Anticipatory behaviour deficits in closed head injury.

Closed head injured patients demonstrated greater anticipatory behaviour deficit than cerebral vascular accident patients on a shuttlebox-analog avoidance task, even though these two groups did not differ on escape behaviour and on performance on the individual tests of the Halstead-Reitan Battery and Wechsler scales. Neither clarification of instructions, additional trials, nor enhancement of the warning cue appeared to improve the anticipatory behaviour deficit. It was concluded that anticipatory behaviour deficit should be considered a relatively dense deficit that is not identified by standard instruments. Clinical and practical implications are discussed.     

Anticipatory control of long-range phase synchronization

Everyday human behaviour relies on our ability to predict outcomes on the basis of moment by moment information. Long-range neural phase synchronization has been hypothesized as a mechanism by which 'predictions' can exert an effect on the processing of incoming sensory events. Using magnetoencephalography (MEG) we have studied the relationship between the modulation of phase synchronization in a cerebral network of areas involved in visual target processing and the predictability of target occurrence. Our results reveal a striking increase in the modulation of phase synchronization associated with an increased probability of target occurrence. These observations are consistent with the hypothesis that long-range phase synchronization plays a critical functional role in humans' ability to effectively employ predictive heuristics.     

Frontal head posture in shunt-treated hydrocephalic patients

Objects: The aim of this study was to evaluate frontal head posture in shunt-treated hydrocephalic patients and its relation to the sidedness of the shunt device. Methods: Natural head position and frontal cephalograms of 55 shunt-treated Finnish hydrocephalic patients and 33 healthy Finnish subjects were analysed using a computerised digitising program (X-METRIX). The following reference angles were used: ORB/HOR, indicating the head position related to the true horizontal; CER/VER, indicating the cervical position related to the true vertical; and CER/CR, indicating the craniocervical position. Conclusions: The results showed an increased skewness of the head in the shunt-treated subjects, which was not related to the shunt side. Received: 26 March 1999 Revised: 10 March 2000     

The control of movement and posture

This report attempts to summarize material discussed at a recent conference on the control of movement and posture, held under the auspices of the Fogarty International Center at the National Institutes of Health, Bethesda, Md., on March 27th and 28th, 1972. The Conference was planned to focus on the cross-over between work in animals on muscles and the central nervous system control of movement, and observations in human clinical neurology and neurophysiology. Major emphasis was placed on recent work dealing with the properties of motor units, the role of muscle receptor systems in movement control and with the role of the motor cortex in both ‘reflex’ as well as ‘voluntary’ movement.Attention was also directed to issues of the prospect for and ethical aspects of future experimentation in human subjects.     

Influence of head position and head position-change on body posture in pre-term infants (A.T.N.R.)

Although body posture in pre-term infants is generally studied to describe developmental aspects, no consensus exists in literature about the influence of head position and head position change upon body posture in pre-term infants. In a weekly assessed longitudinal study of 15 healthy pre-term infants we extensively observed and analysed the flexion and extension patterns of the limbs in relation to a "spontaneous" head position turning from 32 to 36 weeks of conceptional age. A significant flexion/extension pattern was only observed with respect to the leg: turning of the head induced extension of the chin leg and flexion of the other leg. This pattern persisted during the total 3 hours observation sessions, occurred at every age and in all states, but rapidly disappeared within maximal 20 seconds after the head-turning. No consequent significant pattern was observed with respect to the other limbs or the various other combinations of limb posture changes analysed. An Asymmetric Tonic Neck Reflex was seen after only 3 percent of the head position changes.     

Internal models in the control of posture

The aim of the paper is to investigate the application of control schemes based on “internal models” to the stabilization of the standing posture. The computational complexities of the control problems are analyzed, showing that muscle stiffness alone is insufficient to carry out the task. The paper also re-visits the concept of the cerebellum as a Smith's predictor.     

Evaluation of head motility and posture in cats with horizontal torticollis

Unilateral electrolytic lesions and injections of 6-hydroxydopamine (6-OHDA) and 5,7-dihydroxytryptamine (5,7-DHT) were made in structures and pathways linked to the striatopallidal system of cats. The effects of such lesions on horizontal head symmetry and head motility were measured in restrained cats by electrogoniometry. Analysis of electrogoniometric recordings provided (i) an index of head symmetry, (ii) net time-course patterns of head turning in degrees per minute, and (iii) time-course patterns of head motility, measured in number of head movements per minute. All lesions except the electrolytic lesion of the superior colliculus induced an enduring horizontal head asymmetry. Electrolytic, 5,7-DHT, and 6-OHDA lesions made in the medial forebrain bundle induced a nearly total head asymmetry (95 to 98%). Cats in which an electrolytic lesion was made in the substantia nigra reticulata (SNR) also displayed an important head asymmetry (80%). For all lesions except the SNR lesions the direction of the induced head asymmetry was ipsilateral. In 6-OHDA-lesion cats a marked and consistent decrease head motility was also observed. The combined evaluation of head posture and head movements indicated that according to the lesion, head symmetry and head motility are disturbed in different manners. The results further emphasized the complementary contribution of the caudate and SNR in regulation of head symmetry and indicated the advantages of the electrogoniometric method for selectively measuring head posture and movements.     

A basic posture control mechanism: the stabilization of the centre of gravity.

Holding the body's centre of gravity steady represents the crucial variable for the stabilization of posture in upright stance in man. The visual, vestibular and muscle proprioceptive systems have all been shown to contribute to sway stabilization. Nevertheless, earlier work has suggested that an additional receptor system is needed to signal the position of the body's centre of gravity relative to the support surface, i.e., the feet. This proposed receptor system should be 'gravity' dependent. To evaluate the properties of this receptor system, an experiment was designed under simulated 'microgravity', in water immersion. An approximately linear relationship was found between contact force and impulse directed EMG response amplitudes in the leg muscles. Out of water loading of the subjects resulted in no further increase of the response amplitude. A gain control mechanism for postural reflexes which is dependent on body weight was demonstrated. In a further experiment it could be shown that the receptors for this mechanism are distributed along the vertical axis of the body: it is suggested that these force-dependent receptors are pressure receptors within the joints and the vertebral column.     

The role of the substantia nigra in posture control

Disorders implicating the basal ganglia are often characterized by postural deficits, but little is known about the role of the basal ganglia in posture control. Using wireless multi‐electrode recording, we measured single unit activity from GABAergic and dopaminergic neurons in the substantia nigra as unrestrained mice stood on an elevated platform while introducing continuous postural disturbances in the roll plane. We found two major types of neurons – those activated by tilt to the left side of the body and suppressed by tilt to the right side, and others activated by tilt to the right side and suppressed by tilt to the left side. Contrary to the prevailing view that the basal ganglia output from the substantia nigra pars reticulata either inhibits or disinhibits downstream structures in an all or none fashion, we showed that it continuously sends anti‐phase signals to their downstream targets. We also demonstrated for the first time that nigrostriatal dopaminergic transmission is modulated by postural disturbances.     

The effect of decreased visual acuity on control of posture

Objectives

The goal of this study was to investigate the effect of visual acuity on the anticipatory (APAs) and compensatory (CPAs) components of postural control.

Methods

Ten individuals participated in the experiments involving perturbations induced by a pendulum while their visual acuity was altered. The different visual acuity conditions were no glasses, blurred vision induced by wearing glasses with positive or negative lenses, and no vision. EMG activity of trunk and leg muscles and ground reaction forces were recorded during the typical anticipatory and compensatory periods.

Results

In the no vision condition the subjects did not generate APAs, which resulted in the largest displacements of the center of pressure (COP) after the perturbation (p < 0.01). In all other visual conditions APAs were present showing a distal to proximal order of muscle activation. The subjects wearing positive glasses showed earlier and larger anticipatory EMGs than subjects wearing negative glasses or no glasses at all.

Conclusions

The study outcome revealed that changes in visual acuity induced by wearing differently powered eye glasses alter the generation APAs and as a consequence, affect the compensatory components of postural control.

Significance

The observed changes in APAs and CPAs in conditions with blurred vision induced by positive and negative glasses suggest the importance of using glasses with an appropriate power. This outcome should be taken into consideration in balance rehabilitation of individuals wearing glasses.     

Influence of action and expectation on visual control of posture

Previous studies have shown that human subjects presented with a moving visual environment initiate a postural re-adjustment in the direction of motion. The present study investigated how active control or expectation of the displacement of a visual scene affects this postural response. Center of foot pressure (COP) and head displacement were recorded using a sway platform and a tracking system, respectively. The subjects faced a visual scene (1 x 1 m, at a distance of 45 cm) which moved transiently (with a velocity of 1 cm/s) in a direction parallel to the interaural axis. When the displacement of the visual scene was under the active control of the subjects, visually induced body sway was strongly inhibited, in comparison with the response to unexpected stimuli. Prior knowledge of the characteristics of the forthcoming displacement was sufficient, in most subjects, to reduce postural re-adjustment, even when subjects did not exert active control. Finally, the visually induced postural response was strongly reduced even when subjects only triggered the stimulus, without any knowledge about the direction of motion. In conclusion, it appears that although vision is of primary importance in the control of postural orientation, high level processes such as expectation can modulate its impact by providing cues as to whether forthcoming visual flow is the consequence of self-motion or object-motion.     

Effects of hand posture on preparatory control processes and sensory modulations in tactile-spatial attention.

OBJECTIVE: Event-related brain potentials (ERPs) were measured to investigate spatial coordinate systems involved in the control of preparatory tactile-spatial orienting, and in subsequent attentional modulations of somatosensory processing. METHODS: On each trial, a visual precue directed attention to the left or right hand, where infrequent tactile targets had to be detected. Hands were positioned either close together or wide apart. ERPs were recorded in the cue-target interval and in response to attended and unattended tactile non-targets. RESULTS: A frontal anterior directing attention negativity (ADAN) and a posterior late directing attention positivity (LDAP) were elicited in the cue-target interval contralateral to the direction of an attentional shift. The ADAN was unaffected by hand posture, but the LDAP was attenuated when hands were close together. N140 amplitudes were enhanced in response to tactile stimuli presented to the attended hand, and this effect was more pronounced when hands were wide apart. CONCLUSIONS: ADAN and LDAP are linked to separable anterior and posterior attentional control systems, which use coordinate systems based on somatotopic and external space, respectively. Effects of spatial attention on somatosensory stimulus processing are affected by variations in body posture. SIGNIFICANCE: Our results demonstrate that representations of body locations in external space play a central role in the control of tactile attention.     

What startles tell us about control of posture and gait

Recently, there has been an increase in studies evaluating startle reflexes and StartReact, many in tasks involving postural control and gait. These studies have provided important new insights. First, several experiments indicate a superimposition of startle reflex activity on the postural response during unexpected balance perturbations. Overlap in the expression of startle reflexes and postural responses emphasizes the possibility of, at least partly, a common substrate for these two types of behavior. Second, it is recognized that the range of behaviors, susceptible to StartReact, has expanded considerably. Originally this work was concentrated on simple voluntary ballistic movements, but gait initiation, online step adjustments and postural responses can be initiated earlier by a startling stimulus as well, indicating advanced motor preparation of posture and gait. Third, recent experiments on StartReact using TMS and patients with corticospinal lesions suggest that this motor preparation involves a close interaction between cortical and subcortical structures. In this review, we provide a comprehensive overview on startle reflexes, StartReact, and their interaction with posture and gait.