Physiology & Behavior, Vol. 21, pp. 829-830. Pergamon Press and Brain Research Publ., 1978. Printed in the U.S.A.
BRIEF COMMUNICATION Inexpensive Stimulus Artifact Suppressor/Signal Inverter for Use While Recording Unit Activity 1 R. E. M c C L U N G ,
A. GOSALIA AND N. DAFNY
Department o f Neurobiology and A n a t o m y The University o f Texas Medical School at Houston, Houston, T X 77025
( R e c e i v e d 20 F e b r u a r y 1978) McCLUNG, R. E., A. GOSALIA AND N. DAFNY. Inexpensive stimulus artifact suppressor~signal inverterfor use while recording unit activity. PHYSIOL. BEHAV. 21(5) 829-830, 1978.--An inexpensive artifact suppressor/signal inverter has been developed for use with commercially available window discriminators in unit recordings. This device provides a triggered blockade of the signal to prevent erroneous triggering of the window discriminator by the stimulus artifact. The unit is also capable of inverting the signal for easier unit discrimination when the positive component is too close to baseline or there is more than one positive component present. Unit recordings
Stimulation artifact
Inverter
W I N D O W discriminators are often used in electrophysiological experiments to discriminate single cell activity from baseline noise or other interference. Electrical stimulation within the central nervous system produces a stimulus artifact, a product of current flow from the stimulus source through non-neuronal pathways such as extracellular fluid. This artifact interferes with the recording of unit activity and is often computed erroneously by a window discriminator as one or more unit discharges. Most commercially available window discriminators are only capable of triggering on a positive (rising) spike. However, recordings are often made in which the positive component is not above the baseline while a large negative component is present. It is then impossible for this unit to trigger the discriminator. Also, a common triphasic waveform (positive-negative-positive) results in two counts per event by the discriminator. In order to solve some of these problems, we have developed a simple and inexpensive artifact suppressor and spike inverter. By using a simple switch, the unit is capable of inverting the signal without otherwise altering the waveforms. The suppression unit is triggered by a signal prior to or at the initiation of stimulation and blocks the output for a variable period of time (0 to 50 msec) eliminating the artifact. Figure 1 demonstrates two sets of responses following 20 repetitive stimuli (1 every 1.1 sec), recorded from the parafascicular nucleus of the thalamus in a rat during stimulation of the dorsal raphe nucleus. In Fig. 1A the stimulus artifact is present, while in Fig. 1B the artifact has been suppressed. The pulses above the units are the output
from a window discriminator. These pulses are fed into a minicomputer to generate histograms for evaluation of the data. As Fig. 1A illustrates, without the artifact suppressor, several components of the artifact will trigger the output from the discriminator. This erroneous output will result in an altered histograms such as the post-stimulus time histograms in Fig. 1A. The corrected histogram is seen in Fig. lB. Often the effect of a stimulus or drug may be hidden by the over-inflated histogram values obtained if the artifact is not suppressed. Figure 2 demonstrates a frequency histogram where the effect of the stimulation (spinal tract of the trigeminal nerve) is a decrease of the firing rate in this parafascicular unit, but if the artifact was counted it would appear as an increase. Figure 3 is a schematic of the device. Either the inverter or the artifact suppressor may be built individually (the components in the first stage prior to the 10K 1% resistor make up the inverter). Basically the artifact is suppressed by using a controlled integrated circuit switch (CD4016). The turn-off timing of the switch, when the trigger input is activated, is controlled by monostable multivibrator outputs (CD4047). Two trigger inputs are provided, a positive 3V for triggering off tape and a negative 12V for triggering from a timing device such as a pulse generator. The amount of time the input is blocked is dependent on the resistance of the potentiometer. By using two ranges of capacitance for this monostable circuit, greater sensitivity of the suppression time (0-5 msec and 0-50 msec), is obtained. Since the input goes both positive and negative, a bias of 6.5 V is applied at the input and
1Supported by USPHS DA00803 and DA05075.
C o p y r i g h t © 1978 B r a i n R e s e a r c h P u b l i c a t i o n s Inc.--0031-9384/78/110829-02502.00/0
830
McCLUNG, GOSALIA AND DAFNY
PFN
FREQUENCY HISTOGRAM PARAFASCICULAR NUCLEUS
spo.
PST
E-J 15-
L
[]
SpV Stim without artifact
[]
SpV Stim with artifact
U) UJ
smso¢
I
O. U~
10-
_
'-7
rqnl 1 U-
',-:
5-
]
!
B PST
40
80
120
160
Sec FIG. 2. Three superimposed frequency histograms of neuronal activity recordings from the parafascicular nucleus of the thalamus during a 180 sec period. Spontaneous activity (dashed lines) and activity during stimulation (1 every 1. I sec) of the spinal tract of the trigeminal nerve are compared with (clear area) and without (stippled area) the artifact suppressed.
2|
~R
J 3
StoNe
10"
lb
,ix I ~ T * ' 2 v l 20
30
40
10;(~12V
I
5'0met
FIG. 1. Unit discharges recorded from the parafascicular nucleus of the thalamus during 20 repetitive stimulations (1 every 1.1 see), of the dorsal raphe nucleus, and respective post-stimulus time histograms. (A). Stimulus artifact not suppressed. (B). Stimulus artifact suppressed.
removed at the output. The 1K trim pot in the output is to balance the output bias. All operational amplifiers are Model 741 and all diodes are IN4007. The power supply may be any _+ 12 V regulated supply. It should be noted that 15 V is the upper operational limit of the ICs and thus 12 V is the optimum power supply choice. Within our lab, we simply draw power from the regulated supply used for the recording amplifiers (Grass RPS 107 power supply for P511 amplifiers). This artifact suppression device has proven to be both easy to construct and inexpensive (under $40) and solves the problems of blocking the stimulus artifact and discriminating the desired component of a spike discharge.
K
21K t
00T,G, &gK
'
1OK t
.... ~K o I2V TRIGGER
4 K
e
~'-
•
3V TRIGGER
FIG. 3. Schematic design of the artifact suppressor/signal inverter. The t superscript on some resistors designates the 1% tolerance components. The first stage from the input, prior to the 10 K i% resistor make up the signal inverter. All diodes are 1N4007 and all op-amps are 741.
BRIEF COMMUNICATION Inexpensive Stimulus Artifact Suppressor/Signal Inverter for Use While Recording Unit Activity 1 R. E. M c C L U N G ,
A. GOSALIA AND N. DAFNY
Department o f Neurobiology and A n a t o m y The University o f Texas Medical School at Houston, Houston, T X 77025
( R e c e i v e d 20 F e b r u a r y 1978) McCLUNG, R. E., A. GOSALIA AND N. DAFNY. Inexpensive stimulus artifact suppressor~signal inverterfor use while recording unit activity. PHYSIOL. BEHAV. 21(5) 829-830, 1978.--An inexpensive artifact suppressor/signal inverter has been developed for use with commercially available window discriminators in unit recordings. This device provides a triggered blockade of the signal to prevent erroneous triggering of the window discriminator by the stimulus artifact. The unit is also capable of inverting the signal for easier unit discrimination when the positive component is too close to baseline or there is more than one positive component present. Unit recordings
Stimulation artifact
Inverter
W I N D O W discriminators are often used in electrophysiological experiments to discriminate single cell activity from baseline noise or other interference. Electrical stimulation within the central nervous system produces a stimulus artifact, a product of current flow from the stimulus source through non-neuronal pathways such as extracellular fluid. This artifact interferes with the recording of unit activity and is often computed erroneously by a window discriminator as one or more unit discharges. Most commercially available window discriminators are only capable of triggering on a positive (rising) spike. However, recordings are often made in which the positive component is not above the baseline while a large negative component is present. It is then impossible for this unit to trigger the discriminator. Also, a common triphasic waveform (positive-negative-positive) results in two counts per event by the discriminator. In order to solve some of these problems, we have developed a simple and inexpensive artifact suppressor and spike inverter. By using a simple switch, the unit is capable of inverting the signal without otherwise altering the waveforms. The suppression unit is triggered by a signal prior to or at the initiation of stimulation and blocks the output for a variable period of time (0 to 50 msec) eliminating the artifact. Figure 1 demonstrates two sets of responses following 20 repetitive stimuli (1 every 1.1 sec), recorded from the parafascicular nucleus of the thalamus in a rat during stimulation of the dorsal raphe nucleus. In Fig. 1A the stimulus artifact is present, while in Fig. 1B the artifact has been suppressed. The pulses above the units are the output
from a window discriminator. These pulses are fed into a minicomputer to generate histograms for evaluation of the data. As Fig. 1A illustrates, without the artifact suppressor, several components of the artifact will trigger the output from the discriminator. This erroneous output will result in an altered histograms such as the post-stimulus time histograms in Fig. 1A. The corrected histogram is seen in Fig. lB. Often the effect of a stimulus or drug may be hidden by the over-inflated histogram values obtained if the artifact is not suppressed. Figure 2 demonstrates a frequency histogram where the effect of the stimulation (spinal tract of the trigeminal nerve) is a decrease of the firing rate in this parafascicular unit, but if the artifact was counted it would appear as an increase. Figure 3 is a schematic of the device. Either the inverter or the artifact suppressor may be built individually (the components in the first stage prior to the 10K 1% resistor make up the inverter). Basically the artifact is suppressed by using a controlled integrated circuit switch (CD4016). The turn-off timing of the switch, when the trigger input is activated, is controlled by monostable multivibrator outputs (CD4047). Two trigger inputs are provided, a positive 3V for triggering off tape and a negative 12V for triggering from a timing device such as a pulse generator. The amount of time the input is blocked is dependent on the resistance of the potentiometer. By using two ranges of capacitance for this monostable circuit, greater sensitivity of the suppression time (0-5 msec and 0-50 msec), is obtained. Since the input goes both positive and negative, a bias of 6.5 V is applied at the input and
1Supported by USPHS DA00803 and DA05075.
C o p y r i g h t © 1978 B r a i n R e s e a r c h P u b l i c a t i o n s Inc.--0031-9384/78/110829-02502.00/0
830
McCLUNG, GOSALIA AND DAFNY
PFN
FREQUENCY HISTOGRAM PARAFASCICULAR NUCLEUS
spo.
PST
E-J 15-
L
[]
SpV Stim without artifact
[]
SpV Stim with artifact
U) UJ
smso¢
I
O. U~
10-
_
'-7
rqnl 1 U-
',-:
5-
]
!
B PST
40
80
120
160
Sec FIG. 2. Three superimposed frequency histograms of neuronal activity recordings from the parafascicular nucleus of the thalamus during a 180 sec period. Spontaneous activity (dashed lines) and activity during stimulation (1 every 1. I sec) of the spinal tract of the trigeminal nerve are compared with (clear area) and without (stippled area) the artifact suppressed.
2|
~R
J 3
StoNe
10"
lb
,ix I ~ T * ' 2 v l 20
30
40
10;(~12V
I
5'0met
FIG. 1. Unit discharges recorded from the parafascicular nucleus of the thalamus during 20 repetitive stimulations (1 every 1.1 see), of the dorsal raphe nucleus, and respective post-stimulus time histograms. (A). Stimulus artifact not suppressed. (B). Stimulus artifact suppressed.
removed at the output. The 1K trim pot in the output is to balance the output bias. All operational amplifiers are Model 741 and all diodes are IN4007. The power supply may be any _+ 12 V regulated supply. It should be noted that 15 V is the upper operational limit of the ICs and thus 12 V is the optimum power supply choice. Within our lab, we simply draw power from the regulated supply used for the recording amplifiers (Grass RPS 107 power supply for P511 amplifiers). This artifact suppression device has proven to be both easy to construct and inexpensive (under $40) and solves the problems of blocking the stimulus artifact and discriminating the desired component of a spike discharge.
K
21K t
00T,G, &gK
'
1OK t
.... ~K o I2V TRIGGER
4 K
e
~'-
•
3V TRIGGER
FIG. 3. Schematic design of the artifact suppressor/signal inverter. The t superscript on some resistors designates the 1% tolerance components. The first stage from the input, prior to the 10 K i% resistor make up the signal inverter. All diodes are 1N4007 and all op-amps are 741.
