Correlation between regional cerebral blood flow and EEG frequency in the contralateral hemisphere in acute cerebral infarction

Causal relationship between neuronal activity and cerebral hemodynamics in patients with ischemic stroke

OBJECTIVE

Neurovascular coupling enables rapid adaptation of cerebral blood flow (CBF) to support neuronal activity. Modern techniques enable the simultaneous recording of neuronal activities and hemodynamic parameters. However, the causal relationship between electrical brain activity and CBF is still unclarified. In this study, we investigated the causal relationship between surface electroencephalogram (EEG) and cerebral blood flow velocity (FV) from transcranial Doppler using Granger causality (GC) analysis.

APPROACH

Twenty simultaneous recordings of EEG and FV from 17 acute ischemic stroke patients were studied. Each patient had simultaneous, continuous monitoring of EEG and bilateral FVs in either the middle cerebral arteries or posterior cerebral arteries. The causal interactions between FV (0.006-0.4 Hz) and EEG (delta, theta, alpha, beta and gamma bands) were investigated through GC index (GCI). In order to make the GCIs comparable, the proportion of GCI (PGCI) values where G-causality is statistically significant were calculated. Scores on the NIH Stroke Scale (NIHSS) and the modified Rankin Scale (mRS) for neurologic disability were recorded respectively at discharge. Patients were divided into a deceased (mRS = 6) and a survival group (mRS = 1 to 5), and a favorable (mRS: 1 to 2) and unfavorable outcome group (mRS: 3 ~ 6).

MAIN RESULTS

This study identified a causal relationship from EEG→FV, indicating EEG contained information that can be used for FV prediction. PGCI was negatively related with mRS (p < 0.05), indicating that stronger causalities between EEG and FV exist in patients with better outcome. The NIHSS was negatively related with the asymmetry of the two-side PGCI, calculated as the difference between the lesional side and non-lesional side PGCI.

SIGNIFICANCE

A causal relationship from EEG→FV may exist in patients with ischemic stroke. The strength of G-causality may be related to stroke severity at discharge.

Cross-Frequency Coupling Between Cerebral Blood Flow Velocity and EEG in Ischemic Stroke Patients With Large Vessel Occlusion

Background: Neurovascular coupling enables a rapid adaptation of cerebral blood flow (CBF) to support neuronal activities. Whether this mechanism is compromised during the acute phase after ischemic stroke remains unknown. In this study, we applied a phase-amplitude cross-frequency coupling (PAC) algorithm to investigate multimodal neuro signals including CBF velocity (CBFV), and electroencephalography (EEG). Methods: Acute ischemic stroke patients admitted to the Neurointensive Care Unit, Tiantan Hospital, Capital Medical University (Beijing, China) with continuous monitoring of 8-lead EEG (F3-C3, T3-P3, P3-O1, F4-C4, T4-P4, P4-O2), non-invasive arterial blood pressure (ABP), and bilateral CBFV of the middle cerebral arteries or posterior cerebral arteries were retrospectively analyzed. PAC was calculated between the phase of CBFV in frequency bands (0-0.05 and 0.05-0.15 Hz) and the EEG amplitude in five bands (δ, θ, α, β, γ). The global PAC was calculated as the sum of all PACs across the six EEG channels and five EEG bands for each patient. The hemispherical asymmetry of cross-frequency coupling (CFC) was calculated as the difference between left and right PAC. Results: Sixteen patients (3 males) met our inclusion criteria. Their age was 60.9 ± 7.9 years old. The mean ABP, mean left CBFV, and mean right CBFV were 90.2 ± 31.2 mmHg, 57.3 ± 20.6 cm/s, and 68.4 ± 20.9 cm/s, respectively. The PAC between CBFV and EEG was significantly higher in β and γ bands than in the other three bands. Occipital region (P3-O1 and P4-O2 channels) showed stronger PAC than the other regions. The deceased group tended to have smaller global PAC than the survival group (the area under the receiver operating characteristic curve [AUROC] was 0.81, p = 0.57). The unfavorable outcome group showed smaller global PAC than the favorable group (AUROC = 0.65, p = 0.23). The PAC asymmetry between the two brain hemispheres correlates with the degree of stenosis in stroke patients (p = 0.01). Conclusion: We showed that CBFV interacts with EEG in β and γ bands through a phase-amplitude CFC relationship, with the strongest PAC found in the occipital region and that the degree of hemispherical asymmetry of CFC correlates with the degree of stenosis.

Longitudinal quantitative electroencephalographic study in mono-hemispheric stroke patients

The identification of individual factors modulating clinical recovery after a stroke is fundamental to personalize the therapeutic intervention to enhance the final clinical outcome. In this framework, electrophysiological factors are promising since are more directly related to neuroplasticity, which supports recovery in stroke patients, than neurovascular factors. In this retrospective observational study, we investigated brain neuronal activity assessed via spectral features and Higuchi’s fractal dimension (HFD) of electroencephalographic signals in acute phase (2–10 days from symptom onset, T0) and sub-acute phase (2.5 months, T1) in 24 patients affected by unilateral middle cerebral artery stroke. Longitudinal assessment of the clinical deficits was performed using the National Institutes of Health Stroke Scale (NIHSS), together with the effective recovery calculated as the ratio between difference of NIHSS at T0 and T1 over the NIHSS value at T0. We observed that delta and alpha band electroencephalographic signal power changed between the two phases in both the hemispheres ipsilateral (ILH) and contralateral (CHL) to the lesion. Moreover, at T0, bilateral higher delta band power correlated with worse clinical conditions (Spearman’s r_s = 0.460, P = 0.027 for ILH and r_s = 0.508, P = 0.013 for CLH), whereas at T1 this occurred only for delta power in ILH (r_s = 0.411, P = 0.046) and not for CHL. Inter-hemispheric difference (ILH vs. CLH) of alpha power in patients was lower at T0 than at T1 (P = 0.020). HFD at T0 was lower than at T1 (P = 0.005), and at both phases, ILH HFD was lower than CLH HFD (P = 0.020). These data suggest that inter-hemispheric low band asymmetry and fractal dimension changes from the acute to the sub-acute phase are sensitive to neuroplasticity processes which subtend clinical recovery. The study protocol was approved by the Bioethical Committee of Ospedale San Giovanni Calibita Fatebenefretelli (No. 40/2011) on July 14, 2011.

Intraoperative 16-Channel Electroencephalography and Bilateral Near Infrared Spectroscopy Monitorization in Aortic Surgery

Transient neurologic dysfunction is common after aortic surgery. Major causes of postoperative complications followed by cardiac surgery are due to hypoperfusion states such as selective cerebral perfusion, embolic debris during cardiopulmonary bypass and ulcerated plaque emboli originated from carotid arteries. Neurologic complications prolong periods of intensive care unit and hospital stay, worsens quality of life and unfortunately they are an important cause of morbidity. Anaesthesia during a carotid and aortic surgery constitutes of providing adequate brain perfusion pressure, attenuating cerebral metabolism by anaesthetic agents and monitoring the cerebral metabolic supply and demand relationship during the intraoperative period. We present a monitoring approach with an intraoperative 16-channel electroencephalography and bilateral near infrared spectroscopy during redo aneurysm of the sinus of Valsalva surgery.

Analysis of Brain Functional Changes in High-Frequency Repetitive Transcranial Magnetic Stimulation in Treatment-Resistant Depression

Repetitive transcranial magnetic stimulation (rTMS) is a treatment procedure that uses magnetic fields to stimulate nerve cells in the brain, and is associated with significant improvements in clinical symptoms of major depressive disorder (MDD). The effect of rTMS treatment on the brain can be evaluated by cordance, a quantitative electroencephalography (QEEG) method that extracts information from absolute and relative power of EEG spectra. In this study, to analyze brain functional changes, pre- and post-rTMS, QEEG data were collected from 6 frontal electrodes (Fp1, Fp2, F3, F4, F7, and F8) in 2 slow bands (delta and theta) for 55 MDD subjects. To examine brain changes, cordance scores were determined, using repeated-measures analysis of variance (ANOVA). High-frequency rTMS was associated with cordance decrease in left frontal and right prefrontal regions in both delta and theta for nonresponders; it was associated with cordance increase in all right and left frontal electrodes, except F8, for responders.

Outcome prediction in acute monohemispheric stroke via magnetoencephalography

BACKGROUND

Following an ischemic stroke a highly variable clinical outcome is commonly evident despite similar onset symptoms as well as lesion characteristics. The aim of this study was to identify indexes providing early prediction of functional recovery, in addition to clinical severity and lesion dimension at onset of stroke.

METHODS

In 32 patients, magnetoencephalographic (MEG) parameters collected in the acute phase (<10 days from symptoms onset, T0) from affected (AH) and unaffected (UH) hemispheres at rest and evoked by sensory stimuli were evaluated in association with the clinical outcome in a stabilized phase (T1, median 7.8 months) classified with three levels: worsening, partial and full recovery.

RESULTS

Multiple multinomial logistic regression indicated AH gamma and UH delta band powers able to prognosticate clinical outcome at T1. After inclusion in this analysis, lesion volume had the strongest predictive ability, and UH delta band power remained as a predictive factor with a measurable cut-off, maximizing both sensitivity and specificity of the prediction: a patient with UH delta below cut-off would recover to some extent; a patient with UH delta above cut-off would have a probability of about 70% to worsen.

CONCLUSIONS

MEG UH delta and AH gamma band powers were found to provide useful information about long-term outcome prognosis. Only the increase of delta band activity in the unaffected hemisphere contains information about the outcome in addition to the lesion volume.

Delta dipole density and strength in acute monohemispheric stroke

Previous electroencephalographic and magnetoencephalographic (MEG) studies demonstrate that the activity in the delta band can increase not only in the perilesional area, but also in the contralesional hemisphere in patients affected by a monolateral stroke. The increase of delta activity in the unaffected hemisphere (UH) in the acute phase after an unilateral stroke seems to add prognostic information about clinical recovery. Delta activity in perirolandic regions was investigated via MEG in a group of 27 patients affected by stroke in the territory of middle cerebral artery in the first week following the symptom onset. Clinical evaluation was performed in the acute and the post-acute (median 9 months) phase. Delta band power, delta dipole density (DDD, the number of accepted single dipole fits per second in parieto-frontal region) and delta dipole strength (DDS, the average of the accepted dipoles strengths) were evaluated in both hemispheres, separated on the basis of the lesion level (cortical and subcortical involvement) and correlated with lesion volume, clinical status in acute phase and recovery level. Although in our patient cohort DDD did not differ in both hemispheres with respect to control values, DDS showed higher level than in controls both in affected hemisphere (AH) and UH, was dependent on the lesion level and positively correlated with the lesion volume. Moreover, while AH and UH DDSs were not associated with clinical status in acute phase, they correlated with clinical recovery in post-acute phase. These properties confirmed findings obtained by spectral power analysis and provided a localized delta activity amplitude estimate, independent of measuring system and allowing inter-laboratory standardization.

Comparison of simultaneously recorded [H2(15)O]-PET and LORETA during cognitive and pharmacological activation

The complementary strengths and weaknesses of established functional brain imaging methods (high spatial, low temporal resolution) and EEG-based techniques (low spatial, high temporal resolution) make their combined use a promising avenue for studying brain processes at a more fine-grained level. However, this strategy requires a better understanding of the relationship between hemodynamic/metabolic and neuroelectric measures of brain activity. We investigated possible correspondences between cerebral blood flow (CBF) as measured by [H2O]-PET and intracerebral electric activity computed by Low Resolution Brain Electromagnetic Tomography (LORETA) from scalp-recorded multichannel EEG in healthy human subjects during cognitive and pharmacological stimulation. The two imaging modalities were compared by descriptive, correlational, and variance analyses, the latter carried out using statistical parametric mapping (SPM99). Descriptive visual comparison showed a partial overlap between the sets of active brain regions detected by the two modalities. A number of exclusively positive correlations of neuroelectric activity with regional CBF were found across the whole EEG frequency range, including slow wave activity, the latter finding being in contrast to most previous studies conducted in patients. Analysis of variance revealed an extensive lack of statistically significant correspondences between brain activity changes as measured by PET vs. EEG-LORETA. In general, correspondences, to the extent they were found, were dependent on experimental condition, brain region, and EEG frequency.

Permanent or transitory effects on neurocognitive components of the CNV complex induced by brain dysfunctions, lesions and ablations in humans

Since the mid-1960s, essentially using electrophysiological methods, our research group has examined the effects of different brain diseases in humans, both on first- and second-order conditioned responses and on some types of neurocognitive potentials of the CNV complex. This didactic lecture will focus on our various attempts to identify and understand the neuroanatomical and neurophysiological substrates involved in cognitive information processing followed by the conception and execution of sensory-motor and behavioural responses evoked by significant acoustic stimuli, in both pathological situations and normal control subjects. Great interest was, e.g. aroused in the early 1970s by the rare, fortunately unrepeatable, opportunity of examining the CNV patterns in various psychiatric patients treated with psychosurgical Freeman-Watts bilateral prefrontal 'radical' lobotomy, also with repeated recordings (The Responsive Brain (1976) 158; Multidisciplinary Perspectives in Event-Related Brain-Potentials Research (1978) 376) or bimedial bifrontal cingulotomy (Multidisciplinary Perspectives in Event-Related Brain Potential Research (1978) 383). In the same period, investigations into CNV activity recorded in patients submitted to complete callosotomy ('split brain': Attention and Performance, vol. IV (1972) 221; Electroenceph. Clin. Neurophysiol. Suppl. 33 (1973) 161) were also begun and were continued into the 1980s, also with regard to other types of ERP (Brain 111 (1988) 553; J. Cog. Neurosci. 2 (1990) 258). All these data furnished unique information about the sub-second dynamics of unilateral or bihemispheric cortico-cortical and cortico-subcortical interconnections in humans. In recent years, with a classic method of analysis based on sequential scalp-topographic bidimensional neuroelectric mapping and 21/19 electrodes connected to three different references, and binaural/monaural clicks as warning signals (S1), we have repeatedly examined the CNV activity of 11 selected patients submitted to complete ablation of the damaged cortical areas, with uni- or bilateral lesions restricted to the prefrontal or associative parieto-temporal areas. We have always used the standard CNV paradigm (S1-S2 motor-response) which evokes a complex of neurocognitive potentials, including the P300 from S1, which are well-known, since they are certainly among the most studied ERPs in the various ages and races of normal subjects, psychiatric patients and subjects with different brain diseases. The most important results have been, (1) In normal subjects the MRI and the latency differences of CNV component measurements along the bidirectional pathways functionally interconnecting ipsilateral distant associative cortical areas (e.g. the arcuate-superior longitudinal complex bundle) were accounted for by the transcortical conduction time, which varies in our scalp recordings from 1 cm/0.74 to 1.28 ms ( approximately 9.8 m/s). (2) Constantly, no true auditory S1-elicited N1a, b, c, P2, N2, P300 components or CNV slow waves (O- and E-wave) were recordable over the whole of the ablated cortical areas, but only clearly identifiable volume-conducted EP/ERPs generated in other hemispheric structures. (3) The post-S1 ERP/CNV complexes on the intact hemisphere were found to be within the normal limits. (4) Effects of severe disruption on the S1 ERP/CNV complexes evocable on the site and on remote ipsilateral apparently normal anatomo-functionally interconnected brain regions were observed in 5 patients, 4 of whom had extensive frontocortical ablations. In two of the latter the distant disruptive action on the CNV components over the neuroradiologically normal ipsilateral two-way connected post-rolandic sensory and association areas was seen to be partially reversible, showing aspects of a probable slowly evolving diaschisis-like effect. Similar deactivation of some ERP components was observed in reverse on the ipsilateral dorsolateral frontocortical region in the fifth patient with a large parieto-temporal cortex ablation. These data require confirmahese data require confirmation, and when this phenomenon is observable, it must be appropriately monitored with different methods of functional neuroimaging. This will serve not only for medical and neuropsychophysiological diagnosis purposes, but also particularly for a correct and really useful planning of neuro-rehabilitation activities in selected cases.

Visual and spectral analysis of sleep EEG in acute hemispheric stroke

BACKGROUND

Reports on the effects of focal hemispheric damage on sleep EEG are rare and contradictory.

PATIENTS AND METHODS

Twenty patients (mean age +/- SD 53 +/- 14 years) with a first acute hemispheric stroke and no sleep apnea were studied. Stroke severity [National Institute of Health Stroke Scale (NIHSS)], volume (diffusion-weighted brain MRI), and short-term outcome (Rankin score) were assessed. Within the first 8 days after stroke onset, 1-3 sleep EEG recordings per patient were performed. Sleep scoring and spectral analysis were based on the central derivation of the healthy hemisphere. Data were compared with those of 10 age-matched and gender-matched hospitalized controls with no brain damage and no sleep apnea.

RESULTS

Stroke patients had higher amounts of wakefulness after sleep onset (112 +/- 53 min vs. 60 +/- 38 min, p < 0.05) and a lower sleep efficiency (76 +/- 10% vs. 86 +/- 8%, p < 0.05) than controls. Time spent in slow-wave sleep (SWS) and rapid eye movement (REM) sleep and total sleep time were lower in stroke patients, but differences were not significant. A positive correlation was found between the amount of SWS and stroke volume (r = 0.79). The slow-wave activity (SWA) ratio NREM sleep/wakefulness was lower in patients than in controls (p < 0.05), and correlated with NIHSS (r = -0.47).

CONCLUSION

Acute hemispheric stroke is accompanied by alterations of sleep EEG over the healthy hemisphere that correlate with stroke volume and outcome. The increased SWA during wakefulness and SWS over the healthy hemisphere contralaterally to large strokes may reflect neuronal hypometabolism induced transhemispherically (diaschisis).

Frontal and parieto-temporal cortical ablations and diaschisis-like effects on auditory neurocognitive potentials evocable from apparently intact ipsilateral association areas in humans: five case reports

The aim of this study was to investigate the effects of disruption on the warning auditory S1-elicited ERP and CNV complexes recordable on the site and on remote ipsilateral apparently normal anatomo-functionally interconnected brain regions. These effects in some cases showed aspects of a probable diaschisis-like phenomenon, due to resections of extensive frontal association cortex or of primary and secondary sensory parieto-temporal areas damaged by differing pathological processes. Using a standard CNV paradigm, 21/19 EEG electrodes connected with three different references, and scalp-topographic bidimensional mapping analysis, the S1 auditory binaural/monaural clicks N1a,b,c, P2, N2, P3 and CNV waves were recorded in 10 normal subjects and 11 patients. Nine of the latter had been submitted to unilateral frontal dorsolateral cortex ablation, one to bihemispheric dorsomedial cortex ablation, and one to unilateral ablation of sensory parieto-temporal cortex and underlying white matter, verified through CT/MRI examinations. No true S1ERP/CNV components were recordable over the ablated cortical areas, whereas normal ERP/CNV complexes were observable on the intact hemispheres. In five patients, four of whom with frontocortical ablations, the S1 ERP/CNV complexes appeared severely diminished or disrupted, in two cases in a slow, partially-reversible manner, also in the neuroradiologically normal ipsilateral functionally-connected post-rolandic sensory and association areas. Similar deactivation of some ERP components was observed in reverse on the unilateral dorsolateral frontocortical region in the fifth patient with parieto-temporal cortex ablation. Even when they are partially reversible, these ipsilateral remote ERP changes in apparently intact brain regions, due to ablations of functionally-interconnected cortical formations, probably reflect cortical deactivation or simply dysfacilitation deriving from functional unilateral diaschisis. If these changes are instead irreversible they may probably be interpreted as transneuronal degeneration phenomena, though they are not at present easy to document either neuroradiologically or electroclinically.

Regional correlations between the EEG and oxygen metabolism in dementia of Alzheimer's type

To determine the relationship between EEG slowing and cerebral hypometabolism in dementia, 10 patients with dementia of Alzheimer's type (DAT) were evaluated with quantitative topographic EEG and positron emission tomography (PET). Power in each 1-Hz frequency band from 2-20 Hz, power ratio index, and normalised PET data from corresponding cortical sites were compared to data obtained from 20 normal volunteers. PET revealed significant parieto-temporal hypometabolism, and topographic EEG mapping and power spectrum analysis revealed a slowing of the background EEG that was most pronounced in the parietal-temporal areas. Correlation analysis between EEG power spectrum data and CMRO2 revealed significant negative correlations for frequencies below 8 Hz and significant positive correlations above 8 Hz in the parieto-temporal regions, which have previously been identified as the areas most severely affected by pathological changes associated with DAT. Correlation coefficients plotted as functions of frequency illustrated the relationships between EEG changes and reduced CMRO2, supporting previous views that EEG slowing in DAT may be related to hypometabolism in cortical regions most affected by the disease.

Electrophysiological transcortical diaschisis after cortical photothrombosis in rat brain

BACKGROUND AND PURPOSE

The severity of functional deficits after a cortical infarction often does not correlate with lesion size. The stroke may affect pathways connecting to distant brain regions and therefore may also alter the function of remote parts of the cortex. Remote changes in electric activity, blood flow, and metabolism are called diaschisis. In the present study we addressed the question of whether in brain areas contralateral to a photochemically induced cortical infarction alteration of excitability can be observed as an indication of the effects of diaschisis.

METHODS

We induced focal lesions in the sensory area at the border of the motor and occipital cortices by injecting the photosensitizing dye rose bengal and illuminating the skull stereotaxically. Seven days after induction of photothrombosis, electrophysiological recordings were obtained with standard methods from 400-microns-thick neocortical coronal slices. As an indication of inhibition we used a paired-pulse stimulus protocol and calculated a ratio of the amplitudes of the second versus the first excitatory postsynaptic potential.

RESULTS

In lesioned animals we found a significant increase of the ratio over a wide zone of the neocortex, both ipsilateral and contralateral, compared with unlesioned animals.

CONCLUSIONS

Our results suggest that a neocortical infarction leads to hyperexcitability not only in its direct vicinity but also in the contralateral hemisphere. Such hyperexcitability may contribute to increased activation of contralateral brain areas and to functional reorganization after stroke.

Preoperative cerebrovascular symptoms and electroencephalographic abnormalities do not predict cerebral ischemia during carotid endarterectomy

BACKGROUND AND PURPOSE

The purpose of this prospective study was to establish (1) whether patients with neurological symptoms scheduled for carotid endarterectomy had an increased incidence of electroencephalographic (EEG) abnormalities during awake baseline recordings, (2) whether these symptoms and EEG abnormalities predicted ischemic EEG pattern changes at carotid artery cross-clamp, and (3) whether there was an association between age, presence of EEG baseline abnormalities, and ischemic pattern changes at carotid artery cross-clamp.

METHODS

We reviewed the medical record of each patient scheduled to undergo carotid endarterectomy and recorded the patient's age and history of previous neurological symptoms. We then continuously monitored and analyzed 16 channels of anteroposterior bipolar EEG and two of referential derivations from at least 5 minutes before induction of anesthesia and throughout the operation.

RESULTS

We completed 394 consecutive studies. Preoperative neurological symptoms were related to EEG abnormalities in awake patients (P < .001) and to EEG asymmetries in anesthetized patients (P < .001). Abnormal awake EEG findings were associated with asymmetries after anesthesia (P < .0001). Twenty-eight percent of both symptomatic (70/249) and asymptomatic (41/145) patients had EEG ischemic pattern changes at carotid artery cross-clamp. Neither neurological symptoms nor EEG abnormalities were associated with age or the development of EEG ischemic pattern changes at carotid artery cross-clamp.

CONCLUSIONS

Despite the strong association between a history of cerebral ischemic symptoms and preoperative EEG abnormalities in patients undergoing carotid endarterectomy, patients who have suffered strokes or transient ischemic events are at no greater risk of having EEG evidence of cerebral ischemia during carotid artery cross-clamp than patients without symptoms and with normal baseline EEGs. We conclude that preoperative EEG abnormalities in symptomatic patients are not due to age or to insufficiency of regional cerebral blood flow.

Microvascular morphometry in primate diaschisis

Focal cerebral ischemia was produced in monkeys by transorbital occlusion of the right middle cerebral artery. Following this, in one group of animals the total microvasculature, including both perfused and nonperfused vessels of the opposite caudate nucleus and insula, was examined by alkaline phosphatase staining of the endothelium. In another group, the patency of the microvascular bed was visualized by india ink perfusion. The number, diameter, and length of visualized vessels were measured by means of a Wild ASBA image analysis system. The perfused patient microvascular bed was significantly reduced in both insula and caudate nucleus in the supposedly normal left side, although the total microvascular volume showed an increase at 4 and 12 hr in the insula and at 48 hr in the caudate nucleus. Reduced perfusion in the hemisphere opposite to the occluded middle cerebral artery provides an anatomical substrate for the phenomenon of "diaschisis."

Transhemispheric diaschisis. A review and comment

We review here the literature in both animal models and humans concerning electrical activity, blood flow, and metabolism in the hemisphere contralateral to unilateral cerebral ischemia. We analyze the data by periods based on the time from initial injury to emphasize the time course of transhemispheric diaschisis. Contralateral electrical activity, such as evoked potential amplitude, is increased in the late stages after unilateral infarction, with the data from the more acute periods being inconclusive. Contralateral blood flow changes probably depend on the magnitude of the ischemic injury, with a larger insult resulting in a decrease not seen with smaller insults. Some studies have shown a decrease in contralateral blood flow over the first week followed by a gradual return toward baseline. Most measures of contralateral metabolism show a time course similar to blood flow, that is, a decrease followed by gradual recovery. The effects of corpus callosum section on transhemispheric diaschisis are not yet established. We provide examples to show that under certain conditions, diaschisis may represent a loss of remote inhibition rather than a loss of remote facilitation, as von Monakow originally suggested. By following the contralateral changes over time, particularly during the first minutes and hours of ischemia, insight will be gained into the brain's responses remote from the focus of ischemic injury. These responses should bear a relation to the brain's defense mechanisms ipsilaterally to the region of ischemia.

Topographic EEG mapping in cerebrovascular disease

Topographic EEG based on the power spectral data were correlated with cortical CBF and CMRO2 which were provided by positron emission tomography (PET) in patients with cerebral infarction. Delta and theta activities correlated negatively with CBF and CMRO2 whereas alpha activity correlated positively. For delta activity, both absolute (AP) and relative power (RP) showed significant correlation with CBF and CMRO2. For alpha activity, RP showed closer correlation with CBF and CMRO2 than did AP. The z-scores for these power data also showed significant correlation with the PET data although the degree of correlations did not improved even with the z-score. Topographic EEG images including AP, RP and their z-score maps well corresponded with the PET images: z-score maps were considered to be useful tool in topographical extraction of the features of the EEG power data.

Electroencephalographic correlates of blood flow and oxygen metabolism provided by positron emission tomography in patients with cerebral infarction

Quantitative EEG data were analyzed statistically with respect to cortical cerebral blood flow (CBF) and oxygen metabolism (CMRO2) measured by positron emission tomography in 47 patients with unilateral cerebral infarction. Relative value of the square root of average power was used as a percentage power fraction (PPF) for each frequency category. Power ratio index (PRI) was calculated by dividing the combined delta-PPF and theta-PPF by the combined alpha-PPF and beta-PPF. Delta-PPF, theta-PPF and PRI correlated negatively with regional CBF (rCBF) and CMRO2 (rCMRO2) whereas alpha-PPF and beta-PPF correlated positively. In the acute stage, delta-PPF, alpha-PPF and PRI correlated with rCBF at all but the frontopolar region whereas the correlation with rCMRO2 was poor. Alpha-PPF and PRI correlated also with rCMRO2 in the frontal, central, parietal and occipital regions while delta-PPF correlated with rCBF only in the parietal and occipital regions in the subacute stage. In the chronic stage, all EEG quotients correlated significantly with both rCBF and CMRO2 in the central and parietal regions. In the frontopolar region, only the theta-PPF correlated with rCBF throughout. In the comparison of hemispheric mean values, the correlations were always closer for the affected hemisphere than for the contralateral hemisphere. Although hemispheric mean CBF and CMRO2 were significantly lower in patients with cortical infarcts on CT than in those with small subcortical infarcts, there was no significant difference in the EEG data between the 2 groups.

Topographic EEG in brain ischemia--correlation with blood flow and metabolism

A review is made of topographic EEG analyses in patients with brain ischemia. Features correlating EEG measures and vascular and metabolic studies are presented and discussed within the content of the stage of ischemia. Quantitative EEG data was found to provide useful information regarding the effects of brain ischemia.

Homovanillic acid and 5-hydroxyindoleacetic acid modifications in CSF of patients with stroke and multi-infarct dementia

Thirty four patients who had complete ischemic stroke confirmed by neurologic examination, were divided into three groups according to the time elapsed between the first signs of stroke and lumbar puncture: group A, 22-47 h; group B, 48-71 h; group C, 72-96 h. Nineteen patients with multi-infarct dementia (MID) assessed by neurologic and neurophysiologic examinations were also studied. The severity of the neurological deficit was assessed by the Norris rating scale. Nine age-matched subjects without neurologic disease served as controls. Levels of homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in lumbar CSF by a fluorimetric method after separation on Sephadex G-10 columns. HVA levels decreased as the length of time after stroke increased and were lower than controls in MID, while 5-HIAA levels were low in group B and MID. Our results in stroke can be interpreted as showing they are the consequence of dopamine and serotonin global depletion in the early phases of brain ischemia. In MID, the CSF changes might reflect not only tissue loss secondary to multiple infarcts but also the persistence of a state of diffuse ischemia.

Serial measurements of quantitative EEG and cerebral blood flow and circulation time after brain infarction

The quantitative EEG (QEEG), regional cerebral blood flow (rCBF) and circulation time of 17 patients were examined semisimultaneously thrice during the first 3 months after a cerebral supratentorial infarction. The EEG was quantified according to normalized slope descriptor technique in nine patients and by means of a combined period and amplitude analysis in eight patients. Intravenously injected isotopes 133Xenon and 99TcmO4 were used for blood flow and circulation time measurements. The QEEG-values improved during the whole follow-up period. Cerebral blood flow stayed low for all 3 months and did not alter during this period, while initially prolonged circulation time to some extent improved within 2 weeks remaining, however, prolonged even thereafter. A tendency for a positive correlation between QEEG and rCBF values in the infarcted hemisphere could be seen.

EEG frequency analysis in the course of acute ischemic stroke

In 18 patients with acute cerebrovascular disease (17 ischemic, 1 hemorrhagic stroke) neurological symptoms were scored repeatedly using a rating scale for disturbance of consciousness, motor dysfunctions, disturbance of higher cortical functions, abnormalities of cranial nerves, and impairment of sensations, and related to EEG-abnormalities quantified by frequency analysis. A correspondence between location of neurologic lesion and EEG focus was found in 87%, but correlation between neurologic score and the degree of EEG-abnormality was low. Changes of clinical defects were not significantly related to various quantified EEG parameters. These results suggest that computerized EEG analysis has to be used with caution for quantifying the clinical course of stroke patients.

Diaschisis with cerebral infarction

Fifteen patients admitted to Philadelphia General Hospital with acute strokes had repeated measurements of cerebral blood flow measured by the 133Xenon inhalation method. A progressive decline in cerebral blood flow in both hemispheres was observed during the first week after infarction in twelve of these patients. This decline could be partially explained by loss of autoregulation, but could not be correlated with level of consciousness, clinical status of PCO2. This progressive decline in flow in the non-ischemic hemisphere indicates a process more complex than a simple destruction of axonal afferants to neurons as implied by the term diaschisis. The flow changes in the non-ischemic hemisphere are likely caused by a combination of the immediate effects of decreased neuronal stimulation modified by loss of autoregulation, release of vasoactive substances, cerebral edema, and other factors.