Hz Tremor Research Articles

Pulsatile control of the human masticatory muscles.

Spectral analysis of jaw acceleration confirmed that the human mandible 'trembles' at a peak frequency around 6 Hz when held in its rest position and at other stationary jaw openings. The 6 Hz tremor increased during very slow movements of the mandible, but other lower-frequency peaks became prominent during more rapid jaw movements. These lower-frequency peaks are likely to be the result of asymmetries in the underlying, voluntarily produced, 'saw-tooth' movements. In comparison, finger tremor at rest and during slow voluntary movements had a mean peak frequency of about 8 Hz: this frequency did not change during rhythmical finger flexion and extension movements, but the power of the tremor increased non-linearly with the speed of the movement. The resting jaw tremor was weakly coherent with the activity of the masseter and digastric muscles at the tremor frequency in about half the subjects, but was more strongly coherent during voluntary movements in all subjects. The masseter activity was at least 150 deg out of phase with the digastric activity at the tremor frequency (and at all frequencies from 2.5-15 Hz). The alternating pattern of activity in antagonistic muscles at rest and during slow voluntary movements supports the idea that the masticatory system is subject to pulsatile control in a manner analogous to that seen in the finger.

The dynamics of resting and postural tremor in Parkinson's disease

Objective: The study examines the time and frequency structure of Parkinson's disease tremor in patients that exhibit no clinical signs of tremor. Methods: Eight mild to moderate Parkinson's disease and 8 matched control subjects maintained their limb in a constant position (30 s) under a postural finger, postural hand and resting tremor condition. Finger acceleration from the middle phalange, electromyographic (EMG) activity from extensor digitorum communis and flexor digitorum superficialis (FDS) were recorded. Results: The data confirmed that there were no differences in the amount of limb motion and the modal frequency was around 9 Hz for each subject group. The time-dependent organization of tremor was more regular (lower approximate entropy [ApEn]) in Parkinson's disease. Both time and frequency analyses between the acceleration and extensor EMG signals demonstrate a reduction in the 20–25 Hz tremor component and an increase in the 8–12 Hz region of tremor. Conclusions: The results are discussed in relation to the proposal that increased regularity results from an increase in motor unit synchronization at 8–12 Hz and a reduction in the amplitude of the 20–25 Hz tremor component. The time and frequency structure of tremor may be useful in assessing individuals with Parkinson's disease.

Acute hypoxia activates human 8–12 Hz physiological tremor

Hypoxia causes arousal. Therefore, we hypothesized that hypoxia activates the human somatomotor system and should augment tremor. We determined the effects of hypoxia, PET O2=45±2.2 mm Hg, hypocapnia, and the hypocapnic–hypoxic interaction on finger tremor during elastic loading. A total of 12 healthy male volunteers were studied during five conditions: eupnea, hypocapnic hypoxia, eucapnic hypoxia, hypocapnic normoxia, and eucapnic normoxia. Acceleration power spectra were computed to quantify 8–12 Hz tremor. Hypoxia significantly augmented 8–12 Hz physiological tremor ( P=0.002). Furthermore, six subjects (50%) exhibited significantly more tremor during hypocapnic hypoxia (hH) than during eucapnic hypoxia (eH). We conclude that acute hypoxia augments 8–12 Hz physiological tremor, and hypocapnia further augments this tremor in some subjects. As such, hypoxic tremor is activated physiological tremor, and entrainment of spinal α-motoneuron activity may be the final common pathway.

Load-dependence of fatigue related changes in tremor around 10 Hz

Objectives: The aim of the study was to investigate the effects of different loads on tremor around 10 Hz during fatiguing contractions.Methods: Eighteen healthy volunteers performed sustained isometric knee extensions at 30%, 50% and 70% maximum voluntary contraction (MVC). During the fatiguing contractions, mechanical recordings were made with a high-resolution force sensor. Tremor-power was calculated for the 6–20 Hz frequency window as a function of time normalized to endurance time.Results: Initial tremor power was different between the high and low load tasks. Changes of tremor with contraction time differed between the three tasks, in that tremor of the 30% MVC contraction showed the least decrease throughout the sustained contraction, whilst that of the 50% and 70% MVC showed progressively higher decreases. At failure, all 3 contractions merged to the same tremor level.Conclusion: Load-dependent, fatigue-related 6–20 Hz tremor changes during sustained submaximum voluntary contractions seem mainly the consequence of recruitment of new units and fatigue-related properties of the high threshold motor units of muscles.

Seismicity associated with the 1995–1996 eruptions of Ruapehu volcano, New Zealand: narrative and insights into physical processes

Seismicity associated with the 1995–1996 eruptions of Ruapehu reflects processes associated with the intrusion of magma to shallow depth in the volcanic edifice, its subsequent eruption, and changes in the volcanic plumbing system resulting from the eruptions. The sequence consisted of two distinct periods of eruptive activity, the first lasting from September 17, 1995 until late-October or early-November 1995 and the second from June 16, 1996 until late-July 1996. Immediately prior to and during the early stages of the 1995 eruptions, seismicity was similar to that recorded at Ruapehu during the previous 25 years, with the exception of the occurrence between September 17 and 25, 1995 of sub-1 Hz tremor, which is thought to represent magmatic intrusion. In early-October, a new pattern of seismicity was established with the disappearance of the 2 Hz tremor resonator source and a change to wideband (2–10 Hz) tremor and wideband volcanic earthquakes. This change coincided with the ejection of the last vestiges of Crater Lake and the change in eruptive style from phreatomagmatic to magmatic. Seismicity associated with the 1996 eruptions was very similar to that which accompanied the later part of the 1995 activity, implying the same eruption processes and that no significant changes had occurred in the volcanic plumbing system during the intervening period. Geochemical, geodetic, and seismic precursors to the 1995 eruptions were both minor and inconsistent, highlighting the difficulty in forecasting these eruptions. Furthermore, deep volcano-tectonic earthquakes were extremely rare throughout the 1995 and 1996 eruptive sequences, suggesting that stresses associated with magmatic intrusion were minor. This most likely resulted from the existence of either an open or a ductile pathway from the deep magma source to the surface prior to the eruptions and because the volume of magma intruded and subsequently erupted was relatively small (<0.05 km 3).

Seismicity of Ruapehu volcano, New Zealand, 1971–1996: a review

From 1971 until 1995, the style of seismicity at Ruapehu changed little, reflecting a period of relatively low eruptive activity and consequent long-term stability within the vent system. Volcanic earthquakes and volcanic tremor were both dominated by a frequency of about 2 Hz. Volcanic earthquakes accompanied all phreatic and phreatomagmatic eruptions, but not small hydrothermal eruptions that originated within Crater Lake. Furthermore, more than half of the M L>3 volcanic earthquakes and changes in the reduced displacement of 2 Hz volcanic tremor by as much as a factor of 20 occurred without any accompanying eruptive activity. Three and 7 Hz volcanic tremor were also recorded, although never at lower-elevation seismometers. At times, this tremor was stronger at the summit seismometer than the 2 Hz tremor. Their source regions were independent of the 2 Hz source, and located at shallower depths. Volcano-tectonic earthquakes were generally unrelated to eruptive activity. The seismicity accompanying the 1995–1996 eruptive activity was significantly different from that of the period 1971 to 1995, and included volcanic tremor with a frequency of less than 1 Hz, simultaneous changes in the amplitude of the previously independent 2 Hz and 7 Hz volcanic tremor, and finally a change in the frequency content of volcanic earthquakes and volcanic tremor from 2 Hz to wideband. Path transmission effects play an important role in determining the characteristics of seismograms at Ruapehu. The presence of Crater Lake affects both the style of eruptions and the accompanying seismicity.

Evidence for a non-orthostatic origin of orthostatic tremor

OBJECTIVESOrthostatic tremor was first described by Heilman in 1984. It usually occurs in the legs during stance and decreases markedly during sitting or walking. The aim of this study was...

Adaptive canceling of physiological tremor for improved precision in microsurgery.

Physiological hand tremor impedes microsurgery. We present both a novel adaptive algorithm for tremor estimation and a new technique for active real-time canceling of physiological tremor. Tremor is modeled online using the weighted-frequency Fourier linear combiner (WFLC). This adaptive algorithm models tremor as a modulating sinusoid, and tracks its frequency, amplitude, and phase. Piezoelectric actuators move the surgical instrument tip in opposition to the motion of tremor, effectively subtracting the tremor from the total motion. We demonstrate the technique in one dimension using a cantilever apparatus as a benchtop simulation of the surgical instrument. Actual hand motion, prerecorded during simulated surgery, is used as input. In 25 tests, WFLC tremor compensation reduces the rms tip motion in the 6-16 Hz tremor band by 67%, and reduces the rms error with respect to an a posteriori estimate of voluntary motion by 30%. The technique can be implemented in a hand-held microsurgical instrument.

Removal of the inferior olive abolishes myoclonic seizures associated with a loss of olivary serotonin

Several lines of clinical evidence suggest that myoclonus is caused by a reduction of serotonin in the brain and hyperactivity of the inferior olive. We determined whether a change in serotonin content within the olivocerebellar system accompanied a predisposition to myoclonus and investigated the necessity of the inferior olive for a myoclonic seizure. The experiments employed the genetically epilepsy-prone rat that exhibits a profound myoclonic seizure in response to an auditory stimulus. We found that these animals demonstrated a significant reduction in the serotonergic innervation of the inferior olive without a significant change in the serotonergic innervation at any other level of the olivocerebellar circuit. The deficit in olivary serotonin was verified physiologically and pharmacologically by a reduced sensitivity of the genetically epilepsy-prone rat to the tremorogenic effect of harmaline, which is known to produce tremor through a mechanism that requires serotonergic innervation of the inferior olive. We quantified the timing of the myoclonic seizure of the genetically epilepsy-prone rat and found that its large amplitude 2–6 Hz clonus was always preceded by 9–10 Hz tremor that was synchronized among limbs. Ablation of the inferior olive by 3-acetylpyridine abolished the myoclonic seizure. The specificity of the deficit in olivary serotonin, the timing of the seizure, and the demonstration of the necessity of the inferior olive for myoclonus suggest that pathological inferior olivary activity contributes to the genesis of a myoclonic seizure.

Gain of the triceps surae stretch reflex in decerebrate and spinal cats during postural and locomotor activities.

1. The triceps surae (TS) stretch reflex was measured in decerebrate cats during crossed extensor stimulation and after spinalization during rhythmic locomotor activity induced by clonidine and manual perineal stimulation. The TS force in response to sinusoidal stretch was measured at a given contraction level before and after deafferentation, and the 'reflex force' was computed by subtracting these two responses. Reflex 'gain' was computed as the ratio of the reflex and deafferented force responses (a unitless estimate of the open loop feedback gain). 2. Prior to locomotion the spontaneous muscle activity was low (less than 15% of maximum), but the reflex gain was relatively high (close to 1.0 with a 5 Hz stretch). When locomotion commenced the reflex gain was markedly lowered when measured at the same contraction level as before locomotion (25% of the gain prior to locomotion). At higher contraction levels the reflex gain was not significantly increased. The reflex force and EMG responses to stretch increased with the contraction level, but their effect on the total reflex gain was cancelled by an associated increase in the intrinsic muscle stiffness. 3. In the decerebrate cat, during weak tonic contractions (spontaneous), the reflex gain was high and comparable with the gain in the resting spinal cat. However, with increased tonic contractions produced by crossed extensor stimulation the reflex gain dropped. At higher contraction levels the gain was not significantly different from the gain during spinal locomotion. 4. When the frequency of stretch was increased from 3 to 20 Hz, EMG responses to stretch increased, but the reflex force decreased, since a more fused contraction developed with the more frequent reflex activations. Overall, the reflex gain decreased with frequency in both spinal and decerebrate cats. The phase lag of the reflex force, relative to the intrinsic muscle force, increased with increasing frequency, due to reflex delays, with a 180 deg lag occurring between 12 and 18 Hz (tremor frequencies). The mean gain was significantly lower and the phase lag was significantly greater during locomotion than during tonic crossed extensor contractions, suggesting different reflex mechanisms. 5. In conclusion, during locomotion in spinal cats afferent feedback from low frequency ankle movements, similar to those occurring during the normal step cycle, reflexly produces a small but significant fraction of the extensor force (about a quarter of the stretch-related force modulation). This fraction is remarkably constant at the different contraction levels of the step cycle. Afferent feedback during higher frequency movement is less effective, minimizing the chance of instability and tremor. In contrast during tonic contractions afferent feedback produces half of the total muscle force during perturbations, clearly contributing to the maintenance of posture.

Central motor loop oscillations in parkinsonian resting tremor revealed magnetoencephalography

A variety of clinical and experimental findings suggest that parkinsonian resting tremor results from the involuntary activation of a central mechanism normally used for the production of rapid voluntary alternating movements. However, such central motor loop oscillations have never been directly demonstrated in parkinsonian patients. Using magnetoencephalography, we recorded synchronized and tremor-related neuromagnetic activity over wide areas of the frontal and parietal cortex. The spatial and temporal organization of this activity was studied in seven patients suffering from early-stage idiopathic Parkinson's disease (PD). Single equivalent current dipole (ECD) analysis and fully three-dimensional distributed source solutions (magnetic field tomography, MFT) were used in this analysis. ECD and MFT solutions were superimposed on high-resolution MRI. The findings indicate that 3 to 6 Hz tremor in PD is accompanied by rhythmic subsequent electrical activation at the diencephalic level and in lateral premotor, somatomotor, and somatosensory cortex. Tremor-evoked magnetic activity can be attributed to source generators that were previously described for voluntary movements. The interference of such slow central motor loop oscillations with voluntary motor activity may therefore constitute a pathophysiologic link between tremor and bradykinesia in PD.

Levodopa reduces muscle tone and lower extremity tremor in Parkinson's disease.

We have quantified the effects of levodopa treatment in Parkinsonian subjects during maintained stance. Electromyographic muscle activity during quiet stance was assessed in subjects with Parkinson's disease, who exhibited a fluctuating response to levodopa, and in age-matched control subjects. Stance stability was also assessed from mean displacement and velocity of the center of pressure excursions during stance. Lower extremity and trunk muscles showed high amplitude activity in all Parkinson's subjects when "off", and a 4-5 Hz tremor in three of these subjects. When "on", the amplitude of muscle activity was reduced in the distal muscles more than the proximal, while tremor was suppressed in all muscles. Corresponding to the excessive muscle activity, the Parkinson's subjects had increased velocity and variability of velocity in the anterior-posterior center of foot pressure excursions, but the mean displacement of the center of pressure excursion was not different from the controls. The velocity of center of pressure excursions in the Parkinson's subjects "on", approached those of the control subjects suggesting that the excessive distal muscle amplitude and tremor contributed to the high velocity of the center of pressure. These findings suggest that dopaminergic systems are involved in the regulation of muscle tone during stance. Depletion of dopaminergic transmission results in increased muscle tone and tremor in the lower extremities which may contribute to changes in posture and stability.

Changes in finger tremor during prolonged submaximal contractions

This study was undertaken to resolve conflicting reports of the effect of fatigue on tremor. Finger tremor was recorded continuously during a middle finger extension task lasting 50–60 min. A progressive increase of 8–12 Hz physiological tremor was observed in 12 subjects during prolonged contractions of extensor digitorum. Stretch reflexes decreased in four of six subjects after contractions, consistent with decreases contributing to enhanced 8–12 Hz tremor. Four subjects showed the onset of a separate 4–7 Hz tremor after 15 min; after 30 min, three of these subjects showed the 8–12 Hz peak shifted downward from the original peak. Results included qualitative changes in finger tremor in different subjects.

Parkinsonismo associado a tumor cerebral relato de caso

Descreve-se o caso de paciente com síndrome parkinsoniana à direita, associada a disfunções cognitivas e síndrome de hipertensão intracraniana. A tomografia de crânio e o estudo angiográfico de vasos intracranianos demonstraram a presença de volumoso processo expansivo fronto-temporal esquerdo. A eletromiografia revelou tremor de repouso com frequência de 4 a 6 ciclos por segundo. A paciente foi submetida a ressecção cirúrgica da massa tumoral, cujo exame histológico revelou tratar-se de meningioma. A evolução pós-operatória foi excelente e após dois meses todas as anormalidades neurológicas haviam desaparecido. Um ano após a remoção do tumor a paciente permanecia assintomática sem uso de qualquer medicação. São discutidos aspectos fisiopatológicos do parkinsonismo por processo expansivo e as particularidades do presente caso são analisadas em confronto a dados da literatura.

Observations on the Compound Eyes of the Deep-Sea Ostracod Macrocypridina Castanea

ABSTRACT Macrocypridina lives at depths of 800 m, where residual daylight is very weak. It has a pair of mobile apposition compound eyes with large lenses, wide rhabdoms and high acceptance angles, all of which contribute to a calculated sensitivity comparable with the superposition eyes of deep-water decapod crustaceans. The axes of the 27 ommatidia in each eye are not uniformly distributed in space, with a modest acute zone in the anteroventral region. Here the interommatidial angles are about 6°, compared with 20° at the rear of the eye. The eyes make two kinds of spontaneous movements: large slow rotations of up to 50° around a transverse axis, and a superimposed 2 Hz tremor with an amplitude of 5 °.

Stability of frequency during long-term recordings of hand tremor

During recording of physiological postural hand tremor over a period of 60 min tremor peak frequency (PF) did not change in 14 normal subjects as long as the mechanical conditions were not changed. In contrast, tremor amplitude and synchronization of the corresponding EMG varied considerably. Any alteration in hand mechanics such as changing hand position or adding masses led to changes of PF according to the alteration in mechanical resonant properties. The results show that PF of physiological postural hand tremor is mainly determined by mechanical factors. There is no evidence for a systematic decrease of PF (Stiles et al. 1976) or for the emergence of a formerly described (Lippold 1981) 4–6 Hz tremor component with prolonged maintenance of posture. In the pathological tremor forms of Parkinson's disease or essential tremor PF also remained unchanged during prolonged maintenance of posture.

The 4-6 HZ tremor during sustained contraction in normal human subjects.

Continuous elevation of the middle finger for 15-60 min gave rise to modulation of the e.m.g. at 4-6 Hz. A marked peak (50-150% of the amplitude of the coexisting 8-12 Hz peak) at 4-6 Hz was produced in sixteen out of twenty-one subjects. The 8-12 Hz peak was also enhanced (2-14 times with respect to its initial amplitude in eighteen subjects) during the course of the prolonged contraction but its frequency did not change. The 4-6 Hz and the 8-12 Hz peaks were present simultaneously; it is concluded that the two phenomena are separate entities. A step-function mechanical perturbation of the finger generates, time-locked to the stimulus, a train of waves at the frequency of the slow tremor, which can be abolished by local ischaemia. It is proposed that this slow tremor is due to an oscillatory process, possibly involving the reflex arc, but entailing a longer neuronal delay than that responsible for 8-12 Hz tremor.

Different types of tremor in the human thumb.

1. The upper limbs of normal subjects were immobilized in a way that allowed measurement of forces and movements at the thumb interphalangeal joint without significant movement elsewhere in the limb. 2. When the subject attempted to maintain a steady flexing force at the joint against a rigid stop, the actual force showed the irregular 8-11 Hz fluctuations characteristic of a 'physiological tremor'. This force fluctuation increased when the mean flexing force increased. 3. If the subject exerted his flexing force against a light complaint spring, there was an analogous irregular 8-11 Hz movement at the joint. 4. When, however, an extra inertial load was added to the terminal phalanx, flexion against a complaint spring was often accompanied by a different type of tremor. This was a more regular oscillation, of lower frequency (3-6 Hz), and of much larger amplitude. 5. The precise frequency and amplitude of this type of tremor depended on the characteristics of the added inertia and spring, in a way that could have been predicted from the responses of the joint to an imposed sinusoidal movement (Brown, Rack & Ross, 1982a). The movement appeared to arise from re-excitation within stretch reflex pathways. 6. The irregular 8-11 Hz tremor at this joint could not be attributed to reflex re-excitation, since the responses to sinusoidal movement indicated a stretch reflex whose timing would not support a movement at that frequency. It is, however, emphasized that other joints of the hand and fingers may behave in different ways.

Tremor, the cogwheel phenomenon and clonus in Parkinson's disease.

Resting and postural tremor, intention and action tremor, clonus and the cogwheel phenomenon in Parkinson's disease have been characterised in terms of frequency content using spectral analysis. Typical resting tremor ranged in peak frequency from 4 to 5.3 HZ with tremor in each individual varying only by 0.2 to 0.3 HZ. The peak frequency of postural tremor ranged between 6 and 6.2 HZ. Intention tremor appeared to be an exaggeration of postural tremor. Clonus evoked by active or passive stretch at the wrist had a frequency of 6 HZ and appeared to be a continuation of postural tremor. The cogwheel phenomenon was found at frequencies between 6 and 6.5 HZ and between 7.5 to 9 HZ. Action tremor was indistinguishable from the cogwheel phenomenon. Some patients had either a symptomatic resting tremor with a concurrent 6 HZ component of smaller amplitude or a symptomatic postural tremor with a 4-5 HZ component of smaller amplitude. These combinations would produce two peaks in the power spectrum. When this occurred EMG studies showed that individual muscles had two types of rhythmical activation suggesting that the tremors have separate mechanisms. Likewise some patients had a symptomatic 6 HZ tremor on posture with a second peak at 8-10 HZ in the physiological band. Therefore, the 6 HZ postural tremor is not an exaggeration of physiological tremor. On the basis of wave form and frequency similarities postural tremor, the low frequency type of active or passive cogwheeling, intention tremor and clonus possibly involve a common spinal mechanism. Higher frequency cogwheel phenomenon and action tremor may be an exaggeration of physiological tremor. More than 80% of patients with Parkinson's disease manifest tremors at both 4-5 HZ and 6 HZ. This combination would appear to be the strongest objective criterion for the diagnosis of basal ganglia disease.

Effects of arrested cerebellar development on locomotion in the rat. Cinematographic and electromyographic analysis.

The activity of the rat hindlimb during treadmill stepping was studied in normal adult rats and in rats in which cerebellar development was interfered with by early-postnatal focal X-irradiation. Based on cinematographic and electromyographic data from over 100 step cycles in 15 normal rats, correlations were made between joint angles and muscle activity to obtain a detailed picture of the locomotor pattern of the rat hindlimb. It was possible to relate most of the features of limb movement to activity in one or more of six primary flexors and extensors of the hindlimb. Compared with available data in the cat or dog, the joint angle curves were similar in shape except that the knee joint angle was usually greater at foot contact than at lift-off, while in cats and dogs the reverse is usually the case. This difference is due to a more crouched stepping posture in the rat in which the leg is not extended as far backward as in the cat or dog. It was also noticed that there was more side-to-side bowing of the spine in the rat during stepping. Finally, in rats there was no correlate to the stance phase burst seen in the semitendinosus in cats. In rats with cerebellar X-irradiation there was little effect on the stepping cycle if the animal's equilibrium was maintained externally, either by a supporting harness or by immersion in water (swimming). However, when stepping without external support, animals were unable to adequately compensate for perturbations in equilibrium, resulting in an ataxic gait. This problem was compound by the presence of high-frequency (18 Hz) tremor which, by producing hyper- or hypotonia during critical periods of stepping such as foot placement or during corrective reflex movements, was a major disturbing force to the animal's equilibrium.