Existence of solutions for stress-rate type strain-limiting viscoelasticity in Gevrey spaces.

In this work, we deal with a one-dimensional stress-rate type model for the response of viscoelastic materials, in relation to the strain-limiting theory. The model is based on a constitutive relation of stress-rate type. Unlike classical models in elasticity, the unknown of the model under consideration is uniquely the stress, avoiding the use of the deformation. Here, we treat the case of periodic boundary conditions for a linearized model. We determine an optimal function space that ensures the local existence of solutions to the linearized model around certain steady states. This optimal space is known as the Gevrey-class [Formula: see text], which characterizes the regularity properties of the solutions. The exponent [Formula: see text] in the Gevrey-class reflects the specific dispersion properties of the equation itself. This article is part of the theme issue 'Foundational issues, analysis and geometry in continuum mechanics'.

Brain microstructural changes and cognitive function in non-demented essential tremor patients: a diffusion tensor imaging study.

BACKGROUND: Essential tremor (ET) is disease with both motor and non-motor features. Notable among the non-motor features is cognitive impairment. While this impairment has been attributed to cortico-thalamo-cerebellar pathway pathology, it is likely that a more complicated involvement of brain structures underlies cognitive function in ET. OBJECTIVE: To evaluate the brain microstructural changes of both white matter and grey matter in ET using region of interest based diffusion tensor imaging (DTI), and to correlate these changes with cognitive function assessed during detailed neuropsychological testing. METHOD: Thirty-five non-demented ET patients with a range of cognitive function (Clinical Dementia Rating = 0-0.5, mean age = 57.5 ± 16.7 years, age range = 23-76 years) underwent a comprehensive neuropsychological evaluation and brain magnetic resonance imaging, including DTI. DTI findings were reported as fractional anisotropy, average diffusion coefficient, these values were evaluated for 32 ROIs. Cognitive domains included attention, visuospatial functions, executive function, verbal memory, visual memory, and language. Domain Z-scores were calculated each cognitive domain and compared for each brain region. RESULTS: Microstructural changes in prefrontal cortical areas (dorsolateral, ventrolateral), paralimbic and limbic structures (posterior cingulate cortex, precuneus, hippocampus), basal ganglia (substantia nigra, putamen, caudate nucleus) and white matter bundles (corpus callosum, anterior thalamic radiation, longitudinal fasciculus, frontooccipital fasciculus, etc.) correlated with specific domains of cognitive function in ET patients. CONCLUSION: These data suggest that not only the cerebello thalamocortical pathway, but numerous other brain structures are related to level of cognitive performance and possibly underlie cognitive dysfunction in ET.

Cervical multisegmental motor responses in healthy subjects.

STUDY DESIGN: Experimental design. OBJECTIVES: This descriptive design study presents multisegmental motor responses in the upper extremities after stimulation of cervical spinal vertebrae. SETTING: Neuro Lab of Texas Woman's University, School of Physical Therapy, Texas, USA. METHODS: In trial 1, C7 spinal segment was electrically stimulated in 13 healthy subjects using surface electrodes while recording responses from abductor digiti minimi (ADM), abductor pollicis brevis (APB), flexor carpi radialis (FCR) and biceps brachii (BB) in the right upper extremity. In trial 2, C7 stimulation was carried out while recording responses from the APB and BB bilaterally. In trial 3, C7 stimulation was carried out while recording responses from the flexor hallucis brevis (FHB), soleus, vastus medialis (VMO) and gluteus medius (GM) in the right lower extremity. The amplitude of the signal and the deflection latency were the measured parameters. Descriptive statistics were completed on the data. RESULTS: Results showed response amplitudes in all muscles of the upper extremities ranging from 328 to 1239 µV, with the largest recorded from the APB and ADM, then the FCR and BB. Muscular responses were recorded simultaneously in bilateral muscles. Response latency was comparable, in bilateral similar muscles, and was varied from 6 to 16.5 msec, being longer in the ADM and APB, shorter in FCR and shortest in the BB. No lower limb muscles responded to C7 spinal stimulation, using current setup/method. CONCLUSION: These responses appear to be caused by stimulating the dorsal roots or motor nuclei of the cervical region and could be useful in testing patients with cervical spinal disorders.

Thoracolumbar multisegmental motor responses in the upper and lower limbs in healthy subjects.

STUDY DESIGN: Experimental design. OBJECTIVES: This descriptive study presents muscular responses from both the upper and the lower extremities during T11-12 segmental stimulation. SETTING: Neuro Lab of the Texas Woman's University (School of Physical Therapy, TX, USA). METHODS: A total of 13 healthy subjects were electrically stimulated using surface electrodes. In trial 1, signals were recorded from the flexor hallucis brevis, soleus, vastus medialis and gluteus medius in the lower right extremity. In trial 2, responses were recorded from the abductor digiti minimi, abductor pollicis brevis (APB), flexor carpi radialis and biceps brachii in the right upper extremity. In trial 3, stimulation was carried out and signals were recorded for both the upper and the lower extremities simultaneously, using different muscle combinations. Five traces per muscle were averaged for each step of the testing. Amplitude and deflection latency were the measured parameters and were compared using descriptive statistics. RESULTS: Results showed signal amplitudes ranging from 85 to 821 µV in the upper extremity and from 582 to 3927 µV in the lower extremity, with the largest signal recorded in the soleus muscle and the APB. Response latency varies between 5.5 and 14 ms in the upper limbs and between 7.7 and 27 ms in the lower limbs and was comparable in bilateral recording. CONCLUSION: These muscular responses seem to be elicited from electrical stimulation of motor nuclei in lower limb muscles or from pathways to those nuclei in upper limb muscles, and could be useful in testing patients with spinal disorders.