The complete frequency spectrum of physiological tremor can be recreated by broadband mechanical or electrical drive

2015 ◽  
Vol 113 (2) ◽  
pp. 647-656 ◽  
Author(s):  
Carlijn Andrea Vernooij ◽  
Martin Lakie ◽  
Raymond Francis Reynolds
Keyword(s):  
Middle Finger ◽  
Muscle Stiffness ◽  
Emg Activity ◽  
Physiological Tremor ◽  
Mechanical Resonance ◽  
Low Frequencies ◽  
High Frequency Peak ◽  
Input Intensity ◽  
Frequency Peak ◽  
Finger Tremor

Two frequency peaks of variable preponderance have been reported for human physiological finger tremor. The high-frequency peak (20–25 Hz, seen only in postural tremor) is generally attributed to mechanical resonance, whereas the lower frequency peak (8–12 Hz, seen in both postural and kinetic tremor) is usually attributed to synchronous central or reflexive neural drive. In this study, we determine whether mechanical resonance could generate both peaks. In relaxed subjects, an artificial finger tremor was evoked by random mechanical perturbations of the middle finger or random electrical muscular stimulation of the finger extensor muscle. The high and the low frequencies observed in physiological tremor could both be created by either type of artificial input at appropriate input intensity. Resonance, inferred from cross-spectral gain and phase, occurred at both frequencies. To determine any neural contribution, we compared truly passive subjects with those who exhibited some electromyographic (EMG) activity in the finger extensor; artificially created tremor spectra were almost identical between groups. We also applied electrical stimuli to two clinically deafferented subjects lacking stretch reflexes. They exhibited the same artificial tremor spectrum as control subjects. These results suggest that both typical physiological finger tremor frequencies can be reproduced by random artificial input; neither requires synchronized neural input. We therefore suggest that mechanical resonance could generate both dominant frequency peaks characteristic of physiological finger tremor. The inverse relationship between the input intensity and the resulting tremor frequency can be explained by a movement-dependent reduction in muscle stiffness, a conjecture we support using a simple computational model.

Postmovement Changes in the Frequency and Amplitude of Physiological Tremor Despite Unchanged Neural Output

2010 ◽  
Vol 104 (4) ◽  
pp. 2020-2023 ◽  
Author(s):  
Raymond Reynolds ◽  
Martin Lakie
Keyword(s):  
Passive Movement ◽  
Muscle Stiffness ◽  
Emg Activity ◽  
Hand Position ◽  
Vertical Acceleration ◽  
Physiological Tremor ◽  
Joint Mechanics ◽  
Wrist Flexion ◽  
Temporary Reduction ◽  
Flexion Extension

Active or passive movement causes a temporary reduction in muscle stiffness that gradually returns to baseline levels when the muscle remains still. This effect, termed muscle thixotropy, alters the mechanical properties of the joint around which the muscle acts, reducing its resonant frequency. Because physiological tremor is affected by joint mechanics, this suggests that prior movement may alter tremor independently of neural output. To address this possibility, vertical acceleration of the outstretched prone hand was recorded in eight healthy subjects, along with EMG activity of the extensor digitorum communis muscle. A series of voluntary wrist flexion/extension movements was performed every 20 s, interspersed by periods during which hand position was maintained. Time-dependent changes in the amplitude and frequency of acceleration and EMG were analyzed using a continuous wavelet transform. Immediately following movement, acceleration displayed a significant increase in wavelet power accompanied by a reduction in peak frequency. During the postmovement period, power declined by 63%, and frequency increased from 7.2 to 8.0 Hz. These changes occurred with an exponential time constant of 2–4 s, consistent with a thixotropic mechanism. In contrast to acceleration, EMG activity showed no significant changes despite being strongly related to acceleration during the movement itself. These results show that prior movement transiently increases the amplitude and reduces the frequency of physiological tremor, despite unchanging neural output. This effect is best explained by a reduction in joint stiffness caused by muscle thixotropy, highlighting the importance of mechanical factors in the genesis of physiological tremor.

scholarly journals On the non-linear energy transfer in a gravity-wave spectrum. Part 3. Evaluation of the energy flux and swell-sea interaction for a Neumann spectrum

1963 ◽  
Vol 15 (3) ◽  
pp. 385-398 ◽  
Author(s):  
K. Hasselmann
Keyword(s):  
Energy Transfer ◽  
Gravity Wave ◽  
Wave Spectrum ◽  
Low Frequency ◽  
Low Frequencies ◽  
Frequency Peak ◽  
Non Linear ◽  
Gain Energy ◽  
Rate Of Decay ◽  
Linear Interactions

The energy transfer due to non-linear interactions between the components of a gravity-wave spectrum discussed in Parts 1 and 2 of this paper is evaluated for a fully and partially developed Neumann spectrum with various spreading factors. The characteristic time scales of the energy transfer are found to be typically of the order of a few hours. In all cases the high frequencies and the low-frequency peak are found to gain energy from an intermediate range of frequencies. The transfer of energy to very low frequencies and to waves travelling at large angles to the main propagation direction of the spectrum is negligible. Computations are presented also for the rate of decay of swell interacting with local wind-generated seas (represented by a Neumann spectrum). An appreciable decay is found only for swell frequencies in the same range as those of the local sea.

scholarly journals Low-Frequency Oscillations in the Cerebellar Cortex of the Tottering Mouse

2009 ◽  
Vol 101 (1) ◽  
pp. 234-245 ◽  
Author(s):  
Gang Chen ◽  
Laurentiu S. Popa ◽  
Xinming Wang ◽  
Wangcai Gao ◽  
Justin Barnes ◽  
...  
Keyword(s):  
Cerebellar Cortex ◽  
Ampa Receptors ◽  
Cortical Neurons ◽  
Low Frequency ◽  
Autosomal Recessive Disorder ◽  
Parallel Fiber ◽  
Emg Activity ◽  
Gene Encoding ◽  
Low Frequencies ◽  
Low Frequency Oscillations

The tottering mouse is an autosomal recessive disorder involving a missense mutation in the gene encoding P/Q-type voltage-gated Ca2+channels. The tottering mouse has a characteristic phenotype consisting of transient attacks of dystonia triggered by stress, caffeine, or ethanol. The neural events underlying these episodes of dystonia are unknown. Flavoprotein autofluorescence optical imaging revealed transient, low-frequency oscillations in the cerebellar cortex of anesthetized and awake tottering mice but not in wild-type mice. Analysis of the frequencies, spatial extent, and power were used to characterize the oscillations. In anesthetized mice, the dominant frequencies of the oscillations are between 0.039 and 0.078 Hz. The spontaneous oscillations in the tottering mouse organize into high power domains that propagate to neighboring cerebellar cortical regions. In the tottering mouse, the spontaneous firing of 83% (73/88) of cerebellar cortical neurons exhibit oscillations at the same low frequencies. The oscillations are reduced by removing extracellular Ca2+and blocking L-type Ca2+channels. The oscillations are likely generated intrinsically in the cerebellar cortex because they are not affected by blocking AMPA receptors or by electrical stimulation of the parallel fiber–Purkinje cell circuit. Furthermore, local application of an L-type Ca2+agonist in the tottering mouse generates oscillations with similar properties. The beam-like response evoked by parallel fiber stimulation is reduced in the tottering mouse. In the awake tottering mouse, transcranial flavoprotein imaging revealed low-frequency oscillations that are accentuated during caffeine-induced attacks of dystonia. During dystonia, oscillations are also present in the face and hindlimb electromyographic (EMG) activity that become significantly coherent with the oscillations in the cerebellar cortex. These low-frequency oscillations and associated cerebellar cortical dysfunction demonstrate a novel abnormality in the tottering mouse. These oscillations are hypothesized to be involved in the episodic movement disorder in this mouse model of episodic ataxia type 2.

scholarly journals The nature of the unassociated 2FGL sources

2014 ◽  
Vol 10 (S313) ◽  
pp. 91-92
Author(s):  
T. Pursimo ◽  
R. Ojha ◽  
E. Ferrara ◽  
F. Acero ◽  
H. Johnston ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
Low Frequency ◽  
Spectral Energy ◽  
High Frequency Peak ◽  
X Ray ◽  
Frequency Peak ◽  
Inverse Compton ◽  
Multi Wavelength ◽  
Error Circle

AbstractThe majority of Fermi-LAT detected (2FGL) sources are AGN, mostly blazars. However, the second largest category in the 2FGL are unassociated sources (~30% or 575 sources), whose multi-wavelength counterpart is either inconclusive or absent. Follow-up observations and archival data at X-ray, optical, and radio frequencies suggest that many unassociated 2FGL sources are strong candidates to be AGN. Typical observed characteristics of 2FGL detected AGN include variability at all frequencies and a spectral energy distribution (SED) with two “bumps”; a low-frequency synchrotron peak in the radio to optical/X-ray region and a high-frequency peak, possibly due to synchrotron self-Compton or Inverse Compton processes, that extends up to TeV energies. We present optical follow-up observations of a sample of Fermi unassociated sources with one or more potential X-ray counterparts detected within the LAT error circle.

Responses of midbrain dopamine neurons to behavioral trigger stimuli in the monkey

1986 ◽  
Vol 56 (5) ◽  
pp. 1439-1461 ◽  
Author(s):  
W. Schultz
Keyword(s):  
Food Reward ◽  
Arm Movement ◽  
Dopamine Neurons ◽  
Emg Activity ◽  
Cognitive Mechanisms ◽  
Low Frequencies ◽  
Long Duration ◽  
Trigger Stimulus ◽  
Midbrain Dopamine ◽  
Physically Identical

Destruction of the midbrain dopamine (DA) system in Parkinsonian man and experimental animals leads to deficits in initiation of behavior, motor performance, and cognitive mechanisms. We have investigated the extracellular impulse activity of single midbrain DA neurons in unlesioned monkeys performing in a controlled behavioral task that was designed to paradigmatically test behavioral reactivity. Animals were trained to execute natural forelimb reaching movements for food reward in response to a trigger stimulus. Presumptive DA neurons were histologically located in the pars compacta of substantia nigra and in neighboring areas A8 and A10. They spontaneously discharged polyphasic impulses of relatively long duration (1.4-3.6 ms) and at low frequencies (0.5-8.5/s). Systemic injections of low doses of the DA autoreceptor agonist apomorphine (0.05-0.2 mg/kg) depressed the activity of virtually all thus tested DA neurons. In following established criteria, these characteristics strongly suggest the DAergic nature of the recorded neurons. The majority of midbrain DA neurons (70 of 128) responded to the behavioral trigger stimulus of the task with a short burst of impulses. Latencies ranged from 39 to 105 ms (median 65 ms) for onset and from 65 to 165 ms (median 95 ms) for peak of responses. Responses occurred before arm movement and at the time of or before onset of electromyographic (EMG) activity in prime mover muscles. Responses were time-locked to the stimulus and not to the onset of movement or EMG. Responses remained present in most neurons but were reduced when vision of the behavioral trigger stimulus was prevented while maintaining the associated acoustic signals. In another variation of the task, most neurons also responded to a stimulus that was physically identical to the behavioral trigger but to which the animal made no movement. The activity of a few DA neurons (11 of 128) was reduced following presentation of the behavioral trigger stimulus, with latencies comparable to those of activations. The activity of many DA neurons was increased (40 of 128) or reduced (22 of 128) during execution of the forelimb reaching movement. These changes were of a slow and moderate nature, and were minor compared with responses to the behavioral trigger stimulus. About half of movement-related neurons also responded to the behavioral trigger. The activity of a few DA neurons was increased (11 to 128) or reduced (1 to 128) when the food reward reached the mouth. These changes did not occur with spontaneous mouth movements. About half of these neurons also responded to the behavioral trigger.(ABSTRACT TRUNCATED AT 400 WORDS)

Abrupt Climatic Change at 90,000 yr BP: Faunal Evidence from Gulf of Mexico Cores

1972 ◽  
Vol 2 (3) ◽  
pp. 384-395 ◽  
Author(s):  
James P. Kennett ◽  
Paul Huddlestun
Keyword(s):  
Gulf Of Mexico ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Apparent Temperature ◽  
Time Interval ◽  
Sedimentation Rates ◽  
High Frequency Peak ◽  
Southern France ◽  
Frequency Peak ◽  
Abrupt Climatic Change

Planktonic foraminiferal studies have been carried out on 28 piston cores of late Pleistocene age from the western Gulf of Mexico, an area of high sedimentation rates. For the interval between 73 × 103 and 95 × 103 yr BP, two of these cores have sedimentation rates of 12 and 15 cm/1000 yr. Calculation of the speed of faunal changes within this interval reveals an extremely rapid paleoclimatic-paleooceanographic change at approximately 90 × 103 years BP. Several species including distinctly warm-sensitive forms, then disappeared from the Gulf of Mexico in less than 350 yr, leaving a depleted planktonic foraminiferal fauna greatly dominated by only three species with little apparent temperature preference. This fauna existed for 2.5 × 103 yr after which distinctly cooler water elements increased in abundance rapidly and formed a high frequency peak approx 83.5–85 × 103 years BP. This increase in cooler water elements reflects either a return to more stable environmental conditions or a lag in their migration to the Gulf of Mexico after the severe climatic cooling, rather than further cooling.The faunal event in the Gulf of Mexico correlates with an even more spectacular event recorded in the Greenland ice sheet by a drop in 18O values within a time interval of only about 100 yr (Dansgaard et al., 1971, 1972). A possibly correlative climatic event of similarly rapid nature has also been reported for speleothems from southern France (Duplessy et al., 1970).The paleoclimatic event is closely associated stratigraphically with a widespread volcanic ash layer, although it is possibly significant that the increased volcanism occurred 1000 yr after the paleoclimatic event. A rapid lowering of the lysocline occurs simultaneously with the paleoclimatic event although faunal diversity is low in the succeeding fauna despite decreased calcium carbonate solution. Both the association with volcanism and changes in the position of the lysocline may be significant in consideration of mechanisms of such rapid climatic changes. In turn, such rapid paleoclimatic-paleooceanographic changes as observed in tropical Gulf of Mexico cores, in the Greenland ice sheet and in caves of southern France must be considered in the evaluation of causal mechanisms of glacial and interglacial oscillations.

Positive phototaxis of the brine shrimp Artemia salina to monochromatic light

1978 ◽  
Vol 56 (4) ◽  
pp. 708-711 ◽  
Author(s):  
Ronald B. Aiken ◽  
Jack P. Hailman
Keyword(s):  
High Frequency ◽  
Brine Shrimp ◽  
Spectral Response ◽  
Monochromatic Light ◽  
Artemia Salina ◽  
Visual Pigments ◽  
High Frequency Peak ◽  
Crab Larva ◽  
Positive Phototaxis ◽  
Frequency Peak

The brine shrimp Artemia salina was photopositive in response to monochromatic light of approximately equal quantum intensity of two absolute levels. At the higher level (about 3 × 1014 quanta s−1 cm−2), the spectral response was bimodal with peaks near 560 and 700 THz frequency (about 535 and 430 nm wavelength, respectively), with an antimode at about 640 THz (465 nm). Response at the lower level (about 2 × 1014) was slightly lower and the midspectrum peak was shifted to higher frequencies (shorter wavelengths) and depressed relative to the high-frequency peak near 700 THz. The results suggest that positive phototaxis is mediated by two visual pigments, the high-frequency (short-wavelength) pigment being activated at lower illuminations than the midspectrum pigment. A similar bimodal response is known from a crab larva, but this appears to be the first anostracan crustacean to have been tested.

Estimation of Wind-Sea and Swell Components in a Bimodal Sea State

2004 ◽  
Vol 128 (4) ◽  
pp. 265-270 ◽  
Author(s):  
K. C. Ewans ◽  
E. M. Bitner-Gregersen ◽  
C. Guedes Soares
Keyword(s):  
Wave Spectrum ◽  
Low Frequency ◽  
Wave Spectra ◽  
Spectral Parameters ◽  
High Frequency Peak ◽  
Wave Measurements ◽  
Frequency Peak ◽  
Directional Wave ◽  
Wind Sea ◽  
Complete Frequency

Methods for separating the spectral components and describing bimodal wave spectra are evaluated with reference to wave spectra from directional wave measurements made at the Maui location off the west coast of New Zealand. Two methods involve partitioning bimodal wave spectra into wind-sea and swell components and then fitting a spectral function to each component, while the third assigns an average spectral shape based on the integrated spectral parameters. The partitioning methods involve separating the wave spectrum into two frequency bands: a low-frequency peak, the swell component, and a high-frequency peak, the wind-sea. One partitioning method uses only the frequency spectrum while the other analyzes the complete frequency-direction spectrum. Comparison of the spectral descriptions and derived parameters against the measured counterparts provides insight into the accuracy of the different approaches to describing actual bimodal sea states.

Sign in / Sign up

Export Citation Format

Share Document