A repetitive intracortical microstimulation pattern induces long-lasting synaptic depression in brain slices of the rat primary somatosensory cortex

Repetitive intracortical microstimulation (ICMS) applied to the rat primary somatosensory cortex (SI) in vivo was reported to induce reorganization of receptive fields and cortical maps. The present study was designed to examine the effect of such an ICMS pattern applied to layer IV of brain slices containing SI on the efficacy of synaptic input to layer II/III. Effects of ICMS on the synaptic strength was quantified for the first synaptic component (s1) of cortical field potentials (FPs) recorded from layer II/III of SI. FPs were evoked by stimulation in layer IV. The pattern of ICMS was identical to that used in vivo. However, stimulation intensity had to be raised to induce an alteration of synaptic strength. In brain slices superfused with standard ACSF, repetitive ICMS induced a short-lasting (60 min) reduction of the amplitude (-37%) and the slope (-61%) of s1 evoked from the ICMS site, while the amplitude and the slope of s1 evoked from a control stimulation site in cortical layer IV underwent a slow onset increase (13% and 50%, respectively). In brain slices superfused with ACSF containing 1.25 microM bicuculline, ICMS induced an initial strong reduction of the amplitude (-50%) and the slope (-79%) of s1 evoked from the ICMS site. These effects decayed to a sustained level of depression by -30% (amplitude) and -60% (slope). In contrast to experiments using standard ACSF, s1 evoked from the control site was not affected by ICMS. The presynaptic volley was not affected in either of the two groups of experiments. A conventional high frequency stimulation (HFS) protocol induced input-specific long-term potentiation (LTP) of the amplitude and slope of s1 (25% and 76%, respectively). Low frequency stimulation (LFS) induced input-specific long-term depression (LTD) of the amplitude and slope of s1 (24% and 30%, respectively). Application of common forms of conditioning stimulation (HFS and LFS) resulted in LTP or LTD of s1, indicating normal susceptibility of the brain slices studied to the induction of common forms of synaptic plasticity. Therefore, the effects of repetitive ICMS on synaptic FP components were considered ICMS-specific forms of short-lasting (standard ACSF) or long-lasting synaptic depression (ACSF containing bicuculline), the latter resembling neocortical LTD. Results of this study suggest that synaptic depression of excitatory mechanisms are involved in the cortical reorganization induced by repetitive ICMS in vivo. An additional contribution of an ICMS-induced modification of inhibitory mechanisms to cortical reorganization is discussed.     

重复多次硬膜外阻滞效果分析

本文分析重复多次硬膜外阻滞１８４例，（１）根据硬膜外阻滞的重复次数分为：Ｉ组（重复二次）优良率占８２．９％，Ⅱ组（重复三次）占６１．５％，Ⅲ组占５７．１％，Ｉ组与Ⅱ、Ⅲ组比较有显著性差异（Ｐ〈０．０５）。硬外腔用药量Ｉ组１３．８ｍｌ／ｈ，Ⅱ组８．９ｍｌ／ｈ，Ⅲ组７６．ｍｌ／ｈ，Ｉ组与Ⅱ、Ⅲ组相比较有非常显著性差异（Ｐ〈０．０１），Ⅱ组与Ⅲ组比较没有显著性差异（Ｐ〉０．０５）。（２）按重复间隔时间分     

Data entry on a computer terminal: Repetitive work strains on the oculomotor and central nervous systems

Summary Continuous telemetric recordings including E.K.G., E.O.G., and E.E.G. were carried out on two subjects during 4 working days: 1 day of reference work or classical clerical activities, 3 days of data entry work. Although the time allowed for the task was not limited, the performance assessed from oculomotor patterns remained stable throughout the day, from one day to the next and from one subject to another. This stability was reflected on the stereotyped E.E.G. patterns recorded during the work period, the differences occurring between reading and typing were more acute in the left cortical hemisphere than in the right. As a result of these stable patterns, the ultradian oscillations of the behavioural and physiological parameters were less during data entry than during work reference. The only possible time adjustments were the interruptions or breaks between two document pages and their variations could be considered as indicators of work load.This study was supported partly by a grant INRS 81/6360.570.001, and partly by the Department of Employment and by CNRS     

Prefrontal TMS produces smaller EEG responses than motor-cortex TMS: implications for rTMS treatment in depression

Rationale The stimulus intensity of prefrontal repetitive transcranial magnetic stimulation (rTMS) during depression treatment is usually determined by adjusting it with respect to the motor threshold (MT). There is some evidence that reactivity of the prefrontal cortex to transcranial magnetic stimulation (TMS) is lower than that of the motor cortex at MT stimulation. However, it is unknown whether this is true when other stimulus intensities are used. We investigated whether the magnitude and shape of the overall TMS-evoked electroencephalographic (EEG) responses differ between prefrontal and motor cortices. Methods Magnetic pulses to the left motor and prefrontal cortices (the middle frontal gyrus identified from magnetic resonance images) were delivered at four intensities (60, 80, 100, and 120% of MT of the right abductor digiti minimi muscle) for six subjects. Simultaneously, EEG was recorded with 60 scalp electrodes. Results Global mean-field amplitudes (GMFAs) reflecting overall cortical activity were significantly smaller after prefrontal- than after motor-cortex TMS. A significant positive correlation (r _s=0.84, p<0.01) was found between GMFAs of motor- and prefrontal-cortex TMS across the experiments. However, when correlation between the responses of motor and prefrontal cortices was examined, significant positive correlations were found at 80 and 100% intensities only. Conclusions This study provides further evidence that the prefrontal and motor cortices have different reactivity to TMS, but the MT may be used for determining the stimulus intensity of prefrontal rTMS treatment in depression, at least at motor threshold intensities or near to it.     

Absorption, metabolism and excretion of safrole in the rat and man.

The metabolic disposition of different doses of [14C] safrole were studied in rat and man. In both species, small amounts of orally administered safrole were absorbed rapidly and then excreted almost entirely within 24 h in the urine. In the rat, when the dose was raised from 0.6 to 750 mg/kg, a marked decrease in the rate of elimination occurred as only 25% of the dose was excreted in the urine in 24 h. Furthermore, at the high dose level, plasma and tissue concentrations of both unchanged safrole and its metabolites remained elevated for 48 h probably indicating impairment of the degradation/excretion pathways. The main urinary metabolite in both species was 1,2-dihydroxy-4-allylbenzene which was excreted in a conjugated form. Small amounts of eugenol or its isomer 1-methoxy-2-hydroxy-4-allylbenzene were also detected in rat and man. 1'-Hydroxysafrole, a proximate carcinogen of safrole, and 3'-hydroxyisosafrole were detected as conjugates in the urine of the rat. However, in these investigations we were unable to demonstrate the presence of the latter metabolites in man.     

What is said or how it is said makes a difference: role of the right fronto-parietal operculum in emotional prosody as revealed by repetitive TMS

Emotional signals in spoken language can be conveyed by semantic as well as prosodic cues. We investigated the role of the fronto-parietal operculum, a somatosensory area where the lips, tongue and jaw are represented, in the right hemisphere to detection of emotion in prosody vs. semantics. A total of 14 healthy volunteers participated in the present experiment, which involved transcranial magnetic stimulation (TMS) in combination with frameless stereotaxy. As predicted, compared with sham stimulation, TMS over the right fronto-parietal operculum differentially affected the reaction times for detection of emotional prosody vs. emotional semantics, showing that there is a dissociation at a neuroanatomical level. Detection of withdrawal emotions (fear and sadness) in prosody was delayed significantly by TMS. No effects of TMS were observed for approach emotions (happiness and anger). We propose that the right fronto-parietal operculum is not globally involved in emotion evaluation, but sensitive to specific forms of emotional discrimination and emotion types.     

Role of primary visual cortex in the binocular integration of plaid motion perception

This study assessed the early mechanisms underlying perception of plaid motion. Thus, two superimposed gratings drifting in a rightward direction composed plaid stimuli whose global motion direction was perceived as the vector sum of the two components. The first experiment was aimed at comparing the perception of plaid motion when both components were presented to both eyes (dioptic) or separately to each eye (dichoptic). When components of the patterns had identical spatial frequencies, coherent motion was correctly perceived under dioptic and dichoptic viewing condition. However, the perceived direction deviated from the predicted direction when spatial frequency differences were introduced between components in both conditions. The results suggest that motion integration follows similar rules for dioptic and dichoptic plaids even though performance under dichoptic viewing did not reach dioptic levels. In the second experiment, the role of early cortical areas in the processing of both plaids was examined. As convergence of monocular inputs is needed for dichoptic perception, we tested the hypothesis that primary visual cortex (V1) is required for dichoptic plaid processing by delivering repetitive transcranial magnetic stimulation to this area. Ten minutes of magnetic stimulation disrupted subsequent dichoptic perception for approximately 15 min, whereas no significant changes were observed for dioptic plaid perception. Taken together, these findings suggest that V1 is not crucial for the processing of dioptic plaids but it is necessary for the binocular integration underlying dichoptic plaid motion perception.     

The effects of cerebellar stimulation on the motor cortical excitability in neurological disorders: A review

The cerebellum regulates execution of skilled movements through neural connections with the primary motor cortex. A main projection from the cerebellum to the primary motor cortex is a disynaptic excitatory pathway relayed at the ventral thalamus. This dentatothalamocortical pathway receives inhibitory inputs from Purkinje cells of the cerebellar cortex. These pathways (cerebellothalamocortical pathways) have been characterized extensively using cellular approaches in animals. Advances in non-invasive transcranial activation of neural structures using electrical and magnetic stimulation have allowed us to investigate these neural connections in humans. This review summarizes various studies of the cerebellothalamocortical pathway in humans using current transcranial electrical and magnetic stimulation techniques. We studied effects on motor cortical excitability elicited by electrical or magnetic stimulation over the cerebellum by recording surface electromyographic (EMG) responses from the first dorsal interosseous (FDI) muscle. Magnetic stimuli were given with a round or figure eight coil (test stimulation) for primary motor cortical activation. For cerebellar stimulation, we gave high-voltage electrical stimuli or magnetic stimuli through a cone-shaped coil ipsilateral to the surface EMG recording (conditioning stimulation). We examined effects of interstimulus intervals (ISIs) with randomized condition-test paradigm, using a test stimulus given preceded by a conditioning stimulus by ISIs of several milliseconds. We demonstrated significant gain of EMG responses at an ISI of 3 ms (facilitatory effect) and reduced responses starting at 5 ms, which lasted 3-7 ms (inhibitory effect). We applied this method to patients with ataxia and showed that the inhibitory effect was only absent in patients with a lesion at cerebellar efferent pathways or dentatothalamocortical pathway. These results imply that this method activates the unilateral cerebellar structures. We confirmed facilitatory and inhibitory natures of cerebellothalamocortical pathways in humans. We can differentiate ataxia attributable to somewhere in the cerebello-thalamo-cortical pathways from that caused by other pathways.     

Controlled sleep restriction for rhythmic movement disorder

Rhythmic movement disorder is a parasomnia that is difficult to treat. In our study, 3 weeks of controlled sleep restriction with hypnotic administration in the first week resulted in almost complete resolution of the movements in 6 children. This therapeutic success suggests that rhythmic movement disorder results from a voluntary self-soothing behavior.