Dynamical coupling between locomotion and respiration

In search of the formative principles underwriting locomotor-respiratory coupling, we reanalyzed and modeled the data collected by Siegmund and coworkers (1999) on the synchronization of respiration during rowing. Apart from the frequency doubling in respiration reported earlier, detailed time-resolved spectral analyses revealed decreasing stability of entrainment close to abrupt changes in frequency relations as well as switches in the relative phase between respiration and locomotion. A single physiological, albeit mechanically constrained, quantity sufficed to explain the observed frequency and phase locking phenomena: the effective value of oxygen volume in the lungs. The cyclic abdominal pressure modulates the self-sustaining rhythmic respiration, modifies the total lung pressure, and causes (local) maxima at frequency ratios between movement and respiration that are composed of small integers. Hence, optimizing the effective oxygen volume can be seen as the mechanism that drives respiration to synchronize with locomotion.Acknowledgements The contribution of the second author was supported by the Netherlands Organization for Scientific Research (NWO), grant # 425 – 202–01. We would like to thank Gunter Siegmund and David Sanderson for the fruitful discussions and for providing the experimental data that inspired the present study.     

Travelling wave patterns in a model of the spinal pattern generator using spiking neurons

The aim of this study is to produce travelling waves in a planar net of artificial spiking neurons. Provided that the parameters of the waves – frequency, wavelength and orientation – can be sufficiently controlled, such a network can serve as a model of the spinal pattern generator for swimming and terrestrial quadruped locomotion. A previous implementation using non-spiking, sigmoid neurons lacked the physiological plausibility that can only be attained using more realistic spiking neurons. Simulations were conducted using three types of spiking neuronal models. First, leaky integrate-and-fire neurons were used. Second, we introduced a phenomenological bursting neuron. And third, a canonical model neuron was implemented which could reproduce the full dynamics of the Hodgkin–Huxley neuron. The conditions necessary to produce appropriate travelling waves corresponded largely to the known anatomy and physiology of the spinal cord. Especially important features for the generation of travelling waves were the topology of the local connections – so-called off-centre connectivity – the availability of dynamic synapses and, to some extent, the availability of bursting cell types. The latter were necessary to produce stable waves at the low frequencies observed in quadruped locomotion. In general, the phenomenon of travelling waves was very robust and largely independent of the network parameters and emulated cell types.     

Sensory Feedback Mechanism Underlying Entrainment of Central Pattern Generator to Mechanical Resonance

Rhythmic body motions observed in animal locomotion are known to be controlled by neuronal circuits called central pattern generators (CPGs). It appears that CPGs are energy efficient controllers that cooperate with biomechanical and environmental constraints through sensory feedback. In particular, the CPGs tend to induce rhythmic motion of the body at a natural frequency, i.e., the CPGs are entrained to a mechanical resonance by sensory feedback. The objective of this paper is to uncover the mechanism of entrainment resulting from the dynamic interaction of the CPG and mechanical system. We first develop multiple CPG models for the reciprocal inhibition oscillator (RIO) and examine through numerical experiments whether they can be entrained to a simple pendulum. This comparative study identifies the neuronal properties essential for the entrainment. We then analyze the simplest model that captures the essential dynamics via the method of harmonic balance. It is shown that robust entrainment results from a strong, positive-feedback coupling of a lightly damped mechanical system and the RIO consisting of neurons with the complete adaptation property     

Formal properties of the circadian rhythm of locomotor activity in Japanese quail

Summary Japanese quail have a circadian rhythm of locomotor activity whose free-run period () in constant darkness (DD) was 22.5±0.1 h (45). A phase response curve of typical form was obtained by illuminating the free-running rhythm with single 1 h light pulses. Using entrainment theory a derived phase response curve was calculated from the phase relationships between the locomotor rhythm and 1 h light periods in light-dark cycles of various lengths (T). Although the limits of entrainment to theseT cycles differed slightly from those predicted, there was a close correlation between the two phase response curves. The phase relationships between the locomotor rhythm and 1–9 h photoperiods in 24 h cycles were in general accord with a prediction based on the short free-run period and the relative sizes of the delay and advance portions of the phase response curve for 1 h light pulses.     

Activity of lumbar interneurons during fictitious locomotion in thalamic cats

Unit activity of the lumbar interneurons was recorded in thalamic cats during fictitious locomotion. Neurons whose activity was modulated in the rhythm of fictitious locomotion were found in the lateral parts of the intermediate zone of gray matter and ventral horn. Of these neurons, 41.2% were activated mainly in the phase of "flexion," 48.5% in the phase of extension, and 10.3% in both phases. Neurons with tonically increasing or decreasing activity during rhythmic discharges and neurons whose activity was unchanged during fictitious locomotion also were observed. During later discharges all these neurons were similarly activated, although a depth of modulation of unit activity was lower than during fictitious locomotion. Afferent inputs to the recorded interneurons also were studied. The neuronal organization of the spinal locomotor generator is discussed on the basis of these results.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 4, pp. 329–338, July–August, 1979.     

Frequency analysis of motor responses evoked in unanesthetized cats by stimulation of the motor cortex

Frequency characteristics of motor responses evoked by stimulation of the motor cortex by amplitude- and frequency-modulated stimulus sequences were investigated in chronic experiments on unanesthetized cats. The variable component of evoked muscular contraction was studied. Frequency characteristic curves were plotted by the harmonic linearization method. Transformation of controlling signals in the motor system was shown to take place by low-frequency filtration and to be characterized by nonstationary, nonlinear, and frequency-dependent properties. Phase delay of the principal harmonic of the variable component of evoked muscular contraction was minimal at a frequency of 0.2 Hz and it varied in different experiments from 40 to 90°. The increase in the phase delay and decline of the amplitude-frequency characteristic curves were particularly marked if the frequency exceeded 1–2 Hz. The mean phase delay at a frequency of 5 Hz was about 108°; the mean slope of the amplitude characteristic curves in the 2–10 Hz region was –12 dB/decade. It is suggested that definite correlation between the dynamic properties of the motor system may be determined, in particular, by the adaptive properties of the spike discharge of neurons concerned in the transmission of motor command signals.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 6, pp. 571–579, November–December, 1980.     

Entrainment of leech swimming activity by the ventral stretch receptor

Rhythmic animal movements originate in CNS oscillator circuits; however, sensory inputs play an important role in shaping motor output. Our recent studies demonstrated that leeches with severed nerve cords swim with excellent coordination between the two ends, indicating that sensory inputs are sufficient for maintaining intersegmental coordination. In this study, we examined the neuronal substrates that underlie intersegmental coordination via sensory mechanisms. Among the identified sensory neurons in the leech, we found the ventral stretch receptor (VSR) to be the best candidate for our study because of its sensitivity to tension in longitudinal muscle. Our experiments demonstrate that (1) the membrane potential of the VSR is depolarized during swimming and oscillates with an amplitude of 1.5–5.0 mV, (2) rhythmic currents injected into the VSR can entrain ongoing swimming over a large frequency range (0.9–1.8 Hz), and (3) large current pulses injected into the VSR shift the phase of the swimming rhythm. These results suggest that VSRs play an important role in generating and modulating the swim rhythm. We propose that coordinated swimming in leech preparations with severed nerve cords results from mutual entrainment between the two ends of the leech mediated by stretch receptors.     

A neural mechanism of hyperaccurate detection of phase advance and delay in the jamming avoidance response of weakly electric fish

 The weakly electric fish Eigenmannia can detect the phase difference between a jamming signal and its own signal down to 1 s. To clarify the neuronal mechanism of this hyperaccurate detection of phase difference, we present a neural network model of the torus of the midbrain which plays an essential role in the detection of phase advances and delays. The small-cell model functions as a coincidence detector and can discriminate a time difference of more than 100 s. The torus model consists of laminae 6 and 8. The model of lamina 6 is made with multiple encoding units, each of which consists of a single linear array of small cells and a single giant cell. The encoding unit encodes the phase difference into its spatio-temporal firing pattern. The spatially random distribution of small cells in each encoding unit improves the encoding ability of phase modulation. The neurons in lamina 8 can discriminate the phase advance and delay of jamming electric organ discharges (EODs) compared with the phase of the fish's own EOD by integrating simultaneously the outputs from multiple encoding units in lamina 6. The discrimination accuracy of the feature-detection neurons is of the order of 1 s. The neuronal mechanism generating this hyperacuity arises from the spatial feature of the system that the innervation sites of small cells in different encoding units are distributed randomly and differently on the dendrites of single feature-detection neurons. The mechanism is similar to that of noise-enhanced information transmission. Received: 10 July 2000 / Accepted in revised form: 19 January 2001     

Heart and circulatory functions in a spider (Eurypelma californicum): the effects of hydraulic force generation

Summary In the tarantulaEurypelma californicum, the relationships between heart activity, circulation and the generation of hydraulic pressure for locomotion were studied. Several new techniques were employed.Mean resting heart rate was 21 beats min^–1 rising to 90 beats min^–1 after burst activity. Decay time to resting rates was related to the increase of heart rate. Post-recovery resting rates were usually elevated in comparison with rates after very long resting periods.A relative measure of heart amplitude was obtained. Four distinct patterns could be distinguished: (i) regular beats; (ii) short-term fluctuations of amplitude within a few heart beats; (iii) a slow rhythmic change of heart/pericardium filling, and (iv) non-periodic, stronger amplitude changes during periods of activity.During locomotion, heart rate rises with maximum rates often reached only minutes after the onset of activity. The rising phase is often characterized by irregularities and a reduction of heart amplitude.Prosomal hemolymph pressure in resting, restrained animals was 41±19 Torr, rising to ca. 90, and 217±48 Torr during walking and fast sprints, respectively. Values in unrestrained spiders were similar. Opisthosomal hemolymph pressures were ca. 20 Torr in resting animals, rising to 40–60 Torr during locomotion.Opisthosomal volume changes were measured. A small volume of hemolymph moved from the prosoma to the opisthosoma at the onset of locomotion, but following activity this volume quickly returned to the prosoma.The simultaneous measurement of carapace depression, opisthosomal volume changes and hemolymph pressures, and heart activity revealed the relationship between circulation and hydraulic force generation. The direction of hemolymph flow was also studied. In non-active animals, the heart occasionally changes its main pumping direction. During locomotion, hemolymph flow from the heart to the prosoma is often reduced or stopped. With a slight delay, hemolymph flow to the opisthosoma is increased. The critical pressure at which prosomal perfusion from the heart is halted is 50–70 Torr.It is concluded that anterior and posterior circulations are separate: hemolymph returning from the prosoma passes only through the anterior lungs, while hemolymph returning from the opisthosoma passes through the posterior lungs.Dedicated to Dr. Rosemarie John, in recognition of her unflagging enthusiasm and support for zoological researchProf. B. Linzen unexpectedly died on August 5, 1988     

The physical basis of alpha waves in the electroencephalogram and the origin of the “Berger effect”

Synchronised activity, differing in phase in different populations of neurons, plays an important role in existing theories on the function of brain oscillations (e.g., temporal correlation hypothesis). A prerequisite for this synchronisation is that stimuli are capable of affecting (resetting) the phase of brain oscillations. Such a change in the phase of brain waves is also assumed to underlie the Berger effect: when observers open their eyes, the amplitude of EEG oscillations in the alpha band (8–13 Hz) decreases significantly. This finding is usually thought to involve a desynchronisation of activity in different neurons. For functional interpretations of brain oscillations in the visual system, it therefore seems to be crucial to find out whether or not the phase of brain oscillations can be affected by visual stimuli. To answer this question, we investigated whether alpha waves are generated by a linear or a nonlinear mechanism. If the mechanism is linear – in contrast to nonlinear ones – phases cannot be reset by a stimulus. It is shown that alpha-wave activity in the EEG comprises both linear and nonlinear components. The generation of alpha waves basically is a linear process and flash-evoked potentials are superimposed on ongoing alpha waves without resetting their phase. One nonlinear component is due to light adaptation, which contributes to the Berger effect. The results call into question theories about brain-wave function based on temporal correlation or event-related desynchronisation.Electronic Supplementary Material: Supplementary material is available for this article at     

Human Chronotypes from a Theoretical Perspective

The endogenous circadian timing system has evolved to synchronize an organism to periodically recurring environmental conditions. Those external time cues are called Zeitgebers. When entrained by a Zeitgeber, the intrinsic oscillator adopts a fixed phase relation to the Zeitgeber. Here, we systematically study how the phase of entrainment depends on clock and Zeitgeber properties. We combine numerical simulations of amplitude-phase models with predictions from analytically tractable models. In this way we derive relations between the phase of entrainment to the mismatch between the endogenous and Zeitgeber period, the Zeitgeber strength, and the range of entrainment. A core result is the “180° rule” asserting that the phase varies over a range of about 180° within the entrainment range. The 180° rule implies that clocks with a narrow entrainment range (“strong oscillators”) exhibit quite flexible entrainment phases. We argue that this high sensitivity of the entrainment phase contributes to the wide range of human chronotypes.     

Symmetrical and asymmetrical gaits in the mouse: patterns to increase velocity

The gaits of the adult SWISS mice during treadmill locomotion at velocities ranging from 15 to 85 cm s^–1 have been analysed using a high-speed video camera combined with cinefluoroscopic equipment. The sequences of locomotion were analysed to determine the various space and time parameters of limb kinematics. We found that velocity adjustments are accounted for differently by the stride frequency and the stride length if the animal showed a symmetrical or an asymmetrical gait. In symmetrical gaits, the increase of velocity is provided by an equal increase in the stride length and the stride frequency. In asymmetrical gaits, the increase in velocity is mainly assured by an increase in the stride frequency in velocities ranging from 15 to 29 cm s^–1. Above 68 cm s^–1, velocity increase is achieved by stride length increase. In velocities ranging from 29 to 68 cm s^–1, the contribution of both variables is equal as in symmetrical gaits. Both stance time and swing time shortening contributed to the increase of the stride frequency in both gaits, though with a major contribution from stance time decrease. The pattern of locomotion obtained in a normal mouse should be used as a template for studying locomotor control deficits after lesions or in different mutations affecting the nervous system.     

3–Nitropropionic Acid–Induced Changes in Bilayer Fluidity in Synaptosomal Membranes: Implications for Huntington's Disease

The use of 3–nitropropionic acid (3–NP) and other mitochondria inhibitors to effectuate animal models of Huntington's disease has been well established. 3–NP administration has been shown to lead to pathology similar to that of HD, including massive loss of striatal neurons associated with oxidative stress. Oxidative stress induced by 3–NP also extends to the cortex, an area where little neuron loss occurs. No mechanism as of yet accounts for selective loss of striatal neurons while sparing cortical neurons. In the present study, a nitroxide stearate lipid bilayer-specific spin-label was utilized to probe 3–NP-induced fluidity changes in striatal and cortical synaptosomal membranes. In cortical synaptosomes, membrane fluidity increased in animals previously treated with 3–NP when compared to controls injected with saline vehicle, while in striatal synaptosomes, membrane fluidity decreased in animals treated with 3–NP when compared to controls. The results of the present study suggest that oxidatively-induced changes in membrane fluidity may be involved in mechanisms by which selective striatal neuronal loss occurs in this animal model of Huntington's disease.     

Localization of neurons innervating the columellar muscles of the snail

The topographic arrangement of large and small neurons participating in the mechanism of the defensive reflex was studied in the circumesophageal nerve ring ofHelix pomatia by a modified retrograde cobalt ion transport method. Comparison of the results with those of previous electrophysiological investigations of the mechanism of the defensive relfex leads to the conclusion that this reflex is effected by a system of neurons consisting of nine large and 60–80 small nerve cells.Research Institute of Neurocybernetics, State University, Rostov-on-Don. Translated from Neirofiziologiya, Vol. 12, No. 6, pp. 637–641, November–December, 1980.     

时滞援助的两抑制性突触耦合的Chay 神经元的同步

一对抑制性突触耦合的混沌Chay神经元的同步模式被研究。结果表明当耦合强度超过临界值时,两抑制耦合的混沌Chay神经元能达到反相的同步。与此同时,两混沌的神经元变为周期而不是原来的混沌运动。然而,如果考虑耦合神经元信息的传导时滞,在有效的时滞下,两个耦合神经元的在相簇同步能增加。在相簇同步窗口的大小随着耦合强度的增加而增加。此结果对于我们理解神经元集群的运动是一个指导。     

Recurrent inhibition of sympathetic preganglionic neurons of the lateral horns of the spinal cord

Experiments on anesthetized and immobilized cats showed that repeated antidromic discharges can be evoked in 32.5% of sympathetic preganglionic neurons of the lateral horns in segments T3, T8–9, and L2 of the spinal cord, with intervals of 16 msec or more between them, which is much greater than the refractory period of these neurons. This feature was shown not to be connected with the properties of axons of that group of neurons and, in particular, with their after-subnormality. After orthodromic discharges in neurons of this group, for a much longer period of time than could be accounted for by possible collision, no antidromic discharges likewise were evoked. As a result of antidromic activation of some of these neurons in one segment, definite inhibition of the orthodromic response of other neurons of the same segment appeared, etiher by a reflex mechanism or through stimulation of descending pathways. The results point definitely to the existence of a mechanism of recurrent inhibition in some sympathetic preganglionic neurons of the lateral horns.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 9, No. 4, pp. 382–389, July–August, 1977.     

Biphasic response of human polymorphonuclear leucocytes and keratinocytes (epitheliocytes) fromXenopus laevis to mechanical stimulation

Summary Human polymorphonuclear leucocytes and epitheliocytes isolated from tadpole tails ofXenopus laevis were used to observe the responses of cells to mechanical stimulation with a microneedle. Biphasic responses were observed: a retraction phase lasting 1–3 s was followed by an extension phase lasting 10–40s. Weak stimulation evoked alocal response whilst on strong stimulation the whole cells rounded up. Spreading after induced rounding was at least one order of magnitude faster (it lasted less than 1–2min) than cell spreading after chemical dissociation of cell cultures. Local or extended loss of cell attachment to the substratum (observed with reflection interference contrast microscopy) preceded changes in cell morphology, visible with phase contrast microscopy. Repeated weak stimulation of one cell side induced extension and locomotion of the cell in this direction. The reported biphasic responses of cells to mechanical stimulation highlight the significance of exact timing when following any cell response to external stimuli.     

Neuronal and synaptic mechanisms of cortical inhibition

The latent periods, amplitude, and duration of IPSPs arising in neurons in different parts of the cat cortex in response to afferent stimuli, stimulation of thalamocortical fibers, and intracortical microstimulation are described. The duration of IPSPs evoked in cortical neurons in response to single afferent stimuli varied from 20 to 250 msec (most common frequency 30–60 msec). During intracortical microstimulation of the auditory cortex, IPSPs with a duration of 5–10 msec also appeared. Barbiturates and chloralose increased the duration of the IPSPs to 300–500 msec. The latent period of 73% of IPSPs arising in auditory cortical neurons in response to stimulation of thalamocortical fibers was 1.2 msec longer than the latent period of monosynaptic EPSPs evoked in the same way. It is concluded from these data that inhibition arising in most neurons of cortical projection areas as a result of the arrival of corresponding afferent impulsation is direct afferent inhibition involving the participation of cortical inhibitory interneurons. A mechanism of recurrent inhibition takes part in the development of inhibition in a certain proportion of neurons. IPSPs arise monosynaptically in 2% of cells. A study of responses of cortical neurons to intracortical microstimulation showed that synaptic delay of IPSPs in these cells is 0.3–0.4 msec. The length of axons of inhibitory neurons in layer IV of the auditory cortex reaches 1.5 mm. The velocity of spread of excitation along these axons is 1.6–2.8 msec (mean 2.2 msec).A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 394–403, May–June, 1984.