Theta oscillations in the rat MS/DB complex in vitro: a locally generated, inhibition-based brain rhythm

The medial septum/diagonal band (MS/DB) complex, which forms part of the septohippocampal feedback loop, is thought to be critical for the generation and/or maintenance of the hippocampal theta rhythm (4-15 Hz) in vivo. Previously we demonstrated the presence of theta frequency rhythmic activity, within an in vitro slice preparation of the MS/DB, following application of the AMPA/kainate receptor agonist kainate (25–100 nM). Here we further investigate this rhythmic activity, in particular the effects of GABAA receptor mediated inhibition, on kainate induced theta activity in the MS/DB, using bath application of bicuculline. Longitudinal slices of the MS/DB (450 μm), from 21 day old rats, were maintained at 32°C in an interface recording chamber perfused with oxygenated ACSF. Following the bath application of kainate at 100 nM to the MS/DB, extracellular recordings of neuronal population activity, using ACSF-filled micropipettes, revealed rhythmic theta frequency activity. Bicuculline was then applied to the recording chamber and subsequent changes to the kainate induced activity were recorded at 30 and 60 minutes there after. Application of 10 µM bicuculline produced a significant reduction (P< 0.05, Student's T test) in the activity recorded at theta frequency (spectral integral in 4-15 Hz range) and in peak amplitude within 60 minutes of application (n=6). These results indicate a pivotal role for inhibitory transmission in pacing and maintaining the rhythmic activity that is observed in the MS/DB slice preparation following kainate induced theta frequency oscillations. SPONSOR: British Neuroscience Association

History effects and pinning regimes in solid vortex matter

We propose a phenomenological model that accounts for the history effects observed in ac susceptibility measurements in YBa2Cu3O7 single crystals [Phys. Rev. Lett. 84, 4200 (2000) and Phys. Rev. Lett. 86, 504 (2001)]. Central to the model is the assumption that the penetrating ac magnetic field modifies the vortex lattice mobility, trapping different robust dynamical states in different regions of the sample. We discuss in detail on the response of the superconductor to an ac magnetic field when the vortex lattice mobility is not uniform inside the sample. We begin with an analytical description for a simple geometry (slab) and then we perform numerical calculations for a strip in a transverse magnetic field which include relaxation effects. In calculations, the vortex system is assumed to coexist in different pinning regimes. The vortex behavior in the regions where the induced current density j has been always below a given threshold (j_c^>) is described by an elastic Campbell-like regime (or a critical state regime with local high critical current density, j_c^>). When the VS is shaken by symmetrical (e.g. sinusoidal) ac fields, the critical current density is modified to j_c^) at regions where vortices have been forced to oscillate by a current density larger than j_c^>. Experimentally, an initial state with high critical current density (j_c^>) can be obtained by zero field cooling, field cooling (with no applied ac field) or by shaking the vortex lattice with an asymmetrical (e.g. sawtooth) field. We compare our calculations with experimental ac susceptibility results in YBa2Cu3O7 single crystals.Comment: 11 pages, 7 figures. To be published in PR

Involvement of electrical signalling in theta frequency oscillations generated in the medial septum/diagonal band of Broca in vitro

Theta frequency (4 – 15 Hz) extracellular field activity can be reliably and repeatedly evoked in the medial septum/diagonal band of Broca (MS/DB) in vitro by the application of kainate. We have previously demonstrated a critical role for inhibitory neurotransmission in the maintenance of this activity and presented data that indicates parvalbumin GABAergic neurons are responsible for pacing rhythmic theta activity in the MS/DB. Evidence of functional electrical coupling between GABAergic interneurons has been reported in the hippocampus and neocortex and it has recently become clear that gap junctions may have a significant function in the generation of neuronal population activity. Here we demonstrate that application of the gap-junction uncoupling agent carbenoxolone causes a significant reduction (P< 0.05, Paired T test) in the kainate induced activity recorded at theta frequency (spectral integral in 4-15 Hz range) in the MS/DB slice in vitro. MS/DB slices were prepared from male Wistar rats (21 days), which were terminally anaesthetised with pentobarbitone sodium (120 mg.kg-1, i.p.). The animals were transcardially perfused with ~ 25ml of modified ACSF and rapidly decapitated. Longitudinal slices (450 µm) were placed in an interface recording chamber and maintained at 32°C. Persistent theta oscillations were induced by bath application of 100 nM kainate. Carbenoxolone was bath applied to stabilized kainate induced activity at a concentration of 100 μM for 60 minutes. At 60 minutes there was a significant reduction in the theta frequency activity recorded (56.6% ± 2.3) and in peak amplitude (n = 6). These results indicate a pivotal role for electrical signalling in the theta frequency rhythmic activity induced in the MS/DB upon application of kainate

Involvement of electrical signalling in theta frequency oscillations generated in the medial septum/diagonal band of Broca in vitro

Theta frequency (4 – 15 Hz) extracellular field activity can be reliably and repeatedly evoked in the medial septum/diagonal band of Broca (MS/DB) in vitro by the application of kainate. We have previously demonstrated a critical role for inhibitory neurotransmission in the maintenance of this activity and presented data that indicates parvalbumin GABAergic neurons are responsible for pacing rhythmic theta activity in the MS/DB. Evidence of functional electrical coupling between GABAergic interneurons has been reported in the hippocampus and neocortex and it has recently become clear that gap junctions may have a significant function in the generation of neuronal population activity. Here we demonstrate that application of the gap-junction uncoupling agent carbenoxolone causes a significant reduction (P< 0.05, Paired T test) in the kainate induced activity recorded at theta frequency (spectral integral in 4-15 Hz range) in the MS/DB slice in vitro. MS/DB slices were prepared from male Wistar rats (21 days), which were terminally anaesthetised with pentobarbitone sodium (120 mg.kg-1, i.p.). The animals were transcardially perfused with ~ 25ml of modified ACSF and rapidly decapitated. Longitudinal slices (450 µm) were placed in an interface recording chamber and maintained at 32°C. Persistent theta oscillations were induced by bath application of 100 nM kainate. Carbenoxolone was bath applied to stabilized kainate induced activity at a concentration of 100 μM for 60 minutes. At 60 minutes there was a significant reduction in the theta frequency activity recorded (56.6% ± 2.3) and in peak amplitude (n = 6). These results indicate a pivotal role for electrical signalling in the theta frequency rhythmic activity induced in the MS/DB upon application of kainate

Developmental dyslexia: predicting individual risk

Background: Causal theories of dyslexia suggest that it is a heritable disorder, which is the outcome of multiple risk factors. However, whether early screening for dyslexia is viable is not yet known. Methods: The study followed children at high risk of dyslexia from preschool through the early primary years assessing them from age 3 years and 6 months (T1) at approximately annual intervals on tasks tapping cognitive, language, and executive-motor skills. The children were recruited to three groups: children at family risk of dyslexia, children with concerns regarding speech, and language development at 3;06 years and controls considered to be typically developing. At 8 years, children were classified as 'dyslexic' or not. Logistic regression models were used to predict the individual risk of dyslexia and to investigate how risk factors accumulate to predict poor literacy outcomes. Results: Family-risk status was a stronger predictor of dyslexia at 8 years than low language in preschool. Additional predictors in the preschool years include letter knowledge, phonological awareness, rapid automatized naming, and executive skills. At the time of school entry, language skills become significant predictors, and motor skills add a small but significant increase to the prediction probability. We present classification accuracy using different probability cutoffs for logistic regression models and ROC curves to highlight the accumulation of risk factors at the individual level. Conclusions: Dyslexia is the outcome of multiple risk factors and children with language difficulties at school entry are at high risk. Family history of dyslexia is a predictor of literacy outcome from the preschool years. However, screening does not reach an acceptable clinical level until close to school entry when letter knowledge, phonological awareness, and RAN, rather than family risk, together provide good sensitivity and specificity as a screening battery

The field theoretic derivation of the contact value theorem in planar geometries and its modification by the Casimir effect

The contact value theorem for Coulomb gases in planar or film-like geometries is derived using a Hamiltonian field theoretic representation of the system. The case where the film is enclosed by a material of different dielectric constant to that of the film is shown to contain an additional Casimir-like term which is generated by fluctuations of the electric potential about its mean-field value.Comment: Link between Sine-Gordon and Coulomb gas pressures via subtraction of self interaction terms included. Discussion of results within Debye-Huckel approximation included. Added reference

Slow relaxations and history dependence of the transport properties of layered superconductors

We study numerically the time evolution of the transport properties of layered superconductors after different preparations. We show that, in accordance with recent experiments in BSCCO performed in the second peak region of the phase diagram (Portier et al, 2001), the relaxation strongly depends on the initial conditions and is extremely slow. We investigate the dependence on the pinning center density and the perturbation applied. We compare the measurements to recent findings in tapped granular matter and we interpret our results with a rather simple picture.Comment: 4 pages, 4 fig

Peak effect and its evolution with defect structure in YBa2Cu3O7-d thin films at microwave frequencies

The vortex dynamics in YBa2Cu3O7-d thin films have been studied at microwave frequencies. A pronounced peak in the surface resistance, Rs, is observed in these films at frequencies of 4.88 and 9.55 GHz for magnetic fields varying from 0.2 to 0.8 T. The peak is associated with an order-disorder transformation of the flux line lattice as the temperature or field is increased. The occurrence of the peak in Rs is crucially dependent on the depinning frequency, wp and on the nature and concentration of growth defects present in these films. Introduction of artificial defects by swift heavy ion irradiation with 200 MeV Ag ion at a fluence of 4x1010 ions/cm2 enhances wp and suppresses the peak at 4.88 GHz but the peak at 9.55 GHz remains unaffected. A second peak at lower temperature has also been observed at 9.55 GHz. This is related to twin boundaries from angular dependence studies of Rs. Based on the temperature variation of Rs, vortex phase diagrams have been constructed at 9.55 GHz.Comment: 8 pages, 4 figures Submitted to Physical Review

Metastability and Transient Effects in Vortex Matter Near a Decoupling Transition

We examine metastable and transient effects both above and below the first-order decoupling line in a 3D simulation of magnetically interacting pancake vortices. We observe pronounced transient and history effects as well as supercooling and superheating between the 3D coupled, ordered and 2D decoupled, disordered phases. In the disordered supercooled state as a function of DC driving, reordering occurs through the formation of growing moving channels of the ordered phase. No channels form in the superheated region; instead the ordered state is homogeneously destroyed. When a sequence of current pulses is applied we observe memory effects. We find a ramp rate dependence of the V(I) curves on both sides of the decoupling transition. The critical current that we obtain depends on how the system is prepared.Comment: 10 pages, 15 postscript figures, version to appear in PR

Sudden switch of generalized Lieb-Robinson velocity in a transverse field Ising spin chain

The Lieb-Robinson theorem states that the speed at which the correlations between two distant nodes in a spin network can be built through local interactions has an upper bound, which is called the Lieb-Robinson velocity. Our central aim is to demonstrate how to observe the Lieb-Robinson velocity in an Ising spin chain with a strong transverse field. We adopt and compare four correlation measures for characterizing different types of correlations, which include correlation function, mutual information, quantum discord, and entanglement of formation. We prove that one of correlation functions shows a special behavior depending on the parity of the spin number. All the information-theoretical correlation measures demonstrate the existence of the Lieb-Robinson velocity. In particular, we find that there is a sudden switch of the Lieb-Robinson speed with the increasing of the number of spin