DOES ABNORMAL SPINAL RECIPROCAL INHIBITION LEAD TO CO-CONTRACTION OF ANTAGONIST MOTOR UNITS? A MODELING STUDY

Connectivity concepts in neuronal network modeling

Sustainable research on computational models of neuronal networks requires published models to be understandable, reproducible, and extendable. Missing details or ambiguities about mathematical concepts and assumptions, algorithmic implementations, or parameterizations hinder progress. Such flaws are unfortunately frequent and one reason is a lack of readily applicable standards and tools for model description. Our work aims to advance complete and concise descriptions of network connectivity but also to guide the implementation of connection routines in simulation software and neuromorphic hardware systems. We first review models made available by the computational neuroscience community in the repositories ModelDB and Open Source Brain, and investigate the corresponding connectivity structures and their descriptions in both manuscript and code. The review comprises the connectivity of networks with diverse levels of neuroanatomical detail and exposes how connectivity is abstracted in existing description languages and simulator interfaces. We find that a substantial proportion of the published descriptions of connectivity is ambiguous. Based on this review, we derive a set of connectivity concepts for deterministically and probabilistically connected networks and also address networks embedded in metric space. Beside these mathematical and textual guidelines, we propose a unified graphical notation for network diagrams to facilitate an intuitive understanding of network properties. Examples of representative network models demonstrate the practical use of the ideas. We hope that the proposed standardizations will contribute to unambiguous descriptions and reproducible implementations of neuronal network connectivity in computational neuroscience.

Do functional hamstring to quadriceps ratio differ between men and women with and without stroke?

BACKGROUND

The functional hamstrings/quadriceps ratio (FH/Q) is useful to detect muscle imbalances after stroke. However, is necessary to investigate possible differences between men and women affected by stroke and controls.

OBJECTIVES

To compare the FH/Q between men and women with stroke and matched controls.

METHOD

Cross-sectional study. Fifty-six participants (10 men - MSTK and 18 women - WSTK with stroke; and 10 men - MCONT and 18 women - WCONT, matched controls) were recruited. The concentric knee extension (conc) and eccentric flexion exercises (ecc) were performed, and peak torque (PT) was used to calculate the FH/Q. Comparisons of PT between sexes (MSTK vs WSTK; MCONT vs WCONT) and comparisons of FH/Q between sexes and groups (MSTK vs MCONT; WSTK vs WCONT), considering dominant vs non-paretic side and non-dominant vs paretic side were performed by ANOVA and Kruskal-Wallis test, when applicable.

RESULTS

No significant FH/Q differences were found between STK vs CONT and sexes (non-paretic vs dominant). The paretic FH/Q was significantly higher than the non-dominant (CONT), for both sexes. PTconc and PTecc were significant higher for men, considering limbs comparisons. No significant PTecc an PTconc differences were found between STK vs CONT, for men's non-paretic and paretic limb's. However, men's non-dominant limb presented a higher PTconc compared to men's paretic limbs.

CONCLUSIONS

Our study demonstrated that individuals affected by stroke had a higher FH/Q in the paretic limb compared to the non-dominant limb of the control group, for both men and women. One interesting finding was the absence of significant FH/Q differences between men and women with stroke.

Origins of a repetitive and co-contractive biphasic pattern of muscle activation in Parkinson's disease

In studies of electromyographic (EMG) patterns during movements in Parkinson's disease, often a repetitive and sometimes co-contractive pattern of antagonist muscle activation is observed. It has been suggested that the origin of such patterns of muscle activation is a central one arising from impairments in the basal ganglia structures and/or the cortex, although afferent inputs can also modulate the voluntary activity. A neural network model of Parkinson's disease, bradykinesia and rigidity, is extended to quantitatively study the conditions under which such a repetitive and co-contractive pattern of muscle activation appears. Computer simulations show that an oscillatory disrupted globus pallidus internal segment (GPi) response signal comprising at least two excitation-inhibition sequences as an input to a normally functioning cortico-spinal model of movement generation results in a repetitive, but not co-contractive agonist-antagonist pattern of muscle activation. A repetitive and co-contractive pattern of muscle activation results when also dopamine is depleted in the cortex. Finally, additional dopamine depletion in the spinal cord sites results in a reduction of the size, duration and rate of change of the repetitive and co-contractive EMG bursts. These results have important consequences in the development of Parkinson's Disease therapies such as dopamine replacement in cortex and spinal cord, which can alleviate some of the impairments of Parkinson's Disease such as slowness of movement (bradykinesia) and rigidity.