Y P O Transcranial Alternating Current Stimulation - tACS C T O N O Emiliano Santarnecchi D - Berenson-Allen Center for Non-invasive Brain Stimulation, Department of Cognitive Neurology | Beth E Israel Deaconess Medical Center | Harvard Medical School | Boston, MA, USA S - Center for Complex System study, Engineering and Mathematics Department, University of Siena, Italy A E esantarn@bidmc.harvard.edu L P Boston, 31th October 2016
Y A growing field P O “tACS allows to modulate brain oscillations in a frequency specific manner” C T O TMS: Transcranial Magnetic Stimulation N O tDCS: transcranial Direct D Current Stimulation E tACS: transcranial Alternate S Current Stimulation A tRNS: transcranial Random E Noise Stimulation L P Santarnecchi et al. 2015 Curr Opin Behav Sci * PubMed Search : “Transcranial magnetic Stimulation”, “Transcranial Direct Current Stimulation”, Transcranial Alternating Current Stimulation”
Y Outline P O • Oscillatory pattern and synchronicity in the brain C tACS - Mechanism of action T tACS evidence • O N Perception (Hands-On session tomorrow) Cortico-spinal excitability and motor system O D Cognition E Phase-Related activity S State and Trait – dependency A E Therapeutic potential L • Future Directions P
Y P O Questions? Comments? Ideas? Feedback? C T O N O D E S • Kirsten Building - KS-450 A E • esantarn@bidmc.harvard.edu L P
Y Disclosure P O Emiliano Santarnecchi serves as consultant for EBNeuro , a joint stock company C developing biomedical devices for neurostimulation, neuromodulation and T electroencephalography. O N He has no actual or potential conflict of interest in relation to this presentation, O none of the tools presented in the following slides are property of EBNeuro. D E S A E L P
Y P O • Experience with EEG/Brain Oscillations? C T O N O D • Experience with tACS? E S A E L P
Y tCS techniques P O C T O N O D E S A E L P Santarnecchi et al. 2015 Curr Opin Behav Sci
Y P O C T O N Why tACS? O D E S A E L P
Y Brain oscillations 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 and periodicity in behaviour P O Phase ? Cyclic patterns in behaviour C T O N Sleep–wake cycles are evident even if external O light conditions are held constant (grey shade) D Phase, angles, degrees….. Intrinsic oscillators (circadian clocks) which cause Oscillators are in opposite E periodicity in bodily function phase (anti-phase) S A Frequency? E Number of cycles x second L (1 cycle * second=1Hz) P 2Hz 10Hz
Y “Entrainment” phenomenon P • Are these oscillatory patterns immutable? O C T O N O D E Entrainment of endogenous oscillatory pattern Changes in behaviour S • Oscillatory cycle establishes a recurrent temporal reference frame that allows for the A coding of temporal relations between groups of neural elements E • This reference frame is not fixed but is subject to dynamic changes (phase resetting), L especially in pathological states . P tACS induces entrainment of brain oscillations following the same principle (theta, alpha, beta, gamma, ..) Tuth et al. 2012, Current Biology
Y Mechanism of action P O DC Stimulation AC Stimulation C Constant Oscillating T Fields Fields Synchrony Effect O N E O Membrane Network D Polarization Synchrony E Amplify S the Output Spike Rate A Spike Phase Synchronize E Change Change the I nput L P
tACS effect Y P O C T O N O D E S A E L P
Y P O C T O N Why tACS? (2) O D E S A E L P
Y EEG Oscillations and BEHAVIOURAL CORRELATES P O Sleep, learning, motivational processing C T O Memory, emotional regulation, creativity N O Active inhibition of task- D irrelevant areas E S A Mainly Motor activity E L P Abstract mental activity, cognitive control, perceptual binding
Y EEG Oscillations and PATHOLOGY P O • Reduced synchrony in Schizophrenia • Reduced amplitude in Alzheimer C • Increased Amplitude in Bipolar dis. T O • Reduced synchrony in Schizophrenia • Reduced synchrony in Alzheimer N O • Reduced coherence in Alzheimer D • Increased phase-locking at Frontal and Central electrodes in Schizophrenia E S • Reduced Coherence in Alzheimer and Schizophrenia A • Increased amplitude in Parkinson E • Increased Coherence in Bipolar dis. L • Decreased/increased amplitude in P Schizophrenia (?) • Increased Phase-locked response in ADHD
Y P O Frequency-specific effects? C T O N O D E S A E L P
Y P O C T O N tACS: experimental evidence O D E S A E L P
tACS effect on brain oscillations: in vitro evidence Y P O C T tACS might shift intrinsic O dominant oscillations and N “tune the system” O D E S Higher stimulation frequency A E L P
Y First animal evidence P Ozen et al., 2010 • tACS induce AC Fields in the Brain O C Rat (in-vivo) T O N O D 0.8-1.7Hz • Effect of Stimulation Amplitude • AC fields can phase-locked spiking activity E Homogenous Phase Larger Amplitude S More Neurons A E L P
Y Endogenous Resonance Principle P Ozen et al., 2010 O tACS induced Synaptic mediated C Oscillations Oscillations Push & pull T O Coherent I ncoherent N cooperate or compete Exploring O S =sleep Sleep D R =rest tACS ~ 1.5Hz E =exploration E S A Phase-locked E (25-50% ) L P No Phase-locked
Y tACS and Phosphene P Kanai et al., 2008 Rationale O C alpha T O beta gamma N Eye Open/Closed Alpha (Adrian, 1934) O What is frequency sensitivity of tACS evoked Visual Sensation? D tACS Frequency Phosphene Threshold E S Design A E Electrodes Inion (+ 4cm) - Vertex L Current 0-40Hz, 0-1mA, 5s each P Subjects 8 Healthy
Y tACS and Phosphene: frequency specific effects P Kanai et al., 2008 O Results C T O N O D E S A • Occipital tACS can evoke phosphene perception E • Greater stimulation at alpha band (dark) and beta band (light) L P
Y P O C T O tACS and Cortico-spinal N O Excitability D E S A E L P
Y tACS and Corticospinal Excitability Mot ot or or Mod odalit y P Feurra et al., 2011 Journal of Neuroscience O Question • C Are beta oscillations in motor cortex functional or epiphenomenon? T Amplitude of TMS induced MEP* tACS over M1 O N Design O 10xTMS 10xTMS 10xTMS 10xTMS 10xTMS 10xTMS 10xTMS D tACS E S A Electrodes C4 (TMS hot-spot) + P4 (control) – Pz E Current 5, 10, 20, 40Hz, 0.5mA* , 90s L Subjects 15 Healthy P * Kept below phosphene or skin sensation threshold. * MEP- Motor Evoked Potential ,indicating the strength of the corticospinal response
Y tACS and Corticospinal Excitability P Feurra et al., 2011 Journal of Neuroscience Results O C MEP Amplitude (µV) T O N O D E S A E • Parietal tACS @ 20HZ specifically increases MEP amplitude L P
Y P O C T O tACS and Motor performance N O D E S A E L P Institute of Biomedical Engineering Division of neuroscience
Y tACS and Motor performance P Santarnecchi et al., under revision O Question C • Are Gamma oscillations in motor cortex functional or epiphenomenon? T O Muthukumaraswamy 2010 N • Tracking task using MEG O • Observed an Increase in D Gamma activity (~90HZ) in E the motor cortex during movement. S A E • What does Gamma L oscillations in the motor P cortex represent..?
Y tACS and Motor performance - II P Santarnecchi et al., under revision O Question C • Are Gamma oscillations in motor cortex functional or epiphenomenon? T Visuomotor task + 10, 20, 60, 80Hz and O Sham tACS on the motor cortex. N Effects on several components of the motor program: Acceleration, Pursuit, Loops, Turns, etc.. O (o) D High spatial and temporal resolution analyses. E S A E L P
Y tACS and Motor performance - II P O C 60Hz 80Hz • Significant enhancement of performance during T TURNS during Gamma O tACS (80Hz) , with a trending result for 60Hz N tACS. O • Effect is present in a D specific time window (200-700ms after each E TURN) , coherently with S MEG studies showing increase in EEG power at A 90HZ during a similar task. E • No effects during Loop, L Acceleration, Pursuit P
Y tACS and Motor performance P Pogosyan et al., 2009 O Question C • Are beta oscillations in motor cortex functional or epiphenomenon? T Visuomotor Task + 20Hz tACS/Sham Reaction time + EEG-EMG O N Design O D E S A E Electrodes C4 (TMS hot-spot) – P3 L Current 20Hz, 0.6mA* , -2s to +8s P Subjects 14 Healthy * Kept below phosphene or skin sensation threshold.
Y tACS and Motor performance P Pogosyan et al., 2009 Results O C EEG-EMG Coherence I nitial Velocity sham= active T O active N sham O D E S A E • Parietal 20Hz tACS slowed initial velocity L (small effect) P • Parietal 20Hz tACS increased somatosensory- arm 20Hz coherence
Y P O C T O tACS and Cognition N O D E S A E L P Institute of Biomedical Engineering Division of neuroscience
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