RESUMO
After limb amputation, patients often wake up with a vivid perception of the presence of the missing limb, called "phantom limb". Phantom limbs have mostly been studied with respect to pain sensation. But patients can experience many other phantom sensations, including voluntary movements. The goal of the present study was to quantify phantom movement kinematics and relate these to intact limb kinematics and to the time elapsed since amputation. Six upper arm and two forearm amputees with various delays since amputation (6months to 32years) performed phantom finger, hand and wrist movements at self-chosen comfortable velocities. The kinematics of the phantom movements was indirectly obtained via the intact limb that synchronously mimicked the phantom limb movements, using a Cyberglove® for measuring finger movements and an inertial measurement unit for wrist movements. Results show that the execution of phantom movements is perceived as "natural" but effortful. The types of phantom movements that can be performed are variable between the patients but they could all perform thumb flexion/extension and global hand opening/closure. Finger extension movements appeared to be 24% faster than finger flexion movements. Neither the number of types of phantom movements that can be executed nor the kinematic characteristics were related to the elapsed time since amputation, highlighting the persistence of post-amputation neural adaptation. We hypothesize that the perceived slowness of phantom movements is related to altered proprioceptive feedback that cannot be recalibrated by lack of visual feedback during phantom movement execution.
Assuntos
Retroalimentação Sensorial/fisiologia , Dedos/fisiopatologia , Atividade Motora/fisiologia , Plasticidade Neuronal/fisiologia , Membro Fantasma/fisiopatologia , Propriocepção/fisiologia , Punho/fisiopatologia , Adulto , Idoso , Amputados , Fenômenos Biomecânicos , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Fatores de TempoRESUMO
REASONS FOR PERFORMING STUDY: The relationship between the biomechanical horserider interaction and endurance race performance requires further investigation. OBJECTIVES: To characterise, both quantitatively and qualitatively, elite and advanced horserider dyads on the basis of the biomechanical horserider interaction during endurance races. STUDY DESIGN: Five elite and 5 advanced horserider dyads were recorded during CEI*/CEI** endurance races using 2 synchronised triaxial accelerometers each placed close to horse and rider centres of mass. METHODS: For each horserider dyad, analyses focused on the vertical displacements of horse and rider per stride. This allowed quantification of the proportional use of each gait and riding technique per loop. The quality of the biomechanical horserider interaction was examined through the relative phases (RP) of their respective vertical displacement minima. Instantaneous speed and rider heart rates were recorded using a global positioning system device/heart rate monitor. RESULTS: All dyads predominantly used 2 riding techniques per gait. The 2-point trot proportion was limited in both groups (11%). Throughout the race, the advanced horserider dyads showed a global stability in speed, in the proportion of 4 combinations of gait and riding techniques and in mean RP. However, the elite horserider dyads initially had higher mean RP values (P<0.01), and from mid-race to the end an increasing proportion of sitting canter, with associated increases in racing speed (P<0.001) and in mean heart rate (P<0.01). Intradyad RP variability in 2-point canter increased in both groups (P<0.01). CONCLUSIONS: Accelerometers are a valuable tool to follow the quantitative and qualitative trends of the biomechanical horserider interaction during international endurance races. The overall results emphasise the influence of the level of expertise on the adopted gait and riding techniques, thus influencing the racing speed. It remains to be established whether fatigue and/or strategy underlie our observations.
Assuntos
Fadiga , Cavalos/fisiologia , Condicionamento Físico Animal/fisiologia , Resistência Física/fisiologia , Esportes , Adulto , Animais , Feminino , Humanos , MasculinoRESUMO
Human subjects are able to prepare cognitively to resist an involuntary movement evoked by a suprathreshold transcranial magnetic stimulation (TMS) applied over the primary motor cortex (M1) by anticipatory selective modulation of corticospinal excitability. Uncovering how the sensorimotor cortical network is involved in this process could reveal directly how a prior intention can tune the intrinsic dynamics of M1 before any peripheral intervention. Here, we used combined TMS-EEG to study the cortical integrative processes that are engaged both in the preparation to react to TMS (Resist vs. Assist) and in the subsequent response to it. During the preparatory period, the contingent negative variation (CNV) amplitude was found to be smaller over central electrodes (FC1, C1, Cz) when preparing to resist compared with preparing to assist the evoked movement whereas alpha-oscillation power was similar in the two conditions. Following TMS, the amplitude of the TMS evoked-N100 component was higher in the Resist than in the Assist condition for some central electrodes (FCz, C1, Cz, CP1, CP3). Moreover, for six out of eight subjects, a single-trial-based analysis revealed a negative correlation between CNV amplitude and N100 amplitude. In conclusion, prior intention can tune the excitability of M1. When subjects prepare to resist a TMS-evoked movement, the anticipatory processes cause a decreased cortical excitability by locally increasing the inhibitory processes.
Assuntos
Variação Contingente Negativa/fisiologia , Intenção , Córtex Motor/fisiologia , Inibição Neural/fisiologia , Adulto , Análise de Variância , Mapeamento Encefálico , Estimulação Elétrica , Eletroencefalografia , Eletromiografia , Potencial Evocado Motor/fisiologia , Feminino , Humanos , Processamento de Imagem Assistida por Computador , Masculino , Movimento , Estimulação Luminosa , Desempenho Psicomotor/fisiologia , Processamento de Sinais Assistido por Computador , Estimulação Magnética Transcraniana , PunhoRESUMO
The corticospinal system (CS) is well known to be of major importance for controlling the thumb-index grip, in particular for force grading. However, for a given force level, the way in which the involvement of this system could vary with increasing demands on precise force control is not well-known. Using transcranial magnetic stimulation and functional magnetic resonance imagery, the present experiments investigated whether increasing the precision demands while keeping the averaged force level similar during an isometric dynamic low-force control task, involving the thumb-index grip, does affect the corticospinal excitability to the thumb-index muscles and the activation of the motor cortices, primary and non-primary (supplementary motor area, dorsal and ventral premotor and in the contralateral area), at the origin of the CS. With transcranial magnetic stimulation, we showed that, when precision demands increased, the CS excitability increased to either the first dorsal interosseus or the opponens pollicis, and never to both, for similar ongoing electromyographic activation patterns of these muscles. With functional magnetic resonance imagery, we demonstrated that, for the same averaged force level, the amplitude of blood oxygen level-dependent signal increased in relation to the precision demands in the hand area of the contralateral primary motor cortex in the contralateral supplementary motor area, ventral and dorsal premotor area. Together these results show that, during the course of force generation, the CS integrates online top-down information to precisely fit the motor output to the task's constraints and that its multiple cortical origins are involved in this process, with the ventral premotor area appearing to have a special role.
Assuntos
Força da Mão/fisiologia , Imageamento por Ressonância Magnética , Córtex Motor/fisiologia , Tratos Piramidais/fisiologia , Polegar/fisiologia , Estimulação Magnética Transcraniana , Adulto , Vias Eferentes/fisiologia , Eletromiografia , Potencial Evocado Motor/fisiologia , Feminino , Humanos , Contração Isométrica/fisiologia , Masculino , Córtex Motor/citologia , Músculo Esquelético/inervação , Músculo Esquelético/fisiologia , Oxigênio/sangue , Tratos Piramidais/citologia , Polegar/inervaçãoRESUMO
OBJECTIVE: To compare the localizations of different neural sources (a) obtained from intracerebral evoked responses and (b) calculated from surface auditory evoked field responses recorded in the same subjects. Our aim was to evaluate the resolving power of a source localization method currently used in our laboratory, which is based on a recent spatio-temporal algorithm used in magneto-encephalography (MEG). METHODS: Auditory evoked responses were studied in 4 patients with medically intractable epilepsy. These responses were recorded from depth electrodes implanted in the auditory cortex for pre-surgical evaluation (stereo-electro-encephalography (SEEG)), as well as from surface captors (for MEG) placed on the scalp after removal of the depth electrodes. Auditory stimuli were clicks and short tone bursts with different frequencies. RESULTS: All middle-latency components (from 13 to 70 ms post-stimulus onset) were recorded and localized (via SEEG) along Heschl's gyrus (HG). MEG reliably localized Pam and P1m in the same area of HG that intracerebral recordings localized them in. No significant delay between SEEG and MEG latencies was observed. Both methods suggest that N1 is generated from different sources in the intermediate and lateral parts of the HG and in the planum temporale (PT). The source of P2 (PT and/or Area 22) remains unclear and was in one case, localized in different regions according to the method used. This latter component may therefore also be generated by different sources. CONCLUSIONS: The results suggest that both techniques are useful and may be used together in a complementary fashion. Intracerebral recordings allow the researcher to validate and interpret surface recordings.
Assuntos
Epilepsias Parciais/fisiopatologia , Potenciais Evocados Auditivos/fisiologia , Estimulação Acústica , Adulto , Atenção/fisiologia , Mapeamento Encefálico , Eletroencefalografia , Feminino , Lateralidade Funcional , Humanos , Masculino , Microeletrodos , Tempo de Reação/fisiologiaRESUMO
We explored the degree to which the duration of acoustic cues contributes to the respective involvement of the two hemispheres in the perception of speech. To this end, we recorded the reaction time needed to identify monaurally presented natural French plosives with varying VOT values. The results show that a right-ear advantage is significant only when the phonetic boundary is close to the release burst, i.e., when the identification of the two successive acoustical events (the onset of voicing and the release from closure) needed to perceive a phoneme as voiced or voiceless requires rapid information processing. These results are consistent with the recent hypothesis that the left hemisphere is superior in the processing of rapidly changing acoustical information.
Assuntos
Encéfalo/fisiologia , Lateralidade Funcional/fisiologia , Percepção da Fala/fisiologia , Voz/fisiologia , Adulto , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Fonética , Tempo de Reação , Espectrografia do Som , Fatores de TempoRESUMO
Speech perception requires cortical mechanisms capable of analysing and encoding successive spectral (frequency) changes in the acoustic signal. To study temporal speech processing in the human auditory cortex, we recorded intracerebral evoked potentials to syllables in right and left human auditory cortices including Heschl's gyrus (HG), planum temporale (PT) and the posterior part of superior temporal gyrus (area 22). Natural voiced /ba/, /da/, /ga/) and voiceless (/pa/, /ta/, /ka/) syllables, spoken by a native French speaker, were used to study the processing of a specific temporally based acoustico-phonetic feature, the voice onset time (VOT). This acoustic feature is present in nearly all languages, and it is the VOT that provides the basis for the perceptual distinction between voiced and voiceless consonants. The present results show a lateralized processing of acoustic elements of syllables. First, processing of voiced and voiceless syllables is distinct in the left, but not in the right HG and PT. Second, only the evoked potentials in the left HG, and to a lesser extent in PT, reflect a sequential processing of the different components of the syllables. Third, we show that this acoustic temporal processing is not limited to speech sounds but applies also to non-verbal sounds mimicking the temporal structure of the syllable. Fourth, there was no difference between responses to voiced and voiceless syllables in either left or right areas 22. Our data suggest that a single mechanism in the auditory cortex, involved in general (not only speech-specific) temporal processing, may underlie the further processing of verbal (and non-verbal) stimuli. This coding, bilaterally localized in auditory cortex in animals, takes place specifically in the left HG in man. A defect of this mechanism could account for hearing discrimination impairments associated with language disorders.
Assuntos
Córtex Auditivo/fisiologia , Aprendizagem por Discriminação/fisiologia , Lateralidade Funcional/fisiologia , Tempo de Reação/fisiologia , Percepção da Fala/fisiologia , Estimulação Acústica , Adolescente , Adulto , Epilepsia/fisiopatologia , Potenciais Evocados Auditivos/fisiologia , Feminino , Humanos , Masculino , FonéticaRESUMO
We investigated whether and how adaptive changes in saccadic amplitudes (short-term saccadic adaptation) modify hand movements when subjects are involved in a pointing task to visual targets without vision of the hand. An experiment consisted of the pre-adaptation test of hand pointing (placing the finger tip on a LED position), a period of adaptation, and a post-adaptation test of hand pointing. In a basic task (transfer paradigm A), the pre- and post-adaptation trials were performed without accompanying eye and head movements: in the double-step gaze adaptation task, subjects had to fixate a single, suddenly displaced visual target by moving eyes and head in a natural way. Two experimental sessions were run with the visual target jumping during the saccades, either backwards (from 30 to 20 degrees, gaze saccade shortening) or onwards (30 to 40 degrees, gaze saccade lengthening). Following gaze-shortening adaptation (level of adaptation 79+/-10%, mean and s.d.), we found a statistically significant shift (t-test, error level P<0.05) in the final hand-movement points, possibly due to adaptation transfer, representing 15.2% of the respective gaze adaptation. After gaze-lengthening adaptation (level of adaptation 92+/-17%). a non-significant shift occurred in the opposite direction to that expected from adaptation transfer. The applied computations were also performed on some data of an earlier transfer paradigm (B, three target displacements at a time) with gain shortening. They revealed a significant transfer relative to the amount of adaptation of 18.5< or = 17.5% (P<0.05). In the coupling paradigm (C), we studied the influence of gaze saccade adaptation of hand-pointing movements with concomitant orienting gaze shifts. The adaptation levels achieved were 59+/-20% (shortening) and 61+/-27% (lengthening). Shifts in the final fingertip positions were congruent with internal coupling between gaze and hand, representing 53% of the respective gaze-amplitude changes in the shortening session and 6% in the lengthening session. With an adaptation transfer of less than 20% (paradigm A and B), we concluded that saccadic adaptation does not "automatically" produce a functionally meaningful change in the skeleto-motor system controlling hand-pointing movements. In tasks with concomitant gaze saccades (coupling paradigm C), the modification of hand pointing by the adapted gaze comes out more clearly, but only in the shortening session.
Assuntos
Adaptação Fisiológica/fisiologia , Fixação Ocular/fisiologia , Mãos/fisiologia , Movimento/fisiologia , Desempenho Psicomotor/fisiologia , Movimentos Sacádicos/fisiologia , Eletroculografia , Humanos , Fatores de TempoRESUMO
It has been found that the estimate of relative target direction is consistently biased. Relative target direction refers to the direction in which a target is located relative to another location in space (e.g., a starting position in the case of goal-directed movements). In this study, we have tested two models that could underlie this biased estimate. The first proposed model is based on a distorted internal representation of locations (i.e., we perceive a target at the "wrong" location). We call this the distorted location model. The second model is based on the idea that the derivation of target direction from spatial information about starting and target position is biased. We call this the biased direction model. These two models lead to different predictions of the deviations that occur when the distance between the starting position and the target position is increased. Since we know from previous studies that the initial direction of slow arm movements reflects the target direction estimate, we tested the two models by analyzing the initial direction of slow arm movements. The results show that the biased direction model can account for the biases we find in the target direction estimate for various target distances, whereas the distorted location model cannot. In two additional experiments, we explored this model further. The results show that the biases depend only on the orientation of the line through starting position and target position relative to the plane through longitudinal head or body axis and starting position. We conclude that the initial part of (slow) goal-directed arm movements is planned on the basis of a (biased) target direction estimate and not on the basis of a wrong internal representation of target location. This supports the hypothesis that we code displacements of our limbs in space as a vector.
Assuntos
Atenção , Orientação , Desempenho Psicomotor , Tempo de Reação , Adulto , Idoso , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Distorção da Percepção , PsicofísicaRESUMO
We investigated whether short-term saccadic adaptation modifies hand pointing. Subjects were presented with double-step targets, the second target jump occurring during the saccade to the first one and bringing the target back to 66% of the first target eccentricity, in order to reduce the gain of their gaze saccades. Before and after this adaptation phase, they pointed with their hand to single step targets while keeping their gaze straight ahead. The results show that the hand movements terminated at positions that were significantly less eccentric following the adaptation phase, resembling the adaptive modification seen in the gaze movements. These results suggest that the motor systems controlling gaze and hand use common information about target position.
Assuntos
Adaptação Fisiológica , Movimento/fisiologia , Desempenho Psicomotor , Movimentos Sacádicos/fisiologia , Análise de Variância , Braço , Feminino , Humanos , Masculino , Fatores de TempoRESUMO
Subjects performed a three-dot alignment in the frontoparallel plane. We found systematic deviations in alignment, especially for diagonally oriented stimuli. The biases did not depend on the angular size of the stimuli which was varied between 0.8 and 20 deg. We put forward a tentative explanation based on saccade trajectories. Extending the task to judgements of the straightness of virtual lines consisting of a varying number of dots showed that the biases decrease gradually when the number of dots increases. This suggests that there are two different and competing mechanisms to judge the straightness of virtual lines.
Assuntos
Percepção Visual/fisiologia , Adulto , Movimentos Oculares/fisiologia , Humanos , Julgamento , Pessoa de Meia-Idade , RotaçãoRESUMO
In a previous study we found that the initial direction of slow, goal-directed arm movements deviates consistently from the direction of the actual straight line between the starting position and the target position. We now investigate whether these deviations are caused by imperfections or peculiarities in the processing of vision-related spatial information, such as retinal information, and eye- and head-position information. This could lead to incorrect localization of the target relative to the starting position. Subjects were seated in front of a horizontal surface and had to move their arm slowly and accurately in the direction of target positions. We varied the amount of vision-related spatial information. In experiment 1, subjects were presented with visual targets and could see their moving arm. In experiment 2, the subjects were again presented with visual targets, but now they could not see their moving arm. In experiment 3, the subjects were blindfolded and had to move their arm towards tactile targets. In all three experiments we found comparable consistent deviations in the initial movement direction. We also instructed congenitally and early-blind subjects to move their arm towards tactile targets. Their performance showed deviations congruous with those found in the sighted subjects, and possibly somewhat larger. We conclude that the deviations in the initial movement direction of slow, goal-directed arm movements are not primarily visually based. The deviations are generated after all spatial information has been integrated.
Assuntos
Braço/fisiologia , Cegueira/fisiopatologia , Movimento/fisiologia , Visão Ocular/fisiologia , Adulto , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Percepção Espacial/fisiologia , Tato/fisiologiaRESUMO
Information about the direction of the virtual line between two positions in space (directional information) is used in many decision-making and motor tasks. We investigated how accurately directional information is processed by the brain. Subjects performed two types of task. In both tasks they sat at a table. In the first task they had to move their hand slowly and accurately from an initial position 40 cm in from of them to visually presented targets at a distance of 30 cm from the initial position (movement task). We analysed the initial movement direction. In the second task subjects had to position pointers in the direction of the targets as accurately as they could (perceptive task). We found that in the movement task the subjects started the movements to most targets in a direction that deviated consistently from the direction of the straight line between initial position and target position. The maximum deviation ranged from 5-10 degrees for the various subjects. The mean standard deviation was 4 degrees. In the perceptive task the subjects positioned the pointer in similarly deviating directions. Furthermore, we found that the maximum deviation in the pointer direction depended on the length of the pointer: the smaller the pointer, the larger the consistent deviations in the pointer direction. The shortest pointer showed deviations comparable to the deviations found in the movement task. These findings suggest that the deviations in the two tasks stem from the same source.
Assuntos
Atividade Motora , Movimento , Percepção Visual , Braço , Humanos , Percepção , Estimulação LuminosaRESUMO
Force-velocity and force-length relations were obtained for the edl of four Wistar rats in order to characterise the contractile properties (CE) of these muscle-tendon complexes. Compliances of the undamped part of the series components (SE) were measured in quick length decreases. Force-extension relations of SEs were obtained by integration of compliance to force. A muscle model consisting of CE, SE and a visco-elastic element was used to simulate the force output of the muscle tendon complex in response to a changing muscle length lOI as input. This simulated force was compared with the experimental force of the same muscle measured in response to the same lOI as input. Tetanic contractions were used in all experiments. The results show that this muscle model can predict the experimental force within a mean maximal error not larger than approximately 14% of the force amplitude. However the comparison of simulated force with experimental force and a few additional experiments show that the muscles do not have a unique instantaneous force-velocity characteristic. As shown by several other studies, force seems to be influenced by many other variables (time, history etc.) than CE length and velocity.