Simultaneous BOLD fMRI and local field potential measurements during kainic acid-induced seizures.

PURPOSE: To investigate how kainic acid-induced epileptiform activity is related to hemodynamic changes probed by blood oxygenation level-dependent functional magnetic resonance imaging (BOLD fMRI). METHODS: Epileptiform activity was induced with kainic acid (KA) (10 mg/kg, i.p.), and simultaneous fMRI at 7 Tesla, and deep electrode local field potential (LFP) recordings were performed from the right hippocampus in awake and medetomidine-sedated adult Wistar rats. KEY FINDINGS: Recurrent seizure activity induced by KA was detected in LFP both in medetomidine-sedated and awake rats, even though medetomidine sedation reduced the mean duration of individual seizures as compared to awake rats (33 ± 24 and 46 ± 34 s, respectively, mean ± SD p < 0.01). KA administration also triggered robust positive BOLD responses bilaterally in the hippocampus both in awake and medetomidine-sedated rats; however, in both animal groups some of the seizures detected in LFP recording did not cause detectable BOLD signal change. SIGNIFICANCE: Our data suggest that medetomidine sedation can be used for simultaneous fMRI and electrophysiologic studies of normal and epileptic brain function, even though seizure duration after medetomidine administration was shorter than that in awake animals. The results also indicate that neuronal activity and BOLD response can become decoupled during recurrent kainic acid-induced seizures, which may have implications to interpretation of fMRI data obtained during prolonged epileptiform activity.

Evoked local field potentials can explain temporal variation in blood oxygenation level-dependent responses in rat somatosensory cortex.

The aim of this study was to explain the temporal variations between subjects in the blood oxygenation level-dependent (BOLD) response. Somatosensory responses were elicited with the electrical forepaw stimulus at a frequency of 10 Hz in urethane-anesthetized rats, and functional magnetic resonance imaging (fMRI) with BOLD contrast and local field potential (LFP) measurements were performed simultaneously. BOLD fMRI activation was evaluated by two different models, one based on the stimulus paradigm (the block model) and the other on the simultaneously measured evoked LFP responses. In the initial analysis, the LFP model captured the BOLD activation in the primary somatosensory cortex in all cases, and the block model in 10 of 12 rats. A statistical comparison of the two models revealed that the LFP-derived model was able to explain additional BOLD variation over the block model in the somatosensory cortex in nine of 12 rats. These results suggest that there is more information regarding neuronal activity in the BOLD signal than can be exploited using the block model alone. Furthermore, the hemodynamic coupling remains unchanged in the case of temporally variable BOLD signals.

Simultaneous fMRI and local field potential measurements during epileptic seizures in medetomidine-sedated rats using raser pulse sequence.

Simultaneous electrophysiological and functional magnetic resonance imaging measurements of animal models of epilepsy are methodologically challenging, but essential to better understand abnormal brain activity and hemodynamics during seizures. In this study, functional magnetic resonance imaging of medetomidine-sedated rats was performed using novel rapid acquisition by sequential excitation and refocusing (RASER) fast imaging pulse sequence and simultaneous local field potential measurements during kainic acid-induced seizures. The image distortion caused by the hippocampal-measuring electrode was clearly seen in echo planar imaging images, whereas no artifact was seen in RASER images. Robust blood oxygenation level-dependent responses were observed in the hippocampus during kainic acid-induced seizures. The recurrent epileptic seizures were detected in the local field potential signal after kainic acid injection. The presented combination of deep electrode local field potential measurements and functional magnetic resonance imaging under medetomidine anesthesia, which does not significantly suppress kainic acid-induced seizures, provides a unique tool for studying abnormal brain activity in rats.

Detection of Hyperexcitability by Functional Magnetic Resonance Imaging after Experimental Traumatic Brain Injury.

Diagnosis of ongoing epileptogenesis and associated hyperexcitability after brain injury is a major challenge. Given that increased neuronal activity in the brain triggers a blood oxygenation level-dependent (BOLD) response in functional magnetic resonance imaging (fMRI), we hypothesized that fMRI could be used to identify the brain area(s) with hyperexcitability during post-injury epileptogenesis. We applied fMRI to detect onset and spread of BOLD activation after pentylenetetrazol (PTZ)-induced seizures (PTZ, 30 mg/kg, intraperitoneally) in 16 adult male rats at 2 months after lateral fluid percussion (FPI)-induced traumatic brain injury (TBI). In sham-operated controls, onset of the PTZ-induced BOLD response was bilateral and first appeared in the cortex. After TBI, 5 of 9 (56%) rats exhibited ipsilateral perilesional cortical BOLD activation, followed by activation of the contralateral cortex. In 4 of 9 (44%) rats, onset of BOLD response was bilateral. Interestingly, latency from the PTZ injection to onset of the BOLD response increased in the following order: sham-operated controls (ipsilateral 132 ± 57 sec, contralateral 132 ± 57 sec; p > 0.05) < TBI with bilateral BOLD onset (ipsilateral 176 ± 54 sec, contralateral 178 ± 52 sec; p > 0.05) < TBI with ipsilateral BOLD onset (ipsilateral 406 ± 178 sec, contralateral 509 ± 140 sec; p < 0.05). Cortical lesion area did not differ between rats with ipsilateral versus bilateral BOLD onset (p > 0.05). In the group of rats with ipsilateral onset of PTZ-induced BOLD activation, none of the rats showed a robust bilateral thalamic BOLD response, only 1 of 5 rats had robust ipsilateral thalamic calcifications, and 4 of 5 rats had perilesional astrocytosis. These findings suggest the evolution of the epileptogenic zone in the perilesional cortex after TBI, which is sensitive to PTZ-induced hyperexcitability. Further studies are warranted to explore the evolution of thalamo-cortical pathology as a driver of epileptogenesis after lateral FPI.

Nutritive sucking induces age-specific EEG-changes in 0-24 week-old infants.

Little is known how the brain of the newborn infant responds to the postnatal nutrition and care. No systematic studies exist in which the effects of nutritional and non-nutritional sucking on the brain activity of the infant were compared. We recorded the EEG activity of 40 infants at the ages of 0,6,12 and 24 weeks in four successive behavioral stages: while the infants were hungry and waiting for sucking, during non-nutritional and nutritional sucking, and during satiation after completed feeding. Quantitative EEG analysis was performed using occipital, parietal and central EEG channels. In the newborn infants, a significant reduction in the EEG power was found after nutritional sucking in the all EEG frequency bands studied (1-10Hz), which was paralleled by a significant behavioral alertness decline. This response decayed during the subsequent neonatal period and was completely absent at the age of 12 weeks. In 24-week-old infants, nutritional sucking was accompanied with an increase in rhythmic theta activity during which no significant alertness change took place. Non-nutritional sucking was connected with minor and non-significant effects on the EEG. We conclude that in newborn infants nutritional sucking has a direct effect on the EEG, which has a soothing character and is connected with an alertness decline. In 24-week-old infants the response to nutritional sucking is of a different type and consists of an organized, rhythmical theta activity in the EEG not directly linked with alertness change. Our findings suggest a developmental relationship between nursing and infant brain function with plausible affective and cognitive implications.

Software for advanced HRV analysis.

A computer program for advanced heart rate variability (HRV) analysis is presented. The program calculates all the commonly used time- and frequency-domain measures of HRV as well as the nonlinear Poincaré plot. In frequency-domain analysis parametric and nonparametric spectrum estimates are calculated. The program generates an informative printable report sheet which can be exported to various file formats including the portable document format (PDF). Results can also be saved as an ASCII file from which they can be imported to a spreadsheet program such as the Microsoft Excel. Together with a modern heart rate monitor capable of recording RR intervals this freely distributed program forms a complete low-cost HRV measuring and analysis system.

Kubios HRV--heart rate variability analysis software.

Kubios HRV is an advanced and easy to use software for heart rate variability (HRV) analysis. The software supports several input data formats for electrocardiogram (ECG) data and beat-to-beat RR interval data. It includes an adaptive QRS detection algorithm and tools for artifact correction, trend removal and analysis sample selection. The software computes all the commonly used time-domain and frequency-domain HRV parameters and several nonlinear parameters. There are several adjustable analysis settings through which the analysis methods can be optimized for different data. The ECG derived respiratory frequency is also computed, which is important for reliable interpretation of the analysis results. The analysis results can be saved as an ASCII text file (easy to import into MS Excel or SPSS), Matlab MAT-file, or as a PDF report. The software is easy to use through its compact graphical user interface. The software is available free of charge for Windows and Linux operating systems at http://kubios.uef.fi.

Monitoring functional impairment and recovery after traumatic brain injury in rats by FMRI.

The present study was designed to test a hypothesis that functional magnetic resonance imaging (fMRI) can be used to monitor functional impairment and recovery after moderate experimental traumatic brain injury (TBI). Moderate TBI was induced by lateral fluid percussion injury in adult rats. The severity of brain damage and functional recovery in the primary somatosensory cortex (S1) was monitored for up to 56 days using fMRI, cerebral blood flow (CBF) by arterial spin labeling, local field potential measurements (LFP), behavioral assessment, and histology. All the rats had reduced blood-oxygen-level-dependent (BOLD) responses during the 1st week after trauma in the ipsilateral S1. Forty percent of these animals showed recovery of the BOLD response during the 56 day follow-up. Unexpectedly, no association was found between the recovery in BOLD response and the volume of the cortical lesion or thalamic neurodegeneration. Instead, the functional recovery occurred in rats with preserved myelinated fibers in layer VI of S1. This is, to our knowledge, the first study demonstrating that fMRI can be used to monitor post-TBI functional impairment and consequent spontaneous recovery. Moreover, the BOLD response was associated with the density of myelinated fibers in the S1, rather than with neurodegeneration. The present findings encourage exploration of the usefulness of fMRI as a noninvasive prognostic biomarker for human post-TBI outcomes and therapy responses.

Quantitative assessment of water pools by T 1 rho and T 2 rho MRI in acute cerebral ischemia of the rat.

The rotating frame longitudinal relaxation magnetic resonance imaging (MRI) contrast, T(1 rho), obtained with on-resonance continuous wave (CW) spin-lock field is a sensitive indicator of tissue changes associated with hyperacute stroke. Here, the rotating frame relaxation concept was extended by acquiring both T(1 rho) and transverse rotating frame (T(2 rho)) MRI data using both CW and adiabatic hyperbolic secant (HSn; n=1, 4, or 8) pulses in a rat stroke model of middle cerebral artery occlusion. The results show differences in the sensitivity of spin-lock T(1 rho) and T(2 rho) MRI to detect hyperacute ischemia. The most sensitive techniques were CW-T(1 rho) and T(1 rho) using HS4 or HS8 pulses. Fitting a two-pool exchange model to the T(1 rho) and T(2 rho) MRI data acquired from the infarcting brain indicated time-dependent increase in free water fraction, decrease in the correlation time of water fraction associated with macromolecules, and increase in the exchange correlation time. These findings are consistent with known pathology in acute stroke, including vasogenic edema, destructive processes, and tissue acidification. Our results show that the sensitivity of the spin-lock MRI contrast in vivo can be modified using different spin-lock preparation blocks, and that physicochemical models of the rotating frame relaxation may provide insight into progression of ischemia in vivo.

Distinct MRI pattern in lesional and perilesional area after traumatic brain injury in rat--11 months follow-up.

To understand the dynamics of progressive brain damage after lateral fluid-percussion induced traumatic brain injury (TBI) in rat, which is the most widely used animal model of closed head TBI in humans, MRI follow-up of 11 months was performed. The evolution of tissue damage was quantified using MRI contrast parameters T(2), T(1rho), diffusion (D(av)), and tissue atrophy in the focal cortical lesion and adjacent areas: the perifocal and contralateral cortex, and the ipsilateral and contralateral hippocampus. In the primary cortical lesion area, which undergoes remarkable irreversible pathologic changes, MRI alterations start at 3 h post-injury and continue to progress for up to 6 months. In more mildly affected perifocal and hippocampal regions, the robust alterations in T(2), T(1rho), and D(av) at 3 h to 3 d post-injury normalize within the next 9-23 d, and thereafter, progressively increase for several weeks. The severity of damage in the perifocal and hippocampal areas 23 d post-injury appeared independent of the focal lesion volume. Magnetic resonance spectroscopy (MRS) performed at 5 and 10 months post-injury detected metabolic alterations in the ipsilateral hippocampus, suggesting ongoing neurodegeneration and inflammation. Our data show that TBI induced by lateral fluid-percussion injury triggers long-lasting alterations with region-dependent temporal profiles. Importantly, the temporal pattern in MRI parameters during the first 23 d post-injury can indicate the regions that will develop secondary damage. This information is valuable for targeting and timing interventions in studies aiming at alleviating or reversing the molecular and/or cellular cascades causing the delayed injury.

Noise sensitivity of a principal component regression based RT interval variability estimation method.

Ventricular repolarization duration (VRD) is controlled by neural regulatory system same way as heart rate and, thus, also VRD varies in time. Traditionally, VRD variability is assessed by determining the time differences between successive R and T-waves, i.e. RT intervals. We have recently proposed a method based on principal component regression (PCR) for quantifying RT variability. The main benefit of the method is that it does not necessitate T-wave detection. In this paper, the noise sensitivity of the PCR based method is evaluated by examining the effect of simulated Gaussian noise on the spectral characteristics of the estimated RT variability series.