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PubMed2002

Functional connectivity in the resting brain: a network analysis of the default mode hypothesis.

Functional imaging studies have shown that certain brain regions, including posterior cingulate cortex (PCC) and ventral anterior cingulate cortex (vACC), consistently show greater activity during resting states than during cognitive tasks. This finding led to the hypothesis that these regions constitute a network supporting a default mode of brain function. In this study, we investigate three questions pertaining to this hypothesis: Does such a resting-state network exist in the human brain? Is it modulated during simple sensory processing? How is it modulated during cognitive processing? To address these questions, we defined PCC and vACC regions that showed decreased activity during a cognitive (working memory) task, then examined their functional connectivity during rest. PCC was strongly coupled with vACC and several other brain regions implicated in the default mode network. Next, we examined the functional connectivity of PCC and vACC during a visual processing task and show that the resultant connectivity maps are virtually identical to those obtained during rest. Last, we defined three lateral prefrontal regions showing increased activity during the cognitive task and examined their resting-state connectivity. We report significant inverse correlations among all three lateral prefrontal regions and PCC, suggesting a mechanism for attenuation of default mode network activity during cognitive processing. This study constitutes, to our knowledge, the first resting-state connectivity analysis of the default mode and provides the most compelling evidence to date for the existence of a cohesive default mode network. Our findings also provide insight into how this network is modulated by task demands and what functions it might subserve.

Adult↗

PubMed2004

Searching for intellectual turning points: progressive knowledge domain visualization.

This article introduces a previously undescribed method progressively visualizing the evolution of a knowledge domain's cocitation network. The method first derives a sequence of cocitation networks from a series of equal-length time interval slices. These time-registered networks are merged and visualized in a panoramic view in such a way that intellectually significant articles can be identified based on their visually salient features. The method is applied to a cocitation study of the superstring field in theoretical physics. The study focuses on the search of articles that triggered two superstring revolutions. Visually salient nodes in the panoramic view are identified, and the nature of their intellectual contributions is validated by leading scientists in the field. The analysis has demonstrated that a search for intellectual turning points can be narrowed down to visually salient nodes in the visualized network. The method provides a promising way to simplify otherwise cognitively demanding tasks to a search for landmarks, pivots, and hubs.

Internet↗

PubMed2004

Diagnostic tool for the identification of MLL rearrangements including unknown partner genes.

Approximately 50 different chromosomal translocations of the human MLL gene are currently known and associated with high-risk acute leukemia. The large number of different MLL translocation partner genes makes a precise diagnosis a demanding task. After their cytogenetic identification, only the most common MLL translocations are investigated by RT-PCR analyses, whereas infrequent or unknown MLL translocations are excluded from further analyses. Therefore, we aimed at establishing a method that enables the detection of any MLL rearrangement by using genomic DNA isolated from patient biopsy material. This goal was achieved by establishing a universal long-distance inverse-PCR approach that allows the identification of any kind of MLL rearrangement if located within the breakpoint cluster region. This method was applied to biopsy material derived from 40 leukemia patients known to carry MLL abnormalities. Thirty-six patients carried known MLL fusions (34 with der(11) and 2 with reciprocal alleles), whereas 3 patients were found to carry novel MLL fusions to ACACA, SELB, and SMAP1, respectively. One patient carried a genomic fusion between MLL and TIRAP, resulting from an interstitial deletion. Because of this interstitial deletion, portions of the MLL and TIRAP genes were deleted, together with 123 genes located within the 13-Mbp interval between both chromosomal loci. Therefore, this previously undescribed diagnostic tool has been proven successful for analyzing any MLL rearrangement including previously unrecognized partner genes. Furthermore, the determined patient-specific fusion sequences are useful for minimal residual disease monitoring of MLL associated acute leukemias.

DNA-Binding Proteins↗

PubMed2006

Failing to deactivate: resting functional abnormalities in autism.

Several regions of the brain (including medial prefrontal cortex, rostral anterior cingulate, posterior cingulate, and precuneus) are known to have high metabolic activity during rest, which is suppressed during cognitively demanding tasks. With functional magnetic resonance imaging (fMRI), this suppression of activity is observed as "deactivations," which are thought to be indicative of an interruption of the mental activity that persists during rest. Thus, measuring deactivation provides a means by which rest-associated functional activity can be quantitatively examined. Applying this approach to autism, we found that the autism group failed to demonstrate this deactivation effect. Furthermore, there was a strong correlation between a clinical measure of social impairment and functional activity within the ventral medial prefrontal cortex. We speculate that the lack of deactivation in the autism group is indicative of abnormal internally directed processes at rest, which may be an important contribution to the social and emotional deficits of autism.

Adult↗

PubMed1996

Neural mechanisms for visual memory and their role in attention.

Recent studies show that neuronal mechanisms for learning and memory both dynamically modulate and permanently alter the representations of visual stimuli in the adult monkey cortex. Three commonly observed neuronal effects in memory-demanding tasks are repetition suppression, enhancement, and delay activity. In repetition suppression, repeated experience with the same visual stimulus leads to both short- and long-term suppression of neuronal responses in subpopulations of visual neurons. Enhancement works in an opposite fashion, in that neuronal responses are enhanced for objects with learned behavioral relevance. Delay activity is found in tasks in which animals are required to actively hold specific information "on-line" for short periods. Repetition suppression appears to be an intrinsic property of visual cortical areas such as inferior temporal cortex and is thought to be important for perceptual learning and priming. By contrast, enhancement and delay activity may depend on feedback to temporal cortex from prefrontal cortex and are thought to be important for working memory. All of these mnemonic effects on neuronal responses bias the competitive interactions that take place between stimulus representations in the cortex when there is more than one stimulus in the visual field. As a result, memory will often determine the winner of these competitions and, thus, will determine which stimulus is attended.

Animals↗

PubMed1999

Eating habits and appetite control: a psychobiological perspective.

An individual's eating behaviour is shaped by factors ranging from economic conditions and cultural practices to biological influences. The physiological system controlling appetite appears to be adapted to solving the problem of an unevenness of food supply across time, and is fairly permissive in its response to undereating and overeating. Consequently, when food is abundant, the diet is energy dense and energy expenditure is low, there is a strong tendency to become obese (i.e. obesity is better viewed as due to a 'toxic' environment than to faulty physiological control of appetite). Under such conditions the most common method of avoiding obesity is through the cognitive control of eating. However, dietary restraint and dieting are demanding tasks, and are associated with psychological costs, including significant impairment of cognitive performance. Restraint is also prone to disinhibition, with the result that it can sometimes undermine eating control, even leading to the development of highly disordered eating patterns. In part, these difficulties are due to the self-perpetuating nature of dietary habits: for example, hunger tends to be diminished during strict unbroken dieting, but increased in individuals having a highly variable eating pattern (such as occurs when eating is frequently disinhibited). These features of appetite control provide both barriers and opportunities for changing behaviour. Accordingly, there is a need for future research to focus on the psycho-social factors and the dieting practices predicting successful eating and weight control, with the objective of identifying the actual cognitive and behavioural strategies used by the many dieters and restrained eaters who are able to achieve weight loss and maintain long-term weight stability.

Appetite Regulation↗

PubMed1993

Comparing the concepts of mental load and stress.

This paper delineates mental load and stress as two related concepts that originate from different theoretical frameworks. A proper distinction between the two concepts is important, not only for theory building, but because it may lead also to different interpretations of experimental results, and, consequently, to different recommendations in applied situations. High workload is regarded as an important but not a critical factor in the development of stress symptoms. It is quite possible to work hard in difficult and complex tasks, even under unfavourable conditions, without cognitive strain, psychosomatic complaints, or adverse physiological effects. High task demands can be met by mobilizing extra energy through mental effort. This 'trying harder' reaction is a normal and healthy coping strategy to adapt to situational demands. In contrast, stress is regarded as a state in which the equilibrium between cognitive and energetical processes is disturbed by ineffective energy mobilization and negative emotions. Stress typically is characterized by inefficient behaviour, overreactivity, and the incapacity to recover from work. Stress is regarded as a state in which the physiological system is disorganized, which results in decreased well-being, sleeping problems, psychosomatic complaints, and increased health risks.

Arousal↗

PubMed1995

Loads on spinal tissues during simultaneous lifting and ventilatory challenge.

Muscles of the torso have been implicated to play a role in stabilization of the low back, and to assist in ventilation. This motivated an investigation to combine a load challenge to the low back with a breathing challenge, similar to that which a worker might experience when shovelling snow. Perhaps modulation of muscle activity needed to facilitate breathing may compromise the margin of safety of tissues that depend on constant muscle activity for support. Eight young healthy males dynamically lifted, and isometrically held, large loads (73-95 kg) and breathed a 10% CO2 gas mixture to elevate breathing (both with and without hand-held loads). Individual tissue forces were calculated using an anatomically detailed, dynamic model of the torso that was sensitive to individual variation by utilizing myoelectric signals, intra-abdominal pressure, ventilation rate and spine kinematics, obtained from each subject, as input. For large loads in the hands, most subjects appeared to stabilize the trunk with large muscle forces relegating the responsibility of creating lung air flow to the diaphragm. When reasonably small low-back demands were coupled with a breathing challenge and higher ventilation rates two out of eight subjects demonstrated entrainment of abdominal activity to breathing that resulted in additional cyclic low-back compressive loading of the order of 1000 N. Ergonomists should consider the additional tissue loading from physiologically demanding tasks and the related ventilation challenge, together with the tissue loads required to support external objects and maintain body posture.

Adult↗

PubMed1999

Mental strain and the problem of repeated measurements.

In the past, stress and strain arising from the execution of mentally demanding tasks have been measured by means of surveys. Such methods require repeated investigation of the individual perceptions and valuations during task fulfilment to record time-dependent changes in strain levels. However, it is possible that the individual measurement procedures employed in surveys--as artefacts--may cause a change in the stress situation and subsequently in the resulting mental strain. The results of the experiments carried out to investigate this hypothesis verify that repeated measurements have a similar effect as a short break. The repeated measurements taken during progressive studies are, therefore, likely to affect the conditions of stress. A change in the level of mental strain recorded can be expected, particularly if the post-test rating is preceded by a long period of low stress before or during which an additional measurement of strain is implemented.

Adult↗

PubMed1999

Comparison of the sensitivity of three psychophysical techniques to three manual materials handling task variables.

The primary objective of the study was to determine the absolute and relative sensitivity of three psychophysical techniques of physical stress determination (Borg's Scale, the Visual Analogue Scale, and the Body Part Discomfort Rating) in varied manual materials handling tasks. Ten young male and ten young female university students lifted a 22 kg box onto a shelf 132 cm high. The industrial-size box (40 x 20 x 20 cm) had two cut-out handles on the top middle of the two side panels. The shelf had restricted access allowing 5 and 10 mm clearance for access. The palletizing was performed in sagittal and 45 degrees asymmetrical postures under unlimited, 90% and 80% of stature headroom. The subjects lifted the box six times per minute for 5 min. After every lift the load was automatically delivered to the starting position. The 12 experimental conditions were randomized. Following each 5-min palletizing task the subjects were required to assess the immediately foregoing task on Borg's scale, the Visual Analogue scale, and a Body Part Discomfort Rating scale. All data were subjected to statistical analysis including multivariate analysis of variance and Scheffé post-hoc multiple range test. Borg's scale was able to discriminate between two clearances, two symmetries and the three headrooms (p < 0.001). The Visual Analogue scale was able to differentiate between two symmetries and three headrooms (p < 0.01), but the Body Part Discomfort Rating could not differentiate between any task conditions. Based on the study it is suggested that an appropriate match between the task demands and the basis of a psychophysical tool is essential for valid and reliable information.

Adult↗

PubMed1975

The relation of reflection-impulsivity to field dependence-independence and internal-external control in children.

First- and third-grade black children were administered Kagan's Matching Familiar Figures Test, Karp and Konstadt's Children's Embedded Figures Test (CEFT), and Shore, Milgram, and Malasky's Locus of Control Interview (LCI). It was hypothesized that reflective children would be (a) more field-independent and (b) more internal than their impulsive counterparts. The first hypothesis was supported and discussed in terms of the task demands of the CEFT. The failure to find strong support for the second hypothesis was attributed to the generalized nature of the LCI.

Black or African American↗

PubMed2003

The role of video in facilitating perception and action of a novel coordination movement.

Two groups (n = 10 in each) practiced a novel, bimanual coordination pattern that was demonstrated on video. One of the groups received augmented video feedback of their own responses after each trial following a demonstration. The video-feedback group showed better performance in acquisition and retention than the no-feedback group. On error-detection tests, the video-feedback group was better able to distinguish between correct and incorrect movement patterns. The authors concluded that video feedback helps to make relative phase information salient by aiding the discrimination process. Prepractice ability on a scanning task revealed that individuals who persevered with in-phase-type movements, even though the task demands dictated otherwise, had the most difficulty determining and subsequently performing the required movement. Video feedback helped them to compensate for those difficulties.

Adult↗

PubMed1982

Explorations of individual differences relevant to high level skill.

Past research has uncovered few broad abilities that underlie high skill. In this paper, attempts to isolate three different abilities of potential relevance to skill are described. No evidence was found for a general time-sharing ability in common to different kinds of tasks. Modest evidence was found for a trait of attentional flexibility. That trait could potentially be of use in predicting success for skills that require rapid shifts of attention because of rapidly changing task demands. Finally, the rate of repetitive activity is correlated across different muscle groups. For example, finger tapping speed is correlated with foot tapping speed, suggesting a common rate limiting factor. In turn, those rates predict handwriting speed and, according to Book (1924), championship typing.

Journal Article↗

PubMed1976

A method for small group training of psychiatric ward staff.

On a psychiatric ward for adolescents a change in organizational structure provided more autonomy and responsibility to the ward staff. As part of a program to help staff meet these new responsibilities, training groups were instituted to teach staff how to use their work groups more effectively. A method for staff training was used which promoted the development of group cohesiveness in the work groups and the transfer of insights made in training to job performance. In order to articulate clearly the conceptual rationale for the method, it is analyzed here in three parts: the goals of training and their impediments; the conditions under which learning will occur; and the processes through which learning takes place. In the description of the learning processes, "work" is conceived of as a group problem-solving process, involving the balancing and synthesizing of formal task demands and interpersonal pressures. Ward staff resistance to this form of training is discussed, and examples of improved performance on the job are presented. The training groups are defined in comparison to other types of groups and to more traditional didactic teaching.

Adolescent↗

PubMed1993

Lateralization of verbal memory and unilateral hippocampal sclerosis: evidence of task-specific effects.

This study retrospectively investigated the effect of left (LHS) versus right (RHS) hippocampal sclerosis on verbal memory, measured by means of the Paired Associate Learning and Logical Memory subtests of the Wechsler Memory Scale (WMS) administered as part of a routine preoperative assessment. Patients were selected for the presence of unilateral hippocampal sclerosis by means of preoperative magnetic resonance imaging (MRI) and postoperative neuropathology. The LHS patients (n = 20) were significantly worse on paired associate learning than RHS patients (n = 18), the performance of RHS patients being consistent with normative standards. In contrast, no laterality effect was seen on the immediate and delayed recall of passages; the evidence suggests that both groups performed at a mildly impaired level. It was suggested that the laterality of verbal memory is conditional upon specific task demands in patients with damage to mesial temporal structures.

Adult↗

PubMed2001

Intermuscular coordination during pendulum rebound exercises.

In this study, we assessed coordination during pendulum rebound jumps. To gain insight into the movement coordination strategy, nine experienced male volleyball players performed maximal rebound jumps in a pendulum swing device using three different seat arrangements (90 degrees, 135 degrees and 180 degrees). Two-dimensional filming was performed in the right sagittal plane (200 Hz) synchronized with a force platform fitted to the wall (1000 Hz). The surface electromyograms of five muscles were recorded (200 Hz), in conjunction with kinematic and kinetic assessment. During the countermovement phase, the impact forces were attenuated by eccentric contractions of most muscles, which helped to reduce the energy input into the system. The wall reaction forces, net moments and joint power profiles were comparable between conditions. The small differences found between the extreme seat arrangements were attributed to differences in muscle length and the position of the feet. The strategy used during landing was similar to that observed in unconstrained vertical and drop jumps, where the neuromuscular system attenuates the impact forces. During the push-off phase, most muscles were found to contribute to positive work generation, except the semitendinosus, which was stretching throughout the propulsive phase. Despite not being able to exert a large influence over the trunk segment, this muscle was deemed to play an important role in regulating and synchronizing the onset of knee extension, enabling hip extension to occur before extension in the other more distal joints. Our findings show that the neuromuscular system is able to produce consistent movement coordination across experimental conditions and in accordance with the specific task demands and constraints imposed in the movement structure.

Adult↗

PubMed1989

The underarm throw for accuracy in children.

Forty boys and girls of two age groups (mean ages 52 and 70 months, respectively) performed 35 trials on a throwing task demanding accuracy. As might be expected, the older children were significantly more accurate than the younger ones but there were no sex differences. Film analysis of the throws showed that, although both age groups attempted to employ the adult strategy of varying velocity while keeping ball-release angle constant, the younger group was less successful in the latter aspect. The manner in which consistent release angles were arrived at by the older group was through the use of a movement pattern in which the elbow angle did not change during the forward swing. Such a movement pattern appeared less frequently in the younger age group. The results of this study provide support for a mode of research identifying functionally relevant kinematic variables that can subsequently be shown to follow from distinctive execution categories. In such a way, changes in outcome measures with increasing age and/or skill level can be functionally understood and identified.

Arm↗

PubMed2002

Recovery in memory function in the first year following TBI in children.

PRIMARY OBJECTIVE: To examine memory skills, at acute, 6- and 12-monthly stages, following childhood traumatic brain injury (TBI). RESEARCH DESIGN: Prospective, longitudinal, between-group design, comparing pre-injury and postinjury intellectual and memory measures, across three levels of injury severity. METHODS AND PROCEDURES: Investigation of memory skills in a group of 76 children who had sustained a mild, moderate or severe TBI. Specific tests were used to measure immediate and short-term memory, and more complex multi-trial learning. MAIN OUTCOMES AND RESULTS: The severe TBI group exhibited greater deficits on memory tasks, irrespective of modality, in the acute, 6- and 12-month post-injury stages, in comparison to mild and moderate TBI groups. Performance was dependent on both injury severity and task demands. CONCLUSIONS: Memory difficulties are present during the acute, 6- and 12-months following childhood TBI. With a clearer understanding of the memory deficits following TBI, appropriate strategies can be taught and interventions implemented for these children.

Amnesia↗