• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 323
  • 251
  • 41
  • 23
  • 11
  • 9
  • 8
  • 8
  • 7
  • 7
  • 7
  • 7
  • 7
  • 5
  • 4
  • Tagged with
  • 808
  • 521
  • 322
  • 191
  • 190
  • 181
  • 176
  • 162
  • 158
  • 124
  • 110
  • 103
  • 100
  • 92
  • 86
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
51

Differential effects of calcium and tetanic stimulation frequencies on hippocampal synaptic potentiation and depression

Chirwa, Sanika Samuel January 1985 (has links)
In the hippocampus, tetanic stimulation of an input results in a long lasting potentiation (LLP) of synaptic transmission involving that input. While high frequency tetanic stimulations are preferred to elicit LLP, low frequency tetanus induces homosynaptic and heterosynaptic depressions. The present investigations were conducted to (1) analyse the characteristics of pulses in orthodromic and antidromic tetanic stimulations and relate them to post-tetanic changes in evoked potentials (2) determine if potentiation and depression co-occur and (3) determine whether an established LLP in one input is subsequently modified by the initiation of LLP in another input (to the same CAlb neurons) or whether LLP can be reversed by homosynaptic and heterosynaptic depressions and lastly (4) determine how interference or enhancements of calcium and potassium fluxes with pharmacological substances related to potentiation and depression. Experiments were conducted on transversely sectioned rat hippocampal slices. Evoked potentials in subfield CAlb were elicited with stimulations of CAlb axons, commissural (Com), or Schaffer collaterals (Sch). Sch terminal excitability was tested with a stimulating electrode placed in the Sch/CAlb synaptic regions. Recordings were made with microelectrodes positioned in the CAlb cell bodies and/or dendritic regions, and in field CA3. It was found that potentiation and depressions co-occur. Presynaptic volleys accompanied all tested tetanic trains. Similarly, antidromic trains discharged CAlb neurons continuously but did not cause LLP. Low frequency tetanic trains caused facilitated synchronous discharges of CAlb neurons during significant portions of these trains. In contrast, few if any syn- chronous discharges followed high frequency tetanus. Yet high frequency tetanus elicited LLP and low frequency tetanus caused homo- and heterosynaptic depressions. An established LLP could be masked but not reversed by homo- and heterosynaptic depressions but this LLP was not interrupted by subsequently induced LLP of a separate input. Iontophoretic L-glutamate on CAlb cell bodies caused depression which was more pronounced if a tetanus was evoked during L-glutamate ejections. The depressions to low frequency tetanus and L-glutamate were counteracted by verapamil. Lastly, barium and 4-aminopyridine potentiations were reversed with washing. Applications of these drugs did not alter Sch terminal excitability. Tetanus induced during the presence of 4-aminopyridine still elicited LLP. It is concluded that homo- and heterosynaptic depressions are partly due to the accumulation of calcium into the CAlb neurons. The magnitude of calcium entry into presynaptic and postsynaptic regions is governed by the tetanic frequencies evoked. The results are consistent with a presynaptic mediated LLP. / Medicine, Faculty of / Anesthesiology, Pharmacology and Therapeutics, Department of / Graduate
52

The extraction of auditory and somatosensory evoked potentials for use in depth of anaesthesia monitoring

Potgieter, Brent Vivian 06 April 2017 (has links)
No description available.
53

Comparison between auditory electrophysiological and behavioral responses in normally and abnormally hearing chinchillas /

Davis, Robert I. January 1981 (has links)
No description available.
54

The effects of high repetition rate stimuli on electrocochleography performed on normal hearing subjects

Bowker, Caren Anne 17 August 2016 (has links)
THE DEPARTMENT OF SPEECH PATHOLOGY AND AUDIOLOGY. FACULTY OF ARTS, UNIVERSITY OF THE WITWATERSRAND, JOHANNESBURG In partial fulfillment of the requirements for the degree of Master of Arts by coursework in Audiology June 1999 / High stimulus repetition rates have been proposed as a solution to the poor sensitivity and specificity of the standard electrocochleogram. The use of this approach has been confounded, however, by conflicting literature reports on the effects of high stimulus repetition rates on normal subjects. This study aimed to confirm the effects of high stimulus repetition rates on normal hearing subjects as a precursor to clinical high stimulus repetition rate electrocochleography trials. Electrocochleogram tracings were recorded binaurally from 51 normal hearing subjects at 7.1 cps, 51.1 cps, 101.1 cps and 151.1 cps and the summating potential and action potential latencies and amplitudes, summating potential/action potential amplitude ratios and waveform widths were recorded. Statistical analyses showed that increasing the stimulus repetition rate caused statistically (p<O.05) and clinically (p<O.O1 for latency and p<O.005 for amplitude) significant changes to the action potential latency and amplitude, summating potential/action potential amplitude ratio and waveform width, but caused only limited statistical (p<O.05) and clinical (p<O.OI for latency and p<O.005 for amplitude) changes to the summating potential amplitude and latency. Subject age had no effect on the results and there was no interaction between age and stimulus repetition rates. These findings provide the most comprehensive data on the effects of fast stimulus repetition rates to date, and have provided the beginnings of a valid clinical normative database for high stimulus repetition rate tympanic electrode electrocochleography.
55

Topograhic distribution of human brain electrical activity associated with schizophrenia

Ciorciari, Joseph, jciorciari@swin.edu.au January 1999 (has links)
A literature review of the schizophrenia brain electrophysiology was undertaken with specific emphasis placed on the topographical distribution of evoked potentials (EPs). The outcomes of this review suggests that schizophrenia brain electrophysiology, demonstrate some differences, but with a variability reflective of the symptom heterogeneity. The literature associated with the use of attentional tasks while recording EPs, tended to demonstrate some consistency. The methodological issues associated with the EEG and EP recordings may also account for this variability. An evoked potential technique, which has been demonstrated to be sensitive to the changes in cognitive processes associated with attention, is the Steady State Probe Topography (SSPT) technique. The SSPT is a combination of both the Steady State Visual Evoked Potential (SSVEP) and the Probe-ERP paradigm. This technique allows the SSVEP to be measured continuously, is relatively insensitive to artifact, and can display the topographic distribution of the SSVEP measures during the attentional task. The technique employs the use of a sixty-four channel EEG recording system. This consists of a multichannel electrode helmet; multichannel amplifier/filter, task presentation computer and a computer controlled data acquisition system. Software was also developed to analyse the recorded brain electrical activity to produce the SSVEP magnitude and phase versus time series for each electrode site. The topographic distribution of the SSVEP measures associated with specific events during attentional tasks could also be displayed. At the time of the pilot study, this technique had not been applied previously to the study of schizophrenia and therefore warranted further study. Two separate studies are reported; an investigative pilot study and a chronic group study. The pilot SSVEP and schizophrenia study was designed to examine the changes in the SSVEP and its topography, during the performance of a number of attentional or activation tasks to examine the possibility of hypofrontality. The tasks selected for the study were those previously used for the examination of hypofrontality with metabolic imaging techniques; the Continuous Performance Task (CPT) and the Wisconsin Card Sort (WCS). The SSVEP was elicited by a superimposed 13Hz flicker on the visual field, while subjects performed computerised versions of the neuropsychological tasks. Topographical maps of the SSVEP magnitude distribution were then interpolated and displayed as an animated sequence synchronised with particular events occurring during the tasks. In comparison to the male control group, male schizophrenic patients exhibited differences in the SSVEP topography for all tasks, possibly reflecting the deficits in behavioural indices. Overall, the findings indicated that the technique demonstrated some merit for further examination of frontal SSVEP topography in schizophrenia. In a larger study of twenty chronic schizophrenia patients, the frontal topographical distribution of the SSVEP was examined. The earlier pilot study finding of reduced frontal SSVEP amplitude was replicated. The issue of hypofrontality in schizophrenia was applied as a possible interpretation.
56

Conventional and topographic electroencephalography and somatosensory evoked potential studies in ischaemic stroke

Hamilton-Bruce, Monica Anne. January 1998 (has links) (PDF)
Copies of author's previously published articles inserted. Bibliography: leaves I-LXIV. Assesses the diagnostic and prognostic value of early electroencephalography (EEG) and somatosensory evoked potential studies in cortical and non-cortical ischaemic stroke. Both conventional and topographic/quantitative studies were performed. A parallel study was carried out on healthy volunteers to provide an effective control. Equipment and quantitative EEG (qEEG) variability was also assessed.
57

Auditory evoked response suppression in schizophrenia /

Blumenfeld, Laura D. January 2001 (has links)
Thesis (Ph. D.)--University of California, San Diego, 2001. / Vita. Includes bibliographical references.
58

Evaluation of distortion products produced by the human auditory system in response to two-tone signals

Bhagat, Shaum P., January 2003 (has links)
Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.
59

Attentional workload and the ERPS negative difference (ND) and mismatch negativity (MMN) /

Singhal, Anthony. January 1998 (has links)
Thesis (M.A.)--York University, 1998. Graduate Programme in Kinesiology and Health Science. / Typescript. Includes bibliographical references (leaves 52-59). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ39233.
60

Evaluation of distortion products produced by the human auditory system in response to two-tone signals

Bhagat, Shaum P., 1968- 29 June 2011 (has links)
Not available / text

Page generated in 0.0202 seconds