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At least 397 records · Page 22Linked to original sources
PubMed1999

Executive Functions in Persons with Sleep Apnea.

Seventeen patients with sleep apnea syndrome [SAS, Respiratory Disturbance Index (RDI) = 12-85] were compared with 16 normal controls (RDI < 7) on neuropsychological tests of executive functions, a domain in which SAS patients have been suggested to have deficits. SAS patients demonstrated greater deficits in the retrieval of information from semantic memory (Controlled Oral Word Association task) and in shifting responses in the face of error (Wisconsin Card Sort Test), but differences in working memory were not observed. Eliciting deficits in cognitive executive functions in SAS may require more sensitive measures than are typically used in neuropsychiatric research.

Journal Article↗
PubMed1984

Computer assisted instruction for radiotherapy residents.

In order for radiotherapy residents to become proficient with physics concepts, a certain amount of reinforcement and repetition is necessary. An assembly of computer programs has been developed for the RSX operating system with the aim of shifting these repetitive tasks from the physics staff to a computer. Three types of interactions are employed: (1) textual summaries of key concepts, (2) numerical problems, and (3) typical board exam questions. A file is maintained which records the resident's performances as they work through the programs.

Computer-Assisted Instruction↗
PubMed2005

The response-cued completion hypothesis and the nature of residual cost in regular switch.

Three experiments are presented that compare the residual cost found when shifting from one task to another under different extra-response conditions, to test whether the response is the main factor to complete mental set reconfiguration. We investigated whether residual costs can be eliminated if participants carry out a response prior to completing switch trials. In all experiments, participants were required to press an extra key during the inter-trial interval (ITI) to proceed. In experiment 1, this extra response consisted of pressing the space bar. In experiment 2, the response consisted of pressing one of the two possible keys that belonged to the alternating tasks response set. In experiment 3, the interpolated response involved pressing one of the two possible keys, not belonging to the response set of the alternating tasks. We found no residual cost in the second or the third experiments. To explain the nature of residual cost we discuss the data in the context of a response cued completion hypothesis.

Cues↗
PubMed2005

Vitellogenin regulates hormonal dynamics in the worker caste of a eusocial insect.

Functionally sterile honey bee workers synthesize the yolk protein vitellogenin while performing nest tasks. The subsequent shift to foraging is linked to a reduced vitellogenin and an increased juvenile hormone (JH) titer. JH is a principal controller of vitellogenin expression and behavioral development. Yet, we show here that silencing of vitellogenin expression causes a significant increase in JH titer and its putative receptor. Mathematically, the increase corresponds to a dynamic dose-response. This role of vitellogenin in the tuning of the endocrine system is uncommon and may elucidate how an ancestral pathway of fertility regulation has been remodeled into a novel circuit controlling social behavior.

Animals↗
PubMed2001

Heart rate strain in cable hauler choker setters in New Zealand logging operations.

This study examined the physical strain experienced by cable hauler choker setters, and the applicability of heart rate indices for measuring physical strain in commercial forest harvesting operations in New Zealand. The heart rate of four choker setters were recorded continuously throughout the working day and applied to heart rate indices. Based on the relative heart rate at work (%HRR), ratio of working heart rate to resting heart rate and 50% level indices, the mean working heart rate (HRw) of 106 bt. min(-1) +/- 6.9 (mean +/- SD) placed choker setting in the moderate workload category. The specific tasks of line shifts (120.3 +/- 4.8 bt. min(-1)), hooking up drags (118.8 +/- 6.6 bt. min(-1)) and uphill travel (126.1 +/- 12.9 bt. min(-1)), imposed the most severe workloads on the choker setters. This research also demonstrated that heart rate indices could be used as an effective means of determining the physiological strain of subjects working in New Zealand's commercial forest harvesting operations.

Adult↗
PubMed1996

Moderate peripheral neuropathy impairs weight transfer and unipedal balance in the elderly.

OBJECTIVE: To quantitatively assess the performance of elderly with and without moderate, electrodiagnostically confirmed peripheral neuropathy (PN) on tasks of weight shifting and maintenance of unipedal balance. PATIENTS AND METHODS: A case control study with PN subjects selected from a computerized data bank of all patients who had undergone electrodiagnostic studies at a university-based referral center. Control subjects of similar age and same gender were selected from the same source. Clinical examination included neurological and gross motor components. Quantitative evaluation included testing while the subjects stood with a force plate under each foot. Center of reaction (CR) excursions and ground reaction forces were quantified in: (1) six trials as subjects transferred their weight from bipedal stance to unipedal stance, on command, and attempted to maintain it for at least 3 seconds; and (2) in two additional trials in which subjects held unipedal stance for as long as possible. RESULTS: No subjects in either group had difficulty with level gait, a 180-degree turn, or required examiner assistance during an eyes-closed Romberg test. Biomechanical testing revealed that although the PN group used the same time to transfer their weight onto one foot as the C group, they achieved a significantly (1) lower rate of success in reliably maintaining 3 seconds of unipedal stance (.12 vs .58, p = .021), and (2) shorter mean maximum unipedal stance time (3.8 vs 32.3sec, p < .001). Furthermore, the PN group experienced greater difficulty in maintaining unipedal stance, as evidenced by significantly greater fluctuations in their ground reaction forces. CONCLUSIONS: The demonstrated impairment in reliability of unipedal stance in elderly with PN likely contributes to their known high rate of falls. Furthermore, unipedal stance testing serves to sharpen the physical examination by verifying the functional significance of impaired distal sensation-a common finding in the elderly.

Aged↗
PubMed1999

The influences of rearing environment and neonatal choline dietary supplementation on spatial learning and memory in adult rats.

The facilitative effects of early environmental enrichment and perinatal choline chloride dietary supplementation on adult rat spatial learning and memory were examined using delayed match-to-place (DMTP) and delayed spatial win-shift (DSWSh) discrimination tasks. Animals were either maintained in a standard lighted colony (LR) or were given supplementary exposure to a complex environment (CR) for 2-h daily from 20 to 90 days of age. In each case, half the animals were exposed to the choline supplementation both prenatally (through the diet of pregnant rats) and postnatally (subcutaneous injection) for 24 days. In the first experiment, all 90-day-old rats were given trials in which they first found a hidden platform in a Morris water maze (MWM) in a particular location (acquisition trial), and then were required to remember that position 10 min later (test trial). Both environmental enrichment and early diet had significant impacts on performance. CR animals, given neonatal choline pretreatment, found the platform on test trials significantly faster than any of the other groups. CR animals exposed to the control saline diet showed better retention than did the LR animals given the early choline diet, which in turn, were superior to animals given neither environmental enrichment nor choline. All animals were subsequently tested in the same paradigm immediately following atropine sulfate injections. The atropine eliminated the difference between the four groups of animals on test trials. In a second experiment, both CR, and neonatal choline treatment facilitated performance on a DSWSh radial arm maze (RAM) task previously found to be sensitive to hippocampal and/or medial prefrontal lesions. Performance differences between groups were facilitated by the anticholinesterase drug, tacrine and attenuated by the cholinergic antagonist, Atropine. The present study extends the descriptions of long-term functional enhancements produced by perinatal choline supplementation and environmental enrichment and to relate these effects to common modifications to targets of cholinergic basal forebrain systems.

Animals↗
PubMed2002

Functional MRI experiments: acquisition, analysis and interpretation of data.

Functional MRI is widely used to address basic and clinical neuroscience questions. In the key domains of fMRI experiments, i.e. acquisition, processing and analysis, and interpretation of data, developments are ongoing. The main issues are sensitivity for changes in fMRI signal that are associated with brain function, and the design of tasks with which brain functions are invoked. In this paper we address these issues, in terms of strengths, weaknesses and future developments. Acquisition of data is commonly achieved with techniques that measure blood oxygen level-dependent (BOLD) signal changes. Although the mechanisms that affect BOLD signal are complex and not well understood, fMRI yields results that agree with known functional topography. Sensitivity for task-related brain activity is expected to benefit from technological advances in acquisition, i.e. SENSE or parallel imaging, and higher field scanners (3 T). Data analysis is geared towards modelling sources of signal variation, i.e. reducing noise in the data time-series, and the cerebrovascular response to task-related changes in neuronal activity. Analytical algorithms such as connectivity and component analysis contribute to the extraction of meaningful information from fMRI datasets. The choice of tasks, and consequently of the statistical evaluation procedures, is best guided by the specific questions that are formulated a priori. The future is expected to bring more sophisticated questions, and tasks that allow for accurate modelling of involved brain functions. An example of a hypothesis-driven experiment is presented, where we investigated whether practise of a working memory task caused a shift in the neuronal representation of working memory or not.

Brain↗
PubMed1997

Sources and topography of supramodal effects of spatial attention in ERP.

This study aimed to finding modality-independent event-related potentials (ERP) modulations related to spatial attention by minimising several possible methodological constrains which may account for the rareness of this finding in past spatial attention ERP research. ERP were recorded while subjects performed a shifting spatial attention task of either auditory, visual or mixed (both auditory and visual) modality. Task requirements and stimulation devices were identical for either modality. Stimuli could appear (80%, valid trials) or not (invalid trials) at predicted locations, and subjects had to perform a speeded response to every stimulus. Reaction time benefits were found for valid trials. Instead of the usually found enhancement of sensory-evoked modality-specific components for valid trials, ERP showed modality-independent modulations as a function of attention. They consisted of a fronto-central activity starting 240 ms after stimulus onset and originated in the anterior cingulate gyrus, followed 40 ms later by a bilateral parietal cortex activation. These processes would be reflecting the activity, respectively, of the anterior and posterior attention systems postulated in Posner's model (Posner and Peterson 1990), which showed a higher degree of participation during invalid trials. P300-like processes were also observed for invalid trials. These results demonstrate that supramodal effects of spatial attention of ERP can be obtained. Furthermore, they extend Posner's model by indicating the timings of implication of the attention subsystems.

Acoustic Stimulation↗
PubMed1998

Response bias in visual serial order memory.

The recency-to-primacy shift represents a major challenge for all theories that attempt to explain the effects of serial order on memory. At short retention intervals, strong recency and no primacy effects occur, but as the retention interval increases, recency is attenuated and primacy increases. In 2 experiments, 24 participants were presented with sets of 4 unfamiliar faces and were asked to state the serial position of a probe face after 0 or 10 s. The predicted recency-to-primacy shift was obtained with accuracy responses. However, the distribution of responses also showed that there was a change in response bias with retention interval. When this was corrected for, the recency-to-primacy shift was eliminated. Response bias is suggested as the underlying cause of the recency-to-primacy shift in this task.

Adult↗
PubMed2004

Recalibration of audiovisual simultaneity.

To perceive the auditory and visual aspects of a physical event as occurring simultaneously, the brain must adjust for differences between the two modalities in both physical transmission time and sensory processing time. One possible strategy to overcome this difficulty is to adaptively recalibrate the simultaneity point from daily experience of audiovisual events. Here we report that after exposure to a fixed audiovisual time lag for several minutes, human participants showed shifts in their subjective simultaneity responses toward that particular lag. This 'lag adaptation' also altered the temporal tuning of an auditory-induced visual illusion, suggesting that adaptation occurred via changes in sensory processing, rather than as a result of a cognitive shift while making task responses. Our findings suggest that the brain attempts to adjust subjective simultaneity across different modalities by detecting and reducing time lags between inputs that likely arise from the same physical events.

Acoustic Stimulation↗
PubMed2005

Linkage between proton binding and folding in RNA: implications for RNA catalysis.

Small ribozymes use their nucleobases to catalyse phosphodiester bond cleavage. The hepatitis delta virus ribozyme employs C75 as a general acid to protonate the 5'-bridging oxygen leaving group, and to accomplish this task efficiently, it shifts its pKa towards neutrality. Simulations and thermodynamic experiments implicate linkage between folding and protonation in nucleobase pKa shifting. Even small oligonucleotides are shown to fold in a highly co-operative manner, although they do so in a context-specific fashion. Linkage between protonation and co-operativity of folding may drive pKa shifting and provide for enhanced function in RNA.

Base Sequence↗
PubMed1995

Acute and chronic nicotinic interactions with dopamine systems and working memory performance.

Nicotine has been found to improve memory performance in a variety of tests in rats, monkeys, and humans. Interactions of nicotinic systems with dopamine (DA) systems may be important for this effect. We conducted a series of studies of nicotinic agonist and antagonist interactions with DA systems using rats in a win-shift working memory task in the radial-arm maze. The working memory deficit caused by the nicotinic antagonist mecamylamine was potentiated by the D1/D2 DA antagonist haloperidol and the specific D2 antagonist raclopride. In contrast, the mecamylamine-induced deficit was reversed by co-administration of the D2/D3 agonist quinpirole. Nicotine also has significant interactions with dopamine drugs with regard to working memory performance in the radial-arm maze. The DA agonist pergolide did not by itself improve radial-arm maze memory performance, but when given together with nicotine it produced an elevated dose-dependent increase in choice accuracy. The D1 agonist SKF 38393 significantly impaired radial-arm maze choice accuracy. Nicotine was effective in reversing this deficit. When given together with nicotine, the D2/D3 agonist quinpirole improved RAM choice accuracy relative to either drug alone. Acute local infusion of mecamylamine to the midbrain DA nuclei effectively impairs working memory function in the radial-arm maze. In contrast to acute nicotinic manipulations, considerably less evidence exists that the effects of chronic nicotine administration are influenced by DA systems. This may be an example of the different neural substrates that underlie the memory improvement caused by acute and chronic nicotine.

Animals↗
PubMed2004

Direction-dependent phasing of locomotor muscle activity is altered post-stroke.

A major contributor to impaired locomotion post-stroke is abnormal phasing of muscle activity. While inappropriate paretic muscle phasing adapts to changing body orientation, load, and speed, it remains unclear whether paretic muscle phasing adapts to reversal of locomotor direction. We examined muscle phasing in backward pedaling, a task that requires shifts in biarticular but not uniarticular muscle phasing relative to forward pedaling. We hypothesized that if paretic and neurologically intact muscle phasing adapt similarly, then paretic biarticular but not paretic uniarticular muscles would shift phasing in backward pedaling. Paretic and neurologically intact individuals pedaled forward and backward while recording electromyograms (EMGs) from vastus medialis (VM), soleus (SOL), rectus femoris (RF), semimembranosus (SM), and biceps femoris (BF). Changes in muscle phasing were assessed by comparing the probability of muscle activity in forward and backward pedaling throughout 18 pedaling cycles. Paretic uniarticular muscles (VM and SOL) showed phase-advanced activity in backward versus forward pedaling, whereas the corresponding neurologically intact muscles showed little to no phasing change. Paretic biarticular muscles were less likely than neurologically intact biarticular muscles to display phasing changes in backward pedaling. Paretic RF displayed no phase change during backward pedaling, and paretic BF displayed no consistent adaptation to backward pedaling. Paretic SM was the only muscle to display backward/forward phase changes that were similar to the neurologically intact group. We conclude that paretic uniarticular muscles are more susceptible and paretic biarticular muscles are less susceptible to direction-dependent phase shifts, consistent with altered sensory integration and impaired cortical control of locomotion.

Adaptation, Physiological↗
PubMed2002

Executive dysfunction in geriatric depression.

OBJECTIVE: The purpose of this study was to characterize the neuropsychological presentation of geriatric depression and to determine whether depression-related executive dysfunction is more pronounced during advanced age. METHOD: The attention and executive functioning of 40 adults with major depression were compared with those of 40 healthy comparison subjects; 20 subjects were 20-60 years old, and 20 were > or =61 years. It was hypothesized that depressed subjects, regardless of age, would perform more poorly than comparison subjects on both attention and executive tasks but that the older depressed adults would evidence significantly greater impairment on executive measures. RESULTS: A significant interaction between age and depressive status was noted for tasks of executive functioning, while no age-depression interaction was found for tasks of selective or sustained attention. Older depressed adults demonstrated the slowest psychomotor speed and the poorest performance on tasks requiring set shifting, problem solving, and initiation of novel responses. CONCLUSIONS: Patients with late-life depression have significant impairment in executive functioning. These findings can guide the development of stimulated functional neuroimaging paradigms that may clarify the pathophysiology of geriatric depression. Timely identification of attentional and executive processes fundamental to the daily functioning of depressed older adults may lead to compensatory strategies that will improve the outcomes of late-life depression.

Adult↗
PubMedDate not supplied

Chronic cognitive disturbances after a single supratentorial lacunar infarct.

OBJECTIVE: At a minimum of 6 months after their stroke, 16 single supratentorial lacunar infarct (SSLI) patients and 16 controls underwent neuropsychological testing. After 6 months, neuropsychological testing was repeated to investigate the robustness and validity of the initial test results. BACKGROUND: An SSLI can cause subtle cognitive disturbances, which could explain the decrease in quality of life often observed in patients with these lesions. It is unclear at which stage after the occurrence of neurologic deficit possible neuropsychological impairment can be interpreted as chronic and at what moment neuropsychological testing can best be performed. METHOD: Patients and controls were administered a specifically developed neuropsychological test battery that included 14 standardized tasks tapping the main cognitive domains. Differences in test-performances between the groups were analyzed by parametric statistics. RESULTS: At both examinations, similar abnormalities were found on five demanding neuropsychological tasks (language, concept shifting, abstraction, incidental memory, and verbal fluency), suggesting a generalized energetic deficiency. CONCLUSIONS: This long-term follow-up study showed evidence of subtle neurocognitive deficits after the occurrence of an SSLI, which are robust after 6 months. These mild cognitive disturbances may explain the decrease in quality of life that patients with an SSLI often experience.

Adult↗
PubMed2001

On conceptualization of a decision support system in health informatics.

A decision support system can be approached from two major disciplinary perspectives, those of information systems science (IS) and artificial intelligence (AI). We present in this study an extended ontology for a decision support system in health informatics, which is founded on experience from related research fields as well as being informed by our case studies. The ontology emphasises the need to cover environmental and contextual variables as an integral part of a decision support systems development methodology. With the addition of these variables, the focus in decision support systems development shifts from a task ontology towards a domain ontology. The results of this study help the system developers to take the system's context into account through the set of defined variables that are linked to the application domain. These variables explicate relevant constructs and present a vocabulary for a decision support system. However, applying the ontology requires a more thorough analysis of the domain and therefore more qualified resources for systems development. This indicates the need to focus more on education and training in health informatics.

Artificial Intelligence↗
PubMed2006

Procedural errors in air traffic control: effects of traffic density, expertise, and automation.

INTRODUCTION: Air traffic management requires operators to frequently shift between multiple tasks and/or goals with different levels of accomplishment. Procedural errors can occur when a controller accomplishes one of the tasks before the entire operation has been completed. The present study had two goals: first, to verify the occurrence of post-completion errors in air traffic control (ATC) tasks; and second, to assess effects on performance of medium term conflict detection (MTCD) tools. METHODS: There were 18 military controllers who performed a simulated ATC task with and without automation support (MTCD vs. manual) in high and low air traffic density conditions. During the task, which consisted of managing several simulated flights in an enroute ATC scenario, a trace suddenly disappeared "after" the operator took the aircraft in charge, "during" the management of the trace, or "before" the pilot's first contact. RESULTS: In the manual condition, only the fault type "during" was found to be significantly different from the other two. On the contrary, when in the MTCD condition, the fault type "after" generated significantly less errors than the fault type "before." Additionally, automation was found to affect performance of junior controllers, whereas seniors' performance was not affected. DISCUSSION: Procedural errors can happen in ATC, but automation can mitigate this effect. Lack of benefits for the "before" fault type may be due to the fact that operators extend their reliance to a part of the task that is unsupported by the automated system.

Accidents, Aviation↗