Decades of rodent research have established the role of hippocampal sharp wave ripples (SPW-Rs) in consolidating and guiding experience. More recently, intracranial recordings in humans have suggested their role in episodic and semantic memory. Yet, common standards for recording, detection, and reporting do not exist. Here, we outline the methodological challenges involved in detecting ripple events and offer practical recommendations to improve separation from other high-frequency oscillations. We argue that shared experimental, detection, and reporting standards will provide a solid foundation for future translational discovery.

Summary: Objective: To investigate possible electroencephalography (EEG) correlates of epileptogenesis after traumatic brain injury (TBI) using the fluid percussion model.Methods: Experiments were conducted on adult 2‐ to 4‐month‐old male Sprague‐Dawley rats. Two groups of animals were studied: (1) theTBIgroup with depth and screw electrodes implanted immediately after the fluid percussion injury (FPI) procedure, and (2) a naive age‐matched control group with the same electrode implantation montage. Pairs of tungsten microelectrodes (50 μm outer diameter) and screw electrodes were implanted in neocortex inside theTBIcore, areas adjacent toTBI, and remote areas.EEGactivity, recorded on the day ofFPI, and continuously for 2 weeks, was analyzed for possible electrographic biomarkers of epileptogenesis. Video‐EEGmonitoring was also performed continuously in theTBIgroup to capture electrographic and behavioral seizures until the caps came off (28–189 days), and for 1 week, at 2, 3, and 6 months of age, in the control group.Results: Pathologic high‐frequency oscillations (pHFOs) with a central frequency between 100 and 600 Hz, were recorded from microelectrodes, beginning during the first two post‐FPIweeks, in 7 of 12 animals in theTBIgroup (58%) and never in the controls.pHFOs only occurred in cortical areas within or adjacent to theTBIcore. These were associated with synchronous multiunit discharges and popSpikes, duration 15–40 msec. RepetitivepHFOs andEEGspikes (rHFOSs) formed paroxysmal activity, with a unique arcuate pattern, in the frequency band 10–16 Hz in the same areas as isolatedpHFOs, and these events were also recorded by screw electrodes. Although loss of caps prevented long‐term recordings from all rats,pHFOs andrHFOSs occurred during the first 2 weeks in all four animals that later developed seizures, and none of the rats without these events developed late seizures.Significance: pHFOs, similar to those associated with epileptogenesis in the status rat model of epilepsy, may also reflect epileptogenesis afterFPI.rHFOSs could be noninvasive biomarkers of epileptogenesis.

Test-retest reliability of neuroimaging measurements is an important concern in the investigation of cognitive functions in the human brain. To date, intraclass correlation coefficients (ICCs), originally used in inter-rater reliability studies in behavioral sciences, have become commonly used metrics in reliability studies on neuroimaging and functional near-infrared spectroscopy (fNIRS). However, as there are six popular forms of ICC, the adequateness of the comprehensive understanding of ICCs will affect how one may appropriately select, use, and interpret ICCs toward a reliability study. We first offer a brief review and tutorial on the statistical rationale of ICCs, including their underlying analysis of variance models and technical definitions, in the context of assessment on intertest reliability. Second, we provide general guidelines on the selection and interpretation of ICCs. Third, we illustrate the proposed approach by using an actual research study to assess intertest reliability of fNIRS-based, volumetric diffuse optical tomography of brain activities stimulated by a risk decision-making protocol. Last, special issues that may arise in reliability assessment using ICCs are discussed and solutions are suggested.

Summary: The current study aimed to investigate the spatial and temporal patterns of high‐frequency oscillations (HFOs) in the intra‐/extrahippocampal areas during epileptogenesis. Local field potentials were bilaterally recorded from hippocampus (CA1), thalamus, motor cortex, and prefrontal cortex in 13 rats before and after intrahippocampal kainic acid (KA) lesions. HFOs in the ripple (100‐200 Hz) and fast ripple (250‐500 Hz) ranges were detected and their rates were computed during different time periods (1‐5 weeks) after KA‐induced status epilepticus (SE). Recurrent spontaneous seizures were observed in 7 rats after SE, and the other 6 rats did not develop epilepsy. During the latent period, the rate of hippocampal HFOs increased at the ipsilateral site of the KA lesion in both groups, and the HFO rate was significantly higher in the animals that later developed epilepsy. Animals that later developed epilepsy also demonstrated widespread appearance of HFOs, in both the ripple and the fast ripple range, whereas animals that did not develop epilepsy only exhibited changes in the ipsilateral intrahippocampal HFO rate. This study demonstrates an association between an increased rate of widespread HFOs and the later development of epilepsy, suggesting the formation of large‐scale distributed pathological networks during epileptogenesis.

We studied the role of temporal and spatial changes in high-frequency oscillation (HFO, 80–500 Hz) generation in epileptogenesis following traumatic brain injury (TBI).