Characterization of K-Complexes and Slow Wave Activity in a Neural Mass Model

NREM sleep is characterized by two hallmarks, namely K-complexes (KCs) during sleep stage N2 and cortical slow oscillations (SOs) during sleep stage N3. While the underlying dynamics on the neuronal level is well known and can be easily measured, the resulting behavior on the macroscopic population level remains unclear. On the basis of an extended neural mass model of the cortex, we suggest a new interpretation of the mechanisms responsible for the generation of KCs and SOs. As the cortex transitions from wake to deep sleep, in our model it approaches an oscillatory regime via a Hopf bifurcation. Importantly, there is a canard phenomenon arising from a homoclinic bifurcation, whose orbit determines the shape of large amplitude SOs. A KC corresponds to a single excursion along the homoclinic orbit, while SOs are noise-driven oscillations around a stable focus. The model generates both time series and spectra that strikingly resemble real electroencephalogram data and points out possible differences between the different stages of natural sleep

A Thalamocortical Neural Mass Model of the EEG during NREM Sleep and Its Response to Auditory Stimulation

Few models exist that accurately reproduce the complex rhythms of the thalamocortical system that are apparent in measured scalp EEG and at the same time, are suitable for large-scale simulations of brain activity. Here, we present a neural mass model of the thalamocortical system during natural non-REM sleep, which is able to generate fast sleep spindles (12–15 Hz), slow oscillations (<1 Hz) and K-complexes, as well as their distinct temporal relations, and response to auditory stimuli. We show that with the inclusion of detailed calcium currents, the thalamic neural mass model is able to generate different firing modes, and validate the model with EEG-data from a recent sleep study in humans, where closed-loop auditory stimulation was applied. The model output relates directly to the EEG, which makes it a useful basis to develop new stimulation protocols

Changes of gluteus medius muscle in the adult patients with unilateral developmental dysplasia of the hip

<p>Abstract</p> <p>Background</p> <p>The gluteus medius muscle is essential for gait and hip stability. Changes that occur in the gluteus medius muscles in patients with developmental dysplasia of the hip (DDH) are not well understood. A better understanding of DDH related changes will have positive repercussions toward hip soft tissue reconstruction.</p> <p>Methods</p> <p>19 adult patients with unilateral DDH scheduled for total hip arthroplasty were assessed for: cross-sectional area (CSA), radiological density (RD) and the length of gluteus medius using computed tomograhpy(CT) (scanned before THA). Hip abductor moment arm and gluteus medius activation angle were also measured <it>via</it> hip anteroposterior radiographs.</p> <p>Results</p> <p>Both CSA and RD of gluteus medius muscle were significantly reduced (p < 0.05) in the affected hip compared to the control. In the affected hip, the length of the gluteus medius muscle was reduced by 8-11 % (p < 0.05) while the gluteus medius activation angle was significantly increased (p < 0.05) and the hip abductor moment arm was decreased (p < 0.05).</p> <p>Conclusions</p> <p>The gluteus medius showed substantial loss of CSA, RD as well as decreased length in patients with DDH in the affected hip. These changes should be considered in both hip reconstruction and postoperative rehabilitation training in patients with DDH.</p