Auditory Reaction Time Task Research Articles

Novel cyclic homogeneous oscillation detection method for high accuracy and specific characterization of neural dynamics.

Determining the presence and frequency of neural oscillations is essential to understanding dynamic brain function. Traditional methods that detect peaks over 1/f noise within the power spectrum fail to distinguish between the fundamental frequency and harmonics of often highly non-sinusoidal neural oscillations. To overcome this limitation, we define fundamental criteria that characterize neural oscillations and introduce the cyclic homogeneous oscillation (CHO) detection method. We implemented these criteria based on an autocorrelation approach to determine an oscillation's fundamental frequency. We evaluated CHO by verifying its performance on simulated non-sinusoidal oscillatory bursts and validated its ability to determine the fundamental frequency of neural oscillations in electrocorticographic (ECoG), electroencephalographic (EEG), and stereoelectroencephalographic (SEEG) signals recorded from 27 human subjects. Our results demonstrate that CHO outperforms conventional techniques in accurately detecting oscillations. In summary, CHO demonstrates high precision and specificity in detecting neural oscillations in time and frequency domains. The method's specificity enables the detailed study of non-sinusoidal characteristics of oscillations, such as the degree of asymmetry and waveform of an oscillation. Furthermore, CHO can be applied to identify how neural oscillations govern interactions throughout the brain and to determine oscillatory biomarkers that index abnormal brain function.

The role of general cognitive skills in integrating visual and linguistic information during sentence comprehension: individual differences across the lifespan

Individuals exhibit massive variability in general cognitive skills that affect language processing. This variability is partly developmental. Here, we recruited a large sample of participants (N = 487), ranging from 9 to 90 years of age, and examined the involvement of nonverbal processing speed (assessed using visual and auditory reaction time tasks) and working memory (assessed using forward and backward Digit Span tasks) in a visual world task. Participants saw two objects on the screen and heard a sentence that referred to one of them. In half of the sentences, the target object could be predicted based on verb-selectional restrictions. We observed evidence for anticipatory processing on predictable compared to non-predictable trials. Visual and auditory processing speed had main effects on sentence comprehension and facilitated predictive processing, as evidenced by an interaction. We observed only weak evidence for the involvement of working memory in predictive sentence comprehension. Age had a nonlinear main effect (younger adults responded faster than children and older adults), but it did not differentially modulate predictive and non-predictive processing, nor did it modulate the involvement of processing speed and working memory. Our results contribute to delineating the cognitive skills that are involved in language-vision interactions.

Ways to Improve Multitasking: Effects of Predictability after Single- and Dual-Task Training.

In this study we investigated the effect of predictability on dual-task performance in two experiments. In the first experiment 33 participants separately practiced a continuous tracking task and an auditory reaction time task. Both tasks had a repeating element that made them predictable; in the tracking task this was a repeating segment, and in the auditory task this was an auditory sequence. In addition, one group obtained explicit knowledge about the repeating sequence in the tracking task while the other group trained implicitly. After training, single- and dual-task performance was tested at a post test and retention test. Results showed that predictability only improved performance in the predictable tasks themselves and dual-task costs disappeared for the tracking task. To see whether the task-specific effect of predictability was the results of task prioritization, or because task representations did not have much chance to interact with each other, we conducted a second experiment. Using the same tasks as in Experiment 1, 39 participants now trained both tasks simultaneously. Results largely mirrored those of the first experiment, demonstrating that freed-up resources due to predictability in one task could not be re-invested to improve in the other task. We conclude that predictability has a positive but task-specific effect on dual-task performance.

Influence of post-stroke fatigue on reaction times and corticospinal excitability during movement preparation

ObjectivesReduced corticospinal excitability at rest is associated with post-stroke fatigue (PSF). However, it is not known if corticospinal excitability prior to a movement is also altered in fatigue which may then influence subsequent behaviour. We hypothesized that the levels of PSF can be explained by differences in modulation of corticospinal excitability during movement preparation. Methods73 stroke survivors performed an auditory reaction time task. Corticospinal excitability was measured using transcranial magnetic stimulation. Fatigue was quantified using the fatigue severity scale. The effect of time and fatigue on corticospinal excitability and reaction time was analysed using a mixed effects model. ResultsThose with greater levels of PSF showed reduced suppression of corticospinal excitability during movement preparation and increased facilitation immediately prior to movement onset (β = −0.0066, t = −2.22, p = 0.0263). Greater the fatigue, slower the reaction times the closer the stimulation time to movement onset (β = 0.0024, t = 2.47, p = 0.0159). ConclusionsLack of pre-movement modulation of corticospinal excitability in high fatigue may indicate poor sensory processing supporting the sensory attenuation model of fatigue. SignificanceWe take a systems-based approach and investigate the motor system and its role in pathological fatigue allowing us to move towards gaining a mechanistic understanding of chronic pathological fatigue.

Additive Effects of Prior Knowledge and Predictive Visual Information in Improving Continuous Tracking Performance.

Visual information and prior knowledge represent two different sources of predictability for tasks which each have been reported to have a beneficial effect on dual-task performance. What if the two were combined? Adding multiple sources of predictability might, on the one hand, lead to additive, beneficial effects on dual-tasking. On the other hand, it is conceivable that multiple sources of predictability do not increase dual-task performance further, as they complicate performance due to having to process information from multiple sources. In this study, we combined two sources of predictability, predictive visual information and prior knowledge (implicit learning and explicit learning) in a dual-task setup. 22 participants performed a continuous tracking task together with an auditory reaction time task over three days. The middle segment of the tracking task was repeating to promote motor learning, but only half of the participants was informed about this. After the practice blocks (day 3), we provided participants with predictive visual information about the tracking path to test whether visual information would add to beneficial effects of prior knowledge (additive effects of predictability). Results show that both predictive visual information and prior knowledge improved dual-task performance, presented simultaneously or in absence of each other. These results show that processing of information relevant for enhancement of task performance is unhindered by dual-task demands.

Navigating with peripheral field loss in a museum: learning impairments due to environmental complexity

BackgroundPrevious research has found that spatial learning while navigating in novel spaces is impaired with extreme restricted peripheral field of view (FOV) (remaining FOV of 4°, but not of 10°) in an indoor environment with long hallways and mostly orthogonal turns. Here we tested effects of restricted peripheral field on a similar real-world spatial learning task in an art museum, a more challenging environment for navigation because of valuable obstacles and unpredictable paths, in which participants were guided along paths through the museum and learned the locations of pieces of art. At the end of each path, participants pointed to the remembered landmarks. Throughout the spatial learning task, participants completed a concurrent auditory reaction time task to measure cognitive load.ResultsUnlike the previous study in a typical hallway environment, spatial learning was impaired with a simulated 10° FOV compared to a wider 60° FOV, as indicated by greater average pointing error with restricted FOV. Reaction time to the secondary task also revealed slower responses, suggesting increased attentional demands.ConclusionsWe suggest that the presence of a spatial learning deficit in the current experiment with this level of FOV restriction is due to the complex and unpredictable paths traveled in the museum environment. Our results also convey the importance of the study of low-vision spatial cognition in irregularly structured environments that are representative of many real-world settings, which may increase the difficulty of spatial learning while navigating.

Does narrative drive dynamic attention to a prolonged stimulus?

Attention in the “real world” fluctuates over time, but these fluctuations are hard to examine using a timed trial-based experimental paradigm. Here we use film to study attention. To achieve short-term engagement, filmmakers make use of low-level cinematic techniques such as color, movement and sound design to influence attention. To engage audiences over prolonged periods of time, narrative structure is used. In this experiment, participants performed a secondary auditory choice reaction time (RT) task to measure attention while watching a film. In order to explore the role of narrative on attention, we manipulated the order that film segments were presented. The influence of narrative was then compared to the contribution of low-level features (extracted using a computer-based saliency model) in a multiple regression analysis predicting choice RT. The regression model successfully predicted 28% of the variance in choice RT: 13% was due to low-level saliency, and 8% due to the narrative. This study shows the importance of narrative in determining attention and the value of studying attention with a prolonged stimulus such as film.

Implicit and Explicit Knowledge Both Improve Dual Task Performance in a Continuous Pursuit Tracking Task.

The goal of this study was to investigate the effect of predictability on dual-task performance in a continuous tracking task. Participants practiced either informed (explicit group) or uninformed (implicit group) about a repeated segment in the curves they had to track. In Experiment 1 participants practices the tracking task only, dual-task performance was assessed after by combining the tracking task with an auditory reaction time task. Results showed both groups learned equally well and tracking performance on a predictable segment in the dual-task condition was better than on random segments. However, reaction times did not benefit from a predictable tracking segment. To investigate the effect of learning under dual-task situation participants in Experiment 2 practiced the tracking task while simultaneously performing the auditory reaction time task. No learning of the repeated segment could be demonstrated for either group during the training blocks, in contrast to the test-block and retention test, where participants performed better on the repeated segment in both dual-task and single-task conditions. Only the explicit group improved from test-block to retention test. As in Experiment 1, reaction times while tracking a predictable segment were no better than reaction times while tracking a random segment. We concluded that predictability has a positive effect only on the predictable task itself possibly because of a task-shielding mechanism. For dual-task training there seems to be an initial negative effect of explicit instructions, possibly because of fatigue, but the advantage of explicit instructions was demonstrated in a retention test. This might be due to the explicit memory system informing or aiding the implicit memory system.

Sensory and motoric influences on attention dynamics during standing balance recovery in young and older adults.

This study investigated the impact of attention on the sensory and motor actions during postural recovery from underfoot perturbations in young and older adults. A dual-task paradigm was used involving disjunctive and choice reaction time (RT) tasks to auditory and visual stimuli at different delays from the onset of two types of platform perturbations (rotations and translations). The RTs were increased prior to the perturbation (preparation phase) and during the immediate recovery response (response initiation) in young and older adults, but this interference dissipated rapidly after the perturbation response was initiated (<220ms). The sensory modality of the RT task impacted the results with interference being greater for the auditory task compared to the visual task. As motor complexity of the RT task increased (disjunctive versus choice) there was greater interference from the perturbation. Finally, increasing the complexity of the postural perturbation by mixing the rotational and translational perturbations together increased interference for the auditory RT tasks, but did not affect the visual RT responses. These results suggest that sensory and motoric components of postural control are under the influence of different dynamic attentional processes.

Left and right reaction time differences to the sound intensity in normal and AD/HD children

ObjectivesRight hemisphere, which is attributed to the sound intensity discrimination, has abnormality in people with attention deficit/hyperactivity disorder (AD/HD). However, it is not studied whether the defect in the right hemisphere has influenced on the intensity sensation of AD/HD subjects or not. In this study, the sensitivity of normal and AD/HD children to the sound intensity was investigated. MethodsNineteen normal and fourteen AD/HD children participated in the study and performed a simple auditory reaction time task. Using the regression analysis, the sensitivity of right and left ears to various sound intensity levels was examined. ResultsThe statistical results showed that the sensitivity of AD/HD subjects to the intensity was lower than the normal group (p < 0.0001). Left and right pathways of the auditory system had the same pattern of response in AD/HD subjects (p > 0.05). However, in control group the left pathway was more sensitive to the sound intensity level than the right one (p = 0.0156). ConclusionsIt can be probable that the deficit of the right hemisphere has influenced on the auditory sensitivity of AD/HD children. The possible existent deficits of other auditory system components such as middle ear, inner ear, or involved brain stem nucleuses may also lead to the observed results. The development of new biomarkers based on the sensitivity of the brain hemispheres to the sound intensity has been suggested to estimate the risk of AD/HD. Designing new technique to correct the auditory feedback has been also proposed in behavioral treatment sessions.

Related Factors and Predictors of Cognitive Dysfunction in Chronic Kidney Disease on Maintenance Hemodialysis in Nigeria.

Background:Previous studies suggest a high frequency of cognitive impairment (CI) in persons with chronic kidney disease (CKD); however, factors associated with CI and predictors of CI in persons with CKD remain largely unclear. The aim of this study was to determine the factors associated with CI and predictors of CI in CKD patients on maintenance hemodialysis.Materials and Methods:The first stage of the study included recruitment of 100 apparently healthy participants aimed at determining the reference values. The second stage of the study included eighty CKD patients on maintenance hemodialysis. The iron psychology (FEPSY) was used to assess the memory, psychomotor speed, concentration, and attention using simple auditory reaction time (ART) and visual reaction time (VRT) tasks, recognition memory tests (RMT), finger tapping task (FTT), and binary choice task (BCT).Results:Using normative values generated in this study, 41 (51.3%) and 43 (53.8%) CKD patients had abnormal scores on ART dominant (D) and nondominant (ND) sides, respectively. Forty (50%) and 42 (52.5%) patients had abnormal scores on VRT D and ND sides, respectively. Twenty-one (26.3%) and 68 (85%) had abnormal scores on BCT and computer-assisted visual scanning task, respectively. Sixty-four (80%) and 65 (81.3%) had abnormal scores on RMT (words) and RMT, respectively. Fifty-two (65%) and 48 (60%) patients had abnormal scores on D and ND sides of (FTT), respectively. Factors associated with psychomotor speed impairment were duration of CKD from diagnosis (P = 0.0001 and 0.043 in D and ND ART, respectively), duration on dialysis (P = 0.0001 across board in D and ND ART as well as in D and ND VRT, respectively), and plasma urea (PU) and plasma creatinine (PCr) (P < 0.05). Factors found to be associated with memory impairment included age (P = 0.045 and 0.025 on words and figures RMT, respectively), PU (P = 0.002 and 0.005 on words and figures RMT, respectively), and PCr (P = 0.012 and 0.040 on words and figures RMT, respectively). Duration on dialysis (P = 0.032) and PCr (P = 0.001) were associated with attention and concentration. Only psychomotor speed was independently predicted by duration of CKD.Conclusion:Factors associated with psychomotor speed impairment were duration of CKD, duration on dialysis, and PU and PCr while age, PU, and PCr were associated with memory. Duration on dialysis and PCr were associated with attention and concentration. Only psychomotor speed was independently predicted by duration of CKD.

The Effects of Restricted Peripheral Field-of-View on Spatial Learning while Navigating.

Recent work with simulated reductions in visual acuity and contrast sensitivity has found decrements in survey spatial learning as well as increased attentional demands when navigating, compared to performance with normal vision. Given these findings, and previous work showing that peripheral field loss has been associated with impaired mobility and spatial memory for room-sized spaces, we investigated the role of peripheral vision during navigation using a large-scale spatial learning paradigm. First, we aimed to establish the magnitude of spatial memory errors at different levels of field restriction. Second, we tested the hypothesis that navigation under these different levels of restriction would use additional attentional resources. Normally sighted participants walked on novel real-world paths wearing goggles that restricted the field-of-view (FOV) to severe (15°, 10°, 4°, or 0°) or mild angles (60°) and then pointed to remembered target locations using a verbal reporting measure. They completed a concurrent auditory reaction time task throughout each path to measure cognitive load. Only the most severe restrictions (4° and blindfolded) showed impairment in pointing error compared to the mild restriction (within-subjects). The 10° and 4° conditions also showed an increase in reaction time on the secondary attention task, suggesting that navigating with these extreme peripheral field restrictions demands the use of limited cognitive resources. This comparison of different levels of field restriction suggests that although peripheral field loss requires the actor to use more attentional resources while navigating starting at a less extreme level (10°), spatial memory is not negatively affected until the restriction is very severe (4°). These results have implications for understanding of the mechanisms underlying spatial learning during navigation and the approaches that may be taken to develop assistance for navigation with visual impairment.

Interaction between visual and motor cortex: a transcranial magnetic stimulation study.

The major link between the visual and motor systems is via the dorsal stream pathways from visual to parietal and frontal areas of the cortex. Although the pathway appears to be indirect, there is evidence that visual input can reach the motor cortex at relatively short latency. To shed some light on its neural basis, we studied the visuomotor interaction using paired transcranial magnetic stimulation (TMS). Motor-evoked potentials (MEPs) were recorded from the right first dorsal interosseous in sixteen healthy volunteers. A conditioning stimulus (CS) was applied over the phosphene hotspot of the visual cortex, followed by a test stimulus over the left primary motor cortex (M1) with a random interstimulus interval (ISI) in range 12-40 ms. The effects of paired stimulation were retested during visual and auditory reaction-time tasks (RT). Finally, we measured the effects of a CS on short-interval intracortical inhibition (SICI). At rest, a CS over the occiput significantly (P < 0.001) suppressed test MEPs with an ISI in the range 18-40 ms. In the visual RT, inhibition with an ISI of 40 ms (but not 18 ms) was replaced by a time-specific facilitation (P < 0.001), whereas, in the auditory RT, the CS no longer had any effect on MEPs. Finally, an occipital CS facilitated SICI with an ISI of 40 ms (P < 0.01). We conclude that it is possible to study separate functional connections from visual to motor cortices using paired-TMS with an ISI in the range 18-40 ms. The connections are inhibitory at rest and possibly mediated by inhibitory interneurones in the motor cortex. The effect with an ISI of 40 ms reverses into facilitation during a visuomotor RT but not an audiomotor RT. This suggests that it plays a role in visuomotor integration.

Electrophysiological evidence of temporal preparation driven by rhythms in audition

Reaction speed to respond to an auditory target stimulus is enhanced when it is presented at a moment matching the temporal structure of a preceding regular rhythm (Sanabria et al., 2011). However, the electrophysiological correlates of this behavioural enhancement remain unknown. In the present study, participants’ performed a simple auditory reaction time task in which a regular rhythm with either a fast (400ms interval between the tones making the rhythm) or a slow (900ms interval between the tones making the rhythm) was presented prior to the target. The target tone could be presented, with the same probability, 400ms or 900ms after the offset of the rhythmic sequence. The behavioural results showed that the fastest responses were obtained when the target appeared in synchrony with the preceding rhythm (e.g., the target was presented 900ms after the slow rhythm). This behavioural benefit was accompanied by amplitude modulations of the N1 potential and the P2 potential, both related to the processing of the auditory target. Crucially, these electrophysiological modulations were obtained in both the fast and the slow rhythm conditions. The current research demonstrates that rhythms with different paces can drive temporal preparation exogenously, affecting early and late stages of auditory neural processing.

Does It Really Matter Where You Look When Walking on Stairs? Insights from a Dual-Task Study

Although the visual system is known to provide relevant information to guide stair locomotion, there is less understanding of the specific contributions of foveal and peripheral visual field information. The present study investigated the specific role of foveal vision during stair locomotion and ground-stairs transitions by using a dual-task paradigm to influence the ability to rely on foveal vision. Fifteen healthy adults (26.9±3.3 years; 8 females) ascended a 7-step staircase under four conditions: no secondary tasks (CONTROL); gaze fixation on a fixed target located at the end of the pathway (TARGET); visual reaction time task (VRT); and auditory reaction time task (ART). Gaze fixations towards stair features were significantly reduced in TARGET and VRT compared to CONTROL and ART. Despite the reduced fixations, participants were able to successfully ascend stairs and rarely used the handrail. Step time was increased during VRT compared to CONTROL in most stair steps. Navigating on the transition steps did not require more gaze fixations than the middle steps. However, reaction time tended to increase during locomotion on transitions suggesting additional executive demands during this phase. These findings suggest that foveal vision may not be an essential source of visual information regarding stair features to guide stair walking, despite the unique control challenges at transition phases as highlighted by phase-specific challenges in dual-tasking. Instead, the tendency to look at the steps in usual conditions likely provides a stable reference frame for extraction of visual information regarding step features from the entire visual field.

Comparison of Dynamic Balance under Dual and Simple Task Conditions in Children with Attention Deficit Hyperactivity Disorder

Purpose) The purpose of this study was to make a comparison of dynamic balance ability between dual and simple task conditions. (Subjects and Methods) Nine children with attention deficit hyperactivity disorder (9.00 ± 2.12 years) and 10 healthy children (9.67 ± 2.75 years) were recruited. Each group was asked to do an obstacle crossing alone and the obstacle crossing combined with a stimulus response task. The Qualisys motion capture system was used to capture full-body motion. The parameters measured included crossing speed, step width, and reaction time. (Results) Children with attention deficit hyperactivity disorder had greater problems than controls in performing the primary balance task while concurrently completing the auditory reaction time task and showed greater variability in step width and a longer reaction time. The balance scores assessed using the Movement As- sessment Battery for Children test were significantly worse in the attention deficit hyperactivity disorder group and were significantly correlated to the crossing reaction time and variance of crossing speeds.(Conclusion) The attention deficit hyperactivity disorder group preferred to complete the obstacle crossings before responding to the stimulus. This resulted in a longer reaction time for the secondary task and also changed the gait strategy.

Age-Related Changes in the Auditory Reaction Time of Healthy Elderly Person while Walking

[Purpose] This study aimed to investigate the age-related changes in the attentional demand of walking in healthy elderly people by assessing auditory reaction time during walking in several age groups. [Subjects] The participants were 59 healthy elderly people with no history of falls in the previous 12 months, who were divided into 4 age groups (65-69, 70-74, 75-79, and 80-84). [Methods] In the dual-task condition, participants were asked to perform an auditory reaction time task while walking indoors; the Timed Up-and-Go Test, 10-meter walk time and Trail Making Test Part A were also measured. We compared the reaction times and the stride-to-stride time coefficients of variation between the single- and dual-task conditions. [Results] We found that mean reaction time and stride time coefficient of variation increased significantly in the dual task. However, in both task conditions, neither the reaction time nor stride-to-stride time coefficient of variation differed significantly among the age groups. [Conclusion] These findings indicate that an auditory reaction time task can affect walking as a second task in the healthy elderly, and that aging has minimal effects on the attentional demand of walking in this population.

Hippocampal P300 recorded during a simple auditory reaction time task (intracerebral study)

Event Abstract Back to Event Hippocampal P300 recorded during a simple auditory reaction time task (intracerebral study) Robert Roman1*, Jan Chladek2, Milan Brazdil3, Ivan Rektor3, Pavel Jurak2 and Miloslav Kukleta4 1 Faculty of Medicine, Masaryk University, Czechia 2 Academy of Science, Czechia 3 St. Anne Hospital, Czechia 4 CEITEC - Central European Institute of Technology, Masaryk University, Czechia This paper attempts to make possible time relationship of hippocampal P300, evoked by 1 kHz tone during a simple sensorimotor task, to stimulus or motor response. In 9 patients with medically intractable epilepsies, depth electrodes were implanted to localize the seizure origin prior to surgical treatment. 19 of 70 electrodes were targeted into the hippocampus. Each subject was instructed to respond to the 1 kHz tone by pressing a button in the dominant hand. P300 components recorded in the hippocampus were analyzed both in stimulus-locked and response-locked averages, which were separately averaged for fast and slow responses. Local generation of hippocampal P300 was demonstrated in all 19 electrodes. The mean latency was 415±58 ms, the mean amplitude was 108±87 mV. Three different types of time relationships of hippocampal P300 were found: 1) time-locked to the stimulus - in 12 cases/6 patients; 2) time-locked to the motor response - in 2 cases/1 patient; and 3) ambiguous time relationship to stimulus and motor response - in 5 cases/3 patients. The three types of relationships were found in both left and right hemispheres. Our results show that the hippocampus in all the patients evoked a response during a simple sensorimotor task. The finding of the three different types of time relationships to stimulus and to motor response is in accordance with the results we obtained during visual oddball task. It may suggest that at least certain parts of this structure are involved in simple sensorimotor tasks in all steps of information processing. Funding: Partially supported by the grant MSM0021622404 and grant P103/11/0933 GACR and EC project CZ.1.05/2.1.00/01.0017. Keywords: Intra-cranial Electrophysiology, P300 Conference: XI International Conference on Cognitive Neuroscience (ICON XI), Palma, Mallorca, Spain, 25 Sep - 29 Sep, 2011. Presentation Type: Poster Presentation Topic: Abstracts Citation: Roman R, Chladek J, Brazdil M, Rektor I, Jurak P and Kukleta M (2011). Hippocampal P300 recorded during a simple auditory reaction time task (intracerebral study). Conference Abstract: XI International Conference on Cognitive Neuroscience (ICON XI). doi: 10.3389/conf.fnhum.2011.207.00059 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 15 Nov 2011; Published Online: 25 Nov 2011. * Correspondence: Dr. Robert Roman, Faculty of Medicine, Masaryk University, Brno, Czechia, roman@med.muni.cz Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Robert Roman Jan Chladek Milan Brazdil Ivan Rektor Pavel Jurak Miloslav Kukleta Google Robert Roman Jan Chladek Milan Brazdil Ivan Rektor Pavel Jurak Miloslav Kukleta Google Scholar Robert Roman Jan Chladek Milan Brazdil Ivan Rektor Pavel Jurak Miloslav Kukleta PubMed Robert Roman Jan Chladek Milan Brazdil Ivan Rektor Pavel Jurak Miloslav Kukleta Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Obesity Impact on the Attentional Cost for Controlling Posture

BackgroundThis study investigated the effects of obesity on attentional resources allocated to postural control in seating and unipedal standing.MethodsTen non obese adults (BMI = 22.4±1.3, age = 42.4±15.1) and 10 obese adult patients (BMI = 35.2±2.8, age = 46.2±19.6) maintained postural stability on a force platform in two postural tasks (seated and unipedal). The two postural tasks were performed (1) alone and (2) in a dual-task paradigm in combination with an auditory reaction time task (RT). Performing the RT task together with the postural one was supposed to require some attentional resources that allowed estimating the attentional cost of postural control. 4 trials were performed in each condition for a total of 16 trials.Findings(1) Whereas seated non obese and obese patients exhibited similar centre of foot pressure oscillations (CoP), in the unipedal stance only obese patients strongly increased their CoP sway in comparison to controls. (2) Whatever the postural task, the additional RT task did not affect postural stability. (3) Seated, RT did not differ between the two groups. (4) RT strongly increased between the two postural conditions in the obese patients only, suggesting that body schema and the use of internal models was altered with obesity.InterpretationObese patients needed more attentional resources to control postural stability during unipedal stance than non obese participants. This was not the case in a more simple posture such as seating. To reduce the risk of fall as indicated by the critical values of CoP displacement, obese patients must dedicate a strong large part of their attentional resources to postural control, to the detriment of non-postural events. Obese patients were not able to easily perform multitasking as healthy adults do, reflecting weakened psycho-motor abilities.

Abnormal brain processing in hepatic encephalopathy

Hepatic encephalopathy (HE) is a severe and frequent complication of liver cirrhosis characterized by abnormal cerebral function. Little is known about the underlying neural mechanisms in HE and human data are sparse. Electrophysiological methods such as evoked brain potentials after somatic stimuli can be combined with inverse modeling of the underlying brain activity. Thereby, information on neuronal dynamics and brain activity can be studied in vivo. The aim of this study was to investigate the sensory brain processing in patients with HE. Twelve patients with minimal or overt HE and 26 healthy volunteers were included in the study. Cerebral sensory processing was investigated as (i) an auditory reaction time task; (ii) visual and somatosensory evoked brain potentials, and (iii) reconstruction of the underlying brain activity. Somatosensory evoked potentials were reproducible (all P>0.05), whereas flash evoked potentials were not reproducible (all P<0.05). Compared with healthy volunteers, the patient group had a prolonged reaction time index (P=0.03) along with increasing prolongation of latencies of median nerve evoked potentials (P<0.03). Reconstruction of the underlying brain sources showed a lateral shift in source localization of the P45 (P<0.001) and N60 components (P=0.02). A correlation between the psychometric hepatic encephalopathy score and the dipole shift corresponding to the N60 (P=0.003) component was seen. HE patients have evidence of prolonged intracerebral nerve conduction, along with lateralization of brain activity following median nerve stimulation. This possibly represents cortical reorganization and may be important in our understanding of this condition.