Y P O Combining tCS and EEG C T O N O D Emiliano Santarnecchi E - Berenson-Allen Center for Non-invasive Brain Stimulation, Department of Cognitive Neurology | Beth S Israel Deaconess Medical Center | Harvard Medical School | Boston, MA, USA A - Center for Complex System study, Engineering and Mathematics Department, University of Siena, Italy E esantarn@bidmc.harvard.edu L P Boston, 31th October 2016
Y Outline P O Measuring tCS effects without EEG • C Measuring effects outside the motor cortex T Measuring focality of tCS interventions O N Basics of EEG • O EEG signal: features and opportunities D Analysis (ERP, Microstates, Source analysis, ...) E Examples of EEG-tCS combination S A Beyond EEG E • L TMS-EEG recording P
Y P O Questions? Comments? Ideas? Feedback? C T O N O D E • Kirsten Building - KS-450 S A • esantarn@bidmc.harvard.edu E L • emilianosantarnecchi@gmail.com P
Y Measuring tCS effects without EEG P O C T O N O D E S A E First evidence of tDCS after effect from Nitsche and Paulus, 2000 L P Changes in cortical excitability assessed using TMS-EMG
Y Corticospinal excitability as an index of Brain excitability P O Applied to tCS: limitation for online recording, only after effects C T O N O D E S A E L P
Y tDCS effect on corticospinal excitability: Online and Offline effects P Santarnecchi et al., 2014 O C T O N O D E S A E L P
Y tDCS effect on Subcortical Structures? P O C T O N O D E S A E L P Modeling based on tractography, structural MRI, CT scans…. Rossi, Santarnecchi 2016, Philos. Trans A
Y tDCS Effects on the motor cortex: pre/during/post P O C Anodal and Cathodal PRE ONLINE POST (30’) tDCS modulate (15’) (15’) T (increase/decrease excitability) right O after the stimulation N respect to Sham. O No significant effects During the D stimulation. E S Still limited A to the motor E cortex! L P
Y Are we stimulating the motor cortex? P O C T O N O D E S Montage, Timing, Stimulation A site, Duration, Intensity, etc. E suggest a complex scenario L underlying tCS effects P Kuo et al., 2013 TMS-EMG is not enough
Multifactorial model Y P O C Brain state T Behavioural scores (electrophysiological O recording - EEG) N Individual trait Electrophysiological ? O …Brain… responses – (personality, cognitive D EEG/ERPs/etc.. profile) E Behavioural performance Genetics Neuroimaging ($$$) (e.g. BDNF) S Physiological measuments (EKG, EDR,..) A Neuroimaging ($$$) EEG/ERPs/??? E fMRI? L P BEFORE DURING AFTER
Y Open questions.. P O • the effect of tCS on Non-Motor regions? C • distant effects and changes in the interplay between regions T (connectivity) Network effects? O N • the Online effects of tCS on brain activity other than O “excitability”? D E S A Useful information to define tCS parameters E and increase efficacy of interventions L P
Y Electroencephalography P O C T O N O Hans Berger D E S A E L P 1934: Fisher and Lowenback first demonstration of epileptiform spikes.
Y Pros and cons of EEG P O C T O N O D E S A E L P
Y Dominant Oscillations for Different brain regions P Beta: movement Alpha: automatic O movements C Gamma: selective attention T O N O Ѳ : working /long-term memory D E S Alpha: visual perception A E L P Θ : spatial orienting
Y Oscillatory pattern in the brain P • Why are oscillatory pattern so important ? O 2 . Hierarchical information processing C 1. Pulse processing T O N O Cyclic Excitability Changes D Rhythmic fluctuations in the local field potential (LFP), synchronous transmembrane currents in E populations of neurons and thus represent cyclic Multiplexing / Cross- S changes in the excitability of local neuronal frequency coupling A populations . • Various aspects of the stimulus are E encoded in different oscillations simultaneously , but at different L Ongoing oscillatory phase significantly modulates the frequencies. P probability of perceiving a near-threshold visual • Efficient coding scheme relying on stimulus. the hierarchical organization of oscillations.
Y Oscillatory pattern in the brain P O C T O N O S. Sternberg , High speed scanning in human memory, Science 153 1966. 652–654. D E Theta-alpha oscillations Gamma-oscillations S A • theta (6Hz) = 6 cycles * second = 1 cycle 0.16 seconds E • gamma (40Hz) = 40 cycles * second = 1 cycle 0.025 seconds L • gamma cycles in each theta cycle = 0,16/0.025 = 6.7 (~7). P
Y Oscillatory pattern and periodicity in behaviour P Canolty, Science 2005 • Why are oscillatory patterns so important? O 3. “Communication-through-coherence” Theory C T O • Communication being facilitated when two N oscillatory populations are aligned to their high excitability phases. O D • Effective communication relies on spikes from the sending population reaching the receiving population E at a phase of high excitability. S • Changes in synchronization between distant brain A areas (possibly reflecting communication) are E systematically related to task performance . L P
Y P O C T O N EEG recording and analysis O D E S A E L P
EEG recording Y P O • International 10-20 system High-Density EEG C • Left side: odd numbers (64-256 Channels) • Right side: even numbers T O • Numbers increase from the hemispheric line towards the edges.. N Letter indicates brain regions (lobes). O D – Fp prefrontal E – F frontal S – C central A – T temporal E – P parietal L – O Occipital P
EEG recording Y P O 1. SPONTENEOUS C • Meaningful data with ~5’ of recording T • Eyes open/closed O 2. EVOCKED N O D E S A E L Well known Evoked Response P Potential (ERP )(P300, N100, ..) TMS-EEG
EEG features Y P O C T O N O D E S A E L P fMRI
Y Time vs Frequency Analysis P O C T O N O D E S A E L P
Y Event-Related Potentials (ERPs) P O C T O N O D E S EEG response to visual stimuli A E L P Example of auditory evoked potentials
Y Event-Related Potentials and Source Analysis P O Attempt to localize cortical/subcortical Sources responsible for the EEG topography of interest. C T O N O D E S A E L P Algorithm-threshold-model dependent….
Y EEG Connectivity analysis P Zhavoronkova et al., 2013 O Traumatic Brain Injury C T O N O D E S A Extract signal for all the electrodes E L P Correlation / coherence / etc
Y EEG Connectivity analysis P O Temporal correlation/synchrony between electrodes pairs, both during resting and evoked activity. C T O N O D E S A E L P
EEG Microstates Y P Khanna et al. 2014 O C T O N O D E S A E L P Sequence of spatially defined Topographies
EEG Microstates Y P O C T O N O D E S A E L P Four major Microstates (explain ~75% variance)
EEG Microstates Y P O C T O N O D EEG Microstates and fMRI Resting-state networks E S A E Significant differences in 1 2 3 4 Alzheimer, Schizophrenia, ADHD L P Synthax analysis
EEG Microstates and Cognition Y P Santarnecchi et al., under revision O C T O N O D E S A E L Microstate Topography changes with P Cognitive Training Microstate Frequency correlates with Abstract Reasoning
Y Advantages of tCS + EEG P O • Understanding the role of brain oscillations in both motor and non- C motor regions , in both the healthy and pathological brain . T O • Measure both local and distant effects. N • Guide tCS intervention on the basis of and online/offline monitoring O of brain states. D E S A How can tCS + EEG be implemented? E L P
Y tCS + EEG approaches P O Resting or Resting or tCS C OFFLINE Event Event (no EEG T related EEG related EEG recording) O N ? Resting or EEG Resting or O ONLINE Event recording Event D related EEG during tCS related EEG E S A ? EEG-Guided, tCS guided Resting or Resting or E closed-loop Event related Event related by EEG L system EEG EEG recording P
Y tCS and EEG: variables P O C T O N O D E S A E L P
Y EEG-Guided tCS: Location P Faria et al., 2012 O C T EEG evaluation of a patient with O Continuous spike-wave N discharges during slow-wave sleep allowed identification of an O epileptogenic focus. D E S Cathodal tDCS over the focus A resulted in a significant decrease in interictal spikes. E L P
Y EEG-Guided tCS: Stimulation Parameters (Frequency, phase,etc.) P Zahele et al., 2012 O Frequency C Individual Alpha frequency T O N O D E S A • tACS on the occipital cortex at individual alpha frequency E • Resting EEG increase in alpha in parieto-central electrodes, no effects on L surrounding frequencies P
Y EEG-Guided tCS: Stimulation Parameters (Frequency, phase,etc.) P Vossen et al., 2015 O Frequency C Individual Alpha frequency T O N O D E S A E L P
Y EEG-Guided tCS: Stimulation Parameters (Frequency, phase,etc.) P Neuling et al., 2012 O Phase C T O N O D E S A E L P
Y P O C T O N O D E S A E L P
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