Electroencephalography and clinical neurophysiology
-
Electroencephalogr Clin Neurophysiol · Jul 1996
Nocturnal sleep latencies among alert, alert-deprived and sleepy subjects.
Twenty-seven healthy, asymptomatic subjects participated in a study to determine repeated nocturnal sleep latencies as a function of level of daytime sleepiness. Subjects were screened polysomnographically and were determined to be free of any sleep pathology. Nine subjects had a screening multiple sleep latency test (MSLT) of < or = 5 min and 18 had a MSLT of > or = 10 min. ⋯ The 0310 h latency was significantly shorter than the 0110 h latency and comparable to the 2300 and 0510 h latency. Significant correlations were found between daytime MSLT, repeated nocturnal sleep latencies, and nocturnal sleep time. These results show systematic differences in repeated nocturnal sleep latencies among sleep and alert subjects and extend the already described characteristics of these subjects by comparing them to a group of alert sleep-deprived subjects.
-
Electroencephalogr Clin Neurophysiol · Apr 1996
The impact of repeated short episodes of circulatory arrest on cerebral function. Reassuring electroencephalographic (EEG) findings during defibrillation threshold testing at defibrillator implantation.
The impact of circulatory arrest on EEG features during defibrillation threshold testing for implantation of a cardioverter defibrillator has been disputed. Cumulation of cerebral ischemic effects during threshold testing has been observed, and consequently the advice was given to avoid short intervals between tests and to limit the test number. This study investigated the duration of EEG signs of cerebral ischemia as well as the occurrence of cumulation. ⋯ Test interval was not related with either onset or recovery time. We conclude that repeated threshold tests which are monitored by assessment of EEG and hemodynamics are not associated with cumulative EEG changes as a result of ischemia. Our results do not support the advice that the number of tests should be limited.
-
Electroencephalogr Clin Neurophysiol · Mar 1996
Evidence of neuronal plasticity within the inferior colliculus after noise exposure: a study of evoked potentials in the rat.
Recent investigations have implicated that the central nervous system has a role in the changes that occur in auditory function following acoustic trauma caused by noise exposure. These investigations indicate that the inferior colliculus may be the primary anatomical location in the ascending auditory pathway where noise-induced neuronal plasticity occurs, thereby resulting in changes in the neuronal processing of auditory information. In the present investigation, we show that the amplitudes of all peaks in the click-evoked response from the external nucleus of the inferior colliculus decrease during a 30 min exposure to a tone (104 dB sound pressure level (SPL) at 4 kHz and 8 kHz). ⋯ We also show that exposure to a 4 kHz tone at 104 dB SPL causes changes in the neuronal processing of tonebursts in the form of changes in the temporal integration function for one of the peaks of the response from the external nucleus of the inferior colliculus that originates in the inferior colliculus. Before tone exposure the amplitude of this peak decreased with increasing stimulus duration, but after tone exposure the amplitude of this peak was independent of the duration of the toneburst stimulus. We interpret these changes as evidence that noise exposure (tone exposure) causes changes in the excitability of the inferior colliculus that are not seen in more caudal structures, and these changes are probably a result of a change in the balance between inhibition and excitation in the inferior colliculus.
-
Electroencephalogr Clin Neurophysiol · Dec 1995
Comparison of various coils used for magnetic stimulation of peripheral motor nerves: physiological considerations and consequences for diagnostic use.
We compared the ability of 4 magnetic coils to activate peripheral nerves in healthy subjects. No differences in motor threshold intensities were found between the coils, but the intensities needed to elicit maximum compound muscle action potential (CMAP) amplitudes were different. For superficial nerves maximum CMAPs in comparison with electrical stimulation were usually but not always found. ⋯ Coactivation of nearby nerves and underlying muscles was another main drawback especially at proximal sites and for coils of large diameter. Despite better focusing, double coils are less useful due to their great diameter. Magnetic stimulation cannot replace electrical neurography at the moment, even if different coils are used at different sites of stimulation.
-
Electroencephalogr Clin Neurophysiol · Mar 1995
Mental representations of movements. Brain potentials associated with imagination of hand movements.
The present study was designed in order to contribute towards the understanding of the physiology of motor imagery. DC potentials were recorded when subjects either imagined or executed a sequence of unilateral or bilateral hand movements. The sequence consisted of hand movements in 4 directions, forwards, backwards, to the right and to the left, and varied from trial to trial. ⋯ This result is consistent with the assumption that the primary motor cortex is active with motor imagery. Finally, the question has been addressed whether motor imagery may involve the left hemisphere to a larger extent than the execution of the movement. It is shown that a particular contribution of the left hemisphere associated with motor imagery may only show up under strictly controlled conditions.