On March 20th, Dr. Takamitsu Iwata’s paper was published in the Annals of Clinical and Translational Neurology.
The paper is titled: “Abnormal Synchronization Between Cortical Delta Powerand Ripples in Hippocampal Sclerosis”.
https://onlinelibrary.wiley.com/doi/10.1002/acn3.70032
Synchronization Between Hippocampal and Cortical Activity Enables Detection of Hippocampal Sclerosis
Epilepsy is a neurological disorder caused by abnormal electrical activity in the brain, leading to seizures and cognitive impairment. Electroencephalography (EEG) is essential for diagnosing epilepsy, and among EEG signals, high-frequency oscillations (HFOs) are key indicators for identifying epileptic foci. In the hippocampus of epilepsy patients, two types of HFOs are observed: pathological epileptic ripples and physiological sharp-wave ripples, which play a crucial role in memory consolidation. However, distinguishing between these two types of HFOs has been a significant challenge due to their similar waveforms.
In a previous study, Takamitsu Iwata and colleagues demonstrated that physiological sharp-wave ripples in the hippocampus fluctuate significantly according to sleep-wake rhythms and strongly synchronize with cortical delta-band (0.5–4 Hz) activity.
Building on this finding, the research team investigated the relationship between hippocampal ripples and cortical delta waves in epilepsy patients with hippocampal sclerosis (HS). HS is a condition characterized by neuronal degeneration in the hippocampus, leading to epilepsy that is often resistant to medication.
The team analyzed data from 16 patients with implanted intracranial electrodes, examining the synchronization between hippocampal ripples and delta waves. Their results revealed that in patients with hippocampal sclerosis, hippocampal ripples exhibited significantly lower synchronization with delta waves compared to those with lower epileptogenicity.
This study suggests that the “synchronization between hippocampal ripples and cortical delta waves” could serve as a novel biomarker for estimating hippocampal epileptogenicity and identifying hippocampal sclerosis. Using this approach, hippocampal sclerosis could be detected with high accuracy (94.1%) from EEG data, even before hippocampal resection.
Hippocampal sharp-wave ripples play an important role in organizing and consolidating memories. A decrease in sharp-wave ripples or an increase in epileptic ripples may lead to memory impairment. Previous research has reported frequent memory deficits in epilepsy patients, and this study provides new insights into the mechanisms underlying memory dysfunction in epilepsy.
This discovery has the potential to improve the accuracy of epilepsy diagnosis and enable more precise treatment planning. Further investigation into the relationship between hippocampal ripples and cortical delta waves could also contribute to the development of novel treatments for memory disorders.
Beyond epilepsy, this study is expected to have a significant impact on research into memory and cognitive function.
Fig. 1.
(A) An image showing preoperative magnetic resonance imaging (MRI) and postimplantation computed tomography (CT) data illustrating the electrode placement within the hippocampus. (B) Hippocampal LFPs are the bipolar potential recorded from A1–A2 (top) processed using a bandpass filter with a range of 70 to 180 Hz (bottom). The blue shaded area indicates the detected ripples. (C) Magnified views of three representative ripples.
Fig. 2.
The lines show the mean and 95% confidence intervals of the Z-scored ripple event rate (red) and delta power (blue) over 24 h for patients in the NE group (left) and EP group (right).