The relationship between epileptiform discharges and background activity in the visual analysis of electroencephalographic examinations in dogs with seizures of different etiologies.

Electroencephalographic (EEG) recordings in 125 outpatient dogs with various epileptiform encephalopathies were acquired under medetomidine sedation using subdermal wire electrodes. The features of canine EEG (background activity [BGA] and epileptiform discharges [EDs]) were assessed, described and compared. The dogs included neurologically healthy controls (N, n = 19), dogs with portosystemic shunt (PSS, n = 9), dogs with intracranial pathologies (IP, n = 27) and dogs with idiopathic epilepsy (IE, n = 70). A visual EEG analysis revealed significantly more pronounced high voltage, low-frequency BGA in the PSS and IP groups in comparison to the N and IE groups (PSS vs. N, PSS vs. IE P <0.0001; IP vs. N, IP vs. IE P = 0.043). At least one ED in the recording was found in 47.37% (n = 9/19) of the individuals in the N group, 88.9% (n = 8/9) of the dogs in the PSS group, 77.78% (n = 21/27) of the dogs in the IP group and 61.43% (n = 43/70) of the dogs in the IE group. The presence of bilateral symmetric triphasic (BST) waves was significantly higher in the PSS group than in the remaining groups. There was a strong prevalence of spike-waves in dogs with idiopathic epilepsy and of BST waves in dogs with portosystemic shunt. None of the dogs in group N had spike-waves or BST activity. EDs were observed more frequently in high and very high voltage, low frequency BGA than in low voltage, high frequency BGA.

Sleep-inducing effects of low doses of melatonin ingested in the evening.

We previously observed tht low oral doses of melatonin given at noon increase blood melatonin concentrations to those normally occurring nocturnally and facilitate sleep onset, as assessed using and involuntary muscle relaxation test. In this study we examined the induction of polysomnographically recorded sleep by similar doses given later in the evening, close to the times of endogenous melatonin release and habitual sleep onset. Volunteers received the hormone (oral doses of 0.3 or 1.0 mg) or placebo at 6, 8, or 9 PM. Latencies to sleep onset, to stage 2 sleep, and to rapid eye movement (REM) sleep were measured polysomnographically. Either dose given at any of the three time points decreased sleep onset latency and latency to stage 2 sleep. Melatonin did not suppress REM sleep or delay its onset. Most volunteers could clearly distinguish between the effects of melatonin and those of placebo when the hormone was tested at 6 or 8 PM. Neither melatonin dose induced "hangover" effects, as assessed with mood and performance tests administered on the morning after treatment. These data provide new evidence that nocturnal melatonin secretion may be involved in physiologic sleep onset and that exogenous melatonin may be useful in treating insomnia.

EEG-triggered echo-planar functional MRI in epilepsy.

We investigated whether: (1) EEG recordings could be successfully performed in an MRI imager, (2) subclinical epileptic discharges could be used to trigger ultrafast functional MRI images, (3) artifact-free functional MRI images could be obtained while the patient was having the EEG monitored, and (4) the functional MRI images so obtained would show focal signal increases in relation to epileptic discharges. We report our results in two patients who showed focally higher signal intensity, reflective of increased local blood flow, in ultrafast functional MRI timed to epileptic discharges recorded while the patients were in the imager and compared with images not associated with discharges. One patient showed a focal increase despite a clinical and EEG history of generalized discharges. This approach may have the potential to identify brain regions activated during brief focal epileptic discharges.

Postictal heart rate oscillations in partial epilepsy.

We report postictal heart rate oscillations in a heterogeneous group of patients with partial epilepsy. This pattern is marked by the appearance of transient but prominent low-frequency heart rate oscillations (0.01 to 0.1 Hz) immediately after 5 of 11 seizures recorded in 5 patients. This finding may be a marker of neuroautonomic instability and, therefore, may have implications for understanding perturbations of heart rate control associated with partial seizures.

EEG abnormalities in patients with atypical panic attacks.

BACKGROUND: Panic attacks and certain partial seizures have phenomenologic similarities which suggest that they may somehow be related. No evidence of such a relationship, however, was found when the routine EEGs of patients with panic attacks were examined. METHOD: Fifteen subjects with atypical panic attacks who met DSM-III-R criteria for panic disorder agreed to have routine followed by prolonged ambulatory EEG monitoring with sphenoidal electrodes. Fourteen subjects actually underwent monitoring; 1 had a panic attack during premonitoring routine EEG. RESULTS: Focal paroxysmal EEG changes consistent with partial seizure activity occurred during panic attacks in 33% (N = 5) of the 15 subjects; 2 (40%) of the 5 subjects with panic-related EEG changes had normal routine EEGs. Multiple attacks were recorded before panic-related EEG changes were demonstrated in several subjects. CONCLUSION: It may be necessary to monitor the EEG during multiple panic attacks to reveal an association between atypical panic attacks and epileptiform EEG changes.

Experimental tests of EEG source localization accuracy in spherical head models.

OBJECTIVES: The locations of electrical sources in the brain can be calculated using EEG data. However, the accuracy of these calculations is not well known because it is usually not possible to compare calculated source locations with actual locations since little accurate location information is available about most sources in the brain. METHODS: In this study, sources at known locations are created by injecting current into electrodes implanted in the brains of human subjects. The locations of the implanted and scalp EEG electrodes are determined from CTs. The EEG signals produced by these dipolar sources are used to calculate source locations in spherical head models containing brain, skull, and scalp layers. The brain and scalp layers have the same electrical conductivity while 3 different skull conductivity ratios of 1/80th, 1/40th, and 1/20th of brain and scalp conductivity are used. Localization errors have been determined for 177 sources in 13 subjects. RESULTS: An average localization error of 10.6 (SD=5.5) mm for all 177 source was obtained for a skull conductivity ratio of 1/40. The average errors for the other ratios are only a few millimeters larger. The average localization error for 108 sources at superior locations in the brain is 9.2 (4.4) mm. The average error for 69 inferior location sources is 12.8 (6.2) mm. There are no significant differences in localization accuracy for deep and superficial sources. CONCLUSIONS: These results indicate that the best average localization that can be achieved using a spherical head model is approximately 10 mm. More realistic head models will be required for greater localization accuracy.

Experimental tests of EEG source localization accuracy in realistically shaped head models.

OBJECTIVES: To determine the accuracy with which electrical sources in the human brain can be located using realistically shaped boundary element models of the head and to compare this accuracy with that using spherical head models. METHODS: In a previous study, electroencephalographs (EEGs) produced by sources at known locations in the brains of human subjects were recorded. The sources were created by injecting current into implanted depth electrodes. The locations of the implanted depth and scalp EEG electrodes and head shape were determined from computerized tomography images. The EEGs were used to calculate source locations in spherical head models and localization accuracy was determined by comparing the calculated and actual locations. In this study, these same EEGs are used to determine localization accuracy in realistically shaped head models. RESULTS: An average localization error of 10.5 (SD=5.4) mm was obtained in the realistically shaped models for all 176 sources in 13 subjects. This compares with 10.6 (5.5) mm in the spherical models. The average localization error for 105 sources at superior locations in the brain is 9.1 (4.2) mm. The average error for 71 inferior location sources is 12.4 (6.4) mm. The corresponding values for the spherical models are 9.2 (4.4) and 12.8 (6.2) mm. CONCLUSIONS: The realistically shaped head boundary element models used in this study produced very nearly the same localization accuracy as spherical models.

Effects of single-pulse transcranial magnetic stimulation (TMS) on functional brain activity: a combined event-related TMS and evoked potential study.

OBJECTIVE: To further evaluate the potential of slew-rate limiting amplifiers to record electrophysiological signals in spite of concurrent transcranial magnetic stimulation (TMS), and to explore the effects of single-pulse TMS on electroencephalographic (EEG) correlates of functional brain activity. METHODS: Visual-evoked potentials (VEPs) to checkerboards were recorded in 7 right-handed subjects, while single-pulse TMS was applied to the occipital pole either at visual stimulus onset, during the build-up or at the expected peak of the early VEP component P1 (VIS&TMS). Timing of TMS was individually adjusted based on each subject's VEP-latency. A condition of TMS without concurrent visual stimulation (TMS(alone)) served for subtraction purposes (VIS&TMS minus TMS(alone)) to partial out TMS-related contaminations of the EEG signal. RESULTS: When TMS was applied at visual stimulus onset, VEPs (as calculated by subtraction) perfectly matched control VEPs to visual stimulation alone. TMS at around P1, in contrast, modified the targeted (P1) and the subsequent VEP component (N1), independently of whether TMS was given at build-up or peak. CONCLUSIONS: The retrieval of regular VEPs with concomitant TMS at visual stimulus onset suggests that the employed EEG system and subtraction procedure are suited for combined EEG-TMS studies. The VEP changes following TMS at around P1 provide direct clues on the temporal dynamics of TMS pulse effects on functional activity in the human brain. Our data suggest effects of relatively long duration (approximately 100 ms) when TMS is applied while functional neuronal activity evolves.

Echo-planar functional MR imaging of epilepsy with concurrent EEG monitoring.

BACKGROUND AND PURPOSE: The role of functional MR (fMR) imaging in the evaluation of patients with epilepsy has not been systematically studied. Our purpose was to identify the fMR correlates of interictal epileptiform discharges. METHODS: Twenty patients with epilepsy and frequent interictal discharges were studied with concurrent EEG monitoring on a 1.5-T echo-planar magnet to acquire blood-oxygenation-level-dependent (BOLD) images in the baseline (OFF) and immediate post-discharge (ON) states. Analysis was performed using subtraction of average ON and OFF data (method I); cross-correlation analysis between the ON and OFF states (method II); and individual spike analysis (ISA), with which signal intensity in the individual ON states was statistically analyzed using a weighted comparison with the mean and variance of the OFF states (method III). Agreement of fMR activation with EEG localization was determined. RESULTS: Eighteen of 20 patients had interictal discharges during the monitoring period. Method I yielded visually detectable sites of BOLD signal differences in only one patient. Method II resulted in two patients with sites of BOLD activation. Method III, ISA, resulted in regions of increased BOLD signal corresponding to the EEG focus in nine of 10 patients. CONCLUSION: fMR studies can often reveal sites of increased BOLD signal that correspond to sites of interictal EEG discharge activity. Because of variable intensity changes associated with discharge activity, ISA resulted in increased sensitivity.

Reappraisal of filter effects on P300 voltage and latency.

The selection of which high-pass filter cutoff to use in P300 studies continues to be a serious methodological consideration. To determine whether there was an optimal range of bandpass widths-a range in which P300 voltage and latency would not show statistically significant differences-the authors recorded P300 responses to the auditory "oddball" paradigm from Cz and Pz electrodes in a group of eight healthy males. The authors used high-pass filter cutoffs of 0.01, 0.1, 0.3, and 1.0 Hz with low-pass filter cutoffs of 30 and 100 Hz and measured both P300 peak voltages and P300 integrated mean voltages at 12 bandpass settings. There were statistically significant differences in 7 out of 12 bandpass comparisons for P300 peak voltages and in 7 out of 12 bandwidth comparisons for P300 integrated mean voltages. For P300 latencies, there were statistically significant differences in 9 out of 12 bandwidth comparisons. Based on these results, the best recommendation, therefore, is that the high-pass filter be set no higher than 0.3 Hz.

MR imaging-compatible electroencephalography electrode system for an epilepsy monitoring unit.

We studied the usefulness of an MR imaging-compatible electroencephalography (EEG) electrode system for continuous EEG recordings in our epilepsy monitoring unit (EMU) by comparing 100 consecutive patients with MR imaging-compatible and MR imaging-incompatible EEG recording electrodes who underwent MR imaging between 3:00 pm and 7:00 am. The MR imaging-compatible system captured seizures in 21/50 (42%) patients and clinically valuable new electrographic data in 13/50 (26%) patients during the study interval, whereas possible seizures were lost to recording in 19/50 (38%) patients in the MR imaging-incompatible system. EEG recording was comparable by both systems, but the nurses could disconnect and reconnect the patients to their electrode cables only in the MR imaging-compatible system during the study interval while the EEG technologists were off duty. This study shows that the MR imaging-compatible system could be used routinely for long-term monitoring of the patients in EMUs.

4-channel 24 hour cassette recorder for long-term EEG monitoring of ambulatory patients.

A 4-channel cassette recorder capable of continuously recording the EEG for 24 h on a C-120 cassette is currently in use at the Montreal Neurological Institute. We have done a limited study on 20 patients with over 2000 h of recording to evaluate the recording system, its limitations and its capabilities, and to develop methodology for its operations. The use of preamplifiers enables one to record the background EEG with a noise level of 3-5 muVpp on 4 channels continuously for 1 day. The electrodes can be hidden in the hair and the preamplifier under the collar, to allow the patient to carry on his normal activities at home and at work. Since the cassette and the batteries can be easily changed, the patient himself can prolong the recording for several days. The cassette can be played back as fast as 60 times on a Minograf EEG machine for compressed analysis or 20 times for more detailed write-out, to obtain a record equivalent to standard EEG recordings. The system was not designed to replace or compete with standard EEG recordings but when used on well defined clinical problems, or in specific research projects, it can enhance the diagnostic or research value of the EEG.

Recording media for the EEG.

Long-term EEG monitoring usually implies the continuous recording (or the continuous monitoring of the EEG coupled with periodic or event recording) of the data on some medium other than paper. This involves a variety of technologies and methodologies and can become fairly complicated depending on the amount of data reduction, data analysis and type of replay used.

Recording the time of day.

The recording of the time-of-day (TOD) information (e.g., hours, minutes, and seconds) is an important part of a prolonged EEG and video study. The transcribing techniques for this information on paper (chart recorders), video tape, analog tape, and by digital computers are reviewed.

A 6-pole filter for improving the readability of muscle contaminated EEGs.

A multi-channel switched-capacitor 6-pole filter for significantly reducing the EMG artifact present during seizures recorded by long-term monitoring procedures has been implemented for routine use. This permits repeated replay of the seizures with different filter settings. All of the channels can be simultaneously dialed to any cut-off frequency (3 dB down) between 8 Hz and 70 Hz and the event replayed for filtering and write-out onto any standard EEG machine. The advantage of the 6-pole switched-capacitor filter is that it does not require a complex design with high precision RC components. The cut-off frequency is determined by the frequency of a simple clock that is used to select the same cut-off point for all 16 channels. By changing the clock frequency, the operator moves the cut-off point linearly. The dramatic improvement obtained by off-line digital filtering that was recently reported (Gotman et al. 1981) indicates that more efficient filtering of EMG contaminated seizures is diagnostically significant in selected cases. This approach is limited by the availability and expense of not only the computer's hardware but also the dedicated software. Specially designed 4-pole analog filters (Barlow 1984) are less expensive than digital filtering, but are difficult to design even at specific frequencies and do not allow for a range of frequencies. The switched-capacitor 6-pole filters have all the advantages of the above but are even more efficient in reducing EMG artifact. They also do not have any of the above disadvantages and cost only a few dollars per channel.