Mechanisms of impairment of precise movements during long-term hypokinesia

Antiorthostaic hypokinesia (AOHK) was found to entail a considerable diminishing of the control system's precision abilities. In the first 14-30 days of the AOHK (the 1st stage), variability of interimpike intervals (ISI) was sharply increased as well as the degree of synchronisation of the motor units' (MU) activity; starting from the 30th day (the 2nd stage), a regular diminishing of the ISI occurred and the MU synchronisation disappeared. The data obtained suggest the different nature of the precision disorders during the 1st and the 2nd stages of the AOHK: a reflex responses to support unloading and the atrophic processes in the muscles, respectively.     

Interspike interval patterns of taste neurons in the hamster solitary nucleus

The central nervous system first processes taste informationin the solitary nucleus, which has been almost exclusively studiedin terms of average firing rate. We analyzed interspike intervals(ISI's) of 25 taste-responsive single units in the hamster (Mesocricetusauratus) solitary nucleus. ISI's were measured during spontaneousactivity and during stimulation with NaCl, KCl, sucrose, ora mixture of the three, and graphed on semi-logarithmic plots.Two different ISI patterns were evident: simple (13 units) andcomplex (12 units). Simple ISI patterns had a single broad peakat 284.7 ± 70.4 ms spontaneous and 78.8 ± 12.8ms stimulated. All complex ISI patterns had one distinct, sharppeak for an interval about 10 ms (11.3 ± 0.4 ms: spontaneous,9.3 ± 0.5 ms: stimulated), and a second, broader peakat 273.9 ± 45.9 ms spontaneous and 71.5 ± 14.6ms stimulated. As rate of firing increased peaks in ISI patternspredictably moved towards lower intervals, but ISI pattern-typedid not change. This constancy of ISI pattern held for responsesof a unit across all stimuli and did not depend upon the stimulusspecificity or location of the unit within the rostral poleof the solitary nucleus. Apparently, the pattern that a tasteneuron generates is intrinsic to the neuron and may relate tothe way it processes tast information.     

Depression and/or potentiation of cortical responses after status epilepticus in immature rats

Lithium-pilocarpine status epilepticus (SE) resulted in delayed changes of single cortical interhemisperic (transcallosal) responses in immature rats. Low-frequency stimulation inducing depression and/or potentiation was studied to analyze possible dynamic changes in cortical responses. Status was elicited in 12-day-old (SE12) or 25-day-old (SE25) rats. Control siblings received saline instead of pilocarpine. Interhemispheric responses were elicited by stimulation of the sensorimotor region of the cerebral cortex 3, 6, 9, 13, or 26 days after status. A series of 5 biphasic pulses with intensity equal to twofold threshold were used for stimulation. The interval between pulses was 100, 125, 160, 200 or 300 ms, eight responses were always averaged. Peak amplitude of the first positive, first negative and second positive waves was measured and responses to the second, third, fourth and fifth pulse were compared with the first one. Animals after status epilepticus as well as lithium-paraldehyde controls exhibit a frequency depression at nearly all the intervals studied. An outlined increase of responses in SE rats in comparison with the controls three days after SE stayed just below the level of statistical significance. In addition, animals in the SE12 group exhibited potentiation of responses at this interval after SE. With longer intervals after SE, the relation between SE and control animals changed twice resulting in a tendency to lower amplitude of responses in SE than in control rats 26 days after SE. Rats in the SE25 group exhibited higher responses than controls 13 days after status, but this difference was not present at the longest interval after SE. Low-frequency stimulation did not reveal increased cortical excitability as a long-lasting consequence of status epilepticus induced in immature rats. In addition, the outlined differences between SE and control rats changed with the time after SE.     

The influence of concentration and relaxation on the EEG power spectra during a CNV paradigm

EEG segments of 1 sec duration, beginning 1 sec before the imperative stimulus were analysed by Fast Fourier Transformation in a CNV paradigm with interstimulus intervals (ISI) of different durations (1, 3, 5 sec) and with constant (K1, K3, K5) and randomized (R1, R3, R5) ISI presentation. In the alpha band, there were found differences in the power spectra between the constant and the longer randomized (R3, R5) ISI conditions, the latter having a slower center frequency, a smaller radius of gyration and a higher kurtosis. This describes a sharper alpha line of slower frequency in the R3 and the R5 ISI condition, due to pronounced synchronisation of alpha activity. It is discussed as an expression of increased relaxation and reduced concentration. In the theta band, differences appeared between the short ISI conditions (K1, R1) and the longer ones.     

The time scale of adaptation in tonal sequence processing by the mouse auditory midbrain neurons

The time course of poststimulatory adaptation of the inferior colliculus central nucleus (ICC) of CBB6F₁ hybrid mice to sound sequences, specifically, series of four tonal stimuli presented at intervals of 0, 2, 4, 10, 20, 50, 100, 200, 500, 700, 1000, and 1500 ms were studied. Assessment of the adaptation of the entire neuronal population have shown that, at an interstimulus interval of 0–200 ms, the response to the first tone in a series is significantly stronger than those to the second to fourth tones, the strengths of the latter three responses not differing significantly from one another. If the interstimulus interval is 500 ms or longer, the response to none of the tones in a series differs significantly in strength from the others. The role of adaptation of midbrain neurons to the grouping of components of bioacoustic stimuli is discussed.     

Features of the spontaneous unit activity in the human thalamic parafascicular (CM-Pf) complex and its modification in functional cerebral changes

New data on neural organization of the human thalamic parafascicular (CM-Pf) complex were revealed with microelectrode technique during 11 stereotaxic operations in alert diskinetic patients suffering from the tonic forms of spasmodic torticollis. The data were obtained as follows: the functional heterogeneity in cellular organization of the human CM-Pf thalamic nuclei and the existence of three (A, B and C) different types of neurons in these thalamic nuclei: with the irregular discharges (A-type, 18%); with short (10-20 ms) bursts characterised by unstable rhythmic 2-5 Hz pattern and by the low threshold Ca2+ dependent K+ conductance (B-type, 77%); with long-lasting (0.1-2.0 s) bursts of high-frequency trains and constant interburst intervals (C-type, 5%). The functional cerebral changes after motor test performances were shown to be accompanied by appearance of transient modifications of the background unit activity pattern and by tendency towards an increase of neural activity local synchronisation with some stabilising of oscillatory rhythm of discharging B-type neurons. For the first time, a direct relationship between functional characteristics of the human thalamic CM-Pf units and the motor deviations was found in spasmodic torticollis patients.     

Mechanically induced reflex responses in human triceps brachii

The short and long latency reflex responses of human triceps brachii muscle were recorded in 14 healthy volunteers. An electromechanical hammer was used to stretch the muscle and recordings were made from a surface electromyogram. The monosynaptic tendon reflex occurred at a mean latency of 12.5 ms (SE 0.7 ms). Later responses were observed in activated conditions (weak force production, preparatory period) at a mean latency of 62.8 ms (SE 3.5 ms). The amplitude of the short latency reflex increased during weak tension, the long latency reflex amplitude seemed to increase during the preparatory period testing. The amplitude increases can be attributed to increased lower motoneuron excitability even during weak voluntary activity. The tendency towards an increased amplitude during the preparatory period may be connected with the higher regulation of the long latency reflex.     

Human assessment of time intervals depending on the manner of their representation

On 42 subject three experimental series were carried out: in the first (12 persons) and second (24 persons) series the presented interval was limited by two short clicks, in the third series (6 persons)--by electrocutaneous stimuli. Duration of the stimuli was 1 ms. There were three regimes of work in the first and third series: the intervals successively increased from 100 to 500 ms with a step of 100 ms (1), decreased from 5000 to 100 ms (2) or varied in a random order (3). In the second series only the regime 3 was applied. In all series the method of temporal intervals reproduction was used. The means of the reproduction varied: in the second and third series the interval was reproduced by button pressing according to the presented duration: in the first series the end of the interval was marked by a short button push, and the beginning was the moment of the second stimulus presentation. With the first means a considerable overreproduction was observed of the presented duration at all intervals and all regimes. At the second and third series a phasic character of the reproduction duration was noted: up to 1000 ms the interval mostly was overestimated, over 2000 ms--it was significantly underestimated. It is suggested that as the estimation of the temporal interval implies some motor reaction, the afferent flow of signals from the active muscles can change the value of the reproduced duration. In the first series, the subjects probably do not take into account the time necessary for the realized signal perception.     

Motor unit activity during long-lasting intermittent muscle contractions in humans

Changes accompanying long-lasting intermittent muscle contractions (30%–50% of the maximal) were investigated by tracing the activity of 38 motor units (MU) of the human biceps brachii muscle recorded from fine-wire branched electrodes. The motor task was a continuous repetition of ramp-and-hold cycles of isometric flexion contractions. During ramp-up phases a significant decline in recruitment thresholds was found with no changes in the discharge pattern. During ramp-down phases the unchanged mean value of derecruitment thresholds during the task was accompanied by increased duration of the last two interspike intervals (ISI). These findings would suggest that during fatigue development the main compensatory mechanism during ramp-up contractions is space coding while for ramp-down contractions it is rate coding. During the steady-state phases the mean value of ISI, as well as the firing variability, had increased by the end of the task in most of the MU investigated . In addition 17 recruited MU were also investigated. These units revealed a lower initial discharge rate and a faster decrease in the mean discharge rate with the development of fatigue. The gradual reduction of the recruitment threshold of already active MU and the recruitment of new units demonstrated an increased excitability of the motorneuron pool during fatigue. A typical recruitment pattern (a first short ISI followed by a long one) was observed during ramp-up contractions in units active from the very beginning of the task, as well as during sustained contractions at the onset of the stable discharge of the additionally recruited MU. Accepted: 23 September 1997     

Factors influencing glottic dimensions during forced expiration

To examine the relationship between expiratory effort, expiratory flow, and glottic aperture, we compared the effects of actively and passively produced changes in flow in six normal subjects. During flow transients of 1.08 +/- 0.08 l/s produced by voluntary expiratory effort, glottic width (dg) increased by 54 +/- 13% (mean +/- SE). In contrast transient increases in expiratory flow, produced passively by chest compression, were not accompanied by increases in glottic dimensions. Similarly, when subjects expired through a resistance, transient passive increases in mouth pressure of 8.1 +/- 0.8 cmH2O failed to increase glottic width. However, when similar positive-pressure transients were produced actively, dg increased by 97 +/- 36% even though the expiratory efforts were accompanied by relatively small increases in flow (0.20 +/- 0.05 l/s). During tidal breathing glottic widening commenced 160 +/- 60 ms before the onset of inspiratory flow, whereas the widening associated with active flow and pressure transients did not measurably precede the onset of the change in flow or pressure. Our results indicate that transient expulsive efforts are associated with synchronous increases in dg, regardless of whether expiratory flow increases. The findings are most readily explained by a centrally determined synchronous recruitment of intrinsic laryngeal and expiratory muscles that facilitates lung emptying by minimizing airway resistance during forced exhalation.     

Rapid-Rate Paired Associative Stimulation over the Primary Somatosensory Cortex

Rapid-rate paired associative stimulation (rPAS) involves repeat pairing of peripheral nerve stimulation and Transcranial magnetic stimulation (TMS) pulses at a 5 Hz frequency. RPAS over primary motor cortex (M1) operates with spike-timing dependent plasticity such that increases in corticospinal excitability occur when the nerve and TMS pulse temporally coincide in cortex. The present study investigates the effects of rPAS over primary somatosensory cortex (SI) which has not been performed to date. In a series of experiments, rPAS was delivered over SI and M1 at varying timing intervals between the nerve and TMS pulse based on the latency of the N20 somatosensory evoked potential (SEP) component within each participant (intervals for SI-rPAS: N20, N20-2.5 ms, N20 + 2.5 ms, intervals for M1-rPAS: N20, N20+5 ms). Changes in SI physiology were measured via SEPs (N20, P25, N20-P25) and SEP paired-pulse inhibition, and changes in M1 physiology were measured with motor evoked potentials and short-latency afferent inhibition. Measures were obtained before rPAS and at 5, 25 and 45 minutes following stimulation. Results indicate that paired-pulse inhibition and short-latency afferent inhibition were reduced only when the SI-rPAS nerve-TMS timing interval was set to N20-2.5 ms. SI-rPAS over SI also led to remote effects on motor physiology over a wider range of nerve-TMS intervals (N20-2.5 ms – N20+2.5 ms) during which motor evoked potentials were increased. M1-rPAS increased motor evoked potentials and reduced short-latency afferent inhibition as previously reported. These data provide evidence that, similar to M1, rPAS over SI is spike-timing dependent and is capable of exerting changes in SI and M1 physiology.     

Reflection of the plastic properties of 2 neurons with a common monosynaptic input in the statistical characteristics of their impulse activity

Changes of cross-correlation histograms (CCH) of impulse trains and of mean interspike intervals (ISI) of neurones N1 and N2 with a common monosynaptic excitatory or inhibitory-excitatory input from N3, at changes of efficiency of interneuronal connections, neurone excitability and summate action on them of independent random afferent synaptic inflows were studied by methods of mathematical and biomathematical modelling of neuronal interaction. It was shown that the increase of amplitude of the central peak (trough) of a normalized CCH of N1-N2 accompanied by reduction of mean ISI of N1 and N2, is either a sign of an increase of the amplitude of postsynaptic potentials of N1 and N2 elicited by impulses of the nonrecorded N3 or a sign of an increase of mean ISI of N3.     

How noisy adaptation of neurons shapes interspike interval histograms and correlations

Channel noise is the dominant intrinsic noise source of neurons causing variability in the timing of action potentials and interspike intervals (ISI). Slow adaptation currents are observed in many cells and strongly shape response properties of neurons. These currents are mediated by finite populations of ionic channels and may thus carry a substantial noise component. Here we study the effect of such adaptation noise on the ISI statistics of an integrate-and-fire model neuron by means of analytical techniques and extensive numerical simulations. We contrast this stochastic adaptation with the commonly studied case of a fast fluctuating current noise and a deterministic adaptation current (corresponding to an infinite population of adaptation channels). We derive analytical approximations for the ISI density and ISI serial correlation coefficient for both cases. For fast fluctuations and deterministic adaptation, the ISI density is well approximated by an inverse Gaussian (IG) and the ISI correlations are negative. In marked contrast, for stochastic adaptation, the density is more peaked and has a heavier tail than an IG density and the serial correlations are positive. A numerical study of the mixed case where both fast fluctuations and adaptation channel noise are present reveals a smooth transition between the analytically tractable limiting cases. Our conclusions are furthermore supported by numerical simulations of a biophysically more realistic Hodgkin-Huxley type model. Our results could be used to infer the dominant source of noise in neurons from their ISI statistics.     

Conduction along myelinated and demyelinated nerve fibres during the recovery cycle: Model investigations

The membrane excitability changes as well as the underlying mechanisms of these changes in a normal and in a systematically paranodally demyelinated nerve fibre have been investigated by paired stimulation during the first 30 ms of the recovery cycle. The ionic current kinetics determining the observed changes in the action potential parameters are presented also. The simulation of the conduction in the normal fibre is based on the Frankenhaeuser and Huxley (1964) and Goldman and Albus (1968) equations, while in the case of a demyelinated fibre according to the same equations modified by Stephanova (1988a). It has been shown for the demyelinated membrane that increased demyelination increases both the threshold current for the second potential as well as the absolute refractory period. With increasing interpulse interval, the subnormality of the membrane excitability is followed by supernormality in the case of the demyelinated membrane. For the recovery cycle of 30 ms under consideration no supernormality of the normal membrane excitability is obtained. With interpulse interval from 8.8 to 10.9 ms, the highest degree of demyelination (l=30 m) is accompanied by a refractory period of transmission. The membrane properties of the normal and demyelinated fibres recover 20 ms after the first pulse. For short interpulse intervals, the amplitude of the second action potential is decreased, and a slower propagation velocity is obtained. The most sensitive phenomenon is the excitability of the demyelinated membrane, which remains unrecovered 30 ms after the first pulses has been applied.     

Die Abhängigkeit der Reaktionszeit von der zeitlichen Folge optischer Reize

Summary An apparatus consisting of (a) a small computer, (b) an oscilloscope light-dot controlled by it, and (c) a pencil-shaped peg containing three accelerometers, which are sampled at 150sec intervals by the computer, has been used to measure simple reaction time for human hand-movement. The stimulus, a jump of the light dot, was presented without a warning signal in series of 100 jumps either after a fixed period or a random time. The average interstimulus interval (ISI) was between 1.3 and 15.8 sec. For every parameter set 1,000 reaction times (RTs) were accumulated during 10 different days.The main results are: (a) RT increases with increasing mean ISI; (b) RT is longer for random ISIs than for constant ones; (c) RT increases slightly with time accumulating during runs; (d) within a series of random ISIs, RT is neither depending on the value of the last ISI before reaction nor on that of the last but one; (e) the probability distribution of RTs has a standard deviation increasing with mean ISI and from periodic to random ISI, and a non-negligible, roughly constant skewness.

---

---

Jetzt: Universitäts-Augenklinik Freiburg i.Br.

---

Zur Zeit: CRESS, York University, Toronto, (Canada).

---

Wir danken Herrn Prof. B. Hassenstein für manche Diskussion über kybernetische Probleme und einen ersten Hinweis auf die Fragen der gezielten Handbewegung. Der Rechner stand aus Mitteln zur Verfügung, die vom Bundesministerium für Bildung und Wissenschaft für andere Experimente zur Verfügung gestellt waren, wir möchten auch für diese Unterstützung danken. Schließlich danken wir der Zentralstelle für Luftfahrt-Dokumentation und -Information, München, für wertvolle Literaturhinweise.     

Perineal swelling, intermenstrual cycle, and female sexual behavior in bonobos (Pan paniscus)

Many reports have claimed that the duration of the swelling cycle in female bonobos (Pan paniscus) is longer than that of chimpanzees, and that the bonobo maximum swelling phase is markedly prolonged. Field data on intermenstrual intervals (IMIs) in female bonobos are limited and restricted to interswelling intervals (ISIs), which are assumed to reflect the IMI, though a direct comparison between the duration of ISIs and IMIs is still lacking. Reports on bonobo sexual activity as a function of the swelling phase are often contradictory. Moreover, the function of female homosexual interactions (genito-genital (GG) rubbing) is still debated. This study examines the reliability of the ISI as an approximation of the IMI, and the attractivity of female sexual swellings for other individuals. An analysis of 51 ISI-IMI pairs showed that ISIs are a fair representation of the reproductive cycle. The cycle length was 35.6+/-1.1 SE days relying on the ISI, whereas it was 35.0+/-1.1 SE days considering the IMI. This result is similar to the cycle length reported for chimpanzees. Female homosexual interactions and copulatory rates were higher during maximum tumescence, suggesting that the sexual swelling may be attractive for both males and other females. Furthermore, the GG-rubbing was performed free of a hierarchical postural imposition, and was not correlated with affinitive interactions. We suggest that GG-rubbing, which is generally the most frequent female sexual interaction, is a tool for social assessments among females.     

Diurnal variation in heart rate variability before and after maximal exercise testing

As heart-rate variability (HRV) is under evaluation in clinical applications, the authors sought to better define the interdependent impact of age, maximal exercise, and diurnal variation under physiologic conditions. The authors evaluated the diurnal changes in HRV 24-h pre- and post-maximal aerobic exercise testing to exhaustion in young (19-25 yrs, n?=?12) and middle-aged (40-55 yrs, n?=?12) adults. Subjects wore a portable 5-lead electrocardiogram holter for 48?h (24?h prior to and following a maximal aerobic capacity test). Time-, frequency-, time-frequency-, and scale-invariant-domain measures of HRV were computed from RR-interval data analyzed using a 5-min window size and a 2.5-min step size, resulting in a different set of outputs every 2.5?min. Results were averaged (mean?±?SE) over four prespecified time periods during the morning, afternoon, evening, and night on Day 1 and Day 2. Diurnal changes in HRV in young and middle-aged adults were compared using a two-way, repeated-measures analysis of variance (ANOVA). Young adults demonstrated higher HRV compared to middle-aged adults during periods of wakefulness and sleep prior to maximal exercise stress testing (i.e., high-frequency power during Day 1: young adults: morning 1862?±?496?ms(2), afternoon 1797?±?384?ms(2), evening 1908?±?431?ms(2), and night 3202?±?728?ms(2); middle-aged adults: morning 341?±?53?ms(2), afternoon 405?±?68?ms(2), evening 469?±?80?ms(2), and night 836?±?136?ms(2)) (p < .05). Exercise resulted in reductions in HRV such that multiple measures of HRV were not significantly different between age groups during the afternoon and evening periods. All measures of HRV demonstrated between-group differences overnight on Day 2 (p < .05). Young adults are associated with higher baseline HRV during the daytime. Sleep increases variability equally and proportionally to daytime variability. Given the higher baseline awake HRV and equal rise in HRV during sleep, the change in HRV from sleep to morning with exercise is greater in younger subjects. These physiologic results have clinical significance in understanding the pathophysiology of altered variability in ill patients.     

Airflow and pressure during canary song: direct evidence for mini-breaths

Summary Male canaries (Serinus canaria) produce songs of long duration compared to the normal respiratory cycle. Each phrase in a song contains repetitions of a particular song syllable, with repetition rates for different syllables ranging from 3 to 35 notes/s. We measured tracheal airflow and air sac pressure in order to investigate respiratory dynamics during song.Song syllables (11–280 ms) are always accompanied by expiratory tracheal airflow. The silent intervals (15–90 ms) between successive syllables are accompanied by inspiration, except for a few phrases where airflow ceases instead of reversing. Thus, the mini-breath respiratory pattern is used most often by the five birds studied and pulsatile expiration is used only occasionally.Songs and phrases accompanied by minibreaths were of longer duration than those accompanied by pulsatile expiration, presumably because the animal's finite vital capacity is not a limiting factor when the volume of air expired for one note is replaced by inspiration prior to the next. Pulsatile expiration was used for only a few syllable types from one bird that were produced at higher repetition rates than syllables accompanied by mini-breaths. We suggest that male canaries switch to pulsatile expiration only when the syllable repetition rate is too high (greater than about 30 Hz) for them to achieve mini-breaths.Changes in syringeal configuration that may accompany song are discussed, based on the assumption that changes in the ratio of subsyringeal (air sac) pressure to tracheal flow rate reflect changes in syringeal resistance.     

Human motor unit recruitment and derecruitment during long lasting intermittent contractions.

Seven healthy subjects were investigated in cyclic ramp-and-hold long lasting isometric contractions. Wire branched electrodes were used for selective recording of single motor unit (MU) potentials from m. biceps brachii. MU behaviour was defined in terms of recruitment/derecruitment thresholds (RT and DT) and the duration of interspike intervals (ISI). A total of 63 MUs was investigated: 40 units were active from the beginning of the task performance and another 23 were recruited later. There were no changes in the recruitment pattern of MUs with fatigue development - a short first ISI followed by a very long second one and an almost constant firing rate after this transient phase. The tendency of RT to gradually decrease dominates the results. Thus, the required constant rate of force increase with fatigue development was maintained mostly by the mechanisms of space coding (i.e., decrease of RT and recruitment of additional MUs). Oppositely, the time behaviour of the DT changes was not uniform and rate coding was an essential mechanism in the adaptation of MU activity to muscle fatigue during relaxation phases. The recruitment pattern and fatigue related behaviour of the additionally recruited MUs were similar to those of MUs active from the first cycle of the motor task performance.     

Greater serum GH response to arm than to leg exercise performed at equivalent oxygen uptake

The aim of this study was to provide information concerning the mechanism of exercise-induced stimulation of growth hormone (GH) release in human subjects. For this reason serum GH as well as some hemodynamic variables and blood concentrations of noradrenaline (NA), insulin (IRI), lactate (LA), glucose (BG), and free fatty acids (FFA) were determined in seven healthy male subjects exercising on a bicycle ergometer with arms or legs and running on a treadmill at equivalent oxygen consumption levels. Significantly greater increases in serum GH concentration accompanied arm exercises than those observed during the leg exercises. This was accompanied by greater increases in heart rate, blood pressure, and plasma NA and blood lactate concentrations. Serum IRI decreased during both leg exercises and did not change during the arm exercise. There were no differences in BG and plasma FFA concentrations between the three types of exercise. The role of humoral and neural signals responsible for the greater GH response to arm exercise is discussed. The findings are consistent with the hypothesis that neural afferent signals sent by muscle "metabolic receptors" participate in the activation of GH release during physical exercise. It seems likely that the stimulation of these chemoreceptors is more pronounced when smaller muscle groups are engaged at a given work load. However, a contribution of efferent impulses derived from the brain motor centres to the control system of GH secretion during exercise is also possible.