Endogenous adenosine A1 receptor activation underlies the transient post-ischemic rhythmic delta EEG activity

A method to assess the default EEG macrostate and its reactivity to stimulation

OBJECTIVE

The default mode network (DMN) is deactivated by stimulation. We aimed to assess the DMN reactivity impairment by routine EEG recordings in stroke patients with impaired consciousness.

METHODS

Binocular light flashes were delivered at 1 Hz in 1-minute epochs, following a 1-minute baseline (PRE). The EEG was decomposed in a series of binary oscillatory macrostates by topographic spectral clustering. The most deactivated macrostate was labeled the default EEG macrostate (DEM). Its reactivity (DER) was quantified as the decrease in DEM occurrence probability during stimulation. A normalized DER index (DERI) was calculated as DER/PRE. The measures were compared between 14 healthy controls and 32 comatose patients under EEG monitoring following an acute stroke.

RESULTS

The DEM was mapped to the posterior DMN hubs. In the patients, these DEM source dipoles were 3-4 times less frequent and were associated with an increased theta activity. Even in a reduced 6-channel montage, a DER below 6.26% corresponding to a DERI below 0.25 could discriminate the patients with sensitivity and specificity well above 80%.

CONCLUSION

The method detected the DMN impairment in post-stroke coma patients.

SIGNIFICANCE

The DEM and its reactivity to stimulation could be useful to monitor the DMN function at bedside.

The Purine Salvage Pathway and the Restoration of Cerebral ATP: Implications for Brain Slice Physiology and Brain Injury

Brain slices have been the workhorse for many neuroscience labs since the pioneering work of Henry McIlwain in the 1950s. Their utility is undisputed and their acceptance as appropriate models for the central nervous system is widespread, if not universal. However, the skeleton in the closet is that ATP levels in brain slices are lower than those found in vivo, which may have important implications for cellular physiology and plasticity. Far from this being a disadvantage, the ATP-impoverished slice can serve as a useful and experimentally-tractable surrogate for the injured brain, which experiences similar depletion of cellular ATP. We have shown that the restoration of cellular ATP in brain slices to in vivo values is possible with a simple combination of D-ribose and adenine (RibAde), two substrates for ATP synthesis. Restoration of ATP in slices to physiological levels has implications for synaptic transmission and plasticity, whilst in the injured brain in vivo RibAde shows encouraging positive results. Given that ribose, adenine, and a third compound, allopurinol, are all separately in use in man, their combined application after acute brain injury, in accelerating ATP synthesis and increasing the reservoir of the neuroprotective metabolite, adenosine, may help reduce the morbidity associated with stroke and traumatic brain injury.

Burst-Suppression Ratio on Electrocorticography Depends on Interelectrode Distance

INTRODUCTION

With deepening of anesthesia-induced comatose states, the EEG becomes fragmented by increasing periods of suppression. When measured from conventional EEG recordings, the binary burst-suppression signal (BS) appears similar across the scalp. As such, the BS ratio (BSR), quantifying the fraction of time spent in suppression, is clinically considered a global index of brain function in sedation monitoring. Recent studies indicate that BS may be considerably asynchronous when measured with higher spatial resolution such as on electrocorticography. The authors investigated the magnitude of BSR changes with cortical recording interelectrode distance.

METHODS

The authors selected fronto-parietal electrocorticography recordings showing propofol-induced BS recorded via 8-electrode strips (1-cm interelectrode distance) during cortical motor mapping in 31 patients. For 1-minute epochs, bipolar recordings were computed between each electrode pair. The median BSR, burst duration (BD), and bursting frequency were derived for each interelectrode distance.

RESULTS

At 1-cm interelectrode distance, with increasing BSR, BD decreased exponentially. For a BSR between 50% and 80%, BD reached a plateau of 2.1 seconds while the bursting frequency decreased from 14 to 6 bursts per minute. With increasing interelectrode distance, BD increased at a rate of 0.2 seconds per cm. This correlated with a decrease in BSR with distance that reached the rate of -4.4 percentage per centimeters during deepest anesthesia.

CONCLUSIONS

With increasing cortical interelectrode recording distance, burst summation leads to an increasing BD associated with a reduction in BSR. Standardization of interelectrode distance is important for cortical BSR measurements.

Burst-suppression is reactive to photic stimulation in comatose children with acquired brain injury

OBJECTIVE

Burst-suppression is an electroencephalographic pattern observed during coma. In individuals without known brain pathologies undergoing deep general anesthesia, somatosensory stimulation transiently increases the occurrence of bursts. We investigated the reactivity of burst-suppression in children with acquired brain injury.

METHODS

Intensive care unit electroencephalographic monitoring recordings containing burst-suppression were obtained from 5 comatose children with acquired brain injury of various etiologies. Intermittent photic stimulation was performed at 1Hz for 1min to assess reactivity. We quantified reactivity by measuring the change in the burst ratio (fraction of time in burst) following photic stimulation.

RESULTS

Photic stimulation evoked bursts in all patients, resulting in a transient increase in the burst ratio, while the mean heart rate remained unchanged. The regression slope of the change in burst ratio, referred to as the standardized burst ratio reactivity, correlated with subjects' Glasgow Coma Scale scores.

CONCLUSIONS

Reactivity of the burst-suppression pattern to photic stimulation occurs across diverse coma etiologies. Standardized burst ratio reactivity appears to reflect coma severity.

SIGNIFICANCE

Measurement of burst ratio reactivity could represent a simple method to monitor coma severity in critically ill children.

Polarity-dependent effect of low-frequency stimulation on amygdaloid kindling in rats

BACKGROUND

Low-frequency stimulation (LFS, <5 Hz) has been proposed as an alternative option for the treatment of epilepsy. The stimulation pole, anode and cathode, may make different contributions to the anti-epileptic effect of LFS.

OBJECTIVE

To determine whether electrode polarity influences the anti-epileptic effect of LFS at the kindling focus in amygdaloid kindling rats.

METHODS

The effect of bipolar and monopolar (or unipolar) LFS at the amygdala in different polarity directions on amygdaloid kindling acquisition, kindled seizures and electroencephalogram (EEG) were tested.

RESULTS

Bipolar LFS in the same direction of polarity as the kindling stimulation but not in the reverse direction retarded kindling acquisition. Anodal rather than cathodal monopolar LFS attenuated kindling acquisition and kindled seizures. Bipolar LFS showed a stronger anti-epileptic effect than monopolar LFS. Furthermore, anodal LFS (both bipolar and monopolar) decreased, while cathodal LFS increased the power of the EEG from the amygdala; the main changes in power were in the delta (0.5-4 Hz) band, which was specifically increased during kindling acquisition.

CONCLUSIONS

Our results provide the first evidence that the effect of LFS at the kindling focus on amygdaloid kindling in rats is polarity-dependent, and this may be due to the different effects of anodal and cathodal LFS on the activity in the amygdala, especially on the delta band activity. So, It is likely that the electrode polarity, especially that for anodal current, is a key factor affecting the clinical effects of LFS on epilepsy.