EEG signal background and real-time processing

EEG signal background and real-time processing

Robert Oostenveld

r.oostenveld@donders.ru.nl

Donders Institute, Radboud University, Nijmegen, NL

Karolinska Institute, Stockholm, SE

Outline

Brain activity and how to measure it

The source of EEG signals

Controlling alpha oscillations

Realtime processing and closed-loop systems

Brain activity

spiking activity

(local) field potentials

magnetic fields

blood flow

blood oxigenation

biochemical concentrations

Methods to record brain activity

(sharp-tipped electrodes)

multi electrode array (c.f. Utah array)

sEEG multitrodes

ECoG surface electrodes

(voltage sensitive dyes)

scalp EEG

MEG

NIRS

arterial spin labeling

BOLD

MRS

EEG Instrumentation

Recording EEG

Outline

Brain activity and how to measure it

The source of EEG signals

Controlling alpha oscillations

Realtime processing and closed-loop systems

pre-synapticaction potential

post-synapticpotential

electric current

Superposition of source activity

Standard electrode placement

High-density electrode placement

Outline

Brain activity and how to measure it

The source of EEG signals

Controlling alpha oscillations – and others

Realtime processing and closed-loop systems

Adapted from Jensen & Mazaheri (2010) Frontiers Neurosci.

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Adapted from Jensen & Mazaheri (2010) Frontiers Neurosci.

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b

c

Adapted from Jensen & Mazaheri (2010) Frontiers Neurosci.

a

b

c

High alpha = inattention

Low alpha = attending

Other brain signals used in EEG-BCI

pay attention to one feature, ignore others

SSVEP – steady state visual evoked potential

P300 – positivity around 300 ms after stimulus

imagine movements

Mu rhythm – mix of 10 and 20 Hz over sensory-motor regions

Outline

Brain activity and how to measure it

The source of EEG signals

Controlling alpha oscillations

Realtime processing and closed-loop systems

Conventional experiment

M/EEG, fMRI,...data source

analysis

stimuluspresentation hard disk

hard disk

collect many data from many subjects, analyse later

Realtime experiment / BCI loop

• Challenge: timely handling of incoming data, preprocessing, analysis, sending outputs

M/EEG, fMRI,...data source

preprocessingfeature extract.

analysis

stimuluspresentation

Buffering relaxes timing constraints...

• analysis side can pick data when convenient

• can look back in time if needed

M/EEG, fMRI,...data source

analysissoftware

stimuluspresentation

datastream or

ringbuffer

... and facilitates talking to different devices more easily

MEG: CTF,Neuromag

fMRI:Siemens

EEG: TMSI, Biosemi, OpenBCI

NIRS:Artinis

analysissoftware

FieldTripbuffer

ECoG:Neuralynx,Micromed

Multiple applications for analysis etc.

applications can communicate through buffer („events“)

FieldTripbuffer

analysissoftware

analysissoftware

otherplatforms

onlinedisplay

MEG: CTF,Neuromag

fMRI:Siemens

EEG: TMSI, Biosemi, OpenBCI

NIRS:Artinis

ECoG:Neuralynx,Micromed

Extends naturally to pipelines

EEG system

„raw“EEGdata

translate into control signals

filter & re-reference

„clean“EEG data

monitor data qualitye.g. drift

loose electrodes

Concepts of pipeline sequence

artifactdetection

spectral estimation

classificationor regression

rawdata

“control” signal

many numbers few numbers

amplifier analysis computer

storage

Controlled device

Experimental controlTherapeutic operator

Subject

data

feedback signal

EE

G

co

ntro

l sig

na

l

da

taOptimization

Behavior, analysis and control signals

In green the basic minimal BCI setup.

In pink the additional feedback signal for a neurofeedback system.

In orange the registration and storage of all data to reconstruct and analyze the neurofeedback system.

In yellow the optimization of the analysis and/or control.

In red the control of the experimentor or therapist.

co

ntr

ol fe

ed

back

Pyt

ho

nm

od

ule

s

Red

is

FieldTrip buffer

USBCV/gate

webserver

USB-MIDI interface

OpenBCIinterface

audience/subjectartist/performer

scientist/engineer