Nonlinear wave-wave interactions in the brain.

Neural field theory of the corticothalamic system is used to analyze nonlinear wave-wave interactions in steady state visual evoked potential responses. The nonlinear power spectrum is analytically calculated by convolving the linear power spectrum with itself and other factors. Periodic sine and square wave stimuli are used to generate steady state visual evoked potential responses and to study stimulus-driven nonlinear corticothalamic dynamic interactions. Moreover, we use dual sine drives to analyze the driven dynamics. Numerical analysis shows that the nonlinear power spectrum embodies key nonlinear features, including harmonic and subharmonic generation, entrainment of the alpha rhythm to periodic stimuli at the drive frequency, sum and difference frequencies due to wave-wave coalescence and decay. Further, the scaling properties of the key phenomena observed in nonlinear interactions are studied, verifying some of the theoretical predictions for these being generated by three-wave processes.

Nonlinear harmonic generation in the corticothalamic system.

Neural field theory of the corticothalamic system is applied to quantitatively analyze harmonic generation in normal sleep and wake states. The linear power spectrum is derived analytically via the transfer function and is then convolved with itself and other factors to calculate the nonlinear power spectrum analytically via a recent perturbation expansion. Analysis shows that strong spectral peaks generate a harmonic at twice the original frequency with peak power proportional to the square of that of the original peak. Fits to the data enable absolute normalization to be determined, with the conclusion that the experimentally observed spindle harmonic peak is nonlinear. Using this normalization, the same analysis is applied to the wake state and nonlinear contributions to the alpha and beta peaks are quantified.

Latent autoimmune diabetes of adulthood (LADA) is associated with small fibre neuropathy.

AIM: To assess if latent autoimmune diabetes of adulthood (LADA) is associated with small fibre neuropathy. METHODS: Participants with LADA (n=31), Type 2 diabetes (n=31) and healthy control participants without diabetes (n=31) underwent a detailed assessment of neurologic deficits, quantitative sensory testing, electrophysiology, skin biopsy and corneal confocal microscopy. RESULTS: The groups were matched for age (healthy control without diabetes: 53.5±9.1 vs. Type 2 diabetes: 58.0±6.5 vs. LADA: 53.2±11.6 years), duration of diabetes (Type 2 diabetes: 10.0±8.3 vs. LADA: 11.0±9.1 years) and blood pressure. However, BMI (P=0.01) and triglycerides (P=0.0008) were lower and HbA1c (P=0.0005), total cholesterol (P=0.01) and HDL (P=0.002) were higher in participants with LADA compared with Type 2 diabetes. Peroneal motor nerve conduction velocity (P=0.04) and sural sensory nerve conduction velocity (P=0.008) were lower in participants with latent autoimmune diabetes in adults compared with Type 2 diabetes. Intra-epidermal nerve fibre density (P=0.008), corneal nerve fibre density (P=0.003) and corneal nerve branch density (P=0.006) were significantly lower in participants with LADA compared with Type 2 diabetes. There were no significant differences in the other neuropathy parameters. CONCLUSIONS: Despite comparable age and duration of diabetes, participants with LADA demonstrate more severe neuropathy and particularly small fibre neuropathy, compared with participants with Type 2 diabetes.

Normal value of pulsatility index of umbilical artery in second and third trimester of pregnancy.

This cross sectional study was carried out on 60 pregnant Bangladeshi women in the department of Radiology and Imaging, BIRDEM for measurement of Pulsatility Index (PI) of umbilical artery of their fetuses by duplex colour Doppler sonography during 2nd and 3rd trimester of pregnancies. Considering total 2nd and 3rd trimesters the mean PI value of umbilical artery was 1.24 (SD +/- 0.27). While considering the gestational in separate trimesters, study showed that the value of PI in 2nd trimester was 1.33 (SD +/- 0.29) and in 3rd trimester PI was 1.18 (SD +/- 0.25). Paired t test shows there was a highly significant (t = 35.79, df = 59, Level of significance = 0.001) difference between mean values of PI in different gestational ages. It was observed that there was gradual decrease of PI value with increase of gestational age (r = -0.207) but this decrease of PI was not statistically significant (p = 0.113). Regression analysis between dependent PI value and independent gestational age showed linear negative relationship but this was not statistically significant (p = 0.11). This study revealed that the Pulsatility index of umbilical artery was decreased with increase of gestational age from 2nd to 3rd trimester.