Role of the dorsolateral prefrontal cortex in context-dependent motor performance

Context-dependent motor performance is a phenomenon in which people perform better in the environmental context where they originally practised a task. Some animal and computer simulation studies have suggested that context-dependent performance may be associated with neural activation of the dorsolateral prefrontal cortex (DLPFC). This study aimed to determine the role of the DLPFC in context-dependent motor performance by perturbing the neural processing of the DLPFC with repetitive transcranial magnetic stimulation (rTMS) in healthy adults. Thirty healthy adults were recruited into the Control, rTMS DLPFC and rTMS Vertex groups. The participants practised three finger sequences associated with a specific incidental context (a coloured circle and a location on the computer screen). One day following practice, the rTMS groups received 1 Hz rTMS prior to the testing conditions in which the sequence-context associations remained the same as practice (SAME) or changed (SWITCH). All three groups improved significantly over practice on day 1. The second day testing results showed that the DLPFC group had a significantly lower decrease in motor performance under the SWITCH condition than the Control and Vertex groups. This finding suggests a specific role of the DLPFC in context-dependent motor performance.

The Effects of Exercise on Dopamine Neurotransmission in Parkinson's Disease: Targeting Neuroplasticity to Modulate Basal Ganglia Circuitry

Animal studies have been instrumental in providing evidence for exercise-induced neuroplasticity of corticostriatal circuits that are profoundly affected in Parkinson’s disease. Exercise has been implicated in modulating dopamine and glutamate neurotransmission, altering synaptogenesis, and increasing cerebral blood flow. In addition, recent evidence supports that the type of exercise may have regional effects on brain circuitry, with skilled exercise differentially affecting frontal-striatal related circuits to a greater degree than pure aerobic exercise. Neuroplasticity in models of dopamine depletion will be reviewed with a focus on the influence of exercise on the dorsal lateral striatum and prefrontal related circuitry underlying motor and cognitive impairment in PD. Although clearly more research is needed to address major gaps in our knowledge, we hypothesize that the potential effects of exercise on inducing neuroplasticity in a circuit specific manner may occur through synergistic mechanisms that include the coupling of an increasing neuronal metabolic demand and increased blood flow. Elucidation of these mechanisms may provide important new targets for facilitating brain repair and modifying the course of disease in PD.

Activity-Dependent Factors Affecting Poststroke Functional Outcomes

Over the last several years, there has been increasing recognition of the potential for central nervous system (CNS) recovery after brain damage. One commonality across the recovery and brain plasticity literature is that practice induces plastic, dynamic changes in the CNS. However, more than simply repetition, it is the manipulation of specific practice variables that appears to drive these dynamic processes in the CNS. The experimental manipulations used in the studies on neuroplasticity largely derive from the concept that in the undamaged or healthy brain neuronal connections and cortical maps are continuously remodeled by experience and by the performance of specific, intensive, and complex movements used to solve motor problems and attain goals. Intervention designed to promote recovery rather than compensation after stroke would then manipulate these same practice variables that have consistently promoted behavioral recovery and neuroplasticity in laboratory settings. Three current intervention strategies that incorporate these practice variables are reviewed. Preliminary results provide evidence that manipulation of task intensity and specificity and the sensorimotor experience of the task training are the necessary ingredients for maximizing the tremendous potential for recovery in patients with stroke.

Coccydynia

Coccydynia is a painful disorder characterised by coccygeal pain which is typically exaggerated by pressure. It remains an unsolved mystery because of the perceived unpredictability of the origin of the pain, some psychological traits that may be associated with the disorder, the presence of diverse treatment options, and varied outcomes. A more detailed classification based on the aetiology and pathoanatomy of coccydynia helps to identify patients who may benefit from conservative and surgical management.

This review focuses on the pathoanatomy, aetiology, clinical features, radiology, treatment and outcome of coccydynia.

Contralateral cerebellar damage impairs imperative planning but not updating of aimed arm movements in humans

The specific motor control processes supported by the cerebellum and impaired with cerebellar damage remain unclear. The cerebellum has been implicated in both planning and updating of accurate movements. Previously, we used a statistical model to parcel aiming performance that was constrained by a timed-response paradigm into contributions attributed to a specified plan and feedforward updating. Here, we apply this procedure to determine the putative role of the cerebellum in planning and updating goal-directed aiming by comparing the performance of subjects with unilateral cerebellar stroke to controls. Subjects rapidly moved to targets in predictable or unpredictable conditions and cerebellar subjects used the contralesional limb to control for ipsilesional motor execution deficits. Displacement-derived movement velocity was used in the statistical model to determine the effect of planning and updating on accuracy. Compared to controls, the cerebellar group demonstrated errors in final position that were primarily determined by planning deficits. This finding is manifest in four ways: Cerebellar subjects (1) were less accurate than controls in both predictable and unpredictable conditions; (2) they showed minimal benefit from increased preparation time for target amplitude specification; (3) with ample time to plan direction, wrong direction response frequency was greater; and (4) final position was minimally determined by the plan. Because these deficits were found contralesional to the moving limb, the cerebellum's role in planning is not lateralized to one hemisphere but rather our findings suggest that cerebellar output affects motor planning for both upper limbs. Indeed, a lesion analysis showed that the dentate nucleus, an area implicated in planning motor strategies and the primary cerebellar output nucleus, was the only common region affected by our patient group with contralateral cerebellar strokes.

Deficits in compensatory trajectory adjustments after unilateral sensorimotor stroke

In a previous study, we demonstrated that the time-course for amplitude specification of goal-directed aiming movements is similar for individuals with and without a unilateral sensorimotor (SM) area lesion. However, subjects with a SM lesion performing with the arm ipsilateral to the side of the brain lesion were significantly less accurate than control subjects in an unpredictable condition. The unpredictable condition requires that subjects both formulate an initial plan for movement as well as adjust the response later as additional information about the target (i.e., the goal) is gained. It has been demonstrated that premovement planning and compensatory adjustments are the processes contributing largely to accuracy in targeted, isometric force responses. A statistical model has been described, which partitions response trajectories into the planned and compensatory adjustment components. The purpose of this study was to apply the statistical model to our previous data to determine if the difference in accuracy in those with unilateral stroke was due to a deficit in premovement planning, compensatory adjustments, or a combination of these two factors. We compared the performance of six subjects with unilateral stroke to that of matched control subjects participating in a timed-response movement paradigm. Subjects rapidly flexed or extended the forearm in order to capture a short (20 degrees) or long (45 degrees) target presented in either a fixed (predictable condition) or a random sequence (unpredictable condition). For individuals with stroke, the limb used was that ipsilateral to the side of the SM lesion. Time to prepare the response was manipulated by varying the time of target presentation relative to an auditory cue for movement initiation. Velocity was derived from the displacement data, and multiple regression was used to determine the effect of premovement planning and compensatory adjustments on end-point accuracy. In the predictable condition, premovement planning contributed to final position more for the subjects with stroke [mean (SEM) = 0.50 (0.02)] than for the control subjects [0.36 (0.03)]. In the unpredictable condition, there were no differences between groups in percent variance due to planning [0.54 (2.1) for the stroke group and 0.45 (2.8) for the control group]. This suggests that the ipsilateral (i.e., intact, undamaged) SM hemisphere significantly participates in the premovement planning of an aiming action. In contrast, for both predictable and unpredictable conditions, compensatory adjustments accounted for a smaller percentage of the variability in final position for the subjects with stroke than for the control subjects [0.09 (2.2) for the stroke group and 0.25 (4.8) for the control group]. Therefore, the less accurate responses for the stroke group can be explained by deficits in the compensatory adjustment component. This suggests a substantial role for SM areas in the preparation and implementation of corrective actions while the effects of the pre-planned action are unfolding. In particular, we discuss the role of the ipsilateral SM areas in relation to parallel feedforward processing in unimanual aiming.

Influence of central set on anticipatory and triggered grip-force adjustments

The effects of predictability of load magnitude on anticipatory and triggered grip-force adjustments were studied as nine normal subjects used a precision grip to lift, hold, and replace an instrumented test object. Experience with a predictable stimulus has been shown to enhance magnitude scaling of triggered postural responses to different amplitudes of perturbations. However, this phenomenon, known as a central-set effect, has not been tested systematically for grip-force responses in the hand. In our study, predictability was manipulated by applying load perturbations of different magnitudes to the test object under conditions in which the upcoming load magnitude was presented repeatedly or under conditions in which the load magnitudes were presented randomly, each with two different pre-load grip conditions (unconstrained and constrained). In constrained conditions, initial grip forces were maintained near the minimum level necessary to prevent pre-loaded object slippage, while in unconstrained conditions, no initial grip force restrictions were imposed. The effect of predictable (blocked) and unpredictable (random) load presentations on scaling of anticipatory and triggered grip responses was tested by comparing the slopes of linear regressions between the imposed load and grip response magnitude. Anticipatory and triggered grip force responses were scaled to load magnitude in all conditions. However, regardless of pre-load grip force constraint, the gains (slopes) of grip responses relative to load magnitudes were greater when the magnitude of the upcoming load was predictable than when the load increase was unpredictable. In addition, a central-set effect was evidenced by the fewer number of drop trials in the predictable relative to unpredictable load conditions. Pre-load grip forces showed the greatest set effects. However, grip responses showed larger set effects, based on prediction, when pre-load grip force was constrained to lower levels. These results suggest that anticipatory processes pertaining to load magnitude permit the response gain of both voluntary and triggered rapid grip force adjustments to be set, at least partially, prior to perturbation onset. Comparison of anticipatory set effects for reactive torque and lower extremity EMG postural responses triggered by surface translation perturbations suggests a more general rule governing anticipatory processes.

Floorward thinking

From its creation to its disposal, there are environmental and health problems associated with polyvinyl chloride (vinyl), the major component of vinyl flooring. The production of vinyl creates toxic waste that must be dumped or incinerated. Because very little vinyl is recycled, the waste material must also be landfilled or burned. Furthermore, the heavy chlorine content of these materials result in the release of dioxins into the environment. A new flooring alternative to vinyl recently entered the market. Stratica, manufactured by Amtico Company Limited based in Coventry, United Kingdom, is made from polymer resins and offers the durability of vinyl without the environmental impact.

Testing their metal

Metals continually rank at the top of the U.S. Environmental Protection Agency's annual list of agents that pose the greatest hazard to the people of the United States. Metals aren't going away, either. They do not biodegrade, and they often concentrate in human and animal cells and tissue. Many metals are known human and animal carcinogens, while many others are suspected to play a role in cancer. Little is known, however, about the mechanisms by which metals cause cancer.

Turning over a new leaf. Tobacco

Anticipating a diminishing market for cigarettes and other tobacco products in the future, researchers around the country are studying alternative uses for tobacco plants. The most promising field of research for tobacco involves the genetic engineering of tobacco plants to produce various substances such as industrial chemicals, pharmaceuticals, and consumer product ingredients. Tobacco has been called the "fruit fly of the plant kingdom" because of the ease with which it can be genetically engineered. There are countless possibilities for the use of tobacco, but current efforts are concentrating on engineering tobacco to produce vaccines, human enzymes, and plastics. Tobacco researchers have been successful in expressing bovine lysozyme, an enzyme with antibacterial properties, and insulin.

Organic: What's in a name?

The organic foods industry is booming: by one estimate, the market for organic foods is worth $4 billion annually and is expected to grow at a rate of more than 24% per year. Faced with the threat of pesticide exposures and other food safety problems, many consumers are turning to organic foods in hopes of finding a healthy alternative, but there is currently no consistency in organic food labeling and no guarantee that foods labeled as organic are actually grown and processed in a purely organic fashion. There is also controversy about whether the label "organic" covers such new technologies as irradiation and genetic engineering. As part of the 1990 Farm Bill, the U.S. Department of Agriculture (USDA) is working to develop a proposed rule on organic foods. The rule would regulate the allowable methods, practices, and substances used in producing and handling crops and their processed products. The first draft of the proposed rule, released in December 1997, met with unprecedented opposition, which centered around the fact that the proposal appeared to virtually ignore the recommendations of a standards board formed to assist in the rule's development. Other criticism opposed three practices put forward for comment by the USDA: irradiation, genetic engineering, and the use of sewage sludge in farming. Due to the vehemence of the opposition to its original proposal, the USDA has decided to rewrite the proposed rule. In preparation for that proposal, the USDA Agricultural Marketing Service released three issue papers in October 1998 for public comment. The 10,000-plus comments received in response to those papers will be incorporated into the second draft proposal, due out later this year.

Most unwanted

Persistent organic pollutants (POPs) can travel thousands of miles, accumulate in the food chain, and persist in the environment, taking as long as centuries to degrade. POPs are known to play a role in birth defects, cancer, immune system dysfunction, and reproductive problems in wildlife. While the effects of POPs on human health are unclear, many researchers believe that long-term exposure contributes to increasing rates of birth defects, fertility problems, greater susceptibility to disease, diminished intelligence, and certain cancers. Twelve POPs have been identified by the United Nations Environment Programme as requiring urgent regulatory attention. They include the pesticides aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, hexachlorobenzene, mirex, and toxaphene. Of the remaining three POPs, polychlorinated biphenyls are industrial products (used in electrical transformers), and dioxins and furans are unintentional by-products of industrial processes.

Between a rock and a healthy place

The Federal Mine Safety and Health Act of 1977 consolidated all federal health and safety regulations of the mining industry-coal as well as noncoal mining-under a single mandate administered by the Mine Safety and Health Administration (MSHA). Today, the agency is striving to reduce the environmental health risks associated with mining.

20 years of toxicology

With over 80,000 chemicals being used in commerce worldwide, it is important to identify the human health effects of these chemicals and the levels of exposure at which they are harmful to humans. In order to address this need, the National Toxicology Program (NTP) was established in 1978; since then, the NTP has become the world's leader in designing, conducting, and interpreting various types of toxicity assays.

The locus of age-related movement slowing: sensory processing in continuous goal-directed aiming

Prolonged movement times in elderly persons have been well documented; however, the locus of this slowing is uncertain. Kinematic analysis of discrete aiming has revealed deficits primarily in the target approach phase, suggesting inefficient feedback processing. This study investigated age-related movement slowing in a continuous aiming task, for which movements are mediated by feedforward and on-line sensory processes. Two-dimensional video-recordings were made of young and elderly adults performing reciprocal tapping using the right and left hands under three different accuracy conditions. The elderly subjects exhibited more discrete adjustments in the trajectories coupled with longer times in this period. Further, the elderly spent more time reversing direction between target hits, especially in the high accuracy condition. Longer time on target was seen in the left-hand performance of the elderly. Results suggest that the locus of age-related slowing in the performance of continuous aiming may reflect a greater dependence on slower feedback processes instead of rapid, on-line, and feedforward sensory processes. Age-related differences in hand performance may provide further insight into central processing deficits.

Parents' and children's ratings of sleep behavior, excitement, and tiredness: a 10-week longitudinal study

In a 10-week longitudinal study, 29 parents and their children kept daily records of the children's sleep behaviors, excitement levels, and tiredness levels. Although the hypothesized increase in sleep behaviors such as sleepwalking and restlessness during the week of Christmas did not occur, children rated as more excitable by their parents and themselves exhibited a higher frequency of sleep behaviors. Positive associations were also found between averaged tiredness ratings and sleep scores. The results support previous findings of an association between arousal characteristics of children and their sleep behavior. Moderate validity coefficients were obtained for parents' and children's ratings of excitement, tiredness, and nocturnal waking.

Do diagnostic patterns exist in the sleep behaviors of normal children?

We investigated the factor structure of the Children's Sleep Behavior Scale in an unselected sample of children (N = 838), ages 6 to 12.5 years, drawn from an elementary school population. Although no factor emerged that corresponded exactly to the parasomnias, as described by the Association of Sleep Disorders Centers (1979), all of the variables that loaded on Factor 1 were behaviors characteristic of the parasomnias, with the exception of recalled nightmares. Variables that were expected to load on this factor, but did not, were sleeptalking, teeth grinding, and enuresis. Enuresis was not related to any of the sleep behaviors assessed, and teeth grinding shared less than 9% of the variance with any of the other variables. Many of the variables loaded on more than one factor. The second factor, which was labeled bedtime resistance, was the only clearly unambiguous factor. Of the five factors that emerged, the third reflected positive affect, the fourth was a motor factor, and the fifth was an anxiety factor. Nightmares loaded on the anxiety factor as well as the first factor. The results of the study offered no support for the category of Disorders of Initiating and Maintaining sleep (DIMS), which has a childhood onset.

Children's Sleep Behavior Scale: normative data on 870 children in grades 1 to 6

A 22-item Likert-type rating scale for parents was developed for screening a broad range of specific sleep-related behaviors of elementary school children. The prevalence of these behaviors was reported by parents for boys (n = 459) and girls (n = 411) in three age groups, less than 8.5 yr., between 8.5 and 11.5 yr., and greater than 11.5 yr. For all age groups, the most prevalent behaviors were restlessness, waking up at night, pleasant dreams, getting up to go to the bathroom, talking while asleep, and complaints about not being able to sleep, while the least frequent were rhythmical movements and crying while asleep. The self-reports suggest that many of the behaviors are underestimated in the literature. Some sex and age differences were found, but the number of siblings, birth order, change in family structure, and educational status of father and mother were unrelated to the sleep variables. Test-retest reliabilities of self-reports by these parents to individual items were adequate.

Selected sleep disturbances in school children reported by parents: prevalence, interrelationships, behavioral correlates and parental attributions

Epidemiological, behavioral and etiological variables related to sleep disturbances were investigated in a survey of 1695 children in Grades 1 to 12 from 11 randomly selected schools. Sleep-walking, nightmares and sleep-talking were strongly associated with each other as well as to a family history of sleep-walking. Enuresis, however, was not related to the other sleep variables. Socioeconomic status of father was weakly related to enuresis and sleep-talking but not to sleep-walking or nightmares. Gender was not related to any of the sleep disturbances. The behavioral variables, physical activity, attention, emotional excitability, and feelings easily hurt showed a small association with the sleep disturbances. Parents most frequently attributed causes of sleep-walking and nightmares to over-tiredness and over-excitement. As well, parents' comments indicated that they tend to associate specific events such as illness or more often, frightening TV content with nightmares, but not sleep-walking.