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PubMed1994

Subcortical contributions to head movements in macaques. I. Contrasting effects of electrical stimulation of a medial pontomedullary region and the superior colliculus.

1. These studies were initiated to understand the neural sites and mechanisms controlling head movements during gaze shifts. Gaze shifts are made by saccadic eye movements with and without head movements. Sites were stimulated electrically within the brain stem of awake, trained monkeys relatively free to make head movements to study the head-movement components of gaze shifts. 2. Electrical stimulation in and around the gigantocellular reticular nucleus evoked head movements in the ipsilateral direction. Gaze shifts were never evoked from these sites, presumably because the vestibulo-ocular reflex compensated. The rough topography of this region included large head movements laterally, small movements medially, downward movements from dorsal sites, and upward movements more ventrally. 3. The initial position of the head influenced the magnitude of the elicited movement with larger movements produced when the head was directed to the contralateral side. Attentive fixation was associated with larger and faster head movements when compared with those evoked during spontaneous behavior. 4. The superior colliculus makes a significant contribution to gaze shifts and has been shown to contribute to head movements. Because the colliculus is a major source of afferents to the gigantocellular reticular nucleus, comparable stimulation studies of the superior colliculus were conducted. When the colliculus was excited, shifts of gaze in the contralateral direction were predominant. These were most often accomplished by saccadic eye movements, however, we frequently elicited head movements that had an average latency 10 ms longer than those elicited from the reticular head movement region. Sites evoking head movements tended to be deeper and more caudal than loci eliciting eye movements. Neither the onset latencies, amplitudes, nor peak velocities of head movements and eye movements were correlated. Gaze shifts evoked from the caudal colliculus with the head free were larger than those elicited from the same site with the head fixed. 5. These studies demonstrate that both the superior colliculus and gigantocellular reticular nucleus mediate head movements. The colliculus plays a role in orienting to external events, and so collicular head movements predominantly were associated with gaze shifts, with the eye and head movements uncoupled. The medullary reticular system may play a role in the integration of a wider range of movements. Head movements from the medullary reticular sites probably participate in several forms of head movements, such as those that are related to postural reflexes, started volitionally, and/or oriented to external events.

Animals↗
PubMed1992

The relationship between the quantity and quality of prenatal movements in pregnancies complicated by intra-uterine growth retardation and premature rupture of the membranes.

In 17 fetuses with intrauterine growth retardation (IUGR), we studied the quantity of general movements and fetal breathing movements both cross-sectionally and longitudinally. In IUGR fetuses, cross-sectional comparisons were made between the quantity of fetal movements and (1) the fetal clinical condition and (2) the quality of general movements. In addition, the quantity of fetal movements in IUGR was compared with that in uncomplicated pregnancies and in pregnancies complicated by premature rupture of the amniotic membranes. In IUGR, the quantity of general movements declined from 25 weeks gestation onwards, whereas the quantity of fetal breathing movements increased. Longitudinal assessment of these parameters was obtained in four cases and showed a decline of general movements. No relationship between prenatal longitudinal data and neonatal outcome could be observed. Relating the quantity of general movements and breathing movements to the fetal condition, growth retarded fetuses were divided into three groups according to fetal deterioration. 1. Normal amount of amniotic fluid and normal fetal heart rate patterns. 2. Reduced amount of amniotic fluid. 3. Abnormal fetal heart rate patterns. The quantity of general movements as well as that of breathing movements was low in group 3, compared to group 1. In group 2 only the quantity of breathing movements and not of general movements was low. A similar pattern was found in the relation with the quality of general movements observed during fetal deterioration. Cross-sectional analysis of median values (28-31 weeks gestation) did not reveal differences in the quantity of general movements when IUGR, normal pregnancies and premature rupture of the membranes (with or without oligohydramnios) were compared. The quantity of fetal breathing movements was significantly lower in pregnancies complicated by IUGR and by premature rupture of the membranes with oligohydramnios compared to those of normal pregnancies and premature rupture of the membranes without oligohydramnios. In uncomplicated IUGR, the quantity of general movements and breathing movements is in the same range as in normal uncomplicated pregnancies. Similar to the quality of general movements, the quantitative variables were related to the fetal condition. However, in contrast to the quality of general movements, the quantity of general movements and breathing movements showed a high inter- and intraindividual variation. Therefore, the results of this study discourage the use of quantitative aspects of general movements and breathing movements as reliable indicators of the neurological condition in the individual fetus.

Cross-Sectional Studies↗
PubMed1992

Role of primate basal ganglia and frontal cortex in the internal generation of movements. III. Neuronal activity in the supplementary motor area.

This study is a part of a project investigating neuronal activity in the basal ganglia and frontal cortex and describes externally and internally induced preparatory activity in the supplementary motor area (SMA), which forms a closed neuronal loop with the striatum. Monkeys made self-initiated arm reaching movements toward a constant target in the absence of phasic external stimuli. In separate blocks of trials, animals performed in a delayed go no-go task in which an instruction cue prepared for subsequent movement or no-movement to a trigger stimulus. A total of 328 neurons were tested in the delay task. Of these, 91 responded transiently to the instruction light with a median latency of 262 ms. Three quarters of these responses were restricted to the instruction preparing for arm movement, as opposed to withholding it, and thus may be involved in movement preparation processes. Sustained activation during the instruction-trigger interval was found for 67 neurons and occurred nearly exclusively in movement trials. Activation usually increased gradually after the cue and ended abruptly upon movement onset and thus could be related to the setting and maintenance of processes underlying the preparation of movement. Time-locked responses to the trigger stimulus were found in 38 neurons and were usually restricted to movement trials (median latency 80 ms). Activity time-locked to movement execution occurred in 67 neurons, beginning up to 252 ms before movement onset. A total of 266 neurons were tested with self-initiated arm movements. Of these, 43 showed premovement activity beginning 610-3030 ms before movement onset (median 1430 ms). The activity increased slowly and reached its peak at 370 ms before movement onset. It ended before movement onset or continued until the arm began to move or reached the target. This activity appears to reflect neuronal processes related to the internal generation of movements. Two thirds of activations preceding self-initiated movements occurred in neurons not activated before externally instructed movements, suggesting a selectivity for the internal generation process. Activity related to the execution of self-initiated movements occurred in 67 neurons: it began during and up to 420 ms before movement onset and was usually not associated with premovement activity. Most of these neurons were also activated with stimulus-triggered movements, suggesting a lack of selectivity for the execution of self-initiated movements. In comparison with the striatum, more SMA neurons showed preparatory activity preceding externally instructed movements (transient 27% vs 16%, sustained 20% vs 12%) and self-initiated movements (16% vs 11%).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Merging different motor patterns: coordination between rhythmical and discrete single-joint movements.

Subjects made fast, discrete elbow flexion movements while simultaneously producing rhythmical oscillations about initial and final visual targets embedded on a horizontal surface. Based on kinematic and electromyographic (EMG) analysis, we found that the discrete movement could start at any phase of the cyclical movement. The most likely onset time occurred when the first agonist burst started at the same moment as a rhythmical burst would have appeared. This resulted in a smooth conjugation between discrete and rhythmical movements. The initiation of the discrete movement was associated with the resetting of the phase of the rhythmical movements. Thus, the time characteristics of the two motor tasks were interdependent. A subset of trials with a uniform distribution of discrete movement onset phases could be selected in most subjects and was averaged to eliminate the cyclical component from the combined movement. Mean kinematic and EMG traces up until the peak velocity were practically identical to those of the discrete movement made alone. The averaging procedure was ineffective in eliminating the rhythmical component following the discrete movement because of the resetting of the phase of oscillation. Using the same procedure it has been shown that initiating the rhythmical movement at the same time as beginning the discrete movement did not affect the initial part of discrete movement. The whole discrete movement was not affected when subjects simultaneously terminated the ongoing rhythmical movements. Our findings are consistent with the hypothesis that although the rhythmical movement constrains the onset time of discrete movement, the latter, once initiated, proceeds independently of the ongoing rhythmical movement. We also subtracted the discrete component from the combined movement to see how the former affected the rhythmical movement. The residual pattern showed that the rhythmical movements rapidly attenuated when the discrete movement started and then apparently resumed after the peak velocity of the discrete movement. The results corroborate the hypothesis that the control signals underlying the two motor tasks cannot be applied simultaneously, since they may be associated with conflicting stability requirements. Instead, these control signals may be generated sequentially, but the resulting kinematic responses may outlast them and be superposed.

Arm↗
PubMed2002

Time course and magnitude of movement-related gating of tactile detection in humans. III. Effect of motor tasks.

This study investigated the relative importance of central and peripheral signals for movement-related gating by comparing the time course and magnitude of movement-related decreases in tactile detection during a reference motor task, active isotonic digit 2 (D2) abduction, with that seen during three test tasks: a comparison with active isometric D2 abduction (movement vs. no movement) evaluated the contribution of peripheral reafference generated by the movement to gating; a comparison with passive D2 abduction (motor command vs. no motor command; movement generated by an external agent) allowed us to evaluate the contribution of the central motor command to tactile gating; and finally, the inclusion of an active "no apparatus," or freehand, D2 abduction task allowed us to evaluate the potential contribution of incidental peripheral reafference generated by the position detecting apparatus to the results (apparatus vs. no apparatus). Weak electrical stimuli (2-ms pulse; intensity, 90% detected at rest) were applied to D2 at different delays before and after movement onset or electromyographic (EMG) activity onset. Significant time-dependent movement-related decreases in detection were obtained with all tasks. When the results obtained during the active isotonic movement task were compared with those obtained in the three test tasks, no significant differences in the functions describing detection performance over time were seen. The results obtained with the isometric D2 abduction task show that actual movement of a body part is not necessary to diminish detection of tactile stimuli in a manner similar to the decrease produced by isotonic, active movement. In the passive test task, the peak decrease in detection clearly preceded the onset of passive movement (by 38 ms) despite the lack of a motor command and, presumably, no movement-related peripheral reafference. A slightly but not significantly earlier decrease was obtained with active movement (49 ms before movement onset). Expectation of movement likely did not contribute to the results because stimulus detection during sham passive movement trials (subjects expected but did not receive a passive movement) was not different from performance at rest (no movement). The results obtained with passive movement are best explained by invoking backward masking of the test stimuli by movement-related reafference and demonstrate that movement-related reafference is sufficient to produce decreases in detection with a time course and amplitude not significantly different from that produced by active movement.

Adolescent↗
PubMed1990

Neural maps of head movement vector and speed in the optic tectum of the barn owl.

1. This study investigates the contribution of the optic tectum in encoding the metric and kinetic properties of saccadic head movements. We describe the dependence of head movement components (size, direction, and speed) on parameters of focal electrical stimulation of the barn owl's optic tectum. The results demonstrate that both the site and the amount of activity can influence head saccade metrics and kinetics. 2. Electrical stimulation of the owl's optic tectum elicited rapid head movements that closely resembled natural head movements made in response to auditory and visual stimuli. The kinetics of these movements were similar to those of saccadic eye movements in primates. 3. The metrics and kinetics of head movements evoked from any given site depended strongly on stimulus parameters. Movement duration increased with stimulus duration, as did movement size. Both the size and the maximum speed of the movement increased to a plateau value with current strength and pulse rate. Movement direction was independent of stimulus parameters. 4. The initial position of the head influenced the size, direction, and speed of movements evoked from any given site: when the owl initially faced away from the direction of the induced saccade, the movement was larger and faster than when the owl initially faced toward the direction of the induced movement. 5. A characteristic movement of particular size, direction, and speed could be defined for each site by the use of stimulation parameters that elicited plateau movements with normal kinetic profiles and by having the head initially centered on the body. The size, direction, and speed of these characteristic movements varied systematically with the site of stimulation across the tectum. The map of head movement vector (size and direction) was aligned with the sensory representations of visual and auditory space, such that the movement elicited from a given site when the owl initially faced straight ahead brought the owl to face that region of space represented by the sensory responses of the neurons at the site of stimulation. 6. The results imply that both the site and the amount of neural activity in the optic tectum contribute to encoding the metrics and kinetics of saccadic movements. A comparison of the present findings with previous studies on saccadic eye movements in primates and combined eye and head movements in cats suggests striking similarities in the ways in which tectal activity specifies a redirection in gaze to such dissimilar motor effectors as the eyes and head.

Animals↗