[EEG and ischemic stroke in full-term newborns]

Functional neuropathology of neonatal hypoxia-ischemia by single-mouse longitudinal electroencephalography

OBJECTIVE

Neonatal cerebral hypoxia-ischemia (HI) results in symptomatic seizures and long-term neurodevelopmental disability. The Rice-Vannucci model of rodent neonatal HI has been used extensively to examine and translate the functional consequences of acute and chronic HI-induced encephalopathy. Yet, longitudinal electrophysiological characterization of this brain injury model has been limited by the size of the neonatal mouse's head and postnatal maternal dependency. We overcome this challenge by employing a novel method of longitudinal single-mouse electroencephalography (EEG) using chronically implanted subcranial electrodes in the term-equivalent mouse pup. We characterize the neurophysiological disturbances occurring during awake and sleep states in the acute and chronic phases following newborn brain injury.

METHODS

C57BL/6 mice underwent long-term bilateral subcranial EEG and electromyographic electrode placement at postnatal day 9 followed by unilateral carotid cauterization and exposure to 40 minutes of hypoxia the following day. EEG recordings were obtained prior, during, and intermittently after the HI procedure from postnatal day 10 to weaning age. Quantitative EEG and fast Fourier transform analysis were used to evaluate seizures, cortical cerebral dysfunction, and disturbances in vigilance states.

RESULTS

We observed neonatal HI-provoked electrographic focal and bilateral seizures during or immediately following global hypoxia and most commonly contralateral to the ischemic injury. Spontaneous chronic seizures were not seen. Injured mice developed long-term asymmetric EEG background attenuation in all frequencies and most prominently during non-rapid eye movement (NREM) sleep. HI mice also showed transient impairments in vigilance state duration and transitions during the first 2 days following injury.

SIGNIFICANCE

The functional burden of mouse neonatal HI recorded by EEG resembles closely that of the injured human newborn. The use of single-mouse longitudinal EEG in this immature model can advance our understanding of the developmental and pathophysiological mechanisms of neonatal cerebral injury and help translate novel therapeutic strategies against this devastating condition.

EEG findings and outcomes of continuous video-EEG monitoring started prior to initiation of seizure treatment in the perinatal stroke

BACKGROUND

To analyze the findings in the background EEG activity of infants who suffered perinatal stroke.

METHODS

Eleven neonates born 2009-2014 diagnosed of ischemic stroke by MRI (three of them with multistroke) underwent continuous video-EEG monitoring. Visual and spectral (power spectrum and coherence) analyses of the background EEG was performed in three moments: 1) Onset of EEG recording (prior to initiate seizure treatment), 2) Post-ictal epoch (1-2 h after the last seizure), and 3) one-two days after seizure control. All children aged 2-6 years underwent neurodevelopmental assessment.

RESULTS

Discontinuity, asymmetry, asynchrony, transients, and relative power spectrum in δ and θ frequency bands increased significantly (p < 0.05) in the post-ictal epoch with respect to onset of EEG recording. After seizure control, discontinuity, asynchrony, and θ power spectrum no longer had significant differences with those found at onset of EEG recording. Significant differences between the ischemic and unaffected hemispheres were found in transients and in β coherence (p = 0.002; p = 0.001, respectively) exclusively in the post-ictal epoch. Seizure burden and time-to-control ranged 5-38 min and 0.5-40 h respectively. Currently, only one child is affected by spastic monoparesis. The intelligence quotients ranged 96-123.

CONCLUSIONS

The background EEG can undergo significant changes in the post-ictal epoch due to the seizure activity triggered by the perinatal stroke. Most of these EEG changes involve all brain activity and not exclusively the ischemic hemisphere. Many of these modifications in the EEG background reverse following the seizure control. Video-EEG monitoring allows accurate/immediate diagnosis and rapid/intensive treatment of the stroke-associated seizures.

Between molecules and experience: role of early patterns of coordinated activity for the development of cortical maps and sensory abilities

Sensory systems processing information from the environment rely on precisely formed and refined neuronal networks that build maps of sensory receptor epithelia at different subcortical and cortical levels. These sensory maps share similar principles of function and emerge according to developmental processes common in visual, somatosensory and auditory systems. Whereas molecular cues set the coarse organization of cortico-subcortical topography, its refinement is known to succeed under the influence of experience-dependent electrical activity during critical periods. However, coordinated patterns of activity synchronize the cortico-subcortical networks long before the meaningful impact of environmental inputs on sensory maps. Recent studies elucidated the cellular and network mechanisms underlying the generation of these early patterns of activity and highlighted their similarities across species. Moreover, the experience-independent activity appears to act as a functional template for the maturation of sensory networks and cortico-subcortical maps. A major goal for future research will be to analyze how this early activity interacts with the molecular cues and to determine whether it is permissive or rather supporting for the establishment of sensory topography.

Diagnostic management of neonatal stroke

In this paper the clinical presentation of neonatal arterial ischaemic stroke (NAIS) and neonatal cerebral sinovenous thrombosis (NCSVT) is briefly summarised; then a structured hierarchical diagnostic flow is proposed to discern clinical phenotypes underlying neonatal (ischaemic as well as haemorrhagic) stroke. The diagnostic flow proposed following clinical detection or chance imaging finding is an initial step towards standardisation of the mechanisms leading to stroke. For NAIS the sequence is: infection, trauma, embolism, arteriopathy, other, primary thrombosis and unclassified; for NCSVT the sequence is: infection, trauma, venopathy, other, primary thrombosis and unclassified. Such standardisation should guide attempts at prevention and treatment. The analysis of a retrospective personal cohort of 134 newborn infants with stroke, suggest that-for stroke in general-embolism is the most common identifiable mechanism (25%), preceding trauma (10%) and infection (8%). For NAIS the presence of an embolic phenotype is 33% in this cohort. The designation unclassifiable scored 34% for the entire stroke group, 25% for neonatal arterial ischaemic stroke. Complex arterial stroke, with multiple arteries involved-is regularly seen following embolism, infection and cranial trauma.

[Interest of EEG in full-term newborns with isolated unilateral ischemic stroke]

In full-term newborns, unilateral and recurrent clonic seizures which occur during the first 48 hours of life suggest an isolated unilateral ischemic stroke. These focal seizures are isolated, occuring during a short period, or make up a status epilepticus. Electroencephalogram (EEG) is a key tool for crisis and focal cerebral process diagnosis. It also allows to assess antiepileptic drugs effectiveness. But cerebral imaging is necessary to confirm vascular origin of the cerebral impairment. Hematologic data are also needful to look for a family thromphilia. Some particular unilateral EEG abnormalities could be associated with controlateral motor sequelae or long term behavioral problems. These findings may be used for prospective studies aimed at specifying possible links between EEG abnormalities and long term outcome.