nervous system were confined to the protocerebrum, the medulla externa and interna and the ventral nerve cord. The method allows a distinction between the fluorophores of 5-hydroxytryptamine (and 5-hydroxytryptophan), which emit the yellow light, and the fluorophores deriving from the catecholamines (and DOPA), which emit the green light. Green-fluorescent neurons occurred abundantly in the aforementioned parts of the central nervous system while yellow-fluorescent neurons were sparsely present in the same parts.The present work has been carried out at the departments of Histology and Zoology at the University of Lund. The authors take great pleasure in expressing their warmest thanks for laboratory facilities, provided by Professors Erik Dahl (Zoological Institute) and Bengt Falck (Histological Institute).The research reported in this document has been sponsored by the Air Force Office of Scientific Research under Grant AF EOAR 66-14 through the European Office of Aerospace Research (OAR), United States Air Force and by a grant from the Swedish Natural Science Research Council 99-32 (nr 5995).