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PubMed2007

Infant eye and head movements toward the side opposite the cue in the anti-saccade paradigm.

BACKGROUND: The anti-saccade task, when people must respond in the direction opposite to a visual stimulus, has been used as a marker of operation of the frontal cortical oculomotor area. However, early development of oculomotor control has been little studied with the infant anti-saccade paradigm, and a few studies did not recognize anti-saccades in infants in light of the results of adult anti-saccade. Since the characteristics of infant eye movements are little known, applying the criteria used in adult study is by no means the best way to study infant anti-saccade. As it is indicated that coordinated eye and head movements often enable infants to control the direction of their gaze, head movements should be examined as an infant orienting response. The aim of this study was to address how infants used eye and head movements during the anti-saccade paradigm. To distinguish infants' responses, we also investigated eye and head movements during a task for an inhibition of return. Inhibition of return, in which delayed responses occur in the direction to which attention had previously been oriented, has been thought to mark activity of the superior colliculus. Since the superior colliculus is thought to develop much earlier in life than the frontal lobes, we thought it useful to compare these task performances during infancy. METHODS: Infants were divided into three groups according to age. Anti-saccade and inhibition-of-return tasks were given. Their eye and head movements during tasks were independently recorded by the corneal reflection method in the head-free condition. RESULTS: Younger infants tended to initiate eye movement less than older ones in both tasks. In the anti-saccade task, responses opposite to the cue tended to show longer latency than responses to the cue. Infants made faster responses toward the side opposite the cue when it was to the right than when it was left of fixation. Regarding the comparison of responses toward the side opposite the cue between two tasks, the leftward eye movement was faster than the leftward head movements in the inhibition-of-return task, while no difference of latency was observed between eye and head movements in the anti-saccade task. A qualitative analysis of the trajectory of these responses revealed that head movement trajectories were steeper in the anti-saccade than in the inhibition-of-return task. CONCLUSION: Younger infants move head and eyes together, with head movements frequently starting first. On the other hand, both the leftward latency difference between eye and head and gentle trajectories of head in inhibition of return indicate that eye movements are more predominant over head movements in the inhibition-of-return task than in the anti-saccade task. This would suggest an earlier developing inhibition-of-return mechanism.

Journal Article↗
PubMed2002

[Brain regions activated during the mandibular movement tasks in functional magnetic resonance imaging].

Brain regions activated during the mandibular movement were evaluated by fMRI. Eight healthy right-handed volunteers as examinees were included in this study. Echo planar imaging of fMRI were obtained with the gradient echo sequence using 1.5 T MR scanner. All examinees were subjected to complete six tasks of mandibular movement; simple mouth opening and closing movement, protrusive movement, retrusive movement, right lateral movement, left lateral movement, and imaginary mouth opening and closing movement. The stimulation paradigm consisted of 7 cycles of scans. Each cycle consisted of 10 repeated imagings during "on" and "off" periods of each 5 seconds. The head of examinee in the supine position was fixed, to minimize involuntary motions during all functional measurements, before motions of the head were measured. The following conclusions were obtained. 1. The examinations were achieved with minimal artifacts caused by motions of the head. 2. The region of motor cortex activation by the mandibular movements approximately agreed with those reported by electrophysiological methods in animals, such as cats and monkeys. 3. Activated area of motor cortex and the supplementary motor area were further extended according to the move complex mandibular movements. 4. Possible involvement of the parietal association area was indicated in the lateral movements. 5. Activation of the motor speech area was observed during lateral mandibular movement. Possibility of the involvement of the Broca's area was indicated in mandibular movement. It was thus concluded that fMRI may be useful to analyze the brain regions activated by mandibular movement.

Adult↗
PubMed1997

Differential effect of task conditions on errors of direction and extent of reaching movements.

Invariant patterns in the distribution of the endpoints of reaching movements have been used to suggest that two important movement parameters of reaching movements, direction and extent, are planned by two independent processing channels. This study examined this hypothesis by testing the effect of task conditions on variable errors of direction and extent of reaching movements. Subjects made reaching movements to 25 target locations in a horizontal workspace, in two main task conditions. In task 1, subjects looked directly at the target location on the horizontal workspace before closing their eyes and pointing to it. In task 2, arm movements were made to the same target locations in the same horizontal workspace, but target location was displayed on a vertical screen in front of the subjects. For both tasks, variable errors of movement extent (on-axis error) were greater than for movement direction (off-axis error). As a result, the spatial distributions of endpoints about a given target usually formed an ellipse, with the principal axis oriented in the mean movement direction. Also, both on- and off-axis errors increased with movement amplitude. However, the magnitude of errors, especially on-axis errors, scaled differently with movement amplitude in the two task conditions. This suggests that variable errors of direction and extent can be modified independently by changing the nature of the sensorimotor transformations required to plan the movements. This finding is further evidence that the direction and extent of reaching movements appear to be controlled independently by the motor system.

Adult↗
PubMedDate not supplied

Classification and quantitative aspects of fetal movements during the second half of normal pregnancy.

Qualitative and quantitative aspects of fetal behaviour were studied in nine healthy nulliparae during the second half of pregnancy. Continuous real-time ultrasound observations of 60 min duration were carried-out at four-weekly intervals from 20 to 36 weeks of gestation, using two dynamically focussed linear array transducers positioned lengthwise allowing viewing of sagittal sections through the entire fetus. Various movement patterns were classified according to de Vries et al. (de Vries, J.I.P., Visser, G.H.A. and Prechtl, H.F.R (1982): The emergence of fetal behaviour I. Qualitative aspects. Early Hum. Dev., 7, 301-22). The reproducibility as expressed by the mean standard deviation in the analysis of the percentage incidence of the different movement patterns was good (1.6-2.2%). Both the incidence and percentage of observation time in which general movements were present decreased with advancing gestational age. Breathing movements frequently occurred as an isolated phenomenon; occasionally they were associated with jaw movements, swallowing, hiccups or general movements. The incidence of breathing movements as well as the percentage of observation time in which breathing movements were present, demonstrated an increase up to 32 weeks with a drop at 36 weeks of gestation. Hiccups occurred episodically, following each other in regular succession. Both the incidence and the percentage of observation time in which hiccups were present fluctuated widely. Stretches and startles displayed a decrease in incidence with advancing gestational age, whilst eye movements showed an increase. Rhythmical jaw movements were often followed by swallowing. Occasionally, yawns or tongue movements were seen. They may be combined with breathing and general movements. The incidence of jaw movements increased up to 28 weeks with a decline after. Both brief and longer periods of hand-face contacts were documented with wide variation in incidence. Head rotations frequently occurred as a single event; the incidence showed a decrease up to 28 weeks followed by an increase at 36 weeks of gestation. The incidence of head retroflexion varied widely with gestational age.

Embryonic and Fetal Development↗
PubMed1997

Cognitive difficulty of a peripherally presented visual task affects head movements during gaze displacement.

The maintenance and adjustment of visual gaze are functions both of eye and of head movement. Compared to the factors that affect eye movement during gaze displacement, the factors that affect head movement have received relatively little attention. Most experimenters have restricted head movements to determine how the eye acquires information. Information is commonly acquired without head movements (e.g., it is likely you are moving your eyes without moving your head as you read the words on this page). However, when visual information beyond the written page is acquired head movements in addition to eye movements are likely to occur. The purpose of this experiment was to study gaze displacement under more natural conditions in which the eyes and head were both free to move. Specifically, the purpose of this experiment was to identify the pattern of gaze displacement as a function of cognitive task difficulty. Visual information was presented at an eccentricity of 40 degrees of visual angle either to the left or to the right of a center fixation point (0 degree eccentricity) to 24 undergraduate subjects (12 male). On each trial, five integers were presented in rapid succession; subjects were asked to count the number of odd integers or to arithmetically manipulate the integers. When subjects expected to perform the more difficult task of arithmetic manipulation, they were more likely to make head movements in the direction of the stimuli, F1,16 = 9.34, P < 0.05. Those subjects who made head movements to acquire the peripherally presented visual information made significantly more errors than the 'non-movers', F1,24 = 6.03, P < 0.05. These results suggest subjects who moved their head to acquire peripheral information may have found the task to be more difficult than subjects who did not make head movements. The results confirm that head movements play a critical role in the intake of information even in structured laboratory tasks and suggest the common method of restricting head movements to study eye movements may not be a natural method of information intake.

Adolescent↗
PubMed1980

The superior colliculus and movements of the head and eyes in cats.

1. The superior colliculus has been studied in alert cats which were restrained and whose head and eye movements were monitored.2. Microstimulation within the rostral part of the colliculus, which represents the central 25 deg of the visual field, evokes saccadic eye movements that carry the area centralis to that region of visual space previously occupied by the receptive fields of the cells that were stimulated (;foveation'). These saccades are not generally accompanied by a movement of the head.3. At more caudal locations the visual receptive fields of collicular neurones lie at a greater eccentricity relative to the area centralis than the maximum possible deviation of the eyes from the central position in normal circumstances. At these sites electrical stimulation produces a combined movement of the head and eyes whose co-ordination is identical to that of natural gaze changes in response to novel stimuli. Prolonged stimulation results in the addition of further co-ordinated eye-head movements.4. The addition of a movement of the head does not increase the area of visual space that may be foveated in a single gaze change. Movements of the head are compensated by the vestibulo-ocular reflex. The visual receptive fields of cells at more caudal locations cannot be foveated by a single gaze change.5. A third class of response to electrical stimulation is also occasionally found in the caudal part of the colliculus. The head movement often begins before an accompanying eye movement and continues smoothly for the entire stimulation duration or until limited by the range of mobility.6. Electrical microstimulation was never found to produce so-called ;goal-directed eye movement, in which the eyes move, in a single saccade, to a fixed orbital position regardless of their starting position.7. Ninety-nine cells were recorded from the superior colliculus and classified into four types based on their responses, or lack of responses, during or preceding eye and head movements. Type 1 cells did not show changes in activity prior to gaze changes Type 2 cells were inhibited prior to and during eye movements. Cells discharging before normal saccadic eye movements (type 3) were found only in the rostral part of the colliculus. Cells discharging before head movements (type 4) were found only in the caudal part.8. These results are discussed with respect to the production of gaze changes in the cat.

Action Potentials↗
PubMed2003

Firing behaviour of squirrel monkey eye movement-related vestibular nucleus neurons during gaze saccades.

The firing behaviour of vestibular nucleus neurons putatively involved in producing the vestibulo-ocular reflex (VOR) was studied during active and passive head movements in squirrel monkeys. Single unit recordings were obtained from 14 position-vestibular (PV) neurons, 30 position-vestibular-pause (PVP) neurons and 9 eye-head-vestibular (EHV) neurons. Neurons were sub-classified as type I or II based on whether they were excited or inhibited during ipsilateral head rotation. Different classes of cell exhibited distinctive responses during active head movements produced during and after gaze saccades. Type I PV cells were nearly as sensitive to active head movements as they were to passive head movements during saccades. Type II PV neurons were insensitive to active head movements both during and after gaze saccades. PVP and EHV neurons were insensitive to active head movements during saccadic gaze shifts, and exhibited asymmetric sensitivity to active head movements following the gaze shift. PVP neurons were less sensitive to on-direction head movements during the VOR after gaze saccades, while EHV neurons exhibited an enhanced sensitivity to head movements in their on direction. Vestibular signals related to the passive head movement were faithfully encoded by vestibular nucleus neurons. We conclude that central VOR pathway neurons are differentially sensitive to active and passive head movements both during and after gaze saccades due primarily to an input related to head movement motor commands. The convergence of motor and sensory reafferent inputs on VOR pathways provides a mechanism for separate control of eye and head movements during and after saccadic gaze shifts.

Animals↗
PubMed2003

Coordination of eye and head movements during reading.

PURPOSE: There is little information regarding the characteristics of head movements during reading. This study was undertaken to investigate horizontal and vertical head movements during two different reading tasks. METHODS: Head and eye movements were monitored with an infrared pupil and head tracker in 15 subjects during repeated reading of text from an A4-sized card and a card 90 degrees wide. In addition, head and eye movements were recorded in 45 subjects to compare head movement propensity during an A4 text-reading task and a saccadic task of an equivalent gaze shift. RESULTS: During the A4 standard reading task, horizontal and vertical head movements accounted for 4.7% and 28.7% of the gaze shift, respectively. During the 90 degrees text reading, horizontal head movements accounted for 40.3% of the gaze amplitude, and vertical head movements accounted for 28.4%. Horizontal gaze velocities increased significantly on repeated A4 and 90 degrees text readings, as did horizontal head velocities and amplitudes. Reading head movement propensities were significantly smaller than saccadic head movement propensities (P < 0.001). CONCLUSIONS: Head movement strategies are rapidly switched between the A4 and 90 degrees text-reading paradigms. They are minimized during A4 text reading but actively assist the gaze strategy during 90 degrees text reading. Horizontal head movement is reduced during A4 reading compared to the equivalent saccadic task and may be suppressed to improve fixation stability. The results support the view that the head and eye movement system is a highly coupled but extremely flexible system.

Adult↗
PubMed1992

Striatal neuronal activity during the initiation and execution of hand movements made in response to visual and vibratory cues.

Recordings were obtained from 146 neurons in the neostriatum of rhesus monkeys while they performed wrist movements in response to visual and vibratory cues. Of these, 75 putamena nd 29 caudate neurons exhibited changes in firing rate that were temporally related to the onset of the wrist movements and that began prior to movement onset. This premovement activity (PMA) usually was directionally specific, in that the magnitude or direction of change in firing rates was different during flexion trials as compared to trials involving wrist extension. PMA onset usually preceded movement onset by more than 100 ms and in most instances preceded the average onset of task-related changes in electromyographic (EMG) activity in muscles of the wrist and forelimb. For most neurons, the changes in neuronal activity that began prior to movement were maintained during movement execution. However, approximately one-third of the neurons that exhibited PMA changed their firing rate in the opposite direction, relative to their PMA and to their baseline rate of activity, once the movement began. Several other neurons either exhibited PMA only or they altered their discharge rates during movement execution but did not exhibit PMA. These observations suggest that, despite the close temporal relationship between the onset of PMA and the onset of wrist movement, the neuronal mechanisms mediating the PMA may differ from those that occur during movement execution. The PMA onset of neostriatal neurons occurred earlier in visually cued than in vibratory cued trials. These differences were statistically significant only for flexion trials, however, in which movements were made against a load and in the same direction as the palmar vibratory stimulus. For trials involving wrist extension, PMA onsets for visually cued as compared with vibratory cued trials were not statistically different. These findings contrast with data obtained previously from somatosensory cortical neurons during performance of the same behavioral task. On average, PMA in the putamen began earlier, relative to movement onset, than it did in the somatosensory cortex. Moreover, in the somatosensory cortex, PMA onset occurred earlier in vibratory cued than in visually cued trials, irrespective of movement direction (Nelson 1988; Nelson and Douglas 1989). For putamen neurons, but not for caudate or cortical neurons, the onset of PMA also occurred significantly earlier during extension trials than flexion trials, irrespective of the modality of the "go-cue".(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Neuronal activities in the primate motor fields of the agranular frontal cortex preceding visually triggered and self-paced movement.

Single cell activity was examined in the three motor fields of the monkey frontal cortex with the aim of comparing the neuronal activity preceding movements triggered by a visual signal to that preceding nontriggered (self-paced) movements. The following findings emerged from this study. 1. Neuronal activity changes were observed at two different phases in relation to the movement onset; the short-lead type observed within 480 ms prior to the movement onset and the long-lead type, beginning earlier (typically 1 to 2 s). 2. Neurons in both the supplementary motor area (SMA) and premotor area (PM) exhibited the short-lead activity changes prior to the triggered and self-paced movement. Their magnitudes were similar in 63% of SMA and in 36% of PM neurons, whether the movement was triggered or self-paced. 3. SMA neurons, as a whole, were not less active before the triggered than self-paced movement. 4. On the other hand, as many as 92 PM neurons (61%) were related exclusively or peferentially to the triggered movement. 5. The majority of precentral motor cortex (MC) neurons exhibited similar activity changes before the two modes of movement initiation. 6. The long lead type of activity changes were observed mainly prior to the self-paced and much less frequently before the triggered movement. They were particularly abundant among SMA neurons. These results do not support the simple dichotomy hypothesis that SMA primarily takes part in self-paced movement and PM is only involved in visually triggered movement. However, PM neurons show relatively more prominent responses to the visual trigger signal and SMA neurons are intimately related to a long-lasting process leading to initiation of the self-paced movement.

Animals↗
PubMed1977

Functional linkage between the electrical activity in the vermal cerebellar cortex and saccadic eye movements.

The temporal relation between the onset of electrical activity of Purkinje cells and the occurrence of rapid eye movements was studied. Experiments were performed in unanesthetized animals, the recordings being made under direct vision through the use of a chronically implanted teflon sleeve. The following results were obtained. 1. Correlation between the activity of Purkinje cells and eye movements indicates that Purkinje cell firing in vermal lobules VI and VII precedes eye movement by 11-12 msec, peak activity corresponding to the time of onset of eye movement. 2. This eye movement related activity of Purkinje cells occurred regardless of the direction of the eye movements but some cells showed directional biases. Best correlation between eye movement and Purkinje cell activity was found with fast eye movements toward the right regardless of recording side. 3. Electrical activity of Purkinje cells was mainly related to saccades. Slow eye movement modulation, although probably present, was not studied in detail. 4. In those cells where an extensive set of measurements could be made, Purkinje cell firing was found to be inversely proportional to the amplitude of the eye movement, small movements being preceded by highest Purkinje cell activity. The present results suggest that cerebellar vermis responds prior to the generation of eye movement and may probably serve to control eye movements in a ballistic manner.

Animals↗
PubMed1983

Magnetic fields of the human brain (Bereitschaftsmagnetfeld) preceding voluntary foot and toe movements.

Voluntary movements are preceded by a slow electrical potential of the brain (Bereitschafts-potential, BP) or readiness potential. The BP is accompanied by a magnetic field shift of similar time characteristics (Bereitschaftsmagnetfeld, BM). The BM preceding volitional right foot or toe movements was recorded from anterior, posterior, and lateral positions of the scalp using a SQUID (Superconducting Quantum Interference Device) third-order gradiometer. Controls were implemented to reduce head movements, which were simultaneously recorded with a mechanograph. The results showed that movements of the lower extremities are also preceded by a BM. However, contrary to finger movements, BMs with field lines directed into the head were found predominantly for foot movements and exclusively for toe movements. The BM preceding foot movements was maximum over a position 2 cm left of the vertex, i.e., contralateral to the movement. Two centimeters right of the vertex it was smaller, thus exhibiting a normal contralateral preponderance and not sharing the paradoxical side preponderance of the electrical BP preceding foot or toe movements. The BM preceding toe movements was only apparent at the vertex and was smaller than the one preceding foot movement. This may suggest a source that is located still deeper in the brain than with foot movements.

Brain↗
PubMed1983

Vibration-induced changes in movement-related EMG activity in humans.

The effect of muscle tendon vibration during voluntary arm movement was studied in normal humans. Subjects made alternating step flexion and extension movements about the elbow. A small vibrator was mounted over either the biceps or the triceps muscle and vibration was applied during flexion or extension movements. The vibrator was turned off between movements. After a period of practice, subjects learned the required movements and were able to make them with their eyes closed. Application of vibration to the muscle antagonist to the movement being performed produced an undershoot of the required end-movement position. The undershoot was 20-30% of the total movement amplitude. In contrast, vibration of the muscle agonist to the movement resulted in no change in movement end position. The vibration-induced undershoot was associated with an increase in the EMG activity of the vibrated (antagonist) muscle and a resultant increase in the ratio of the antagonist to agonist EMG activity. The increase in antagonist EMG produced by the vibration occurred with a latency of approximately 60 ms from vibration onset. The observed results are consistent with vibration-induced activation of muscle spindle receptors in the lengthening muscle during movement. It is suggested that, during movement, the sensitivity of the spindle receptors in the shortening muscle is decreased and the information concerning limb position during movement comes primarily from the lengthening muscle.

Electromyography↗
PubMed1989

Asymmetric velocity and acceleration profiles of human arm movements.

Displacement, velocity, acceleration and jerk (change of acceleration with time) were analyzed for arm flexion movement over a wide range of movement amplitudes and speeds. Relative time to peak velocity or relative duration of acceleration, k, was approximately 0.5 for the movements with intermediate speed (about 0.5 s in movement time), i.e., symmetric velocity and acceleration profiles. For the slow and ballistic movements, k shifted towards values below and above 0.5, respectively creating asymmetric profiles. Consistent k-dependence of movement time, peak velocity, maximum acceleration and maximum deceleration were observed. "Jerk cost", the square of the magnitude of jerk integrated over the entire movement, was calculated for each movement. A dynamic optimization technique to minimize jerk cost under the constraint on jerk input was applied to interpret the results, assuming that a major goal of skilled movements was to produce optimally smooth movements. The constrained minimum-jerk model explained speed-dependent asymmetry of the velocity and acceleration profiles. Jerk cost consumed by the movements with intermediate speed approximately satisfied minimum-cost criterion predicted by the model but was higher than the criterion for slow and ballistic movements. The results suggested that optimality criteria other than jerk cost also should be considered to predict movement profiles over the entire range of speeds.

Acceleration↗
PubMed2002

Commonalities and differences in control of various drawing movements.

Characteristics of control at the shoulder and elbow during nine types of drawing movements were studied in the present work. The task was to repetitively track a template, depicted on a horizontal table, with the index finger at a cyclic frequency of 1.5 Hz. The templates were a circle, four ovals and four lines of different orientations. The wrist was immobilized and the movement consisted of rotations at the shoulder and elbow joints. The studied movements varied in a wide range with respect to the amplitude of elbow and shoulder movements and relative phase between them. Kinetic analysis included analysis of torque signs, impulses, and timing. It demonstrated that the role of muscle torque in movement production was different at the two joints. During eight out of the nine movement types, the muscle torque at the shoulder accelerated and decelerated this joint and almost completely coped with the influence of the interactive torque arising from elbow motion. Conversely, interactive torque generated by shoulder motion played a dominant role in elbow acceleration and deceleration, whereas muscle torque at the elbow adjusted passive elbow movement to the various template shapes. EMG data were in agreement with the conclusions made from the kinetic analysis. Collectively, these data support the hypothesis that the two joints have different functions in movement production. The shoulder creates a foundation for motion of the entire arm through the interactive torque, and the elbow serves as a fine-tuner of the end-point movement. Control of the shoulder was similar across the eight movement types and the differences in the end-point path were provided by variations in elbow control. The two joints exchanged roles during one movement type, namely, drawing the line tilted right. During this movement, the elbow musculature generated motion at this joint and the shoulder musculature counteracted mechanical influence of this motion on the shoulder position. The findings suggest that during drawing movements, the control strategy exploits intersegmental dynamics of the shoulder-elbow mechanical linkage.

Adolescent↗
PubMed2002

Timing of bimanual movements in human and non-human primates in relation to neuronal activity in primary motor cortex and supplementary motor area.

This study investigates the timing of bimanual movements in a combined behavioral and physiological approach. Human subjects and rhesus monkeys performed the same bimanual task. In monkeys, we simultaneously recorded neuronal activity in the two hemispheres of primary motor cortex (MI) or supplementary motor area (SMA), and related it to bimanual coordination in the temporal domain. Both for monkeys and humans, the reaction times of bimanual movements never significantly exceeded the reaction times of the slower arm in unimanual movements. Consistent with this, the longest delay between neural activity onset in SMA and MI and movement initiation was observed in unimanual movements of the slower arm and not in bimanual movements. Both results suggest that the programming of bimanual movements does not require more processing time than unimanual movements. They are also consistent with the view that bimanual movements are programmed in a single process, rather than by combining two separate unimanual movement plans. In both humans and monkeys, movement initiation was highly correlated between the arms. However, once movements began, the temporal correlation between the arms progressively declined. Movement decorrelation was accompanied by a net decorrelation of neuronal population activity in MI and SMA, suggesting a functional connection between neuronal interactions and the level of bimanual coupling and decoupling. The similarity of neuronal activities in MI and SMA in relationship to behavioral timing lends support to the idea that both areas are involved in the temporal coordination of the arms.

Adult↗
PubMed2002

Interjoint coordination in lower limbs during different movements in humans.

Redundancy is associated with the ability of the nervous system to select different interjoint coordinations and movement trajectories to achieve the same motor goal. The nervous system may coordinate multiple degrees of freedom (DF) by combining them in a task-specific way to control them as a unit or synergy. Some movements may be accomplished using only one synergy, whereas other movements may employ several synergies. To investigate the problem of interjoint coordination, we applied principal component (PC) analysis to eight types of movement in healthy male subjects: forward squats, backward squats, sideways squats, squats on one leg, walking three steps, stepping in place, going up a step, and going down a step. Angular changes in four DF were analyzed: thigh flexion-extension, knee flexion-extension, ankle flexion-extension, thigh abduction-adduction, with the former three DF investigated in all movements. For many movements, two synergies were sufficient to account for more than 95% of DF angular excursions. Squatting on one leg could be described using only one synergy (99%). The angle between the vectors representing PCs for movements produced with the right and left legs could be less than 10 degrees for some movements but could reach 25 degrees for other movements. The nervous system may thus use somewhat different interjoint coordinations while producing movements on the right and the left sides. The angle between the first PCs of different movements could be smaller than 10 degrees. Thus there may be a common but adjustable basic synergy that is used to produce different movements. Additional synergies provide the transition from one movement to another.

Adolescent↗
PubMed2004

Eye movement-related responses of neurons in human subthalamic nucleus.

Intraoperative microelectrode single unit recordings are routinely made in the subthalamic nucleus (STN) of awake and alert Parkinson's disease (PD) patients during surgery for implantation of deep brain stimulation (DBS) electrodes. These recordings not only assist in determining the optimal target for electrode implantation, but also offer the unique opportunity to study movement-evoked responses from the basal ganglia. We report on the responses of human STN neurons to eye movements from eight PD patients (five men and three women). Twenty percent (18/89) of tested STN neurons showed responses to eye movements. Patients made pro-saccades, voluntary saccades or smooth pursuit eye movements in four directions: up, down, left, right. The majority of STN neurons (72% or 13/18), that responded to eye movements were found in the ventral half of the nucleus, while 58% (22/38) of STN neurons that had somatic responses were found in the dorsal half of the nucleus. The firing rate for STN oculomotor neurons was 33+/-15 Hz (n = 18), which was not different from that reported previously for STN neurons. Most neurons only responded to eye movements in a single direction, but 17% (3/18) showed responses to more than one direction. The majority of responses (17/18) to eye movements were increases in firing rate although one neuron did show a pause in firing with eye movement onset. The phasic changes in firing rate in response to eye movement usually occurred up to 250 ms following eye movement onset. Neurons were found that showed task-specific responses to cued versus self-paced saccades, responded to both passive limb movement and voluntary eye movement, and appeared to show either visual or attentional responses. These human physiological data, in conjunction with previous anatomical studies, suggest that the STN might have an oculomotor role. Although there is no evidence that STN is responsible for driving eye movements, it may have a role in either sensory feedback, corollary discharge, or in focusing the substantia nigra pars reticulata to allow a saccade to occur through disinhibition of the superior colliculus.

Action Potentials↗