Differential effects of theta-gamma tACS on motor skill acquisition in young individuals and stroke survivors: A double-blind, randomized, sham-controlled study.

BACKGROUND: Theta-gamma transcranial alternating current stimulation (tACS) was recently found to enhance thumb acceleration in young, healthy participants, suggesting a potential role in facilitating motor skill acquisition. Given the relevance of motor skill acquisition in stroke rehabilitation, theta-gamma tACS may hold potential for treating stroke survivors. OBJECTIVE: We aimed to examine the effects of theta-gamma tACS on motor skill acquisition in young, healthy participants and stroke survivors. METHODS: In a pre-registered, double-blind, randomized, sham-controlled study, 78 young, healthy participants received either theta-gamma peak-coupled (TGP) tACS, theta-gamma trough-coupled (TGT) tACS or sham stimulation. 20 individuals with a chronic stroke received either TGP or sham. TACS was applied over motor cortical areas while participants performed an acceleration-dependent thumb movement task. Stroke survivors were characterized using standardized testing, with a subgroup receiving additional structural brain imaging. RESULTS: Neither TGP nor TGT tACS significantly modified general motor skill acquisition in the young, healthy cohort. In contrast, in the stroke cohort, TGP diminished motor skill acquisition compared to sham. Exploratory analyses revealed that, independent of general motor skill acquisition, healthy participants receiving TGP or TGT exhibited greater peak thumb acceleration than those receiving sham. CONCLUSION: Although theta-gamma tACS increased thumb acceleration in young, healthy participants, consistent with previous reports, it did not enhance overall motor skill acquisition in a more complex motor task. Furthermore, it even had detrimental effects on motor skill acquisition in stroke survivors.

Single trial discrimination of individual finger movements on one hand: a combined MEG and EEG study.

It is crucial to understand what brain signals can be decoded from single trials with different recording techniques for the development of Brain-Machine Interfaces. A specific challenge for non-invasive recording methods are activations confined to small spatial areas on the cortex such as the finger representation of one hand. Here we study the information content of single trial brain activity in non-invasive MEG and EEG recordings elicited by finger movements of one hand. We investigate the feasibility of decoding which of four fingers of one hand performed a slight button press. With MEG we demonstrate reliable discrimination of single button presses performed with the thumb, the index, the middle or the little finger (average over all subjects and fingers 57%, best subject 70%, empirical guessing level: 25.1%). EEG decoding performance was less robust (average over all subjects and fingers 43%, best subject 54%, empirical guessing level 25.1%). Spatiotemporal patterns of amplitude variations in the time series provided best information for discriminating finger movements. Non-phase-locked changes of mu and beta oscillations were less predictive. Movement related high gamma oscillations were observed in average induced oscillation amplitudes in the MEG but did not provide sufficient information about the finger's identity in single trials. Importantly, pre-movement neuronal activity provided information about the preparation of the movement of a specific finger. Our study demonstrates the potential of non-invasive MEG to provide informative features for individual finger control in a Brain-Machine Interface neuroprosthesis.

[The patient in the psychiatric emergency ambulance: diagnoses, reasons and comparison of layperson vs. physician viewpoints]. / Der Patient in der psychiatrischen Notambulanz: Erstdiagnosen, Vorstellungsgründe und Vergleich der Laien- vs. Arztsicht.

A survey in specialties other than psychiatry showed that "emergency room"-patients have factors other than the presenting disease that determine the usage of urgent medical evaluation. In the following prospective study 104 outpatients presenting at daytime in a university psychiatric emergency care unit were included over 6 months. Apart from social and epidemiological data, illnesses according to ICD-10, reason for presentation from the patient's point of view and in this regard the physician's evaluation were included. The most prevalent diagnoses were depression, adjustment disorders and anxiety disorders, comprising together 75 %. Organic disorders or addictive disorders were less frequent; psychoses were found in 8 %. Concerning the presentation as an emergency, 70 % of patients reported a subjective clinical deterioration but only 44 % were regarded as an urgent need in the responsible physician's point of view (Cohen's kappa 0.39). Our findings show that patients presenting as "psychiatric emergency cases" without appointment mainly suffer from depression, adjustment disorders and panic disorders. Furthermore, the layperson's point of view of clinical deterioration justifying an emergency presentation differs from physician's evaluation. The most likely cause for this disagreement between physicians and patients in the assessment to utilise a medical emergency care service in psychiatry might be dysfunctional or, respectively, negative-biased cognitions accompanying depressive syndromes.

Isolation and kinetic analysis of inward currents in neuroblastoma cells.

The suction pipette method for combined voltage clamp and intracellular dialysis was applied to isolate the two components of voltage-gated inward current across membranes of NIE-115 neuroblastoma cells. In order to analyze the kinetic behavior of the Na+ and Ca2+ channels responsible for generating these components, current through K+ channels was effectively blocked by substituting impermeant Cs+ for internal and external K+. Block was confirmed independently by examining the effects of the application of external tetraethylammonium or Cd2+; and comparing the time course of Ca2+ tail currents with the decay of current during a maintained depolarization. Na+ currents studied at 8-10 degrees C, developed as a fourth order process giving a maximum e-fold conductance change for a 3 mV depolarization, with half activation occurring at -10 mV. The instantaneous current-voltage relationship was linear. Time constants of the activation parameter (m) varied from 0.5 ms (-50 mV) to 3-4 ms (-10 to -40 mV) at 10 degrees C. Inactivation (h) was a first order process having a time constant between 4 ms (+10 to +60 mV) and 225 ms (-60 mV). Steady-state inactivation for Na+ channels attained a value of 0.5 at -50 mV. A slow inactivation process, however, also is involved in gating of Na+ channels, and has a time course at least two orders of magnitude slower than that for h. The temperature sensitivity of Na+ currents was found to be similar to that found for other preparations. Ca2+ currents were studied at 24-29 degrees C in the presence of internal ethyleneglycolbis-(aminoethylether)-tetra-acetate (EGTA) and an external Ca2+ concentration of 20 mM. Ca2+ channel activation could also be described by a fourth order process giving an e-fold conductance change for a 5-6 mV change in potential and the half activation potential of -13 mV. Internal EGTA (20 mM) did not abolish inactivation of Ca2+ currents and no recovery from inactivation caused by a prepulse could be measured as the prepulse potential approached the null potential for Ca2+ influx. Time constants of both activation and inactivation of Ca2+ channels were measured between -20 and +50 mV. Currents through K+ channels could be completely eliminated by substitution of K+ with Cs+, although a residual non-linear leakage current remained, in addition to currents through the Na+ and Ca2+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium activated potassium channels in cultured astrocytes.

The patch clamp technique was used to analyze single channel currents in intact and excised patches of glial cell membranes grown in primary cultures from newborn rat brain. Glial cells were morphologically identified by immunohistochemical staining for glial fibrillary acidic protein. Outward currents due to single channels were observed in recordings from both intact and excised patches obtained from the cell body region. The channel responsible for these currents was preferentially permeable to K+ because the reversal potential for this current was correlated with changes in the potassium equilibrium potential, when experimentally altered. The single channel conductance was 25 pS when measured between -20 and +20 mV in solutions with physiological K+ concentrations (10 degrees C). Channel gating was dependent on both the internal Ca2+ concentration and the membrane potential. Either depolarization of the membrane patch, or the addition of increasing Ca2+ concentrations to the internal surface, increased the probability of channel opening. Tetraethylammonium reversibly blocked the channel whereas 4-aminopyridine had no effect. The characteristics exhibited by this channel indicate that a Ca2+-activated K+ channel is present in the membrane of astrocytes grown in culture. These results, combined with previous evidence for a voltage dependent Ca2+ channel, suggest a dynamic role for glial cells in controlling excitability in the central nervous system. Influx of Ca2+ upon depolarization would increase the membrane permeability to K+ and could increase the "buffering" capacity of glial cells for extracellular K+.

Acetylcholine-induced electrical responses in neuroblastoma cells.

The response to iontophoretic application of acetylcholine in the mouse neuroblastoma cell line N1E-115 was composed of three phases. The initial fast depolarizing phase was blocked by 10 microM d-tubocurarine, but not by 0.1 microM atropine. This phase was followed by a transient hyperpolarization which in turn was followed by a secondary slow depolarization. Both the hyperpolarization and slow depolarization were blocked by atropine (0.1 microM), but not by d-tubocurarine (10 microM). The hyperpolarization and slow depolarization were also evoked by iontophoretic application of the muscarinic agonist methacholine. Under voltage-clamp conditions, an initial fast inward current, a transient outward current, and a secondary slow inward current were recorded in response to acetylcholine application. These three phases of current correspond to the three phases of the membrane potential response. The initial fast inward current increased in amplitude by hyperpolarization of the membrane, and decreased by depolarization. The mean reversal potential was estimated to be -1 mV. The outward current increased in amplitude by depolarization, decreased by hyperpolarization, and reversed its polarity at -67 mV. Alteration of external K+ concentration shifted the reversal potential in the manner expected for an increase in potassium permeability. The slow inward current increased in amplitude by hyperpolarization, decreased by depolarization, and reversed its polarity at +20 mV. It is concluded that the initial fast inward current is mediated by a nicotinic receptor similar to that in muscle end-plate membranes and in postsynaptic membranes of the sympathetic ganglia. Both the outward current and the slow inward current are mediated by muscarinic receptors. The outward current results from an increase in the membrane permeability to K+, and the slow current appears to be carried, at least in part, by Na+.

Voltage-dependent gating and block of the cyclic-GMP-dependent current in bovine rod outer segments.

The properties of the cyclic-GMP-activated conductance in the plasma membrane of bovine rod outer segments were studied in excised membranes. Multiple-channel and single-channel currents were recorded by the patch-clamp technique in symmetrical NaCl solutions which were free of divalent cations. The current-voltage relationship for the current, recorded when a large population of channels was activated, exhibited outward rectification. Rectification decreased as the concentration of cyclic-GMP was increased, and the concentration of cyclic-GMP required for half maximal activation of the channel decreased with depolarization. At a concentration of 1-3 microM cyclic-GMP, single-channel activity could be observed from these excised patches. The conductance of the open channel was 6 pS and was independent of the membrane potential. These results are consistent with the interpretation that under these conditions, the mechanism responsible for the outward rectification is due to an increase in the probability of an open channel as the membrane is depolarized. The cyclic-GMP-activated current could be blocked by L-cis-diltiazem. Block was voltage and time dependent. The time constant for the onset of block and its steady state level increased with depolarization. The extent of block by diltiazem was not enhanced as the cyclic-GMP concentration was increased, suggesting that the channel is not required to be open for block to occur. Complete block was never attained even for high concentrations of diltiazem. However, the diltiazem-resistant component of the cyclic-GMP-activated current could be blocked by tetracaine.

Single inward rectifier channels in horizontal cells.

The ion channels responsible for inward rectification in horizontal cells were studied using the patch clamp technique applied to isolated cells from goldfish retina. Inward currents recorded from these cells were identified as due to the opening of inward rectifier channels based on their ion selectivity, channel gating behavior, and the effects of external blocking ions. The single channel conductance was 20 pS in 125 mM external K+. The null current potential shifted with changes in the K+ concentration as expected for a channel permeable to K+, and the channel appeared to have little permeability to Na+. The probability of a channel being in an open state increased as the membrane was hyperpolarized from the K+ equilibrium potential (0 to -10 mV) over potentials ranging to -80 mV, in the presence of external Na+. The closing rate was insensitive to membrane potential in the presence of external Na+. The opening rate of the channel increased as the membrane was hyperpolarized. The increase in the probability of a channel being open at negative potentials was therefore caused by the voltage sensitivity of the rate of channel opening.

Down-regulation of Na channel expression by A23187 in N1E-115 neuroblastoma cells.

Growth of cultured N1E-115 neuroblastoma cells in 1 microM A23187 for 2 days to elevate internal Ca reduced both membrane Na current and the transient, but not steady state, component of outward K current. Na channel mRNA abundance was reduced by an average value of 45% without effect on Kv3.1. Increases in internal Ca may therefore control excitability by independent regulation of Na and K channel mRNA abundance in neurons.

Modification of single sodium channels by the insecticide tetramethrin.

(+)-trans-Tetramethrin, a pyrethroid insecticide, markedly prolongs the open time of single sodium channels recorded by the gigaohm-seal voltage clamp technique in a membrane patch excised from the N1E-115 neuroblastoma cell. Single channel conductance is not altered by tetramethrin. The modification by tetramethrin occurs in an all-or-none manner in a population of sodium channels. The observed tetramethrin-induced modification of single sodium channels is compatible with previous sodium current data from axons.

All or none block of single Na+ channels by tetrodotoxin.

The effects of tetrodotoxin on single Na+-channel currents recorded from excised patches of neuroblastoma cells were examined. Tetrodotoxin was found to cause a dose-dependent reduction in the frequency at which Na+ channels conduct during a series of depolarizations. Surviving conducting states had normal open times and current amplitudes. These effects could be explained by a model which includes initial binding of tetrodotoxin to a closed state of the channel with stable, complete block during the time the channel would normally be gated open.

Effects of methylmercury on electrical responses of neuroblastoma cells.

The effects of methylmercury on a variety of electrophysiological properties of the N1E-115 neuroblastoma cells were studied using microelectrode and voltage clamp techniques. The action potential was reduced in amplitude with an apparent dissociation constant of the order of 20 microM in the face of relatively small membrane depolarization. Voltage clamp experiments revealed that both peak sodium current and steady-state potassium current were suppressed by 20-60 microM methylmercury, with a stronger effect on the sodium current than on the potassium current. The protein reagents dithiodipyridine and N-ethylmaleimide suppressed both currents. Acetylcholine receptor/channel complexes are vulnerable to the action of methylmercury; the nicotinic fast depolarizing response, the muscarinic hyperpolarizing response, and the muscarinic slow depolarizing response, were all suppressed by 10-30 microM methylmercury. In contrast, the dopamine induced response was not affected by methylmercury at 30 microM. It was concluded that methylmercury impairs both sodium and potassium channel gating mechanisms and suppresses acetylcholine receptor/channel complexes. It remains to be seen whether the effect of chronic exposure is similar to that seen after acute and high level exposure in the present study.

Burst kinetics of sodium channels which lack fast inactivation in mouse neuroblastoma cells.

1. The kinetics of the slow inactivation process of Na+ channels were examined by recording single-channel currents from cultured neuroblastoma cells. 2. In order to directly examine slow inactivation, fast inactivation was first removed irreversibly by briefly exposing the internal surface of excised membranes to papain. Following treatment, the time constant for the inactivation of averaged membrane Na+ current increased by over two orders of magnitude, while the open time of individual channels increased by a factor of three. The two effects are consistent with the idea that papain can selectively remove fast inactivation of Na+ channels. 3. In the absence of fast inactivation, Na+ channels continued to open during maintained depolarization of the membrane to potentials less negative than -60 mV. Under these conditions, the opening occurred in bursts 50 ms to hundreds of milliseconds long, followed by silent periods lasting many seconds. The average burst length was found to be equal to the time constant of the decline in average evoked current measured at the same potential, indicating that a burst was terminated by entry of the channel into the slow inactivated state. 4. Histograms of open times revealed two populations of open states at any potential. Bursts could also be classified as either short or long bursts. Bursts appeared to be due to the gating of a single channel, and long bursts contained both types of open states, suggesting that a Na+ channel could have more than one open state. 5. The kinetics of bursts of Na+ channels were voltage dependent. As the membrane was depolarized, the burst length, interval between bursts, and open time all increased. Although the probability of an open channel during a burst increased to almost 1.0 with depolarization, any channel was open less than 0.5% of the time when measured throughout the depolarization. The increase in burst duration with depolarization would occur if the rate of slow inactivation is faster from closed states of the channel than from open states. 6. Records of membrane current evoked by a series of step depolarizations were clustered into those with openings of Na+ channels and those without openings. Records in which a channel did not inactivate during the depolarization were less likely to lead to hibernation, suggesting that this phenomenon is caused by the slow inactivation process.

Modification of slow inactivation of single sodium channels by phenytoin in neuroblastoma cells.

Modifications of Na+ channels by phenytoin (PT), an anticonvulsant drug, were examined. Previous work using voltage-clamp methods indicated that PT could interact with inactivated states of the channel to reduce excitability. Single-channel analysis was used to test the idea that the fast inactivation process was not required for modification of the channel. The hypothesis that PT could interact with open or slow inactivated states to produce a drug-bound, long duration, nonconducting state was also tested. Currents due to the opening of single Na+ channels were measured in inside-out patches of membrane excised from N1E-115 mouse neuroblastoma cells grown in tissue culture. After the removal of the fast inactivation process enzymatically, the average Na+ current in response to a step depolarization decayed due to the slow inactivation process. The time constant of decay decreased as a function of the concentration of PT. The average current appeared to be caused by extensive reopening of Na+ channels. During maintained depolarization, the reopening of Na+ channels occurred in bursts interrupted by long silent periods, due to the slow inactivated state. PT decreased the burst duration and increased the interval between bursts. The average open time of Na+ channels was reduced in the presence of PT. All of the alterations were enhanced as the concentration of PT was increased. The amplitude of current through the open channel was not effected by PT. PT was able to modify the Na+ channel in the absence of fast inactivation. The results suggest that PT can bind to the Na+ channel and produce a nonconducting state from which the probability of a channel opening is small. These modifications could underly the selective block of action potentials during chronic depolarization of the membrane or during high frequency discharge.

Three kinetically distinct potassium channels in mouse neuroblastoma cells.

1. Mouse neuroblastoma cells were utilized to examine the electrical properties of single K+ channels which might underlie multiple components of outward current in vertebrate neurones. The conductance, kinetics of activation, inactivation, and pharmacology of three types of channels were compared. 2. Two types of voltage-dependent channels, primarily permeable to K+, were identified which did not require the presence of internal Ca2+. The first had gating kinetics best classified as a delayed rectifier. The conductance of the open channel was 35 pS (22 degrees C) in solutions having symmetrical 125 mM-K+ concentrations. 3. The second type of channel had a conductance of 14 pS under identical conditions. The gating kinetics of this type of channel were distinct from those of the delayed rectifier. The mean first latency, and lifetime of the open state at any voltage, were longer. The maximum probability of an open channel was smaller, so that this parameter appeared less sensitive to the membrane potential. The rate of inactivation of the channel was slower. Further, at the more negative membrane potentials tested, the level of steady-state inactivation was less for this type of channel. 4. The delayed rectifier channel was more sensitive to the blocking action of 4-aminopyridine than the channel with low conductance. 5. A Ca2+ -activated, voltage-dependent K+ channel, having a conductance of 140 pS, was also identified. The maximum probability of an open channel increased, and the voltage for half-maximal activation shifted to a more negative potential as the internal Ca2+ was increased. 6. The time course of inactivation of K+ currents recorded from the whole cell declined in two phases, probably due to the presence of the two types of voltage-dependent K+ channels.

Separable phases of light-evoked depolarizations in the retina of Strombus.

The waveforms of light-evoked depolarizations in Strombus retinal neurones can exhibit two sequential peaks or phases, the relative amplitudes of which vary with changes in stimulus intensity and interstimulus interval. Experiments employing either the passage of constant intracellular current or voltage clamp techniques indicate that both phases reverse polarity at intracellular potentials less negative than the resting potential. The potential at which the first phase reverses its polarity is considerably more positive than that of the second phase. The results indicate that the light-evoked depolarizations are generated by at least two different processes; these appear to be separate conductance changes, neither of which is voltage dependent. Under certain conditions, the second phase was inhibited by high extracellular concentrations of Mg2+, indicating that it may arise as a result of chemically mediated synaptic transmission. The first phase did not show such inhibition and appears to be caused by the direct action of light on the cell.

Tetraalkylammonium ion block of potassium currents in mouse neuroblastoma cells.

Experiments were performed to compare the mechanism of block of the delayed rectifier K+ channels in cultured mouse neuroblastoma cells by various derivatives of tetraethylammonium (TEA) which have symmetric alkyl chains of one to six carbons. Current from the whole cell was studied using the patch clamp technique. TEA blocked the whole cell K+ current with a Ki of 0.6 mM when applied to the external solution. The Ki for block by other derivatives were (mM): tetrapropylammonium, 9.2; tetrabutylammonium (TBA), 1.9; tetrapentylammonium (TPeA), 0.088; and tetrahexylammonium, (THA), 0.006. Block of the whole cell current by TEA or tetrapropylammonium did not increase with time after a step depolarization. However, block by TBA, TPeA or THA was time dependent. TEA did not compete with TPeA for the same receptor. Block by externally applied TEA was not appreciably voltage dependent, and the receptor for TPeA had an apparent electrical distance of 0.3. These observations suggest that TEA and TPeA block at separate receptors. THA could block the open channel in cell-attached patches when the compound was applied to the bath. This observation and the observation that externally applied TPeA and TEA do not occupy the same receptor suggest that derivatives having long alkyl chain lengths can reach the internal receptor from the external solution.

Aminopyridine block of potassium channels in mouse neuroblastoma cells.

Although 4-aminopyridine (4-AP) is known to block a variety of voltage-dependent K channels, details as to the site of action and the mechanism of block are known for relatively few. Single channel analysis has not been extensively used to answer these questions. The actions of 4-AP on whole cell K currents and single voltage-dependent K channels that exhibit fast activation and inactivation were therefore examined in N1E-115 neuroblastoma cells. The concentration for half block (K0.5) of the whole cell K current for externally applied compounds was found to be 56 microns for 4-AP and 0.3 mM for 3,4-diaminopyridine. 4-AP slowed the rate of development of outward K current, and the rate of decay after repolarization. These effects were consistent with the idea that 4-AP preferentially blocked a type of K channel generating a transient current. Block of this component of current was time- and use-dependent. 4-AP blocked the channel responsible for the transient outward current by decreasing the probability of an open channel in inside-out patches. 4-AP reduced the open time, indicating that 4-AP can interact with the open channel. The first latency to opening was also increased. 4-Aminopyridine methiodide (4-APMI), a permanently charged derivative, blocked the whole cell current with a K0.5 = 0.19 mM. Block by 4-APMI was found to be by a different mechanism at a different site compared to 4-AP.(ABSTRACT TRUNCATED AT 250 WORDS)

Action potential refractory period in axonal demyelination: a computer simulation.

Axonal demyelination leads to an increase in the refractory period for propagation of the action potential. Computer simulations were used to investigate the mechanism by which changes in the passive properties of the internodal membrane increase the refractory period. The properties of the voltage dependent ion channels can be altered to restore conduction in demyelinated nerve fibers. The ability of these alterations to decrease the refractory period of demyelinated model nerve fibers was compared. The model nerve fiber contained six nodes. The action potential was stimulated at node one and propagated to node six. The internode between nodes three and four was demyelinated in a graded manner. The absolute refractory period for propagation of the action potential through the demyelinated internode increased as the number of myelin wraps was reduced to less than 25% of the normal value. The increase in refractory period was found to be due to a reduction in the rate or repolarization of the action potential at node three. The delay in repolarization reduced the rate of recovery of inactivated Na channels and slowed the closing of K channels. The rate of repolarization of node three was reduced by the conduction delay for the depolarization of node four caused by demyelination of the preceding internode. In these simulations the increase in refractory period due to demyelination was eliminated by slowing the onset of Na channel inactivation. A small reduction of the K conductance also decreased the refractory period. However, larger reductions eliminated this effect.