Xiang Lab

  • High-Frequency Neuromagnetic Signals

    High-Frequency Neuromagnetic Signals in the Developing Brain

    This project uses magnetoencephalography (MEG) to characterize the normal neuromagnetic profile in children of intrinsic neuromagnetic activities and sensorimotor, auditory, visual and language elicited magnetic fields in 0-2,000 Hz. Since MEG can detect neuromagnetic signals with high spatial and temporal resolution, many brain properties can be studied. Currently, we are focusing on three areas:

    • The patterns of synchronization and de-synchronization of resting state activity and elicited cortical activation
    • The volumetric extent of these active sensorimotor, auditory, visual and language cortices
    • The coherency pattern of neuromagnetic activation in the developing brain (see figure 2)

    This approach may lead to a new way to study the brain functions in normal children and in children with various brain disorders.

    Funded by a trustee grant.

    Pathologic High-Frequency Neuromagnetic Signals in Childhood Epilepsy

    This project has three aims:  

    • Quantify the differences and similarities of HFBS recorded noninvasively with MEG to those recorded invasively with intracranial EEG
    • Determine how outcome of epilepsy surgery correlates with resection of the regions generating epileptic HFBS recorded noninvasively with MEG
    • Determine spatial and temporal differences in primary and secondary ictogenic zones noninvasively with causality analysis of MEG data in 0-3,000 Hz

    Visual identification of spikes (14-70 Hz) in invasive EEG recordings is the widely used method for estimating ictogenic zones. This work is innovative because it examines the relationship between HFBS and ictogenic zones noninvasively (using MEG). This is a novel use of MEG, and we will use new data analysis techniques to accomplish this work.

    If successful, MEG localization of HFBS could replace risky intracranial recordings and improve the outcome of epilepsy surgery. After causality analysis of MEG HFBS, a single ictogenic focus may be identified in patients thought to have multiple epileptic areas based on current methodologies. As a result, additional patients may have successful surgery.

    Funded by a trustee grant, NIH / NINDS R01-NS072341 (pending).

 
  • Source coherence.

    click to enlarge

    Source coherence.

    Images of source coherence show the functional connectivity of the brain activities in 8-12 Hz. Each small ball represents a center of source activity; each line represents one connection between two sources. The four images of source coherence are from four representative participants aged 9 to 26 (age is indicated at right). Noticeably, adolescents (16 years old) and adults (26 years old) have more connections than small children (9 and 12 years of age). The occipital-temporal connection is identifiable for all participants while the temporal-frontal and occipital-frontal connections are identifiable after age 12. Two participants (16 years and 26 years) have a source in the right frontal, which correlates with other sources.

  • Spectrograms, magnetic source imaging (MSI) and intracranial recordings from a patient show the frequency and spatial features of interictal and ictal high-frequency brain signals (HFBS).

    click to enlarge

    Spectrograms, magnetic source imaging (MSI) and intracranial recordings from a patient show the frequency and spatial features of interictal and ictal high-frequency brain signals (HFBS).

    Spectrograms, magnetic source imaging (MSI) and intracranial recordings from a patient show the frequency and spatial features of interictal and ictal high-frequency brain signals (HFBS). Noticeably, a component around 310 Hz is identifiable in both ictal and interictal spectrograms. The magnetic source imaging (MSI) shows the source location of neuromagnetic signals in 310 Hz in the left frontal cortex. There is no significant difference between the ictal and interictal activity in source localization. The intracranial recording (ECoG) shows the location of ictal onset zone (green) in the left frontal cortex. The results indicate that the localization of the high-frequency epileptic activity is concordant with the intracranial recording. In the accumulated spectrograms, the y-axis indicates frequency range in 100-1,000 Hz; the x-axis indicates the time window for multiple epochs of data.