Changes In EP Research Articles

Responses of Cochlear Potentials to Changes in Hydrostatic Pressure

Sustained and transient changes in hydrostatic pressure were transmitted directly to the perilymphatic space of guinea pigs. EP, as well as SP, CM, and AP, was measured before, during, and after pressure changes. Pressure applied to scala vestibuli led to an increase EP and SP, while pressure applied to scala tympani resulted in a decrease of these potentials. Comparable data were also obtained the anoxic cochlea. CM and AP failed to change when moderate amounts of pressure were applied. In guinea pigs whose organ of Corti was largely degenerated EP was normal, but it did not increase when pressure was applied to scala vestibuli, nor did it consistently decrease during pressure applications to scala tympani. These data were interpreted to mean that changes in EP normally occurring response to changes in hydrostatic pressure reflect variations in the output of dc generators located on the basilar membrane.

The relationship between steady potential and other electrical activities of cerebral cortex.

The changes in EEG and EP were investigated on the rat and the rabbit, in relation to the SP shift produced by DC application and repetitive brainstem stimulation.1. EEG and EP changed correlatively very often, if not always, with the forced SP-shift generated by DC application.2. In general, the cortical surface, in resting state, showed a slight positive steady potential relative to indifferent electrode placed on the nasal area. Therefore the application of slight negative DC was observed to supersede this positive steady potential. EP changed not only in amplitude, but also in polarity associated with the forced SP-shift, namely in positive direction by negative SP level and in negative direction by positive SP level.3. The slow component in EEG and EP changed (mainly in amplitude) in many cases in proportion to the magnitude of SP-shift.4. Repetitive stimulation of lower reticular formation caused sometimes the changes in SP, EEG and EP. However, there could not be found any consistent and regular correlation between them.5. RF stimulation of very low frequency caused the arousal reaction in EEG, when it was very low or very high in intensity. When the stimulation was moderate in intensity, the arousal reaction could not be produced by lower frequency. However, with increase in intensity, even very low frequency showed the significant arousal effect on EEG.

Coupled evolution of N220-P300 Evoked Potential components during the Go-No Go trials. Effects of Frontal and Temporal Lobe lesions

Event Abstract Back to Event Coupled evolution of N220-P300 Evoked Potential components during the Go-No Go trials. Effects of Frontal and Temporal Lobe lesions Dan M. Psatta1* and Michaela Matei1 1 Colentina Hospital, Center for Neuroscience, Romania Aim: To elucidate the physiologic mechanisms of the Go-No Go behavior. Methods: Average Auditory (AEPs) and Visual Evoked Potentials (VEPs) were tested on a 500 ms time base during performance of a Go-No Go task (pressing a button to differen- tiated warning stimuli). We used, as a reference, the responses obtained in resting conditions. This study was carried out on 26 normal subjects, 26 Frontal Lobe (FLE) and 28 Temporal Lobe Epilepsy (TLE) patients. Late EP component amplitudes were compared statistically between situations and groups. Results: Either with AEP or VEP investigation, a characteristic enlargement of the P300 depth amplitude and a concurrent reduction of the N220 peak amplitude occurred on the application of random target stimuli in the normal subjects. A N220 enhancement (widening) and the disappearance of P300 occurred on the application of non-target stimuli in the same subjects. Making associations between left ear stimulation- left hand finger responses, and right ear stimulation- right hand finger responses, the AEP changes could be compared between cerebral hemispheres (to reveal the activating or inhibitory effects on the motor response). Making concomittant recordings of the motor response, it was shown that this coincides ordinarily with the appearance of P300. When urged to respond rapidly, the latency of the motor reponse could decrease in normal subjects up to 200 ms, in line with a complete suppression of N220. Both types of EP changes (target, non target) were severely altered or disappeared in the TLE subjects group. Both AEPs and VEPs were instead globaly enhanced in FLE subjects and the typical N220 P300 changes persisted on application of Go- No Go stimuli. In a previuous paper (1) we showed that N220-P300 VEP components are signifi- cantly altered in patients with TL pathology (Depression, Epilepsy, Hippocampal sclerosis). Conclusion: The characteristic amplitude changes of the late Evoked Potential components during the Go-No Go trials depend on the integrity of the Temporal Lobe structures. These changes are essential for the motor control, exerting alternative activatory or inhibitory iinfluences. In view of the neuropsychological investigation, these effects should work mainly on the delayed motor repsonses (short term memory). FLE patients can also exhibit immediate alternation deficits in the Go-No Go situation, in spite of the normal N220-P300 development, induced by choice deficits (perseveration) and completely different physiological mechanisms.