Limiting parameter range for cortical-spherical mapping improves activated domain estimation for attention modulated auditory response.

BACKGROUND: Attention is one of the factors involved in selecting input information for the brain. We applied a method for estimating domains with clear boundaries using magnetoencephalography (the domain estimation method) for auditory-evoked responses (N100m) to evaluate the effects of attention in milliseconds. However, because the surface around the auditory cortex is folded in a complicated manner, it is unknown whether the activity in the auditory cortex can be estimated. NEW METHOD: The parameter range to express current sources was set to include the auditory cortex. Their search region was expressed as a direct product of the parameter ranges used in the adaptive diagonal curves. RESULTS: Without a limitation of the range, activity was estimated in regions other than the auditory cortex in all cases. However, with the limitation of the range, the activity was estimated in the primary or higher auditory cortex. Further analysis of the limitation of the range showed that the domains activated during attention included the regions activated during no attention for the participants whose amplitudes of N100m were higher during attention. COMPARISON WITH EXISTING METHOD: We proposed a method for effectively limiting the search region to evaluate the extent of the activated domain in regions with complex folded structures. CONCLUSION: To evaluate the extent of activated domains in regions with complex folded structures, it is necessary to limit the parameter search range. The area of the activated domains in the auditory cortex may increase by attention on the millisecond timescale.

Functional innervation of human induced pluripotent stem cell-derived cardiomyocytes by co-culture with sympathetic neurons developed using a microtunnel technique.

Microelectrode array (MEA) based-drug screening with human induced pluripotent stem cell-derived cardiomyocytes (hiPSCM) is a potent pre-clinical assay for efficiently assessing proarrhythmic risks in new candidates. Furthermore, predicting sympathetic modulation of the proarrhythmic side-effects is an important issue. Although we have previously developed an MEA-based co-culture system of rat primary cardiomyocyte and sympathetic neurons (rSNs), it is unclear if this co-culture approach is applicable to develop and investigate sympathetic innervation of hiPSCMs. In this study, we developed a co-culture of rSNs and hiPSCMs on MEA substrate, and assessed functional connections. The inter-beat interval of hiPSCM was significantly shortened by stimulation in SNs depending on frequency and pulse number, indicating functional connections between rSNs and hiPSCM and the dependency of chronotropic effects on rSN activity pattern. These results suggest that our co-culture approach can evaluate sympathetic effects on hiPSCMs and would be a useful tool for assessing sympathetic modulated-cardiotoxicity in human cardiac tissue.

A co-culture microtunnel technique demonstrating a significant contribution of unmyelinated Schwann cells to the acceleration of axonal conduction in Schwann cell-regulated peripheral nerve development.

Schwann cells (SCs) contribute to the regulation of axonal conduction in a myelin-dependent and -independent manner. However, due to the lack of investigative techniques that are able to record axonal conduction under conditions that control the proliferation of specific SC types, little is known about the extent to which myelinated SCs (mSCs) and unmyelinated SCs (umSCs) modulate axonal conduction. In this study, a microtunnel-electrode approach was applied to a neuron/SC co-culture technique. Rat dorsal root ganglion neurons and SCs were co-cultured in a microtunnel-electrode device, which enabled recording of the conduction delay in multiple axons passing through microtunnels. Despite the absence of nuclei in the microtunnel when SCs were eliminated, cultured cells were densely packed and expressed S100 beta (an SC marker) at a rate of 96% in neuron/SC co-culture, indicating that SCs migrated into the microtunnel. In addition, supplementation with ascorbic acid after 6 days in vitro (DIV) successfully induced myelination from 22 DIV. Activity recording experiments indicated that the conduction delay decreased with culture length from 17 DIV in the neuron/SC co-culture but not in neuron monoculture. Interestingly, the SC-modulated shortening of conduction delay was attenuated at 17 DIV and 22 DIV by supplementing the culture medium with ascorbic acid and, at the same time, suppressing SC proliferation, suggesting that immature umSCs increased axonal conduction velocity in a cell density-dependent manner before the onset of myelination. These results suggest that this method is an effective tool for investigating the contributions of mSCs or umSCs to the regulation of axonal conduction.

Deriving theoretical phase locking values of a coupled cortico-thalamic neural mass model using center manifold reduction.

Cognitive functions such as sensory processing and memory processes lead to phase synchronization in the electroencephalogram or local field potential between different brain regions. There are a lot of computational researches deriving phase locking values (PLVs), which are an index of phase synchronization intensity, from neural models. However, these researches derive PLVs numerically. To the best of our knowledge, there have been no reports on the derivation of a theoretical PLV. In this study, we propose an analytical method for deriving theoretical PLVs from a cortico-thalamic neural mass model described by a delay differential equation. First, the model for generating neural signals is transformed into a normal form of the Hopf bifurcation using center manifold reduction. Second, the normal form is transformed into a phase model that is suitable for analyzing synchronization phenomena. Third, the Fokker-Planck equation of the phase model is derived and the phase difference distribution is obtained. Finally, the PLVs are calculated from the stationary distribution of the phase difference. The validity of the proposed method is confirmed via numerical simulations. Furthermore, we apply the proposed method to a working memory process, and discuss the neurophysiological basis behind the phase synchronization phenomenon. The results demonstrate the importance of decreasing the intensity of independent noise during the working memory process. The proposed method will be of great use in various experimental studies and simulations relevant to phase synchronization, because it enables the effect of neurophysiological changes on PLVs to be analyzed from a mathematical perspective.