Thermal-equilibrium processes and electronic transport in undoped hydrogenated amorphous silicon

Abstract

The temperature and time dependence of the d.c. conductivity of undoped hydrogenated amorphous silicon is presented. Measurements of the electronic transport are reported, with particular emphasis on the effects of annealing and cooling the samples. Two regimes of behaviour are observed. When samples are rapidly cooled from 200°C below a temperature T _E～145°C a non-equilibrium dark conductivity, higher than that corresponding to slow cooling, is observed. The electronic and atomic structure then slowly relax and the time dependence of the excess conductivity is well described by a stretched exponential function. The second regime above T _E corresponds to a relaxation time short compared to experimental times and the conductivity is independent of which order the annealing temperature is chosen. Thus the thermal equilibrium processes observed in undoped samples are qualitatively very similar to those observed in doped samples as recently reported in the literature.     

Determination of F-wave conductivity in the normal N. ulnaris]

The methodical procedure for the determination of the F-wave conductivity in the ulnar nerve (in total - conductivity, afferent, conduction frequency forearm, afferent-efferent in the proximal segment of the peripheral motor neuron) and the results of a hundred examinations are presented. The results are compared with the motor nerve conduction velocity. No influences of sex, age or the site of lead could be discovered.     

Cholinergic-dopaminergic interactions in radial-arm maze performance

Although acetylcholine and dopamine are believed to play complementary roles in motor function, a comparable neurochemical interaction has not been established for cognitive function. The muscarinic receptor blocker scopolamine and the dopaminergic antagonist haloperidol have been found to impair choice accuracy of rats in the radial-arm maze. In the present study, low doses of these two drugs were administered intraperitoneally either alone or in combination to rats trained on a working memory task (food reward) in an eight-arm radial maze. Scopolamine, 0.125 mg/kg, produced a significant decrease in choice accuracy (i.e., arm entries until an error). Haloperidol, 0.0625 mg/kg, did not cause a significant decrease in accuracy, but there was a trend in that direction. The combination of haloperidol with scopolamine attenuated significantly the amnestic effect of scopolamine. These results suggest that, like motor behavior, cognitive function may be influenced by the balance between acetylcholine and dopamine.     

Mentalizing skills of non-native,early signers: A longitudinal perspective

Using a population-based sample consisting of 401 6- to 12-year-olds, this study examined normative age and sex distributions on motor activity as measured in an actigraphic-based motion tracking system (MTS) and on attention-related functions derived from a Continuous Performance Test (CPT). Specific objectives were to present new knowledge on age-related change in motor activity and to study age effects on changes in motor activity and CPT performance as a function of time on task. Further, continuous relations between the two ADHD symptom domains and CPT performance and motor activity, and importantly, age effects in these relations were examined. CPT performance improved, and level of motor activity decreased with age. Linear associations between the two ADHD symptom domains and several of the CPT and MTS parameters support available research describing the nature of ADHD as a continuous dimension with variable expression throughout the general population. Further, our study is one of the first to provide developmental data using a time on task design, particularly with regard to motor activity. Imperative for ADHD future research are our results showing that age matters in the relation between ADHD behaviours and neuropsychological function.     

Neuroendocrine and behavioral correlates of constitutional differences

Consistent and stable individual differences were observed in the renal responses of water-loaded dogs during the development of Pavlovian conditional motor defense reflexes by electrocutaneous reinforcement. Some dogs developed persistent and intense conditional antidiuretic responses (with a high urine osmolality) to the entire Pavlovian conditioning room complex, whereas other dogs failed to exhibit conditional antidiuresis. In contradistinction to the conditional motor defense reflexes, the conditional antidiuretic responses showed poor differentiation, thus demonstrating the phenomenon of schizokinesis discovered by Gantt. In addition to conditional water retention, the antidiuretic dogs also exhibited persistent hyperpnea, copious salivation and tachycardia. The physiologic responses of the antidiuretic dogs to the Pavlovian conditioning room resemble those described by Walter B. Cannon for a “fight or flight” response,i.e., physiologic reactions of animals engaged in intense muscular effort. The antidiuresis serves the function of conserving body water so that it may be available for evaporative cooling in order to maintain thermal homeostasis. Since our experimental dogs cannot engage in a consummatory “fight or flight” response, their physiologic reaction to a stressful psychologic environment can be considered maladaptive. Pharmacologic analysis suggested that the antidiuretic responses may involve cholinergic transmitters.     

Decreasing motor stereotypy in leisure contexts: Analysis of stimulus control with response interruption and redirection

Noncontingent access to preferred stimuli and activities may decrease stereotypic behavior in individuals with autism or other developmental disorders. However, prompted engagement, response interruption and redirection (RIRD), and/or contingent access to stereotypy may be required to achieve clinically significant reductions in stereotypy. Antecedent stimuli may also be manipulated during intervention to establish stimulus control by signaling when stereotypy will receive programmed consequences. The purpose of the current project was to replicate prior research in this area by a) evaluating the effectiveness of RIRD on motor stereotypy in an adolescent with autism and b) providing contingent access to stereotypy as a function of successively longer intervals without stereotypic behavior. We also assessed the extent that these procedures gained acceptable stimulus control. Results from this project suggest RIRD and contingent access to stereotypy may effectively decrease motor stereotypy in leisure contexts, though consistent inhibitory stimulus control may be difficult to establish.     

Individual differences in components of slow cortical potentials: implications for models of information processing

Individual differences in the effects of pharmacological and behavioural manipulations on slow cortical potentials (SCP), may reflect personality differences in type of informational control under attentional stress. Two experiments were conducted to examine SCP component differences in extraverts and introverts under different attentional tasks and with and without nicotine smoking ‘stressor’ conditions. In an initial experiment a decrease in late negativity for introverts and an increase in late negativity for extraverts suggested that smoking enhanced introverts' stimulus set and extraverts' motor set. In a second experiment, personality differences in SCP were examined again, but within a signal-detection paradigm, which allows separate assessment of the contribution of sensory sensitivity and response bias factors to performance. Smoking increased sensitivity in both personality groups, but response bias (caution) increased in introverts only. Extraverts showed an increase in central negativity during smoking whilst introverts showed a decrease in negativity and a decrease in positive wave components. The results are explained in terms of a motor model of attentional control whereby smoking regulates inhibitory controlled actions in introverts, but activates general motor processes for extraverts.     

Antiaggressive and motor effects of the DA release inhibitor CGS 10746B

In the present study the effects of a wide range of doses of the dopamine release inhibitor CGS 10746B were evaluated in spontaneous activity and in aggressive behaviour using the paradigm of isolation‐induced aggression. The two higher doses (8 and 16 mg/kg) produced a decrease in spontaneous motor activity. Antiaggressive effects were observed after administration of doses from 4 mg/kg upwards. At this dose, CGS 10746B diminished threat and attack, and although an increase in immobility was observed, no impairment of other motor behaviours was presented. With higher doses, aggression was practically abolished but with a concomitant effect on many other behaviours. When animals were separated depending on their latency of attack, those that showed a long attack latency (LAL) presented a stronger response to 4 mg/kg than those that had a short attack latency (SAL), which were not affected in their aggression by this dose. We can conclude that presynaptic dopamine function is necessary for the normal expression of aggressive behaviours, since CGS 10746B reduces aggression at doses that do not affect spontaneous motor activity. Aggr. Behav. 27:382–390, 2001. © 2001 Wiley‐Liss, Inc.     

The possible interaction of Harderian material and saliva for thermoregulation in the Mongolian gerbil, Meriones unguiculatus

Self-grooming in Meriones unguiculatus is associated with saliva spread and the release and spread of Harderian material from the external nares. Saliva spread results in evaporative cooling and Harderian spread insulates the pelage. Two experiments tested the predictions that (1) saliva production and Harderian material decrease systematically following a self-groom, (2) high ambient temperature (34 degrees C) increases saliva production but decreases Harderian release, and (3) low ambient temperature (7 degrees C) decreases saliva production but increases Harderian release. The predictions were generally confirmed, suggesting that short-term and long-term thermoregulatory reactions are differentially affected by ambient temperatures. Thus, an animal will tend to emphasize saliva production when evaporative cooling is needed and will exaggerate Harderian release when insulation of the pelage is required.     

Effects of motor programming on the power spectral density function of finger and wrist movements

Power spectral density analysis was applied to the frequency content of the acceleration signal of pen movements in line drawing. The relative power in frequency bands between 1 and 32 Hz was measured as a function of motoric and anatomic task demands. Results showed a decrease of power at the lower frequencies (1-4 Hz) of the spectrum and an increase in the middle (9-12 Hz), with increasing motor demands. These findings evidence the inhibition of visual control and the disinhibition of physiological tremor under conditions of increased programming demands. Adductive movements displayed less power than abductive movements in the lower end of the spectrum, with a simultaneous increase at the higher frequencies. The relevance of the method for the measurement of neuromotor noise as a possible origin of delays in motor behavior is discussed.     

The influence of motor function on processing speed in preterm and term-born children

This study investigates the relationship between motor function and processing speed in preterm children. Processing speed was compared in 145 adolescents, born 25–41 weeks gestational age, utilizing tasks including differing motor demands. The influence of motor cortex excitability and functional motor skills on task performance was assessed. For tasks with motoric demands, differences in performance between preterm and term-born children were mediated by the relationship between gestational age, corticomotor excitability, and motor function. There were no differences in non-motor processing speed task performance between preterm and term-born children. Measures of processing speed may be confounded by a timed motor component.     

Pathophysiology of writer's cramp

Writer's cramp is a task-specific focal hand dystonia. The abnormality of task specificity is a curious one and indicates that we need to learn more about the coupling of motor programs and their effectors. Writer's cramp appears to be triggered by spending much time writing by an individual with a fertile physiological substrate for producing the disorder. The fertile background, which is likely genetic, may be a decrease of inhibition, an increase of plasticity or an impairment in sensory function. Recent pathophysiological findings have implications for new therapies.     

Motor performance improved by exercises in cerebral ischemic rats

Physical exercise may induce neuroprotective effects against brain damage after stroke. The authors aimed to investigate the effects of various exercises on motor function, striatal angiogenesis, and infarct volume in cerebral ischemic rats. Adult male Sprague Dawley rats were subjected to middle cerebral artery occlusion and randomly assigned to 1 of the 4 groups: Rota-rod training, lower speed treadmill training, higher speed treadmill training, or no exercise control. Motor function, striatal angiogenesis, and infarct volume were evaluated before or after motor training. After training, motor function and striatal angiogenesis changed significantly in Rota-rod and higher speed treadmill training groups as compared with the control group. Improvement in motor function significantly correlated with striatal angiogenesis after motor training. Infarct volumes were significantly decreased in lower and higher speed treadmill training groups. The results indicated that both motor training procedures can be used as effective training programs in stroke rehabilitation.     

Task goals and change in dynamical degrees of freedom with motor learning

In this article, the authors examined the hypothesis that the direction of the change (increase or decrease) in the dynamical degrees of freedom (dimension) regulated as a function of motor learning is task-dependent. Adult participants learned 1 of 2 isometric force-production tasks (Experiment 1: constant force output; Experiment 2: sinusoidal force output) over 5 days of practice and a 6th day with augmented information withdrawal. The results showed that over practice, the task goal induced either an increase (Experiment 1) or a decrease (Experiment 2) in the dimension of force output as performance error was reduced. These findings support the proposition that the observed increase or decrease in dimension with learning is dependent on both the intrinsic dynamics of the system and the short-term change required to realize the task goal.     

the cooling out of two-year college women

The author describes the concept of “cooling out” as developed by Burton Clark and examines its applicability to the experience of women in the two-year college. She looks at four cooling out agents: parents, uncontrollable circumstances, counselors, and the two-year college itself. The discussion is based on interviews with 62 women in three two-year colleges. The author concludes that cooling out as experienced by women is congruent with but not exactly like the process as described by Clark. Nevertheless, the importance of counseling to the cooling out function is reasserted.     

Adaptation in motor strategies for postural control associated with sensory reweighting

The purpose of this study was to identify and differentiate the motor strategies associated with sensory reweighting adapted during specific sensory integration tasks by healthy young adults. Thirty-six subjects (age range: 21–33 years) performed standing computerized dynamic posturography balance tasks across progressively increasing amplitudes of visual (VIS), somatosensory (SOM) and both (VIS+SOM) systems perturbation conditions. Adaptation in the motor strategy was measured as changes in electromyographic (EMG) activities and joint angles. The contribution of the perturbed sensory input in maintaining postural stability was calculated to determine the sensory reweighting. A multivariate design was used to model a linear combination of motor adaptation variables that discriminates specific sensory integration tasks. Results showed a significant progressive decrease in postural sway per unit amplitude of sensory perturbation in each condition, indicating dynamic sensory reweighting. Linear discriminant function analysis indicated that the adaptation in motor strategy during the VIS condition was associated with increased activity of EMG and joint angles in the upper body compared to the lower body. Conversely, during the SOM and VIS+SOM conditions, the adaptation in motor strategy was associated with decreased activity of EMG and joint angles in the lower body compared to the upper body. Therefore, the adaptation in motor strategies associated with sensory reweighting were different for different sensory integration tasks.     

Linguistic correlates of asymmetric motor symptom severity in Parkinson’s Disease

Asymmetric motor severity is common in Parkinson’s Disease (PD) and provides a method for examining the neurobiologic mechanisms underlying cognitive and linguistic deficits associated with the disorder. In the present research, PD participants (N = 31) were assessed in terms of the asymmetry of their motor symptoms. Interviews with the participants were analyzed with the Linguistic Inquiry and Word Count (LIWC) program. Three measures of linguistic complexity – the proportion of verbs, proportion of function words, and sentence length – were found to be affected by symptom asymmetry. Greater left-side motor severity (and hence greater right-hemisphere dysfunction) was associated with the production of significantly fewer verbs, function words, and shorter sentences. Hence, the production of linguistic complexity in a natural language context was associated with relatively greater right hemisphere involvement. The potential neurobiological mechanisms underlying this effect are discussed.     

A neurobehavioral investigation into judgmental processes: effect of bilateral motor behaviors

Two experiments were conducted in order to examine how different bilateral motor activations of the approach and avoidance motivational systems influenced participants' evaluations of valenced stimuli (figurative expressions and pictures of everyday situations). The first Study (Study 1) showed that participants judged valenced expressions according to the motor congruence model put forward by Cretenet and Dru (2004). This may depend on the compatibility of the valenced stimuli with the congruency of the bilateral motor behaviors that involved two unilateral motor behaviors that are congruent to each other. These results were duplicated in Study 2 with the use of valenced pictures taken from the International Affective Picture System. The overall results shed new light on the influence of motor behaviors on judgments, by determining the motor system as operative in evaluative mechanisms, and not merely a simple executive function of higher cognitive processes.     

Using transcranial magnetic stimulation methods to probe connectivity between motor areas of the brain

Transcranial magnetic stimulation is increasingly used as a tool to explore cortical motor function in healthy subjects and in patients with neurological disease or injury. This review describes a “twin coil” TMS approach that allows investigation of time related changes in functional connectivity between primary motor cortex and other areas in preparation for a forthcoming movement. Investigations into premotor–motor interactions show that these are specific to the type of task that is performed as well as the muscles used to control the movement, allowing us to monitor information flow within motor networks with millisecond time resolution.     

Proprioception and Motor Control in Parkinson's Disease

ABSTRACT

Parkinson's disease (PD) is a neurodegenerative disorder that leads to a progressive decline in motor function. Growing evidence indicates that PD patients also experience an array of sensory problems that negatively impact motor function. This is especially true for proprioceptive deficits, which profoundly degrade motor performance. This review specifically address the relation between proprioception and motor impairments in PD. It is structured around 4 themes: (a) It examines whether the sensitivity of kinaesthetic perception, which is based on proprioceptive inputs, is actually altered in PD. (b) It discusses whether failed processes of proprioceptive-motor integration are central to the motor problems in PD. (c) It presents recent findings focusing on the link between the proprioception and the balance problems in PD. And (d) it discusses the current state of knowledge of how levodopa medication and deep brain stimulation affect proprioceptive and motor function in PD. The authors conclude that a failure to evaluate and to map proprioceptive information onto voluntary and reflexive motor commands is an integral part of the observed motor symptoms in PD.