Impulse Interval Research Articles

The response of the antennal cold receptor of Periplaneta americana to rapid temperature changes and to steady temperature

1. Ventrally located cold sensilla on the antennae of male adult Periplaneta americana are ring-shaped structures about 8 μ in diameter with a short hair emerging from their center (Figs. 1, 2). 2. Further experiments (cf. Loftus, 1966) have substantiated the exclusion of the motion of air streams (2.5 m/sec) as a stimulus. The list of pure and mixed chemicals has been extended. The results of all tests including the odor of crushed abdomens of virginal female cockroaches were negative. 3. Extracellularly recorded impulses which were either monophasic negative or diphasic at higher temperatures often became either diphasic or monophasic positive at lower temperatures. The effect was reversible (Fig. 4). 4. When peak frequency is driven over 200 imp/sec, the time course of instantaneous frequency, F=f(t), plotted on double log scale displays 3 linear phases: 1 rising and 2 falling, followed by a fourth phase of recovery. At lower peak frequency only one falling phase develops. Before the onset of the recovery phase instantaneous frequency values determined from single impulse intervals lie within ±20% of a linear function on double log scale (Figs. 6, 7, 8). 5. Instantaneous frequency values, even when formed from groups of as many as 10 successive impulse intervals, cease to convey unambiguous information on stimulus magnitude within about 300 msec after peak frequency (Figs. 9, 10). 6. The reciprocal of the total number of impulses from stimulus onset up to about 800 msec afterwards (mean frequency), shows a much more precise relationship to ({ΔT) than instantaneous frequencies after Fmax do (Figs. 12, 13). 7. When instantaneous frequency is plotted against temperature drop, the slope of the curves, F=f({ΔT), falls off with increasing ({ΔT) and time since stimulus onset. Thus the sensitivity of peak frequency is the highest of all instantaneous frequencies and itself higher at smaller temperature drops. An average receptor attains a sensitivity of -155 imp/sec/°C (Fig. 11). 8. When peak frequency is plotted against initial temperature and temperature drop, a bulging surface develops. Hence a given peak frequency determines only a set of values for initial temperature and temperature drop. Three receptors with different characteristic surfaces should permit both components to be distinguished quantitatively (Fig. 14). 9. As shown in peak frequency, the receptor's sensitivity to temperature drop diminishes, whereas the effect of initial temperature on peak frequency rises, towards the extremes of the temperature range investigated (Fig. 15). 10. Treatment of 13 receptors and 280 responses indicate sufficient reliability of peak frequency response to permit discrimination of 7 to 17 discrete temperature drops between ({ΔT)=0.2° and ({ΔT) = 5.5° C (Fig. 16). 11. A second identical short temperature drop repeated after 1.5 sec rewarniing evokes a peak frequency on the average 15% lower than the first. This effect could diminish resolving power severely (Fig. 17). 12. The longest single impulse intervals occur at rapid temperature rises. Reckoned as frequencies they attain values in the order of 0.1 imp/sec. These frequency minima show good quantitative relationship to the extent of temperature rise and indicate the possibility of this cold receptor's providing the CNS with information on warming (Fig. 18). 13. Some receptors show a sharp activity maximum between 17° and 37° C in response to steady temperature. The responses (mean frequencies) of many receptors, however, manifest variation up to and beyond 20% of the frequency range corresponding to steady temperature between 17° and 37° C. Hence the receptor is a poor thermometer (Figs. 19, 20, 21). 14. Taken absolutely the sensitivity of Periplaneta's cold receptor to temperature change (-155 imp/sec/°C) seems second only to infrared sensitive crotalid facial pits (+500 imp/sec/°C).

Temperature acclimation of the functional parameters of the giant nerve fibres in Lumbricus terrestris L. II. The refractory period.

ABSTRACT The effect of temperature on the refractory period in nerve fibres is of the same magnitude as its effect on the duration of the action potential (Tasaki, 1949) or as the effect of temperature on the duration of the falling phase of the spike (Adrian, 1921). Temperature coefficients (Q10) as high as 4 have been calculated for the refractory period in single fibres of the frog by Schoepfle & Erlanger (1941). According to Tasaki (1949), the Q10 value of the absolute refractory period is about 3·5 for a single node in the myelinated fibres of the frog, when determined for the temperature interval 13·7-19° C.

RELATIONSHIPS BETWEEN INTER-FLASH INTERVALS AT FUSION, UNDER CONDITIONS INTENDED TO ELIMINATE NEURAL "OFF" EFFECTS.

Short, low intensity photic pulses were used to study flicker perception. According to available evidence, such stimuli will induce no neural “off” effects. Although the pulse trains used in the experiment are, from a physical viewpoint, harmonically complex, absence of induced neural “off” effects makes their neurophysiological concomitants relatively uncomplicated and it is for the latter reason that stimuli of the type described were used. The data were interpreted as additional confirmation of the concept that neural impulse interval modulation is a mechanism for transmission of information in the nervous system. In the particular case of our experiment, results led us to postulate (a) that the mechanism responsible for perception of flicker, in the absence of “off” effects as cues, is the detection by the visual system of an increase in intervals between neural impulses that occur between successive photic pulses, and (b) that the time required for such detection is dependent upon and varies in direct proportion to initial periods between neural spikes induced by flashes in the stimulus train.

Slow membrane potential changes accompanying excitation and inhibition in spinal moto- and interneurons in the cat during natural activation.

Summary.Slow membrane potential changes accompanying excitation and inhibition processes have been studied in spinal moto‐ and inter‐neurons of spinal cats, using intracellular recording technique.Section I. Long‐lasting shifts in membrane potential level have been recorded in both moto‐ and interneurons during sustained rhythmical activity.A closer study of the slow membrane potential changes and their relation to spike potentials has revealed fundamentally similar events in moto‐ and interneurons; the quantitative analyses have mainly been performed on niotoneurons whose steady membrane potentials allow of studies for sufficiently long periods. Special attention has been given to the slow membrane potential oscillations during rhythmical firing.The firing level for the onset of rhythmical spike discharges was found to be relatively constant in one and the same neuron; with increase in discharge frequency a definite lowering of the firing level occurs, an approximately linear relation being found to exist between firing level and impulse interval.During periods of regular rhythmical firing subthreshold membrane potential oscillations may occasionally he seen associated with spikes of reduced amplitude or not accompanied by any recordable spikes.The potential analysis has led to a tentative differentiation between an initial quick and a later slow phase of repolarization. The quick repolarization level, more or less marked in different neurons, is of approximately the same value during natural activation and single ortho‐ or antidromic stimulation; it varies within relatively narrow limits during the large natural variations in membrane potential observed in the experiments.The slow repolarization level, which may show great variations even at one and the same membrane potential level, undergoes a pronounced reduction with increasing frequency of the rhythmical activity. The relation hetween the slow repolarization level and the impulse interval is found to be approximately linear.The typical variations in quick and slow membrane processes during various activity levels of a motoneuron have been diagrammatically represented. The possibility is discussed that the quick spike processes and slow potential variations represent changes in different membrane potential fractions, analogous to the Q‐ and L‐fractions established in peripheral nerve.The evidences in favour of an inherent oscillation mechanism in the inembrane activated at a critical level of depolarization and primarily responsible for the discharge frequency are discussed.Section II. Membrane potential changes during inhibition have been studied in moto‐ and interneurons using exteroceptive inhibitory stimulation. In both types of neurons natural activation of inhihitory sources resulted in a slow repolarization not exceeding the highest membrane potential recorded in the absence of excitatory stimulation.The inhibitory effects of synchronized afferent volleys have been analysed in motoneurons in different states of rhythmical activity. The amplitude of the repolarization dip produced by each afferent volley was found to depend on the membrane potential level at the onset of inhibition. During repetitive stimulation a steady state was gradually attained, the level of which varied with the initial state of activity of the neuron.Section III. Both in moto‐ and interneurons the occurrence of random miniature potentials of varying amplitude has been demonstrated, those of larger amplitude (10 mV) apparently being built up out of the smaller “unitary potentials” of 1–3 mV.Increase as well as decrease of the miniature potential activity could be produced by natural activation of extero‐ or proprioceptive sources influencing the neuron. Correlations to the membrane potential level showed a reduced amplitude range of miniature potentials during increased membrane potential.In addition to the most common type of miniature potentials representing an inside positive change, potentials of the opposite sign were occasionally observed. The functional role of such randomly occurring repolarization potentials has been exemplified and a comparison made with similar phenomena observed in other types of nerve cells.

Maintained activity in the cat's retina in light and darkness.

Nervous activity has been recorded from the unopened eye of decerebrate cats. Recordings were made with metal electrodes or with small micropipettes from ganglion cells or nerve fibers. Continuous maintained discharges were seen in all ganglion cells during steady illumination of their receptive fields, as well as in complete darkness. Possible artefacts, such as electrode pressure, abnormal circulation, anesthetic, and several other factors have been excluded as the source of the maintained discharge. Visual stimuli are therefore transmitted by modulating the ever present background activity. Discharge frequencies were measured following changes of retinal illumination. No consistent patterns of frequency change were found. The maintained discharge frequency may be permanently increased or decreased, or may remain practically unchanged by altering the steady level of illumination. In addition, there were often transient frequency changes during the first 5 to 10 minutes after changing illumination, before a final steady rate was established. A statistical analysis of the impulse intervals of the maintained discharge showed: (a) the intervals were distributed according to the gamma distribution (Pearson's type III), (b) the first serial correlation coefficient of the intervals was between -0.10 and -0.24, with a mean value of -0.17, which is significantly different from zero, (c) the higher order serial correlation coefficients were not significantly different from zero. Thus the firing probability at any time depends on the times of occurrence of the two preceding impulses only, and in such a way as to indicate that each impulse is followed by a transient depression of excitability that outlasts the following impulse. The possible sites at which spontaneous or maintained activity may originate in the retina are discussed.

Electromyographical studies on Graves' disease.

The characteristics of the EMG of Graves' disease is that the dis-tribution of spike discharge becomes more irregular than normal during, voluntary muscle contraction. This irregularity is due to the following 3 factors. 1. The spike discharges of different motor units are apt to approach. 2. The fluctuation of impulse interval of single motor unit becomes remarkable. 3. Mean impulse interval becomes shorter. This phenomenon shows a tendency of increase or decrease with toxic symptoms, i.e., high basal metabolism, tachycardia and the instability of the pulse. It is still unknown how this fluctuation occurs in what part of the motor unit. Further study is required.

Some electronic switching circuits

Referring to the letter to the editor by H. A. Brown and P. W. Ryburn, published on page 36 of the August 1938 issue of Electrical Engineering and to the last paragraph of my article “Some electronic switching circuits” on page 211 in the May 1938 issue, I would like to point out that this paragraph states that the minimum R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</inf> C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> product rather than the minimum impulse interval would be 0.25 microsecond. There is considerable difference in meaning because the time constant, as Brown and Ryburn are aware, gives the time only for the interval during which the voltage across the condenser C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> has dropped to about 37 per cent of its peak value. The impulsing interval, while dependent on the time constant, will be much greater since the voltage must drop approximately exponentially below the deionizing potential of the type-885 tube before the 885 will stop conducting and the cycle can be repeated.

Electronic: Switching circuits

We read with much interest the article in the May 1938 issue of Electrical Engineering entitled “Some Electronic Switching Circuits,” by C. C. Shumard. We should like very much to discuss one feature of this paper. We developed an impulse-voltage generator somewhat similar in principle to that described in figure 6 of Mr. Shumard's article. We arranged the circuit as indicated in figure 1 of this letter. By supporting the type-34 linearity tube on porcelain insulators, together with its filament and screen-biasing batteries, we were able to reduce the capacitance until we could get a voltage impulse lasting one microsecond. We were not able to reduce the time of the impulse below this minimum figure. Mr. Shumard states that with the assumed values of resistance and capacitance the minimum impulse interval should be &1/4; microsecond. We attempted to use a circuit like that described in figure 6a of his article, but found that the capacitance between ground and the anode side of the type-885 tube was too great to obtain the impulse duration mentioned. We should like very much to know if Mr. Shumard was successful in obtaining an impulse of &1/4; microfarad duration. If he obtained this low time interval, we should like to know what special provisions, if any, he made in the design of the sweep circuit.