How self-initiated memorized movements become automatic: a functional MRI study

We used functional magnetic resonance imaging (fMRI) and dual tasks to investigate the physiology of how movements become automatic. Normal subjects were asked to practice some self-initiated, self-paced, memorized sequential finger movements with different complexity until they could perform the tasks automatically. Automaticity was evaluated by having subjects perform a secondary task simultaneously with the sequential movements. Our secondary task was a letter-counting task where subjects were asked to identify the number of times a target letter from the letter sequences was seen. Only the performances that achieved high accuracy in both single and dual tasks were considered automatic. The fMRI results before and after automaticity was achieved were compared. Our data showed that for both conditions, sequential movements activated similar brain regions. No additional activity was observed in the automatic condition. There was less activity in bilateral cerebellum, presupplementary motor area, cingulate cortex, left caudate nucleus, premotor cortex, parietal cortex, and prefrontal cortex during the automatic stage. These findings suggest that most of the motor network participates in executing automatic movements and that it becomes more efficient as movements become more automatic. Our results do not provide evidence for any area to become more activated for automatic movements.     

Timing of onset of afferent responses and of use of kinesthetic information for control of movement in normal and cerebellar-impaired subjects

A coordinated triggering task requiring use of kinesthetic information was employed to assess the timing of use of kinesthetic information in normal subjects and patients with cerebellar dysfunction. Passive movements of varying velocity were imposed in the flexor direction about the metacarpophalangeal joint of the right index finger. Subjects attempted to depress a switch with their left thumb when the index finger moved, past a specified angle that was learned during a training session. The velocities ranged from 10°/s to 88°/s in 2°/s increments. After 200 trials, subjects were then instructed instead to react as quickly as possible (reaction-time task) to the onset of movement for an additional 200 trials. For the same movements, the timing of onset of responses of muscle spindle afferents and cutaneous mechanoreceptors was determined by recording the responses of these afferents using microneurography. For slow velocities, patients were able to perform similarly to normals but at faster velocities patients triggered too late compared with normals. Patients required more time to use kinesthetic information than did normal subjects. An estimate of kinesthetic processing was not longer in patients. The chief explanation for the prolonged time required to use kinesthetic information in patients was that their reaction times were prolonged by 93 ms. In addition, the movement time was also prolonged, but this accounted for only 23 ms. Impaired motor performance in tasks requiring the use of kinesthetic information in cerebellar patients can be explained largely by their prolonged reaction times. Muscle spindle afferents responded on average much sooner than cutaneous mechanoreceptors. Because of the limited time available to perfomr the kinesthetic triggering task, the role for cutaneous mechanoreceptors, to provide singals for on-line coordination of movement appears limited compared with muscle spindle afferents.     

Primary generalised epileptic myoclonus: a frequent manifestation of minipolymyoclonus of central origin.

A group of patients with myoclonus is described whose jerks are preceded by a bilaterally synchronous, frontocentrally predominant, negative cerebral potential in the EEG. This potential may be a slow wave with variable timing in relation to EMG bursts, and in this circumstance the muscle jerks are usually small amplitude and multifocal ("minipolymyoclonus"). The cerebral negativity can also be shorter in duration and time-locked to limb jerks, which are larger in amplitude and more widespread. We propose that the physiology of this distinct form of myoclonus is similar to that of primary generalised epilepsy.     

Primary writing tremor and myoclonic writer's cramp

Four patients with primary writing tremor had a focal, task-specific tremor that responded to anticholinergic drugs. Physiologic features included EMG activity alternating in antagonist muscles, 5- to 20-microV cerebral potentials evoked by stretch of pronator teres, and no C-reflexes. Another patient had myoclonic jerks of the forearm on attempts to write ("myoclonic writer's cramp") that also responded to anticholinergic drugs; EMG activity appeared synchronously or alternating in antagonist muscles. These disorders have features of dystonia and enlarge the spectrum of writer's cramp.     

Postural adjustments associated with rapid voluntary arm movements 1. Electromyographic data.

Normal subjects made bilaterally symmetric rapid elbow flexions or extensions ("focal movement") while free standing or when supported by being strapped to a firm wall behind them (different "postural set"). In some trials a load opposed the movement two thirds of the way into its course. Electromyographic activity in leg and trunk muscles ("associated postural adjustments") demonstrated specific patterns for each type of movement. Activity in these muscles began prior to activity in the arm muscles and demonstrated a distal-to-proximal order of activation. The EMG patterns were characterised by alternating activity in the antagonist pairs similar to the triphasic pattern seen in the arm muscles. When the movement type was changed change of the pattern of the postural muscles occurred over several trials. It is concluded that the associated postural adjustments are pre-programmed motor activity linked to the focal movement, specific for the focal movement including anticipated events and the postural set.     

Working conditions and health behavior as causes of educational inequalities in self-rated health: an inverse odds weighting approach

Objective:Using a novel mediation method that presents unbiased results even in the presence of exposure–mediator interactions, this study estimated the extent to which working conditions and health behaviors contribute to educational inequalities in self-rated health in the workforce.Methods:Respondents of the longitudinal Survey of Health, Ageing, and Retirement in Europe (SHARE) in 16 countries were selected, aged 50–64 years, in paid employment at baseline and with information on education and self-rated health (N=15 028). Education, health behaviors [including body mass index (BMI)] and working conditions were measured at baseline and self-rated health at baseline and two-year follow-up. Causal mediation analysis with inverse odds weighting was used to estimate the total effect of education on self-rated health, decomposed into a natural direct effect (NDE) and natural indirect effect (NIE).Results:Lower educated workers were more likely to perceive their health as poor than higher educated workers [relative risk (RR) 1.48, 95% confidence interval (CI) 1.37–1.60]. They were also more likely to have unfavorable working conditions and unhealthy behaviors, except for alcohol consumption. When all working conditions were included, the remaining NDE was RR 1.30 (95% CI 1.15–1.44). When BMI and health behaviors were included, the remaining NDE was RR 1.40 (95% CI 1.27–1.54). Working conditions explained 38% and health behaviors and BMI explained 16% of educational inequalities in health. Including all mediators explained 64% of educational inequalities in self-rated health.Conclusions:Working conditions and health behaviors explain over half of the educational inequalities in self-rated health. To reduce health inequalities, improving working conditions seems to be more important than introducing health promotion programs in the workforce.     

Uptake of planar polychlorinated biphenyls and 2,3,7,8-substituted polychlorinated dibenzofurans and dibenzo-p-dioxins by birds nesting in the lower fox river and Green Bay,Wisconsin, USA

The uptake of persistent polychlorinated hydrocarbons (PCHs) by four avian species was investigated at upper trophic levels of two aquatic food chains of the lower Fox River and Green Bay, Wisconsin. Accumulation of total and specific planar polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans (PCDFs), polychlorinated dibenzo-p-dioxin (PCDDs), and H411E rat hepatoma cell bioassay-derived 2,37,8-tetrachlorodibenzop-dioxin equivalents (TCDD-EQ) was evaluated in Forster's tern (Sterna forsteri) and common tern (Sterna hirundo) chicks, and in tree swallow (Tachycineta bicolor) and red-winged blackbird (Agelaius phoeniceus) nestlings from colonies nesting in several locations within the watershed. Concentrations of the PCHs were greatest in eggs and chicks of the two tern species, less in the tree swallows and least in the red-winged blackbirds. Young of all four species accumulated total PCBs, PCB congeners 77, 105, 126, and 169, and TCDD-EQ. The young birds also accumulated small concentrations of several 2,3,7,8-sbustituted PCDF and PCDD congeners. Uptake rates for certain of the PCHs for the Forster's tern chicks were: 15 g/day for total PCBs, 70, 200, 6.5, and 0.14 ng/day for PCB congeners 77, 105, 126, and 169, respectively, and 270 g/day for TCDD-EQ. Principal components analysis revealed that the patterns of PCH concentrations in the samples were influenced by species of bird, their age (or length of exposure) and nesting location. Collectively, our findings demonstrate that exposure of avian species to contaminants derived from aquatic food chains can be characterized and quantified for the purposes of ecological risk assessment.     

Corticomuscular coherence: a review.

Corticomuscular coherence measured between electroencephalography (EEG), magnetoencephalography, or local field potentials and electromyography (EMG) should be helpful in understanding the cortical control of movement. EEG-EMG coherence and phase spectra depend on the types of EEG derivation and current source density function of EEG appears to be the most appropriate for computation of EEG-EMG coherence. A new model for the interpretation of the phase spectra ("constant phase shift plus constant time lag model") shows that cortical surface negative potentials are phase-locked to EMG firing. There are functional differences of EEG-EMG coherence among the alpha, beta, and gamma bands suggesting differences in their possible generator mechanisms. Since corticomuscular coherence is a noninvasive measure of corticomotoneuronal function in a specific frequency range, clinical application of this method might be very fruitful in tremor research.