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A simple method for producing, in quantity, metal micro-electrodes with a desired taper and impedance
623
Electroencephatography and Clinical Neurophysiology Elsevier Publishing Company, Amsterdam -- Printed in The Netherlands
TECHNICAL
CONTRIBUTIONS
A SIMPLE M E T H O D FOR P R O D U C I N G , IN Q U A N T I T Y , M E T A L M I C R O - E L E C T R O D E S WITH A D E S I R E D T A P E R A N D I M P E D A N C E 1 JOHN A. FREEMAN", M.D., PH.D., MAJOR, USAF (MC) Department o[ Biology attd Research Laboratoo' o f Electronics, Communications Bh~physics Group, Massachusetts htstitute o f Technology, Cambridge, Mass. 02139 (U.S.A.) (Accepted for publication: August 27, 1968)
The suitability of an electrode depends not only on its mechanical and electrical properties, but also on the application for which it is intended; metal micro-electrodes are better suited for extracellular recordings than are fluid-filled pipettes (Gesteland et al. 1959). The electrical properties of a metal micro-electrode are determined mainly by the electrochemical reactions occurring at its tip (Baldwin et al. 1965). The type of metal used for the body of the electrode is an important determinant of its mechanical but not its electrical properties. Electrodes made from wire are mechanically more robust than those made with a low melting point metal such as indium (Dowben and Rose 1953; Gesteland et al. 1959) or Agsolder (Gray and Svaetichin 1951 ). Numerous methods have been described for producing, from various kinds of wire, micro-electrodes suitable for recording from single neurons or from single muscle fil:ers (Pierce and Wagman 1964). Methods for sharpening include electrolytic etching (Grundfest et al. 1950; Hubel 1957; Green 1958; Mills 1962), fire polishing (Baldwin et al. 1965) and grinding (Wilksa 1940). Insulation, a more critical problem, utilizes various kinds of varnish, epoxy resins, or paint (Kinnard and MacLean 1967). The technique of applying insulation by centrifugal force (Bartlett 1966), while rapid, is apt to be rather imprecise. The final tip impedance, after retraction of the insulating material from the tip has occurred (caused by surface tension, evaporation and shrinkage), is a matter of chance. The alternative technique is to insulate the entire electrode, and then remove a small patch of insulation (mechanically, electrically or with a laser). Mechanical methods (e.g., breaking off the terminal This study was supported by the National Institutes of Health (Grant S RO1 NB-04897-04), the United States Air Force (Aerospace Medical Division) under contract AF 33 (615)-3885, and the Joint Services Electronics Program, contract FR-28-043-J6-00495. 2 Present address: Institute for Biomedical Research, American Medical Association, Chicago, Ill. 60610.
whisker of glass of a glass-insulated electrode) may bend the tip or crack the insulation. Electrical methods, e.g., passing high-density current through the electrode (Wolbarsht et al. 1960; Gerstein and Clark 1964), risks dislodging either too much or too little of the insulation, and can destroy the tip. The use of a laser to vaporize a small patch of insulation (Mela 1966), while precise, remains up to now a rather exclusive technique. The preceding considerations point up the desirability for a simple, standardized method of producing microelectrodes in quantity, whose tip impedances and dimensions can be controlled. We present here such a method using tungsten wire. (The method is, however, useful for making electrodes from platinum, steel, or any other kind of wire.) PROCEDURE
Sharpening The electrodes are held in a jig (Fig. 1) consisting of a metal disk, 3 in. in diameter, along whose circumference are mounted (at 0.5 in. intervals) 27 gauge hypodermic needles. The center of the disk is threaded onto the shaft of a small motor (DC, 1-5 rev/min) which in turn is held by a'clamp. Straight pieces of tungsten wire 1.5 in. (3.8 cm) in length and 0.005 in. (0.0127 cm) in diameter are bent slightly near one end and inserted into the needles. The disk is positioned over a dish of saturated aqueous potassium nitrite (KNOD solution (Hubel 1957), and is tilted approximately 45 ° with respect to the surface of the solution. The disk is lowered and the wires are aligned so that their tips come to within 2 mm of the solution when the disk is rotated. The motor is then turned on (at approximately 3 rev/min; the speed is not critical) and the disk assembly is lowered until the tips of the wires sweep to a depth of 3-5 mm in their traverse through the solution. A platinum wire immersed in the solution and a clip attached to the housing of the motor are connected to any convenient variable AC voltage supply, such as a Variac. Very nearly uniform tapers of approximately 30° Electroenceph. olin. Neurophyshd., 1969, 26:623 626
624
J . A . FREEMAN
Fig. 1 Device for semi-automatically producing metal micro-electrodes with a uniform taper. are obtained by applying 7 V for 10 rain at 3 rev/min. More acute tapers are obtained by using higher voltages (excessive voltages cause pitting) or longer times, and vice versa, and a great range of tapers can be obtained by different settings. The extreme tip can be tapered more acutely, thereby increasing its stiffness, by lowering the electrode until it just touches the surface, and then briefly applying 1-3 V. This results in tip diameters of 0.5-1.5 t~, as shown in Fig. 2, B. The electrodes are washed by rotating them in distilled H20 through several revolutions.
btsu!ation Any one of a number of insulating substance; can be used. We prefer to use No. 6001 M Epoxylite (Epoxylite Corp., S. El Monte, Calif.) because it requires no thickening, and a single coating forms an exceedingly durable insulation. The sharpened electrodes, still in the jig, are slowly rotated through a dish of Epoxylite several times. The thickness of the insulation increase; with each revolution. As the electrodes exit from the Epoxylite, surface tension produces a wiping action (viscous drag) which creates a smooth, even coat of insulation. The dish assembly and electrodes are baked at 150-180 ° C for 1.5-2 h, and then replaced on the jig. Production o f desired impedance The electrodes, now encased in a tough sheath of insulation, have an impedance in excess of 108 ~.L This
can I:e reduced to the desired range by use of the circuit shown in Fig. 2, A. This circuit provides a precisely controlled current; the current density through tke electrode is greatest at its tip, where the insulation is selectively removed. The circuit measure; the current passing through the electrodes. When the current which corresponds to a desired impedance is reached the current is automatically switched off. The sequence of events is as follows. The electrode-bearing disk is lowered so that a single electrode is submerged 2-3 mm beneath the surface of a saline solution. This electrode (Rn in the diagram) is connected to the circuit through a wire in the saline solution, and through a lead attached to the metal disk. The circuit consists essentially of a free-running multivibrator (transistors Q1 and Q2) oscillating between 0 and + 36 V at 1000 c/sec; a bistable multi-vibrator (Q~ ~), and a voltage comparator (operational amplifier A). In the quiescent state (battery connected, push-button switch--outlined by dashed lines--contacts pointing down) Qd, Qs and Q7 are conducting and no voltage is applied to RE. When the push-button switch is closed, voltage (the maximum of 12 V DC, and a 36 V, 1000 c/sec square wave voltage) is applied to RE. Initially, because of its high resistance, no current flows through R~,:. As the insulation begins to peel off, current begins to flow, producing a voltage across the 30 kf2 resistor. As this voltage rises it offsets the (negative) voltage at pin 2 of the comparator. The comparator is exceedingly sensitive : the instant that the current through RE achieves
Electroenceph. clin. Neurophysiol., 1969, 26:623-626
625
METAL MICRO-ELECTRODES
B A
mmmmmm.-5p
EXTERNAL
I
2K
',t .os~,f / \
,,o,q
IKt
REt --
.os~,f K'q2 q
I
45Vr ......
I
"i
f4701l
]
.
~
6.8K
L ........ J .01~.f
r'~l~ '
~
,I
IN--
~K:
t
lOOKi
~
6.6K
m!
D
C
r m ' ~ i
i
500 Hv
I ~
!
200/~v
m-I-
lOO msec
Fig. 2 A : Circuit for producing desired tip impedance of metal micro-electrodes. All transistors are 2N3565 (NPN Silicon). All diodes are IN67A (general purpose germanium). The operational amplifier is an "Op-Amp" model 4009 (Op-Amp Labs, Los Angeles, Calif.). The IK potentiometer is a 20-turn trim-pot (Compar Corp, Burlingame, Calif.). B: Light microscopic picture of two electrodes made by the techniques described in this note. C: Response of Purkinje cell in lobule VI of cat to tone burst (arrow). D: Response of Purkinje cell in lobule VI of cat to electrical stimulation of contralateral inferior olive.
the value determined by the setting of 1 k~q potentiometer, the comparator produces a negative-going pulse which turns off QT, which in turn forward-biases Q6, shortcircuiting the voltage across the electrode so that no further current flows through it and no further insulation is removed. Higher impedances are produced by selecting a less negative voltage with the 1 kf~ potentiometer, and vice versa. The sensitivity of the comparator enables one to consistently produce electrode impedances within 5 ~ of the desired value. ]3ecause only the minimum current (flowing for the minimum time) is used to re-
move insulation, little or no pitting of the electrode tip occurs. Particles of desquamated insulation are removed by rotating the disk briskly. Electrode impedance may be checked (or current may be passed through the electrode to plate the tip, or to check the continuity of the insulation by inspecting with a dissecting microscope the site(s) of bubble formation) with the electrodes still in the jig, by placing the DPST switch on "external". The optimum impedance for single unit recording with unplated electrodes is between 0.5 and 1.5 MD, at 1000 c/sec. Electroenceph. clin. Neurophysiol., 1969, 26:623-626
626
.1. A. FRElcMAN ('()",IMIiN I S
Rlitl RI X( I:g
This method of m a k i n g micro-electrodes ollers the a d \ a n t a g e s that uniforn-t tapers and iml:edances can Ire produced consistently : m.inimal handling of the electrodes is required, reducing tile risk of d a m a g i n g t h e m ; little skill in m a n u f a c t u r i n g is requiled a n d large numl:ers of electrodes can be produced in a short time a n d stored for several m o n t h s . T h e c o m p o n e n t s cost lcss t h a n $25. Electrodes made by this rnethod are suitable for a v, ide range of applications: extraceltular spikes haxe been recorded ( F r e e m a n , in preparation) from single units in cerebellar cortex of cat (Fig. 2, C) and rat: cuneate nucleus of cat : dorsal horn of unrestrained unanesthetized rat (Wall et El. 1967), a n d inferior oli,,e of cat ( F r e e m a n , in preparation) (Fig. 2, D). Their suitability for recording from extremely fine fibers or from very small, densely packed cells has not been tested.
BAll)WIN. tl. A., Fm'~k. S. and IAI iviN. J. Y. Glass coated tungsten n-ticro-clectrodc,,. Science, 1965, 14,Y: 1462-1464. B A R I I I I I , J. R+ Insulating microelectrode,, b5 centrifuging. E/ectroe,c~,ph. c/i,. Vem'oplo'.vio/., 1966, 21: 304 305. l)owf~ex, R. M. and R o s l . J. E. A metal filled micro. electrode. S¢iem'e, ! 953, I I,Y : 22. (il RSI IIN, G. I~. and ('1 \Rk, W. A. Simultaneous studies of Ih'ing patterns in se~cral neurons. Sck, nce, 1964,143: 1325 1327. (itSll i \NI),R. D., |-t()v~ 1 \NiL I~., [A~[ IVIN,J. V. alld PII is, W. H. Comment:> on microelectrodes. Prec. IRL" ( lnYt. Radh* t:5,~.~.). 1959, 47: 1856. (}J~ ~,'r, ,I. A. B. and S v x l l IcHl~,, G. Electrical properties of platinum-lipped microelcctrodes in Ringers solution. /tcta. phl,~hd..~camt., 1951, 24:278 284. ( i g t t ; N . . I . P . A ,,imple micro¢lectrc, de for recording I'rom the central ner,,ous %stem. \'altlre (Loml..,. 1958, 1,~2: 962. G r t , " , D i t s l , tI.,SE',,CiSI',KIX R. W., ()sl]l'-a~nr, W. tt. and ( ; { ; r i ~ , R. W. Slainle,,s steel microelectrode,, made by electrolytic pointing. Rer. Sci. htwr., 1950, 2/: 360. t l t m t . , D. 11. I'ung',tcn nficroclcctrode for recording from single units. Sciem,e, 1957, 125: 549. KI\N \P,I). NI. A. and M .xt I_i \ \ . P. I). A f~latinuin, illictoclectrodc for intracerebrat exploration ,,,Aria a chronically fixed stereotaxic dcvicc, li'lecm~enccph, clhz. \eUrOldtwiol.. 196% 22 : I S3 1,X,g. \ l ' , l ~ ; , F. ,\ rugged, reliable and stcrilizable microelectrode for recording single units from tile brain. \~tture (Lon,J.). 1964, 202 : 601 603. Mii .\. M. J. Microperforation x~itla laser I:cam in the preparation of micio-eleclrodes. I. E. E. E. 7)'an~. biomed, lJ,.a,~'., 1966, / 3 : 7 0 76. MHi s. L. VV. A. A. fast. incxl:ensi\e inethod of producing knge quantities of metallic microelectrodes, lT[ectr,,em'eph, el/n. Ne,rophv,~iol., 1962, 1 4 : 2 7 8 279. PIERCE, D. S. and Wao'.t.',',;. I. H. A n-tethod of recording fl:om single muscle fibers or m o t o r units in hnnlan skeletal muscle. J. app[. Phlsh~/., 1964, 22: 366.368. W,,,ll, P. I)., FREEM.~..!. A. and MAJOR, D. Dorsal horn cells in spinal and freely nloving c~.lt~. ['~vp. ,\'eurol., 1967, 19: 51') 52t). W n KS,'<, A. i \ k t i o n s p o t e n i i a l e n t l a d u n g e n einzelner Net~,hautelemente des Fro-,ches. ~tcto Sot. ~h'd. t"eH##. "Duodechn", 1940, 72:¢~3 -'5. W[)LBARSHT, M. L., Ma, cNt~ HOt J r . , E. F. a n d W&(;NI.R, tt. G. Glass insulated platinum microclectrode. Scie,ce, 1960, 132:1309 1310.
SUMMAP, Y A technique is described for rapidly producing quantities of metal micro-electrodes having uniform tal;ers and tip impedances. Uniform tapers of any desired angle are achie\ed by use of a simple, rotating jig. The desired tip in-q3edances are produced b', an inexpensi,,e, but precisely controlled current source. Electrodes produced by this technique have proved quite satisfactory for recording the activity f i o m single n e u r o n s in a variety of preparations. R~sUM(~ METHODE SIMPLE DE PRODUCTION EN GRANI)E QUANTITI(-~, DE MICRO-ELECI"RODES MI~TAI.I.IQUES DE DIAMETRE E l
D'IMPI~DANCE DONNt'!S
Les auteurs decrivent u n e technique permettant de produire rapidement des quantitf.s de micro-dlectrodes mdtalliques ayant des diam;atres et des impedances d'extr~mit6 uniforn',es. L'uniforlnit6 de diam~tre p o u r n ' i m p o r t e quel angle ddsir6 est obtenuc au m o y e n d ' u n simple crible t o u r n a n t . Les impddances d'extr6mitd ddsirdes sent obtenues au m o y e n d ' u n e source de c o u r a n t b e n march6, mats contr61de de faqon pr6cise. Les 61ectrodes fabriqudes au m o y e n de cette technique se sent montr6es tout h fait satisfaisantes pour l'enregistrement de l'activit6 de neurones isol6s dans route une s6rie de pr,Sparations. The a u t h o r wishes to express his t h a n k s to Prof, S. Burns and Dr. E. Merrill of M.I.T. for their ideas a n d efforts relating to this work.
ReJerence: FREEMAN, J. A. A simple m e t h o d for producing, in quantity, metal micro-electrodes with a desired taper a n d impedance. Electroenceph. clin. Neurophysiol., 1969, 26: 623-626.
Electroencephatography and Clinical Neurophysiology Elsevier Publishing Company, Amsterdam -- Printed in The Netherlands
TECHNICAL
CONTRIBUTIONS
A SIMPLE M E T H O D FOR P R O D U C I N G , IN Q U A N T I T Y , M E T A L M I C R O - E L E C T R O D E S WITH A D E S I R E D T A P E R A N D I M P E D A N C E 1 JOHN A. FREEMAN", M.D., PH.D., MAJOR, USAF (MC) Department o[ Biology attd Research Laboratoo' o f Electronics, Communications Bh~physics Group, Massachusetts htstitute o f Technology, Cambridge, Mass. 02139 (U.S.A.) (Accepted for publication: August 27, 1968)
The suitability of an electrode depends not only on its mechanical and electrical properties, but also on the application for which it is intended; metal micro-electrodes are better suited for extracellular recordings than are fluid-filled pipettes (Gesteland et al. 1959). The electrical properties of a metal micro-electrode are determined mainly by the electrochemical reactions occurring at its tip (Baldwin et al. 1965). The type of metal used for the body of the electrode is an important determinant of its mechanical but not its electrical properties. Electrodes made from wire are mechanically more robust than those made with a low melting point metal such as indium (Dowben and Rose 1953; Gesteland et al. 1959) or Agsolder (Gray and Svaetichin 1951 ). Numerous methods have been described for producing, from various kinds of wire, micro-electrodes suitable for recording from single neurons or from single muscle fil:ers (Pierce and Wagman 1964). Methods for sharpening include electrolytic etching (Grundfest et al. 1950; Hubel 1957; Green 1958; Mills 1962), fire polishing (Baldwin et al. 1965) and grinding (Wilksa 1940). Insulation, a more critical problem, utilizes various kinds of varnish, epoxy resins, or paint (Kinnard and MacLean 1967). The technique of applying insulation by centrifugal force (Bartlett 1966), while rapid, is apt to be rather imprecise. The final tip impedance, after retraction of the insulating material from the tip has occurred (caused by surface tension, evaporation and shrinkage), is a matter of chance. The alternative technique is to insulate the entire electrode, and then remove a small patch of insulation (mechanically, electrically or with a laser). Mechanical methods (e.g., breaking off the terminal This study was supported by the National Institutes of Health (Grant S RO1 NB-04897-04), the United States Air Force (Aerospace Medical Division) under contract AF 33 (615)-3885, and the Joint Services Electronics Program, contract FR-28-043-J6-00495. 2 Present address: Institute for Biomedical Research, American Medical Association, Chicago, Ill. 60610.
whisker of glass of a glass-insulated electrode) may bend the tip or crack the insulation. Electrical methods, e.g., passing high-density current through the electrode (Wolbarsht et al. 1960; Gerstein and Clark 1964), risks dislodging either too much or too little of the insulation, and can destroy the tip. The use of a laser to vaporize a small patch of insulation (Mela 1966), while precise, remains up to now a rather exclusive technique. The preceding considerations point up the desirability for a simple, standardized method of producing microelectrodes in quantity, whose tip impedances and dimensions can be controlled. We present here such a method using tungsten wire. (The method is, however, useful for making electrodes from platinum, steel, or any other kind of wire.) PROCEDURE
Sharpening The electrodes are held in a jig (Fig. 1) consisting of a metal disk, 3 in. in diameter, along whose circumference are mounted (at 0.5 in. intervals) 27 gauge hypodermic needles. The center of the disk is threaded onto the shaft of a small motor (DC, 1-5 rev/min) which in turn is held by a'clamp. Straight pieces of tungsten wire 1.5 in. (3.8 cm) in length and 0.005 in. (0.0127 cm) in diameter are bent slightly near one end and inserted into the needles. The disk is positioned over a dish of saturated aqueous potassium nitrite (KNOD solution (Hubel 1957), and is tilted approximately 45 ° with respect to the surface of the solution. The disk is lowered and the wires are aligned so that their tips come to within 2 mm of the solution when the disk is rotated. The motor is then turned on (at approximately 3 rev/min; the speed is not critical) and the disk assembly is lowered until the tips of the wires sweep to a depth of 3-5 mm in their traverse through the solution. A platinum wire immersed in the solution and a clip attached to the housing of the motor are connected to any convenient variable AC voltage supply, such as a Variac. Very nearly uniform tapers of approximately 30° Electroenceph. olin. Neurophyshd., 1969, 26:623 626
624
J . A . FREEMAN
Fig. 1 Device for semi-automatically producing metal micro-electrodes with a uniform taper. are obtained by applying 7 V for 10 rain at 3 rev/min. More acute tapers are obtained by using higher voltages (excessive voltages cause pitting) or longer times, and vice versa, and a great range of tapers can be obtained by different settings. The extreme tip can be tapered more acutely, thereby increasing its stiffness, by lowering the electrode until it just touches the surface, and then briefly applying 1-3 V. This results in tip diameters of 0.5-1.5 t~, as shown in Fig. 2, B. The electrodes are washed by rotating them in distilled H20 through several revolutions.
btsu!ation Any one of a number of insulating substance; can be used. We prefer to use No. 6001 M Epoxylite (Epoxylite Corp., S. El Monte, Calif.) because it requires no thickening, and a single coating forms an exceedingly durable insulation. The sharpened electrodes, still in the jig, are slowly rotated through a dish of Epoxylite several times. The thickness of the insulation increase; with each revolution. As the electrodes exit from the Epoxylite, surface tension produces a wiping action (viscous drag) which creates a smooth, even coat of insulation. The dish assembly and electrodes are baked at 150-180 ° C for 1.5-2 h, and then replaced on the jig. Production o f desired impedance The electrodes, now encased in a tough sheath of insulation, have an impedance in excess of 108 ~.L This
can I:e reduced to the desired range by use of the circuit shown in Fig. 2, A. This circuit provides a precisely controlled current; the current density through tke electrode is greatest at its tip, where the insulation is selectively removed. The circuit measure; the current passing through the electrodes. When the current which corresponds to a desired impedance is reached the current is automatically switched off. The sequence of events is as follows. The electrode-bearing disk is lowered so that a single electrode is submerged 2-3 mm beneath the surface of a saline solution. This electrode (Rn in the diagram) is connected to the circuit through a wire in the saline solution, and through a lead attached to the metal disk. The circuit consists essentially of a free-running multivibrator (transistors Q1 and Q2) oscillating between 0 and + 36 V at 1000 c/sec; a bistable multi-vibrator (Q~ ~), and a voltage comparator (operational amplifier A). In the quiescent state (battery connected, push-button switch--outlined by dashed lines--contacts pointing down) Qd, Qs and Q7 are conducting and no voltage is applied to RE. When the push-button switch is closed, voltage (the maximum of 12 V DC, and a 36 V, 1000 c/sec square wave voltage) is applied to RE. Initially, because of its high resistance, no current flows through R~,:. As the insulation begins to peel off, current begins to flow, producing a voltage across the 30 kf2 resistor. As this voltage rises it offsets the (negative) voltage at pin 2 of the comparator. The comparator is exceedingly sensitive : the instant that the current through RE achieves
Electroenceph. clin. Neurophysiol., 1969, 26:623-626
625
METAL MICRO-ELECTRODES
B A
mmmmmm.-5p
EXTERNAL
I
2K
',t .os~,f / \
,,o,q
IKt
REt --
.os~,f K'q2 q
I
45Vr ......
I
"i
f4701l
]
.
~
6.8K
L ........ J .01~.f
r'~l~ '
~
,I
IN--
~K:
t
lOOKi
~
6.6K
m!
D
C
r m ' ~ i
i
500 Hv
I ~
!
200/~v
m-I-
lOO msec
Fig. 2 A : Circuit for producing desired tip impedance of metal micro-electrodes. All transistors are 2N3565 (NPN Silicon). All diodes are IN67A (general purpose germanium). The operational amplifier is an "Op-Amp" model 4009 (Op-Amp Labs, Los Angeles, Calif.). The IK potentiometer is a 20-turn trim-pot (Compar Corp, Burlingame, Calif.). B: Light microscopic picture of two electrodes made by the techniques described in this note. C: Response of Purkinje cell in lobule VI of cat to tone burst (arrow). D: Response of Purkinje cell in lobule VI of cat to electrical stimulation of contralateral inferior olive.
the value determined by the setting of 1 k~q potentiometer, the comparator produces a negative-going pulse which turns off QT, which in turn forward-biases Q6, shortcircuiting the voltage across the electrode so that no further current flows through it and no further insulation is removed. Higher impedances are produced by selecting a less negative voltage with the 1 kf~ potentiometer, and vice versa. The sensitivity of the comparator enables one to consistently produce electrode impedances within 5 ~ of the desired value. ]3ecause only the minimum current (flowing for the minimum time) is used to re-
move insulation, little or no pitting of the electrode tip occurs. Particles of desquamated insulation are removed by rotating the disk briskly. Electrode impedance may be checked (or current may be passed through the electrode to plate the tip, or to check the continuity of the insulation by inspecting with a dissecting microscope the site(s) of bubble formation) with the electrodes still in the jig, by placing the DPST switch on "external". The optimum impedance for single unit recording with unplated electrodes is between 0.5 and 1.5 MD, at 1000 c/sec. Electroenceph. clin. Neurophysiol., 1969, 26:623-626
626
.1. A. FRElcMAN ('()",IMIiN I S
Rlitl RI X( I:g
This method of m a k i n g micro-electrodes ollers the a d \ a n t a g e s that uniforn-t tapers and iml:edances can Ire produced consistently : m.inimal handling of the electrodes is required, reducing tile risk of d a m a g i n g t h e m ; little skill in m a n u f a c t u r i n g is requiled a n d large numl:ers of electrodes can be produced in a short time a n d stored for several m o n t h s . T h e c o m p o n e n t s cost lcss t h a n $25. Electrodes made by this rnethod are suitable for a v, ide range of applications: extraceltular spikes haxe been recorded ( F r e e m a n , in preparation) from single units in cerebellar cortex of cat (Fig. 2, C) and rat: cuneate nucleus of cat : dorsal horn of unrestrained unanesthetized rat (Wall et El. 1967), a n d inferior oli,,e of cat ( F r e e m a n , in preparation) (Fig. 2, D). Their suitability for recording from extremely fine fibers or from very small, densely packed cells has not been tested.
BAll)WIN. tl. A., Fm'~k. S. and IAI iviN. J. Y. Glass coated tungsten n-ticro-clectrodc,,. Science, 1965, 14,Y: 1462-1464. B A R I I I I I , J. R+ Insulating microelectrode,, b5 centrifuging. E/ectroe,c~,ph. c/i,. Vem'oplo'.vio/., 1966, 21: 304 305. l)owf~ex, R. M. and R o s l . J. E. A metal filled micro. electrode. S¢iem'e, ! 953, I I,Y : 22. (il RSI IIN, G. I~. and ('1 \Rk, W. A. Simultaneous studies of Ih'ing patterns in se~cral neurons. Sck, nce, 1964,143: 1325 1327. (itSll i \NI),R. D., |-t()v~ 1 \NiL I~., [A~[ IVIN,J. V. alld PII is, W. H. Comment:> on microelectrodes. Prec. IRL" ( lnYt. Radh* t:5,~.~.). 1959, 47: 1856. (}J~ ~,'r, ,I. A. B. and S v x l l IcHl~,, G. Electrical properties of platinum-lipped microelcctrodes in Ringers solution. /tcta. phl,~hd..~camt., 1951, 24:278 284. ( i g t t ; N . . I . P . A ,,imple micro¢lectrc, de for recording I'rom the central ner,,ous %stem. \'altlre (Loml..,. 1958, 1,~2: 962. G r t , " , D i t s l , tI.,SE',,CiSI',KIX R. W., ()sl]l'-a~nr, W. tt. and ( ; { ; r i ~ , R. W. Slainle,,s steel microelectrode,, made by electrolytic pointing. Rer. Sci. htwr., 1950, 2/: 360. t l t m t . , D. 11. I'ung',tcn nficroclcctrode for recording from single units. Sciem,e, 1957, 125: 549. KI\N \P,I). NI. A. and M .xt I_i \ \ . P. I). A f~latinuin, illictoclectrodc for intracerebrat exploration ,,,Aria a chronically fixed stereotaxic dcvicc, li'lecm~enccph, clhz. \eUrOldtwiol.. 196% 22 : I S3 1,X,g. \ l ' , l ~ ; , F. ,\ rugged, reliable and stcrilizable microelectrode for recording single units from tile brain. \~tture (Lon,J.). 1964, 202 : 601 603. Mii .\. M. J. Microperforation x~itla laser I:cam in the preparation of micio-eleclrodes. I. E. E. E. 7)'an~. biomed, lJ,.a,~'., 1966, / 3 : 7 0 76. MHi s. L. VV. A. A. fast. incxl:ensi\e inethod of producing knge quantities of metallic microelectrodes, lT[ectr,,em'eph, el/n. Ne,rophv,~iol., 1962, 1 4 : 2 7 8 279. PIERCE, D. S. and Wao'.t.',',;. I. H. A n-tethod of recording fl:om single muscle fibers or m o t o r units in hnnlan skeletal muscle. J. app[. Phlsh~/., 1964, 22: 366.368. W,,,ll, P. I)., FREEM.~..!. A. and MAJOR, D. Dorsal horn cells in spinal and freely nloving c~.lt~. ['~vp. ,\'eurol., 1967, 19: 51') 52t). W n KS,'<, A. i \ k t i o n s p o t e n i i a l e n t l a d u n g e n einzelner Net~,hautelemente des Fro-,ches. ~tcto Sot. ~h'd. t"eH##. "Duodechn", 1940, 72:¢~3 -'5. W[)LBARSHT, M. L., Ma, cNt~ HOt J r . , E. F. a n d W&(;NI.R, tt. G. Glass insulated platinum microclectrode. Scie,ce, 1960, 132:1309 1310.
SUMMAP, Y A technique is described for rapidly producing quantities of metal micro-electrodes having uniform tal;ers and tip impedances. Uniform tapers of any desired angle are achie\ed by use of a simple, rotating jig. The desired tip in-q3edances are produced b', an inexpensi,,e, but precisely controlled current source. Electrodes produced by this technique have proved quite satisfactory for recording the activity f i o m single n e u r o n s in a variety of preparations. R~sUM(~ METHODE SIMPLE DE PRODUCTION EN GRANI)E QUANTITI(-~, DE MICRO-ELECI"RODES MI~TAI.I.IQUES DE DIAMETRE E l
D'IMPI~DANCE DONNt'!S
Les auteurs decrivent u n e technique permettant de produire rapidement des quantitf.s de micro-dlectrodes mdtalliques ayant des diam;atres et des impedances d'extr~mit6 uniforn',es. L'uniforlnit6 de diam~tre p o u r n ' i m p o r t e quel angle ddsir6 est obtenuc au m o y e n d ' u n simple crible t o u r n a n t . Les impddances d'extr6mitd ddsirdes sent obtenues au m o y e n d ' u n e source de c o u r a n t b e n march6, mats contr61de de faqon pr6cise. Les 61ectrodes fabriqudes au m o y e n de cette technique se sent montr6es tout h fait satisfaisantes pour l'enregistrement de l'activit6 de neurones isol6s dans route une s6rie de pr,Sparations. The a u t h o r wishes to express his t h a n k s to Prof, S. Burns and Dr. E. Merrill of M.I.T. for their ideas a n d efforts relating to this work.
ReJerence: FREEMAN, J. A. A simple m e t h o d for producing, in quantity, metal micro-electrodes with a desired taper a n d impedance. Electroenceph. clin. Neurophysiol., 1969, 26: 623-626.