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Dissertations / Theses on the topic 'Evoked potentials'

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Published: 4 June 2021
Last updated: 29 July 2024

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1

Murnane, Owen D. "Vestibular Evoked Myogenic Potentials." Digital Commons @ East Tennessee State University, 2011. https://dc.etsu.edu/etsu-works/1933.

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Murnane, Owen D. "Vestibular Evoked Myogenic Potentials." Digital Commons @ East Tennessee State University, 2004. https://dc.etsu.edu/etsu-works/1948.

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Murnane, Owen D. "Vestibular Evoked Myogenic Potentials." Digital Commons @ East Tennessee State University, 2005. https://dc.etsu.edu/etsu-works/1947.

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Murnane, Owen D. "Vestibular Evoked Myogenic Potentials." Digital Commons @ East Tennessee State University, 2013. https://dc.etsu.edu/etsu-works/1932.

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Akin, Faith W. "Vestibular Evoked Myogenic Potentials." Digital Commons @ East Tennessee State University, 2006. https://dc.etsu.edu/etsu-works/2452.

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Akin, Faith W., and Owen D. Murnane. "Vestibular Evoked Myogenic Potentials." Digital Commons @ East Tennessee State University, 2008. https://dc.etsu.edu/etsu-works/1939.

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7

Murnane, Owen D., and Faith W. Akin. "Vestibular-Evoked Myogenic Potentials." Digital Commons @ East Tennessee State University, 2009. https://dc.etsu.edu/etsu-works/1795.

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Cervical vestibular-evoked myogenic potentials (cVEMPs) are recorded from the sternocleidomastoid muscle using air conduction or bone conduction acoustic stimuli, skull taps, or transmastoid current. The diagnostic usefulness of the cVEMP has been examined for various peripheral and central vestibulopathies. Recent reports indicate that it is possible to record short-latency ocular vestibular-evoked myogenic potentials (oVEMPs) from surface electrodes below the eyes in response to air conduction and bone conduction stimuli. Both methods provide diagnostic information about otolith function. This article provides an overview of each method and highlights the similarities and differences. Several cases are presented to illustrate the relation between the results for cVEMPs and oVEMPs in patients with well-defined audiovestibular disorders.
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Akin, Faith W., and Owen D. Murnane. "Vestibular Evoked Myogenic Potentials." Digital Commons @ East Tennessee State University, 2001. https://dc.etsu.edu/etsu-works/1916.

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Akin, Faith W., and Owen D. Murnane. "Vestibular Evoked Myogenic Potentials." Digital Commons @ East Tennessee State University, 2007. https://dc.etsu.edu/etsu-works/1944.

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Akin, Faith W. "Vestibular Evoked Myogenic Potentials." Digital Commons @ East Tennessee State University, 2007. https://dc.etsu.edu/etsu-works/2450.

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11

Akin, Faith W., and Owen D. Murnane. "Vestibular Evoked Myogenic Potentials." Digital Commons @ East Tennessee State University, 2000. https://dc.etsu.edu/etsu-works/1920.

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Akin, Faith W., and Owen D. Murnane. "Vestibular Evoked Myogenic Potentials." Digital Commons @ East Tennessee State University, 2006. https://dc.etsu.edu/etsu-works/1945.

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13

Akin, Faith W., and Owen D. Murnane. "Vestibular Evoked Myogenic Potentials (VEMP)." Digital Commons @ East Tennessee State University, 2004. https://dc.etsu.edu/etsu-works/1797.

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14

Murnane, Owen D., Faith W. Akin, and T. Medley. "Tone-Evoked Vestibular Myogenic Potentials." Digital Commons @ East Tennessee State University, 2002. https://dc.etsu.edu/etsu-works/1911.

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15

Murnane, Owen D., Faith W. Akin, J. K. Kelly, and J. Tampas. "Ocular Vestibular Evoked Myogenic Potentials." Digital Commons @ East Tennessee State University, 2009. https://dc.etsu.edu/etsu-works/1894.

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16

Hamilton-Bruce, Monica Anne. "Conventional and topographic electroencephalography and somatosensory evoked potential studies in ischaemic stroke." Adelaide, 1998. http://web4.library.adelaide.edu.au/theses/09PH/09phh222.pdf.

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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.
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17

Linden, Roger Dean. "Human auditory steady state evoked potentials." Thesis, University of Ottawa (Canada), 1985. http://hdl.handle.net/10393/4602.

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18

Heath, P. D. "Cortical somatosensory evoked potentials in parkinsonism." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233645.

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19

Bergkvist, Linn. "Visual Evoked Potentials : Referensvärden och könsskillnader." Thesis, Umeå universitet, Biomedicinsk laboratorievetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-171567.

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20

Akin, Faith W., and Owen Murnane. "Vestibular Evoked Myogenic Potentials: Preliminary Report." Digital Commons @ East Tennessee State University, 2001. https://dc.etsu.edu/etsu-works/1792.

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Vestibular evoked myogenic potentials (VEMPs) are short-latency electromyograms evoked by high-level acoustic stimuli recorded from surface electrodes over the tonically contracted sternocleidomastoid (SCM) muscle. These responses are presumed to originate in the saccule. The purpose of this preliminary report is to provide an overview of our initial experience with the VEMP by describing the responses obtained in five subjects. Click-evoked VEMPs were present at short latencies in two normal-hearing subjects, one patient with profound congenital sensorineural hearing loss, and one patient with a severe sensorineural hearing loss due to Meniere's disease. Additionally, VEMPs were absent in a patient with profound sensorineural hearing loss following removal of a cerebellopontine angle tumor. The amplitude of the VEMP was influenced by the amount of background activity of the SCM muscle, stimulus level, and stimulus frequency. Tone-burst evoked responses showed an inverse relationship between stimulus frequency and response latency. VEMPs may prove to be a reliable technique in the clinical assessment of vestibular function.
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Akin, Faith W., and Owen D. Murnane. "Vestibular Evoked Myogenic Potentials: Stimulus Parameters." Digital Commons @ East Tennessee State University, 2002. https://dc.etsu.edu/etsu-works/1913.

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Murnane, Owen D., and Faith W. Akin. "Vestibular Evoked Myogenic Potentials: Recording Methods." Digital Commons @ East Tennessee State University, 2002. https://dc.etsu.edu/etsu-works/1912.

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Stampe, Dave M. "A comparison of visually evoked saccadic inhibition and visually evoked potentials." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq41045.pdf.

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Hamilton-Bruce, Monica Anne. "Conventional and topographic electroencephalography and somatosensory evoked potential studies in ischaemic stroke / Monica Anne Hamilton-Bruce." Thesis, Adelaide, 1998. http://hdl.handle.net/2440/19249.

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Copies of author's previously published articles inserted.
Bibliography: leaves I-LXIV.
xxxviii, 239 [77], Lxiv leaves : ill. (chiefly col.) ; 30 cm.
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.
Thesis (Ph.D.)--University of Adelaide, Dept. of Medicine, 1998?
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25

Ostrovska, Alexsandra. "Vestibular evoked myogenic potentials in clinical applications." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=80345.

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It is uncertain whether clinically useful information of otolith function can be well characterized by vestibular-evoked-myogenic-potentials (VEMPs), i.e., electromyogenic activity recorded from sternomastoid muscles in response to brief loud auditory clicks. We aimed to assess the utility of VEMP testing in the differential diagnosis of dizziness (81 dizzy patients, 12 normals). We found that: (1) VEMP was reliably elicited from all controls and from 96% of patients without loss of vestibular function; (2) in patients with documented unilateral peripheral vestibular disorders, VEMP could reveal loss of otolith function that usefully facilitated diagnoses; and (3) such otolith function loss was independent of canal function loss revealed by caloric testing. We conclude that the VEMP-test is clinically useful to assess vestibular (otolith and/or inferior vestibular nerve) function, providing information complementary to that obtained from caloric testing (horizontal semicircular canal and/or superior vestibular nerve function).
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26

Katifi, Haider A. "Dermatomal somatosensory evoked potentials in lumbosacral radiculopathy." Thesis, University of Southampton, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278543.

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27

Murnane, Owen D., Faith W. Akin, J. K. Kelly, Stephanie M. Byrd, and A. Pearson. "Bone Conduction Ocular Vestibular Evoked Myogenic Potentials." Digital Commons @ East Tennessee State University, 2011. https://dc.etsu.edu/etsu-works/1890.

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28

Murnane, Owen D., and Faith W. Akin. "Vestibular Evoked Myogenic Potentials: I. Recording Methods." Digital Commons @ East Tennessee State University, 2001. https://dc.etsu.edu/etsu-works/1917.

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29

Akin, Faith W., Owen D. Murnane, and T. Medley. "Clinical Application of Vestibular Evoked Myogenic Potentials." Digital Commons @ East Tennessee State University, 2002. https://dc.etsu.edu/etsu-works/1910.

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30

Akin, Faith W., Owen D. Murnane, and T. Medley. "Vestibular Evoked Myogenic Potentials Using Tonal Stimuli." Digital Commons @ East Tennessee State University, 2002. https://dc.etsu.edu/etsu-works/1914.

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31

Carey, Marc Brandon. "Brainstem auditory evoked potentials in anuran amphibians." PDXScholar, 1992. https://pdxscholar.library.pdx.edu/open_access_etds/4267.

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In this study, I looked at the effects of sound level, temperature and dehydration/hypernatremia on the brainstem auditory evoked potential (BAEP) of four species of anuran amphibians (Rana pipiens, Rana catesbeiana, Bufo americanus and Bufo terrestris). The BAEP was used because it allowed me to monitor both the peripheral and central aspects of auditory nervous function simultaneously and over a long period of time.
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32

Potgieter, Brent Vivian. "The extraction of auditory and somatosensory evoked potentials for use in depth of anaesthesia monitoring." Thesis, University of Cape Town, 1995. http://hdl.handle.net/11427/25627.

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33

Aydin, Serap. "Extraction Of Auditory Evoked Potentials From Ongoing Eeg." Phd thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606641/index.pdf.

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In estimating auditory Evoked Potentials (EPs) from ongoing EEG the number of sweeps should be reduced to decrease the experimental time and to increase the reliability of diagnosis. The ¯
rst goal of this study is to demon- strate the use of basic estimation techniques in extracting auditory EPs (AEPs) from small number of sweeps relative to ensemble averaging (EA). For this purpose, three groups of basic estimation techniques are compared to the traditional EA with respect to the signal-to-noise ratio(SNR) improve- ments in extracting the template AEP. Group A includes the combinations of the Subspace Method (SM) with the Wiener Filtering (WF) approaches (the conventional WF and coherence weighted WF (CWWF). Group B con- sists of standard adaptive algorithms (Least Mean Square (LMS), Recursive Least Square (RLS), and one-step Kalman ¯
ltering (KF). The regularization techniques (the Standard Tikhonov Regularization (STR) and the Subspace Regularization (SR) methods) forms Group C. All methods are tested in sim- ulations and pseudo-simulations which are performed with white noise and EEG measurements, respectively. The same methods are also tested with experimental AEPs. Comparisons based on the output signal-to-noise ratio (SNR) show that: 1) the KF and STR methods are the best methods among the algorithms tested in this study,2) the SM can reduce the large amount of the background EEG noise from the raw data, 3) the LMS and WF algo- rithms show poor performance compared to EA. The SM should be used as 1 a pre-¯
lter to increase their performance. 4) the CWWF works better than the WF when it is combined with the SM, 5) the STR method is better than the SR method. It is observed that, most of the basic estimation techniques show de¯
nitely better performance compared to EA in extracting the EPs. The KF or the STR e®
ectively reduce the experimental time (to one-fourth of that required by EA). The SM is a useful pre-¯
lter to signi¯
cantly reduce the noise on the raw data. The KF and STR are shown to be computationally inexpensive tools to extract the template AEPs and should be used instead of EA. They provide a clear template AEP for various analysis methods. To reduce the noise level on single sweeps, the SM can be used as a pre-¯
lter before various single sweep analysis methods. The second goal of this study is to to present a new approach to extract single sweep AEPs without using a template signal. The SM and a modi- ¯
ed scale-space ¯
lter (MSSF) are applied consecutively. The SM is applied to raw data to increase the SNR. The less-noisy sweeps are then individu- ally ¯
ltered with the MSSF. This new approach is assessed in both pseudo- simulations and experimental studies. The MSSF is also applied to actual auditory brainstem response (ABR) data to obtain a clear ABR from a rel- atively small number of sweeps. The wavelet transform coe±
cients (WTCs) corresponding to the signal and noise become distinguishable after the SM. The MSSF is an e®
ective ¯
lter in selecting the WTCs of the noise. The esti- mated single sweep EPs highly resemble the grand average EP although less number of sweeps are evaluated. Small amplitude variations are observed among the estimations. The MSSF applied to EA of 50 sweeps yields an ABR that best ¯
ts to the grand average of 250 sweeps. We concluded that the combination of SM and MSSF is an e±
cient tool to obtain clear single sweep AEPs. The MSSF reduces the recording time to one-¯
fth of that re- quired by EA in template ABR estimation. The proposed approach does not use a template signal (which is generally obtained using the average of small number of sweeps). It provides unprecedented results that support the basic assumptions in the additive signal model.
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34

Sadid, Atefah. "Påverkan av vigilansnivån på visuell evoked potentials latenstid." Thesis, Örebro universitet, Institutionen för hälsovetenskaper, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-51320.

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35

Friesen, Lendra M. "Speech-evoked auditory potentials in cochlear implant listeners /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/8239.

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36

Sarfarazi, Mehri. "Cognitive evoked potentials during word and picture recognition." Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390673.

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37

Akin, Faith W., Owen D. Murnane, J. Tampas, and C. Clinard. "Air and Bone-Conducted Vestibular Evoked Myogenic Potentials." Digital Commons @ East Tennessee State University, 2005. https://dc.etsu.edu/etsu-works/1906.

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38

Al-Nashi, Hamid Rasheed. "A maximum likelihood method to estimate EEG evoked potentials /." Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=72016.

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A new method for the estimation of the EEG evoked potential (EP) is presented in this thesis. This method is based on a new model of the EEG response which is assumed to be the sum of the EP and independent correlated Gaussian noise representing the spontaneous EEG activity. The EP is assumed to vary in both shape and latency, with the shape variation represented by correlated Gaussian noise which is modulated by the EP. The latency of the EP is also assumed to vary over the ensemble of responses in a random manner governed by some unspecified probability density. No assumption on stationarity is needed for the noise.
With the model described in state-space form, a Kalman filter is constructed, and the variance of the innovation process of the response measurements is derived. A maximum likelihood solution to the EP estimation problem is then obtained via this innovation process.
Tests using simulated responses show that the method is effective in estimating the EP signal at signal-to-noise ratio as low as -6db. Other tests using real normal visual response data yield reasonably consistent EP estimates whose main components are narrower and larger than the ensemble average. In addition, the likelihood function obtained by our method can be used as a discriminant between normal and abnormal responses, and it requires smaller ensembles than other methods.
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39

Chirwa, Sanika Samuel. "Differential effects of calcium and tetanic stimulation frequencies on hippocampal synaptic potentiation and depression." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/24594.

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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
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40

O’Toole, Dennis Michael. "Removal of ocular artifact from visual evoked response recordings." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25502.

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Potentials generated by the eye cause unwanted artifact in Visual Evoked Response (VER) recordings. These artifacts often contaminate the data in a systematic way that can lead to spurious experimental results. Although it is widely agreed that ocular artifact must be accounted for, the methods used to deal with this problem are varied. The present study compared four methods used to control ocular artifact; blink rejection, eyes closed, subtraction and regression. Twenty normal, female subjects were tested twice within the same session. Subjects watched light flashes of 4 intensities; 2, 30, 80, and 240 ft lamberts. The lights were presented at 1 hertz, reached maximum brightness in 0.5 msec and lasted for 0.5 sec. During testing the VER, and electroocculographic (EOG) response generated by a blink, were recorded. In the blink rejection method, any VER epoch that contained blink artifact was excluded from the average. The eyes closed method consisted of having subjects watch the stimuli through closed eyelids. The subtraction method corrects blink artifact by digitally subtracting the averaged EOG from the EEG. The proportion of EOG subtracted was determined by the EEG/EOG ratio estimated while subjects blinked spontaneously in a darkened environment. The regression method determines what proportion of EOG is to be subtracted on the basis of the correlation between EOG and EEG within VER epochs. Two correction, factors are calculated, one to correct for vertical movements and one to correct for horizontal movements. The blink rejection method was found to be useful with subjects who had 40% or more blink-free epochs, but was an unreliable method for the majority of subjects. The eyes closed method was also found to produce poor VER data. The eyelids appear to attenuate the light reaching the retina and there may be eyeball movement despite having the eyes closed. Both the subtraction and regression methods substantially reduced the ocular artifact. Horizontal eye movements do not appear to be a significant problem over the short intervals of VER recording because the regression method was not superior to the subtraction method in removing artifact. Although the subtraction and regression methods effectively reduce ocular artifact, both are less effective at posterior electrode placements. The reason for this may be that ocular potential is not propagated across the scalp in a linear fashion, as often assumed. Using spontaneously generated blinks in a darkened environment, it was found that the ocular potential waveform changes shape as it moves towards the back of the head.
Arts, Faculty of
Psychology, Department of
Graduate
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41

Leung, Nga-man Julia. "Affecting factors on reliability of intra-operative somatosensory evoked potentials monitoring /." View the Table of Contents & Abstract, 2007. http://sunzi.lib.hku.hk/hkuto/record/B38480608.

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42

Leung, Nga-man Julia, and 梁雅雯. "Affecting factors on reliability of intra-operative somatosensory evoked potentials monitoring." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B45011254.

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43

Liu, Hongtao, and 刘洪涛. "Fast signal extraction of somatosensory evoked potentials for intraoperative spinal cord monitoring." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2010. http://hub.hku.hk/bib/B45697139.

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44

Li, Jiewei, and 李杰威. "Electroencephalograph feature extraction of somatosensory event related potential (ERP)." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/206587.

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Background: The event related potential (ERP) is an important electrophysiological response to an internal or external stimulus on human body. In some studies, the ERP-based brain computer interface (BCI) systems were created in visual or auditory modality. However, in these type of BCIs, either the eyes or ears of the users are occupied when they are making a choice. It is not convenient to communicate with others. Thus, a somatosensory ERP based BCI can be developed to overcome this issue. According to this, the analysis of somatosensory ERP features is necessary to evaluate if somatosensory ERP is eligible for BCIs as an input. Objective: 1. To study ERP features and design of P300 experiment. 2. To compare three types of P300 features elicited by three modalities. 3. To produce ERP response by electrical stimuli delivered to different position, and analyze ERP features. Methods: Two experiments were conducted. In experiment 1, three modalities, including visual, auditory and electrical modality, were used to produce P300 response. Experiment 2 only presented electrical stimuli. In experiment 1 two electrical stimuli were presented with different intensities at one location, whereas four electrical stimuli were showed at different location with the same intensity. The amplitude and latency were compared among three modalities, and the ERP topography of experiment 2 was also analyzed. Result and conclusion: Fourteen subjects’ data were analyzed in our study. The amplitude and latency of electrical P300 were similar to auditory ERP. But the ERP of visual modality had the largest amplitude and shortest latency. This result shows that electrical P300 can work as well as auditory P300 in BCIs, but not as good as visual P300. In experiment 2, the latency of electrical ERP occurred around 280 ms, and the amplitude and the topography showed that the largest amplitude was located around Cz electrode. This type of ERP in experiment 2 was considered as P3a, which also can be used in BCI systems.
published_or_final_version
Orthopaedics and Traumatology
Master
Master of Medical Sciences
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45

Whittle, Ian Roger. "Clinical applications of somatosensory evoked potentials in pediatric neurosurgery /." Title page, contents and summary only, 1985. http://web4.library.adelaide.edu.au/theses/09MD/09mdw627.pdf.

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46

Richardson, Thomas Lewellyn. "The contribution of ephaptic interactions to recruitment and synchronization of neuronal discharge during evoked potentials in the hippocampal formation." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/29173.

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The mechanisms underlying the generation and spread of seizure activity have remained elusive despite a considerable research effort over the last two decades. Most of this work has concentrated on the characteristics of neuronal excitability and burst discharge at the single cell level. These studies have provided some understanding of the possible abnormalities of neurons within an epileptic focus, but little direct insight into the factors responsible for the striking synchronization of action potentials during interictal discharge or in the spread of synchronous activity across apparently normal brain tissue. Although synaptic activation probably plays a role in the generation of seizure activity, recent evidence indicates that seizure-like discharge can occur during chemical blockade of synaptic transmission (Jefferys and Haas 1982; Taylor and Dudek 1982). This rather surprising result emphasizes the importance of considering non-synaptic mechanisms for both the synchronization and spread of abnormal neuronal activity in the central nervous system. One important non-synaptic mechanism to consider is ephaptic interactions. This term refers to the direct electrical influence of extracellular field potentials on neuronal excitability. It is possible that ephaptic interactions, generated during seizure activity, simultaneously depolarize an entire population of neurons leading to both recruitment and synchronization of action potential discharge. This thesis investigates ephaptic interactions during evoked potentials in the hippocampal formation. The hippocampus is one of the most seizure-prone regions of the brain and its anatomical structure is ideal for the generation of field effects. Evoked potentials were used as "models" of synchronous neuronal discharge since they are more reproducible, easier to control, and better understood than seizure activity. This initial investigation of ephaptic interactions lays the foundation for further studies involving the complexities of epileptic activity. The first phase of this project examined the spatial characteristics of field potentials evoked in the hippocampus and the dentate gyrus. Current source density (CSD) analysis and voltage gradient determinations obtained from these fields were used to characterize the pattern of current flow within the neuropil and to predict the polarity and relative intensity of ephaptic influences on neuronal excitability. The detailed characteristics of extracellular voltage gradients varied between CAl and the dentate gyrus, and also between anti- and orthodromic responses. In general, voltage gradients during the positive components of a somatic population spike predicted ephaptic hyperpolarization of the neuronal population, whereas gradients observed during the negative component predicted depolarization. They were often an order of magnitude greater than the smallest gradient known to influence granule cell activity. An exception to this rule was the minimal gradient observed during the negative component of the dentate response. In the second phase of the study, extracellular voltage gradients were experimentally applied to the dentate gyrus to determine the sensitivity of granule cells to ephaptic interactions. The magnitude of the applied gradients were in the range observed during the evoked potentials studied in the first phase. These experiments demonstrated a remarkable sensitivity of granule cells to the applied fields. The fields could alter the population spike from near minimal to near maximal. Surprisingly, even antidromic potentials were influenced by the gradients. On the other hand, the EPSP phase of the population spike was not influenced. These findings established that extracellular currents can influence the excitability within a neuronal population without altering synaptic drive. The final phase of the project investigated the transmembrane potential (TMP) of pyramidal and granule cells during applied fields and evoked potentials. The TMP was calculated by subtracting the extracellular from the intracellular response. This potential ultimately determines the voltage dependent behavior of a neuron and gives a direct measure of any ephaptic interactions. In order to measure the intracellular influences of applied fields, the TMP was monitored while the impaled cell was exposed to extracellular voltage gradients spanning the same range as used in phase two of the project. The TMP shifted by as much as plus or minus 5 mV, depending on the amplitude and polarity of the gradient. This large shift in TMP accounts for the observed influence of the applied field potentials, and suggests that the voltage gradients associated with evoked potentials should also have a marked effect on the TMP. A depolarizing wave of the TMP occurred during the negative component of anti- and orthodromic CA1 responses. This depolarization was capable of initiating action potentials, and decreased the latency to discharge during orthodromic responses. During epileptiform discharge, a similar depolarizing wave was associated with each negative component of the burst. These depolarizations recruit and synchronize neuronal discharge by simultaneously increasing the excitability within an entire population of cells. These data support the hypothesis that ephaptic interactions in the hippocampal formation influence the pattern of cell discharge during evoked potentials. It is postulated that similar ephaptic interactions may contribute to recruitment and synchronization during seizure activity.
Medicine, Faculty of
Cellular and Physiological Sciences, Department of
Graduate
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47

Carter, Bradley Graham. "The prediction of both short and long term outcomes follwing severe brain injury using somatosensory evoked potentials." Australasian Digital Theses Program, 2006. http://adt.lib.swin.edu.au/public/adt-VSWT20070130.153020/index.html.

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48

Simpson, David Gordon Giles, and dsimpson@swin edu au. "Instrumentation for high spatial resolution of steady state visual evoked potentials." Swinburne University of Technology, 1998. http://adt.lib.swin.edu.au./public/adt-VSWT20060711.123100.

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This thesis reports on several new and innovative instrumentation developments to solve some of the problems of brain activity monitoring, particularly SSVEP (Steady State Visual Evoked Potentials) studies. SSVEP systems generate suitable stimuli and record the resulting brain biopotentials from scalp electrodes. The instrumentation is configured as a 'Neuropsychiatric Workstation', supporting up to 136 scalp electrodes. Operating in the SSVEP mode, the Neuropsychiatric Workstation reported here significantly improves upon the previously reported spatial resolution and accuracy of maps related to the generated stimuli. These maps allows insights to be gained into the cognitive workings of the brain. A significant component of the work reported here covers the development of the multielectrode EEG measurement modules and the associated techniques for minimising interference and cross-talk. The techniques for synchronising recordings from all electrodes with the stimulus, interfacing to a host computer and real-time storage of the very large amounts of data generated to hard disk, are all reported. The SSVEP paradigm uses a sinusoidal-modulated visual stimuli. A novel linearised LED (light emitting diode) head-up display was developed, in addition to more conventional stimuli, such as the alternating checker-board display, all with sinusoidal modulation capability over a range of frequencies. The Neuropsychiatric Workstation described in thesis has been replicated several times and is in regular use at Brain Sciences Institute (BSI) at Swinburne University of Technology, and other collaborative research institutes.
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49

Ottley, Mark Carlisle. "Posed and genuine smiles: an evoked response potentials study." Thesis, University of Canterbury. Psychology, 2009. http://hdl.handle.net/10092/3075.

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The ability to recognise an individual's affective state from their facial expression is crucial to human social interaction. However, understanding of facial expression recognition processes is limited because mounting evidence has revealed important differences between posed and genuine facial expressions of emotion. Most previous studies of facial expression recognition have used only posed or simulated facial expressions as stimuli, but posed expressions do not reflect underlying affective state unlike genuine expressions. The current study compared behavioural responses and Evoked Response Potentials (ERPs) to neutral expressions, posed smiles and genuine smiles, during three different tasks. In the first task, no behavioural judgment was required, whereas participants were required to judge whether the person was showing happiness in the second task or feeling happiness in the third task. Behavioural results indicated that participants exhibited a high degree of sensitivity in detecting the emotional state of expressions. Genuine smiles were usually labelled as both showing and feeling happiness, but posed smiles were far less likely to be labelled as feeling happiness than as showing happiness. Analysis of P1 and N170 components, and later orbitofrontal activity, revealed differential activity levels in response to neutral expressions as compared to posed and genuine smiles. This differential activity occurred as early as 135ms at occipital locations and from 450ms at orbitofrontal locations. There were significant interactions between participant behavioural sensitivity to emotional state and P1 and N170 amplitudes. However, no significant difference in ERP activity between posed smiles and genuine smiles was observed until 850ms at orbitofrontal locations. An additional finding was greater right temporal and left orbitofrontal activation suggesting hemispheric asymmetry of facial expression processing systems.
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50

劉文慶 and Wenqing Liu. "Fast tracking of evoked potentials variations by wavelet analysis." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31243411.

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