Modulation of tremor amplitude during deep brain stimulation at different frequencies

Rest tremor was quantified in the index finger tip of 16 patients with Parkinson's disease (PD) receiving deep brain stimulation (DBS) of the ventro-intermediate nucleus (Vim) of the thalamus, the subthalamic nucleus (STN), or the internal part of the globus pallidus (GPi) while being off L-dopa for 12h. Clinically, without DBS, tremor amplitude varied from absent to high. Tremor was recorded continuously for about 5 min under three conditions of DBS repeated twice, namely, effective frequency (E), ineffective frequency (I), and no DBS (O). No changes in tremor were observed across conditions in subjects with little or no tremor. However, in subjects with moderate to large amplitude tremor, DBS decreased tremor amplitude to near normal values within a few seconds. Generally, transitions were progressive and occurred with a varying time delay. Occasionally, tremor escaped from control regardless of the stimulation condition considered. In some cases tremor amplitude in one condition appeared to depend on the preceding condition. Finally, the results were reproducible on two consecutive days. We conclude that tremor control with DBS follows specific dynamical rules, which must be compatible with the hypotheses proposed regarding the underlying mechanisms of DBS.     

Adaptation to visual displacement with active and passive limb movements: effect of movement frequency and predictability of movement

Three experiments were performed to evaluate the influence of active and passive limb movements on adaptation to visual displacement. Over a wide frequency range (0·5-1·25 Hz) with constant amplitude, 30°, significant adaptation was achieved with active and passive movements. When arm movement frequency was constant at 1·0 Hz but amplitude of movement was varied, less adaptation was achieved for both active and passive movements than when amplitude was held constant. Even at a frequency above that of most naturally occurring limb movements, 1·67 Hz, and with variable amplitude motion, significant adaptation was achieved with active and passive limb movements. These findings emphasize the importance of visual-proprioceptive discordances for adaptation to visual displacement when only sight of the hand is permitted. Significant differences did not appear between the active and passive movement conditions in any of the experiments.     

Assessing muscular fatigue with a portable tremor measurement system suitable for field use

The utility of a portable tremor measurement system for detecting muscle fatigue was evaluated. Static arm extension was used to induce fatigue. A probe containing two accelerometers, held in the extended hand, recorded horizontal and vertical tremor oscillations in the 1- to 18-Hz range. Several summary amplitude and frequency measures were then derived to analyze hand/arm tremor in the unfatigued and the fatigued states. Large increases from unfatigued to fatigued states were observed in all of the amplitude measures in both axes. Summary frequency measures were far less sensitive to fatigue. Correlations between consecutively measured observations revealed high levels of reliability (r τ .80) in all of the amplitude measures, but not in the frequency measures. The most robust index of fatigue was the total power in the entire 1- to 18-Hz spectrum. The other amplitude measures, however, are suitable for examining the effects of fatigue in isolated portions of the spectrum.     

Changes in the dynamics of tremor during goal-directed pointing.

For successful performance of activities requiring a fine level of manipulative control and dexterity, precise control over the intrinsic oscillations (tremor) in each segment is essential. However, the question of how individuals control (minimize) their tremor during precise postural movements remains unresolved. The aim of this study was to investigate the changes observed in limb tremor during goal-directed postural pointing tasks. Seven subjects attempted to minimize limb tremor during a pointing task whereby progressively greater levels of accuracy were required. Subjects held a small lightweight laser pointer in their extended hand during all tasks, the goal being to maintain the laser emission within a specified target area. Frequency analysis showed that the tremor profile for the hand and index finger was characterized by two prominent frequency peaks, located between 2-4 and 8-12 Hz. When the accuracy requirement of the task increased, there was a significant increase in the amplitude of the 8-12 Hz peak for all segments. Analysis of the time series component of tremor revealed a similar trend with the root mean square (RMS) and approximate entropy (ApEn) of the finger tremor increasing as the accuracy requirement increased. This same pattern was not seen for hand tremor where a small but systematic decrease in both the tremor RMS and ApEn was observed. Overall, it would appear that subjects attempted to reduce tremor at the finger by exerting greater control over the hand (as evidenced by decreased tremor output and increased regularity in the tremor signal). Unfortunately, the consequence of this strategy was that the tremor in the distal effector actually increased. Changes in the tremor output observed as a result of defining an explicit external goal probably resulted from the enhanced visual information provided by the laser emission. However, it would appear that subjects were not able to utilize this feedback effectively to reduce their tremor during the targeting tasks.     

Multidimensional voice program analysis in profoundly deaf children: quantifying frequency and amplitude control

Characterization of the vocal profile of profoundly deaf children using an objective voice analysis was carried out in a university-based pediatric otolaryngology clinic. 21 persons ages 3.5 to 18 years were assessed. From each sustained phonation of the vowel /a/ the following acoustic variables were extracted: fundamental frequency (F0), jitter percentage, shimmer percentage, fundamental frequency variation (vF0), peak amplitude variation (vAM), and first, second, and third formant frequencies (F1, F2, F3). Mean F0 was 267.8 Hz and consistent with established normative data. Mean measurements of jitter (0.88%) and shimmer (3.5%) were also within normal limits. The notable feature of the acoustic analysis was a statistically significant elevation in vF0 (2.81%) and vAM (23.58%). With the exception of one subject, the F1, F2, and F3 formant frequencies were comparable to those for normal hearing children. Auditory deprivation results in poor long-term control of frequency and amplitude during sustained phonation. The inability to maintain a sustained phonation may represent the partial collapse of an internal model of voice and speech.     

Methods of time and frequency domain examination of physiological tremor in the human jaw

This paper discusses, using the human jaw as a model, some of the commonly used techniques for examining physiological tremor. The EMG component driving mandibular physiological tremor approximately 7Hz can be revealed in the time domain manifestation of EMG by demodulation. The co-occurrence of approximately 7Hz physiological tremor (PT) in force and EMG can also be seen in the frequency domain representations of these signals and coherence analysis provides a method by which the degree of co-occurrence can be statistically investigated. Additionally, estimation of time lags between the signals by phase and cumulant density analysis provides evidence of the direction of dependence. Data presented herein using these techniques illustrates that for the human jaw, PT arises from a rhythmic component of EMG. This component is frequency and amplitude invariant across a range of bite forces indicating that it is not due to interaction between the stretch reflex and the mechanical resonance of the system.     

Intentional control and biomechanical exploitation in preparatory handwriting

In this study it was investigated how primary school children perform a graphomotor task which required them to simultaneously achieve multiple movement goals. Thirty-four 1st-grade primary school children were asked to produce with an electronic ink pen loop patterns varying in height (3, 6, 9 and 12 mm) on preprinted sheets of paper attached to a digitizer tablet. The task was paced by means of an acoustic signal of either 1, 2 or 3 Hz. The children were instructed to attain both the imposed amplitude and frequency. By focusing on how local parameter errors changed from one movement to the next, exploitation of biomechanics when the children respected the inverse relationship between movement amplitude and frequency was distinguished from deliberate, cognitive control when the children succeeded in overriding the inverse relationship between movement amplitude and frequency. The results show that children, like adults, exploit biomechanics to a considerable extent. Coupling strength between the acoustic pacing signal and the pen-tip movements increased with age, whereas the temporal errors decreased. The study shows that preparatory writers can pursue multiple movement goals simultaneously at lower speeds but at higher speeds their capacity to do so is reduced.     

关联规则方法在心理测量中的应用

探讨了当相关系数对变量之间相关程度不易进行度量或者无法度量的情况下,是否可以采用关联规则方法来考察变量之间的相互关系。从理论上分析了关联规则方法在心理测量中应用的可能性,并运用Apriori算法挖掘频繁项集,对来华留学生跨文化适应性数据进行了分析,将关联规则方法分析结果与Pearson相关、Spearman相关结果进行比较,发现当使用关联规则方法进行相互关系分析时,能够更加简易、有效地获得变量间的相关规则。研究结果表明关联规则方法可以获得变量各个水平具体的支持度和置信度,推导出多变量之间的相关规则,并且对于处理非线性的多变量以及多分类变量的相关是非常有用的方法。     

Varying the Type and Number of Adaptive Variables in Continuous Tracking

To investigate the effectiveness of various types and numbers of adaptive variables, 48 subjects performed a two-dimensional pursuit tracking task for five 3-min training sessions. In the factorial design resulting in eight experimental conditions, three variables (frequency of the forcing function, ratio of acceleration to rate control, and control stick sensitivity) were either fixed or adaptive. A transfer and retention task in which the tracking situation changed periodically was used to evaluate the ability of subjects to adjust to change. Each adaptive variable was analyzed separately in training. The highest rate of adaptation in frequency occurred when frequency was the only adaptive variable. The rate of adaptation in acceleration was greater early in training when frequency also adapted. More adaptation occurred in gain when another variable also adapted. During transfer subjects trained adaptively generally showed more stable performance in the changing task situation. No reliable differences among conditions appeared in retention. Results are discussed in terms of stimulus and response similarity, the optimum number of adaptive variables, and the appropriateness of a changing task to evaluate adaptive training.     

Wavelet-frequency analysis for the detection of discontinuities in switched system models of human balance

This paper is concerned with detecting the presence of switching behavior in experimentally obtained posturographic data sets by means of a novel algorithm that is based on a combination of wavelet analysis and Hilbert transform. As a test-bed for the algorithm, we first use a switched model of human balance control during quiet standing with known switching behavior in four distinct configurations. We obtain a time–frequency representation of a signal generated by our model system. We are then able to detect manifestations of discontinuities (switchings) in the signal as spiking behavior. The frequency of switchings, measured by means of our algorithm and detected in our models systems, agrees with the frequency of spiking behavior found in the experimentally obtained posturographic data.     

Effect of Hand Posture on the Temporal and Kinematic Properties of Pointing and Drawing Movements Executed by Healthy Subjects and by a Patient With Primary Writing Tremor

Healthy individuals (n = 6) and a patient with "pure" primary writing tremor executed pointing and drawing movements while adopting different hand postures. The control subjects and the patient exhibited similar kinematics for most conditions. The patient displayed a severe right hand 4- to 6-Hz tremor and prolonged movements only when drawing with his normal hand posture. His tremor was manifested after a ready cue, in anticipation of a go command. The premovement tremor was abolished when the authors simply eliminated the ready cue and instructed the patient to relax and not think about drawing until he heard the go cue. Thus, the patient's writing tremor depended not only upon the writing or drawing act but also upon the hand position adopted and the intent to write, even in the absence of movement. The present results suggest that (a) similar high-level control mechanisms exist for pointing and drawing in healthy subjects and (b) the patient's deficits are compatible with a higher motor defect in central nervous system structures involved in the control of pointing and drawing movements.     

Vibrotactile adaptation on the face

Threshold amplitude for vibration is elevated if testing is preceded by extended exposure to a vibratory adapting stimulus of appropriate amplitude and frequency. This phenomenon, previously studied almost exclusively on the hand, is here shown for the first time to occur on the face as well. Adaptation is then used analytically to determine that the two-branched threshold-versus-frequency function obtained on the face by Verrillo and Ecker (1977) represents the activity of two distinct mechanisms. Action spectra of vibrotactile adaptation reveal the presence of both mechanisms even in subjects whose unadapted threshold function (like that reported by Barlow, 1987) shows no sign of duplexity. Finally, the data suggest that on the face (unlike the hand), cross-channel adaptation may occur at high adapting amplitudes.     

Visual adaptation to a spatial contrast enhances visual evoked potentials

The effects of adaptation to the visual contrast of a counterphase grating were studied with visual evoked potentials (VEPs). The spatial frequency of the grating was 4 cpd, and its temporal frequency was 4 or 12 Hz. Steady-state VEPs were analyzed through an FFT (fast Fourier transform) algorithm. In the first experiment, contrast thresholds rose strongly just after the end of adaptation and declined regularly over time. The VEPs recorded in the medio-occipital lead showed an initial decrease in amplitude after adaptation, followed by an enhancement well above the preadaptation level and then a return to that level. The paradoxical enhancement of the VEP was found at both high and low contrast in both the medio-occipital lead and the right temporal lead of a right-handed subject. The left temporal leads showed a VEP enhancement at high contrast and a decline at a low value.     

Conflict adaptation depends on task structure

The dependence of the Simon effect on the correspondence of the previous trial can be explained by the conflict-monitoring theory, which holds that a control system adjusts automatic activation from irrelevant stimulus information (conflict adaptation) on the basis of the congruency of the previous trial. The authors report on 4 experiments showing that conflict adaptation is mediated by task structure as well as previous congruency. Experiment 1 showed that for 2 completely segregated sets of stimulus-response pairs there was no conflict adaptation across sets. However, if the stimulus sets overlapped for 2 separate response sets, conflict adaptation could be observed across the response sets. Experiment 2 showed that this effect was not due to the use of stimulus-response sets lateralized to 1 hemisphere each. Experiment 3 showed that if response sets are common for 2 separate stimulus sets, then conflict adaptation can again be observed across sets. Finally, Experiment 4 showed local control effects in the absence of confounding feature-overlap effects. These results indicate that deployment of control as evidenced by conflict adaptation reflects task structure.     

Preliminary findings suggesting cyclic changes in visual contrast sensitivity during the menstrual cycle

Visual contrast thresholds to both stationary and moving gratings of three spatial frequencies (2, 4, and 16 cyc/deg) were measured over a 32-day period in two women displaying normal menstrual cycles and in two noncycling control subjects. The time-series data of each subject in each condition were Fourier analyzed and the resulting amplitude spectra showed differences between the two sets of subjects. The spectra of the control subjects were relatively flat, whereas those of the experimental subjects showed a number of peaks at several harmonics (periods). Conservative significance tests suggested that the peaks in the spectra of the cycling women were larger than might be expected by chance. The data also suggested that changes in sensitivity were greatest for 4-cyc/deg gratings, those nearest the peak of the normal contrast sensitivity function.     

冲突适应独立于意识：来自行为和ERP的证据

尽管已有研究发现诸如抑制控制和任务转换等认知控制功能独立于意识, 但是对冲突适应是否需要意识的参与目前还存在激烈的争论。为了进一步探讨此问题, 本研究记录了18名被试在完成箭头偏对比掩蔽任务(meta-contrast masking task)时的行为和脑电数据。结果显示, 在有意识和无意识条件下在反应时和额中N2和中顶P3波幅上均表现出了显著的冲突适应效应。这不仅表明冲突控制独立于意识, 而且也表明先前无意识经验对人类信息加工系统的适应性调节作用。本研究对认识认知控制和意识的本质具有重要意义, 也为建构认知控制与意识关系的理论提供了启示。     

网络成瘾者工作记忆水平受影响的机制:来自ERP的证据

本研究采用事件相关电位技术(ERP),以N-back范式为实验任务,考察20名网络成瘾大学生和23名对照组大学生的工作记忆水平,结果发现:对照组的工作记忆具有一定加工优势的趋势,正确率高于成瘾组,反应时低于成瘾组,但均未达到显著差异。网络成瘾组与对照组工作记忆加工时,网络成瘾组P2波幅更高,N2波幅更低,N2潜伏期更长,说明与网络成瘾组相比,对照组工作记忆水平更高。     

Long-lasting modifications of saccadic eye movements following adaptation induced in the double-step target paradigm

The adaptation of saccadic eye movements to environmental changes occurring throughout life is a good model of motor learning and motor memory. Numerous studies have analyzed the behavioral properties and neural substrate of oculomotor learning in short-term saccadic adaptation protocols, but to our knowledge, none have tested the persistence of the oculomotor memory. In the present study, the double-step target protocol was used in five human subjects to adaptively decrease the amplitude of reactive saccades triggered by a horizontally-stepping visual target. We tested the amplitude of visually guided saccades just before and at different times (up to 19 days) after the adaptation session. The results revealed that immediately after the adaptation session, saccade amplitude was significantly reduced by 22% on average. Although progressively recovering over days, this change in saccade gain was still statistically significant on days 1 and 5, with an average retention rate of 36% and 19%, respectively. On day 11, saccade amplitude no longer differed from the pre-adaptation value. Adaptation was more effective and more resistant to recovery for leftward saccades than for rightward ones. Lastly, modifications of saccade gain related to adaptation were accompanied by a decrease of both saccade duration and peak velocity. A control experiment indicated that all these findings were specifically related to the adaptation protocol, and further revealed that no change in the main sequence relationships could be specifically related to adaptation. We conclude that in humans, the modifications of saccade amplitude that quickly develop during a double-step target adaptation protocol can remain in memory for a much longer period of time, reflecting enduring plastic changes in the brain.     

Evoked potentials and sensation

Objective physiological measurements (evoked potentials) were compared with the corresponding psychophysical observations for human Ss. Discrepancies were found between the amplitude of the steady-state evoked potential (EP) and the sensations of flicker produced by visual stimuli of different modulation depths. Poor correlations were also found between subjective De Lange curves and amplitude vs frequency curves for the EP under conditions of chromatic adaptation. It is suggested that two classes of EP can be distinguished; one correlates well and the other correlates poorly with sensation.     

Electroretinogram B-wave amplitude in panic disorder

Abnormal light-related behaviors have been described for patients with panic disorder (PD). The present study was undertaken to investigate the retinal light response in PD using electroretinography (ERG). The authors conducted b-wave ERG measurements with a bright light (after dark adaptation) in 28 patients with PD and 28 control subjects. There were no significant differences in the mean b-wave amplitude between the two groups, but the retinal response to light in PD patients was generally lower than in healthy subjects. A large interindividual variability was found; also noted was a significant difference in the mean b-wave amplitude between the right and left eyes in the control group. The data indicate subtle variation of retinal photosensitivity in a subgroup of patients with PD. Because dopaminergic retinal activity affects b-ERG amplitude, the authors hypothesize that the dopaminergic system is involved in the response to light in PD patients.