Abstracts of the Clinical EEG & Neuroscience Journal, Volume 33
Patients (64) with the Lennox-Gastaut Syndrome (LGS) were followed with EEGs (602) and clinical findings over a 42 yr period, up to 51 yrs of age. Before the slow spike-wave (SSW) complex appeared, in over one half of the patients focal discharges were seen and most often (71%) many discharges were noted, all associated with generalized seizures. With the SSW, two thirds of the patients showed additional focal discharges, again most often (72%) very many or many were noted. Clinical attacks were usually generalized but partial attacks also were seen. Although the largest absolute number of SSW complexes appeared in young children, the highest percentage of recordings with SSW was found between 25-29.9 yrs. Changes in the frequency of the spike-wave complexes were occasionally noted, not only decreasing in frequency from 3-6/sec down to 1-2/sec, but also increasing up to 3-6/sec. After the disappearance of the SSW in time, focal discharges, diffuse and focal slow waves were seen in nearly all records and complex partial seizures increased in number. This study has emphasized the importance of the cortex in the LGS and also the instability of the pattern that occasionally appears.
Outcome Related Electrophysiological Subtypes of Cocaine Dependence
Leslie S. Prichep, Kenneth R. Alper, Lev Sverdlov, Sharon C. Kowalik, E. R. John, Henry Merkin, MeeLee Tom, Bryant Howard and Mitchell S. Rosenthal
We previously described the existence of two quantitative EEG (QEEG) subtypes of cocaine dependent males, identified at baseline, displaying differential proneness to relapse. The current study expands the population to include females and enhances the measure set to include both QEEG and somatosensory EP (SEP) features. Fifty-seven cocaine dependent adults (16 F, 41 M) were evaluated 5-14 days after last cocaine use, while in residence at a drug-free therapeutic community. The median length of stay in treatment (continued abstinence) was 25 weeks. Using a small subset of QEEG and SEP baseline features, three subtypes (CLUS) were identified. CLUS 2 (n=25) and CLUS 3 (n=23) replicated the published subtypes, while CLUS 1 (n=9) was previously undescribed. Cluster membership was significantly associated with length of stay in treatment (c2=13.789, P<0.001), but not with length of exposure to crack cocaine or to any demographic or clinical features. Seventy-eight percent of CLUS 1 and 65% of CLUS 3 left treatment = 25 weeks, whereas 80% of CLUS 2 remained in treatment > 25 weeks. The existence of outcome related subtypes may reflect:  differential neurophysiological vulnerability, "traits," predisposing individuals to cocaine addiction; or  differential neurosensitivity, "states," due to the effects of chronic cocaine exposure, and associated differences in treatment outcome. Using Variable Resolution Electrical Tomographic Analysis (VARETA), the mathematically most probable neuroanatomical source of the scalp recorded EEG data was localized. Computation of VARETA on the baseline Cluster profiles suggest significant differences in the underlying pathophysiology of these subtypes.
We report another technique of transcranial magnetic stimulation (TMS) for exciting the originating cells of the descending corticospinal tract. A cap shaped TMS coil has been described for simultaneously exciting muscles in all four extremities. This TMS coil is useful for monitoring the functional integrity of the descending motor paths during spinal cord surgery, because information regarding the integrity of both the left and right sides of the spinal cord motor paths can be obtained concurrently. Despite the improved design of the cap coil, careful placement is required for achieving bilateral spinal cord motor responses. Cortical mapping was used to identify the optimum scalp foci for the muscles studied. The cap coil must overlap these foci to simultaneously elicit compound muscle action potentials (CMAPs) in all four extremities. Increasing TMS stimulation intensity will increase the magnitude of the acquired CMAPs responses without significantly changing latency.
This report describes our initial clinical experience using transcranial magnetic stimulation for monitoring spinal cord motor function during surgical procedures. Motor evoked potentials were elicited using a cap shaped coil placed on the scalp of 27 patients while recording peripheral motor responses (compound muscle action potentials – CMAPs) from the upper (N=1) or lower limbs (N=26). Wherever possible, cortical somatosensory responses (SEPs) were also monitored by electrically stimulating the left and right posterior tibial nerve (N=25) or the median nerve (N=1). The judicious choice of anesthetic regimens resulted in successfully obtaining motor evoked responses (MEPs) in 21 of 27 patients and SEPs in 26 of 27 patients. Single pulse TMS resulted in peripheral muscle responses having large variability, whereas, the variability of SEPs was much less. Criteria based on response variability for assessing clinically significant changes in both MEPs and SEPs resulted in two false negative predictions for SEPs and none for MEPs when evaluating postoperative motor function. We recommend monitoring both sensory and motor pathways during procedures where placing the spinal cord at risk of damage.
The precision between dipole Brain Electric Source Analysis (BESA) and brain distributed Variable Resolution Electromagnetic Tomography (VARETA) models for the localization of brain sources of interictal epileptiform discharges in patients with partial complex epilepsy was compared. The localization of brain sources calculated with dipole analysis and variable resolution electromagnetic tomography in 20 interictal recordings was analyzed. The origin of the dipoles was temporal in 18 cases, frontal in 1 and occipital in another. One dipole was enough in 7 cases, whereas two dipoles were necessary in 13 cases. The localization of paroxysmal activity was the same with BESA and VARETA in 17 patients. BESA and VARETA are useful methods for EEG sources analysis; BESA has more precision for the localization of punctate epileptogenic regions, and VARETA provides more information concerning the extension of the epileptic zone.
Aim: To explore the epileptogenic potential of a newly introduced police car flash light device (930 Heliobe Lightbar).
Methods: A 930 Heliobe Lightbar was installed in the EEG laboratory. Thirty patients with known epilepsy, 30 subjects with chronic headache who were otherwise healthy and 15 healthy volunteers were examined.
Results: All the subjects signed an informed consent and underwent an EEG during which photostimulation was performed with the standard stroboscope and later with the Police lightbar. In all 75 examined the lightbar did not induce clinical or electrographic seizures. In a single patient with epilepsy the lightbar enhanced epileptiform activity induced by standard photic stimulation.
Conclusion: In this study the new Police lightbar was found to be non-epileptogenic.
The term “pre-aura” is used for the designation of earliest pre-ictal manifestations that escape detection by conventional EEG and both objective and subjective behavioral signs. Fairly recent reports have indicated earliest pre-ictal vascular changes (perifocal ischemia and hyperemia) and also changes found in various methods of quantified EEG.
These changes may precede the seizure onset (in conventional terms) by 1 to 20 minutes.There is good reason to assume that pre-auras are limited to focal epilepsies and do not occur in the various subforms of primary generalized epilepsy. The electrodecremental type of seizure onset, mostly found in the frontal region, could also denote a pre-aura in the earliest decremental phase.
The very earliest pre-aura phenomena are most likely to be neuronal rather than vascular. Further proof could come with the use of ultrafast EEG frequency recordings.
Transient visual evoked potentials (VEP) were recorded simultaneously from 16 electrodes evenly placed over posterior scalp locations covering the occipital, posterior parietal and temporal areas. Interhemispheric amplitude difference of the N70 deflection was established across 6 homologous lateral electrode pairs in 15 normal controls and 32 patients with chiasmatic or retrochiasmatic cerebral lesions. Twenty-three of these had known homonymous or bitemporal field defects while 9 had normal fields on routine perimetry. Significant interhemispheric asymmetry of any single electrode pair occurred in 55% of the 32 patients with known pathology, while the cumulative yield of all electrode pairs was over 80 percent. The diagnostic yield of individual electrode pairs was significantly different: the electrode pair placed over the temporo-parietal junction detected the highest number of abnormalities. The cumulative abnormality taken over all lateral electrode pairs could be described with a curve well fitted with a probability summation function. It is inferred that the contribution of several independent generator sources is reflected in the N70 of the pattern onset VEP. The results suggest that multichannel recording of the interhemispheric amplitude distribution of the N70 of the onset VEP is useful for the evaluation of paracentral visual field defects.
Sources of Abnormal EEG Activity in Spontaneous Intracerebral Hemorrhage
Antonio Fernández-Bouzas, Thalía Harmony, Thalía Fernández, Eduardo Aubert, Josefina Ricardo-Garcell, Pedro Valdés, Jorge Bosch, Gustavo Casián and Raul Sánchez-Conde
This report describes the results obtained with EEG source analysis in the frequency domain (FD-VARETA), in 14 patients with brain hemorrhages; 6 hemorrhages were located in the putaminal region, 1 was mesencephalic and 7 were lobar cerebral hemorrhages. Our goal was to evaluate FD-VARETA accuracy for the localization of fast growth expansive brain lesions. FD-VARETA produces brain electromagnetic tomography images of EEG sources in every frequency. The location of the most abnormal or the maximum Z value across all frequencies was compared with the location of spontaneous hemorrhages in computed tomographies (CT). In all patients the main source was within delta or theta bands. The spatial extent of the sources, in the brain atlas, at these frequency values was almost the same as the volume of hematoma in CT. Putaminal lesions produced larger regions of cortical deafferentation than lobar hematomas, with higher abnormal Z values. FD-VARETA was more accurate in locating the lesions than traditional maps of absolute and relative power in delta, theta, alpha and beta bands.
Conclusion: FD-VARETA is a valuable procedure for the functional evaluation of brain hemorrhages.
The influence of sensory modulation on the early stage of information processing was investigated with a somatosensory contingent negative variation (CNV) paradigm. Whether or not even a somatosensory input as well as auditory or visual stimulus to one hemisphere elicits the symmetrical “early CNV” was also examined. Eleven normal individuals (3 males, 8 females) performed a conventional CNV paradigm with a click sound as the warning stimulus (WS) and a red light flash as the imperative stimulus (IS). Nine individuals (5 males, 4 females) did the somatosensory CNV paradigm with paired electrical stimuli as WS and IS. The subjects were instructed to press a button in response to IS as fast as possible. The early CNV amplitude was smaller and P300 latency was longer in somatosensory paradigm than conventional paradigm. In addition, the latency of P100 in a somatosensory paradigm was longer than that of N100 in a conventional paradigm. These findings suggest that the initiation of early detection, reflected by P100, the initiation of cognition, reflected by P300, and orienting response, reflected by early CNV, are delayed in a somatosensory CNV paradigm. Furthermore, all event-related potentials (ERPs) evoked by somatosensory stimuli showed a bilateral symmetry.
Event-related potentials (ERPs) were recorded while 13 subjects completed a color discrimination task. In task one, subjects were asked to press a button when the presented stimulus was a red or a green spot (Go stimulus), and inhibited any motor response when the stimulus was a yellow or a white spot (No-go stimulus). In task two, subjects were instructed to count the number of the Go stimuli, not to count the No-go stimuli. In order to investigate the influence of probability on ERP components, two sessions were designed in each task. In session one, the probability of the four kinds of stimuli was equal. In session two, the probability of red, green, yellow, and white were 10%, 10%, 10%, and 70% respectively. An enhanced negative potential in the frontal area was recorded in the 200-400 ms range both following No-go stimuli and following No-count stimuli, which was not influenced by the stimulus probability. The result cast doubt on the interpretation of the frontal negative potential enhancement as reflecting response-inhibition processes. The potential might be related to the information processing of response-tendency conflict rather than the suppression of motor execution.
In order to investigate whether Alzheimer’s disease (AD) is the end result of aging of the brain or the result of some other mechanism, we analyzed EEGs showing the absolute power of harmonic responses to photic stimulation (PS) in younger subjects, non-demented elderly subjects and AD patients. At rest, the AD patients generally showed less absolute power than the younger and elderly subjects, with significant differences found at 10Hz and 20Hz. Analysis of EEGs recorded during PS indicated that the elderly subjects generally demonstrated more absolute power than the younger subjects and AD patients. These findings suggest a failure of stimulation-related brain activation in AD patients, and provide further evidence that normal aging and AD employ different mechanisms for functional organization during PS.
Donepezil is a cholinesterase inhibitor which has been previously shown to affect the cognitive evoked potentials (EPs) of patients with Alzheimer’s Disease (AD) during treatment with the drug. The purpose of this study was to determine the effect of treatment with donepezil 5 mg daily for 1 month on quantitative EEG (QEEG) in patients with AD. Treatment was associated with no significant differences between the pre- and post-treatment QEEGs for (1) absolute power (all four frequency bands), (2) percent relative power (all four frequency bands), (3) total mean frequency, (4) mean frequency for theta and beta, (5) absolute power asymmetry across homologous electrode pairs (all four frequency bands), and (6) interhemispheric coherence across homologous electrode pairs (all four frequency bands). There were significant decreases in mean alpha and delta frequencies that were consistent across broad electrode arrays except for an increase in the delta frequency at T3. The implications of these changes are not yet clear. Studies of QEEG changes with higher doses of donepezil over longer periods of time may yield a better understanding of the neurophysiological effects of the medication.
The effects of human immunodeficiency virus (HIV) infection on central nervous system function were studied with the P3a and P3b event-related brain potentials (ERPs) in patients with HIV compared to unaffected matched controls (n=14/group). All patients were on anti-viral medication for at least 2 months before testing. Auditory stimuli were employed in an easy 2-stimulus oddball discrimination task to obtain a typical P3b (P300) subcomponent. A 3-stimulus distractor paradigm also was employed in which the target/standard discrimination was very difficult, and an infrequent high-pitched tone non-target was presented to elicit the P3a subcomponent. Subjects responded only to the target stimulus in each task. P3a amplitude was significantly smaller for HIV compared to control subjects. No reliable P3b effects were obtained. The findings suggest that P3a rather than P3b may be a more sensitive measure of cognitive impairment in HIV patients on anti-viral medication.
The purpose of the study was to examine the P3a and P3b components of the event-related brain potential (ERP) in patients sustaining moderate to severe brain injury. Electrophysiological and behavioral responses were recorded in brain injured (N = 18) and healthy control (N = 21) participants during performance of an auditory 3-stimulus distractor paradigm. Auditory stimuli consisted of a series of repetitive standard tones (75 ms), occasionally interrupted by equiprobable target (25 ms) and distractor sounds (white noise). Tone duration discrimination accuracy was similar in patients and controls, but patients had prolonged reaction times to targets. The reaction time delay was paralleled by a prolongation of P3b latency to targets in the patient group relative to controls. The stimulus and task dependent modulation of ERP responses in the brain injury group was similar to that of controls in terms of the spatial distribution of ERPs over the scalp. However, the brain injury group had attenuated P3a and P3b amplitudes to distractor and target stimuli, respectively. The electrophysiological data suggest a deficit in the allocation of attentional resources to the processing of deviant stimuli in the brain injury group.
We studied 14 patients with well-characterized refractory temporal lobe epilepsy (TLE), 7 with right temporal lobe epilepsy (RTE) and 7 with left temporal lobe epilepsy (LTE), on a word repetition ERP experiment. Much prior literature supports the view that patients with left TLE are more likely to develop verbal memory deficits, often attributable to left hippocampal sclerosis. Our main objectives were to test if abnormalities of the N400 or Late Positive Component (LPC, P600) were associated with a left temporal seizure focus, or left temporal lobe dysfunction. A minimum of 19 channels of EEG/EOG data were collected while subjects performed a semantic categorization task. Auditory category statements were followed by a visual target word, which were 50% “congruous” (category exemplars) and 50% “incongruous” (non-category exemplars) with the preceding semantic context. These auditory-visual pairings were repeated pseudo-randomly at time intervals ranging from ~10–140 seconds later. The ERP data were submitted to repeated-measures ANOVAs, which showed the RTE group had generally normal effects of word repetition on the LPC and the N400. Also, the N400 component was larger to incongruous than congruous new words, as is normally the case. In contrast, the LTE group did not have statistically significant effects of either word repetition or congruity on their ERPs (N400 or LPC), suggesting that this ERP semantic categorization paradigm is sensitive to left temporal lobe dysfunction. Further studies are ongoing to determine if these ERP abnormalities predict hippocampal sclerosis on histopathology, or outcome after anterior temporal lobectomy.
This report compares event-related brain potentials (ERPs) of patients having a depressive disorder alone (n=58), an anxiety disorder alone (n=22), comorbidity of these disorders (n=18), and healthy controls (n=49). ERPs were recorded from 30 electrode sites during auditory oddball tasks using consonant-vowel syllables (phonetic) or complex tones (tonal). Overlapping ERP components were identified and measured using covariance-based principal components analysis. An early P3 subcomponent (P315) was larger in patients having an anxiety disorder alone when compared to depressed patients with or without an anxiety disorder and healthy controls, whereas a late P3 subcomponent (P400) was larger in patients having comorbidity of anxiety and depressive disorders than in the other groups. Also, the N2-P3 complex showed task-dependent hemispheric asymmetries, including larger N2-P3 amplitude over left than right temporoparietal sites during the phonetic oddball task. This hemispheric asymmetry was greatest in patients having a depressive disorder alone and smallest in patients having an anxiety disorder alone. The opposite nature of the alterations of hemispheric asymmetry and early P3 amplitude in depressive and anxiety disorders underscores the importance of taking comorbidity with anxiety into account in studies of cognitive ERPs in depressive disorders.
Event-related brain potentials were recorded from 10 patients with DSM-IV schizophrenia (9 men) and 10 healthy control subjects (9 men) during the performance of two auditory oddball tasks, one using a 1.5 second interstimulus interval (ISI), the other using an 8 second ISI. P300 amplitude to target tones (.20 probability) and standard tones (.80 probability) were measured from midline electrodes Fz, Cz, and Pz. Results showed different effects of ISI in the two groups. Controls showed a slight decrease in P300 amplitude to targets but a marked increase in P300 to standards with the increase in ISI. In contrast, schizophrenic patients showed no change in the P300 to targets and a relatively small increase in P300 to standards with the ISI increase. Moreover, relative to the controls, P300 amplitude to targets was reduced in the schizophrenic patients at the short but not the long ISI. Implications for the cognitive significance of the P300 and its reduction in schizophrenia are discussed.