Electroencephalography and clinical neurophysiology
-
Electroencephalogr Clin Neurophysiol · Nov 1997
Long sensory tracts (cuneate fascicle) in cervical somatosensory evoked potential after median nerve stimulation.
Low amplitude high frequency waves (LHW) were investigated in normal and patient cervical somatosensory evoked potentials after median nerve stimulation (CSEP) in parallel to normal and patient conducted somatosensory evoked potentials (SEP) after tibial nerve stimulation. Normal recordings were obtained in five subjects undergoing dorsal root entry zone (DREZ) coagulation for pain relief. Patient recordings were obtained in 11 subjects suffering from either syringomyelia, spinal cord tumour, or both. ⋯ These changes of LHW could not be connected with distortion of N13 seen in patient CSEP. A shorter duration and worsening of configuration in patient LHW were most prominent in cases with a loss of vibration and posture senses, but were also observed in cases where only pain and temperature senses were affected. We therefore concluded that cuneate fascicle is the most likely generator of LHW, although the participation of other cervical long sensory tracts, e.g. spinothalamic tract, cannot be ruled out.
-
Electroencephalogr Clin Neurophysiol · Apr 1997
Clinical use of polysynaptic flexion reflexes in the management of spasticity with intrathecal baclofen.
The aim of this study was to evaluate the clinical usefulness of lower limb flexion reflexes (FR) in the assessment of spinal excitability responsible for spontaneous or induced spasms. FR were recorded on the short head of biceps femoris, after electrical stimulation of the ipsilateral sural nerve at the ankle, in 17 spastic patients selected for chronic intrathecal administration of baclofen. The results obtained before and after treatment were compared with clinical scores commonly used to assess spasticity (Ashworth and spasm scores). ⋯ Intrathecal baclofen attenuated flexor reflex amplitude and increased reflex threshold in all patients. Our results suggest that FR investigate the intrinsic features of the spasms (threshold, intensity and duration) not assessed clinically, and that therefore the information gathered from FR recordings is not redundant with, and adds significantly to, that obtained by clinical scales. In our experience, FR recordings appeared to be a useful tool for quantifying the benefit of antispastic treatment and might be used as an ancillary indicator to determine the minimal effective dose of intrathecal baclofen.
-
Electroencephalogr Clin Neurophysiol · Jan 1997
Randomized Controlled Trial Clinical TrialPerioperative electroencephalographic seizures in infants undergoing repair of complex congenital cardiac defects.
Many infants with cardiac anomalies undergo repair early in life. Both commonly used support techniques, deep hypothermic circulatory arrest (DHCA) and low-flow cardiopulmonary bypass (LFB), may be associated with adverse neurological outcomes, including seizures. In a single center study, 171 infants undergoing correction for D-transposition of the great arteries were randomized to one of these support techniques. ⋯ Factors associated with EEG seizures included randomization to DHCA, longer duration of circulatory arrest, and diagnosis of VSD. In this study EEG seizures were common following this type of cardiac surgery, illustrating the importance of EEG monitoring in detecting seizures. This data adds insight into mechanisms of seizures in infants undergoing cardiac surgery.
-
Electroencephalogr Clin Neurophysiol · Nov 1996
Effects of interstimulus interval on somatosensory evoked magnetic fields (SEFs): a hypothesis concerning SEF generation at the primary sensorimotor cortex.
Cerebral responses evoked by peripheral stimuli are known to depend critically on the interstimulus interval (ISI). Here we report on the effects of ISI on somatosensory evoked magnetic fields (SEFs) to right median nerve stimulation, obtained in 9 healthy adults with ISIs of 0.15 0.3, 1,3 and 5 s. At the contralateral (left) primary sensorimotor cortex (SMI), the first cortical response, N20m, was stable between the ISIs 0.3 and 5 s, but slightly attenuated at the shortest ISI of 0.15 s. ⋯ Responses from second somatosensory cortex (SII) and posterior parietal cortex (PPC) were seen only with ISIs of 1 s or greater, being strongest at the 5 s ISI. Based on known effects of the ISI on intracellular evoked potentials, we present the following tentative model for the generation mechanism of the SMI response: N20m represents early excitatory postsynaptic potentials (EPSPs), P35m early inhibitory postsynaptic potentials (IPSPs), N45m secondary EPSPs and P60m late IPSPs in pyramidal neurones of area 3b. For practical purposes, SEFs from SMI can be obtained with short ISIs, while responses from SII and PPC require an ISI of at least 1 s.
-
Electroencephalogr Clin Neurophysiol · Aug 1996
Facilitation of motor evoked potentials by postcontraction response (Kohnstamm phenomenon).
We have applied repeated transcranial magnetic stimuli during the involuntary postcontraction muscle activity (Kohnstamm phenomenon) or during a tonic vibration reflex, both presumably arising from subcortical levels. The motor evoked potentials (MEPs) were compared with the MEPs evoked during a comparable voluntary contraction (cortical origin). The MEP amplitudes from the deltoid muscle appeared linearly related to the mean amplitude of the smoothed rectified background EMG preceding the stimulus. ⋯ If we accept the hypothesis of a subcortical origin of the involuntary muscle activity in the Kohnstamm phenomenon, the similar facilitatory effect of involuntary and voluntary background EMG supports a predominantly spinal localisation of the facilitatory mechanism in this proximal muscle both during involuntary and during voluntary activity, at least under the present conditions of rather low stimulus strengths. In about 20-30% of all the trials an extra facilitatory effect on the MEP amplitude was observed during the shortening contraction compared to an MEP elicited during the lengthening contraction, in spite of a similar background EMG. This extra facilitatory effect of the shortening contraction was observed during involuntary and voluntary preactivation, suggesting an elevated excitatory state at the spinal level.