Towards Optimal Testing of Auditory Memory : Methodological development of recording of the mismatch negativity (MMN) of the auditory event-related potential (ERP)

The overlapping sound pressure waves that enter our brain via the ears and auditory nerves must be organized into a coherent percept. Modelling the regularities of the auditory environment and detecting unexpected changes in these regularities, even in the absence of attention, is a necessary prerequisite for orientating towards significant information as well as speech perception and communication, for instance. The processing of auditory information, in particular the detection of changes in the regularities of the auditory input, gives rise to neural activity in the brain that is seen as a mismatch negativity (MMN) response of the event-related potential (ERP) recorded by electroencephalography (EEG). --- As the recording of MMN requires neither a subject s behavioural response nor attention towards the sounds, it can be done even with subjects with problems in communicating or difficulties in performing a discrimination task, for example, from aphasic and comatose patients, newborns, and even fetuses. Thus with MMN one can follow the evolution of central auditory processing from the very early, often critical stages of development, and also in subjects who cannot be examined with the more traditional behavioural measures of auditory discrimination. Indeed, recent studies show that central auditory processing, as indicated by MMN, is affected in different clinical populations, such as schizophrenics, as well as during normal aging and abnormal childhood development. Moreover, the processing of auditory information can be selectively impaired for certain auditory attributes (e.g., sound duration, frequency) and can also depend on the context of the sound changes (e.g., speech or non-speech). Although its advantages over behavioral measures are undeniable, a major obstacle to the larger-scale routine use of the MMN method, especially in clinical settings, is the relatively long duration of its measurement. Typically, approximately 15 minutes of recording time is needed for measuring the MMN for a single auditory attribute. Recording a complete central auditory processing profile consisting of several auditory attributes would thus require from one hour to several hours. In this research, I have contributed to the development of new fast multi-attribute MMN recording paradigms in which several types and magnitudes of sound changes are presented in both speech and non-speech contexts in order to obtain a comprehensive profile of auditory sensory memory and discrimination accuracy in a short measurement time (altogether approximately 15 min for 5 auditory attributes). The speed of the paradigms makes them highly attractive for clinical research, their reliability brings fidelity to longitudinal studies, and the language context is especially suitable for studies on language impairments such as dyslexia and aphasia. In addition I have presented an even more ecological paradigm, and more importantly, an interesting result in view of the theory of MMN where the MMN responses are recorded entirely without a repetitive standard tone. All in all, these paradigms contribute to the development of the theory of auditory perception, and increase the feasibility of MMN recordings in both basic and clinical research. Moreover, they have already proven useful in studying for instance dyslexia, Asperger syndrome and schizophrenia.

Physico-chemical properties of pure and x-ray irradiated single crystals of KAP

Single crystals of potassium hydrogen phthalate (KAP) have been grown by slow evaporation method from aqueous solutions. Thermal analyses indicate that KAP crystals decompose into phthalic anhydride and KOH around 520 K. Electrical properties of single crystals of KAP have been studied along with the effect of X-ray irradiation of the crystals. The electrical transport appears to be associated with tunneling of protons. The irradiated crystal exhibits lower dielectric constant and higher ac conductivity.

Effect of primary system damping on the optimum design of an untuned viscous dynamic vibration absorber

Explicit criteria for the optimum design of an untuned viscous dynamic vibration absorber are developed for the case of a viscously damped single degree of freedom springmass system. It is shown that for the particular case of an undamped main system, the results reduce to the classical ones obtained by using the concept of a fixed point on the response curve.

X-ray and molecular-dynamics studies on Mycobacterium leprae single-stranded DNA-binding protein and comparison with other eubacterial SSB structures

The crystal structures of two forms of Mycobacterium leprae single-stranded DNA-binding protein (SSB) have been determined at 2.05 and 2.8 A resolution. Comparison of these structures with the structures of other eubacterial SSBs indicates considerable variation in their quaternary association, although the DNA-binding domains in all of them exhibit the same OB-fold. This variation has no linear correlation with sequence variation, but could be related to variation in protein stability. Molecular-dynamics simulations have been carried out on tetrameric molecules derived from the two forms and the prototype Escherichia coli SSB and the individual subunits of both proteins. Together, the X-ray studies and molecular-dynamics simulations yield information on the relatively rigid and flexible regions of the molecule and on the effect of oligomerization on flexibility. The simulations provide insight into the changes in subunit structure on oligomerization. They also provide insight into the stability and time evolution of the hydrogen bonds/water bridges that connect the two pairs of monomers in the tetramer.

Effect of a QSO on the interstellar medium of its host galaxy

We consider the hydrodynamic evolution of gas in the interstellar medium of the host galaxy of a quasar due to Compton heating by the QSO radiation. We show that a Lagrangean formulation of the problem is necessary. It is found that the "hydrodynamic time scale" becomes important compared to the Compton heating time scale. We also relax the "single fluid" approximation by considering the existence of clouds and taking into account the mass loss from stars. The results predict star burst activity, and thus we explain the blue colors of the active galaxies.

Effect of specific FSH or LH deprivation on testicular function of the adult rat

While the need for FSH in initiating spermatogenesis in the immature rat is well accepted, its requirement for maintenance of spermatogenesis in adulthood is questioned. In the current study, using gonadotropin antisera to neutralize specifically either endogenous FSH or LH, we have investigated the effect of either FSH or LH deprivation for a 10-day period on (i) testicular macromolecular synthesis in vitro, (ii) the activities of testicular germ cell specific LDH-X and hyaluronidase enzymes, and finally (iii) on the concentration of sulphated glycoprotein (SGP-2), one of the Sertoli cell marker proteins. Both immature (35-day-old) and adult (100-day-old) rats have been used in this study. Since LH deprivation leads to a near total blockade of testosterone production, the ability of exogenous testosterone supplementation to override the effects of LH deficiency has also been evaluated. Deprivation of either of the gonadotropins significantly affected in vitro RNA and protein synthesis by both testicular minces as well as single cell preparations. Fractionation of dispersed testicular cells preincubated with labelled precursors of RNA and protein on Percoll density gradient revealed that FSH deprivation affected specifically the rate of RNA and protein synthesis of germ cell and not Leydig cell fraction. LH but not FSH deprivation inhibited [3H]thymidine incorporation into DNA. The inhibitory effect of LH could mostly be overriden by testosterone supplementation. LDH-X and hyaluronidase activities of testicular homogenates of adult rats showed significant reduction (50%; P less than .05) following either FSH or LH deprivation. Again testosterone supplementation was able to reverse the LH inhibitory effect.

Effect of V2O5 on the Surface and Structural Characteristics of Potassium Lithium Niobate

It has been suggested that materials with interesting and useful bulk non-linear optical properties might result by substituting vanadium, the lightest element in the group V of periodic table, for Nb or Ta atoms along with Li and three oxygens. It is with this motivation that we have been making attempts to grow single crystals of LiNbO3 doped with various concentrations of V2O5. Unfortunately the results obtained on the ceramic samples of this material have not been very encouraging, owing to their hygroscopic nature. However, our attempts to prepare both ceramic and single-crystalline samples of potassium lithium niobate (K3Li2Nb5O15; KLN) doped V2O5 were successful. In this letter we report the preliminary results concerning our studies on the effect of V2O5 doping on the structural as well as topographic features of both ceramic and single-crystalline samples of KLN.

Surface recombination at semiconductor electrodes: a single level study

The recombination and the faradaic fluxes are shown to be sensitive to the location of a single level recombination center, when it is located near the band edges. As the surface level is shifted deeper into the band gap from either of the band edges, the back emission terms are dominated by electron capture and hole capture terms, and the occupancy of the surface level is no longer determined by its location in the band gap. However, when one of the back emission terms determines the surface state occupancy, it is shown that there exists a simple relation between the value of the surface level and the recombination and the faradaic fluxes respectively. Expressions to this effect are derived and verified in the case of the recombination flux, which characterized by the potential at which it attains its maximum value. For the faradaic flux the results are qualitative.

Switching studies and the effect of irradiation on ferroelectric properties of TAAP and DTAAP

Polarization switching processes in TAAP and DTAAP have been studied by the Merz method. The switching process in DTAAP is slower than in TAAP. The temperature dependence of switching time indicates that the crystal might contain groups of domain nuclei with different activation energies. X-ray irradiation causes an increase in the threshold field below which switching could not occur and decrease in the mobility of domain walls. Irradiation decreases the peak value of dielectric constant, Tc and increases the value of coercive field. Domain structure studies on TAAP crystals have shown that the crystals grow as both predominantly single domain and multi domains, depending on which the internal bias increases or remains unaffected upon irradiation.

Effect of coordinated ions on structure and flexiblity of parallel G-quandruplexes: a molecular dynamics study

Single tract guanine residues can associate to form stable parallel quadruplex structures in the presence of certain cations. Nanosecond scale molecular dynamics simulations have been performed on fully solvated fibre model of parallel d(G7) quadruplex structures with Na+ or K+ ions coordinated in the cavity formed by the 06 atoms of the guanine bases. The AMBER 4.1 force field and Particle Mesh Ewald technique for electrostatic interactions have been used in all simulations. These quadruplex structures are stable during the simulation, with the middle four base tetrads showing root mean square deviation values between 0.5 to 0.8 A from the initial structure as well the high resolution crystal structure. Even in the absence of any coordinated ion in the initial structure, the G-quadruplex structure remains intact throughout the simulation. During the 1.1 ns MD simulation, one Na+ counter ion from the solvent as well as several water molecules enter the central cavity to occupy the empty coordination sites within the parallel quadruplex and help stabilize the structure. Hydrogen bonding pattern depends on the nature of the coordinated ion, with the G-tetrad undergoing local structural variation to accommodate cations of different sizes. In the absence of any coordinated ion, due to strong mutual repulsion, 06 atoms within G-tetrad are forced farther apart from each other, which leads to a considerably different hydrogen bonding scheme within the G-tetrads and very favourable interaction energy between the guanine bases constituting a G-tetrad. However, a coordinated ion between G-tetrads provides extra stacking energy for the G-tetrads and makes the quadruplex structure more rigid. Na+ ions, within the quadruplex cavity, are more mobile than coordinated K+ ions. A number of hydrogen bonded water molecules are observed within the grooves of all quadruplex structures

Effect of High Pressure on the Electrical Conductivity of TlInX2 (X = Se, Te) Layered Semiconductors

The dc electrical conductivity of TlInX2 (X = Se, Te) single crystals, parallel and perpendicular to the (001) c-axis is studied under high quasi-hydrostatic pressure up to 7.0 GPa, at room temperature. Conductivity measurements parallel to the c-axis are carried out at high pressures and down to liquid nitrogen temperatures. These materials show continuous metallization under pressure. Both compounds have almost the same pressure coefficient of the electrical activation energy parallel to the c-axis, d(ΔE∥)/dP = −2.9 × 10−10 eV/Pa, which results from the narrowing of the band gap under pressure. The results are discussed in the light of the band structure of these compounds.

Effect of Substitution of Ca on Thermal Expansion of Cordierite (Mg2Al4Si5O18)

The effect of substitution of calcium on the anisotropic axial thermal expansion of cordierite was investigated by using a high-temperature X-ray diffraction technique. The compositions were prepared by the sol–gel route. In the Mg2-xCax-Al4Si5O18 system, single-phase cordierite can be prepared for x up to 0.5. Thermal expansion anisotropy (αa–αc) of cordierites reduces progressively by the substitution of increasing amounts of Ca for Mg.

Effect of the pyrethroid insecticide fenvalerate on sodium current of rat dorsal root ganglion neuron

Fenvalerate is a widely used pyrethroid insecticide. The report presents our findings on the effect of fenvalerate on isolated whole-cell sodium currents in single rat dorsal root ganglionic neurons in culture, studied with patch-clamp technique. Fenvalerate decreased the amplitude of whole-cell sodium current and slowed the inactivation and tail current kinetics.

Influence of crack tip constraint on void growth in ductile FCC single crystals

Effect of constraint (stress triaxiality) on void growth near a notch tip in a FCC single crystal is investigated. Finite element simulations within the modified boundary layer framework are conducted using crystal plasticity constitutive equations and neglecting elastic anisotropy. Displacement boundary conditions based on model, elastic, two term K-T field are applied on the outer boundary of a large circular domain. A pre-nucleated void is considered ahead of a stationary notch tip. The interaction between the notch tip and the void is studied under different constraints (T-stress levels) and crystal orientations. It is found that negative T-stress retards the mechanisms of ductile fracture. However, the extent of retardation depends on the crystal orientation. Further, it is found that there exists a particular orientation which delays the ductile fracture processes and hence can potentially improve ductility. This optimal orientation depends on the constraint level. (C) 2010 Published by Elsevier B.V.

Dynamics of zeolite cage and its effect on the diffusion properties of sorbate: persistence of diffusion anomaly in NaA zeolite

Recent computer simulations on zeolites Y and A have found that the diffusion coefficient and the rate of intercage diffusion exhibit, apart from a linear dependence on the reciprocal of the square of the sorbate diameter, an anomalous peak as sorbate diameter approaches the window diameter. Here we report molecular dynamics simulations of zeolite NaA incorporating framework flexibility as a function of sorbate diameter in order to verify the existence of anomalous diffusion. Results suggest persistence of anomalous diffusion or ring effect. This suggests that the anomalous behavior is a general effect characteristic of zeolites Y and A. The barrier for diffusion across the eight-ring window is seen to be negative and is found to decrease with sorbate size. The effect of sorbate on the cage motion has also been investigated. Results suggest that the window expands during intercage migration only if the sorbate size is comparable to the window diameter. Flexible cage simulations yield a higher value for the diffusion coefficient and also the rate of intercage diffusion. This increase has been shown to be due to an increase in the intercage diffusions via the centralized diffusion mode rather than the surface-mediated mode. It is shown that this increase arises from an increase in the single particle density distribution in the region near the cage center.