Analysis of postural sway in patients with normal pressure hydrocephalus: effects of shunt implantation.

Poor postural balance is one of the major risk factors for falling in normal pressure hydrocephalus (NPH). Postural instability in the clinic is commonly assessed based upon force platform posturography. In this study we focused on the identification of changes in sway characteristics while standing quiet in patients with NPH before and after shunt implantation. Postural sway area and sway radius were analyzed in a group of 9 patients and 46 controls of both genders. Subject's spontaneous sway was recorded while standing quiet on a force platform for 30-60 s, with eyes open and then closed. Both analyzed sway descriptors identified between-group differences and also an effect of shunt implantation in the NPH group. Sway radius and sway area in patients exhibited very high values compared with those in the control group. Importantly, the effect of eyesight in patients was not observed before shunt implantation and reappeared after the surgical treatment. The study documents that static force platform posturography may be a reliable measure of postural control improvement due to shunt surgery.

Assessment of postural instability in patients with Parkinson's disease.

Postural instability is one of the most disabling features of idiopathic Parkinson's disease (PD). In this study, we focused on postural instability as the main factor predisposing parkinsonians to falls. For this purpose, changes in sway characteristics during quiet stance due to visual feedback exclusion were studied. We searched for postural sway measures that could be potential discriminators for an increased fall risk. A group of 110 subjects: 55 parkinsonians (Hoehn and Yahr: 1-3), and 55 age-matched healthy volunteers participated in the experiment. Their spontaneous sway characteristics while standing quiet with eyes open and eyes closed were analyzed. We found that an increased mediolateral sway and sway area while standing with eyes closed are characteristic of parkinsonian postural instability and may serve to quantify well a tendency to fall. These sway indices significantly correlated with disease severity rated both by the Hoehn and Yahr scale as well as by the Motor Section of the UPDRS. A forward shift of a mean COP position in parkinsonians which reflects their flexed posture was also significantly greater to compare with the elderly subjects and exhibited a high sensitivity to visual conditions. Both groups of postural sway abnormalities identified here may be used as accessible and reliable measures which allow for quantitative assessment of postural instability in Parkinson's disease.

Gait transitions during unrestrained locomotion in dogs.

Gait transitions during long distance, unrestrained locomotion were studied in 22 mongrel dogs. Spatial and temporal limb movement parameters were collected and the phase relationships between limb movements based upon a 2-dimensional (2-D) gait diagram were computed. During most of the trials, the dogs trotted within a relatively narrow velocity range. Gait transitions were observed during radical changes of the movement velocity. In most cases the gait switches were abrupt and completed within 2 strides of the gait cycle. The dogs walked, depending on the animal size, within the upper velocity range of 0.93-1.21 m/s. Most of the walk-trot transitions were observed within this range. All of them had a typical pattern that involved changes of the phase shift between diagonal limb movements from 0.31 +/- 0.02 (a typical value for a walking dog) down to 0.02 +/- 0.03. These changes appeared abruptly within one stride cycle for each diagonal pair of limbs; therefore, the transition was completed in 2 strides of the gait cycle. The switch involved momentary shortening of the hindlimb amplitudes. During the next gait cycle, all limb movement amplitudes were reduced with a concomitant increase in limb movement frequencies. In contrast to the clear border between the symmetrical gaits, the dogs switched to gallop at any speed within the trot range (most frequently between 1.5-2.6 m/s). The transitions were usually completed within one stride of the diagonal limbs. In most cases, the switch from trot to gallop had a similar pattern; while maintaining synchronous movement of one diagonal pair of limbs, the other pair movement control was modified accordingly. The typical transition pattern involved the shortening of the swing phase in the front limb with simultaneous lengthening of the swing phase in the diagonal hindlimb. These transient modifications had their equivalent in the analogous limb movement amplitude changes. A mirror-image pattern of phase changes was observed in the majority (82%) of the gallop-trot transitions. Three of the dogs, however, besides the typical gallop-trot switch, occasionally employed a second pattern of transition.

Postural stability and fractal dynamics.

Methods of non-linear dynamics and deterministic chaos may provide us with effective quantitative descriptors of the dynamics of postural control. The goal of this study was to introduce a new measure, which would allow to determine the fractal structure of posturographic signals and to measure the effect of the loss of visual feedback information in postural control. The results of the study show that fractal dimension (Df) is a very useful, reliable and sensitive measure of the complexity of posturographic signals. Therefore Df can be used for the evaluation of postural stability and its changes due to pathology or an age-related decline.

Acoustic startle and open-field behavior in mice bred for magnitude of swim analgesia.

Acoustic startle response (ASR) and open-field activity was examined in the 46th generation of mice that have been selectively bred for high analgesia (HA) and for low analgesia (LA) induced by 3-min swimming in 20 degrees C water. These lines were earlier found to differ in brain opioid receptor density and in the expression of opioid-mediated phenomena, as analgesic sensitivity to opiates and reversibility of swim stress-induced analgesia (SSIA) by naloxone. For comparison, a randomly bred control (C) line was used. To measure the amplitude of ASR, the mice were exposed to 110-dB acoustic stimuli in a Coulbourn apparatus. In saline-injected mice, the ASR force was found significantly lower in the LA than in the HA, as well in the C line, but did not differ between the two last lines. Naltrexone hydrochloride (10 mg/kg IP 30 min before ASR testing) augmented the startle in the opioid receptor-dense HA line, but had no effect in the opioid receptor-deficient LA line, as well in the C line; therefore, the ASR magnitude in naltrexone-injected HA mice was significantly higher compared to the C line. HA mice displayed less activity in an open-field test; that is, they remained immobile longer in the center of the field, and thereafter performed less ambulation and less rearing against the wall compared to the LA line. Naltrexone failed to modify the open-field activity in any line. The results confirm that the pattern of ASR depends on the genetic makeup of the animals. The higher amplitude of ASR, taken together with the lower open-field activity of HA mice, can be interpreted in terms of higher anxiety level, compared to the LA line. It is suggested that the higher ASR in HA mice relies on a nonopioid mechanism, which is tonically inhibited by the opioid system.

Effect of ageing and vision on limb load asymmetry during quiet stance.

Although the identification and characterization of limb load asymmetries during quiet standing has not received much research attention, they may greatly extend our understanding of the upright stance stability control. It seems that the limb load asymmetry factor may serve as a veridical measure of postural stability and thus it can be used for early diagnostic of the age-related decline in balance control. The effects of ageing and of vision on limb load asymmetry (LLA) during quiet stance were studied in 43 healthy subjects (22 elderly, mean age 72.3+/-4.0 yr, and 21 young, mean age 23.9+/-4.8 yr). Postural sway and body weight distribution were recorded while the subject was standing on two adjacent force platforms during two 120 s trials: one trial was performed with the eyes open (EO), while the other trial was with the eyes closed (EC). The results indicate that LLA was greater in the old adults when compared with the young control subjects. The LLA values were correlated with the postural sway magnitudes especially in the anteroposterior direction. Eyes closure which destabilized posture resulted in a significant increase of body weight distribution asymmetry in the elderly but not in the young persons. The limb load difference between EO and EC conditions showed a significantly greater effect of vision on LLA in the elderly compared to the young subjects. The observed differences in the LLA may be attributed to the decline of postural stability control in the elderly. Ageing results in the progressive decline of postural control and usually the nervous system requires more time to complete a balance recovery action. To compensate for such a deficiency, different compensatory strategies are developed. One of them, as evidenced in our study, is preparatory limb unload strategy (a stance asymmetry strategy) which could significantly shorten reaction time in balance recovery.

Effect of nonaversive and aversive stimulations in infancy on the acoustic startle response in adult rats.

Two groups, each consisting of 8 three-week-old rat pups, were exposed to different behavioral treatments with the aim to determine how the experimental manipulation influenced their adult emotional reactivity. Every day for two weeks the pups from the first group received 15 min of handling whereas the animals from the second group were exposed to various aversive stimuli, differing each day. Following these manipulations, after a 5-day break the acoustic startle response (ASR) was measured in all animals and the testing was repeated after another four weeks. Statistical analysis of the data revealed significant differences between groups in the ASR parameters. Surprisingly, in the test which directly followed the treatment the mean ASR amplitudes were similar in both groups. Highly significant differences, however, were observed in the ASR amplitude four weeks later. The rats from the handling group responded with greater amplitudes. The latency of the ASR was significantly shorter in the nonaversive group compared with the second group exposed to aversive stimuli. The results suggest that early exposure to aversive stimulation significantly decreases rats emotional reactivity whereas nonaversive and impoverished stimulation clearly elevates arousal levels when the animal is placed in a novel situation.

Motor deficiency in Parkinson's disease.

The basal ganglia comprise a group of gray matter structures beneath the cerebral cortex, that surrounds the thalamus and hypothalamus. The basal ganglia play an important role in controlling movement. The motor circuits within the striato-pallidal complex are thought to facilitate desired movement and inhibit unwanted movement through their influence, via the thalamus, mainly on cortical precentral motor regions. Localized damage to parts of the basal ganglia occurs in certain diseases such as Parkinson's disease. Parkinsonism is a common neurological disorder that affects about one person in every 1,000 of the general population and about 2% in the elderly. The diagnosis of Parkinson's disease is based on the presence of two or more of the major symptoms: tremor, rigidity, postural instability, and bradykinesia. The pathological process behind the motor disabilities of Parkinsonism is a progressive degeneration of dopaminergic neurons of the substantia nigra, that results in dopamine depletion in the striatum. Brain dopamine deficiency is sufficient to explain all of the major symptoms of Parkinson's disease.

Age-related differences in performance of stereotype arm movements: movement and posture interaction.

Postural destabilizations in response to cyclic pull-and-push arm movements were compared in young and elderly subjects, with the goal of determining how age-related differences in postural stability influence strategies of cyclic arm movements made at different speeds, against different loads and while standing on support surfaces of different compliances. The results show that elderly subjects performed the experimental task more slowly with a lower mean movement frequency and a smaller amplitude. Despite of this fact, the elderly's upright posture was destabilized by this movement to a greater extent than in young subjects. The older adults exhibited lower damping of the disturbing torques produced by arm movements as evidenced by a higher amplitude of the center of foot pressure excursions. The results document close reciprocal motor and posture interaction and indicate that parameters of the voluntary movement task such as cyclic arm movements might be used as a sensitive measure of postural stability.

Effect of acoustic stimulus characteristics on the startle response in hooded rats.

The acoustic startle response (ASR) depends on stimulus parameters such as duration, intensity and particularly on the stimulus rise time. The aim of our study was to determine to what extent the ASR parameters are affected by the spectral characteristics of the stimulus. Therefore, in this experiment the amplitude and the latency of the acoustic startle reflex were assessed for a fixed pulse duration and for a variety of stimulus frequencies ranging between 3 and 23 kHz. The ASRs were studied in 11 adult hooded rats exposed to 2-ms (120 dB SPL) tone pulses of different frequencies presented in random order, with or without 70 dB white noise background. Statistical analysis of the data revealed significant differences between ASR amplitudes for different frequencies. In our experimental situation the rats responded more readily to a low frequency stimulus. The startle amplitude decreased with tonal frequencies and distinguishable difference were seen for 3, 7, and 10 kHz pulses. However, such differences were not readily observed for higher frequencies i.e. 15, 20, 23 kHz. The same pattern of differences was observed when the acoustic stimulus was presented with the white noise background. The observed differences may be attributed, firstly, to a spectral characteristic of the stimulus and thus to an audibility in rats and secondly to a behavioral meaning of a stimulus of a different frequency.

Effects of unilateral somatosensory cortex lesion upon locomotion in dogs.

Locomotive limb movements were studied in 6 dogs before and after unilateral (right) primary somatosensory cortex (SI) lesion. Single limb movement parameters as well as interlimb coordination in lesioned dogs differed significantly from the parameters measured before surgery. Both left limbs showed a proprioceptive deficit and were more flexed during normal posture and during locomotion. This resulted in prolonged stance in the left fore and in the right hind legs. The symptoms were greatly pronounced in the left fore limb compared to a slightly impaired left hindlimb. Due to the proprioceptive deficit, the dogs did not have satisfactory control over the position of the distal part of the front limb which caused frequent stumbling and even falling. The symptoms were transient and fully compensated after 3-4 weeks.

Postural sway and perception of the upright stance stability borders.

Decline in the perception of the borders of postural stability due to increase in sway was evaluated in young and elderly subjects. Ranges of lateral and anteroposterior postural sway were measured in eleven young and eleven elderly subjects during maximum voluntary excursions of center of gravity while leaning forward, backward, left, and right. In both age groups, displacement of the center of gravity out of the reference position resulted in increases in the range of sway in the plane corresponding to the direction of lean. Young subjects who further displaced their center of gravity within the base of support also exhibited significantly elevated anteroposterior sway range while leaning forward and backward, both in eyes-closed and in eyes-open experimental conditions. The elderly subjects, however, showed greater mediolateral oscillation of center of gravity while leaning forward with their eyes open. No significant intergroup differences in the anteroposterior sway range during leans in the mediolateral plane were found. However, a greater mediolateral component of sway range at lateral borders of stability was observed in the young adults. Analysis of signal-to-noise ratios indicated a greater decline in stability control in the elderly, due to impairment of perception of postural stability borders.

Evaluation of the postural stability in man: movement and posture interaction.

The stability of upright posture was evaluated in 13 young and 13 elderly subjects by measuring the amplitude of centre of foot pressure (COFP) excursion in the anteroposterior and mediolateral directions while performing voluntary motor tasks requiring precise center of gravity control i.e., circular and forward-backward sways, squatting and rising on toes. The elderly subjects exhibited a significantly smaller COFP excursion than the young in the circular and forward-backward sways and a nonsignificant reduction in the COFP progression in the rise on toes and squatting tasks. The data document significant reorganization of the motor program execution due to decline in the postural stability in old adults.

Alteration in the pattern of locomotion following a partial movement restraint in puppies.

The pattern of locomotion following a partial movement restraint was studied in five mongrel puppies. The locomotion of the animals was characterized by enforced pacing during the restraint period and exhibited significant, time dependent gait alterations after removal of the restraint. These changes involved gradual recovery to normal trotting. The time course and the degree of recovery in the animals were dependent on the period of movement restraint. Puppy that was forced to practice pacing for only two months switched almost instantaneously to the normal trotting, whereas in those dogs with a longer selective movement restraint, a significant long lasting incidence of pacing was observed. The study describes an animal model which can be useful as tool in future studies of the plasticity of motor system and its basic mechanisms in various physiological conditions.

Speed control in quadrupedal locomotion: principles of limb coordination in the dog.

Long distance, overground locomotion in the dog was observed and analyzed using the two dimensional gait diagram method. Though the velocity of locomotion chosen by the animals over a 1,000 m course varied, a preferred speed generally emerged and was used during most of the experiment. This animal-specific preferred overground velocity was strongly correlated with the animal's limb lengths, and corresponded to the minimum observed swinging velocity of the limbs. Changes in the pattern of limb coordination during three-limb locomotion were also investigated. Depending upon which limb was restrained, dogs used trot-like or gallop-like gaits which exhibited the same temporal and spatial phase differences as were observed during normal locomotion. However, stride length and swing-stance durations were increased relative to those observed in four legged locomotion. Animals with an additional 2 kg weight trotted slowly, but no significant changes in limb movement parameters were found. Locomotion studies performed in darkness resulted in an immediate switch from asymmetrical (galloping) to symmetrical gaits (walking and trotting). These gaits allow for precise foot placement.