Transcranial magnetic stimulation of the brain: What is stimulated? - A consensus and critical position paper

Transcranial (electro)magnetic stimulation (TMS) is currently the method of choice to non-invasively induce neural activity in the human brain. A single transcranial stimulus induces a time-varying electric field in the brain that may evoke action potentials in cortical neurons. The spatial relationship between the locally induced electric field and the stimulated neurons determines axonal depolarization. The induced electric field is influenced by the conductive properties of the tissue compartments and is strongest in the superficial parts of the targeted cortical gyri and underlying white matter. TMS likely targets axons of both excitatory and inhibitory neurons. The propensity of individual axons to fire an action potential in response to TMS depends on their geometry, myelination and spatial relation to the imposed electric field and the physiological state of the neuron. The latter is determined by its transsynaptic dendritic and somatic inputs, intrinsic membrane potential and firing rate. Modeling work suggests that the primary target of TMS is axonal terminals in the crown top and lip regions of cortical gyri. The induced electric field may additionally excite bends of myelinated axons in the juxtacortical white matter below the gyral crown. Neuronal excitation spreads ortho- and antidromically along the stimulated axons and causes secondary excitation of connected neuronal populations within local intracortical microcircuits in the target area. Axonal and transsynaptic spread of excitation also occurs along cortico-cortical and cortico-subcortical connections, impacting on neuronal activity in the targeted network. Both local and remote neural excitation depend critically on the functional state of the stimulated target area and network. TMS also causes substantial direct co-stimulation of the peripheral nervous system. Peripheral co-excitation propagates centrally in auditory and somatosensory networks, but also produces brain responses in other networks subserving multisensory integration, orienting or arousal. The complexity of the response to TMS warrants cautious interpretation of its physiological and behavioural consequences, and a deeper understanding of the mechanistic underpinnings of TMS will be critical for advancing it as a scientific and therapeutic tool.

Effects of iTBS-rTMS on the Behavioral Phenotype of a Rat Model of Maternal Immune Activation

Repetitive transcranial magnetic stimulation (rTMS) is considered a promising therapeutic tool for treating neuropsychiatric diseases. Previously, we found intermittent theta-burst stimulation (iTBS) rTMS to be most effective in modulating cortical excitation-inhibition balance in rats, accompanied by improved cortical sensory processing and sensory learning performance. Using an animal schizophrenia model based on maternal immune activation (MIA) we tested if iTBS applied to either adult or juvenile rats can affect the behavioral phenotype in a therapeutic or preventive manner, respectively. In a sham-controlled fashion, iTBS effects in MIA rats were compared with rats receiving vehicle NaCl injection instead of the synthetic viral strand. Prior to iTBS, adult MIA rats showed deficits in sensory gating, as tested with prepulse inhibition (PPI) of the acoustic startle reflex, and deficits in novel object recognition (NOR). No differences between MIA and control rats were evident with regard to signs of anxiety, anhedonia and depression but MIA rats were somewhat superior to controls during the training phase of Morris Water Maze (MWM) test. MIA but not control rats significantly improved in PPI following iTBS at adulthood but without significant differences between verum and sham application. If applied during adolescence, verum but not sham-iTBS improved NOR at adulthood but no difference in PPI was evident in rats treated either with sham or verum-iTBS. MIA and control rat responses to sham-iTBS applied at adulthood differed remarkably, indicating a different physiological reaction to the experimental experiences. Although verum-iTBS was not superior to sham-iTBS, MIA rats seemed to benefit from the treatment procedure in general, since differences-in relation to control rats declined or disappeared. Even if classical placebo effects can be excluded, motor or cognitive challenges or the entire handling procedure during the experiments appear to alleviate the behavioral impairments of MIA rats.

Effects of repetitive transcranial magnetic and deep brain stimulation on long-range synchrony of oscillatory activity in a rat model of developmental schizophrenia

Aberrant neuronal network activity likely resulting from disturbed interactions of excitatory and inhibitory systems may be a major cause of cognitive deficits in neuropsychiatric diseases, like within the spectrum of schizophrenic phenotypes. In particular, the synchrony and pattern of oscillatory brain activity appears to be disturbed within limbic networks, e.g. between prefrontal cortex and hippocampus. In a rat model of maternal immune activation (MIA), we compared the acute effects of deep brain stimulation within either medial prefrontal cortex or ventral hippocampus with the effects of repetitive transcranial magnetic stimulation (rTMS), using the intermittent theta-burst protocol (iTBS), on oscillatory activity within limbic structures. Simultaneous local field potential recordings were made from medial prefrontal cortex, ventral hippocampus, nucleus accumbens and rostral part of ventral tegmental area before and after deep brain stimulation in anaesthetized rats previously (~3 h) treated with sham or verum rTMS. We found a waxing and waning pattern of theta and gamma activity in all structures which was less synchronous in particular between medial prefrontal cortex and ventral hippocampus in MIA offspring. Deep brain stimulation in medial prefrontal cortex and pre-treatment with iTBS-rTMS partly improved this pattern. Gamma-theta cross-frequency coupling was stronger in MIA offspring and could partly be reduced by deep brain stimulation in medial prefrontal cortex. We can confirm aberrant limbic network activity in a rat MIA model, and at least acute normalizing effects of the neuromodulatory methods. It has to be proven whether these procedures can have chronic effects suitable for therapeutic purposes.

Repetitive transcranial magnetic stimulation reverses reduced excitability of rat visual cortex induced by dark rearing during early critical period

Early critical period of visual cortex is characterized by enhanced activity-driven neuronal plasticity establishing the specificity of neuronal connections required for optimal processing of sensory signals. Deprivation from visual input by dark rearing (DR) during this period leads to a lasting impairment of visual performance. Previously, we demonstrated that repetitive transcranial magnetic stimulation (rTMS) applied with intermittent theta-burst (iTBS) pattern during the critical period improved the visual performance of the DR rats. In this study, we describe that the excitability of the binocular part of the visual cortex (V1b), as measured in acute brain slices by input-output ratios of field excitatory synaptic potentials (fEPSPs), is lowered in DR rats compared to normal controls. Verum rTMS applied with the iTBS pattern during DR reversed this DR effect, while no rTMS effect was evident in the non-DR (nDR) rats. In addition, verum rTMS reduced the number of neurons expressing the 67 kD isoform of glutamic acid decarboxylase (GAD67), the calcium-binding protein calbindin (CB) and the zinc-finger transcription factor zif268/EGR1, as determined via immunohistochemistry, only in DR rats but not in nDR rats. Moreover, rTMS reduced the number of neurons expressing the calcium-binding protein parvalbumin (PV) only in nDR rats which showed more PV+ neurons compared to DR rats. This study confirms that iTBS-rTMS may be able to prevent or reverse the effects of DR on visual cortex physiology, likely through a modulation of the activity of inhibitory interneurons.

AMPA Induces NO-Dependent cGMP Signals in Hippocampal and Cortical Neurons via L-Type Voltage-Gated Calcium Channels

The nitric oxide (NO)/cGMP signaling cascade has an established role in synaptic plasticity. However, with conventional methods, the underlying cGMP signals were barely detectable. Here, we set out to confirm the well-known NMDA-induced cGMP increases, to test the impact of AMPA on those signals, and to identify the relevant phosphodiesterases (PDEs) using a more sensitive fluorescence resonance energy transfer (FRET)-based method. Therefore, a “knock-in” mouse was generated that expresses a FRET-based cGMP indicator (cGi-500) allowing detection of cGMP concentrations between 100 nM and 3 μM. Measurements were performed in cultured hippocampal and cortical neurons as well as acute hippocampal slices. In hippocampal and cortical neurons, NMDA elicited cGMP signals half as high as the ones elicited by exogenous NO. Interestingly, AMPA increased cGMP independently of NMDA receptors and dependent on NO synthase (NOS) activation. NMDA- and AMPA-induced cGMP signals were not additive indicating that both pathways converge on the level of NOS. Accordingly, the same PDEs, PDE1 and PDE2, were responsible for degradation of NMDA- as well as AMPA-induced cGMP signals. Mechanistically, AMPAR induced calcium influx through L-type voltage-gated calcium channels leading to NOS and finally NO-sensitive guanylyl cyclase activation. Our results demonstrate that in addition to NMDA also AMPA triggers endogenous NO formation and hence cGMP production.

Repetitive transcranial magnetic stimulation recovers cortical map plasticity induced by sensory deprivation due to deafferentiation

KEY POINTS

Partial sensory deprivation (deafferentation) by removing whiskers from the rat snout resulted in a reduced responsiveness of related cortical representations. Repetitive transcranial magnetic stimulation (three blocks of intermittent theta-burst) applied for 5 days in combination with sensory exploration restored the normal responsiveness level of the deafferented barrel cortex. However, intracortical inhibition (lateral and recurrent) appeared to be reduced after repetitive transcranial magnetic stimulation, probably as the cause of improved responsiveness. Repetitive transcranial magnetic stimulation also reduced the asymmetry of the lateral spread of sensory activity.

ABSTRACT

Repetitive transcranial magnetic stimulation (rTMS) modulates human cortical excitability. It has the potential to support recovery to normal cortical function when the excitation-inhibition balance is altered (e.g. after a stroke or loss of sensory input). We tested cortical map plasticity on the basis of sensory responses (local field potentials, LFPs) and expression of neuronal activity marker proteins within the barrel cortex of rats receiving either active or sham rTMS after selective unilateral deafferentation by whiskers plucking. Rats received daily rTMS [intermittent theta-burst (iTBS), active or sham] for 5 days before exploring an enriched environment. Our previous studies indicated a disinhibitory effect of iTBS on cortical activity. Therefore, we also expected disinhibitory effects if deafferentation causes depression of sensory responses. Deafferentation resulted in an acute general reduction of sensory responsiveness and enhanced expression of inhibitory activity markers (GAD67, parvalbumin) in the deafferented hemisphere. Active but not sham-iTBS-rTMS normalized these measures. The stronger caudal-to-frontal horizontal spread of activity across barrels was reduced after deafferentation but not restored after active iTBS, despite generally increased responses. Fitting the LFP data with a computational model of different strengths and types of excitatory and inhibitory connections further revealed an iTBS-induced reduction of lateral and recurrent inhibition as the most probable scenario. Whether the disinhibitory effect of iTBS for the restoration of normal cortical function in the acute phase of depression after deafferentiation is also beneficial in humans remains to be demonstrated. As recently discussed, disinhibition appears to be required to open a window for neuronal plasticity.

GABA-from Inhibition to Cognition: Emerging Concepts

Neural functioning and plasticity can be studied on different levels of organization and complexity ranging from the molecular and synaptic level to neural circuitry of whole brain networks. Across neuroscience different methods are being applied to better understand the role of various neurotransmitter systems in the evolution of perception and cognition. GABA is the main inhibitory neurotransmitter in the adult mammalian brain and, depending on the brain region, up to 25% of the total number of cortical neurons are GABAergic interneurons. At the one end of the spectrum, GABAergic neurons have been accurately described with regard to cell morphological, molecular, and electrophysiological properties; at the other end researchers try to link GABA concentrations in specific brain regions to human behavior using magnetic resonance spectroscopy. One of the main challenges of modern neuroscience currently is to integrate knowledge from highly specialized subfields at distinct biological scales into a coherent picture that bridges the gap between molecules and behavior. In the current review, recent findings from different fields of GABA research are summarized delineating a potential strategy to develop a more holistic picture of the function and role of GABA.

Real-World Data Collection Regarding Titration Algorithms for Insulin Glargine in Patients With Type 2 Diabetes Mellitus

The primary objective of this study was to collect data regarding the effectiveness of different dose titration algorithms (TAs) for optimization or initiation of basal insulin supported oral therapy (BOT) in patients with type 2 diabetes. A total of 50 patients were enrolled in this trial (17 women, 33 men, age 63 ± 8 years, HbA1c 7.9 ± 0.8%). The investigator decided on an individual basis to apply any of 4 standard TAs: standard (S: fasting glucose target 90-130 mg/dL, n = 39), standard-fast titration (S-FT: 90-130 mg/dL, larger dose increments at FBG < 180 mg/dl, n = 1), less tight (LT: 110-150 mg/dL, n = 5), and tight (T: 70-100 mg/dL, n = 5). During the next 30 days daily contacts were used to adapt the insulin dose. The majority of all patients (70%) achieved a stable insulin glargine dose within 5 ± 6 days after initiation of the dose titration. HbA1c improved from 7.9 ± 0.8% to 7.5 ± 0.7% (P < .001). In total, 1300 dose decisions were made (1192 according to the TA and 108 by the physicians independently from the TA in 29 patients [58% of study population]). Reasons for TA-overruling dosing decisions were hypoglycemic events (14 mild/4 moderate) in 9 patients. In the majority of these cases (89.8%), the physician recommended continuation of the previous dose or a higher dose. The majority of FBG values were within the respective target range after 4 weeks. In conclusion, the insulin glargine TAs delivered safe dose recommendations with a low risk of hypoglycemia, which successfully led to a stable dose in the vast majority of patients.

Intermittent Theta-Burst Transcranial Magnetic Stimulation Alters Electrical Properties of Fast-Spiking Neocortical Interneurons in an Age-Dependent Fashion

Modulation of human cortical excitability by repetitive transcranial magnetic stimulation (rTMS) appears to be in part related to changed activity of inhibitory systems. Our own studies showed that intermittent theta-burst stimulation (iTBS) applied via rTMS to rat cortex primarily affects the parvalbumin-expressing (PV) fast-spiking interneurons (FSIs), evident via a strongly reduced PV expression. We further found the iTBS effect on PV to be age-dependent since no reduction in PV could be induced before the perineuronal nets (PNNs) of FSIs start to grow around postnatal day (PD) 30. To elucidate possible iTBS-induced changes in the electrical properties of FSIs and cortical network activity during cortical critical period, we performed ex vivo-in vitro whole-cell patch clamp recordings from pre-labeled FSIs in the current study. FSIs of verum iTBS-treated rats displayed a higher excitability than sham-treated controls at PD29-38, evident as higher rates of induced action potential firing at low current injections (100-200 pA) and a more depolarized resting membrane potential. This effect was absent in younger (PD26-28) and older animals (PD40-62). Slices of verum iTBS-treated rats further showed higher rates of spontaneous excitatory postsynaptic currents (sEPSCs). Based on these and previous findings we conclude that FSIs are particularly sensitive to TBS during early cortical development, when FSIs show an activity-driven step of maturation which is paralleled by intense growth of the PNNs and subsequent closure of the cortical critical period. Although to be proven further, rTMS may be a possible early intervention to compensate for hypo-activity related mal-development of cortical neuronal circuits.

Repetitive magnetic stimulation induces plasticity of inhibitory synapses

Repetitive transcranial magnetic stimulation (rTMS) is used as a therapeutic tool in neurology and psychiatry. While repetitive magnetic stimulation (rMS) has been shown to induce plasticity of excitatory synapses, it is unclear whether rMS can also modify structural and functional properties of inhibitory inputs. Here we employed 10-Hz rMS of entorhinohippocampal slice cultures to study plasticity of inhibitory neurotransmission on CA1 pyramidal neurons. Our experiments reveal a rMS-induced reduction in GABAergic synaptic strength (2-4 h after stimulation), which is Ca(2+)-dependent and accompanied by the remodelling of postsynaptic gephyrin scaffolds. Furthermore, we present evidence that 10-Hz rMS predominantly acts on dendritic, but not somatic inhibition. Consistent with this finding, a reduction in clustered gephyrin is detected in CA1 stratum radiatum of rTMS-treated anaesthetized mice. These results disclose that rTMS induces coordinated Ca(2+)-dependent structural and functional changes of specific inhibitory postsynapses on principal neurons.

Multiple blocks of intermittent and continuous theta-burst stimulation applied via transcranial magnetic stimulation differently affect sensory responses in rat barrel cortex

KEY POINTS

Theta-burst stimulation (TBS) applied via transcranial magnetic stimulation is able to modulate human cortical excitability. Here we investigated in a rat model how two different forms of TBS, intermittent (iTBS) and continuous (cTBS), affect sensory responses in rat barrel cortex. We found that iTBS but less cTBS promoted late (>18 ms) sensory response components while not affecting the earliest response (8-18 ms). The effect increased with each of the five iTBS blocks applied. cTBS somewhat reduced the early response component after the first block but had a similar effect as iTBS after four to five blocks. We conclude that iTBS primarly modulates the activity of (inhibitory) cortical interneurons while cTBS may first reduce general neuronal excitability with a single block but reverse to iTBS-like effects with application of several blocks.

ABSTRACT

Cortical sensory processing varies with cortical state and the balance of inhibition to excitation. Repetitive transcranial magnetic stimulation (rTMS) has been shown to modulate human cortical excitability. In a rat model, we recently showed that intermittent theta-burst stimulation (iTBS) applied to the corpus callosum, to activate primarily supragranular cortical pyramidal cells but fewer subcortical neurons, strongly reduced the cortical expression of parvalbumin (PV), indicating reduced activity of fast-spiking interneurons. Here, we used the well-studied rodent barrel cortex system to test how iTBS and continuous TBS (cTBS) modulate sensory responses evoked by either single or double stimuli applied to the principal (PW) and/or adjacent whisker (AW) in urethane-anaesthetized rats. Compared to sham stimulation, iTBS but not cTBS particularly enhanced late (>18 ms) response components of multi-unit spiking and local field potential responses in layer 4 but not the very early response (<18 ms). Similarly, only iTBS diminished the suppression of the second response evoked by paired PW or AW-PW stimulation at 20 ms intervals. The effects increased with each of the five iTBS blocks applied. With cTBS a mild effect similar to that of iTBS was first evident after 4-5 stimulation blocks. Enhanced cortical c-Fos and zif268 expression but reduced PV and GAD67 expression was found only after iTBS, indicating increased cortical activity due to lowered inhibition. We conclude that iTBS but less cTBS may primarily weaken a late recurrent-type cortical inhibition mediated via a subset of PV+ interneurons, enabling stronger late response components believed to contribute to the perception of sensory events.

High-Frequency Conductivity Plateau and Ionic Hopping Processes in a Ternary Lithium Borate Glass

Complete conductivity spectra of a lithium ion conducting glass of composition B2O3-0.56Li2O - 0.45 LiBr have been taken at twelve temperatures from 173 K to 573 K, covering the frequency range from a few Hertz up to about 50 THz. For the first time, a separation of the hopping and vibrational contributions to the spectra has been performed. The resulting frequency dependent hopping conductivity displays a high-frequency plateau similar to those known to exist in crystalline solid electrolytes like RbAg4I5 and Na-β-alumina. In the dispersive regime of the conductivity, there is an increase of the apparent power-law exponent from p = 0.6 to q = 1.3. The spectra are evaluated by combined application of the jump relaxation model and the dynamic structure model. Besides the translational hopping of the lithium ions via the preferred Ā sites, more localized kinds of motion are also detected, viz., hops into the less favoured C̄ sites (and mostly back again) as well as smaller displacements of the ions within their local environment.

Creation and Recombination of Frenkel Defects in AgBr

Complete ionic conductivity spectra as well as quasielastic and inelastic neutron scattering spectra have been taken of solid silver bromide at various temperatures. High-amplitude vibrational move­ments, essentially of the silver ions, contribute to both kinds of spectra. In particular, a conductivity maximum, located at about 500 GHz, reflects oscillations of individual silver ions along directions. -The microwave and millimetre-wave conductivities are dominated by a thermally activated Debye-type relaxation process. The effect is consistently explained by the frequent hopping of silver ions from regular octahedral lattice sites into tetrahedral interstitial sites and back again, i.e., by the frequent creation and recombination of Frenkel pairs. -The effect is also responsible for the existence of thermally activated quasielastic components in the neutron scattering spectra. The width of the coherent quasielastic scattering shows that the forward-backward hopping of a silver ion is accompanied by fast correlated movements of ions in its immediate neighbourhood.

Low Frequency Lattice Absorption in RbAg4I5 Solid Electrolyte

Far infrared transmission and reflexion measurements were performed on polycrystalline samples of α-RbAg4I5 solid electrolyte. As in α-AgI, an anomalous broad low frequency ab­sorption band centred at 5 · 1011 Hz is found in addition to the lattice absorption at ca. 3 · 1012 Hz. Since it is rather tempera­ture insensitive, the low frequency band indicates the exis­tence of very slow high amplitude lattice vibrations in this material.

The Barmer study: impact of standardized warming of the injection site to enhance insulin absorption and reduce prandial insulin requirements and hypoglycemia in obese patients with diabetes mellitus

BACKGROUND

The primary objective of this prospective controlled study was to investigate the impact of standardized injection-site warming on prandial rapid acting insulin dose and glycemic control when studied under real-world conditions.

METHODS

All 145 participating patients (51 female, 94 male, 13 type 1 and 132 type 2 patients, age: 61.6 ± 8.4 yrs, HbA1c: 7.19 ± 0.50%) were treated with intensive insulin glargine and short-acting insulin analog therapy. After a 4 week treatment optimization run-in period, patients were randomized to continue therapy for three months without (control) or with a local injection-site warming device (InsuPad * ). Observation parameters included HbA1c, insulin dose, frequency of hypoglycemia, body weight and adverse events.

RESULTS

HbA1c improved in both arms until study end (control group: 6.3 ± 0.5%; injection-site warming device: 6.3 ± 0.5%; both p < 0.001 vs. baseline). To achieve this good control, patients in the control group needed to increase the daily prandial insulin dose by 8.1% (from 66 ± 31 U to 71 ± 38 U, p < 0.05) with stable basal insulin requirements. Patients who used the injection-site warming device required less prandial insulin (70 ± 43 U to 55 ± 34 U; -19%, p < 0.001) and slightly more basal insulin (+3.9%). Total daily insulin dose increased in the control group (+3.7%) and decreased with warming device use (-8.6%, p < 0.001). The number of hypoglycemic events (<63 mg/dL) during the observation period was higher in the control group (6.2 ± 9.9/patient vs. injection-site warming device: 3.3 ± 4.8/patient, p < 0.05). Main study limitations can be seen in the open label design reliability of the collected dose information and the very obese patient cohort.

CONCLUSION

When treating obese patients to target with insulin therapy, use of an injection-site warming device for 3 months resulted in a lower frequency of hypoglycemic events and a reduction in prandial insulin analog requirements. If these results are confirmed in other patient populations, an injection-site warming device may be useful in achieving treatment targets with a safer and more efficient basal bolus therapy in insulin-treated patients with type 1 and type 2 diabetes.

Synergistic effects of noradrenergic modulation with atomoxetine and 10 Hz repetitive transcranial magnetic stimulation on motor learning in healthy humans

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is able to induce changes in neuronal activity that outlast stimulation. The underlying mechanisms are not completely understood. They might be analogous to long-term potentiation or depression, as the duration of the effects seems to implicate changes in synaptic plasticity. Norepinephrine (NE) has been shown to play a crucial role in neuronal plasticity in the healthy and injured human brain. Atomoxetine (ATX) and other NE reuptake inhibitors have been shown to increase excitability in different systems and to influence learning processes. Thus, the combination of two facilitative interventions may lead to further increase in excitability and motor learning. But in some cases homeostatic metaplasticity might protect the brain from harmful hyperexcitability. In this study, the combination of 60 mg ATX and 10 Hz rTMS over the primary motor cortex was used to examine changes in cortical excitability and motor learning and to investigate their influence on synaptic plasticity mechanisms.

RESULTS

The results of this double-blind placebo-controlled study showed that ATX facilitated corticospinal and intracortical excitability in motor cortex. 10 Hertz rTMS applied during a motor task was able to further increase intracortical excitability only in combination with ATX. In addition, only the combination of 10 Hz rTMS and ATX was capable of enhancing the total number of correct responses and reaction time significantly, indicating an interaction effect between rTMS and ATX without signs of homeostatic metaplasticity.

CONCLUSION

These results suggest that pharmacologically enhanced NE transmission and 10 Hz rTMS exert a synergistic effect on motor cortex excitability and motor learning in healthy humans.

Strain differences in the effect of rTMS on cortical expression of calcium-binding proteins in rats

Using a rat model to study the cellular effects of repetitive transcranial magnetic stimulation (rTMS) with regard to changes in cortical excitability, we previously described opposite effects of continuous and intermittent theta-burst stimulation (cTBS, iTBS) on the expression of the calcium-binding proteins (CaBP) parvalbumin (PV), calbindin (CB) and calretinin (CR) in Dark Agouti rats (DA). While iTBS significantly reduced the number of cortical PV+ cells but did not affect the CB+ cells, cTBS resulted in a decrease in CB+ cells with no effects on PV+ cells. We concluded that activity of these classes of cortical interneurons is differently modulated by iTBS and cTBS. When testing two further rat strains, Sprague-Dawley (SD) and Long Evans (LE), we obtained deviating results. In SD, iTBS reduced PV and CB expression, while cTBS only reduced PV expression. In contrast, reanalysed DA showed reduced CB expression after cTBS and reduced PV expression after iTBS, while LE shows an intermediate reaction. CR expression was unaffected in any case. Interestingly, we found significantly different basal expression patterns of the CaBPs for the strains, with DA and LE showing much higher numbers of PV+, CB+ and CR+ cells than SD, and with particularly higher number of CB+ and CR+ cells in DA compared to the other two strains. These findings demonstrate that inhibitory systems may be either differently developed in rats belonging to diverse strains or show different basal levels of activity and CaBP expression and may therefore be differently sensitive to the rTMS protocols.

Solid State Ionics: from Michael Faraday to green energy-the European dimension

Solid State Ionics has its roots essentially in Europe. First foundations were laid by Michael Faraday who discovered the solid electrolytes Ag2S and PbF2 and coined terms such as cation and anion, electrode and electrolyte. In the 19th and early 20th centuries, the main lines of development toward Solid State Ionics, pursued in Europe, concerned the linear laws of transport, structural analysis, disorder and entropy and the electrochemical storage and conversion of energy. Fundamental contributions were then made by Walther Nernst, who derived the Nernst equation and detected ionic conduction in heterovalently doped zirconia, which he utilized in his Nernst lamp. Another big step forward was the discovery of the extraordinary properties of alpha silver iodide in 1914. In the late 1920s and early 1930s, the concept of point defects was established by Yakov Il'ich Frenkel, Walter Schottky and Carl Wagner, including the development of point-defect thermodynamics by Schottky and Wagner. In terms of point defects, ionic (and electronic) transport in ionic crystals became easy to visualize. In an 'evolving scheme of materials science', point disorder precedes structural disorder, as displayed by the AgI-type solid electrolytes (and other ionic crystals), by ion-conducting glasses, polymer electrolytes and nano-composites. During the last few decades, much progress has been made in finding and investigating novel solid electrolytes and in using them for the preservation of our environment, in particular in advanced solid state battery systems, fuel cells and sensors. Since 1972, international conferences have been held in the field of Solid State Ionics, and the International Society for Solid State Ionics was founded at one of them, held at Garmisch-Partenkirchen, Germany, in 1987.

Modulation of cortical inhibition by rTMS - findings obtained from animal models

Transcranial magnetic stimulation (TMS) has become a popular method to non-invasively stimulate the human brain. The opportunity to modify cortical excitability with repetitive stimulation (rTMS) has especially gained interest for its therapeutic potential. However, details of the cellular mechanisms of the effects of rTMS are scarce. Currently favoured are long-term changes in the efficiency of excitatory synaptic transmission, with low-frequency rTMS depressing it, but high-frequency rTMS augmenting. Only recently has modulation of cortical inhibition been considered as an alternative way to explain lasting changes in cortical excitability induced by rTMS. Adequate animal models help to highlight stimulation-induced changes in cellular processes which are not assessable in human rTMS studies. In this review article, we summarize findings obtained with our rat models which indicate that distinct inhibitory cell classes, like the fast-spiking cells characterized by parvalbumin expression, are most sensitive to certain stimulation protocols, e.g. intermittent theta burst stimulation. We discuss how our findings can support the recently suggested models of gating and homeostatic plasticity as possible mechanisms of rTMS-induced changes in cortical excitability.

Jump Relaxation: Simple Equations, Relevant Functions, and Kohlrausch-Williams-Watts Behavior

Solid electrolytes with structural disorder generally exhibit characteristic deviations from standard-theory spectra. The effect is known as “universal” dynamic response. In the jump-relaxation model, the phenomena are consistently explained in terms of the non-random hopping resulting from the repulsive Coulomb interaction among the mobile ions. In previous stages of the development of the model, the treatment required either crude approximations or extensive numerical calculations. Now. however, we are able to present, for the first time. simple analytic expressions for the relevant time correlation functions, derived from the rate equations of the model. In particular, the dependence of the ionic conductivity on frequency and temperature is now expressed by a simple equation. Furthermore, we recover the Kohlrausch-Williams- Watts behavior and find the KWW exponent. β. and the mismatch parameter of our model, α. to be identical. The validity of the KWW law is shown to be limited to the dispersive regime on the frequency and time scales.

The Migration Concept for Ionic Motion in Materials With Disordered Structures

The dynamics of the mobile ions in materials with disordered structures are a challengingly complicated many-particle process. In this paper, we consider characteristic frequency-dependent conductivities and permittivities of such materials and show that they can be well reproduced within the framework of the MIGRATION concept. The meaning of the acronym is MIsmatch Generated Relaxation for the Accommodation and Transport of IONs. In the MIGRATION concept, we attempt to grasp the essence of the ion dynamics in a simple set of rules which convey a physical picture of the most relevant elementary processes. The rules are expressed in terms of three coupled rate equations which then form the basis for deriving frequency-dependent model conductivities and permittivities.

Concept of Mismatch and Relaxation Derived from Conductivity Spectra of Solid Electrolytes

Crystalline ion conductors like RbAg4I5 and others display a characteristic shape of their dispersive conductivities at frequencies below the microwave regime. As the temperature is decreased, the onset of the dispersion is shifted to lower frequencies and thus the characteristic shape of the dispersion becomes visible in an increasingly broad frequency range. In a log-log plot of the frequency-dependent conductivity, the slope is found to increase continuously, but not to surpass unity. For the first time, this behavior is now consistently explained. The particular shape of the dispersion is shown to be equivalent to a proportionality of the rates of relaxation via the singleand many-particle routes. This is the essence of the concept of mismatch and relaxation (CMR). Model conductivity spectra based on the CMR include the UDR (universal dynamic response) as well as the NCL (nearly constant loss) behavior. Both universalities are thus traced back to a common dynamic origin.

Cortical cellular actions of transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS) can be used in two different ways to manipulate cortical information processing, either by applying a single pulse around the time point of expected task processing or by persistently shifting cortical excitability by repetitive stimulation (rTMS). Single pulses applied when specific cortical processing takes place always impair cortical function due to increased noise or enhanced inhibition, both resulting in decreased signal-to-noise ratio, while repetitive stimulation may allow to weaken or improve cortical processing depending on the type of stimulation. The opposite effects of low- ( approximately 1 Hz) and high-frequency rTMS (5-20 Hz), as well as the opposing effects of continuous versus intermittent theta-burst trains, lowering or raising cortical excitability respectively, have mainly been attributed to synaptic plasticity. As reviewed in this article, in a series of electrophysiological, immunohistochemical and molecular-biological animal experiments we obtained evidence for modulation of inhibitory cortical activity as a further reason of changing cortical excitability following rTMS.

First and Second Universalities: Expeditions Towards and Beyond

Understanding the mechanisms of translational and localised ionic movements in disordered materials has seen intense activity spanning several decades. This article attempts to convey a concise overview of our contribution to this field over the period from 2005 to 2010 and to place it in its broad context.

Continuous and intermittent transcranial magnetic theta burst stimulation modify tactile learning performance and cortical protein expression in the rat differently

Repetitive transcranial magnetic stimulation (rTMS) can modulate cortical excitability in a stimulus-frequency-dependent manner. Two kinds of theta burst stimulation (TBS) [intermittent TBS (iTBS) and continuous TBS (cTBS)] modulate human cortical excitability differently, with iTBS increasing it and cTBS decreasing it. In rats, we recently showed that this is accompanied by changes in the cortical expression of proteins related to the activity of inhibitory neurons. Expression levels of the calcium-binding protein parvalbumin (PV) and of the 67-kDa isoform of glutamic acid decarboxylase (GAD67) were strongly reduced following iTBS, but not cTBS, whereas both increased expression of the 65-kDa isoform of glutamic acid decarboxylase. In the present study, to investigate possible functional consequences, we applied iTBS and cTBS to rats learning a tactile discrimination task. Conscious rats received either verum or sham rTMS prior to the task. Finally, to investigate how rTMS and learning effects interact, protein expression was determined for cortical areas directly involved in the task and for those either not, or indirectly, involved. We found that iTBS, but not cTBS, improved learning and strongly reduced cortical PV and GAD67 expression. However, the combination of learning and iTBS prevented this effect in those cortical areas involved in the task, but not in unrelated areas. We conclude that the improved learning found following iTBS is a result of the interaction of two effects, possibly in a homeostatic manner: a general weakening of inhibition mediated by the fast-spiking interneurons, and re-established activity in those neurons specifically involved in the learning task, leading to enhanced contrast between learning-induced and background activity.