2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 1 Developmentof ComplexCurriculaforMolecularBionicsand InfobionicsProgramswithina consortial* framework** Consortiumleader PETER PAZMANY CATHOLIC UNIVERSITY Consortiummembers SEMMELWEIS UNIVERSITY, DIALOG CAMPUS PUBLISHER The Project has beenrealisedwiththesupportof theEuropean Union and has beenco-financedbytheEuropean SocialFund*** **Molekuláris bionika és Infobionika Szakok tananyagának komplex fejlesztése konzorciumi keretben ***A projekt az Európai Unió támogatásával, az Európai Szociális Alap társfinanszírozásával valósul meg. PETER PAZMANY CATHOLIC UNIVERSITY SEMMELWEIS UNIVERSITY sote_logo.jpg dk_fejlec.gif INFOBLOKK 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 2 Peter Pazmany Catholic University Faculty of Information Technology ELECTROPHYSIOLOGICAL METHODS OF THE STUDY OF THE NERVOUS-AND MUSCULAR SYSTEM LECTURE 5 PROPERTIES AND CHARACTERISTICS OF ELECTRODES (Elektródok tulajdonságai, jellemzői) www.itk.ppke.hu Az ideg-és izomrendszer elektrofiziológiai vizsgálómódszerei DOMONKOS HORVÁTH, GYÖRGY KARMOS Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes BIOPOTENTIAL RECORDINGS Biopotential recording: connection between recording object (inanimate) and living structure Recording object: electrode, i. e. electron conductor or complex of an electron conductor and an electrolyte In an electron conductor, charge is conducted by electron movement In an electrolyte, charge is conducted by charged particle (ion) movement In a recording, always at least two electrodes is used because always potential difference between two electrodes is measured Electrode potential: potential energy measured on an electrode. Only theoretical definition, this is a potential compared to an arbitrary zero electrode potential, the potential of a standard hydrogen electrode 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 3 Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes GENERAL PROPERTIES OF RECORDING ELECTRODES Ideal electrode does not exist: electrodes cannot have ideal signal transmission characteristics. Living tissue is a chemically aggressive medium for electrodes: there is always a chemical reaction between the electrode and the tissue Electrode impedance: many contributing factors, including electrode material, electrolyte type, etc. Electrode potential: when electrode is placed in a conducting solution a potential difference can be measured between the electrode and the bulk of the solution Electrode stability, biocompatibility: on the one hand, electrodes have to withstand the chemically aggressive living tissue, on the other hand, electrode-caused harm to the living tissue has to minimized 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 4 Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes REPLACEMENT DIAGRAM OF ELECTRODE IMPEDANCE • Rs: electrode paste resistance • Rf: electrode resistance • C: electrode capacitance • : Wartburg resistance –frequency dependent • C0: stray capacitance 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 5 electimp.JPG W Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes TYPES OF BIOPOTENTIAL RECORDING Bipolar recording: Both electrodes are in active tissue. Signal of an active electrode is compared to a neighboring active electrode as zero potential. Unipolar recording: there is an indifferent electrode in inactive tissue as a zero potential electrode. The signal of active electrode is compared to this zero potential. 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 6 bipolar_unipolar A: Bipolar recordingB: Unipolar recording Source: http://www-psych.nmsu.edu/~jkroger/lab/principles.html Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes REPLACEMENT DIAGRAM OF BIPOLAR RECORDING 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 7 e: Biological signal(V)e1ande2: Electrode potentials (V) RH: Scalp resistanceR1andR2: Electrode resistances CH: Scalp capacitanceC1, C2: Electrode capacitances P: Amplifier elvhelyett.JPG Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes REPLACEMENT DIAGRAM OF MICROELECTRODE RECORDING 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 8 Z: electrode tip impedanceCg: connection capacitance Cg(E): electrode-ground capacitanceRa: amplifier input impedance Cg(W): wire-ground capacitanceR0: amplifier output impedance Cg(A): amplifier input-ground capacitance The above figures show how many different factors can contribute to signal distortion measured on an electrode. Capacitive factors make changes frequency dependent while input and output impedance mismatch influence signal amplitude. elvhely2.JPG Source: Thompson R, Patterson M, (1973): Bioelectric Recording Techniques: Cellular Processes and Brain Potentials, p. 140, Academic Press, New York Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes ELECTRODE POTENTIAL At a metal-liquid junction ion movement develops that forms polarization. As a result of ion movement between metal and solution balance sets up between the two mediums. This forms the electrode-electrolyte double layer. 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 9 elektrkettosreteg.jpg Forming of double layer: (a) ions enter the solution after immersion of metal (b) number of ions increase in solution (c) in the metal electrode negative potential develops, ion flow out of and into the metal have different amount (d) balance sets up when the two flows are equal. Accumulated positive ions in solution form double layer. Source: Cooper R, OsseltonJW, Shaw JC(1969): EEG Technology, 2nd ed., p. 21, Butterworths, London Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes EFFECTS OF ELECTRODE POTENTIAL • Different metals and solutions have different impedance values due to different ion movement between them. • Some examples for impedance:• Copper: 1.7µ.cm • 3M KCl: 5.cm • Seawater: 22.cm • Physiological solution: 70.cm • Tap water: 0.2-10.cm • Distilled water: 1-5M.cm • Impedances of axonicparts:• Membrane impedance: 10-100k.cm2 • Membrane capacitance: 0.5-1m.cm2 • Intracellular medium impedance: 50-200.cm 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 10 Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes GALVANIC CELL FORMED BY METAL-LIQUID-METAL JUNCTION 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 11 The galvanic cell formed by the metal-liquid-metal junction follows the electrochemical series. Electrode potential is compared to an arbitrary zero electrode potential, the standard hydrogen electrode potential. The electrochemical series shows potential differences of different metal electrodes compared to standard hydrogen electrode potential. Metals with positive electrode potential are called precious metals. In comparison of two metals the more positive is called the more precious of the two. electrochem.jpg Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes IMPORTANCE OF METAL-LIQUID JUNCTION CHARACTERISTICS: SIGNAL TRANSFER CHARACTERISTICS OF ELECTRODES 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 12 According to the electrochemical series every electrode polarizes differently when immersed into a solution. This polarization determines the signal transfer characteristics of the electrode. Note high fidelity transfer of silver/silver chloride electrode due to its lack of polarization. Other types of metal electrodes distort signal severely. Input waveform: Non polarizableelectrode (Ag/AgCl): Metal electrode: 1 s Source: Cooper R, Osselton JW, Shaw JC (1969): EEG Technology, 2nd ed., p. 27, Butterworths, London Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes FREQUENCY DEPENDENCE OF ELECTRODE IMPEDANCE Electrode impedance changes with frequency due to capacitive properties of electrode-electrolyte double layer. At low frequencies electrode impedance rapidly increases with decrease of frequency. This can distort low-frequency recordings such as EEG recordings. 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 13 freqimp_ed Source: Cooper R, Osselton JW, Shaw JC (1969): EEG Technology, 2nd ed., p. 28, Butterworths, London Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes PROPERTIES OF ELECTRODE-GEL-SKIN JUNCTION In order to improve recordingcharacteristics conductive gel used between electrode and skin. This gel helps forming and contributes to stability of double layer as shown on figure. 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 14 electplusconductgel_ed Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes ELECTRODE TYPES USED FOR BIOPOTENTIAL RECORDINGS Intracellular• Micropipette• Sharp microelectrode • Patch-clamp electrode Extracellular• Micropipette • Single microwire • Tetrodeand multielectrodemicrowire • Silicon-based multielectrodes Macropotential• Surface recordings• Silver/Silver chloride electrode • Intracerebralrecordings• Metal microwire • Multielectrode • Needle electrode 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 15 Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes TYPES OF BIOPOTENTIAL RECORDINGS For every purpose different types of electrode needed. Electrodes can be placed on the scalp, on or under the dura mater surface, or even implanted into the living tissue, depending on the desired type of signal. 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 16 E:\phd\tamop\eegmodes.jpg Place of recording Recorded signal Area of recording surface Signal amplitude Source: Thompson R, Patterson M, (1973): Bioelectric Recording Techniques: Cellular Processes and Brain Potentials, p. 140, Academic Press, New York Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes TYPES OF SILVER/SILVER CHLORIDE SCALP ELECTRODES There are two types of silver-silver chloride scalp electrodes: reusable and single-use. Reusable electrodes have a cavity under the silver/silver chloride-cup for conductive gel and a refill opening to refill gel. 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 17 agagcl.jpg Reusable electrode Single-use electrode Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes TYPES OF CONVENTIONAL EEG ELECTRODES • Electrode pad (a) • Subdermalneedle electrode (b) • Gold disc electrode (d) • Chloridedsilver wire in plastic cup (c,e) • Silver/silver chloride cup (f) 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 18 Source: Cooper R, Osselton JW, Shaw JC (1969): EEG Technology, 2nd ed., Plate II, Butterworths, London Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes TYPES OF EEG ELECTRODE NETS In order to gain more information from a recording more electrodes are used at the same time: electrode nets are built. Two basic types: 1.Electro-cap • Allows skin preparation • Application in 30 minutes • Used with most EEG amplifiers • Disinfection (glutaraldehyde) 2.Geodesic sensor net • Does not allow skin preparation • Application in about 5 minutes • High input-impedance amplifiers • No infection risk 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 19 BrainCap sensor02 Source: http://www.brainproducts.com/productdetails.php?id=9 Source: http://www.miyuki-net.co.jp/jp/seminar/sensornet/sensor03.htm Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes INTRAOPERATIVE ELECTROCORTICOGRAPHY • Intraoperative monitoring is of high importance: gives valuable information for neurosurgeon during operation about the function of different brain areas • Electrodes placed not on scalp but right onto cortical surface, this is why these recordings are called electrocorticographical (ECoG) recordings • Traditionally, this was performed by cotton wick electrodes soaked in sterile saline. The electrodes were placed on the cortical surface and held in place by a metal halo attached to the surgical table • Modern intraoperative ECoG recordings are performed by subdural grids moved from place to place during surgery 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 20 Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes INTRAOPERATIVE ELECTROCORTICOGRAPHY 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 21 dixi_electrode-corticale8 Electrode grid for electrocorticography Electrode grid during brain surgery Source: http://www.diximedical.net/GB/?cat=27 Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes RECORDING TECHNIQUES USED IN ANIMAL EXPERIMENTS • Animal experiments allow researchers to study brain functions in detail and in arbitrary experimental situations • Both surface (for macropotentialrecordings) and implanted electrodes (for extracellular recordings) are used • Implanted electrodes are placed into the brain • Proper position for implanted electrode determined by brain atlas coordinates • Stereotaxic technique: electrode placement in a coordinate system, coordinates based on brain atlas • Stereotaxic apparatus: frame attached around animal’s head to keep head stable and measure coordinates relative to markers on head 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 22 Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes USE OF STEREOTAXIC BRAIN ATLAS A brain atlas contains cell and fiber stained brain sections as well as schematic figures based on these sections. Sections are made in all three dimensions: • Coronal: along front-rear (rostral-caudal) axis • Sagittal: along centre-side (medial-lateral) axis • Horizontal: along top-down (dorsal-ventral) axis Coordinates inratsare given according to marker points on the skull: bregma, lambda and interauralaxis. Scale bars along the sections show appropriate coordinates for shown structures. With help of a stereotaxic brain atlas an experimenter can precisely determine the desired electrode position. 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 23 Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes CHRONICALLY IMPLANTED ELECTRODES • Electrodes implanted during an operation similar to the one seen above are usually implanted chronically. This means that the animal recovers from the operation with the implanted electrodes fixed to its skull. After recovery multiple recording sessions can be performed with this animal. • The chronically implanted electrode types are usually thin enamelinsulatedtissuefriendlymetal wiresor multielectrodes. The electrode is insulated in all cases. • Metal wire electrodes are easy to fabricate, cause relatively little harm to brain tissue and provide stable recordings for long time. • Multielectrodeshave more recording sites, allowing recordings from more brain areas simultaneously. • However, to maintain stable long time recordings electrode position must be refined periodically. Electrode can move from the desired position either during implantation because of bending of the thin wire in brain tissue or due to brain movement caused by head movement of the freelymoving animal. 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 24 Electrophysiological Methods of the Study of the Nervous-and Muscular System: Propertiesand Characteristicsof Electrodes STEREOTAXIC APPARATUS FOR CATS AND MONKEYS 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 25 101-0103_IMG Ear bar Stereotaxic frame Electrode holder Electrode manipulator Eye bar KOPF MODEL 1404 Electrophysiological Methods of the Study of the Nervous-and Muscular System: Propertiesand Characteristicsof Electrodes 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 26 SMALL ANIMALSTEREOTAXIC INSTRUMENT Electrode manipulator Stereotaxic frame Ear bar Electrode holder nose and tooth bar assembly KOPFMODEL 902 Electrophysiological Methods of the Study of the Nervous-and Muscular System: Propertiesand Characteristicsof Electrodes 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 27 RATSKULLINTHESTEREOTAXICFRAME The three coordinates are indicated: A-P.: front -rear direction Lat.: medial -lateral direction Vert.: dorsal -ventral direction Electrophysiological Methods of the Study of the Nervous-and Muscular System: Propertiesand Characteristicsof Electrodes 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 28 STEREOTAXICCOORDINATES Two pages of the stereotaxic atlas. Left the histological section, right the map of the structures with the coordinates. Paxinos, G., Watson, C., The RatBraininStereotaxicCoordinates 6thed., AcademicPress,2009. Electrophysiological Methods of the Study of the Nervous-and Muscular System: Propertiesand Characteristicsof Electrodes 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 29 ANESTHETIZED RAT FIXED IN THE STEREOTAXIC FRAME The head is fixed by the ear bars and the nose and tooth bar assembly. Electrophysiological Methods of the Study of the Nervous-and Muscular System: Propertiesand Characteristicsof Electrodes 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 30 STEREOTAXICELECTRODEIMPLANTATION1 Holesintheskullaremade bya drill fixed inthestereotaxicmanipulator. Electrophysiological Methods of the Study of the Nervous-and Muscular System: Propertiesand Characteristicsof Electrodes 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 31 STEREOTAXICELECTRODEIMPLANTATION2 Three pairs of twisted wire electrodes arefixed in the electrode holder. The enamel insulation isremoved from the tip of the wires (right). At the other end of thewiresfemale connectors are crimped (left). Drops of adhesive are used to fix the twisted wires. Electrophysiological Methods of the Study of the Nervous-and Muscular System: Propertiesand Characteristicsof Electrodes STEREOTAXICELECTRODEIMPLANTATION3 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 32 G:\My Documents\My Pictures\2011patkányműtét\Anna\DSCF6898c.jpg Threepairs of electrodes are inserted into the brain according to the stereotaxic coordinates. Electrophysiological Methods of the Study of the Nervous-and Muscular System: Propertiesand Characteristicsof Electrodes 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 33 STEREOTAXICELECTRODEIMPLANTATION4 The electrodes are fixed to the skull by light curing dental adhesive. Electrophysiological Methods of the Study of the Nervous-and Muscular System: Propertiesand Characteristicsof Electrodes STEREOTAXICELECTRODEIMPLANTATION5 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 34 Sevenpairsof electrodesareimplantedand fixed totheskull. Electrophysiological Methods of the Study of the Nervous-and Muscular System: Propertiesand Characteristicsof Electrodes STEREOTAXICELECTRODEIMPLANTATION6 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 35 The miniature connectors were inserted into the body of the connector and the wholeimplant are fixed to the skull by dental acrylic. Finally the wound is closed by sutures. Electrophysiological Methods of the Study of the Nervous-and Muscular System: Propertiesand Characteristicsof Electrodes STEREOTAXICELECTRODEIMPLANTATION7 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 36 Next day after the implantation the rat is welland readyforthebehavioralexperiments. Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes ADJUSTMENT OF CHRONICALLY IMPLANTED ELECTRODES • In order to adjust electrode position after implantation electrode must be able to move along its axis • In a simple setup for adjustable electrode a metal wire is inserted into a cannula • This cannula can slide along its axis with help of a machine screw moved by a microdrive • The movable cannula is surrounded by a fixed outer cannula for support • The whole setup is covered by protective housing, with connection cables leading out from the housing to a standard connector • Electrode position can then be adjusted by fine microdrive movements while monitoring signal quality 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 37 Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes TYPES OF CHRONICALLY IMPLANTED MULTIELECTRODES • Multielectrodeshave the great advantage over single microwireelectrodes to record from more brain areas at the same time. • The different types of multielectrodes:• Metal (microwire) multielectrode • Silicon multielectrode • Metal multielectrodesare easier to fabricate • Silicon multielectrodedesign is pre-defined and highly reproducible • Microelectrodesand microelectroderecordingtechniquewillbe discussedindetailinLecture6. 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 38 Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 39 TYPES OF CHRONICALLY IMPLANTED MULTIELECTRODES neuronexus Metal wire multielectrodeSilicon multielectrode (seeLecture6) Source: http://www.neuronexustech.com/catalog2011.pdf Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes REVIEW QUESTIONS • What is electrode potential? • Why does an ideal electrode not exist? • What is an electrode conductor? • What is an electrolyte? • What is the difference between bipolar and unipolarrecording? • Which factors can contribute to signal distortion measured on an electrode? • How is the double layer at a metal-liquid junction formed? • Why are non-polarizableelectrodes preferable to polarizableelectrodes? • Why is a conductive gel applied on skin at EEG recordings? • What electrode types are used for biopotentialrecordings? • What is electrocorticography? • What recording techniques are used in animal experiments? 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 40 Electrophysiological Methods of the Study of the Nervous-and Muscular System: Properties and Characteristics of Electrodes REFERENCES Thompson R, Patterson M,: Bioelectric Recording Techniques: Cellular Processes and Brain Potentials, Academic Press, New York,1973 Cooper R., OsseltonJ.W., Shaw J.C.:EEG Technology, 2nd ed, Butterworths, London, 1969 Fisch, B.J.: Fishand Spehlmann’s EEG Primer (3rded.), Elsevier, Amsterdam, 1999. Niedermayer, E., LopesDa Silva, F., (eds): Electroencephalograhy: Basic Principles, ClinicalApplications, and RelatedFields, (5thed.) LippincottWilliams and Wilkins, Philadelphia, 2005. http://www-psych.nmsu.edu/~jkroger/lab/principles.html http://www.brainproducts.com http://www.biosemi.com/flat_electrode.htm http://www.miyuki-net.co.jp/jp/seminar/sensornet/sensor03.htm http://www.diximedical.com www.kopfinstruments.com http://www.neuronexustech.com 2011.10.07.. TÁMOP –4.1.2-08/2/A/KMR-2009-0006 41