Page 179 - MEGIN Book Of Abstracts - 2023

Hospital, Shanghai Jiao Tong University School of Medicine, iEEG electrodes with HMM states based on significant
Shanghai, China; Oxford Centre for Human Brain Activ- correlations was compared to that based on the dis-
ity, University of Oxford, Warneford Hospital, Oxford, UK; tance to peaks in subject-specific state topographies.
Wellcome Centre for Human Neuroimaging, UCL Institute
of Neurology, 12 Queen Square, London WC1N 3BG, UK; RESULTS Five HMM states were inferred from MEG. Two
National Hospital for Neurology and Neurosurgery, Queen of them corresponded to the left and the right tempo-
Square, London, UK; Key Laboratory of Child Development ral activations and had a spectral signature primarily in
and Learning Science of Ministry of Education, School of Bio- the theta/alpha frequency band. All the electrodes had
logical Sciences & Medical Engineering, Southeast University, significant correlations with at least one of the states
Nanjing 210096, Jiangsu, China. Electronic address: luq@ (p < 0.05 uncorrected) and for 27/50 electrodes these
seu.edu.cn; Wellcome Centre for Human Neuroimaging, UCL survived within-subject FDR correction (q < 0.05). These
Institute of Neurology, 12 Queen Square, London WC1N 3BG, correlations peaked in the theta/alpha band. There
UK. Electronic address: [email protected] was a highly significant dependence between the
association of states and electrodes based on func-
BACKGROUND Intracranial electroencephalography tional correlations and that based on spatial proximity
(iEEG) recordings are used for clinical evaluation prior (p = 5.6e[-6,]χ[2] test for independence). Despite the
to surgical resection of the focus of epileptic seizures potentially atypical functional anatomy and physi-
and also provide a window into normal brain function. ological abnormalities related to epilepsy, HMM model
A major difficulty with interpreting iEEG results at the estimated from the patient group was very similar to
group level is inconsistent placement of electrodes that estimated from healthy subjects.
between subjects making it difficult to select contacts
that correspond to the same functional areas. Recent CONCLUSION Epilepsy does not preclude HMM analy-
work using time delay embedded hidden Markov mod- sis of interictal data. The resulting group functional
el (HMM) applied to magnetoencephalography (MEG) states are highly similar to those reported for healthy
resting data revealed a distinct set of brain states with controls. Power changes recorded with iEEG correlate
each state engaging a specific set of cortical regions. with HMM state time courses in the alpha-theta band
Here we use a rare group dataset with simultaneously and the presence of this correlation can be related to
acquired resting iEEG and MEG to test whether there is the spatial location of electrode contacts close to the
correspondence between HMM states and iEEG power individual peaks of the corresponding state topogra-
changes that would allow classifying iEEG contacts into phies. Thus, the hypothesized relation between iEEG
functional clusters. contacts and HMM states exists and HMM could be
further explored as a method for identifying compa-
METHODS Simultaneous MEG-iEEG recordings were rable iEEG channels across subjects for the purposes of
performed at rest on 11 patients with epilepsy whose group analysis.
intracranial electrodes were implanted for pre-surgical
evaluation. Pre-processed MEG sensor data was pro- Keywords: Dynamics, Human, Oscillations, Resting state
jected to source space. Time delay embedded HMM
was then applied to MEG time series. At the same time, NeuroImage (2021), Vol. 233 (33662572) (3 citations)
iEEG time series were analyzed with time-frequency
decomposition to obtain spectral power changes with
time. To relate MEG and iEEG results, correlations were
computed between HMM probability time courses of
state activation and iEEG power time course from the
mid contact pair for each electrode in equally spaced
frequency bins and presented as correlation spectra for
the respective states and iEEG channels. Association of

 ontents  Index 158
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