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PubMed2002

Cerebral lateralization for motor tasks in simulated microgravity a transcranial Doppler technique for astronauts.

In Space, central cognitive operations are unaffected but humans are slower in perceptual-motor performance. Transcranial Doppler ultrasonography was used to monitor blood flow velocity in both middle cerebral arteries during unilateral and bilateral fingers' movements before, during and after -6 degrees 24 hours of head-down tilt (HDT) in 14 (8 males and 6 females) subjects. Physiologic hemisphere dominance was assessed by breath-holding test. There was a significant main effect of motor task, F(4, 328) = 16.05, p<0.00000001, MSe = 48.2. There was a gender vs head-position interaction F(3,246) = 4.90 p<0.002) MSe = 120. At pre-HDT females were right lateralized and males were left lateralized. A left shift in lateralization pattern was seen during 24hrs-HDT for both genders. There was a significant main effect of breath-holding test and a breath-holding test vs head position vs motor task interaction. HDT alters cerebral lateralization for motor control and this may be responsible for slowing in perceptual-motor performance in Space. TCD monitoring may be required for motor performance tasks in Space.

Journal Article↗

PubMed1995

Effect of unweighting on skeletal muscle use during exercise.

Exercise-induced spin-spin relaxation time (T2) shifts in magnetic resonance (MR) images were used to test the hypothesis that more muscle would be used to perform a given submaximal task after 5 wk of unweighting. Before and after unilateral lower limb suspension (ULLS), 7 subjects performed 5 sets of 10 unilateral concentric actions with the quadriceps femoris muscle group (QF) at each of 4 loads: 25, 40, 55, and 70% of maximum. T2-weighted MR images of the thigh were collected at rest and after each relative load. ULLS elicited a 20% decrease in strength of the left unweighted QF and a 14% decrease in average cross-sectional area (CSA) with no changes in the right weight-bearing QF. Average CSA of the left or right QF showing exercise-induced T2 shift increased as a function of exercise intensity both before and after ULLS. On average, 12 +/- 1, 15 +/- 2, 18 +/- 2, and 22 +/- 1 cm2 of either QF showed elevated T2 for the 25, 40, 55, and 70% loads, respectively, before ULLS. Average CSA of the left but not the right QF, showing elevated T2 after ULLS, was increased to 16 +/- 2, 23 +/- 3, 31 +/- 7, and 39 +/- 5 cm2, respectively. The results indicated that unweighting increased exercise-induced T2 shift in MR images, presumably due to greater muscle mass involvement in exercise after than before unweighting, suggesting a change in motor control.

Casts, Surgical↗

PubMed1995

A single-photon emission computed tomographic study of anosognosia in Alzheimer's disease.

OBJECTIVE: To examine the presence of specific regional cerebral blood flow correlates of anosognosia in patients with probable Alzheimer's disease. DESIGN: Case series, group comparisons. SETTING: Ambulatory care referral center. PATIENTS: Twelve patients with probable Alzheimer's disease and anosognosia and 12 patients with probable Alzheimer's disease without anosognosia who were matched for age, duration of illness, and cognitive impairments. MAIN OUTCOME MEASURES: Single-photon emission computed tomographic scan studies with technetium Tc 99m hexamethylpropylene-amine oxime and regional cerebral blood flow measurements. RESULTS: Patients with Alzheimer's disease and anosognosia showed significant blood flow deficits in the frontal inferior and superior (dorsal) areas of the right hemisphere. On the other hand, no significant between-group differences were found in depression scores and neuropsychological tasks that assessed verbal and visual memory, verbal comprehension, naming, verbal fluency, auditory attention, abstract reasoning, and set-shifting abilities. CONCLUSIONS: Our study demonstrates that anosognosia may not be related to deficits in specific cognitive domains, but it may result from dysfunction of the right frontal lobe.

Aged↗

PubMed2005

Costs of managing urinary and faecal incontinence in a sub-acute care facility: a "bottom-up" approach.

AIMS: To measure accurately the direct costs of managing urinary and faecal incontinence in the sub-acute care setting. MATERIALS AND METHODS: Prospective observational study was undertaken in two sub-acute care units in a metropolitan hospital. A consecutive series of 29 consecutive patients with urinary and/or faecal incontinence, who were in-patients in a geriatric rehabilitation or sub-acute neurologic unit underwent routine timed voiding protocol, as per usual care. Face-to-face bedside recordings of all incontinence care, with detailed cost analysis, were undertaken. RESULTS: A total of 3,621 occasions of continence care were costed. The median time per 24 hr spent caring for incontinence per patient was 109 min (interquartile range 88-140). Isolated urinary incontinence episodes occurred in 28 patients (96.5%), mixed urinary/faecal incontinence episodes observed in 79.3%, and episodes of pure faecal incontinence were seen in 62%. The median costs of incontinence care in the sub-acute setting was $49AU per 24 hr, the major share ($41) spent on staff wages. The incontinence tasks of toileting assistance, pad changes, bed changes and catheter care were spread evenly across the three 8 hr shifts of duty. CONCLUSIONS: As our population demographics include an increasingly greater portion of the elderly, for whom long term institutional care is becoming relatively more scarce, provision of care in the sub-acute unit that may allow rehabilitation and return to home warrants scrutiny. This is the first study that delineates the costs of managing urinary and faecal incontinence in the sub-acute care setting. Such costs are substantial and place a heavy burden upon night-time carers.

Aged↗

PubMed1995

Effect of practice on laterality in a mental rotation task.

The purpose of the present study was to investigate the effect of practice on the lateralization of mental rotation skills. Forty-six females and 46 males completed four blocks of 64 trials in a lateralized mental rotation task. Results revealed a reduction in reaction time and error rate across blocks, thus demonstrating a practice effect. A shift from a right hemisphere advantage to a left hemisphere advantage across blocks of trials was also found. The results are discussed in terms of their implication for hypotheses linking laterality and training. Practical implications for laterality research are also discussed.

Brain↗

PubMed1996

Neuropsychological impairments and deficits in theory of mind and emotion recognition in a non-autistic boy.

A 9-year-old non-autistic boy revealed marked deficits in visuo-spatial and visuo-motor skills, in planning and organizational capacities and in impulse inhibition. Particular strengths were his verbal comprehension and reasoning abilities. This neuropsychological pattern of assets and deficits fitted the nonverbal learning disability syndrome as described by Rourke (1989). On a battery of Theory of Mind (TOM) and emotion recognition tests he performed rather poor on several first-order TOM tasks and on all second-order TOM and emotion-matching tasks, compared to samples of autistic and normal subjects. It is suggested that his visuo-spatial and cognitive shifting deficits account for his social cognitive failures, while his superior verbal skills protect him from severe social handicaps.

Affect↗

PubMed2006

Striatal dopamine release during performance of executive functions: A [(11)C] raclopride PET study.

To date, while the contribution of the striatum in executive processes is well documented, the role played by striatal dopamine during tasks requiring executive functions is still unknown. We used D2-dopamine receptor ligand [(11)C] raclopride PET in healthy subjects while performing the Montreal Card Sorting Task (MCST). We observed a striatal reduction in [(11)C] raclopride binding potential during planning of a set-shift when compared with matching according to an ongoing rule. These findings suggest that striatal dopamine neurotransmission increases significantly during the performance of specific executive processes confirming previous evidence of striatal activation during fMRI studies. The present observation may provide some insights on the origin of cognitive deficits underlying certain neurological disorders associated with dopamine dysfunction, such as Parkinson's disease.

Adult↗

PubMed2006

Developmental neural networks in children performing a Categorical N-Back Task.

The prefrontal and temporal networks subserving object working memory tasks in adults have been reported as immature in young children; yet children are adequately capable of performing such tasks. We investigated the basis of this apparent contradiction using a complex object working memory task, a Categorical n-back (CN-BT). We examined whether the neural networks engaged by the CN-BT in children consist of the same brain regions as those in adults, but with a different magnitude of activation, or whether the networks are qualitatively different. Event-related fMRI was used to study differences in brain activation between healthy children ages 6 and 10 years, and young adults (20-28 years). Performance accuracy and RTs in 10-year-olds and adults were comparable, but the performance in 6-year-olds was lower. In adults, the CN-BT was highly effective in engaging the bilateral (L>R) ventral prefrontal cortex, the bilateral fusiform gyrus, posterior cingulate and precuneus, thus suggesting an involvement of the ventral visual stream, with related feature extraction and semantic labeling strategies. In children, the brain networks were distinctly different. They involved the premotor and parietal cortex, anterior insula, caudate/putamen, and the cerebellum, thus suggesting a predominant involvement of the visual dorsal and sensory-motor pathways, with related visual-spatial and action cognitive strategies. The findings indicate engagement of developmental networks in children reflecting task-effective brain activation. The age-related pattern of fMRI activation suggests a working hypothesis of a developmental shift from reliance on the dorsal visual stream and premotor/striatal/cerebellar networks in young children to reliance on the ventral prefrontal and inferior temporal networks in adults.

Adult↗

PubMed2002

Improvement of learning processes following chronic systemic administration of modafinil in mice.

This study was aimed at determining the effects of a chronic modafinil intraperitoneal administration on the rate of learning in a series of five serial spatial discrimination reversals (SSDR) in a T-maze. Results showed that a daily modafinil administration at 64 mg/kg but not at 32 mg/kg induced a faster learning rate as compared to controls. This learning improvement in experimental mice was due to the faster emergence of a win-stay rule over days of testing. In contrast, a second experiment showed that the same modafinil treatment had no significant effect on contingently reinforced alternation rates over five successive days of testing, as compared to controls. Thus, the results show that modafinil spared the ability to shift responses over trials and consequently, that the use of the win-stay rule to solve the SSDR task observed in modafinil-treated animals is due to an improvement of learning processes.

Animals↗

PubMedDate not supplied

Age-related working memory deficits in the allocentric place discrimination task: possible involvement in cholinergic dysfunction.

It is well known that learning and memory ability declines with aging. Age-related long-term changes in learning and memory ability in rats were investigated with the place navigation task and the allocentric place discrimination task (APDT) in a water maze using the same animals for each task. In a working memory place navigation task, aged animals could learn the location of the platform as well as when they were young, although strategy shifts were observed. In contrast, accuracy in the APDT significantly declined from 90% to 65% with aging. This impairment was ameliorated by an acetylcholine esterase inhibitor physostigmine at 22-23 months old. No amelioration was, however, detected in the same animals tested when they further aged to 26-27 months old. These results suggest that the APDT performance is sensitive to age-related memory deficits and that this may be due to the cholinergic dysfunction.

Aging↗

PubMed2002

Delayed onset of inhibition of return in schizophrenia.

Peripheral visual cues occuring before a subsequent target result in an almost immediate facilitatory and then a later inhibitory effect on target detection. In a detailed parametric investigation, the authors compared schizophrenic subjects (SCZ) and control subjects (CONT) to examine whether they showed any differences in the time course of these nonpredictive peripheral cuing effects. Subjects fixated a central position and made saccadic responses to visual targets. Targets were presented 10 degrees to the left or right of fixation and were preceded at various time intervals by visual cues. Targets occurred with equal probability in either the same position as the cue or in the opposite, uncued location, and 10 delay periods were used corresponding to stimulus onset asynchronies (SOAs) of 66, 79, 106, 133, 159, 226, 305, 505, 705, and 1000 ms. All subjects showed facilitation for short cue-target delays and inhibition of return (IOR) for longer delays. SCZ, however, showed an apparent shift in the time course of cuing effects in the form of a delayed onset of IOR. Using a task of reflexive orienting, these results support findings of a delayed rather than an absent inhibitory process in medicated SCZ.

Adult↗

PubMed2003

The time course of spoken word learning and recognition: studies with artificial lexicons.

The time course of spoken word recognition depends largely on the frequencies of a word and its competitors, or neighbors (similar-sounding words). However, variability in natural lexicons makes systematic analysis of frequency and neighbor similarity difficult. Artificial lexicons were used to achieve precise control over word frequency and phonological similarity. Eye tracking provided time course measures of lexical activation and competition (during spoken instructions to perform visually guided tasks) both during and after word learning, as a function of word frequency, neighbor type, and neighbor frequency. Apparent shifts from holistic to incremental competitor effects were observed in adults and neural network simulations, suggesting such shifts reflect general properties of learning rather than changes in the nature of lexical representations.

Artificial Intelligence↗

PubMedDate not supplied

Multi-oscillatory control of circadian rhythms in human performance.

Circadian rhythms are known to exist in many measures of human performance efficiency as well as in physiological processes. The demands of a task, and in particular its 'working memory' load, play a large part in determining the time of day at which it is best performed. Furthermore, task demands may affect the speed with which performance rhythms adjust to the altered sleep/wake schedules occasioned by shift-work and rapid time-zone transitions. These differences in rate of adjustment may be explained by a similar multi-oscillatory model to those proposed for physiological rhythms. These assume any given circadian rhythm to be jointly controlled by two endogenous oscillators. The first is thought to be relatively immune to exogenous factors and to control the temperature rhythm, while the second is thought to be more influenced by exogenous factors and to have the major role in governing the sleep/wake cycle. Normally, the pronounced 24-h time cues, or 'zeitgebers', in our environment result in both oscillators, and hence all circadian rhythms, running with a period of 24 h. However, under altered sleep/wake schedules, and in conditions of temporal isolation, the temperature rhythm and sleep/wake cycle may separate from one another and run with distinctly different periods. When such 'internal desynchronization' occurs, other physiological rhythms have been found to run in synchrony with one or other of these two functions. This finding forms the basis of current multi-oscillatory models. However, studies of abnormal sleep/wake schedules suggest that the rhythm in working memory performance may sometimes separate from both the sleep/wake cycle and temperature rhythm by running with a period of less than 24 h. We have investigated this possibility here and our results indicate control of working memory performance rhythms by a previously unidentified oscillator with an autonomous period of about 21 h.

Adult↗

PubMed1983

A refutation of the hypothesis of the superfidelity of caricatures relative to photographs.

The experiment was designed to test the hypothesis that caricatures, relative to photographs, are 'superfaithful' carriers of information for facial recognition. Subjects were shown fifteen picutres of people's faces and were then asked to pick those same people out of a set of fifty-four pictures. There were three sets of pictures: caricatures, profile-view photographs, and three-quarter-view photographs. There were nine groups of subjecs: for three groups the exposure and test stimuli were in the same medium, for six groups the test stimuli were in one of the media not previously seen. Points were scored for the number of people correctly identified and the number of false positives. Facial recognition within medium was very good, but was seriously disrupted by any medium shift, especially those involving caricatures. It is argued that the superfidelity of caricature may be manifest only when the task involves recognition of actual persons rather than their pictures.

Face↗

PubMed1989

Oral temperature and performance in 8 h and 12 h shifts.

Operators in an 8 h (n = 18) and a 12 h (n = 16) h shift went through an experiment in which oral temperature, disjunctive reaction time (DRT), tapping, logical reasoning, memory and search tasks were measured at 4 h intervals. A performance curve in DRT and in tapping over a 24 h cycle tended to follow the pattern of the body temperature curve. The curves of mental curves were flattened. The values measured in the two groups of Ss revealed differences of statistical significance.

Body Temperature↗

PubMedDate not supplied

Mapping cognition to the brain through neural interactions.

Brain imaging methods, such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), provide a unique opportunity to study the neurobiology of human memory. As these methods can measure most of the brain, it is possible to examine the operations of large-scale neural systems and their relation to cognition. Two neuroimaging studies, one concerning working memory and the other episodic memory retrieval, serve as examples of application of two analytic methods that are optimised for the quantification of neural systems, structural equation modelling, and partial least squares. Structural equation modelling was used to explore shifting prefrontal and limbic interactions from the right to the left hemisphere in a delayed match-to-sample task for faces. A feature of the functional network for short delays was strong right hemisphere interactions between hippocampus, inferior prefrontal, and anterior cingulate cortices. At longer delays, these same three areas were strongly linked, but in the left hemisphere, which was interpreted as reflecting change in task strategy from perceptual to elaborate encoding with increasing delay. The primary manipulation in the memory retrieval study was different levels of retrieval success. The partial least squares method was used to determine whether the image-wide pattern of covariances of Brodmann areas 10 and 45/47 in right prefrontal cortex (RPFC) and the left hippocampus (LGH) could be mapped on to retrieval levels. Area 10 and LGH showed an opposite pattern of functional connectivity with a large expanse of bilateral limbic cortices that was equivalent for all levels of retrieval as well as the baseline task. However, only during high retrieval was area 45/47 included in this pattern. The results suggest that activity in portions of the RPFC can reflect either memory retrieval mode or retrieval success depending on other brain regions to which it is functionally linked, and imply that regional activity must be evaluated within the neural context in which it occurs. The general hypothesis that learning and memory are emergent properties of large-scale neural network interactions is discussed, emphasising that a region can play a different role across many functions and that role is governed by its interactions with anatomically related regions.

Brain↗

PubMed2002

Top-down controlled visual dimension weighting: an event-related fMRI study.

Target detection in visual singleton feature search is slowed when consecutive targets are defined in different visual dimensions. Behavioral data provide evidence that attentional weight needs to be shifted between dimension-specific processing modules. We found similar dimension-specific change effects in a conjunction search task, in which observers searched for an odd-one-out target defined by a unique combination of size and color or, respectively, size and motion direction. Changes of the secondary target dimension (color or motion) across trials, but not target feature changes within a dimension, increased the time required to detect the target. Dimensional change costs were greatly increased for singleton conjunction search compared to singleton feature search. This suggests involvement of top-down control processes in dimensional change in conjunction search, in contrast to stimulus-driven dimensional change in singleton feature search. The functional anatomical correlates of top-down controlled visual dimension changes were investigated in two event-related functional magnetic resonance imaging (fMRI) experiments. In Experiment 1, dimensional change in singleton conjunction search was accompanied by transient activations in a fronto-posterior network of brain areas that was largely non-overlapping with the general network activated during visual search. Experiment 2, which contrasted singleton feature and conjunction search within the same session, revealed a double dissociation in anterior prefrontal cortex: left frontopolar cortex was selectively involved in stimulus-driven dimension changes but not in top-down controlled dimension changes, whereas the reverse was observed in frontomedian cortex.

Adult↗

PubMed2004

Aging-induced shifts from a reliance on sensory input to muscle cocontraction during balanced standing.

BACKGROUND: Peripheral sensation is the most important sensory system in the maintenance of upright posture in all age groups. With aging, visual and somatosensory processing change their prospective contribution to the maintenance of quiet standing, at debated percentages. Aging is associated with a decrease in balance abilities that, in turn, increases the risk of falling. We used force plate data to show that, with aging, while vision plays a significant role in regulating postural stability (PS), the individual's perception of his/her stability becomes more significant than vision. Moreover, under experimental conditions, electromyography (EMG) of the ankle musculature of elderly people reveals the adoption of a different strategy, a cocontraction strategy, with or without visual input. The aim of this study was to look at two distinct age groups to determine whether or not a shift takes place in the sensory modality typically relied on while maintaining PS during a static, postural-related task. METHOD: The participants comprised two groups: a "young" (Y) group of 20 people aged 20-35, and an "old" (O) group of 32 people aged 65-84. The role of vision was tested with regard to two differently sized bases of support. They were tested during quiet upright standing on a single force plate in wide base and then in narrow base conditions. Surface EMG was recorded from the tibialis anterior, soleus, rectus femoris, and semitendinous muscles. RESULTS: The older group differed from the younger group when performing the task under the narrow base condition. When participants stood naturally, our EMG data indicated that, unlike the Y group, the O group used cocontraction around the ankle in order to deal with changing conditions and sensory inputs. Significant increases were found in the area, length, and mean velocity of body sway in the older group as compared with the younger group. DISCUSSION: The visual contribution to postural stabilization is significantly greater in the younger population than in the elderly population. Across the older group, lack of vision seemed to interfere less with PS; however, the EMG data indicated that, unlike the Y group, the O participants used cocontraction around the ankle in order to deal with changing conditions and sensory inputs. CONCLUSION: To cope with the deterioration in their sensory input and processing ability, elderly individuals seemed to have developed a strategy of stiffening and freezing their lower legs during upright standing.

Adult↗