Günther Deuschl

Characteristics of hand tremor time series

Tremor is classified into physiological, essential, and parkinsonian tremor by means of clinical criteria. The aim of our work was to extract quantitative features from the measurements of the acceleration of human postural hand tremor. Different mathematical methods were adopted and modified in order to separate these three types of tremor. Best discrimination between physiological and pathological tremors has been achieved by methods distinguishing nonlinear from linear behavior. On the other hand, methods separating different forms of nonlinear behavior have been found to be superior in discriminating parkinsonian and essential tremor. By these methods physiological and pathological tremors can be separated with an error rate below 20% and essential and parkinsonian tremor with an error rate below 10%. This may help to classify tremor time series by objective mathematical criteria and may increase the understanding of the pathophysiological differences underlying these kinds of tremor.

Cross-spectral analysis of physiological tremor and muscle activity II Application to synchronized electromyogram

Abstract We investigated the relationship between synchronized muscle activity and tremor time series in (enhanced) physiological tremor by cross-spectral analysis. Special attention was directed to the phase spectrum and its potential to clarify the contribution of reflex mechanisms to physiological tremor. The phase spectra are investigated assuming that the electromyogram (EMG) synchronization was caused by a reflex or a central oscillator. Comparing these results to phase spectra of measured data, we found a significant contribution of reflexes. But reflexes only modify existing peaks in the power spectrum. The main agents of physiological tremor are an efferent pace and the resonant behavior of the biomechanical system.

Long-latency responses in human thenar muscles mediated by fast conducting muscle and cutaneous afferents.

Electrical stimulation of median nerve at the wrist near motor threshold evokes two distinct reflexes in voluntarily innervated thenar muscles. The first is the Hoffmann reflex (HR) and the second is the long-latency reflex (LLR). Stimulation of the motor branch of the median nerve at the thenar sub-threshold for motor fibers evokes the same pattern suggesting that group IA muscle afferents are mediating the LLR. Stimulation of pure cutaneous afferents evokes a LLR of similar latency without a preceding HR. Statistical analyses of the reflex latencies of HR and LLR are in favor of a fast conduction velocity for the cutaneous afferents involved. Hence for muscular and cutaneous LLR a long-lasting central conduction time has to be assumed.

Reciprocal inhibition of forearm flexor muscles in spasmodic torticollis

Reciprocal inhibition between forearm extensor and flexor muscles was tested by means of an H-reflex technique in patients with spasmodic torticollis and normal controls. In both, patients and controls three different phases of reciprocal inhibition could be demonstrated with maximal inhibition at conditioning test intervals of 0 ms, 15 ms and 100 ms, respectively. However, the quantitative amount of this inhibition was different for the patients and the controls. Significantly less inhibition was found for the second and the third phase of reciprocal inhibition in the patient group. Discriminant analysis showed a clear separation between normal subjects and patients if the amount of reciprocal inhibition of the second and third phase were taken into account. We were not able to detect any side differences neither for the patients nor for the controls. The findings demonstrate a functional disturbance of motor control mechanisms of a clinically unaffected extremity in spasmodic torticollis. This is believed to reflect a bilateral disturbance most likely within the basal ganglia or their outflow. Therefore, our data support the idea, that spasmodic torticollis is associated with or even due to a generalized rather than a focal disturbance of motor control mechanisms.

The relations between long-latency reflexes in hand muscles, somatosensory evoked potentials and transcranial stimulation of motor tracts.

In 15 normal subjects the latency of electrically elicited long-latency reflexes (LLRs) of thenar muscles was compared with somatosensory evoked potentials (SEPs) after median nerve stimulation and with the latencies of thenar muscle potentials after transcranial stimulation (TCS) of the motor cortex. Assuming a transcortical reflex pathway the intracortical relay time for the LLR was calculated to be 10.4 +/- 1.9 msec (mean +/- S.D.) or 8.1 +/- 1.6 msec depending on the experimental conditions. The duration of the cortical relay time is not correlated with the peripheral or central conduction times, with body size or arm length. If the LLRs of hand muscles are conducted transcortically the long duration of the cortical relay time suggests a polysynaptic pathway.

Tremor classification and tremor time series analysis

The separation between physiologic tremor (PT) in normal subjects and the pathological tremors of essential tremor (ET) or Parkinsons disease (PD) was investigated on the basis of monoaxial accelerometric recordings of 35 s hand tremor epochs. Frequency and amplitude were insufficient to separate between these conditions, except for the trivial distinction between normal and pathologic tremors that is already defined on the basis of amplitude. We found that waveform analysis revealed highly significant differences between normal and pathologic tremors, and, more importantly, among different forms of pathologic tremors. We found in our group of 25 patients with PT and 15 with ET a reasonable distinction with the third momentum and the time reversal invariance. A nearly complete distinction between these two conditions on the basis of the asymmetric decay of the autocorrelation function. We conclude that time series analysis can probably be developed into a powerful tool for the objective analysis of tremors. (c) 1995 American Institute of Physics.

Topography and sources of electromagnetic cerebral responses to electrical and air-puff stimulation of the hand

SEPs and SEFs after air-puff stimulation of index and little fingers have been studied and compared to the responses following electrical stimulation of the same digits and of the median nerve at the wrist in 5 subjects. The differences in morphology of the evoked signals are described and the generator characteristics are analysed for SEFs by means of a moving dipole model inside a homogeneous sphere. In our measurements the magnetic fields following electrical finger stimulation show a 30 msec component, which was absent following air-puff stimulation. This could not be seen in the electric field activity. The generators of the first component of SEFs after air-puff finger stimulation proved to be deeper (8 mm on average across all subjects and for both fingers) than in the case of electrically evoked SEFs. A similar behaviour was also observed for the second component of SEFs for the 2 stimulus modalities.

Frontal and parietal components of enhanced somatosensory evoked potentials: a comparison between pathological and pharmacologically induced conditions.

Pathologically enhanced somatosensory evoked potentials (giant SEPs) were recorded in 10 patients with cortical myoclonus of various origins. With non-cephalic reference electrodes a giant frontal negativity corresponding to normal N30 was found over the contra- and ipsilateral hemispheres which was not simply a phase reversal of the well-known enhanced parietal P25. The preceding far-field P14, parietal N20 and frontal P22 were of normal size. A similar result was found when SEPs were studied during the action of etomidate, an ultrashort-acting non-barbiturate hypnotic which produced a marked increase of the parietal P25 and frontal N30 after intravenous administration. These increased components, on the other hand, were abolished when recording was repeated immediately after application of electroconvulsive shock whereas P14, N20, and P22 remained more or less unchanged in both conditions. Our results indicate that there are neuronal elements in the sensorimotor cortex which are more resistant to influences such as narcotic drugs and seizure activity than others, being highly modifiable by these alterations. It is speculated whether these highly modifiable cortical systems are those in which giant SEPs, as well as pharmacologically increased SEP components, arise.

Hand muscle reflexes following air puff stimulation

Hand muscle reflexes following muscle stretch and electrical nerve stimulation show a typical pattern consisting of short- and long-latency reflexes. The present investigation was designed to test reflexes following pure cutaneous stimulation. Air puffs were delivered to the palmar tip and the nail bed of the first, second and fifth fingers during isotonic contraction of hand muscles. The EMGs from the thenar muscles, the first dorsal interosseous muscle and the hypothenar muscles were recorded. Reflexes were obtained in all muscles, with a typical configuration consisting of a short-latency excitatory component (cutaneous longlatency reflex I, cLLR I) and a second excitatory component (cutaneous long-latency reflex II, cLLR II), with an inhibitory component between them. The size of cLLR II differed depending on the area stimulated and the muscle recorded. We found the largest responses always in the muscle acting on the stimulated finger. The reflex size depended on the strength of air puff stimulation. Allowing small displacements of the fingers led to an additional increase in the size of the reflex. The pattern of reflexes was identical independent of whether the finger tip or the nail bed was stimulated, but the size of the reflexes was smaller following nail bed stimulation. Following blockade of the cutaneous nerve branches of the thumb with local anaesthetics, air puff stimulation of the thumb no longer elicited this reflex pattern. Hence, under our experimental conditions, cutaneous receptors were the only source of afferent input for these reflexes.The results suggest that these cutaneous reflexes are mainly dedicated to controlling the stimulated finger independent of whether the palmar tip or the nail bed is stimulated. A possible physiological function is the adapting of grip force during handling of delicate objects if a perturbation is applied either to the object or the hand.

Effects of local injections of botulinum toxin on electrophysiological parameters in patients with hemifacial spasm: role of synaptic activity and size of motor units

Ten patients with typical hemifacial spasm were examined before and after treatment with local injections of botulinum toxin type A. After a mean follow-up period of 38 days there was a reduction of the compound muscle action potential (CMAP) of the injected orbicularis oculi muscle of 40%. Ephaptic transmission studied by selective stimulation of facial nerve branches revealed a preserved delayed response of the affected mentalis muscle. However, no delayed response could be recorded in the injected orbicularis oculi muscle in nine patients. The discrepancy between complete loss of the delayed (ephaptic) response and only moderate reduction of the CMAP amplitude of the direct response may be explained by preferential uptake of botulinum toxin type A by hyperactive synapses involved in ephaptic transmission.