Non-adjacent Fingers Research Articles

Spectral specificity of gamma-frequency transcranial alternating current stimulation over motor cortex during sequential movements.

Motor control requires the coordination of spatiotemporally precise neural oscillations in the beta and gamma range within the primary motor cortex (M1). Recent studies have shown that motor performance can be differentially modulated based on the spectral target of noninvasive transcranial alternating current stimulation (tACS), with gamma-frequency tACS improving motor performance. However, the spectral specificity for eliciting such improvements remains unknown. Herein, we derived the peak movement-related gamma frequency in 25 healthy adults using magnetoencephalography and a motor control paradigm. These individualized peak gamma frequencies were then used for personalized sessions of tACS. All participants completed 4 sessions of high-definition (HD)-tACS (sham, low-, peak-, and high-gamma frequency) over M1 for 20min during the performance of sequential movements of varying complexity (e.g. tapping adjacent fingers or nonadjacent fingers). Our primary findings demonstrated that individualized tACS dosing over M1 leads to enhanced motor performance/learning (i.e. greatest reduction in time to complete motor sequences) compared to nonspecific gamma-tACS in humans, which suggests that personalized neuromodulation may be advantageous to optimize behavioral outcomes.

Analysis of dystonic tremor in musicians using empirical mode decomposition

ObjectiveTest the hypotheses that tremor amplitude in musicians with task-specific dystonia is higher at the affected finger (dystonic tremor, DT) or the adjacent finger (tremor associated with dystonia, TAD) than (1) in matched fingers of healthy musicians and non-musicians and (2) within patients in the unaffected and non-adjacent fingers of the affected side within patients. MethodsWe measured 21 patients, 21 healthy musicians and 24 non-musicians. Participants exerted a flexion–extension movement. Instantaneous frequency and amplitude values were obtained with empirical mode decomposition and a Hilbert-transform, allowing to compare tremor amplitudes throughout the movement at various frequency ranges. ResultsWe did not find a significant difference in tremor amplitude between patients and controls for either DT or TAD. Neither differed tremor amplitude in the within-patient comparisons. ConclusionBoth hypotheses were rejected and apparently neither DT nor TAD occur in musician’s dystonia of the fingers. SignificanceThis is the first study assessing DT and TAD in musician’s dystonia. Our finding suggests that even though MD is an excellent model for malplasticity due to excessive practice, it does not seem to provide a good model for DT. Rather it seems that musician’s dystonia may manifest itself either as dystonic cramping without tremor or as task-specific tremor without overt dystonic cramping.

Thermal Design of Multifinger Bipolar Transistors

In this paper, design guidelines are provided to improve the thermal stability of three- and four-finger bipolar transistors. Experiments and simulations are first performed on silicon-on-glass (SOG) three-finger bipolar junction transistors (BJTs) with self-heating and mutual thermal resistances varying in a large range of values, depending on the silicon area, presence of heat spreaders, isolation, and distance between fingers. To avoid strong asymmetries between the mutual thermal resistances of two adjacent fingers as compared to nonadjacent fingers, a “hexagonal” topography is proposed. It is demonstrated that, due to the nature of this solution, the onset of thermal instability can be shifted to a higher value of dissipated power. The key role of metal lines and bondpads in fully isolated devices is also highlighted. Subsequently, the electrothermal behavior of SOG four-finger BJTs is investigated and the thermally induced current nonuniformity over the individual fingers is experimentally monitored for the first time. Thermal-only and electrothermal simulations are employed to conceive and analyze more thermally robust layout topographies, referred to here as “rhombus” and “square”.

Spatiotemporal integration of tactile information in human somatosensory cortex

BackgroundOur goal was to examine the spatiotemporal integration of tactile information in the hand representation of human primary somatosensory cortex (anterior parietal somatosensory areas 3b and 1), secondary somatosensory cortex (S2), and the parietal ventral area (PV), using high-resolution whole-head magnetoencephalography (MEG). To examine representational overlap and adaptation in bilateral somatosensory cortices, we used an oddball paradigm to characterize the representation of the index finger (D2; deviant stimulus) as a function of the location of the standard stimulus in both right- and left-handed subjects.ResultsWe found that responses to deviant stimuli presented in the context of standard stimuli with an interstimulus interval (ISI) of 0.33s were significantly and bilaterally attenuated compared to deviant stimulation alone in S2/PV, but not in anterior parietal cortex. This attenuation was dependent upon the distance between the deviant and standard stimuli: greater attenuation was found when the standard was immediately adjacent to the deviant (D3 and D2 respectively), with attenuation decreasing for non-adjacent fingers (D4 and opposite D2). We also found that cutaneous mechanical stimulation consistently elicited not only a strong early contralateral cortical response but also a weak ipsilateral response in anterior parietal cortex. This ipsilateral response appeared an average of 10.7 ± 6.1 ms later than the early contralateral response. In addition, no hemispheric differences either in response amplitude, response latencies or oddball responses were found, independent of handedness.ConclusionOur findings are consistent with the large receptive fields and long neuronal recovery cycles that have been described in S2/PV, and suggest that this expression of spatiotemporal integration underlies the complex functions associated with this region. The early ipsilateral response suggests that anterior parietal fields also receive tactile input from the ipsilateral hand. The lack of a hemispheric difference in responses to digit stimulation supports a lack of any functional asymmetry in human somatosensory cortex.

Cognitive and biomechanical influences in pianists’ finger tapping

Movement sequences such as typing or tapping display important interactions among finger movements arising from anticipatory motion (preparing for upcoming events) and coupling (non-independence among fingers). We examined pianists' finger tapping for the influence of cognitive chunking processes and biomechanical coupling constraints. In a synchronization-continuation task, pianists repeatedly tapped four-finger sequences that differed in terms of the chunks that formed subsequences and in the transitions among physically adjacent or non-adjacent fingers. Chunking influenced intertap intervals, regardless of the particular fingers tapped; the final tap of each chunk was lengthened and less variable relative to other taps. The particular fingers tapped influenced peak finger heights, consistency of motion, and velocity-acceleration patterns, regardless of chunking. Thus, cognitive constraints influenced timing, whereas biomechanical factors influenced motion trajectories. These findings provide an important caveat for study of anticipatory motion by documenting the influence of biomechanical coupling on motion trajectories.

Synergistic finger movements in a skilled motor task.

When skilled typists strike one key, typically all of the fingers of one hand are in motion simultaneously. We studied the extent to which the motion of the individual fingers was similar. Subjects were asked to type lists of words, each word designed so that only one key would be pressed by a finger of one hand, the remaining letters being typed with the other hand. Changes in the lengths (flexion-extension) and orientation (abduction-adduction) of each finger were measured and the similarity of the motion of pairs of fingers was assessed by computing correlation coefficients. For each pair of fingers, the correlation coefficients were broadly distributed, but in most instances the mean was significantly greater than zero. Adjacent fingers showed a higher degree of correlation than did non-adjacent fingers. When one of the fingers was actually used to press the key, the degree of correlation decreased substantially. The results demonstrate that in this skilled motor task, the fingers usually tend to be moved together, but they can be moved independently when the task so requires.

Perceptual processing of adjacent and nonadjacent tactile nontargets.

Previous research has shown that subjects appear unable to restrict processing to a single finger and ignore a stimulus presented to an adjacent finger. Furthermore, the evidence suggests that, at least for moving stimuli, an adjacent nontarget is fully processed to the level of incipient response activation. The present study replicated and expanded upon these original findings. The results of Experiment 1 showed that an equally large response-competition effect occurred when the nontarget was presented to adjacent and nonadjacent fingers (on the same hand). The results of Experiment 2 showed that the effects observed in Experiment 1 (and in previous studies) were also obtained with stationary stimuli. Although small, there was some indication in the results of Experiment 2 that interference may dissipate more rapidly with distance with stationary stimuli. An additional finding was that interference effects were observed in both experiments with temporal separations between the target and nontarget of up to 100 msec. In Experiment 3, target and nontarget stimuli were presented to opposite hands. Although reduced, interference was still evident with target and nontarget stimuli presented to opposite hands. Varying the physical distance between hands did not produce any change in the amount of interference. The results suggest that the focus of attention on the skin extends nearly undiminished across the fingers of one hand and is not dependent upon the physical distance between sites of stimulation.

Nonadjacent syndactyly in the congenital constriction band syndrome

Hand anomalies in the amniotic band sequence are frequently both complex and difficult to explain in terms of our conventional understanding of limb embryogenesis. A case manifesting pseudosyndactyly between nonadjacent fingers confirms the role of an in utero disturbance after the seventh week, in concert with close apposition between nearby but not adjacent parts.

Reorganization of Tactile Perception following the Simulated Amputation of One Finger

The tactile counterpart of diplopia has recently been described: tactile diplopia or diplesthesia. The human fingers show a rather precise organization of the cutaneous areas eliciting diplesthesia. In particular, these areas are very extensive between nonadjacent fingers (second and fourth, second and fifth, and third and fifth), suggesting that the illusory doubling depends on the lack of reciprocal interaction between cutaneous zones during manipulation. In the present study, four subjects agreed to explore and manipulate objects only through nonadjacent fingers for a period of up to six months. The amputation of the third finger was simulated by excluding it from active exploration by means of a bandage. After six months, the diplesthetic areas of the nonadjacent fingers decreased in size or completely disappeared. It is suggested that this reorganization of tactile perception is due to the increase in temporal correlation of the sensory inputs between nonadjacent fingers.

Spatial Organization of the Diplesthetic and Nondiplesthetic Areas of the Fingers

Cutaneous points on different fingers were brought into contact with each other to ascertain whether one stimulus was perceived to be single or double. The perceptual responses were mapped on the five fingertip pads. The results show that there is an extensive cutaneous area on each fingertip pad which elicits one-stimulus perceptions when a single stimulus is applied between each finger and the thumb. This area decreases when the stimulus is applied to adjacent fingers (2-3, 3-4, 4-5), and even more so when it is applied to nonadjacent fingers (2-4, 2-5, 3-5). In fact, in adjacent and nonadjacent fingers the cutaneous surface eliciting a doubling of the single stimulus (diplesthesia) is very extensive. The spatial arrangement of the cutaneous areas eliciting single perceptions appears to be invariant in the proximo-distal plane. Instead, the shift from one kind of perception to another occurs in the medio-lateral plane. It is suggested that this perceptual organization could reflect a neural organization.