Presentation is loading. Please wait.

Presentation is loading. Please wait.

Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain.

Similar presentations


Presentation on theme: "Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain."— Presentation transcript:

1 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Introduction to the methodology of EEG recording Emmanuelle Tognoli The Human Brain and Behavior Center For Complex Systems and Brain Sciences Florida Atlantic University

2 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Summary A. Generators and modulators of EEG signal B. Understanding instrumentation C. Main ethical issues D. Physiological and electronical sources of noise E. Constraints for experimental protocols in EEG F. Configuration of EEG recording system and selection of montage G. Management of connectics H. Paste-up and problem solving during the recording session I. Digitization J. Cleaning/decontamination of sensitive equipment / equipment maintenance

3 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences A. Generators and modulators of EEG signal

4 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Generators of EEG signal When reached by an input, the presynaptic neuron: –Releases some neurotransmitter in the synaptic cleft The dendritic process of the post-synaptic neuron: –shows a local change in its membrane’s permeability –generates a primary (intracellular) current from the locus of the synapse to the soma –Generates a secondary/return extracellular current to close the loop

5 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Generators of EEG signal Cortical pyramidal neurons, arranged in layers –The movement of the ions is creating an open field (no cancellation) When a local community of tens of thousands of neurons are activated simultaneously by some input, a signal can be detected as far as at the surface of the scalp This signal is EXTREMELY tiny, and requires many precautions when measured

6 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Generators of EEG signal And the miracle occurs

7 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Modulators Age –Children: Changes in frequency content due to the size of the loops in the anatomical networks Changes in the conduction time due to myelinization Change in the amplitude of the signal due to myelinization –Adult Increased variability over 40 Vigilance –Chronopsychology (more details next) –Drugs –Caffeine Body temperature Hormonal cycles (women) Laterality

8 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Modulators Circadian rhythms –Global power is maximal during the afternoon –Theta power has two peaks at 4pm and midnight –Induced alpha is maximal in the afternoon –Beta is maximal between 5pm and 7pm The modulation is dependent on the location of the electrodes

9 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences B. Understanding instrumentation

10 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Overview Junction skin-electrode Analog conduction Differential amplifiers ADC Integration of triggers Transfer to the CPU / storage

11 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Transduction The living tissues contain free ions The wire is conveying electrons The transfer of the signal from one material to the other requires a chemical transformation Oxidation or reduction (AC)

12 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Transduction Eg. Ag / AgCl electrode: –OXIDATION wire electrodeconductive gelIf an electron moves from the wire to the electrode toward the conductive gel: –It reacts with AgCl »e - AgClAgCl - »e - + AgCl -> Ag + Cl - –Cl - becomes hydrated and enters the conductive paste –REDUCTION If ion moves from the conductive gel to the electrode: –It reacts with solid Ag »AgCl - e - AgCl »Ag + Cl - -> e - + AgCl –AgCl becomes insoluble –one electron is liberated to the wire REVERSIBLEe- e-

13 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Transduction Eg. Ag / AgCl electrode: The Ag/AgCl electrode is non- polarizable (or minimally polarizable) POLARIZATION –The anion (Cation) is unable to move freely across the gel/electrode border –The concentration of ions at the border is altered. –Ions concentrate over the border with the electrode and create a steady potential (bi-layer, capacitance) –This steady potential hampers the movement of the charges This is important since the biopotential we intend to measure is in the range of 1/1000 of the half-cell potential (local potential at the junction between the conductive paste and the electrode)

14 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Analog conduction As soon as the potentials are digital, they are immune to noise (not to deletion) Between the cap and the ADC, the minuscule currents are traveling through the cables and in the amplifier. –Contamination through movements of the cables –Contamination by cross-talk inside the amplifier and at the multiplexer of the ADC

15 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Differential amplification We amplified to push the deflection of the pens (mechanical) We amplify to bring the signal in the range of the ADC (usually 0-1 to 0-5 V)

16 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Differential amplification Principle of differential amplification: the CMR –(Signal + noise) – (noise) Take a scalp electrode (say F3) and a fixed point (GND) Measure one potential difference Take a reference electrode (say M1) and a fixed point Measure a second potential difference (Signal + noise) – (noise) = “a very clean” signal

17 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Differential amplification The ability of the amplifier to reject the common mode noise is called the CMRR

18 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Differential amplification Amplifier Input impedance –Separate the differential input with a high resistance

19 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Analog-to-Digital Conversion Sampling frequency: Nyquist and aliasing

20 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Analog-to-Digital Conversion Sampling frequency ADC range Quantization

21 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Acquisition and storage Data acquisition and storage –Reasonable sampling rate –Backup

22 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Understanding instrumentation Quikcap Headbox Power unit System unit

23 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences C. Main ethical issues

24 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Electrical safety Security for the subject and security for the equipment –Faulty connections –Additional devices (response pads, sensors) –Ground loops –Static discharges –Chassis leakage –EMI in crossing wires Isolation amplifiers (Neuroscan system) are regulated by IEC specifications. Additional devices connected to Neuroscan have to be detailed in the application to the EEG committee Order to plug or unplug the components

25 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Infection risk Most of the supplies, especially those in contact with the subject (eg. needles), are disposable Any supply in contact with the subject does not return to the main. NEVER –eg. the gel is sampled in a cup. Do NEVER refill a syringe in the main container. Moderate skin preparation: a subject should never be bleeding as a result of skin preparation. –Inspection for the presence of blood after experiment (to choose the decontamination procedure) Decontamination of non-disposable equipment Is regulated by [American Electroencephalographic Society. Report of the Committee on Infectious Diseases. J Clin Neurophysiol 1994;11: ].

26 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Infection risk Object & Classification Use of ItemDecontamination required after cleaning CriticalEnters vascular system or sterile body tissues Sterilization and holding in sterilized state. High level disinfection is not sufficient Semi-CriticalComes in contact with non-intact skin or intact mucous membranes High level disinfection (by heat or chemicals) Non-CriticalComes in contact with intact skin Intermediate or low level disinfection Spaulding's classification of devices/medical instruments

27 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences D. Physiological and electronical sources of noise

28 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Interferences Physiological artifact –Ocular domain –Muscular domain –EKG –Respiratory –Movement –EDR/sweating Subjects’ instruction and online monitoring Instrumental noise –EMI : wireless or line noise (60 Hz) –Sway of the cable –Electrodes poorly attached (pop) –Electrode noise –Amplifier noise –Flicker noise (DC recordings!) –Amplifier blocking Shielding and guarding

29 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Interferences Artifacts from the ocular domain

30 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Interferences With proper alignment of EOG electrodes, horizontal EOG do not pick up the signal from vertical eye movements 1 s GOODBAD

31 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Interferences Saccade / eye movements 1 s

32 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Interferences Muscles

33 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Interferences How life could be easy without muscles

34 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Interferences (and with enough time to average thousands)

35 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Interferences –EKG

36 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Interferences –Respiratory

37 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Interferences –Movement

38 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Interferences –EDR/sweating

39 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Interferences Physiological artifact –Ocular domain –Muscular domain –EKG –Respiratory –Movement –EDR/sweating Subjects’ instruction and online monitoring Instrumental noise –Flicker noise (DC recordings!) –EMI : wireless or line noise –electrode noise –amplifier noise –Sway of the cable –Electrodes poorly attached (pop) –Amplifier blocking Shielding and guarding

40 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Interferences A cell phone

41 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Interferences Poor contact / Electrode pop

42 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Interferences 60 Hz

43 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences E. Constraints for experimental protocols in EEG

44 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Protocols Paradigms –Evoked response –Steady-state paradigms A single source of variation between conditions “All other things being equal” A good Stimulation/recording coupling “time accuracy in analog and digital stimuli/triggers” Subject screening –Day-before instruction –Accepting or rejecting a volunteer –artifacts instruction, task instructions, –Online monitoring of data quality and management of breaks

45 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences F. Configuration of EEG recording system and selection of montage

46 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Configuration Configuration of data recorder (scan-acquire mode) –Sampling frequency –DC/AC recording (DC and EDR resident on the skin; DC and choice of electrodes) –Triggers Selection of montage –Only referential recording –Reference electrodes –Ground electrode Ancillary recording (EOG, surface EMG, EKG)

47 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Montage 10 percent

48 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Montage equidistant (eg. EGI)

49 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Montage 128 NSL

50 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Montage reference Choice of the reference electrode –Cephalic/non cephalic –Well-attached –Single electrode or pair of electrode –Pair physically or digitally linked Position of the ground –In midline for ERL Remontage

51 Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Next session: practical session G. Management of connectics H. Paste-up and problem solving during the recording session I. Digitization J. Cleaning/decontamination of sensitive equipment / equipment maintenance


Download ppt "Human Brain and Behavior Laboratory Center for Complex Systems and Brain Sciences Human Brain and Behavior Laboratory Center for Complex Systems and Brain."

Similar presentations


Ads by Google