Cognitive and motor aging in female chimpanzees

We present the first longitudinal data on cognitive and motor aging in the chimpanzee (Pan troglodytes). Thirty-eight adult female chimpanzees (10–54 years old) were studied. The apes were tested longitudinally for 3 years in a modified Primate Cognition Test Battery, which comprised 12 tests of physical and social cognition. The chimpanzees were also administered a fine motor task requiring them to remove a steel nut from rods of various complexity. There was little evidence for an age-related decline in tasks of Physical Cognition: for most tasks, performance was either stable or improved with repeated testing across age groups. An exception was Spatial Memory, for which 4 individuals more than 50 years old experienced a significant performance decline across the 3 years of testing. Poorer performance with age was found in 2 tasks of Social Cognition, an attention-getting task and a gaze-following task. A slight motor impairment was also observed, with old chimpanzees improving less than younger animals with repeated testing on the simplest rod. Hormonal status effects were restricted to spatial memory, with non-cycling females outperforming cycling females independently of age. Unexpectedly, older chimpanzees were better than younger individuals in understanding causality relationships based on sound.     

Age-related differences in postural control: effects of the complexity of visual manipulation and sensorimotor contribution to postural performance

Patterns of adaptive changes to the exposure to a sinusoidal visual stimulus can be influenced by stimulus characteristics as well as the integrity of the sensory and motor systems involved in the task. Sensorimotor deficits due to aging might alter postural responses to visual manipulation, especially in more demanding tasks. The purpose of this study was to compare postural control between young and older adults at different levels of complexity and to examine whether possible sensory and/or motor changes account for postural performance differences in older adults. Older and young adults were submitted to the following tests: postural control assessments, i.e., body sway during upright stance and induced by movement of a visual scene (moving room paradigm); sensory assessments, i.e., visual (acuity and contrast sensitivity) and somatosensory (tactile foot sensitivity and detection of passive ankle motion); and motor assessments, i.e., isometric ankle torque and muscular activity latency after stance perturbation. Older adults had worse sensory and motor performance, larger body sway amplitude during stance and stronger coupling between body sway and moving room motion than younger adults. Multiple linear regression analyses indicated that the threshold for the detection of passive ankle motion contributed the most to variances in body sway and this contribution was more striking when visual information was manipulated in a more unpredictable way. The present study suggests that less accurate information about body position is more detrimental to controlling body position, mainly for older adults in more demanding tasks.     

Complexity of human postural control in young and older adults during prolonged standing

Aging is known to have a degrading influence on many structures and functions of the human sensorimotor system. The present work assessed aging-related changes in postural sway using fractal and complexity measures of the center of pressure (COP) dynamics with the hypothesis that complexity and fractality decreases in the older individuals. Older subjects (68 ± 4 years) and young adult subjects (28 ± 7 years) performed a quiet stance task (60 s) and a prolonged standing task (30 min) where subjects were allowed to move freely. Long-range correlations (fractality) of the data were estimated by the detrended fluctuation analysis (DFA); changes in entropy were estimated by the multi-scale entropy (MSE) measure. The DFA results showed that the fractal dimension was lower for the older subjects in comparison to the young adults but the fractal dimensions of both groups were not different from a 1/f noise, for time intervals between 10 and 600 s. The MSE analysis performed with the typically applied adjustment to the criterion distance showed a higher degree of complexity in the older subjects, which is inconsistent with the hypothesis that complexity in the human physiological system decreases with aging. The same MSE analysis performed without adjustment showed no differences between the groups. Taken all results together, the decrease in total postural sway and long-range correlations in older individuals are signs of an adaptation process reflecting the diminishing ability to generate adequate responses on a longer time scale.     

Visual–vestibular stimulation interferes with information processing in young and older humans

Attention has been implicated in postural control and other tasks requiring sensory integration. The purpose of this study was to investigate the role of attention in sensory-motor processing of vestibular and combined visual–vestibular information during seated rotations using a dual-task interference approach. We hypothesized that auditory information processing would be influenced by concurrent visual-ocular, vestibulo-ocular, or combined visual-vestibulo-ocular processing. We further hypothesized that the effect would be greater in older subjects. Twenty older subjects (10 women, 10 men, 69.3±3.2 years) and 20 young subjects (10 women, 10 men, 23.5±2.9 years) were asked to perform information-processing tasks while they underwent several types of vestibular, visual–vestibular, and ocular motor paradigms. The information-processing tasks were: (1) an auditory simple reaction-time task (SRT), (2) an auditory go–no-go (disjunctive) reaction-time task (DRT), and (3) an auditory forced-choice task (CRT). The visual–vestibular-ocular motor conditions included: (1) no movement/darkness (NO), (2) no movement/fixation (FIX), (3) no movement/pursuit (P), (4) earth-vertical axis rotation (EVAR) in darkness, (5) EVAR with fixation (E-FIX), (6) off-vertical axis rotation (OVAR) in darkness, and (7) OVAR with fixation (O-FIX). Results showed that older subjects had longer reaction times for all combinations of stimulus condition and reaction-time task compared with young subjects. Compared with the NO baseline, reaction times during EVAR were longer for young and older subjects and during OVAR were longer for the young subjects. For FIX and P, the reaction times during P exceeded those during FIX and during NO for both groups. For E-FIX and O-FIX, reaction times did not differ from those during EVAR and OVAR. The interference with information processing by concurrent vestibular stimulation in the dark may be based upon cortical inhibition of auditory processes by vestibular stimulation. Eye movements induced by EVAR showed an increased phase lead during reaction-time tasks, suggesting altered vestibulo-ocular reflex (VOR) dynamics, possibly based on cerebellar-mediated changes in velocity storage. Since fixation of a head-fixed visual target did not add to the effect of rotation in the dark, a further implication of our results is that VOR-fixation while performing a concurrent information-processing task may be accomplished primarily by VOR suppression rather than by VOR cancellation.Abbreviations NO Stationary in darkness - FIX Stationary while viewing a stationary target - P Stationary while pursuing a moving target - EVAR Earth-vertical axis rotation - OVAR Off-vertical axis rotation - EFIX Earth-vertical axis rotation while viewing a head-fixed visual target - OFIX Off-vertical axis rotation while viewing a head-fixed visual target - SRT Simple reaction-time task - DRT Disjunctive reaction-time task - CRT Choice reaction-time task - VOR Vestibulo-ocular reflex - Task Type of reaction-time task - VVC Visual–vestibular condition - Group Age group - Block First or second repetition     

Effects of aging on the regularity of physiological tremor

The purpose of this investigation was to determine the effects of healthy aging on the regularity of physiological tremor under rest and postural conditions. Additionally, we examined the contribution of mechanical reflex factors to age-related changes in postural physiological tremor. Tremor regularity, tremor-electromyographic (EMG) coherence, tremor amplitude, and tremor modal frequency were calculated for 4 age groups (young: 20-30 yr, young-old: 60-69 yr, old: 70-79 yr, and old-old: 80-94 yr) under resting and loaded postural conditions. There were 6 important findings from this study: 1) there were no differences between the young and elderly subjects for any of the dependent variables measured under the rest condition; 2) postural physiological tremor regularity was increased in the elderly; 3) postural physiological tremor-EMG coherence was also increased in the elderly, and there was a strong linear relation between peak tremor-EMG coherence in the 1- to 8-Hz frequency band and regularity of tremor. This relation was primarily driven by the increased magnitude of tremor-EMG coherence at 5.85 and 6.83 Hz; 4) enhanced mechanical reflex properties were not responsible for the increased magnitude of tremor-EMG coherence in the elderly subjects; 5) tremor amplitude was not different between the 4 age groups, but there was a slight decline in tremor modal frequency in the oldest age group in the unloaded condition; and 6) despite the increases in postural physiological tremor regularity and the magnitude of low frequency tremor-EMG coherence with age, there was a clear demarcation between healthy aging and previously published findings related to tremor pathology.     

Age-related complexity and coupling of children's sitting posture

This study tested the hypothesis that postural complexity increases as the coupling across the axes of motion decreases as children get older. Children aged 6 and 10 years and young adults (18-23 years) were seated on a wooden box placed atop a force platform that recorded their mediolateral and anteroposterior center of pressure (COP) motion with their feet supported and unsupported. The COP path length and complexity decreased with age, and this was paralleled by an increase in relative phase entropy across the axes of sway motion. The postural sway of the younger children was dominated by slower fluctuations that were more tightly coupled across the axes of motion than the adults. The findings support the postulation that the development of children's sitting posture is characterized by increased freedom in postural coordination that realizes a more loosely coupled but adaptive postural motion with a reduced amount of sway.     

Normal aging reduces motor synergies in manual pointing

Depending upon its organization, movement variability may reflect poor or flexible control of a motor task. We studied adult age-related differences in the structure of postural variability in manual pointing using the uncontrolled manifold (UCM) method. Participants from 2 age groups (younger: 20-30 years; older: 70-80 years; 12 subjects per group) completed a total of 120 pointing trials to 2 different targets presented according to 3 schedules: blocked, alternating, and random. The age groups were similar with respect to basic kinematic variables, end point precision, as well as the accuracy of the biomechanical forward model of the arm. Following the uncontrolled manifold approach, goal-equivalent and nongoal-equivalent components of postural variability (goal-equivalent variability [GEV] and nongoal-equivalent variability [NGEV]) were determined for 5 time points of the movements (start, 10%, 50%, 90%, and end) and used to define a synergy index reflecting the flexibility/stability aspect of motor synergies. Toward the end of the movement, younger adults showed higher synergy indexes than older adults. Effects of target schedule were not reliable. We conclude that normal aging alters the organization of common multidegree-of-freedom movements, with older adults making less flexible use of motor abundance than younger adults.     

The Multiple Tasks Test. Strategies in Parkinson's disease

The clinical balance tests presently used cannot predict falls in Parkinson's disease (PD), perhaps because they probe fairly isolated "components" of postural control. The Multiple Tasks Test (MTT) is a new balance test that simultaneously assesses multiple components of postural control. We investigated whether this MTT can detect postural abnormalities in PD patients. Fifty young controls (mean age 27.6 years), 20 elderly controls (mean age 62.5 years), and 20 PD patients (mean age 61.8 years, mean Hoehn and Yahr stage 2.2) participated. The MTT consisted of eight separate tasks of increasing complexity, which were executed sequentially. These tasks were composed of several motor components (standing up, walking, avoiding obstacles, touching the floor, turning around, and sitting down) and one cognitive component (answering serial questions). Four additional components included carrying an empty or loaded tray, wearing slippery shoes, and reduced illumination. All components within each task had to be performed simultaneously or directly sequentially. Errors were defined as Hesitations (slowed performance) or Blocks (complete cessation), which were scored separately for execution of the motor and cognitive components. Speed of performance was not stressed, but we did measure the time taken to complete all tasks. The complete MTT was performed by all subjects, except for a subgroup of seven patients and seven elderly controls who performed a shortened version, with only three of the eight sequential tasks (simple, intermediate, and most difficult). The number of subjects that produced Hesitations or Blocks for the motor components differed between the three groups [two-way repeated measures MANOVA, F(2,7)=20.56; P<0.001], patients making more errors than young and elderly controls. Furthermore, the number of subjects that made motor errors increased as the tasks became more complex [F(2,7)=6.69; P<0.001]. This increase differed across the three groups [significant interaction effect; F(2,7)=3,31; P<0.001] because particularly patients produced motor errors during the more complex tasks. In both control groups, 62% performed all eight consecutive tasks without errors in the motor components. In contrast, only 8% of the patients completed all tasks without motor errors (log rank test, P<0.0001). This difference between patients and controls disappeared if the cognitive component was also scored, because more controls made cognitive errors during complex tasks than patients. Controls apparently gave priority to execution of the motor components, which they performed significantly faster than the patients. Both patients and controls made more errors during the shortened MTT, suggesting that learning effects (gain in performance through practice) influenced performance on the complete test. The MTT is a new balance test that clearly discriminates between healthy subjects and PD patients. Unlike controls, PD patients lend less priority to motor tasks over cognitive tasks. In addition, impaired motor learning may partially explain the higher error rate in PD. Future studies must determine if impaired MTT performance can predict actual falls in daily life. Electronic Publication     

Differential time- and frequency-dependent structure of postural sway and finger tremor in Parkinson's disease

The time- and frequency-dependent patterns of standing balance centre of pressure (COP) and finger postural/resting tremor of 12 older individuals and eight age-matched Parkinsonian (PD) participants (on/off medication) were investigated. Tremor and COP data were analysed using measures of signal amplitude (RMS), time-dependent structure (approximate entropy, ApEn), time-frequency analysis and synchrony (Cross ApEn). Results showed that the PD individuals had significantly greater tremor amplitude and COP excursions in comparison to controls. Differences in the time-dependent structure were also observed between groups. In comparison to the elderly, the resting/postural tremor output of the PD subjects was more regular (lower ApEn). However, for the postural measures, a reciprocal pattern was observed with the COP being more complex (higher ApEn). All group differences were magnified when the PD individuals were off their medication. There was also greater synchrony between tremor and postural sway for the PD individuals, indicating a high degree of association between these motor outputs. These results are consistent with the view that the neural signal driving the enhanced limb tremor in PD is propagated throughout the motor system, consequently emerging within the postural sway dynamics. This commonality of motor output may be a contributing factor in the differential pattern in the dynamics of effector signal structure in PD as a function of task.     

Age-related relative increases in electromyography activity and torque according to the maximal capacity during upright standing

The aim of this study was to assess the relative torque (a percentage of the maximal capacity of torque production) at the ankle joint in young and elderly adults during different postural tasks of increasing difficulty. Seven young (~22 years old) and seven older (~80 years old) men took part in this investigation. Maximal agonist torque was estimated from resultant and antagonist torques in both populations in plantar-flexion (PF) and dorsi-flexion (DF). The sum of PF and DF maximal agonist torques was considered as the maximal capacity of torque production. The centre of pressure (CoP) displacement was analysed during Normal Quiet Stance, Romberg and One Leg Balance. During maximal contractions and postural tasks, the electromyographic (EMG) activity was simultaneously recorded on the triceps surae and tibialis anterior muscles. We observed that the maximal capacity of torque production was negatively correlated with the CoP displacement, whatever the population and the postural tasks. The relative torque during all postural tasks was positively correlated with the CoP displacement in both populations. Moreover, older adults needed more EMG activity than young adults to produce the same torque. From this knowledge, one can assume that increasing strength in the muscles of the ankle joint may improve postural stability in older adults; this might have implications in the prevention of falls in elderly persons and in rehabilitation programs for elderly people who have already fallen.     

Effects of aging on force variability,single motor unit discharge patterns,and the structure of 10, 20, and 40 Hz EMG activity

The purpose of this investigation was to examine the discharge properties of single motor units and the structure of the rectified 10, 20, and 40 Hz electromyographic (EMG) activity to determine a physiological correlate for the greater force variability with aging. Young (n=10; mean: 22+/-1 years), old (n=10; mean: 67+/-2 years), and older-old (n=10; mean: 82+/-5 years) adult humans produced isometric second finger abduction force in both constant and sine-wave tasks at 5, 10, 20, and 40% of their maximal voluntary contraction. Force and fine-wire intramuscular electromyography were recorded from the first dorsal interosseous muscle. The amount and time-dependent structure of the discharge rate variability of single motor units and Fourier analysis of the rectified intramuscular EMG was performed. Force output variability increased across the young, old, and older-old groups. The amount and time-dependent structure of the discharge rate variability of single motor units did not differ between the young and aging groups. There was a progressive decrease in the relative power of approximately 40 Hz EMG activity from the young>old>older-old subjects across the 5, 10, 20, and 40% maximum voluntary contraction (MVC) force levels. There was also a progressive increase in the relative power of the approximately 10 Hz EMG activity from young相似文献   

Inter- and intra-limb coordination in arm tremor

Inter- and intra-limb coordination in arm tremor was examined in adult subjects under vision and no vision conditions using accelerometery techniques. The accelerometer data were analyzed using standard time and frequency domain analyses and the regularity of the acceleration time series was determined using an approximate entropy (Ap En) measure. The data analysis was structured to examine the hypothesis that there is a functional compensatory relation between the motion (tremor) of the limb segments in the arm coordination postural pointing task. The results showed that the level of acceleration increased in a proximal to distal direction within a single arm and was symmetrical across homologous arm segments. The frequency analysis showed the established power spectral profiles for each limb segment in postural tremor tasks, but the finger motion included (beyond the normal 8–12 Hz and 20 Hz tremor) a third slower peak at around 2–3 Hz, due possibly to the reactive forces of the other arm links. There was no effect of vision on the level or frequency patterns of acceleration in the limb segments. The coordination analysis showed that there was no linkage between the arms in either the time or frequency domain in the execution of this postural task. This result would tend to suggest that the neuronal commands underlying normal tremor are not derived from a common central oscillator within the central nervous system but are organized in a parallel fashion. The strength of the coupling of intra-limb coordination varied according to the particular adjacent limb links. There were significant correlations in the time domain and coherence in the frequency domain in the acceleration signals between upper arm and forearm, and between hand and finger. The phase lag of the arm units within each of these respective segment pairs was close to in phase or 0 deg. Significant coherence in the frequency domain was also evident between upper arm and hand motion, with the phase lag between these segments being close to 180 deg out of phase. The Ap En analysis of the acceleration signals revealed that there was more regularity to the upper arm and hand accelerometer signals than the forearm and finger signals. The findings show that the intra-limb coordination of the arm links in a two-limb postural pointing task is effected by a compensatory synergy organized about the action of the wrist and shoulder joints. This compensatory synergy reduces the coordination of the 4 within-limb degrees of freedom (arm links) to, in effect, a single degree of freedom arm control task that is not coupled in organization to the motion of the other limb or the torso. It is proposed that this coordination solution reduces the degrees of freedom independently regulated for realization of the task goal but preserves independent body segment control in critical degrees of freedom for potential adaptation to postural perturbations.     

Motor unit synchronisation is enhanced during slow lengthening contractions of a hand muscle

This study examined the strength of motor unit synchronisation based on time- and frequency-domain measures during postural, shortening and lengthening contractions of a hand muscle in young adults. Single motor unit activity was recorded with intramuscular electrodes in the left first dorsal interosseus muscle as the subject held the index finger at a constant position while supporting a light load for 2-5 min. The subject then performed slow (1.7 deg s⁻¹) shortening and lengthening contractions to lift and lower the load. The movement required subjects to perform 10-25 constant-velocity contractions with the index finger over a 10 deg range of motion by using 6 s shortening and lengthening contractions. Individual discharge times were obtained from 23 pairs of motor units in 14 subjects to assess the strength of motor unit synchronisation and coherence during the three tasks. The strength of motor unit synchronisation was approximately 50 % greater during the lengthening contractions compared with the postural and shortening contractions, and the width of the central synchronous peak in the cross-correlation histogram was ≈4 ms narrower during shortening contractions. These findings reveal that there is an increase in common input to motoneurones during lengthening contractions and a greater relative contribution of direct common inputs to motoneurones during shortening contractions compared with postural tasks. Furthermore, the amount of motor unit coherence in the low-frequency band (2-12 Hz) was reduced during shortening contractions compared with postural and lengthening contractions. These data indicate that the timing of inputs received by the motoneurones innervating the first dorsal interosseus of young adults differs during postural, shortening and lengthening contractions against a light load.     

Balance control and adaptation during vibratory perturbations in middle-aged and elderly humans

The objective was to investigate if healthy elderly people respond and adapt differently to postural disturbances compared to middle-aged people. Thirty middle-aged (mean age 37.8 years, range 24–56 years) and forty healthy elderly subjects (mean age 74.6 years, range 66–88 years) were tested with posturography. Body sway was evoked by applying pseudorandom vibratory stimulation to the belly of the gastrocnemius muscles of both legs simultaneously. The tests were performed both with eyes open and eyes closed. The anteroposterior body sway was measured with a force platform and analyzed with a method that considers the adaptive changes of posture and stimulation responses. The results showed that middle-aged people generally used a different postural control strategy as compared to the elderly. The elderly responded more rapidly to vibratory perturbation, used more high-frequency (>0.1 Hz) motions and the motion dynamics had a higher degree of complexity. Moreover, the elderly had diminished ability to use visual information to improve balance control. Altogether, despite having an effective postural control adaptation similar to that of middle-aged people, the elderly had more difficultly in withstanding balance perturbations. These findings suggest that the balance control deterioration associated with aging cannot be fully compensated for by postural control adaptation.     

Effects of postural support on eye hand interactions across development

Reaching to grasp an object of interest requires a complex sensorimotor transformation-involving eye, head, hand, and postural systems. We show here that discontinuities in development of movement in these systems are dependent not only on age but also vary according to task constraints. Providing external postural support allows us to examine the differential influences of the eye on the hand and the hand on the eye as the ability to isolate and coordinate each system changes with age. Children 4–6 years old had significant difficulty isolating eye movement from head or hand movement, whereas children 7–9 years old showed improved ability to isolate the eye, and by 10–15 years children became proficient in isolating hand movements from eye movements. Postural support had differential effects on the processes of initiation and execution of eye–hand movements. The addition of postural support decreased the time needed for planning the movement, especially in the youngest children, and contributed to increased speed of isolated movements, whereas it caused differential slowing of coordinated movements depending on the child’s developmental level. We suggest that the complexity of the results reflects the complexity of changing task requirements as children transition from simpler ballistic control of all systems to flexible, independent but coordinated control of multiple systems.     

Age-related differences in corrected and inhibited pointing movements

It has been widely reported that aging is accompanied by a decline in motor skill performance and in particular, it has been shown that older subjects take longer to adapt their ongoing reach in response to a target location shift. In the present experiment, we investigated the influence of aging on the ability to perform trajectory corrections in response to a target jump, but also assessed inhibition by asking a younger and an older group of participants to either adapt or stop their ongoing movement in response to a target location change. Results showed that although older subjects took longer to initiate, execute, correct and inhibit an ongoing reach, they performed both tasks with the same level of accuracy as the younger sample. Moreover, the slowing was also observed when older subjects were asked to point to stationary targets. Our findings thus indicate that aging does not specifically influence the ability to perform or inhibit fast online corrections to target location changes, but rather produces a general slowing and increased variability of movement planning, initiation and execution to both perturbed and stationary targets. For the first time, we demonstrate that aging is not accompanied by a decrease in the inhibition of motor control.

Kinesthetic motor imagery modulates body sway

The aim of this study was to investigate the effect of imagining an action implicating the body axis in the kinesthetic and visual motor imagery modalities upon the balance control system. Body sway analysis (measurement of center of pressure, CoP) together with electromyography (EMG) recording and verbal evaluation of imagery abilities were obtained from subjects during four tasks, performed in the upright position: to execute bilateral plantar flexions; to imagine themselves executing bilateral plantar flexions (kinesthetic modality); to imagine someone else executing the same movement (visual modality), and to imagine themselves singing a song (as a control imagery task). Body sway analysis revealed that kinesthetic imagery leads to a general increase in CoP oscillation, as reflected by an enhanced area of displacement. This effect was also verified for the CoP standard deviation in the medial–lateral direction. An increase in the trembling displacement (equivalent to center of pressure minus center of gravity) restricted to the anterior–posterior direction was also observed to occur during kinesthetic imagery. The visual imagery task did not differ from the control (sing) task for any of the analyzed parameters. No difference in the subjects' ability to perform the imagery tasks was found. No modulation of EMG data were observed across imagery tasks, indicating that there was no actual execution during motor imagination. These results suggest that motor imagery performed in the kinesthetic modality evokes motor representations involved in balance control.     

The relationship between physiological tremor and the performance of rapid alternating movements in healthy elderly subjects

The power distribution in the frequency spectrum of tremor is known to vary among individuals and its median power frequency declines with ageing. The purpose of the present study was to determine whether a reduction of the central component of physiological tremor would correlate with a reduction of motor performance. Then, the power distribution in the frequency spectrum of tremor from limb extremities might serve as an index of neural drive in healthy elderly subjects. Rest tremor, postural tremor from the finger, and pronation-supination at the wrist were recorded in 102 healthy nuns living in a convent (mean of 72±12 years). Results reveal that several elderly subjects possessed a power distribution of tremor very similar to that of much younger subjects (mean 27 years±3 SD), showing a preponderance of power within the 7.6- to 12.5-Hz band. Duration of pronation-supination cycles of these elderly subjects was, however, similar to that of other elderly subjects who had a preponderance of power within the 3.6- to 7.5-Hz band. Consequently, healthy elderly subjects who possessed a predominance of power within higher frequencies were not at an advantage over other healthy elderly subjects when performing a pronation-supination task. The age of subjects was, however, a better predictor or motor performance. In conclusion, the present findings suggest that, under normal physiological conditions, a reduction of the central component of physiological tremor does not induce a reduction of motor performance. Consequently, tremor recorded at limb extremities cannot be used as an index of neural drive. Electronic Publication     

The impact of ventrolateral thalamotomy on tremor and voluntary motor behavior in patients with Parkinson’s disease

A preferred target for parkinsonian tremor alleviation is the ventrolateral (VL) thalamus. The goal of the present study is to determine how lesions involving the presumed cerebellar and pallidal recipient areas of the “motor” thalamus would alter the tremor and motor behavior of ten patients with Parkinson’s disease (PD). Tremor amplitude, power dispersion (a measure of sharpness of the power spectrum of tremor), and power distribution were quantified using a laser displacement sensor prior to, and a week after, VL thalamotomy. As well, the impact of surgery on tremor seen during movement was quantified in a manual-tracking (MT) task. Tremor-induced noise (a measure of the amount of tremor present during movement) and ERROR (difference between subject’s performance and target) were quantified. Finally, bradykinesia was assessed with a rapid alternating movement (RAM) task. Duration, range, and amplitude irregularity of wrist pronation–supination cycles were computed. Both motor tasks were quantified using a highly sensitive forearm rotational sensor. Healthy age-matched control subjects were also tested. Magnetic resonance images with an integrated atlas of thalamic nuclei were used to confirm lesion location. Results show that the lesions were centered upon the posterior portion of the ventral lateral (VLp) nucleus of the thalamus, included the posterior part of the ventral lateral anterior nucleus (VLa), and extended posteriorly to encroach upon the most rostral sector of the sensory ventral posterior nucleus (VPLa). VL thalamotomy significantly decreased tremor amplitude in all cases. Power dispersion was increased significantly so that it became similar to that of control subjects. Changes in power distribution indicate that thalamotomy selectively targeted PD tremor oscillations. Tremor detected during the MT task was also markedly decreased, becoming similar to that of controls. Patients also showed significant decrease in ERROR during MT. RAM duration and range were not significantly modified by the surgery, and patients’ performance remained impaired compared to healthy control subjects. Collectively, these results suggest that lesions involving the presumed “cerebellar” and “pallidal” recipient sectors of the motor thalamus do not worsen bradykinesia, suggesting that neural circuits other than the pallido-thalamo-cortical loop may be involved in slowness of movement in PD. A review of alternate pathways is presented.     

Respiration and heart rate complexity: Effects of age and gender assessed by band-limited transfer entropy

Aging and disease are accompanied with a reduction of complex variability in the temporal patterns of heart rate. This reduction has been attributed to a break down of the underlying regulatory feedback mechanisms that maintain a homeodynamic state. Previous work has established the utility of entropy as an index of disorder, for quantification of changes in heart rate complexity. However, questions remain regarding the origin of heart rate complexity and the mechanisms involved in its reduction with aging and disease. In this work we use a newly developed technique based on the concept of band-limited transfer entropy to assess the aging-related changes in contribution of respiration and blood pressure to entropy of heart rate at different frequency bands. Noninvasive measurements of heart beat interval, respiration, and systolic blood pressure were recorded from 20 young (21–34 years) and 20 older (68–85 years) healthy adults. Band-limited transfer entropy analysis revealed a reduction in high-frequency contribution of respiration to heart rate complexity (p < 0.001) with normal aging, particularly in men. These results have the potential for dissecting the relative contributions of respiration and blood pressure-related reflexes to heart rate complexity and their degeneration with normal aging.