Layer-Specific Intracortical Amplification Shortens the Lifetime of Thalamocortical Repetition Suppression in Auditory Cortex

Neural adaptation in sensory cortex serves important sensory functions, and is altered by various neurophsychiatric diseases. Although adaptation is a widely studied phenomenon, much remains unknown about its underlying mechanisms on a cortical circuit level. Here, we investigated repetition suppression as fundamental aspect of adaptation by layer-specific current source density analyses of synaptic mass activities in primary auditory cortex of anesthetized Mongolian gerbils (Meriones unguiculatus). We disentangled different synaptic contributions to repetition suppression in different cortical layers, and separated thalamocortical from intracortical inputs by cortical silencing with GABAA-agonist muscimol. We systematically varied stimulus onset intervals and employed statistically robust model fitting based on bootstrapping to determine the full suppression kinetics of different synaptic responses in the steady state. Whereas thalamocortical input to granular and infragranular layers was governed by longer lasting repetition suppression, most likely reflecting depression of thalamocortical synapses, intracortical amplification in granular layers shortened the lifetime of suppression by re-enhancing granular responses mainly through synchronization of synaptic events. With increasing latency, the shorter lasting suppression kinetics observed in granular layers at early latencies (<100ms) passed on to deeper layers replacing the longer lasting infragranular suppression kinetics. Granular circuit dynamics can therefore actively shape neural adaptation across cortical layers.

Weak Coupling Between Spontaneous Local Cortical Activity State Switches Under Anesthesia Leads to Strongly Correlated Global Cortical States

Under anesthesia, neural dynamics deviate dramatically from those seen during wakefulness. During recovery from this perturbation, thalamocortical activity abruptly switches among a small set of metastable intermediate states. These metastable states and structured transitions among them form a scaffold that guides the brain back to the waking state. Here, we investigate the mechanisms that constrain cortical activity to discrete states and give rise to abrupt transitions among them. If state transitions were imposed onto the thalamocortical system by changes in the subcortical modulation, different cortical sites should exhibit near-synchronous state transitions. To test this hypothesis, we quantified state synchrony at different cortical sites in anesthetized rats. States were defined by compressing spectra of layer-specific local field potentials (LFPs) in visual and motor cortices. Transition synchrony, mutual information, and canonical correlations all demonstrate that most state transitions in the cortex are local and that coupling between sites is weak. Fluctuations in the LFP in the thalamic input layer 4 were particularly dissimilar from those in supra- and infra-granular layers. Thus, our results suggest that the discrete global cortical states are not imposed by the ascending modulatory pathways but emerge from the multitude of weak pairwise interactions within the cortex.

The features of metabolism and structural organization of dental system under conditions of experimental insulin resistance

Peculiarities of calcium homeostasis, the activity of energy synthesis enzymes and structural organization of the dental system in rats under conditions of insulin resistance were analyzed. It was found that impaired glucose tolerance is manifested by a decreased mineralizing ability of hard tissues of alveolar processes and teeth, accompanied by a decrease in calcium content in erythrocyte mass and alveolar processes and an increase in acid phosphatase activity in blood serum. In rats with insulin resistance a decrease in the activity of lactate- and succinate dehydrogenase was detected. Degenerative changes were observed in the bone thickness of the dental area of insulin resistant rats, which were accompanied by the development of hypercellularity of the osteogenic layer of periosteum. Reactive changes in the tooth pulp were manifested by a decrease in the area of its loose connective tissue. Hyperplastic changes with the formation of unexpressed acanthotic bands developed in the oral mucosa of experimental animals, the thickness of the basal and granular layers increased against the background of a decrease in the prickle layer of epitheliocytes. In experimental group we observed a decrease in the nuclear cytoplasmic index and an increase in keratin formation in the epithelium. A narrowing of the lumen of capillaries and arterioles of the dental area, hyperplasia of endothelial cells and an increased accumulation of glycoproteins, especially in small arteries, were also detected in experimental group. Thus, altered carbohydrate metabolism leads to the metabolic changes of teeth supporting apparatus and oral mucosa, aggravating the course of insulin resistance with the development of dental system pathology.

Potential Investigation of Stabilised Fuming Furnace Slag for Road Construction

Fuming furnace (FF) slag is one of the industrial waste materials which is generated during extraction of zinc metal at the zinc industry. It is deposited at the designated FF slag yard near the plant area with very limited use. As a result, the deposits are increasing year after year posing threat to the environment and occupying large area of precious land. The present research explores the possibility of using this waste material in the road construction. The tests like Scanning electron microscope (SEM), Energy dispersive spectrometer (EDS) and X-ray diffraction was carried out on FF slag. To improve its geotechnical properties, it was mechanically stabilised with jarofix (another waste material generated from the same zinc industry) in the range of 25 to 75 percent. Apart from compaction characteristics, shear strength and consolidation characteristics of these mixes were studied to conclude about its feasibility in embankment and granular layers of road pavement. These mixes were further chemically stabilized with cement in the range of 3 to 9 percent to investigate their potential application in sub base and base layers of road construction. Compressive and durability characteristics of these mixes were also studied. Detailed laboratory study concluded that FF slag is a porous; amorphous cohesionless coarse grained material with high angle of internal friction. Engineering properties viz. dry density, CBR, and shear strength characteristics improved significantly after mechanical stabilisation with jarofix. These parameters of FF slag were compared with other industrial waste materials. Unconfined compressive strength and durability characteristics indicated suitability of cement stabilised slag-jarofix mixes for sub base and base layers of road pavement. It was concluded that about 20-30 percent of FF slag can be used as a replacement of fine aggregate in these granular layers. A typical pavement design indicated that it is possible to reduce the total pavement thickness of about 13 percent by using cement stabilised slag-jarofix mix.

Review of Improved Subgrade and Stabilized Subbases to Evaluate Performance of Concrete Pavements

This report presents findings on the evaluation of foundation layers under concrete pavements in the state of Illinois. It also provides recommendations and scenarios where unbound granular layers can be safely used under concrete pavements as economical and well-performing subbase layers. The current practice and mechanistic design methods for constructing concrete pavements in Illinois was first evaluated, including historical studies that led to the current design procedures and policies. The performance of concrete pavements with unbound granular layers in Illinois were then evaluated, and several case studies of well-performing concrete pavements with granular subbases, high traffic levels, and low distress levels and severity were realized. Next, the practices of surrounding states were evaluated, and several Midwest states, i.e., Wisconsin, Minnesota, Iowa, and Michigan, were found to regularly use unbound granular layers under concrete pavements with no issues. A literature review on the most recent requirements and recommendations for designing granular subbases under concrete pavements was then presented. It is concluded that subbase layers under concrete pavements are mainly used to provide uniform support and prevent pumping. Based on the case study evaluations and literature, a stable, drainable, and durable daylighted granular subbase design is recommended for traffic factors up to 10.0. Stability is ensured by limiting the ratio of gravel-to-sand fractions in the aggregate mix between 1.3 and 1.9. Drainability requirements can be met by limiting the percentage of fines passing the No. 200 sieve (0.075 mm) to 4% and by checking the quality of drainage is at least fair based on the time required to drain 50% of the water. Lastly, a geotextile fabric is recommended for use below the granular subbase for separation to ensure drainability throughout design life.

Finite Element Modeling of the Dynamic Response of Critical Zones in a Ballasted Railway Track

The critical zones are the discontinuities along a railway line that are highly susceptible to differential settlement, due to an abrupt variation in the support conditions over a short span. Consequently, these zones require frequent maintenance to ensure adequate levels of passenger safety and comfort. A proper understanding of the behavior of railway tracks at critical zones is imperative to enhance their performance and reduce the frequency of costly maintenance operations. This paper investigates the dynamic behavior of the critical zone along a bridge-open track transition under moving train loads using two-dimensional finite element approach. The influence of different subgrade types on the track behavior is studied. The effectiveness of using geogrids, wedge-shaped engineered backfill and zone with reduced sleeper spacing in improving the performance of the critical zone is evaluated. The numerical model is successfully validated against the field data reported in the literature. The results indicate that the subgrade soil significantly influences the track response on the softer side of the critical zone. The difference in vertical displacement between the stiffer and the softer side of a track transition decreases significantly with an increase in the strength and stiffness of the subgrade soil. The subgrade layer also influences the contribution of the granular layers (ballast and subballast) to the overall track response. As the subgrade becomes stiffer and stronger, the contribution of the granular layers to the overall track displacement increases. The mitigation techniques that improve the stiffness or strength of granular layers may prove more effective for critical zones with stiff subgrade than critical zones with soft subgrade. Among all the mitigation techniques investigated, the wedge-shaped engineered backfill significantly improved the performance of the critical zone by gradually increasing the track stiffness.