Evidence for lateral premotor and parietal overactivity in Parkinson's disease during sequential and bimanual movements. A PET study.
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Brain↗
Biomedical subjects
D F Stegeman
Publications and source records attributed to D F Stegeman.
EEG findings in patients with vascular parkinsonism.
OBJECTIVES: To investigate whether the conventional and quantitative EEGs of patients with vascular parkinsonism (VP) differ from those of idiopathic Parkinson's disease (PD) patients. MATERIAL AND METHODS: The EEGs of 13 patients with vascular parkinsonism and 14 patients with idiopathic Parkinson's disease were scored on a simple scale regarding aspects of conventional EEG variables. Alpha band power asymmetry and EEG slowing (increased delta and theta power) were calculated by the neurometrics method of quantitative EEG data evaluation. RESULTS: Analysis of both conventional and quantitative EEG data shows that VP patients had significantly less EEG slowing than PD patients. CONCLUSION: This study shows that the EEG in a group of patients with vascular parkinsonism differ from a patient group with idiopathic Parkinson's disease. Our results indicate that VP patients are not PD patients with subcortical vascular lesions, because then they would have had at least as much EEG slowing as PD patients.
Aged↗
Motor unit size estimation: confrontation of surface EMG with macro EMG.
Surface EMG (SEMG) is little used for diagnostic purposes in clinical neurophysiology, mainly because it provides little direct information on individual motor units (MUs). One of the techniques to estimate the MU size is intra-muscular Macro EMG. The present study compares SEMG with Macro EMG. Fifty-eight channel SEMG was recorded simultaneously with Macro EMG. Individual MUPs were obtained by single fiber triggered averaging. All recordings were made from the biceps brachii of healthy subjects during voluntary contraction at low force. High positive correlations were found between all Macro and Surface motor unit potential (MUP) parameters: area, peak-to-peak amplitude, negative peak amplitude and positive peak amplitude. The MUPs recorded with SEMG were dependent on the distance between the MU and the skin surface. Normalizing the SEMG parameters for MU location did not improve the correlation coefficient between the parameters of both techniques. The two measurement techniques had almost the same relative range in MUP parameters in any individual subject compared to the others, especially after normalizing the surface MUP parameters for MU location. MUPs recorded with this type of SEMG provide useful information about the MU size.
Adult↗
Motor unit potential contribution to surface electromyography.
The background of the bioelectric activity of muscle recorded from the surface of the skin (surface electromyography) in terms of the representation of single motor units of the underlying muscle(s) is not very well documented or understood. An insight into the composition of an electromyogram is essential for the proper interpretation of one of the most widely applied electrophysiological techniques. In the present paper, a study of the contribution of single motor unit potentials to the surface electromyogram is presented. To this end, the decline of different components of the motor unit potential with depth of the motor unit is quantified. Experimentally, the action potentials from motor units at several positions in the muscle were recorded by 30 skin surface electrodes. Simultaneous use of scanning electromyography provided information about the actual position and size of the motor unit. Observed linear log-log relationships between motor unit potential magnitudes and distance indicated the usefulness of a power function to describe the motor unit potential's dependence on recording distance. It is shown that different specific surface motor unit potential characteristics fall off differently with depth. The magnitude-distance relationship is shown to be dependent on the recording configuration (unipolar vs. bipolar recording, including the inter-electrode distance) and the chosen motor unit potential parameter (negative peak amplitude, positive peak amplitude and area).
Adult↗
The motor unit potential distribution over the skin surface and its use in estimating the motor unit location.
The amplitude of a surface electromyogram is dependent on the number of active motor units, their size and the relative position of the recording electrode. It is not possible to interpret the surface electromyogram quantitatively without disentangling these different aspects. In this study the decline of different components of the motor unit potential with increasing radial distance from the motor unit is quantified. Fifty-two motor units in the biceps brachii muscle were studied using 36-channel surface electromyography combined with intramuscular scanning electromyography. Scanning electromyography was used to locate precisely the motor unit. The dependence of the surface motor unit potential magnitude on the radial distance between the motor unit and the recording electrodes can be described fairly well by an inverse power function. The steepness of this function depends on the chosen motor unit potential parameter and the interelectrode distance, but also varies between motor units. The change of the negative peak amplitude of the motor unit potential over the skin surface can be used to give a fairly accurate estimate of the location of the motor unit under the skin surface. We found that for all practical purposes the depth of a motor unit in the biceps brachii muscle can be estimated as 20% of the distance over the skin surface where motor unit potentials can be recorded with higher amplitudes than 50% of the maximal amplitude recorded at the skin surface caused by activity of the same motor unit.
Action Potentials↗
Near- and far-fields: source characteristics and the conducting medium in neurophysiology.
It is possible to appreciate the production of far-field potentials by considering constant current dipolar source voltage distributions in bounded volumes, especially when they are stretched in one direction, e.g., a cylinder. An essentially nondeclining voltage is detected when the recording electrodes are on opposite sides of, and relatively far from, the dipolar source. This voltage maintains its (a) latency, (b) amplitude, (c) morphology, and (d) polarity even if recordings are performed a whole body length away. These four criteria define far-field potentials. A propagating action potential (AP) can be conceptualized as a linear quadrupole or the summation of two dipoles "back-to-back" (+ - - +). The far-field components of the summated dipoles cancel resulting in the anticipated triphasic waveform for APs with only near-field characteristics, not meeting the first three criteria above. Far-field potentials can be transiently generated when any propagating AP constitutes a net "real" or "virtual" dipolar source. "Real" dipolar sources can occur if an AP encounters the termination of excitable tissue, an alteration in conduction velocity, curvature in excitable tissue resulting in a change in propagation direction, or an abrupt change in resistance of the excitable tissue. Virtual dipolar sources may be produced if an AP encounters a change in the size or shape of the extracellular medium or a transition in extracellular conductivity.
Action Potentials↗
Movement-related potential measures of different modes of movement selection in Parkinson's disease.
Movement-related potentials were recorded preceding self-paced voluntary movements in patients with Parkinson's disease and in healthy subjects of the same age group. We compared the Readiness Potential preceding joystick movements in a fixed direction and preceding joystick movements in freely selected directions. In normal subjects the Readiness Potential amplitude was higher preceding freely selected movements than preceding movements in a fixed direction. The Readiness Potential in Parkinson patients failed to be modified by the different modes of movement selection. The modulation of the Readiness Potential by different ways of preparing for movement might be due to the supplementary motor area (SMA) being more strongly engaged by tasks requiring internal control of movements than by tasks that are externally structured. The results suggest that this task-dependent variation of SMA activity is reduced in Parkinson's disease. A failing capacity to adapt SMA activity to different task demands has previously been suggested by evidence from positron emission tomography studies using similar tasks.
Adult↗
Automatic decomposition electromyography in idiopathic inflammatory myopathies.
Automatic decomposition electromyography (ADEMG) is a commercially available software package with installed reference values that enables the objective measurement of motor unit action potentials (MUAPs). To assess the diagnostic yield of this package in idiopathic inflammatory myopathies (IIM) we performed bicepts brachii ADEMG in 17 patients with polymyositis, dermatomyositis and inclusion body myositis. Results were compared with those in 12 controls, and with the results of conventional EMG of the biceps and other muscles. Decreased mean values for MUAP duration occurred significantly more frequently in IIM patients than in controls; other MUAP characteristics did not differ. In IIM patients, decreased mean amplitude and increased mean number of turns occurred significantly less frequently on ADEMG than did corresponding abnormalities on conventional biceps EMG. Decreased mean values for duration and amplitude, and increased mean values for number of turns were seen significantly less often on ADEMG than corresponding abnormalities on conventional EMG of four different, individually chosen muscles. Overall evaluation of ADEMG resulted in a diagnosis of "possible myopathy" in 1 and "probable myopathy" in 8 patients, whereas overall evaluation of conventional EMG led to a diagnosis "suggestive of IIM" in 13 patients. We conclude that, although measurement of mean MUAP duration might be valuable in IIM diagnosis, our results do not favour the use of biceps brachii ADEMG and the installed reference values for the diagnosis of IIM. We suggest modifications to improve ADEMG's applicability.
Adult↗
Dipole source analysis suggests selective modulation of the supplementary motor area contribution to the readiness potential.
The readiness potential preceding voluntary movement is modulated by the mode of movement selection, i.e. it has a higher amplitude preceding freely selected than before prescribed movements (Praamstra, P., Stegeman, D.F., Horstink, M.W.I.M., Brunia, C.H.M. and Cools, A.R. Movement-related potentials preceding voluntary movement are modulated by the mode of movement selection. Exp. Brain Res., 1995, 103: 429-439). One cortical area that is likely to be involved in this modulation is the supplementary motor area (SMA). Recent attempts to elucidate the neural generators of the readiness potential using spatiotemporal dipole source analysis, however, failed to establish a significant SMA contribution to the readiness potential. This might be explained by a failure of the proposed analyses to discriminate between SMA and motor cortex contributions to the readiness potential. We applied a dipole source analysis approach that better separates these overlapping source activities. The resulting source model includes an SMA source generating pre-movement activity consistent with evidence from intracranial recordings in humans. The SMA source accounts almost completely for the modulation of the readiness potential by different modes of movement selection. On the basis of these results, the relation between scalp-recorded movement-related activity, intracranially recorded potentials, and findings from functional imaging studies of voluntary movement, appears more transparent than suggested by previous dipole source analyses of premovement potentials.
Adult↗
Movement preparation in Parkinson's disease. Time course and distribution of movement-related potentials in a movement precueing task.
Investigations of the effects of advance information on movement preparation in Parkinson's disease using reaction time (RT) measures have yielded contradictory results. In order to obtain direct information regarding the time course of movement preparation, we combined RT measurements in a movement precueing task with multi-channel recordings of movement-related potentials in the present study. Movements of the index and middle fingers of the left and right hand were either precued or not by advance information regarding the side (left or right hand) of the required response. Reaction times were slower for patients than for control subjects. Both groups benefited equally from informative precues, indicating that patients utilized the advance information as effectively as control subjects. Lateralization of the movement-preceding cerebral activity [i.e. the lateralized readiness potential (LRP)] confirmed that patients used the available partial information to prepare their responses and started this process no later than controls. In conjunction with EMG onset times, the LRP onset measures allowed for a fractionation of the RTs, which provided clues to the stages where the slowness of Parkinson's disease patients might arise. No definite abnormalities of temporal parameters were found, but differences in the distribution of the lateralized movement-preceding activity between patients and controls suggested differences in the cortical organization of movement preparation. Differences in amplitude of the contingent negative variation (CNV) and differences in the way in which the CNV was modulated by the information given by the precue pointed in the same direction. A difference in amplitude of the P300 between patients and controls suggested that preprogramming a response required more effort from patients than from control subjects.
Adult↗
Peripheral nerve elongation by laser Doppler flowmetry-monitored expansion: an experimental basis for future application in the management of peripheral nerve defects.
Nerve grafting often fails to achieve optimal functional results and is always associated with donor-site morbidity. Peripheral nerve elongation by the use of a tissue expander may provide a useful adjunct in the management of segmental nerve loss. In the present study, rabbit sciatic nerve (n = 40) was elongated by expansion while nerve blood flow was monitored by laser Doppler flowmetry. Elongation was possible up to 40 percent with preservation of clinical nerve function. Nerve conduction velocity of the expanded nerves decreased in a linear relation to elongation. The reduction in nerve conduction velocity may be secondary to the observed widening of the nodes of Ranvier and altered membrane properties after remyelination. Demyelination and remyelination of whole internodes and axonal degeneration occurred only sporadically. Thus laser Doppler flowmetry-monitored expansion provides a safe method for elongation of intact rabbit sciatic nerve while nerve function and axonal continuity are preserved. Further studies are needed before clinical use is considered. This technique may represent a favorable alternative to nerve grafting for the treatment of peripheral nerve defects.
Action Potentials↗
Conduction velocity distributions compared to fiber size distributions in normal human sural nerve.
Compound action potentials (CAPs) were recorded from the sural nerve of healthy volunteers. A mathematical technique (inverse modeling) was used to compute conduction velocity (CV) histograms from the data. Results were compared to the morphology of age-matched normal sural nerve biopsies. Coefficients of variation (CoVs) revealed the statistical relationship between morphological data (diameter histograms) and electrophysiological data (CV histograms and conventional CAP parameters). No differences were found for the thick fiber group when comparing the CoVs of the diameter histogram parameters with the corresponding CV histogram parameters. Apparently, the same inherent biological interindividual variability is encountered. The CoVs of the CVs of the CAP's main phases are in good agreement with the CoVs of the estimated mean velocity of the thick fiber group. Inverse modeling increases the reliability of the estimation of the number of active fibers as compared to direct CAP amplitude interpretation.
Action Potentials↗
Movement-related potentials preceding voluntary movement are modulated by the mode of movement selection.
In two experiments movement-related cortical potentials preceding voluntary movement were recorded. In experiment 1, subjects performed four motor tasks involving joystick movements. The four tasks differed in complexity (single vs sequential movements) and in the mode of movement selection, i.e., whether a movement or movement sequence was made in fixed or in self-determined directions. The choice of these tasks was based, firstly, on previous electrophysiological studies suggesting an effect of task-complexity on the amplitude of the readiness potential (RP) and, secondly, on previous positron emission tomography (PET) studies showing that activity of the supplementary motor area (SMA) is influenced by the mode of movement selection. The results show that, for single movements, RP amplitude is higher preceding freely selected movements than preceding movements in a fixed direction. In experiment 2 this effect was replicated using button presses instead of joystick movements. The results converge with PET evidence obtained in similar tasks and establish that the RP is modulated by the mode of movement selection. This modulation is probably related to differential involvement of the SMA.
Adult↗
Peripheral nerve elongation by laser Doppler flowmetry controlled expansion: morphological aspects.
Peripheral nerve elongation by a tissue expander may offer an alternative to nerve grafting in the management of segmental nerve loss. We investigated the morphological changes in peripheral nerve following slow nerve elongation by laser Doppler flowmetry controlled expansion in a rabbit sciatic nerve model. The animals were randomly assigned to one of four groups, with an expander volume of 0, 5, 10 or 15 cm3, respectively. An elongation of up to 40% was possible with preservation of clinical function. Nerve conduction velocity decreased in relation to elongation. Paranodal widening, followed by remyelination of the node, were early and constant morphological features. Demyelination and remyelination of whole internodes, and axonal degeneration occurred sporadically and did not correlate with elongation, rate of elongation or neurophysiological parameters. The model of laser Doppler flowmetry controlled nerve expansion provides a method for remodelling of myelin sheaths and lengthening of nerve fibers without axonal damage.
Animals↗
The biphasic morphology of voluntary and spontaneous single muscle fiber action potentials.
The extracellular morphology of single muscle fiber action potentials (SMFAPs) is anticipated by volume conductor theory to be triphasic. Single muscle fiber action potentials recorded during single muscle fiber studies (500 Hz to 20 kHz) usually appear triphasic; however, when recorded with an open bandwidth (1 Hz to 20 kHz) they are found to be biphasic. Fibrillation potentials recorded with a single fiber electrode and open bandwidth have identical biphasic morphologies as volitional SMFAPs. Computer simulations suggest that the intracellular action potential models currently used to derive simulated extracellularly recorded SMFAPs must have the repolarization phase considerably prolonged to yield the clinically recorded potentials. This implies that either the models presently used require significant modification, or there is some distortion of the transmembrane source current induced in needle recording studies such that biphasic and not triphasic potentials are detected.
Action Potentials↗
Peripheral nerve elongation by laser Doppler flowmetry controlled expansion: functional and neurophysiological aspects.
A new method for elongation of peripheral nerves with preservation of function is presented. Nerve blood flow during experimental nerve expansion of rabbit sciatic nerve is controlled by laser Doppler flowmetry in order to avoid nerve ischemia. Using this method, nerve function in relation to gait remained intact in 72.5% of the animals and recovered within 3 weeks in the others. Disturbances in toe-spread reflex recovered completely in all animals after 3 weeks. Significant nerve elongation up to 40% is possible with preservation of function when nerve blood flow is controlled by laser Doppler flowmetry.
Action Potentials↗
Intramuscular potential changes caused by the presence of the recording EMG needle electrode.
A comprehensive volume conductor study of single fiber needle EMG (SF EMG) has been made. The electrode shaft is described as a passive inhomogeneity in the volume conductor. The most important observation is a substantial increase in single fiber action potential (SFAP) amplitude (up to 70%) for muscle fibers observed from a short distance. For SFAPs from muscle fibers located on the back of the SF electrode a shadow effect occurs which can result in a maximal amplitude decrease of 50%. SFAP wave form changes were observed only in situations without practical consequences or beyond physical reality. The presence of the needle shaft causes an anisotropy-like behavior of the relation between leading-off point to muscle fiber distance. The observed amplification due to the presence of the needle cannula decreases faster in the direction parallel to the cannula than in the direction normal to it: due to the amplification of SFAPs from muscle fibers observed from a short distance, the maximal distance from which SFAPs are included in fiber density measurements (amplitude greater than 0.2 mV) is raised from 380 microns to 460 microns. Also, the consequences of the formation of an edematous layer around the needle cannula have been studied. It was shown that the effect of high conductive fluid around the needle electrode can counteract the effects caused by the presence of the electrical double layer.
Action Potentials↗
Chronic cerebral hypotension induces a downward shift of the cerebral autoregulation: a hypothesis based on TCD and OPG-GEE studies in ambulatory patients with occlusive cerebrovascular disease.
In order to establish whether or not the cerebral autoregulation is still effective at blood pressure rates in those who experience a chronic cerebral hypotension 37 patients were subjected to noninvasive CO2 enhanced transcranial Doppler (TCD) and ocular pneumoplethysmographic (OPG-GEE) studies of the middle cerebral and ophthalmic arteries. The patients demonstrating a combination of a unilateral patent internal carotid artery (ICA diameter reduction less than 49%) and a contra-lateral ICA occlusion based on duplex scan examinations were examined. The cerebral blood flow velocities at normocapnia (BFV) and pulsatility indices (PI) were measured by TCD. An equivalent of the reserve capacity of the cerebral autoregulation was estimated by quantification of the CO2 enhanced cerebral vasomotor reactivity (VMR). Cerebral blood pressure equivalents such as the OSP/BSP ratio and the ophthalmo-brachial systolic pressure (OBSP) index were estimated by measuring the ocular systolic blood pressure (OSP) and the systemic systolic blood pressure (BSP). The TCD and OPG-GEE data are both in the normal range distally to a patent ICA (n = 22). If the ICA is occluded the OPG-GEE data show a significant reduction in both OSP/BSP ratio's and OBSP indices. If the VMR was in the normal range, distally to an occluded ICA (n = 25), the pressure drop was mild and the BFV at rest was in the normal range. Nevertheless, the waveforms were more damped as seen from the reduction in pulsatility indices but the reduction did not reach statistical significance when compared to the PI values distally to a patent ICA.(ABSTRACT TRUNCATED AT 250 WORDS)
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