Tissue damage by pulsed electrical stimulation.

Repeated pulsed electrical stimulation is used in a multitude of neural interfaces; damage resulting from such stimulation was studied as a function of pulse duration, electrode size, and number of pulses using a fluorescent assay on chick chorioallontoic membrane (CAM) in vivo and chick retina in vitro. Data from the chick model were verified by repeating some measurements on porcine retina in-vitro. The electrode size varied from 100 microm to 1 mm, pulse duration from 6 micros to 6 ms, and the number of pulses from 1 to 7500. The threshold current density for damage was independent of electrode size for diameters greater than 300 microm, and scaled as 1/r2 for electrodes smaller than 200 microm. Damage threshold decreased with the number of pulses, dropping by a factor of 14 on the CAM and 7 on the retina as the number of pulses increased from 1 to 50, and remained constant for a higher numbers of pulses. The damage threshold current density on large electrodes scaled with pulse duration as approximately 1/t0.5, characteristic of electroporation. The threshold current density for repeated exposure on the retina varied between 0.061 A/cm2 at 6 ms to 1.3 A/cm2 at 6 micros. The highest ratio of the damage threshold to the stimulation threshold in retinal ganglion cells occurred at pulse durations near chronaxie-around 1.3 ms.

Fast proton generation from ultrashort laser pulse interaction with double-layer foil targets.

The results of studies of fast-proton generation from foil targets irradiated by 1-ps laser pulse at 10(17) W/cm (2) are presented. It is shown that a considerable increase in proton energy and current is possible when a double-layer foil target containing a high- Z layer and a low- Z hydrogen-rich layer is used instead of a single-layer target. Proton energies and current increase with the Z of the high- Z layer and depend essentially on the target and the layer thicknesses. Above 10(9) forward-emitted protons of energy >100 keV have been recorded within a cone angle <3 degrees.

The effects of self-movement, observation, and imagination on mu rhythms and readiness potentials (RP's): toward a brain-computer interface (BCI).

Current movement-based brain-computer interfaces (BCI's) utilize spontaneous electroencephalogram (EEG) rhythms associated with movement, such as the mu rhythm, or responses time-locked to movements that are averaged across multiple trials, such as the readiness potential (RP), as control signals. In one study, we report that the mu rhythm is not only modulated by the expression of self-generated movement but also by the observation and imagination of movement. In another study, we show that simultaneous self-generated multiple limb movements exhibit properties distinct from those of single limb movements. Identification and classification of these signals with pattern recognition techniques provides the basis for the development of a practical BCI.

Novelty-elicited, noradrenaline-dependent enhancement of excitability in the dentate gyrus.

In order to relate noradrenaline-dependent potentiation in the dentate gyrus to behavioural events, rats were made to explore an environment in which their encounters with novel stimuli could be strictly controlled and monitored. Previous experiments have shown that an encounter with novel objects in a holeboard elicits a burst response in a large population of noradrenergic neurons of the locus coeruleus. Such a burst response has been demonstrated to produce a large and transient potentiation of the population spike in the dentate gyrus. In the present series of experiments, rats were chronically implanted with stimulating electrodes in the perforant pathway and recording electrodes in the dentate gyrus. Evoked potentials were monitored in the awake rat, first while it was resting quietly in a familiar environment and then while it was exploring the holeboard containing a novel object in a specific hole. There was a tonic increase in population spike amplitude when the rat was placed in the novel holeboard environment, but this effect gradually dissipated. This increase was partly blocked by the beta-noradrenergic antagonist propranolol. In addition there was a robust phasic increase in spike amplitude when the rat encountered a novel stimulus. This phasic response lasted approximately 50-75 s and was absent in animals treated with propranolol. These results show that a behavioural encounter with a novel stimulus can transiently enhance information transmission through the hippocampus, and suggest that activation of the noradrenergic system by the novel stimulus mediates this behavior-dependent gating.

Response to novelty and its rapid habituation in locus coeruleus neurons of the freely exploring rat.

Activity of single units of the noradrenergic nucleus locus coeruleus was recorded in rats during active exploration of a novel environment. Novelty was controlled by the placement of objects in given holes in a hole board. The basic protocol included a habituation session in which the holes were empty and an object session in which a novel object was placed in one of the two holes. During the habituation session, when the whole environment was unfamiliar, there was a phasic response the first time the rat visited any hole, which habituated after one visit. During the second session, when one of the holes contained an object, the cell fired when the rat encountered the novel object. There was no response to empty holes in this session. The neuronal response was markedly diminished or entirely absent on the second and subsequent visits to object-containing holes, indicative of rapid habituation. In some rats it was possible to run a second object session, when a new object was introduced into a previously empty hole. Visits to this hole elicited a robust response, which again habituated after one single visit. The results show that the responses of locus coeruleus to novelty or change, which has been demonstrated in formal learning situations, occurs in freely behaving rats while they are learning about a new environment. Moreover, the response to novelty and change in the environment is short-lived, rapidly habituating after one or two encounters with the stimulus.

Locus coeruleus-evoked responses in behaving rats: a clue to the role of noradrenaline in memory.

Neuromodulatory properties of noradrenaline (NA) suggest that the coreruleo-cortical NA projection should play an important role in attention and memory processes. Our research is aimed at providing some behavioral evidence. Single units of the locus coeruleus (LC) are recorded during controlled behavioral situations, in order to relate LC activation to specific behavioral contexts. LC cells respond in burst to imposed novel sensory stimuli or to novel objects encountered during free exploration. When there is no predictive value of the stimulus or no behavioral response required, there is rapid habituation of the LC response. When a stimulus is then associated with reinforcement, there is a renewed response, which is transient. During extinction, LC neuronal responses reappear. Thus, LC cells respond to novelty or change in incoming information, but do not have a sustained response to stimuli, even when they have a high level of biological significance. The gating and tuning action of NA released in target sensory systems would promote selective attention to relevant stimuli at the critical moment of change. The adaptive behavioral outcome would result from the integration of retrieved memory with the sensory information selected from the environment.

Movement related brain potentials accompanying a non-productive voluntary action in humans.

This study assessed the effects of training and ability to execute a voluntary movement upon movement-related brain potentials (MRBPs). A self-paced thumb flexion initiated a sequence of autotriggered electrical stimuli over the median nerve that caused a twitch opposing the intended thumb extension. The MRBPs had earlier onsets during the first runs of skill acquisition than during later training sessions; they occurred earlier when they preceded a stimulus train than when they preceded a single stimulus; the onset was earlier over the vertex than over the premotor area. MRBP duration was longer during train stimulation when a voluntary effort had to be maintained against tetanic contraction. MRBP amplitude did not reflect task requirements under these experimental conditions.

Force platform for stabilographic studies.

An analysis is made in the paper of a triangular force platform included in a computer system for postural analysis using Pravets 8M personal computer. The tensions generated in steel rings in the three corners of the platform, proportional to the moments of the forces with spontaneous fluctuations of the position of the centre of the force exercised by the experimental subject on the platform, are registered and amplified using three identical amplifying channels comprising tensotransducer, preamplifier and second-order low-frequency filter. The output signals of the three amplifying channels are fed to an analogue decoder generating an electrical signal proportional to the weight and to the anterior-posterior and lateral components of the force. The signals from the outputs of the decoder can be used for introducing visual feedback about postural stabilization. The regulations of the platform are maximally simplified so as to be used in clinical research.

Computerized system for posturographic research based on the ADAPT language for analysis of analogue signals.

A description is given of a system for posture analysis based on a specialized language ADAPT for analysis of analogue data, guaranteeing: 1. Analogue-to-digital conversion of the input signals with dialogue determination of the conversion parameters and monitoring of the signals on the screen. 2. Storage of the data on a diskette in a format guaranteeing high density of the data and fast exchange with the computer. 3. Calculation of the following parameters of the stabilogram and statokinesigram separately for open and for closed eyes: a) Anterior-posterior and lateral components of the path of the projection of the force centre SPAP and SPLAT; b) Mean frequency of the sways: fAP and fLAT; c) Ratio between the anterior-posterior and the lateral sways: AP/LAT. d) Surface A covered by the shifting of the centre of force; e) The path (SP) of the centre of application of the force; f) Mean amplitude (MA) of the sways for one second; g) Mean frequency (MF) of the sways. Romberg's coefficients are calculated for all parameters. 4. High speed of the calculations. 5. Graphic and digital display of all results on the screen from where they can be transferred to a printer, if necessary.

The influence of some brainstem noradrenergic structures on the stress-induced secretion of adrenocorticotrophic hormone (ACTH).

The intensity of the stress-induced secretion of ACTH was investigated in rats after electric lesions of Locus coeruleus and Nucleus subcoeruleus. Plasma ACTH was estimated radioimmunologically. Stress-induced ACTH release in lesioned rats was found to be significantly higher as compared with sham operated and intact animals. Some aspects of the participation of brainstem ascending noradrenergic pathways in neuroendocrine regulation are discussed.

[Changes in spino-bulbo-spinal reflexes during activation and inactivation of the locus coeruleus in the cat]. / Izmenenie spino-bul'bo-spinal'nykh refleksov pri aktivatsii ili inaktivatsii golubogo piatna u koshki.

In cats anesthetized with chloralose the long lasting depression of spino-bulbo-spinal (SBS) discharges following short repetitive stimulation of the locus coeruleus (LC) was revealed. Inactivation of LC by procaine microinjections resulted in remarkable enhancement of SBS discharges. These data evidence for prominent inhibitory modulatory influences from locus coeruleus on SBS reflexes which are presumably performed mainly on supraspinal level.

[Effect of bulbar microinjections of noradrenaline, isoproterenol and phentolamine on the spino-bulbo-spinal reflex in the cat]. / Vliianie bul'barnykh mikroin"ektsii noradrenalina, izoproterenola i fentolamina na spino-bul'bo-spinal'nyi refleks u koshki.

In chloralose-anesthetized cats a long lasting depression of spino-bulbo-spinal (SBS) reflex discharges following microinjections of noradrenaline and its agonist (isoproterenol) in the medial bulbar reticular formation was revealed. Microinjections of phentolamine (alpha-adrenoceptor antagonist) were followed by prominent enhancement of SBS-reflexes. Depressive action of the locus coeruleus stimulation on SBS-responses essentially decreased after these microinjections. The data evidence for a specific noradrenergic nature of inhibitory locus coeruleus influences on reticular centre of SBS-reflexes.