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PubMedDate not supplied

Branched-chain amino acid supplementation during 30-km competitive run: mood and cognitive performance.

It has been suggested that an elevated concentration of the neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) in specific areas of the brain may contribute to the development of central/mental fatigue during and after sustained exercise. Supplementation with branched-chain amino acids (BCAAs) should prevent the exercise-induced increase in the plasma concentration ratio of free tryptophan to other large neutral amino acids (including BCAAs) and thereby prevent an elevation in the level of 5-HT in the brain. In this study, subjects were given either a mixture of BCAAs in a carbohydrate solution or a placebo drink that contained only carbohydrates during a 30-km cross-country race. Several tasks to measure cognitive performance were performed before and after the race. When subjects were supplied with BCAAs, their performance in the different parts of the color-word test (words, colors and color words) was improved by an average of 3-7% (p < 0.05) after exercise, whereas there was no difference in performance before and after exercise in the subjects who were given the placebo. Furthermore, the experimental group, supplied with BCAAs, maintained their performance in the shape-rotation and figure-identification tasks, whereas an impairment in performance in these tests by 25% (p < 0.05) and 15% (p < 0.05), respectively, was found in the subjects who received the placebo. Thus, BCAA supplementation seemed to have an effect on the more complex tasks, whereas no effect could be detected on the less demanding tasks. However, an intake of BCAAs during exercise modified only slightly the exercise-induced changes in mood.

Adult↗

PubMed1989

Human brainstem auditory evoked potentials fail to provide evidence of efferent modulation of auditory input during attentional tasks.

Efferent modulation of auditory input at the level of the brainstem during attention-demanding tasks has been described in animal studies. Attempts to demonstrate these effects in humans have produced conflicting results, however. These studies are reviewed with particular reference to those animal experiments that have demonstrated peripheral effects. The human experiments have used a number of attentional conditions which have not been related either to each other or to the successful animal work. Two of the most important conditions in these studies--the use of an intermodal attention task and the manipulation of attentional states--have been examined rarely or not at all in the human research. Two experiments were conducted to investigate the possibility of attention-related effects on the human brainstem auditory evoked potential. These experiments were designed to examine experimental conditions common to both successful and unsuccessful attempts to demonstrate attention-driven efferent modulation at the periphery in humans. Also examined was the gradation of attention effects on efferent modulation demonstrated in animals but never studied in humans. No significant changes in either the latency or the amplitude of the brainstem auditory evoked potential were found in any of the attention-demanding conditions. Results are discussed in terms of psychophysiological theories of attention. Also, the interpretation of the most recent animal work is questioned.

Adolescent↗

PubMed2006

Visuospatial executive function in Turner syndrome: functional MRI and neurocognitive findings.

Turner syndrome is a genetic disorder that results from an abnormal or missing X chromosome in females and is typically associated with impairments in visuospatial, but not verbal, information processing. These visuospatial processing impairments may be exacerbated with increased task demands, such as those engaged during working memory (WM). While previous studies have examined spatial WM function in Turner syndrome, none have directly compared the neural correlates of spatial and verbal WM processes across the encoding, maintenance and retrieval phases. We employed both neurocognitive assessments and functional MRI (fMRI) to examine the neural circuitry underlying both verbal and visuospatial WM functions in individuals with Turner syndrome and normal controls. We furthermore examined the vulnerability of task-related fMRI activation to distracters presented during WM maintenance. Fifteen healthy female volunteers and eight individuals with Turner syndrome performed a delayed-response WM task during fMRI scanning. Neurocognitive tests revealed impaired performance across both verbal and spatial domains in Turner syndrome, with greater impairment on tasks with WM demands. Frontoparietal regions in controls showed significantly sustained levels of activation during visuospatial WM. This sustained activation was significantly reduced in the group with Turner syndrome. Domain-specific activation of temporal regions, in contrast, did not differ between the two groups. Sensory distraction during the WM maintenance phase did not differentially alter frontoparietal activation between the two groups. The results reveal impaired frontoparietal circuitry recruitment during visuospatial executive processing in Turner syndrome, suggesting a significant role for the X chromosome in the development of these pathways.

Adolescent↗

PubMed2000

Evidence for interactive locomotor and oculomotor deficits in cerebellar patients during visually guided stepping.

Eight patients suffering from primary cerebellar degenerative diseases undertook a walkway task, demanding precise foot placement at each step, and a visual fixation task, requiring only eye movements. Step cycle and horizontal eye movements were recorded throughout the tasks and compared to those of healthy adults (including age- and sex-matched controls). Cerebellar patients displayed both locomotor and oculomotor deficits. Increases in duration of the stance, swing and double support phases of the step cycle were all shown to contribute to ataxic gait. Dysmetric saccades to fixate the footfall targets were seen more frequently in patients than in controls. These hypometric saccades were followed by one or more corrective saccades (patients: >45% accompanied by one or more corrective saccades; controls: <10% accompanied by a single corrective saccade). Similarities between the oculomotor deficits displayed by patients during the visual fixation task and when walking indicate that the latter are not merely a consequence of ataxic gait. The existence of several links between these locomotor and oculomotor deficits provides evidence for considerable interaction between the two control systems in the production of patterned eye and stepping movements. These results also suggest that the cerebellum plays an active role in the co-ordination of visually guided eye and limb movements during visually guided stepping.

Adult↗

PubMed2006

Prosodic processing by children: an fMRI study.

Prosodic information in the speech signal carries information about linguistic structure as well as emotional content. Although children are known to use prosodic information from infancy onward to assist linguistic decoding, the brain correlates of this skill in childhood have not yet been the subject of study. Brain activation associated with processing of linguistic prosody was examined in a study of 284 normally developing children between the ages of 5 and 18 years. Children listened to low-pass filtered sentences and were asked to detect those that matched a target sentence. fMRI scanning revealed multiple regions of activation that predicted behavioral performance, independent of age-related changes in activation. Likewise, age-related changes in task activation were found that were independent of differences in task accuracy. The overall pattern of activation is interpreted in light of task demands and factors that may underlie age-related changes in task performance.

Adolescent↗

PubMed1989

Contextual information and temporal terms.

We report an experiment designed to identify how contextual information can influence children's performance on an experimental task involving temporal terms. Crain (1982) reported improved performance on a comprehension task when subjects were provided with contextual information, and he suggested that the improvement was due to satisfaction of presuppositions. However, this contextual information might have served to simplify task demands by providing prior information concerning an important aspect of the task. The present study distinguishes these factors by incorporating contextual information into the subordinate clause of the test sentences in a comprehension experiment (to satisfy presupposions) or into the main clause (to provide comparable prior information without satisfying presuppositions). We conclude that contextual information results in a significant improvement only when such information can be used to satisfy presuppositions.

Child Language↗

PubMed1994

Psychology of computer use: XXXII. Computer screen-savers as distractors.

The differences in performance of 16 male and 16 female undergraduates on three cognitive tasks were investigated in the presence of visual distractors (computer-generated dynamic graphic images). These tasks included skilled and unskilled proofreading and listening comprehension. The visually demanding task of proofreading (skilled and unskilled) showed no significant decreases in performance in the distractor conditions. Results showed significant decrements, however, in performance on listening comprehension in at least one of the distractor conditions.

Adolescent↗

PubMed2005

A systematic investigation of the functional neuroanatomy of auditory and visual phonological processing.

Neuroimaging studies of auditory and visual phonological processing have revealed activation of the left inferior and middle frontal gyri. However, because of task differences in these studies (e.g., consonant discrimination versus rhyming), the extent to which this frontal activity is due to modality-specific linguistic processes or to more general task demands involved in the comparison and storage of stimuli remains unclear. An fMRI experiment investigated the functional neuroanatomical basis of phonological processing in discrimination and rhyming tasks across auditory and visual modalities. Participants made either "same/different" judgments on the final consonant or rhyme judgments on auditorily or visually presented pairs of words and pseudowords. Control tasks included "same/different" judgments on pairs of single tones or false fonts and on the final member in pairs of sequences of tones or false fonts. Although some regions produced expected modality-specific activation (i.e., left superior temporal gyrus in auditory tasks, and right lingual gyrus in visual tasks), several regions were active across modalities and tasks, including posterior inferior frontal gyrus (BA 44). Greater articulatory recoding demands for processing of pseudowords resulted in increased activation for pseudowords relative to other conditions in this frontal region. Task-specific frontal activation was observed for auditory pseudoword final consonant discrimination, likely due to increased working memory demands of selection (ventrolateral prefrontal cortex) and monitoring (mid-dorsolateral prefrontal cortex). Thus, the current study provides a systematic comparison of phonological tasks across modalities, with patterns of activation corresponding to the cognitive demands of performing phonological judgments on spoken and written stimuli.

Acoustic Stimulation↗

PubMed2002

Emergent polyethism as a consequence of increased colony size in insect societies.

A threshold reinforcement model in insect societies is explored over a range of colony sizes and levels of task demand to examine their effects upon worker polyethism. We find that increasing colony size while keeping the demand proportional to the colony size causes an increase in the differentiation among individuals in their activity levels, thus explaining the occurrence of elitism (individuals that do a disproportionately large proportion of work) in insect societies. Similar results were obtained when the overall work demand is increased while keeping the colony size constant. Our model can reproduce a whole suite of distributions of the activity levels among colony members that have been found in empirical studies. When there are two tasks, we demonstrate that increasing demand and colony size generates highly specialized individuals, but without invoking any strict assumptions about spatial organization of work or any inherent abilities of individuals to tackle different tasks. Importantly, such specialization only occurs above a critical colony size such that smaller colonies contain a set of undifferentiated equally inactive individuals while larger colonies contain both active specialists and inactive generalists, as has been found in empirical studies and is predicted from other theoretical considerations.

Animals↗

PubMed2004

Intelligence and working memory systems: evidence of neural efficiency in alpha band ERD.

Starting from the well-established finding that brighter individuals display a more efficient brain function when performing cognitive tasks (i.e., neural efficiency), we investigated the relationship between intelligence and cortical activation in the context of working memory (WM) tasks. Fifty-five male (n=28) and female (n=27) participants worked on (1) a classical forward digit span task demanding only short-term memory (STM), (2) an attention-switching task drawing on the central executive (CE) of WM and (3) a WM task involving both STM storage and CE processes. During performance of these three types of tasks, cortical activation was quantified by the extent of Event-Related Desynchronization (ERD) in the alpha band of the human EEG. Correlational analyses revealed associations between the amount of ERD in the upper alpha band and intelligence in several brain regions. In all tasks, the males were more likely to display the negative intelligence-cortical activation relationship. Furthermore, stronger associations between ERD and intelligence were found for fluid rather than crystallized intelligence. Analyses also point to topographical differences in neural efficiency depending on sex, task type and the associated cognitive subsystems engaged during task performance.

Adolescent↗

PubMed2006

Divergence of categorical and coordinate spatial processing assessed with ERPs.

The spatial relation between two objects may be described either precisely or more coarsely in abstract terms, denoted as coordinate and categorical descriptions, respectively. These descriptions may reflect the outcomes of two spatial coding processes, which are realized in the left- and right-hemisphere. Support for this account comes from visual field effects in categorical and coordinate judgment tasks and from patient studies. In the current study, this hypothesis was tested by using event-related potentials (ERPs) and source localization. ERPs yield information about the processing stage at which the hypothesized categorical and coordinate processing diverge due to different task demands, especially in our S1-S2 version of the Bar Dot task. A centrally presented Bar Dot (S1) was followed after 2.5s by a second one (S2) in the left or right visual field; participants had to judge whether S2 matched S1 at the categorical, or, in a second task, at the coordinate level. Behavioral measures revealed a left-field advantage in the coordinate task that was absent in the categorical task. S1s elicited stronger early and late bilateral posterior responses in the coordinate than in the categorical task, possibly related to a compensatory strategy at the level of encoding and spatial memory. S2s elicited only stronger early contralateral responses, and stronger late right-hemisphere responses in the categorical task. It is proposed that the left-field advantage in the coordinate task may be due to differences in spatial resolution in perceptual encoding of the left- and right-hemispheres that are largely unaffected by the task at hand.

Adult↗

PubMed2003

Dissociations of personally significant and task-relevant distractors inside and outside the focus of attention: a combined behavioral and psychophysiological study.

Studies of attentional capture by personally significant stimuli have reached inconsistent results, possibly because of improper control of the participants' attention. In the present study, the authors controlled visual attention by using a Stroop-like task. Participants responded to a central color and ignored a word presented either centrally (i.e., at the focus of attention) or peripherally (i.e., outside the focus of attention). Central words led to slower reaction times and larger orienting responses for significant items than for neutral items. These effects largely disappeared when the words appeared in a peripheral location. The peripheral words interfered with performance when they were relevant to task demands. These results indicate that there is a fundamental difference between task-relevant words and personally significant words: The former capture attention even when presented peripherally, whereas the latter do not.

Attention↗

PubMedDate not supplied

Gender differences in patterns of dynamic cardiovascular regulation.

The purpose of this research was to examine the role of gender in hemodynamic response patterns to stress. Sixty-four male and 55 female young adults were administered a protocol of rest, mental arithmetic, video game, and anger recall interview while blood pressure, heart rate, and cardiac impedance measures were obtained. Men had higher levels of systolic blood pressure and cardiac output and greater reactivity to tasks, indexed by increases in cardiac output and diastolic blood pressure. Extreme groups of myocardial and vascular reactors were formed from cardiac output and total peripheral resistance change scores during mental arithmetic. The myocardial reactors exhibited greater sensitivity to task demands, whereas vascular reactors exhibited comparable total peripheral resistance increases to all tasks. Vascular reactors exhibited greater diastolic blood pressure reactivity than myocardial reactors. Future studies should address the predictive validity of these reactor patterns for the subsequent development of coronary heart disease.

Adult↗

PubMed2005

Effect of template complexity on visual search and dual-task performance.

Even dissimilar tasks interfere with one another when done together. We used visual search to examine the underlying cause of such interference. In many models, visual search is a process of biased competition controlled by a template describing the target to be sought. When the display is processed, matching against this template guides attention to the target. We show that increasing template complexity increased interference with a dissimilar concurrent task, story memory. This result was independent of reaction time: Increases in template complexity were associated with no increase in search time in Experiment 1 and with a decrease in search time in Experiment 2. The results show that the dual-task demands of visual search reflect the complexity of the template used in task control, and that this factor can be isolated from other sources of difficulty.

Adolescent↗

PubMed1999

Critical decline in fine motor hand movements in human aging.

BACKGROUND: Slowing of motor movements in human aging is a well-known occurrence, but its biologic basis is poorly understood. Reliable quantitation may refine observations of this phenomenon to better aid research on this entity. METHODS: A panel equipped with timing sensors under computer control was used to measure upper extremity movement times in two groups of healthy individuals: adults younger than 60 years of age (n = 56; range, 18-58 years) and adults older than 60 years of age (n = 38; range, 61-94 years). RESULTS: Fine motor performance was better in the dominant hand (p = 0.0007) regardless of age. Adult and aged groups differed on two basic timing measures, which reflect coarse motor and fine motor performance (p < 0.0001). There were no gender differences on either measure. There was a strong effect of task difficulty with age on coarse motor (p < 0.01) and fine motor (p < 0.0001) measures. The fine motor measure of hand performance in healthy individuals correlated in a nonlinear fashion with age for more difficult tasks (r2 = 0.63) but showed a simple linear relation for less-demanding tasks (r2 = 0.5). CONCLUSION: This technique sensitively detects age-related motor performance decline in humans. There may be a critical period in late midlife when fine motor performance decline either begins or abruptly worsens.

Adolescent↗

PubMed1997

Mood and cognitive performance improved by a small amount of alcohol given with a lunchtime meal.

Three drinks containing 0 g (no alcohol, NA), 8 g (low alcohol, LA) and 24 g (high alcohol, HA) of alcohol were formulated which were found to be indistinguishable from one another in sip-and-swallow triangle tests. In a second study, conducted according to a within-subjects design, 14 healthy human volunteers consumed these drinks as part of a small lunchtime meal, in counterbalanced order on 3 different days. They also completed a battery of cognitive tasks, together with mood ratings, before lunch and during the 4 h following lunch. Compared with NA, LA (approximately 0.12 g/kg) significantly increased hit rate on a difficult rapid information processing vigilance task. In contrast, HA (approximately 0.35 g/kg) tended to impair performance of this task. There were no reliable effects of alcohol on performance on less demanding tasks. The low dose of alcohol also improved mood (for example, it significantly reduced tension and uncertainty), suggesting that the improvement in task performance was mediated by the calming or sedative effects of the alcohol. Volunteers did detect alcohol in the HA, but not the LA drink, when they consumed the full drink, confirming the difficulty of disguising the administration of alcohol.

Adult↗

PubMed2005

Implicit and explicit processing in deep dyslexia: Semantic blocking as a test for failure of inhibition in the phonological output lexicon.

The failure of inhibition hypothesis posits a theoretical distinction between implicit and explicit access in deep dyslexia. Specifically, the effects of failure of inhibition are assumed only in conditions that have an explicit selection requirement in the context of production (i.e., aloud reading). In contrast, the failure of inhibition hypothesis proposes that implicit processing and explicit access to semantic information without production demands are intact in deep dyslexia. Evidence for intact implicit and explicit access requires that performance in deep dyslexia parallels that observed in neurologically intact participants on tasks based on implicit and explicit processes. In other words, deep dyslexics should produce normal effects in conditions with implicit task demands (i.e., lexical decision) and on tasks based on explicit access without production (i.e., forced choice semantic decisions) because failure of inhibition does not impact the availability of lexical information, only explicit retrieval in the context of production. This research examined the distinction between implicit and explicit processes in deep dyslexia using semantic blocking in lexical decision and forced choice semantic decisions as a test for the failure of inhibition hypothesis. The results of the semantic blocking paradigm support the distinction between implicit and explicit processing and provide evidence for failure of inhibition as an explanation for semantic errors in deep dyslexia.

Analysis of Variance↗

PubMed2001

Effects of varying task constraints on solutions to joint coordination in a sit-to-stand task.

The question of how multijoint movement is controlled can be studied by discovering how the variance of joint trajectories is structured in relation to important task-related variables. In a previous study of the sit-to-stand task, for instance, variations of body segment postures that leave the position of the body's center of mass (CM) unchanged were significantly greater than variations of body segment posture that varied the CM position. The present experiments tested the hypothesis that such structuring of joint configuration variability is accentuated when the mechanical or perceptual task demands are made more challenging. Six subjects performed the sit-to-stand task without vision (eyes closed), either on a normal or on a narrow support surface. An additional constraint on the postural task was introduced in a third condition by requiring subjects to maintain light touch (less than 1 N) with the fingertips while coming to a standing position on the narrow base of support. The joint configurations observed at each point in normalized time were analyzed with respect to trial-to-trial variability. The task variables CM and head position were used to define goal-equivalent sets of joint configurations ("uncontrolled manifolds," UCMs) within which variation of joint configuration leaves the task variables unchanged. The variability of joint configurations across trials was decomposed into components that did not affect (within the UCM) and that did affect (orthogonal to the UCM) the values of these task variables. Our results replicate the earlier finding of much larger variability in directions of joint space that leave the CM unchanged compared with directions that affect CM position. This effect was even more pronounced here than in the previous experiment, probably because of the more difficult perceptual conditions in the current study (eyes closed). When the mechanical difficulty of the task was increased, the difference between the two types of joint variability was further accentuated, primarily through increase in goal-equivalent variance. This provides evidence for the hypothesis that under challenging task constraints increased variability is selectively directed into task-irrelevant degrees of freedom. Because differential control along different directions of joint space requires coordination among joint angles, this observation supports the view that the CNS responds to increased task difficulty through enhanced coordination among degrees of freedom. The adaptive nature of this coordination is further illustrated by the similar enhanced use of goal-equivalent joint combinations to achieve a stable CM position when subjects stood up under the additional constraint of maintaining light touch with the fingertips. This was achieved by channeling goal-equivalent variability into different directions of joint configuration space.

Adult↗