ISSN:0309-1902    

DOI:10.3109/03091909509030272

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

This paper describes a rationale and methodology for the use if DC recording techniques to reveal patterns of cerebral functional specialization. Results from a number of recent experiments are described. In each of these studies 15 channels of DC potential were recorded from a widely spaced array of scalp-mounted Ag/AgCl electrodes. The duration of single trial recording was always 40 s although the paradigms involved continuous performance of a complex cognitive task. In this series of experiments we used the following tasks: both visually and aurally presented word target detection with classification on a semantic basis, recognition of famous’faces and discrimination of animal versus non-animal sounds. In each of these tasks the rate of presentation has been systematically varied to evaluate quantitative aspects of task demand. In general, the results from these studies demonstrate that DC recording does provide a method for assessing the degree of activation of different cortical regions at the same time. However. It appears that additional transformation of the data may be required to separate out a number of overlapping slow potentials to increase the sensitivity to more subtle aspects of the cognitive demand. Two different methods to perform the separation are described and applied.

ISSN:0309-1902    

DOI:10.3109/03091909509030273

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

A new non-invasive electrode array h been devised to record electrical signals on the scalp. The electrodes are arranged every 10 mm in a 4×8 grid, thus totalling 32. Electrical coupling is assured by a column of conductor gel with a diameter of 2 mm. The electrode array has been used to record multichannel scalp potentials evoked by stimulation of the median nerve at the wrist. It wm positioned on the parietal region with the midline corresponding to the external acoustic meatus. The high spatial resolution of this device allows a detailed spatial sampling of the scalp potential field where the electrical activity arising from the parietal and premotor cortex is predominant. Scalp potentials with the system are compared with those with the 10/12 system. The improved spatial resolution allows more precise localization of minimum and maximum of the potential field, though the overall distortion introduced by aliasing in the 10/20 system is not striking. Instead, the amplitudes Of the fields are considerably affected by insufficient spatial sampling.

ISSN:0309-1902    

DOI:10.3109/03091909509030274

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

The technique of combined magnetic and electrical stimulation of a peripheral nerve was used to determine the effectiveness of the combined stimulus and its dependence on the relative positioning of electrodes and stimulator coil along the axis of the nerve. The results were used to determine the magnetic stimulation-activating function of a long straight nerve in the arm, and are shown to be consistent with published theoretical models constructed under conditions of simplified tissue geometry. With appropriate positioning of the two stimulators and similar tissue current waveforms, both enhancement and inhibition of an electrical stimulus were demonstrated and the maximum amplitude of the combined stimulus approached the arithmetic sum of that produced by each stimulator individually.

ISSN:0309-1902    

DOI:10.3109/03091909509030275

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

A new bipolar multichannel visual-evoked cortical potential (VECP) procedure is presented, which can supply objective information on visual field losses. The electrical potential is recorded from II electrodes applied to the back of the head in the form of an equidistant rectangular&. Fach neighbouring pair of electrodes feeds one of 14 bipolar channels. The adjacent horizontal and vertical channels are used to calculate an approximation to the direction and amplitude of the electrical field gradients. The gradient distribution is represented by a map of arrows (gradient map) for every instant of the sweep, so that the whole sweep can be plotted as a time series of gradient maps. The maps are easy to scale and are well suited for visual evaluation. Twenty normal subjects were stimulated using checkerboard reversal, partial field patterns to simulate visual field defects. The stimulated area varied between fullhalf-and quarter-field, and the particular area stimulated could be clearly seen in the resulting gradient maps. Additionally, we developed a computerized classification procedure that detected 86% of the disturbed visual fields, from the gradient recordings.

ISSN:0309-1902    

DOI:10.3109/03091909509030276

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

The dependency of the landscapes of visually evoked, 47-channel, event-related potential (ERPs) on the functional microstates (momentary map landscape) just before stimulus arrival was investigated in 12 volunteers. The prestimulus microstates were determined using the map at the last peak of Global Field Power before the stimulus. The landscapes of these maps were described by the electrode locations of the positive and negative extreme potentials? and assigned to basic classes. The two most frequently occurring map-classes were used (left anterior-right posterior, and right anterior-left posterior). ERP map series were averaged for each subject and each prestimulus microstate class. The Randomization-Monte Carlo MANOVA test was used to test the significance of the difference between the ERP map landscapes at each sample point (n = 128, 500 m) associated with the two prestimulus microstates. At 16 samples the difference was significant at p<0·05. The longest uninterrupted sequence (n = 9) of significant differences occurred between 164 and 195 ms, i.e. during the conventional component P200. The results demonstrate that the brain electric microstate at stimulus arrival crucially influences the active neuronal populations that contribute to the ERP. This suggests that the processing of information will differ as a function of the momentary brain microstate at information arrival.

ISSN:0309-1902    

DOI:10.3109/03091909509030277

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Short-latency (10–50 m) median nerve somatosensory evoked potentials (SEPs) from four normal subjects were analysed by means of temporal segmentation techniques and source derivation methods. In each case the responses were recorded using 32 electrodes. Dipolar optimization was carried out with a time-varying technique, using three different approaches: regional source estimation, spherical source estimation (one radial and one tangential component), and multiple dipolar approach.;This was to assess the relative influence on the dipolar solution of the different optimization techniques. The effect of the different number of channels in the estimation procedures has been also investigated. The methods of optimization are crucial, particularly for the orientation of P22. In all cases the source location estimated with the 32-electrode montage was shifted towards the centre of the spheres.

ISSN:0309-1902    

DOI:10.3109/03091909509030278

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

The hypnotic and analgesic components of anaesthesia can be assessed using middle latency auditory evoked potentials (MLAEPs) and somatosensory evoked potentials (SEPs). To monitor these potentials rehab&during clinical anaesthesia, we have developed an evoked potential (EP) system based around a portable personal computer, a DSP board and an isolated pre-amplifier unit. Unlike many current&available systems, this amplifier is largely immune to diathermy interference due to excellent isolation via a digital fibre optical link, small size and RF screening and filtering. The pre-amplifier unit has integral auditoy and somatosensory stimulators, and automatic calibration and impedance checking. Stimulus intensity and profile are under software control and SEP stimulus level is constantly monitored. The unit is powered by two AA cells and battery status continuously monitored by the PC software. Up to eight channels of EEG may be recorded and displayed in a smoothly scrolling window and as moving average MLAEPs and SEPs.

ISSN:0309-1902    

DOI:10.3109/03091909509030279

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

Human visual-evoked potentials (VEPs)from upper and lower hemifield stimulation are thought to reflect the anatomical and functional differences between the hemiretinas and corresponding visual pathways. Conflicting results have, however, been reported in topographic studies on the putative cortical generators. We have estimated by automatic perimetry (Octopus 2000R, Program 32) and compared the sensitivity thresholds of lower and upper hemifields of the retina in 12 healthy subjects with no history or evidence of visual or neurological diseases. A visual P3 that is linked to cognitive function =as recorded in an odd-ball paradigm with presentation of high-contrast checkerboards at two different spatial frequencies at 20°eccentricity in each hemifield. VEP and P3 were recordid at O1and O2and at C2according to the 10/20 intonational system. Lower sensitivity thresholds were obtained, and higher VEP and event-related potential (ERP) amplitude values were obtained dien stimulating the lower, compared with the upper, usual hemifield. The results are consistent with previous, findings and anatomical and physiological evidence in animals and man. Interactions between perceptive process an the visual system and higher cognitive functions are a possible explanation jar this finding.

ISSN:0309-1902    

DOI:10.3109/03091909509030280

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor

摘要:

A computer model has been designed for the calculation of the electrical fields in the head, based on the finite difference method. This method has not previous&been applied for head modelling. The model was validated by using three concentric spheres and comparing it with an analytic model. Three levels of accuracy were tested. The forward solutions show that the finite difference algorithm work correct&and, by selecting the size of the volume elements properly, accurate results are obtained. The model will be applied to accurate and realistic geometries of the human head obtained from magnetic resonance images.

ISSN:0309-1902    

DOI:10.3109/03091909509030281

出版商:Taylor&Francis    

年代:1995

数据来源: Taylor