The effect of different types of cognitive tasks on postural sway fluctuations in older and younger adults: A nonlinear study.

BACKGROUND: There are numerous types of cognitive tasks classified as mental tracking (MT), working memory (WM), reaction time (RT), discrimination and decision-making and verbal fluency (VF). However, limited studies have investigated the effects of cognitive task type on postural control in older adults. PURPOSE: s: The aim of this study was to investigate the effect of aging and several types of cognitive tasks on postural control in terms of nonlinear analysis. METHOD: Postural control was investigated under 6 conditions (single task and dual-task with RT; easy and difficult VF; easy and difficult WM; easy and difficult MT. Outcome measurements were the max Lyapunov, entropy, and correlation dimension at anteroposterior (AP) and mediolateral (ML) directions. RESULTS: The results revealed that within the older group, the AP & ML max Lyapunov at dual-task with difficult WM and MT was significantly higher than all other conditions. In addition, the older group had lower AP entropy at dual-task with easy VF, difficult WM, and easy as well as difficult MT. CONCLUSION: The results can be useful to understand the postural control mechanisms and to detect the alterations following aging and applying different types of cognitive tasks. In addition, the investigated parameters can be a basis for identifying postural control deficiencies.

The effects of excess food nutrient content on a tritrophic food chain model in the aquatic ecosystem.

Ecological stoichiometry is an approach that focuses on the balance of energy and elements in environmental interactions, and it leads to new insights and a better understanding of ecological processes and outcomes. Modeling under this framework enables us to investigate the effects of nutrient content (i.e., food quality) on organisms, whether the imbalance involves insufficient or excess nutrient content. In this paper, we develop and analyze a tritrophic food chain model that captures the phenomenon known as the "stoichiometric knife-edge", where consumer growth is limited under conditions of excess nutrients. The model tracks two essential elements, carbon and phosphorus, in each species. The dynamics of the system such as boundedness and positivity of the solutions, existence and stability conditions of boundary and internal equilibria are analyzed. Through numerical simulations and bifurcation analyses, we observe the dynamics of the system switching between periodic oscillations and chaos. Our findings also show that nutrient-rich food consumption can cause adverse effects on species.

Effects of backpack load and positioning on nonlinear gait features in young adults.

Overloaded backpacks can cause changes in posture and gait dynamic balance. Therefore, the aim of this study was to assess gait regularity and local dynamic stability in young adults as they carried a backpack in different positions, and with different loads. Twenty-one healthy young adults participated in the study, carrying a backpack that was loaded with 10 and 20% of their body weight (BW). The participants walked on a level treadmill at their preferred walking speeds for 4 min under different conditions of backpack load and position (i.e. with backpack positioned back bilaterally, back unilaterally, frontally or without a backpack). Results indicate that backpack load and positioning significantly influence gait stability and regularity, with the exception of the 10% BW bilateral back position. Therefore, the recommended safe load for school-age children and adolescents (10% of BW) should also be considered for young adults. Practitioner summary: Increase in load results in changes in posture, muscle activity and gait parameters, so we investigated the gait adaptations related to regularity and stability. Conditions with high backpack loads significantly influenced gait stability and regularity in a position-dependent manner, except for 10% body weight bilateral back position.

Nonlinear Analysis of EEG in Various Mental States of Normal Person

BACKGROUND: In order to compare the differences between various mental activities and to determine the significance of chaotic patterns, we performed a fractal dimension and Lyapunov exponent analysis of digital EEG data which are known to be non linear biological signals. METHODS: During the EEG recordings, different kinds of tasks were performed, including eye closing, eye opening, calculation, listening to music, and remembering a picture. Performance signals were recorded for each test as a digital EEG for more than one minute. We used our own software, CHASIM, to calculate the fractal dimension and Lyapunov exponent. The statistical analysis performed was an ANOVA using SAS 6.12 for Windows (9.0). RESULTS: The fractal dimensions during the "listening to music and noise", and "moving both toes" tasks were increased. During the "eye opening", "calculation", and "moving both fingers" tasks, the fractal dimensions were decreased. CONCLUSIONS: Auditory stimulation generated a higher correlation dimension than visual stimulation. The interpretation of these results is still not totally clear, but we hope to find future applications for non-linear chaotic analysis for the functional evaluation of the central nervous system.