Analysis of MEG signals of spreading cortical depression with propagation constrained to a rectangular cortical strip. II. Gyrencephalic swine model

Different vulnerability of fast and slow cortical oscillations to suppressive effect of spreading depolarization: state-dependent features potentially relevant to pathogenesis of migraine aura

BACKGROUND

Spreading depolarization (SD), underlying mechanism of migraine aura and potential activator of pain pathways, is known to elicit transient local silencing cortical activity. Sweeping across the cortex, the electrocorticographic depression is supposed to underlie spreading negative symptoms of migraine aura. Main information about the suppressive effect of SD on cortical oscillations was obtained in anesthetized animals while ictal recordings in conscious patients failed to detect EEG depression during migraine aura. Here, we investigate the suppressive effect of SD on spontaneous cortical activity in awake animals and examine whether the anesthesia modifies the SD effect.

METHODS

Spectral and spatiotemporal characteristics of spontaneous cortical activity following a single unilateral SD elicited by amygdala pinprick were analyzed in awake freely behaving rats and after induction of urethane anesthesia.

RESULTS

In wakefulness, SD transiently suppressed cortical oscillations in all frequency bands except delta. Slow delta activity did not decline its power during SD and even increased it afterwards; high-frequency gamma oscillations showed the strongest and longest depression under awake conditions. Unexpectedly, gamma power reduced not only during SD invasion the recording cortical sites but also when SD occupied distant subcortical/cortical areas. Contralateral cortex not invaded by SD also showed transient depression of gamma activity in awake animals. Introduction of general anesthesia modified the pattern of SD-induced depression: SD evoked the strongest cessation of slow delta activity, milder suppression of fast oscillations and no distant changes in gamma activity.

CONCLUSION

Slow and fast cortical oscillations differ in their vulnerability to SD influence, especially in wakefulness. In the conscious brain, SD produces stronger and spatially broader depression of fast cortical oscillations than slow ones. The frequency-specific effects of SD on cortical activity of awake brain may underlie some previously unexplained clinical features of migraine aura.

Spreading Diffusion-Restriction Events in the Gyrencephalic Brain After Subarachnoid Hemorrhage Revealed by Continuous Magnetic Resonance Imaging

BACKGROUND

How widely spreading depolarizations (SDs) propagate through the gyrencephalic brain, including sulci and deeper cortical areas, remains an important clinical question. Here, we investigated SDs that occur spontaneously after subarachnoid placement of autologous blood clots in sulci of the juvenile swine brain.

METHODS

To investigate the three-dimensional spread of waves, animals underwent continuous diffusion-weighted magnetic resonance imaging (DW-MRI) for up to 6 h following clot placement. SD is the mechanism of the cytotoxic edema of developing infarction that is diagnosed by DW-MRI, and DW-MRI also captures transient diffusion restriction caused by SD in less injured or healthy brains. Here, images (b = 0, 375, and 750) were acquired across five coronal slices with 1.25 × 1.25-mm in-plane resolution and 5-mm slice thickness, and the protocol was repeated every 6.83-9.15 s. Spatial drift correction, temporal smoothing, and signal intensity normalization were applied to generate videos of diffusion signal intensity changes for each coronal slice.

RESULTS

Review of video data from five animals revealed ten discrete events consisting of focal diffusion restriction that propagated through cerebral cortex. All events originated in the cortex surrounding the sulcal clot, either in the gyrus (n = 4) or in the sulcal depth (n = 6). In six cases, two to three independent waves spread simultaneously in medial, lateral, and antero-posterior directions. Waves traveled within sulcal walls, traversed the depths of sulci to re-emerge on the adjacent gyrus, and, in three cases, spread fully around the dorsolateral convexity. One event spread deep to olfactory regions along midline cortex, and no events were observed contralateral to the subarachnoid clot.

CONCLUSIONS

Together, these results suggest that SDs in the injured gyrencephalic brain originate near the injury focus and can spread extensively through the cortex to wide and deep uninjured regions. These findings have implications for transient neurologic deficits in the neurocritically ill patient and relevance to patient monitoring and therapeutics.

Migraine Visual Aura and Cortical Spreading Depression-Linking Mathematical Models to Empirical Evidence

This review describes the subjective experience of visual aura in migraine, outlines theoretical models of this phenomenon, and explores how these may be linked to neurochemical, electrophysiological, and psychophysical differences in sensory processing that have been reported in migraine with aura. Reaction-diffusion models have been used to model the hallucinations thought to arise from cortical spreading depolarisation and depression in migraine aura. One aim of this review is to make the underlying principles of these models accessible to a general readership. Cortical spreading depolarisation and depression in these models depends on the balance of the diffusion rate between excitation and inhibition and the occurrence of a large spike in activity to initiate spontaneous pattern formation. We review experimental evidence, including recordings of brain activity made during the aura and attack phase, self-reported triggers of migraine, and psychophysical studies of visual processing in migraine with aura, and how these might relate to mechanisms of excitability that make some people susceptible to aura. Increased cortical excitability, increased neural noise, and fluctuations in oscillatory activity across the migraine cycle are all factors that are likely to contribute to the occurrence of migraine aura. There remain many outstanding questions relating to the current limitations of both models and experimental evidence. Nevertheless, reaction-diffusion models, by providing an integrative theoretical framework, support the generation of testable experimental hypotheses to guide future research.

Therapeutic implications of cortical spreading depression models in migraine

Migraine is among the most common and disabling neurological diseases in the world. Cortical spreading depression (CSD) is a wave of near-complete depolarization of neurons and glial cells that slowly propagates along the cortex creating the perception of aura. Evidence suggests that CSD can trigger migraine headache. Experimental models of CSD have been considered highly translational as they recapitulate migraine-related phenomena and have been validated for screening migraine therapeutics. Here we outline the essential components of validated experimental models of CSD and provide a comprehensive review of potential modulators and targets against CSD. We further focus on novel interventions that have been recently shown to suppress CSD susceptibility that may lead to therapeutic targets in migraine.

Current understanding of cortical structure and function in migraine

OBJECTIVE

To review and discuss the literature on the role of cortical structure and function in migraine.

DISCUSSION

Structural and functional findings suggest that changes in cortical morphology and function contribute to migraine susceptibility by modulating dynamic interactions across cortical and subcortical networks. The involvement of the cortex in migraine is well established for the aura phase with the underlying phenomenon of cortical spreading depolarization, while increasing evidence suggests an important role for the cortex in perception of head pain and associated sensations. As part of trigeminovascular pain and sensory processing networks, cortical dysfunction is likely to also affect initiation of attacks.

CONCLUSION

Morphological and functional changes identified across cortical regions are likely to contribute to initiation, cyclic recurrence and chronification of migraine. Future studies are needed to address underlying mechanisms, including interactions between cortical and subcortical regions and effects of internal (e.g. genetics, gender) and external (e.g. sensory inputs, stress) modifying factors, as well as possible clinical and therapeutic implications.

Photoacoustics can image spreading depolarization deep in gyrencephalic brain

Spreading depolarization (SD) is a self-propagating wave of near-complete neuronal depolarization that is abundant in a wide range of neurological conditions, including stroke. SD was only recently documented in humans and is now considered a therapeutic target for brain injury, but the mechanisms related to SD in complex brains are not well understood. While there are numerous approaches to interventional imaging of SD on the exposed brain surface, measuring SD deep in brain is so far only possible with low spatiotemporal resolution and poor contrast. Here, we show that photoacoustic imaging enables the study of SD and its hemodynamics deep in the gyrencephalic brain with high spatiotemporal resolution. As rapid neuronal depolarization causes tissue hypoxia, we achieve this by continuously estimating blood oxygenation with an intraoperative hybrid photoacoustic and ultrasonic imaging system. Due to its high resolution, promising imaging depth and high contrast, this novel approach to SD imaging can yield new insights into SD and thereby lead to advances in stroke, and brain injury research.

Spreading depression as a preclinical model of migraine

Spreading depression (SD) is a slowly propagating wave of near-complete depolarization of neurons and glial cells across the cortex. SD is thought to contribute to the underlying pathophysiology of migraine aura, and possibly also an intrinsic brain activity causing migraine headache. Experimental models of SD have recapitulated multiple migraine-related phenomena and are considered highly translational. In this review, we summarize conventional and novel methods to trigger SD, with specific focus on optogenetic methods. We outline physiological triggers that might affect SD susceptibility, review a multitude of physiological, biochemical, and behavioral consequences of SD, and elaborate their relevance to migraine pathophysiology. The possibility of constructing a recurrent episodic or chronic migraine model using SD is also discussed.

Clinical neurophysiology of stroke

Stroke constitutes the third most common cause of death and the leading cause of acquired neurologic handicap. During ischemic stroke, very early after the onset of the focal perfusion deficit, excitotoxicity triggers a number of events that can further contribute to tissue death. Such events include peri-infarct depolarizations and spreading depolarizations (SDs) within the ischemic penumbra. SDs spread slowly through continuous gray matter at a typical velocity of 2-5mm/min. SDs exacerbate neuronal injury through prolonged ionic breakdown and SD-related hypoperfusion (spreading ischemia). Scalp EEG alone is not yet sufficient to reliably diagnose SDs. Hyperexcitability occurs in parallel, both in the acute and chronic phases of stroke. Stroke is a common cause of new-onset epileptic seizures after middle age and is the leading cause of symptomatic epilepsy in adults. The last part of this chapter is dedicated to noninvasive neurophysiologic techniques that can be used to promote stroke rehabilitation. These techniques mainly include repetitive transcranial magnetic stimulation and tDCS. These approaches are based on the concept of interhemispheric rivalry and aim at modulating the imbalance of cortical activities between both hemispheres resulting from stroke.

Arguments against the role of cortical spreading depression in migraine

Cortical spreading depression (CSD) is a wave of increased electrocortical activity and vasodilation, followed by sustained decreased activity and prolonged vasoconstriction. Although the discovery of CSD has been ascribed to Leão, rather than vasoconstriction, he only observed a depression of neural activity combined with vasodilation, with much weaker stimulation than used by his followers. There is a longstanding belief that CSD underlies migraine aura, with its positive symptoms such as mosaic patterns and its negative symptoms such as scotoma, and a similar propagation speed and vasoreaction pattern. However, there are many arguments against this theory. CSD is difficult to evoke in man, and electroencephalography (EEG) readings are not flattened during migraine (as opposed to EEG during CSD). Moreover, in contrast to CSD, migraine can occur bilaterally, and is not accompanied by a disrupted blood-brain barrier, increased cerebral metabolism, or cerebral cell swelling. Calcitonin gene-related peptide, which is thought to be characteristic of migraine pain, is increased in the blood from the external jugular vein during migraine in humans, but not during CSD in cats or rats. Moreover, CSD does not explain the appearance of premonitory symptoms or allodynia, long before the actual onset of aura. In addition, there is a variation in the pain mechanisms of migraine and CSD, and in their reaction to transcranial magnetic stimulation and several pharmacologic interventions. Finally, the origin of putative CSD in migraine is currently unknown.

Ketamine modulation of the haemodynamic response to spreading depolarization in the gyrencephalic swine brain

Spreading depolarization (SD) generates significant alterations in cerebral haemodynamics, which can have detrimental consequences on brain function and integrity. Ketamine has shown an important capacity to modulate SD; however, its impact on SD haemodynamic response is incompletely understood. We investigated the effect of two therapeutic ketamine dosages, a low-dose of 2 mg/kg/h and a high-dose of 4 mg/kg/h, on the haemodynamic response to SD in the gyrencephalic swine brain. Cerebral blood volume, pial arterial diameter and cerebral blood flow were assessed through intrinsic optical signal imaging and laser-Doppler flowmetry. Our findings indicate that frequent SDs caused a persistent increase in the baseline pial arterial diameter, which can lead to a diminished capacity to further dilate. Ketamine infused at a low-dose reduced the hyperemic/vasodilative response to SD; however, it did not alter the subsequent oligemic/vasoconstrictive response. This low-dose did not prevent the baseline diameter increase and the diminished dilative capacity. Only infusion of ketamine at a high-dose suppressed SD and the coupled haemodynamic response. Therefore, the haemodynamic response to SD can be modulated by continuous infusion of ketamine. However, its use in pathological models needs to be explored to corroborate its possible clinical benefit.

Cortical Spreading Depression in Migraine

Cortical spreading depression (CSD) is associated with a dramatic failure of brain ion homeostasis as well as efflux of excitatory amino acids from nerve cells and increased energy metabolism. There is strong clinical and experimental evidence to suggest that CSD is involved in the mechanism of migraine. This paper will, based on the experience related to the detection of CSD in humans, discuss pitfalls and possible strategies for detection of CSD in man. Development of reliable methods for detection of CSD in humans will determine the extent to which the large body of experimental findings from animal studies of CSD can be applied to the investigation and treatment of human brain disease. The paper is based on the experience that has been gained from two decades of studies of CSD in relation to clinical neurological diseases.

Migraine: New Molecular Mechanisms

Migraine is an episodic headache disorder affecting more than 10% of the general population. Migraine arises from a primary brain dysfunction that leads to activation and sensitization of the trigeminovascular system. A major incompletely understood issue in the neurobiology of migraine concerns the molecular and cellular mechanisms that underlie the primary brain dysfunction and lead to activation and sensitization of the trigeminovascular system, thus generating and maintaining migraine pain. Here the author reviews recent discoveries that have advanced our understanding of these mechanisms toward a unifying pathophysiological hypothesis, in which cortical spreading depression (CSD), the phenomenon underlying migraine aura, assumes a key role. In particular, the author discusses the main recent findings in the genetics and neurobiology of familial hemiplegic migraine and the insights they provide into the molecular and cellular mechanisms that may lead to the increased susceptibility of CSD in migraineurs.

Cytoarchitecture-Dependent Decrease in Propagation Velocity of Cortical Spreading Depression in the Rat Insular Cortex Revealed by Optical Imaging

Cortical spreading depression (SD) is a self-propagating wave of depolarization accompanied by a substantial disturbance of the ionic distribution between the intra- and extracellular compartments. Glial cells, including astrocytes, play critical roles in maintenance of the extracellular environment, including ionic distribution. Therefore, SD propagation in the cerebral cortex may depend on the density of astrocytes. The present study aimed to examine the profile of SD propagation in the insular cortex (IC), which is located between the neocortex and paleocortex and is where the density of astrocytes gradually changes. The velocity of SD propagation in the neocortex, including the somatosensory, motor, and granular insular cortices (5.7 mm/min), was higher than that (2.8 mm/min) in the paleocortex (agranular insular and piriform cortices). Around thick vessels, including the middle cerebral artery, SD propagation was frequently delayed and sometimes disappeared. Immunohistological analysis of glial fibrillary acidic protein (GFAP) demonstrated the sparse distribution of astrocytes in the somatosensory cortex and the IC dorsal to the rhinal fissure, whereas the ventral IC showed a higher density of astrocytes. These results suggest that cortical cytoarchitectonic features, which possibly involve the distribution of astrocytes, are crucial for regulating the velocity of SD propagation in the cerebral cortex.

Radial, spiral and reverberating waves of spreading depolarization occur in the gyrencephalic brain

OBJECTIVES

The detection of the hemodynamic and propagation patterns of spreading depolarizations (SDs) in the gyrencephalic brain using intrinsic optical signal imaging (IOS).

METHODS

The convexity of the brain surface was surgically exposed in fourteen male swine. Within the boundaries of this window, brains were immersed and preconditioned with an elevated K(+) concentration (7 mmol/l) in the standard Ringer lactate solution for 30-40 min. SDs were triggered using 3-5 μl of 1 mol/l KCl solution. Changes in tissue absorbency or reflection were registered with a CCD camera at a wavelength of 564 nm (14 nm FWHM), which was mounted 25 cm above the exposed cortex. Additional monitoring by electrocorticography and laser-Doppler was used in a subset of animals (n=7) to validate the detection of SD.

RESULTS

Of 198 SDs quantified in all of the experiments, 187 SDs appeared as radial waves that developed semi-planar fronts. The morphology was affected by the surface of the gyri, the sulci and the pial vessels. Other SD patterns such as spirals and reverberating waves, which have not been described before in gyrencephalic brains, were also observed. Diffusion gradients created in the cortex surface (i.e., KCl concentrations), sulci, vessels and SD-SD interactions make the gyrencephalic brain prone to the appearance of irregular SD waves.

CONCLUSION

The gyrencephalic brain is capable of irregular SD propagation patterns. The irregularities of the gyrencephalic brain cortex may promote the presence of re-entrance waves, such as spirals and reverberating waves.

Neuromagnetic abnormality of motor cortical activation and phases of headache attacks in childhood migraine

The cerebral cortex serves a primary role in the pathogenesis of migraine. This aberrant brain activation in migraine can be noninvasively detected with magnetoencephalography (MEG). The objective of this study was to investigate the differences in motor cortical activation between attacks (ictal) and pain free intervals (interictal) in children and adolescents with migraine using both low- and high-frequency neuromagnetic signals. Thirty subjects with an acute migraine and 30 subjects with a history of migraine, while pain free, were compared to age- and gender-matched controls using MEG. Motor cortical activation was elicited by a standardized, validated finger-tapping task. Low-frequency brain activation (1∼50 Hz) was analyzed with waveform measurements and high-frequency oscillations (65–150 Hz) were analyzed with wavelet-based beamforming. MEG waveforms showed that the ictal latency of low-frequency brain activation was significantly delayed as compared with controls, while the interictal latency of brain activation was similar to that of controls. The ictal amplitude of low-frequency brain activation was significantly increased as compared with controls, while the interictal amplitude of brain activation was similar to that of controls. The ictal source power of high-frequency oscillations was significantly stronger than that of the controls, while the interictal source power of high-frequency oscillations was significantly weaker than that of controls. The results suggest that aberrant low-frequency brain activation in migraine during a headache attack returned to normal interictally. However, high-frequency oscillations changed from ictal hyper-activation to interictal hypo-activation. Noninvasive assessment of cortical abnormality in migraine with MEG opens a new window for developing novel therapeutic strategies for childhood migraine by maintaining a balanced cortical excitability.

Alterations of regional spontaneous neuronal activity and corresponding brain circuit changes during resting state in migraine without aura

Although previous resting-state studies have reported abnormal functional cerebral changes in patients with migraine without aura (MwoA), few have focused on alterations in both regional spontaneous neuronal activity and corresponding brain circuits in MwoA patients during rest. Eighteen MwoA patients and 18 age- and gender-matched healthy controls (HC) were recruited in the current study. Baseline cerebral alterations were investigated using amplitude of low-frequency fluctuation (ALFF) and region of interest (ROI)-based functional connectivity (FC) analyses. Compared with HC, MwoA patients showed decreased ALFF values in the left rostral anterior cingulate cortex (rACC) and bilateral prefrontal cortex (PFC) as well as increased ALFF values in the right thalamus. FC analysis also revealed abnormal FCs associated with these ROIs. In addition, ALFF values of the left rACC correlated with duration of disease in MwoA. Our findings could lead to a better understanding of intrinsic functional architecture of baseline brain activity in MwoA, providing both regional and brain circuit spontaneous neuronal activity properties.

Cortical spreading depression dynamics can be studied using intrinsic optical signal imaging in gyrencephalic animal cortex

OBJECTIVE

The aim of this study was to co-record electrical changes using electrocorticography (ECoG) and blood volume changes using intrinsic optical signal (IOS) imaging during the induction, propagation, and termination of cortical spreading depolarizations (CSDs).

METHODS

Anesthetized male swine were craniotomized and monitored over 16-20 h. A ten-contact electrode strip was placed on the cortex of one hemisphere for ECoG. An optical imaging recording was implemented using a camera with an optical bandpass filter (564 nm, FWHM:15 nm) and a full spectrum light source. CSDs were induced by mechanical and KCl stimulation. Co-occurrences of ECoG baseline shifts and blood volume changes around electrodes were identified.

RESULTS

A mean of 3 CSDs per hour were induced, in a total of 4 swine during 80 h of recording. The propagation of the CSDs increased progressively over the monitoring time. IOS enabled us to clearly visualize the induction, propagation, and termination of CSDs with a spatial resolution within the sub-millimeter range. Every CSD recorded using ECoG could also be observed in IOS imaging, although some blood volume changes of CSDs were observed that terminated before reaching any of the ECoG electrodes.

CONCLUSION

IOS imaging enables an in vivo evaluation of CSD dynamics over a large surface of gyrencephalic brain.

Pathophysiologic cascades in ischemic stroke

Many advances have been achieved in terms of understanding the molecular and cellular mechanisms of ischemic stroke. But thus far, clinically effective neuroprotectants remain elusive. In this minireview, we summarize the basics of ischemic cascades after stroke, covering neuronal death mechanisms, white matter pathophysiology, and inflammation with an emphasis on microglia. Translating promising mechanistic knowledge into clinically meaningful stroke drugs is very challenging. An integrative approach that encompasses the multimodal and multicell signaling phenomenon of stroke will be required to move forward.

Slow brain activity (ISA/DC) detected by MEG

Infraslow activity (ISA), direct coupled (DC), and direct current (DC) are the terms used to describe brain activity that occurs in frequencies below 0.1 Hz. Infraslow activity amplitude increase is also associated with epilepsy, traumatic brain injuries, strokes, tumors, and migraines and has been studied since the early 90s at the Henry Ford Hospital MEG Laboratory. We have used a DC-based magnetoencephalography (MEG) system to validate and characterize the ISA from animal models of cortical spreading depression thought to be the underlying mechanism of migraine and other cortical spreading depression-like events seen during ischemia, anoxia, and epilepsy. Magnetoencephalography characterizes these slow shifts easier than electroencephalography because there is no attenuation of these signals by the skull. In the current study, we report on ISA MEG signals of 12 patients with epilepsy in the preictal and postictal states. In the minutes just before the onset of a seizure, large-amplitude ISA MEG waveforms were detected, signaling the onset of the seizure. It is suggested that MEG assessment of ISA, in addition to activity in the conventional frequency band, can at times be useful in the lateralization of epileptic seizures.

Evaluation of μECoG electrode arrays in the minipig: experimental procedure and neurosurgical approach

Emerging research on brain-machine interfaces (BMIs) requires the development of animal models for testing implantable BMI electrodes. New models are necessary in order to characterize and test newly constructed electrodes in an acute environment, and their properties and performance need to be evaluated in long-term, chronic implantations. Owing to their availability, small size and neuroanatomical similarity to the human brain, minipigs are frequently used for neurological studies. Despite this fact, there are still no standardized experimental and neurosurgical procedures available for recording of cortical potentials using implantable BMI electrodes in minipigs, and, until now, it was unclear whether these animals could also be used for long-term subdural electrode implantations. We have therefore evaluated the potential use of minipigs for acute and chronic implantation of micro-electrocorticogram (μECoG) electrodes we newly developed for BMI applications and we present a standardized neurosurgical approach to the minipig's cerebral cortex. A neurophysiological setup is described which is suitable to perform recordings of somatosensory evoked potentials (SEPs) with high spatial resolution - down to approx. 1-mm inter-electrode distance. Perioperative management, anesthesia and anatomical landmarks for electrode placement are discussed and common surgical pitfalls are described. While, due to their specific cranial anatomy, minipigs appear not optimally suited for chronic subdural implantations, the findings of the present study indicate that μECoG recording from the minipig cortex is a valuable new approach for acute in vivo characterization of subdural BMI electrode function.

“Prolonged” migraine aura: New information on underlying mechanisms

The aim of this study is to identify the pathophysiology of “prolonged” migraine aura not clearly understood. We studied cortical cerebral microcirculation by Near Infrared Spectroscopy system (NIRS) and cerebral macrocirculation by transcranial Doppler (TCD) in 8 subjects (3 M and 5 F, age range 21–41 years) during spontaneous “prolonged” migraine aura in according to ICHD-II criteria 2004 (code 1.6.2.) up to 24 hours after the end of aura and compared the results with the headache-free periods. During aura NIRS showed a significant decrease of the Arterial Pulse Wave of Cerebral Microcirculation (APWCM) amplitude (−33 % ± 5.7), p<0.001, and a significant increase of Cerebral Tissue Oxygen Saturation (SctO2) (+15.5 % ± 5.1), p<0.001 contralateral to the symptoms of aura compared with the headache-free periods; TCD showed a significant increase of Pulsatility Index (+36.5 % ± 6.5), p<0.001 and a significant decrease of the diastolic velocity in the posterior and middle cerebral artery contralateral to the symptoms of aura compared with the headache-free periods. In conclusion during “prolonged” migraine aura we find areas of cortical hypoperfusion corresponding to the topography of aura symptoms that are the result of a decreased metabolic demand rather than an ischemic mechanism.

Clinical relevance of cortical spreading depression in neurological disorders: migraine, malignant stroke, subarachnoid and intracranial hemorrhage, and traumatic brain injury

Cortical spreading depression (CSD) and depolarization waves are associated with dramatic failure of brain ion homeostasis, efflux of excitatory amino acids from nerve cells, increased energy metabolism and changes in cerebral blood flow (CBF). There is strong clinical and experimental evidence to suggest that CSD is involved in the mechanism of migraine, stroke, subarachnoid hemorrhage and traumatic brain injury. The implications of these findings are widespread and suggest that intrinsic brain mechanisms have the potential to worsen the outcome of cerebrovascular episodes or brain trauma. The consequences of these intrinsic mechanisms are intimately linked to the composition of the brain extracellular microenvironment and to the level of brain perfusion and in consequence brain energy supply. This paper summarizes the evidence provided by novel invasive techniques, which implicates CSD as a pathophysiological mechanism for this group of acute neurological disorders. The findings have implications for monitoring and treatment of patients with acute brain disorders in the intensive care unit. Drawing on the large body of experimental findings from animal studies of CSD obtained during decades we suggest treatment strategies, which may be used to prevent or attenuate secondary neuronal damage in acutely injured human brain cortex caused by depolarization waves.

Identification of abnormal neuromagnetic signatures in the motor cortex of adolescent migraine

OBJECTIVE

To investigate the functional abnormalities of the motor cortices in children with migraine using magnetoencephalography (MEG) and a finger-tapping task.

BACKGROUND

Cortical hyperexcitability has been reported in adults with migraine using MEG. Many children with migraine report difficulty with motor functioning. There is no report on motor-evoked magnetic activation in children with migraine using MEG and the latest signal processing methods.

METHODS

Ten children with migraine (all female, 9 right-handed and 1 left-handed, aged 13-17 years) and 10 age- and gender-matched healthy children were studied with a 275-channel MEG system. After hearing a unilateral, randomly presented sound cue (500 Hz, 30 milliseconds square tone), each subject immediately performed a brisk index finger tapping with either the right or the left index finger. The auditory stimuli consisted of 200 trials of square tone, 100 trials per ear, randomly distributed. The latency and amplitude of neuromagnetic responses were analyzed with averaged waveforms. Neuromagnetic sources were estimated using synthetic aperture magnetometry (SAM). SAM images were normalized for each participant for group comparison.

RESULTS

In comparison with healthy children, children with migraine had prolonged latency of motor-evoked magnetic response in the right hemispheres during left finger movement (62.33 +/- 34.55 milliseconds vs 34.9 +/- 17.29 milliseconds, P < .05). In addition, children with migraine had stronger activation in the motor cortex during right finger movement (8097.46 +/- 5168.99 vs 4697.54 +/- 3194.74, P < .05).

CONCLUSIONS

The results suggest that there are neurophysiological changes in the motor cortices of children with migraine that can be measured with neuromagnetic imaging techniques. The findings expand the ability to study the cerebral mechanisms of migraine using MEG and may facilitate the development of new therapeutic strategies in migraine treatment via alterations in cortical excitability.

Neuroimaging in headache

The neurobiology of migraine is complex, but considerable progress has been made during recent decades with the aid of functional neuroimaging. Imaging studies have provided evidence of both abnormal brain functioning and structural changes. In migraine aura, the blood flow changes initially occur in V3A, an area also showing morphometric abnormalities. Pontine activation is also associated with increased volumetric changes. Similar findings are observed in the hypothalamic region in cluster headache. Other paroxysmal headache disorders, such as short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT), hemicrania paroxistica and hemicrania continua, share this similar pattern of activation as cluster headache, pointing to a common pathogenic mechanism. Further studies are required in order to determine whether these changes are the cause or the consequence of the disease, as well as the possible role they may play in the progression into a chronic disorder.

Association of seizures with cortical spreading depression and peri-infarct depolarisations in the acutely injured human brain

OBJECTIVE

To test the co-occurrence and interrelation of ictal activity and cortical spreading depressions (CSDs) - including the related periinfarct depolarisations in acute brain injury caused by trauma, and spontaneous subarachnoid and/or intracerebral haemorrhage.

METHODS

63 patients underwent craniotomy and electrocorticographic (ECoG) recordings were taken near foci of damaged cortical tissue for up to 10 days.

RESULTS

32 of 63 patients exhibited CSDs (5-75 episodes) and 11 had ECoGraphic seizure activity (1-81 episodes). Occurrence of seizures was significantly associated with CSD, as 10 of 11 patients with seizures also had CSD (p=0.007, 2-tailed Fishers exact test). Clinically overt seizures were only observed in one patient. Each patient with CSD and seizures displayed one of four different patterns of interaction between CSD and seizures. In four patients CSD was immediately preceded by prolonged seizure activity. In three patients the two phenomena were separated in time: multiple CSDs were replaced by ictal activity. In one patient seizures appeared to trigger repeated CSDs at the adjacent electrode. In 2 patients ongoing repeated seizures were interrupted each time CSD occurred.

CONCLUSIONS

Seizure activity occurs in association with CSD in the injured human brain.

SIGNIFICANCE

ECoG recordings in brain injury patients provide insight into pathophysiological mechanisms, which are not accessible by scalp EEG recordings.

Posterior Cerebral Hypoperfusion in Migraine Without Aura

In cerebral blood flow studies, migraine aura is characterized by a posterior cortical hypoperfusion. In contrast, only rare and mild changes in brain perfusion have been demonstrated in migraine without aura, suggesting two different haemodynamic patterns in migraine with and without aura. Our aim was to study hypoperfusion with positron emission tomography (PET) as early as possible during spontaneous migraine without aura attacks. We used H215O PET to investigate seven patients (six female, one male) with migraine without aura (International Classification of Headache Diseases-II code 1.1) in three situations: during the headache phase, after headache relief following sumatriptan injection, and during an attack-free interval. Statistical analysis was performed with SPM2. Within 4 h after the attack onset, significant relative bilateral posterior cortical hypoperfusion was found and persisted after headache relief following sumatriptan injection. A posterior cortical hypoperfusion demonstrated in migraine without aura could suggest a common pathogenesis in migraine with and without aura. The significance of relative posterior hypoperfusion in migraine without aura is discussed according to the current knowledge of migraine pathogenesis.

Translational imaging studies of cortical spreading depression in experimental models for migraine aura

This perspective discusses cortical spreading depression (CSD) phenomena and their translational significance for human migraine aura and the peri-infarct events following cerebral ischemia and injury. They begin with interstitial K(+) release and accumulation following neuronal stimulation, and a buffering astrocytic K(+) influx and remote liberation propagating waves of neuronal hyperexcitability and depression. Diffusion-weighted echoplanar MRI demonstrates CSD features in gyrencephalic brains recapitulating human migraine aura, spatial and temporal features of single primary events and multiple secondary events, their stimulus dependence, pharmacological properties, and their relationship to blood oxygenation level-dependent signals and late cerebrovascular changes. The article finally explores prospects for physiological studies of CSD gaining fuller insights both into mechanisms underlying the pathology of the corresponding human condition and possible approaches to management.

The brain is hyperexcitable in migraine

Migraine is a very common disorder occurring in 20% of women and 6% of men. Central neuronal hyperexcitability is proposed to be the putative basis for the physiological disturbances in migraine. Since there are no consistent structural disturbances in migraine, physiological and psychophysical studies have provided insight into the underlying mechanisms. This is a review of the neurophysiological studies which have provided an insight to migraine pathogenesis supporting the theory of hyperexcitability.

Simulating the propagation of spreading cortical depression (SCD) wavefront on human brain surface

Spreading cortical depression (SCD) is a slowly spreading supression of electroencephalogram (EEG) activity that was first observed in anaesthetized rabbits in 1944. Since then, the spatial properties of propagation have been investigated on numerous animal experiments. In the folded and complex human cortex, both the occurrence of SCD and the relationship between SCD and migraine have been discussed controversially. This study proposes a software tool to simulate the possible wavefront motion on the surface of human brain. The SCD wavefront motion has been simulated up to an affected surface region of roughly 150 cm(2) and validated by clinical experts.

The use of pigs in neuroscience: Modeling brain disorders

The use of pigs in neuroscience research has increased in the past decade, which has seen broader recognition of the potential of pigs as an animal for experimental modeling of human brain disorders. The volume of available background data concerning pig brain anatomy and neurochemistry has increased considerably in recent years. The pig brain, which is gyrencephalic, resembles the human brain more in anatomy, growth and development than do the brains of commonly used small laboratory animals. The size of the pig brain permits the identification of cortical and subcortical structures by imaging techniques. Furthermore, the pig is an increasingly popular laboratory animal for transgenic manipulations of neural genes. The present paper focuses on evaluating the potential for modeling symptoms, phenomena or constructs of human brain diseases in pigs, the neuropsychiatric disorders in particular. Important practical and ethical aspects of the use of pigs as an experimental animal as pertaining to relevant in vivo experimental brain techniques are reviewed. Finally, current knowledge of aspects of behavioral processes including learning and memory are reviewed so as to complete the summary of the status of pigs as a species suitable for experimental models of diverse human brain disorders.

Influence of anisotropic conductivity on EEG source reconstruction: investigations in a rabbit model

The aim of our work was to quantify the influence of white matter anisotropic conductivity information on electroencephalography (EEG) source reconstruction. We performed this quantification in a rabbit head using both simulations and source localization based on invasive measurements. In vivo anisotropic (tensorial) conductivity information was obtained from magnetic resonance diffusion tensor imaging and included into a high-resolution finite-element model. When neglecting anisotropy in the simulations, we found a shift in source location of up to 1.3 mm with a mean value of 0.3 mm. The averaged orientational deviation was 10 degree and the mean magnitude error of the dipole was 29%. Source localization of the first cortical components after median and tibial nerve stimulation resulted in anatomically verified dipole positions with no significant anisotropy effect. Our results indicate that the expected average source localization error due to anisotropic white matter conductivity is within the principal accuracy limits of current inverse procedures. However, larger localization errors might occur in certain cases. In contrast, dipole orientation and dipole strength are influenced significantly by the anisotropy. We conclude that the inclusion of tissue anisotropy information improves source estimation procedures.

New insights into brain dysfunction in migraine

Headache is one of the most common presenting symptoms to a physician's office. The majority of headaches are in the category known as primary headaches, where there are no structural disturbances. Secondary headaches are uncommon and usually occur in less than 10% of patients. The mechanisms of secondary headaches are usually due to the underlying pathology. These are usually evident on neuroimaging or laboratory testing. This review will focus mainly on mechanisms of primary headache (i.e., migraine and cluster).

Cortical spreading depression and peri-infarct depolarization in acutely injured human cerebral cortex

Electrocorticographic (ECoG) activity was recorded for up to 129 h from 12 acutely brain-injured human patients using six platinum electrodes placed near foci of damaged cortical tissue. The method probes ECoG activity in the immediate vicinity of the injured cortex and in adjacent supposedly healthy tissue. Six out of twelve patients displayed a total of 73 spontaneous episodes of spreading depression of the ECoG. Of the remaining 6 patients 1 displayed an episode of synchronous depression of ECoG during surgery. Using the same electrodes we also measured the slow potential changes (SPC) (0.005-0.05 Hz) to test the hypothesis that the ECoG depressions were identical to Leao's cortical spreading depression (CSD), and to be able to record peri-infarct depolarisations (PIDs) in electrically 'silent' cortical tissue. Changes in the SPC indicate depolarization of brain tissue. For the analysis, the SPCs were enhanced by calculating the time integral of the ECoG signal. Spreading ECoG depressions were accompanied at every single recording site by stereotyped SPCs, which spread across the cortical mantle at 3.3 (0.41-10) mm/min (median, range), i.e. at the same speed of spread as the depression of the ECoG activity. The amplitude of the SPCs was 0.06-3 mV. In 4 out of 6 patients the ECoG recovered spontaneously. In 2 patients we subsequently recorded recurrent SPCs, but without recovery of the initial ECoG background activity until 2-5 h later. This represents the first direct recording of PIDs in acutely injured human brain. Evidence from this and our previous study of 14 brain-injured patients suggests that CSDs in acute brain disorders occur at higher incidence in patients <30 years (83%) than above (33%). CSD was recorded in 4 out of 5 traumatic brain injury patients, and in 2 out of 7 patients with spontaneous haemorrhages. We conclude that the spreading ECoG depressions recorded in patients are identical to CSDs recorded in animal experiments. We furthermore provide direct electrophysiological evidence for the existence of PIDs and hence a penumbra in the human brain. We hypothesize that the depolarization events might contribute to tissue damage in acute disorders in the human brain.

Cortical Hyperexcitability in Migraine Patients Before and After Sodium Valproate Treatment

DC-magnetoencephalography (DC-MEG)waveforms arising during migraine aura were used to determine the effectiveness of prophylactic medication therapy on neuronal hyperexcitability. Nine patients were prescribed valproate (Depakote) for migraine prophylaxis. MEG scans were recorded during visual stimulation before commencing medication and again after 30 days of daily use of valproate. Cortical brain activity was recorded during stimulation with a black-and-white circular checkerboard pattern alternating at 8 Hz and were analyzed with MR-FOCUSS. Large-amplitude DC-MEG signals, imaged to extended areas of occipital cortex, were seen before therapy. After 30 days of prophylactic treatment, reduced DC-MEG shifts in the occipital cortex and reduced incidence of migraine attacks were observed. Using visual stimulation, the authors demonstrated the hyperexcitability of widespread regions throughout occipital cortex in migraine patients, explaining the susceptibility for triggering spreading cortical depression and migraine aura. This study confirms that MEG can noninvasively determine the status of neuronal excitability before and after therapy. This finding may be helpful in determining which prophylactic medications will be most effective in reducing hyperexcitability in particular patients.

Inhomogeneous propagation of cortical spreading depression—detection by electro- and magnetoencephalography in rats

Spreading depression (SD) propagates in cortical regions that are different in their morphological and functional characteristics. We tested whether the propagation pattern of spreading depression was different between parts of the cortex. In six adult rats, we recorded the ECoG by a 4 x 4 electrode array that covered parts of the frontal, parietal cortex and the cingulate cortex. Simultaneously a 16-channel magnetoencephalogram was recorded to characterize the development and direction of intracortical ion movements accompanying this phenomenon. Spreading depression was initiated by occipital application of 0.3 molar KCl solution. Depolarization was observed, at first, at lateral cortical regions and then at medial cortical regions. Thereafter, the propagation velocity increased in medial cortical regions and was faster than in lateral regions. Negative potential shifts were detected by all electrodes, but the depolarization reached a maximum over lateral and caudal cortical regions. The recorded magnetic fields indicated the same orientation of currents underlying these fields, which was perpendicular to the wave front and points away from the depolarization region. Overall, the data indicated that propagation patterns of spreading depression differed between parts of the cortex and, thus, propagation was inhomogeneous. This propagation was accompanied by strong currents parallel to the cortical surface.

Controversies in neurophysiology. MEG is superior to EEG in localization of interictal epileptiform activity: Pro

Both EEG and magnetoencephalography (MEG), with a time resolution of 1 ms or less, provide unique neurophysiologic data not obtainable by other neuroimaging techniques. MEG and EEG have often been compared to each other now although the two are complementary. Now that MEG has emerged as a mature clinical technology, it is worthwhile to compare the relative strengths of each for the localization of interictal epileptiform activity and to describe the strengths of MEG relative to EEG in the localization of interictal epileptiform activity. The sources of MEG and EEG signals will first be reviewed. Issues relevant to solving the forward problem and the inverse problem in MEG and EEG will be addressed followed by a comparison of research concerning the detection and localization of interictal epileptiform activity by MEG and EEG. The emphasis will be upon techniques and software routinely used in clinical applications but some emerging areas of MEG research which are entering clinical practice will also be reviewed.

SIGNIFICANCE

MEG is a new noninvasive neurophysiologic technique which provides unique information for the clinical evaluation of patients with epilepsy, revealing aspects of neuronal function that previously could only be obtained by invasive EEG monitoring, and giving a new window for research of neuronal activity.

Spatio-temporal Imaging of Cortical Desynchronization in Migraine Visual Aura: A Magnetoencephalography Case Study

OBJECTIVE

To determine cortical oscillatory changes involved in migraine visual aura using magnetoencephalography (MEG).

BACKGROUND

Visual aura in the form of scintillating scotoma precedes migraine in many cases. The involvement of cortical spreading depression within striate and extra-striate cortical areas is implicated in the generation of the disturbance, but the details of its progression, the effects on cortical oscillations, and the mechanisms of aura generation are unclear.

METHODS

We used MEG to directly image changes in cortical oscillatory power during an episode of scintillating scotoma in a patient who experiences aura without subsequent migraine headache. Using the synthetic aperture magnetometry method of MEG source imaging, focal changes in cortical oscillatory power were observed over a 20-minute period and visualized in coregistration with the patient's magnetic resonance image.

RESULTS

Alpha band desynchronization in both the left extra-striate and temporal cortex persisted for the duration of reported visual disturbance, terminating abruptly upon disappearance of scintillations. Gamma frequency desynchronization in the left temporal lobe continued for 8 to 10 minutes following the reported end of aura.

CONCLUSIONS

Observations implicate the extra-striate and temporal cortex in migraine visual aura and suggest involvement of alpha desynchronization in generation of phosphenes and gamma desynchronization in sustained inhibition of visual function.

Spreading and synchronous depressions of cortical activity in acutely injured human brain

BACKGROUND AND PURPOSE

Cortical spreading depression (CSD) has been much studied experimentally but never demonstrated unequivocally in human neocortex by direct electrophysiological recording. A similar phenomenon, peri-infarct depolarization, occurs in experimental models of stroke and causes the infarct to enlarge. Our current understanding of the mechanisms of deterioration in the days after major traumatic or ischemic brain injury in humans has not yielded any effective, novel drug treatment. This study sought clear evidence for the occurrence and propagation of CSD in the injured human brain.

METHODS

In 14 patients undergoing neurosurgery after head injury or intracranial hemorrhage, we placed electrocorticographic (ECoG) electrodes near foci of damaged cortical tissue.

RESULTS

Transient episodes of depressed ECoG activity that propagated across the cortex at rates in the range of 0.6 to 5.0 mm/min were observed in 5 patients; this rate of propagation is characteristic of CSD. We also observed, in 8 of the 14 patients, transient depressions of ECoG amplitude that appeared essentially simultaneous in all recording channels, without clear evidence of spread.

CONCLUSIONS

These results indicate that CSD or similar events occur in the injured human brain and are more frequent than previously suggested. On the basis of these observations, we suggest that the related phenomenon, peri-infarct depolarization, is indeed likely to occur in boundary zones in the ischemic human cerebral cortex.

Cortical spreading depression in the feline brain following sustained and transient stimuli studied using diffusion-weighted imaging

Cortical spreading depression (CSD) was induced by transient (10 min) applications of KCl in agar upon the cortical surface of alpha-chloralose anaesthetised cats. Its features were compared with CSD resulting from sustained applications of crystalline KCl through a mapping of the apparent diffusion coefficient (ADC) using diffusion-weighted echo planar imaging (DWI) over a poststimulus period of 60-100 min. Individual CSD events were computationally detected with the aid of Savitzky-Golay smoothing applied to critically sampled data derived from regions of interest (ROIs) made up of 2 x 2 pixel matrices. The latter were consistently placed at three selected sites on the suprasylvian gyrus (SG) and six sites on the marginal gyrus (MG). The CSD events thus detected were then quantitatively characterised for each ROI using the original time series. Both stimuli consistently elicited similar spreading patterns of initial, primary CSD events that propagated over the SG and marginal MG and were restricted to the hemispheres on which the stimuli were applied. There followed secondary events over smaller extents of cortical surface. Sustained stimuli elicited primary and secondary CSD events with similar amplitudes of ADC deflection that were distributed around a single mean. The ADC deflections were also conserved in peak amplitude throughout the course of their propagation. The initial primary event showed a poststimulus latency of 1.1 +/- 0.1 min. Successive secondary events followed at longer, but uniform, time intervals of around 10 min. Primary and secondary CSDs showed significantly different velocities of conduction (3.32 +/- 0.43 mm min(-1) vs. 2.11 +/- 0.21 mm min(-1), respectively; n = 5) across the cerebral hemisphere. In contrast, transient stimuli produced significantly fewer numbers of CSD events (3.8 +/- 0.5 events per animal, n = 5) than did sustained stimuli (7.4 +/- 0.5 events per animal, mean +/- S.E.M., n = 5, P = 0.002). The peak ADC deflection of their primary CSD events declined by approximately 30 % as they propagated from their initiation site to the interhemispheric boundary. The primary CSD event following a transient stimulus showed a latency of 1.4 +/- 0.1 min. It was followed by successive and smaller secondary ADC deflections that were separated by progressively longer time intervals. Conduction velocities of secondary events were similar to those of primary events. Conduction velocities of both primary and secondary events were slower than their counterparts following a sustained stimulus. ADC changes associated with CSD thus persist at times well after stimulus withdrawal and vary markedly with the nature of the initiating stimulus even in brain regions remote from the stimulus site.

Intrinsic optical imaging reveals regionally different manifestation of spreading depression in hippocampal and entorhinal structures in vitro

The spatiotemporal features of spreading depression (SD) were analyzed in vitro by using combined hippocampal-entorhinal cortex slices. SDs were induced by microinjection of 1 M KCl in the stratum radiatum of the CA1 region of the hippocampus. Measurements of extracellular field potentials, extracellular space (ECS) volume changes and intrinsic optical signal changes were combined to study SD features in different regions of the slice. Each SD was associated with a pronounced shrinkage of the extracellular space (ECS) volume and a decrease in light transmittance. The beginning of the optical signal change occurred simultaneously with the electrographic onset as measured with extracellular microelectrodes but outlasted the dc shift for tens of seconds. The amplitude of the intrinsic optical signal change displayed marked regional variations with greatest changes of 12% in cortical regions. The signal amplitudes were considerably lower in hippocampal regions. The analysis of spread patterns revealed two types of waves: fully propagated waves spreading from CA1 all the way to the temporal neocortex and abortive waves that ceased earlier. The spread velocities displayed pronounced regional differences with highest velocities of 5.4 +/- 0.3 mm/min in the area CA3 of the hippocampal formation and lowest velocities of 2.7 +/- 0.1 mm/min in cortical regions.

Diffusion-weighted MRI used to detect in vivo modulation of cortical spreading depression: comparison of sumatriptan and tonabersat

Spreading cortical depolarization and depression of electroencephalographic activity (SD) may underlie the aura and spreading neurovascular events of migraine. Cortical depolarization may also precipitate the progressive development of cerebral pathology following ischemia. However, data on SD in the human brain are sparse, most likely reflecting the technical difficulties involved in performing such clinical studies. We have previously shown that the transient cerebral water disturbances during SD can be quantitatively investigated in the gyrencephalic brain using repetitive diffusion-weighted magnetic resonance imaging (DWI). To investigate whether DWI could detect modulation of the spatiotemporal properties of SD in vivo, the effects of the antimigraine drug sumatriptan (0.3 mg/kg iv) and the novel anticonvulsant tonabersat (10 mg/kg ip) were evaluated in the cat brain. Supporting previous findings, sumatriptan did not affect the numbers of events (range, 4-8), the duration of SD activity (39.8 +/- 4.4 min, mean +/- SEM), and event velocity (2.2 +/- 0.4 mm min(-1)); tonabersat significantly reduced SD event initiation (range, 0-3) and duration (13.2 +/- 5.0 min) and increased primary event velocity (5.4 +/- 0.7 mm min(-1)). However, both drugs significantly decreased, by >50%, the spatial extent of the first KCl-evoked SD event, and sumatriptan significantly increased event propagation across the suprasylvian sulcus (5.5 +/- 0.6 vs 2.4 +/- 0.4 events in controls). These results demonstrate (1) the feasibility of using DWI to evaluate therapeutic effects on SD, and (2) that sumatriptan may directly modulate the spatial distribution of SD activity in the gyrencephalic brain.

Cortical spreading depression and migraine: new insights from imaging?

The possibility that spreading depression (SD) of cortical activity, a phenomenon observed in all vertebrates, causes the aura of migraine remains an open question in spite of nearly half a century of investigation. SD is also thought to be associated with the progressive neuronal injury observed during cerebral ischaemia. Thus, the ability to detect and investigate SD in humans might prove clinically significant. Animal studies of cortical spreading depression (CSD) have benefited greatly from the advent of relatively non-invasive imaging techniques. The use of these new imaging techniques for clinical studies will accelerate progress in this area of neurobiology.

Recurring episodes of spreading depression are spontaneously elicited by an intracerebral hemorrhage in the swine

Intracranial bleeding damages the surrounding tissue in a complex fashion that involves contamination by blood-borne products and loss of ionic homeostasis. We used electrophysiological techniques to examine the functional changes in the developing intracerebral bleed and in surrounding regions using an in vivo swine model. Intracerebral hemorrhage (ICH) was induced by collagenase injection into the primary somatosensory cortex (SI). Somatic evoked potential (SEP) elicited by electrical stimulation of the contralateral snout as well as changes in DC-coupled potential were monitored in the SI from the time of collagenase injection in order to measure the effects of ICH. The SEP decreased in amplitude within minutes of the intracerebral injection. Its short-latency component was abolished within the first hour after collagenase injection without any sign of recovery for the duration of the experiment. As the SEP started decreasing in amplitude, we observed spontaneous, recurring episodes of cortical spreading depression (SD) as early as 20 min post-injection. The timing of SDs in SI is consistent with our interpretation that SDs were initially generated at multiple sites adjacent to the lesion core and propagated into the surrounding area. With time, SD became less frequent near the injection site, shifting to more distant electrodes in the surrounding area. Our results indicate that ICH leads to the reduction in SEP amplitude and induces spontaneous episodes of SD. Loss of ionic homeostasis is most likely the physiological basis for the SEP change and for the induction of SD. Recurring SD spontaneously generated in experimental ICH needs further study in humans with ICH.