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A new microdrive for extracellular recording of single neurons using fine wires
392
Electroencephalograph)' and clinical N europhysiology, 1984, 5 7 : 3 9 2 - 3 9 4 Elsevier Scientific Publishers Ireland, Ltd.
Short communication A NEW MICRODRIVE FOR EXTRACELLULAR R E C O R D I N G OF SINGLE N E U R O N S U S I N G FINE WIRES t J.X. Z H A N G and R.M. H A R P E R
Neuroscience Program, Brain Research Institute, and the Department of Anatomy, University of California at Los Angeles, Los Angeles, CA 90024 (U.S.A.) (Accepted for publication: December 9, 1983)
The fine-wire microelectrode technique for recording activity of single neurons has been used for more than two decades (Strumwasser 1958). The procedure consists of placing flexible insulated fine wires into particular brain areas and allows recording of single neuron activity from unrestrained animals for very long periods of time. The usefulness of the technique is enhanced by an ability to move bundles of fine wires proximally to cell groups. Compact low weight microdrives have been developed for moving these bundles from one position to another (Harper and McGinty 1973). We have developed a new microdrive which is more compact and mechanically stable than previous versions, and still requires only hand tools for construction.
A
Materials and Methods
Microdrioe components The microdrive consists of an outer guide tube, a screw drive apparatus, and fine wires attached to the inside of an electrode guide tube. The electrode guide tube consists of a 36 m m length of thin-walled 23-gauge stainless steel tubing (Fig. 1 B-i). It can be moved within a close-fitting thin-walled 20-gauge stainless steel outer guide tube (Fig. 1B-j) which is 15 m m in length. The outer guide tube is soldered to the outside of the drive apparatus cylinder. The drive apparatus consists of a 0 - 8 0 x 3 / 4 in. machine screw (Small Parts Inc., Miami, FL) (Fig. 1 B-a) which, when turned, moves the electrode guide tube. Rotation of the screw is transformed to electrode guide tube movement via two matching nuts (Fig. 1B-c) which are soldered to the electrode guide tube (Fig. 1B-i). A lock washer (Fig. 1B-d) between the nuts adds to the accuracy of movement. The machine screw is held at the central axis of a cylinder (Fig. 1B-e) by two bearings at each end of the outer cylinder (Fig. 1B-b,f). The outer cylinder is a 19 m m . piece of 6-gauge stainless-steel tubing (Fig. 1B-e) with a longitudinal slot providing space for movement of the electrode guide tube. The machine screw is prevented from movement, other than rotation, by a lock washer (Fig. lB-g) and by a nut (Fig. 1B-h) soldered to its lower end. This research was supported by The National Heart, Lung, and Blood Institute Grant HL-22418-06 and American Heart Association - Greater Los Angeles Chapter 678-1G2.
Fig. 1. A: cross-sectional drawing of microdrive. B: detail of components, a, machine screw; b, upper bearing; c, movable nuts; d, lock washer; e, outer cylinder; f, lower bearing; g, lock washer; h, ground-round nut; i, electrode guide tube; j, outer guide tube. C: relationship of implanted electrodes to dental cement, connector and skull. Silicon grease is applied under the lower nut to prevent infiltration of liquid dental cement.
0013-4649/84/$03.00 © 1984 Elsevier Scientific Publishers Ireland, Ltd.
MICRODRIVE TECHNIQUE
"~'~',,r,',
393
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I00 mSEC Fig. 2. Tracing of single neuron activity from the nucleus parabrachialis medialis of the pons illustrating a typical recording obtained with the technique. The signal was digitized at a 64 kHz sampling rate and plotted on a digital plotter. This neuron was recorded over a period of 6 days.
Assernbly The upper opening of the electrode guide tube is beveled at a 45 ° angle so that the fine wires can easily be inserted during surgery. A 1 mm wide straight slot is cut on one side of 6-gauge tubing which forms the cylinder. The two bearings for the screw are made from two matching 0-80 nuts in which the central holes are widened with a 0.0635 in. diameter drill. The upper bearings are placed on the machine screw, and the electrode guide nuts and lock washer are turned until positioned midway on the machine screw. These two nuts and the interposing lock washer are then locked tightly together. The upper end of the electrode guide tube is soldered to the nuts, taking care to avoid soldering the tube to the lock washer. After soldering, the electrode guide tube lies parallel to the machine screw. The machine screw, as well as the electrode guide nuts, are placed into the cylinder and the upper bearings are soldered to the upper end of the cylinder. The lower bearings are pushed into the lower end of the cylinder, allowing approximately 1.5 mm to ensure adequate space for the lower nuts and the lock washer. The lower bearing is then soldered to the inner wall of the cylinder. The outer guide tube is placed over the inner electrode guide tube and is soldered to the lower end of the cylinder. Finally, a lock washer is placed on the screw below the lower bearing and another nut tightened on the screw until the washer is tightly pressed against the bearing screw. Since the lower nut must turn freely inside the cylinder, its hexagon shape is ground to a round shape before assembling. After the lower nut is soldered to the end of the machine screw, as shown in Fig. 1A, the microdrive assembly is complete.
Electrode preparation and surgical procedure Fine-wire electrodes are made from 25-62 ffm diameter insulated Nichrome wires. A bundle of 4-14 fine wires are cut into 100-120 mm lengths, and insulation is removed from one end of each wire by scraping. These bare ends of wire are then soldered to a male connector, and the wires tied with a small string to form a bundle. The distal ends of the fine wires are cut off bluntly with a pair of sharp scissors. The electrode bundle is
cut so that the wires extend 3-5 mm beyond the microdrive tip after insertion into the guide tube. The remaining fine-wire bundle and the solder joints of the connector are sealed with silicon glue (Dow Corning Silastic 732 RTV adhesive/sealant). Standard surgical procedures and stereotaxic techniques are utilized to place the microdrives. The cylinder and the outer guide tube of the microdrive are secured to the skull with dental cement. The lower nut of the rnicrodrive is covered with a layer of silicon grease to avoid adhesion to the dental cement. After microdrive placement, the fine-wire electrode bundle is lowered through the electrode guide tube of the microdrive to the desired position and glued into position with cyanoacrylate. Using these procedures, single units have been recorded bilaterally from pontine and amygdala areas in cats. By microdrive positioning, neuronal activity over a range of 10 mm can be readily recorded. The microdrive provides positioning of 0.08 mm resolution with 1 / 4 screw turn (0.32 mm/complete turn). Units can be recorded for as long as several days with adequate signal-to-noise ratios (Fig. 2). Since several microwires constitute the bundle, several neurons can often be simultaneously recorded, with each unit on a separate wire. Thus, proximally located cells can be recorded at the same time. The proximity of electrode tips occasionally leads to the simultaneous recording of a single neuron on two wires. Precautions must be taken to prevent misinterpretation of such 'cross-talk,' such as simultaneously displaying spike trains in order to ascertain discharge independence of recorded cell pairs. The microdrive provides substantial improvements in mechanical stability over earlier versions (Harper and McGinty 1973), since drive forces on the microdrive cannula are now exerted on multiple points, and less mechanical 'play' is present in the newer design. Moreover, a larger portion of the moving elements are enclosed than on the previous design, with significantly fewer occurrences of mechanical failure, more precision in electrode placement, and fewer problems from mechanical interference of exposed parts.
394
Summaff We have developed a new microdrive for fine-wire electrode recording of extracellular neuronal potentials. The new microdrive has advantages of durability of construction as well as enhanced precision and stability of electrode movement, and can be easily assembled with c o m m o n laboratory tools.
R~sum~ Un nouveau microdescendeur pour l'enregistrement extracellulaire unitaire h l'aide de fils m~talliques fins Nous avons mis au point un nouveau microdescendeur pour l'enregistrement extracellulaire de potentiels de neurones b. l'aide d'~lectrodes m6talliques fines. Les, avantages de ce nouveau microdescendeur r~sident aussi bien dans la solidit6 de
J.X. Z H A N G , R.M. H A R P E R sa construction que dans la grande precision et la stabilit~ du d~placement de l'61ectrode; de plus, il peut facilement &re construit/t l'aide de l'outillage habituel d'un laboratoire. We thank R. Frysinger, D. Taube and R. Trelease for advice and assistance.
References Harper, R.M. and McGinty, D.J. A technique for recording single neurons from unrestrained animals. In: M.I. Phillips (Ed.), Brain Unit Activity and Behavior. Thomas, Springfield, IL, 1973: 82-104. Strumwasser, F. Long term recording from single neurons in brain of unrestrained mammals. Science, 1958, 127: 469-470.
Electroencephalograph)' and clinical N europhysiology, 1984, 5 7 : 3 9 2 - 3 9 4 Elsevier Scientific Publishers Ireland, Ltd.
Short communication A NEW MICRODRIVE FOR EXTRACELLULAR R E C O R D I N G OF SINGLE N E U R O N S U S I N G FINE WIRES t J.X. Z H A N G and R.M. H A R P E R
Neuroscience Program, Brain Research Institute, and the Department of Anatomy, University of California at Los Angeles, Los Angeles, CA 90024 (U.S.A.) (Accepted for publication: December 9, 1983)
The fine-wire microelectrode technique for recording activity of single neurons has been used for more than two decades (Strumwasser 1958). The procedure consists of placing flexible insulated fine wires into particular brain areas and allows recording of single neuron activity from unrestrained animals for very long periods of time. The usefulness of the technique is enhanced by an ability to move bundles of fine wires proximally to cell groups. Compact low weight microdrives have been developed for moving these bundles from one position to another (Harper and McGinty 1973). We have developed a new microdrive which is more compact and mechanically stable than previous versions, and still requires only hand tools for construction.
A
Materials and Methods
Microdrioe components The microdrive consists of an outer guide tube, a screw drive apparatus, and fine wires attached to the inside of an electrode guide tube. The electrode guide tube consists of a 36 m m length of thin-walled 23-gauge stainless steel tubing (Fig. 1 B-i). It can be moved within a close-fitting thin-walled 20-gauge stainless steel outer guide tube (Fig. 1B-j) which is 15 m m in length. The outer guide tube is soldered to the outside of the drive apparatus cylinder. The drive apparatus consists of a 0 - 8 0 x 3 / 4 in. machine screw (Small Parts Inc., Miami, FL) (Fig. 1 B-a) which, when turned, moves the electrode guide tube. Rotation of the screw is transformed to electrode guide tube movement via two matching nuts (Fig. 1B-c) which are soldered to the electrode guide tube (Fig. 1B-i). A lock washer (Fig. 1B-d) between the nuts adds to the accuracy of movement. The machine screw is held at the central axis of a cylinder (Fig. 1B-e) by two bearings at each end of the outer cylinder (Fig. 1B-b,f). The outer cylinder is a 19 m m . piece of 6-gauge stainless-steel tubing (Fig. 1B-e) with a longitudinal slot providing space for movement of the electrode guide tube. The machine screw is prevented from movement, other than rotation, by a lock washer (Fig. lB-g) and by a nut (Fig. 1B-h) soldered to its lower end. This research was supported by The National Heart, Lung, and Blood Institute Grant HL-22418-06 and American Heart Association - Greater Los Angeles Chapter 678-1G2.
Fig. 1. A: cross-sectional drawing of microdrive. B: detail of components, a, machine screw; b, upper bearing; c, movable nuts; d, lock washer; e, outer cylinder; f, lower bearing; g, lock washer; h, ground-round nut; i, electrode guide tube; j, outer guide tube. C: relationship of implanted electrodes to dental cement, connector and skull. Silicon grease is applied under the lower nut to prevent infiltration of liquid dental cement.
0013-4649/84/$03.00 © 1984 Elsevier Scientific Publishers Ireland, Ltd.
MICRODRIVE TECHNIQUE
"~'~',,r,',
393
,'rTI~F
I00 mSEC Fig. 2. Tracing of single neuron activity from the nucleus parabrachialis medialis of the pons illustrating a typical recording obtained with the technique. The signal was digitized at a 64 kHz sampling rate and plotted on a digital plotter. This neuron was recorded over a period of 6 days.
Assernbly The upper opening of the electrode guide tube is beveled at a 45 ° angle so that the fine wires can easily be inserted during surgery. A 1 mm wide straight slot is cut on one side of 6-gauge tubing which forms the cylinder. The two bearings for the screw are made from two matching 0-80 nuts in which the central holes are widened with a 0.0635 in. diameter drill. The upper bearings are placed on the machine screw, and the electrode guide nuts and lock washer are turned until positioned midway on the machine screw. These two nuts and the interposing lock washer are then locked tightly together. The upper end of the electrode guide tube is soldered to the nuts, taking care to avoid soldering the tube to the lock washer. After soldering, the electrode guide tube lies parallel to the machine screw. The machine screw, as well as the electrode guide nuts, are placed into the cylinder and the upper bearings are soldered to the upper end of the cylinder. The lower bearings are pushed into the lower end of the cylinder, allowing approximately 1.5 mm to ensure adequate space for the lower nuts and the lock washer. The lower bearing is then soldered to the inner wall of the cylinder. The outer guide tube is placed over the inner electrode guide tube and is soldered to the lower end of the cylinder. Finally, a lock washer is placed on the screw below the lower bearing and another nut tightened on the screw until the washer is tightly pressed against the bearing screw. Since the lower nut must turn freely inside the cylinder, its hexagon shape is ground to a round shape before assembling. After the lower nut is soldered to the end of the machine screw, as shown in Fig. 1A, the microdrive assembly is complete.
Electrode preparation and surgical procedure Fine-wire electrodes are made from 25-62 ffm diameter insulated Nichrome wires. A bundle of 4-14 fine wires are cut into 100-120 mm lengths, and insulation is removed from one end of each wire by scraping. These bare ends of wire are then soldered to a male connector, and the wires tied with a small string to form a bundle. The distal ends of the fine wires are cut off bluntly with a pair of sharp scissors. The electrode bundle is
cut so that the wires extend 3-5 mm beyond the microdrive tip after insertion into the guide tube. The remaining fine-wire bundle and the solder joints of the connector are sealed with silicon glue (Dow Corning Silastic 732 RTV adhesive/sealant). Standard surgical procedures and stereotaxic techniques are utilized to place the microdrives. The cylinder and the outer guide tube of the microdrive are secured to the skull with dental cement. The lower nut of the rnicrodrive is covered with a layer of silicon grease to avoid adhesion to the dental cement. After microdrive placement, the fine-wire electrode bundle is lowered through the electrode guide tube of the microdrive to the desired position and glued into position with cyanoacrylate. Using these procedures, single units have been recorded bilaterally from pontine and amygdala areas in cats. By microdrive positioning, neuronal activity over a range of 10 mm can be readily recorded. The microdrive provides positioning of 0.08 mm resolution with 1 / 4 screw turn (0.32 mm/complete turn). Units can be recorded for as long as several days with adequate signal-to-noise ratios (Fig. 2). Since several microwires constitute the bundle, several neurons can often be simultaneously recorded, with each unit on a separate wire. Thus, proximally located cells can be recorded at the same time. The proximity of electrode tips occasionally leads to the simultaneous recording of a single neuron on two wires. Precautions must be taken to prevent misinterpretation of such 'cross-talk,' such as simultaneously displaying spike trains in order to ascertain discharge independence of recorded cell pairs. The microdrive provides substantial improvements in mechanical stability over earlier versions (Harper and McGinty 1973), since drive forces on the microdrive cannula are now exerted on multiple points, and less mechanical 'play' is present in the newer design. Moreover, a larger portion of the moving elements are enclosed than on the previous design, with significantly fewer occurrences of mechanical failure, more precision in electrode placement, and fewer problems from mechanical interference of exposed parts.
394
Summaff We have developed a new microdrive for fine-wire electrode recording of extracellular neuronal potentials. The new microdrive has advantages of durability of construction as well as enhanced precision and stability of electrode movement, and can be easily assembled with c o m m o n laboratory tools.
R~sum~ Un nouveau microdescendeur pour l'enregistrement extracellulaire unitaire h l'aide de fils m~talliques fins Nous avons mis au point un nouveau microdescendeur pour l'enregistrement extracellulaire de potentiels de neurones b. l'aide d'~lectrodes m6talliques fines. Les, avantages de ce nouveau microdescendeur r~sident aussi bien dans la solidit6 de
J.X. Z H A N G , R.M. H A R P E R sa construction que dans la grande precision et la stabilit~ du d~placement de l'61ectrode; de plus, il peut facilement &re construit/t l'aide de l'outillage habituel d'un laboratoire. We thank R. Frysinger, D. Taube and R. Trelease for advice and assistance.
References Harper, R.M. and McGinty, D.J. A technique for recording single neurons from unrestrained animals. In: M.I. Phillips (Ed.), Brain Unit Activity and Behavior. Thomas, Springfield, IL, 1973: 82-104. Strumwasser, F. Long term recording from single neurons in brain of unrestrained mammals. Science, 1958, 127: 469-470.