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A method for gustatory stimulus delivery in awake rhesus monkeys
Ermn Resutiwh
Bulhn,
Vol.
25, pp. 665468.
c Pergamon
Press
plc,
1990.
Pnnted in the CI.S.A
A Method for Gustatory Stimulus Delivery in Awake Rhesus Monkeys ZOLTAN
KARAD1,“I.l THOMAS
HIT00 NISHINO,:$ YUTAKA OOMURA.“t R. SC0TT.I.’ AND SHUJI AOUt
~Departnlen~ ofPhysiology, Fucul~ of medicine, K~us~L~ ~ni~~er~~~~~, Fllkuoka 81.2 fDepartment of Biological Control Systems, National institute for Physiological Sciences, Okazaki 444 $Department of Physiology, Faculty of Medicine, Nagoya City University, Nagoya 467. Jupan Received 6 August 1990
KARADI,
Z., H. NISHINO, Y. OOMURA, T. R. SCO?T AND S. AOU. A mrthod,for gustatory stimu1u.c delivrry in IIN&~ rhesu.v BRAIN RES BULL 25(5) 665-668, 1990.-A novel taste stimulus delivery technique along with a simple electronic onset marking system. designed for complex, neurophysiological-behavioral experiments in awake monkeys, are described. Intraoral implantation of a polyethylene tubing fistula enabled us to perform repeated. deli-standardized application of various taste solutions to hroad al-eas of gustatory receptors on the tongue, palate, pharynx and epiglottis, while activity of single neurons was extracellularly recorded in behaving rhesus monkeys. By introducing an electronic marking system. onset and duration of the stimulation could be determined.
monkrw.
Taste stimulation
Intraoral
tube implantation
Behaving
monkeys
GUSTATION is one of the most important senses in guiding the search, selection and consumption of foods. Thus, investigation of taste coding in feeding-related areas of the central nervous system (3. 8. 9) may elucidate some of the underlying neuronal mechanisms of these functions. Taste stimulation is being conducted by several methods in mammals (2, 4-7, IO-l2), however, the approaches used in primates (3, 10, 11) were either inconvenient for both the monkey and the experimenter or did not allow for standardized administration. Our main goal in designing the present stimulation paradigm was to achieve replicable intraoral application of various taste solutions in a well-quantified manner during extracellular single neuron recording in awake, behaving monkeys. In conjunction with a relatively simple electronic marker system, we were able to determine onset and duration of taste stimulation with accuracy. The efficacy and reliability of the stimulus delivery technique were also tested. METHOD
AND
conditions using light pentobarbital (30 mg/kg) and ketamine (40 mgikgihr) anesthesia. First, a polyethylene tube (HIBIKI. Japan). 2.0-2.6 mm in diameter, was implanted into the oral cavity of the monkey. A narrow slit on the skin was made at the margin of the acrylic headpiece. just rostra1 to the interaural line. and a long, finetipped hemostat was advanced subcutaneously toward the mouth. When the course of the hemostat was clearly defined, a small hole was opened in the upper lateral part of the bucca. just posterior to the last molar. Then the tip of the hemostat was extended into the oral cavity, and the end of the polyethylene tube was pulled up throughout the previously formed subcutaneous duct. To attach the tube firmly inside the oral cavity. we employed two alternative methods. In some cases, the last 3.5-4.5 cm of the polyethylene tube was perforated at regular intervals with a 19-gauge hypodermic needle and secured by means of multiple sutures to the buccal surface and the soft palate. Thus. an arc with broad stimulus flow was implanted in the oral cavity away from the potentially damaging impact of the teeth (Fig. IA). In other cases, a simpler method was employed. Before being pulled through the subcutaneous duct, the lower end of the tube was heat-flared and a plastic washer was slid down to rest against the flared end. Then the tubing was passed through the duct and the widened end fixed to the buccal hole by means of surgical sutures (Fig. 1B). Proper positioning of the tube made it possible for solutions to reach broad areas of the tongue as well as of the palatal surface.
RESULTS
Six rhesus monkeys (Mucaca mulatfu) of both sexes, weighing 3.5-9.0 kg, were used. All animals were cared for in accordance with NIH Guidelines (1985, 1986). Surgical implantation of an intraoral catheter was usually performed as part of the same operation in which a stereotaxic headpiece was attached to the skull as described earlier (1). if done separately, the surgery was always performed under antiseptic
‘Present ad&es\: Institute of Physiology, Faculty of Medicine. University Medical School, P&X, Szigeti str. 12. H-7643. ‘Present address: Department of Psychology, University of Delaware. Newark. DE 19716.
665
Hungary
KARADI.
666
A
B
NISHINO.
OOMURA.
SCOTT’ AND iiC)I
a silicone tube (5 mm outer diameter by 35 mm length) divided in two equal halves, a glass-pipe (3 mm outer diameter by 20 mm length), and two insulated elgiloy wires guided into the holes of the glass-pipe as shown in Fig. 3A. The circuit (demonstrated in Fig. 3B) was completed whenever a (conducting) fluid connected the two wires, that is, whenever a tastant passed the sensor part of the delivery system. When nonionic solutions were used (like the D-glucose), 30 kg/l (0.0005 mM) NaCI wab added to permit conductance (the amount of NaCl remained more than one order of magnitude below the taste threshold for salt), The onset marker emitted a quasi-square wave, whose duration measured the time necessary for the total volume of the taste solution to be injected. Onset marking signals were conducted tn a pen recorder polygraph (Recti-Horiz-8K. San-ei. Japan) and an oscilloscope (Tectronix 5441 Storage scope, Tectronix, USA) where single neuron activity was also visualized. Marking pulses were also fed into a minicomputer (Signal Processor 7Tl7. Sanei, Japan) and led to a data recorder (DFR-3915, Sony Magnescale Inc., Japan) for real time and off-line analyses. [For further details we refer to previous publications, e.g., Nishino et al. 1988 (9).] Figure 4 shows the trace of an onset marker signal at the application of 0.3 M D-glucose solution and the resulting response of a neuron in the lateral hypothalamic area.
DISCUSSION
FIG. 1. Computer image of the frontal view of the oral cavity of a rhesus monkey with alternative settings of the polyethylene tubing (arrows, dotted area) for taste stimulation. (A) Regularly perforated tubing arc of 3.54.5 cm length is fixed intraorally by means of surgical sutures. (B) The widened, strengthened end of the polyethylene tube is positioned then sutured at its entry on the buccal surface. After either of these implantation techniques, the upper part of the polyethylene tube was fixed (Fig. 2). The tubing was laid on the stereotaxic headpiece, and its full length was covered by dental acrylic cement, leaving only the posterior tip exposed. This was capped to prevent the entry of foreign matter. The monkey was permitted one week to recover, during which particular attention was paid to daily cleaning of the headpiece and its environment, and the administration of wide-spectrum antibiotics for at least five postoperative days. Animals were offered softened laboratory monkey chow pellets (Oriental Yeast Co., Ltd., Japan), along with fruits and vegetables. Stimulus Delivery Stimuli were delivered through a 5-mm outer diameter silicone tube, directly connected with the implanted polyethylene tubing, and containing the sensor part of the stimulus onset marker (described later). The dead space of the combined tube system varied from 0.4-0.7 ml, depending on the size of the monkey, and the time required for the fluids to pass the delivery system was 140 2 55 ms. Injection time for 1.2 ml of taste solutions was 4-6 s. Dye injections revealed that this delivery rate was suffcient to apply solutions to all lingual, palatal and pharyngeal surfaces, thus broadly stimulating the taste receptor system. Application of tastants was always followed by one or two injections of deionized water and by air, causing intertrial intervals to extend from 55 to 135 s. Stimulus Onset Marker The sensor part of the onset marker system was composed
of
The gustatory stimulus delivery technique presented here proved to be useful in experiments with awake, behaving monkeys. 1) Recording of single neuron activity could be kept stable during and after taste stimulation. 2) Even during longer recording sessions, well-defined quantities of solutions could be applied repeatedly. 3) Onset and duration of delivery of the tastants were marked with high precision. It is also worth noting that the standardization of stimulus delivery enabled us to distinguish easily between a taste-evoked neuronal response and one that was elicited by mechanical or other provocation. Replicable, constant stimulation of broad areas of the tongue, the palate (as well as that of receptors in the pharynx and the epiglottis) is guaranteed by fixed positioning of the implanted tube along with the predetermined injection volume of taste solutions. Although intraoral setting of the polyethylene tube required only minor surgery and the monkeys were quickly accustomed to the delivery system, in order to prevent infections or other complications, the tubing had to be removed after about two to three months of continuous usage. Thus, experiments of this or similar kinds have a time limit: after specially careful designing they have to be completed within relatively short periods. This, however, is beneficial with regard to the animal’s condition. It is important to emphasize that while gustatory stimulation was accomplished, monkeys were not disturbed in their ongoing activities, tastants could be applied without troubling interactions between the experimenter and the animal. Thus, this taste stimulus delivery technique proved to be a practical and reliable way to investigate gustatory neural coding in neurophysiological-behavioral experiments with awake monkeys.
ACKNOWLEDGEMENTS
The authors thank Mr. K. Fukai for his valuable technical assistance. This work was supported partly by Grants-in-Aid 59225027 (S.A.) and 6044.0097and 57440085 (Y.O.) from the Ministry of Education, Science and Culture of Japan.
NEW TASTE
STIMULATION
METHOD
667
IN MONKEYS
FIG. 2. Position of the polyethylene tubing (illustrated a subcutaneous duct into the mouth.
by dotted lines) guided from the posterior part of the dental acrylic headpiece
through
REFERENCES I. Aou. S.: Oomura. Y.: Nishmo, H.; Inokuchi, A.; Miauno. Y. Influence of catecholamines on reward-related neuronal activity in monkey orbitofrontal cortex. Brain Res. 267:165-170; 1983. 2. Boudreau. J. C.: Oravec. J. J.; Hoang. N. K. Taste systems of goat geniculate ganglion. J. Neurophysiol. 48(5): 1226-1242; 1982. 3. Burton. M. J.; Rolls, E. T.; Mora, F. Effects of hunger on the response\ of neurons in the lateral hypothalamus to the sight and taste of food. Exp. Neurol. 51:668-677: 1976. 4. Chang. F-C. T.; Scott. T. R. A technique for gustatory stimulus delivery in the rodent. Chem. Senses 9:9l-96; 1984. 5. Erickson, R. I’.; Doetsch, G. S.: Marshall, D. A. The gustatory neural response function. J. Gen. Physiol. 49:247-263; 1965. 6. Gjorstrup. P. Taste and chewing as stimuli for the secretion of amylase from the parotid gland of the rabbit. Acta Physiol. Stand. 1 IO: 295-30 I ; 1980. 7. Grill, H. J.: Norgren, R. The taste reactivity test, I. Mimetic responses to gustatory stimuli in neurologically normal rats. Brain Rcs. 143:263-279: 1978.
8. Karadi, Z.; Oomura. Y.; Nishino. H.; Aou. S.: Fujita, I. Functional organization of lateral hypothalamic glucose-sensitive (GS) and glucose-insensitive (GIS) neurons in the monkey. Sot. Neurosci. Abstr. 13:465: 1987. 9. Nishino. H.: Oomura. Y.; Karadi. 2.; Aou, S.: Lenard. L.; Kai. Y.: Fukuda, A.: Ito. C.; Mitt, 8. I.: Plata-Salaman. C. P. Internal and external information processing by lateral hypothalamic glucose-jensitive and insensitive neurons during bar press feeding in the monkey. Brain Res. Bull. 20:839-845: 1988. IO. Sat”, M.; Ogawa, H.; Yamashita, S. Response properties of macaque monkey chorda tympani fibers. J. Gen. Physiol. 66:781-810; 1975. Il. Scott. T. R.; Yaxley, S.: Sienkiewicz. Z. J.: Rolls. E. T. Gustatory responses in the nucleus tractus solitarius of the alert cynomolgus monkey. J. Neurophysiol. 55(l): 182-200: 1986. 12. Travers. S. P.; Smith, D. V. Responsiveness of neurons in the hamster parabrachial nuclei to taste mixtures. J. Gen. Physiol. 84:221250: 1983.
KARADI.
66X
NISHINO,
OOMURA.
X:W’r
AND AU1.
A SENSOR c
elgiloy
epoxy
glass pipe
wire
resin
B ONSET
MARKING to
CIRCUIT
sensor
FIG. 3. Schematic delineation of the sensor (A) and the onset marking circuit (B) of the stimulus delivery system used for rhesus monkeys.
FIG. 4. Trace of elicited activity ia) of a laterai bypt~thalamic neuron as well as onset marking signal (b) of the co~esponding gustatory stimulus (0.3 M D-glucose). Calibration: I50 pV for evoked responses. 5 V fr>l onset mark, respectively; time scale is IO s.
Bulhn,
Vol.
25, pp. 665468.
c Pergamon
Press
plc,
1990.
Pnnted in the CI.S.A
A Method for Gustatory Stimulus Delivery in Awake Rhesus Monkeys ZOLTAN
KARAD1,“I.l THOMAS
HIT00 NISHINO,:$ YUTAKA OOMURA.“t R. SC0TT.I.’ AND SHUJI AOUt
~Departnlen~ ofPhysiology, Fucul~ of medicine, K~us~L~ ~ni~~er~~~~~, Fllkuoka 81.2 fDepartment of Biological Control Systems, National institute for Physiological Sciences, Okazaki 444 $Department of Physiology, Faculty of Medicine, Nagoya City University, Nagoya 467. Jupan Received 6 August 1990
KARADI,
Z., H. NISHINO, Y. OOMURA, T. R. SCO?T AND S. AOU. A mrthod,for gustatory stimu1u.c delivrry in IIN&~ rhesu.v BRAIN RES BULL 25(5) 665-668, 1990.-A novel taste stimulus delivery technique along with a simple electronic onset marking system. designed for complex, neurophysiological-behavioral experiments in awake monkeys, are described. Intraoral implantation of a polyethylene tubing fistula enabled us to perform repeated. deli-standardized application of various taste solutions to hroad al-eas of gustatory receptors on the tongue, palate, pharynx and epiglottis, while activity of single neurons was extracellularly recorded in behaving rhesus monkeys. By introducing an electronic marking system. onset and duration of the stimulation could be determined.
monkrw.
Taste stimulation
Intraoral
tube implantation
Behaving
monkeys
GUSTATION is one of the most important senses in guiding the search, selection and consumption of foods. Thus, investigation of taste coding in feeding-related areas of the central nervous system (3. 8. 9) may elucidate some of the underlying neuronal mechanisms of these functions. Taste stimulation is being conducted by several methods in mammals (2, 4-7, IO-l2), however, the approaches used in primates (3, 10, 11) were either inconvenient for both the monkey and the experimenter or did not allow for standardized administration. Our main goal in designing the present stimulation paradigm was to achieve replicable intraoral application of various taste solutions in a well-quantified manner during extracellular single neuron recording in awake, behaving monkeys. In conjunction with a relatively simple electronic marker system, we were able to determine onset and duration of taste stimulation with accuracy. The efficacy and reliability of the stimulus delivery technique were also tested. METHOD
AND
conditions using light pentobarbital (30 mg/kg) and ketamine (40 mgikgihr) anesthesia. First, a polyethylene tube (HIBIKI. Japan). 2.0-2.6 mm in diameter, was implanted into the oral cavity of the monkey. A narrow slit on the skin was made at the margin of the acrylic headpiece. just rostra1 to the interaural line. and a long, finetipped hemostat was advanced subcutaneously toward the mouth. When the course of the hemostat was clearly defined, a small hole was opened in the upper lateral part of the bucca. just posterior to the last molar. Then the tip of the hemostat was extended into the oral cavity, and the end of the polyethylene tube was pulled up throughout the previously formed subcutaneous duct. To attach the tube firmly inside the oral cavity. we employed two alternative methods. In some cases, the last 3.5-4.5 cm of the polyethylene tube was perforated at regular intervals with a 19-gauge hypodermic needle and secured by means of multiple sutures to the buccal surface and the soft palate. Thus. an arc with broad stimulus flow was implanted in the oral cavity away from the potentially damaging impact of the teeth (Fig. IA). In other cases, a simpler method was employed. Before being pulled through the subcutaneous duct, the lower end of the tube was heat-flared and a plastic washer was slid down to rest against the flared end. Then the tubing was passed through the duct and the widened end fixed to the buccal hole by means of surgical sutures (Fig. 1B). Proper positioning of the tube made it possible for solutions to reach broad areas of the tongue as well as of the palatal surface.
RESULTS
Six rhesus monkeys (Mucaca mulatfu) of both sexes, weighing 3.5-9.0 kg, were used. All animals were cared for in accordance with NIH Guidelines (1985, 1986). Surgical implantation of an intraoral catheter was usually performed as part of the same operation in which a stereotaxic headpiece was attached to the skull as described earlier (1). if done separately, the surgery was always performed under antiseptic
‘Present ad&es\: Institute of Physiology, Faculty of Medicine. University Medical School, P&X, Szigeti str. 12. H-7643. ‘Present address: Department of Psychology, University of Delaware. Newark. DE 19716.
665
Hungary
KARADI.
666
A
B
NISHINO.
OOMURA.
SCOTT’ AND iiC)I
a silicone tube (5 mm outer diameter by 35 mm length) divided in two equal halves, a glass-pipe (3 mm outer diameter by 20 mm length), and two insulated elgiloy wires guided into the holes of the glass-pipe as shown in Fig. 3A. The circuit (demonstrated in Fig. 3B) was completed whenever a (conducting) fluid connected the two wires, that is, whenever a tastant passed the sensor part of the delivery system. When nonionic solutions were used (like the D-glucose), 30 kg/l (0.0005 mM) NaCI wab added to permit conductance (the amount of NaCl remained more than one order of magnitude below the taste threshold for salt), The onset marker emitted a quasi-square wave, whose duration measured the time necessary for the total volume of the taste solution to be injected. Onset marking signals were conducted tn a pen recorder polygraph (Recti-Horiz-8K. San-ei. Japan) and an oscilloscope (Tectronix 5441 Storage scope, Tectronix, USA) where single neuron activity was also visualized. Marking pulses were also fed into a minicomputer (Signal Processor 7Tl7. Sanei, Japan) and led to a data recorder (DFR-3915, Sony Magnescale Inc., Japan) for real time and off-line analyses. [For further details we refer to previous publications, e.g., Nishino et al. 1988 (9).] Figure 4 shows the trace of an onset marker signal at the application of 0.3 M D-glucose solution and the resulting response of a neuron in the lateral hypothalamic area.
DISCUSSION
FIG. 1. Computer image of the frontal view of the oral cavity of a rhesus monkey with alternative settings of the polyethylene tubing (arrows, dotted area) for taste stimulation. (A) Regularly perforated tubing arc of 3.54.5 cm length is fixed intraorally by means of surgical sutures. (B) The widened, strengthened end of the polyethylene tube is positioned then sutured at its entry on the buccal surface. After either of these implantation techniques, the upper part of the polyethylene tube was fixed (Fig. 2). The tubing was laid on the stereotaxic headpiece, and its full length was covered by dental acrylic cement, leaving only the posterior tip exposed. This was capped to prevent the entry of foreign matter. The monkey was permitted one week to recover, during which particular attention was paid to daily cleaning of the headpiece and its environment, and the administration of wide-spectrum antibiotics for at least five postoperative days. Animals were offered softened laboratory monkey chow pellets (Oriental Yeast Co., Ltd., Japan), along with fruits and vegetables. Stimulus Delivery Stimuli were delivered through a 5-mm outer diameter silicone tube, directly connected with the implanted polyethylene tubing, and containing the sensor part of the stimulus onset marker (described later). The dead space of the combined tube system varied from 0.4-0.7 ml, depending on the size of the monkey, and the time required for the fluids to pass the delivery system was 140 2 55 ms. Injection time for 1.2 ml of taste solutions was 4-6 s. Dye injections revealed that this delivery rate was suffcient to apply solutions to all lingual, palatal and pharyngeal surfaces, thus broadly stimulating the taste receptor system. Application of tastants was always followed by one or two injections of deionized water and by air, causing intertrial intervals to extend from 55 to 135 s. Stimulus Onset Marker The sensor part of the onset marker system was composed
of
The gustatory stimulus delivery technique presented here proved to be useful in experiments with awake, behaving monkeys. 1) Recording of single neuron activity could be kept stable during and after taste stimulation. 2) Even during longer recording sessions, well-defined quantities of solutions could be applied repeatedly. 3) Onset and duration of delivery of the tastants were marked with high precision. It is also worth noting that the standardization of stimulus delivery enabled us to distinguish easily between a taste-evoked neuronal response and one that was elicited by mechanical or other provocation. Replicable, constant stimulation of broad areas of the tongue, the palate (as well as that of receptors in the pharynx and the epiglottis) is guaranteed by fixed positioning of the implanted tube along with the predetermined injection volume of taste solutions. Although intraoral setting of the polyethylene tube required only minor surgery and the monkeys were quickly accustomed to the delivery system, in order to prevent infections or other complications, the tubing had to be removed after about two to three months of continuous usage. Thus, experiments of this or similar kinds have a time limit: after specially careful designing they have to be completed within relatively short periods. This, however, is beneficial with regard to the animal’s condition. It is important to emphasize that while gustatory stimulation was accomplished, monkeys were not disturbed in their ongoing activities, tastants could be applied without troubling interactions between the experimenter and the animal. Thus, this taste stimulus delivery technique proved to be a practical and reliable way to investigate gustatory neural coding in neurophysiological-behavioral experiments with awake monkeys.
ACKNOWLEDGEMENTS
The authors thank Mr. K. Fukai for his valuable technical assistance. This work was supported partly by Grants-in-Aid 59225027 (S.A.) and 6044.0097and 57440085 (Y.O.) from the Ministry of Education, Science and Culture of Japan.
NEW TASTE
STIMULATION
METHOD
667
IN MONKEYS
FIG. 2. Position of the polyethylene tubing (illustrated a subcutaneous duct into the mouth.
by dotted lines) guided from the posterior part of the dental acrylic headpiece
through
REFERENCES I. Aou. S.: Oomura. Y.: Nishmo, H.; Inokuchi, A.; Miauno. Y. Influence of catecholamines on reward-related neuronal activity in monkey orbitofrontal cortex. Brain Res. 267:165-170; 1983. 2. Boudreau. J. C.: Oravec. J. J.; Hoang. N. K. Taste systems of goat geniculate ganglion. J. Neurophysiol. 48(5): 1226-1242; 1982. 3. Burton. M. J.; Rolls, E. T.; Mora, F. Effects of hunger on the response\ of neurons in the lateral hypothalamus to the sight and taste of food. Exp. Neurol. 51:668-677: 1976. 4. Chang. F-C. T.; Scott. T. R. A technique for gustatory stimulus delivery in the rodent. Chem. Senses 9:9l-96; 1984. 5. Erickson, R. I’.; Doetsch, G. S.: Marshall, D. A. The gustatory neural response function. J. Gen. Physiol. 49:247-263; 1965. 6. Gjorstrup. P. Taste and chewing as stimuli for the secretion of amylase from the parotid gland of the rabbit. Acta Physiol. Stand. 1 IO: 295-30 I ; 1980. 7. Grill, H. J.: Norgren, R. The taste reactivity test, I. Mimetic responses to gustatory stimuli in neurologically normal rats. Brain Rcs. 143:263-279: 1978.
8. Karadi, Z.; Oomura. Y.; Nishino. H.; Aou. S.: Fujita, I. Functional organization of lateral hypothalamic glucose-sensitive (GS) and glucose-insensitive (GIS) neurons in the monkey. Sot. Neurosci. Abstr. 13:465: 1987. 9. Nishino. H.: Oomura. Y.; Karadi. 2.; Aou, S.: Lenard. L.; Kai. Y.: Fukuda, A.: Ito. C.; Mitt, 8. I.: Plata-Salaman. C. P. Internal and external information processing by lateral hypothalamic glucose-jensitive and insensitive neurons during bar press feeding in the monkey. Brain Res. Bull. 20:839-845: 1988. IO. Sat”, M.; Ogawa, H.; Yamashita, S. Response properties of macaque monkey chorda tympani fibers. J. Gen. Physiol. 66:781-810; 1975. Il. Scott. T. R.; Yaxley, S.: Sienkiewicz. Z. J.: Rolls. E. T. Gustatory responses in the nucleus tractus solitarius of the alert cynomolgus monkey. J. Neurophysiol. 55(l): 182-200: 1986. 12. Travers. S. P.; Smith, D. V. Responsiveness of neurons in the hamster parabrachial nuclei to taste mixtures. J. Gen. Physiol. 84:221250: 1983.
KARADI.
66X
NISHINO,
OOMURA.
X:W’r
AND AU1.
A SENSOR c
elgiloy
epoxy
glass pipe
wire
resin
B ONSET
MARKING to
CIRCUIT
sensor
FIG. 3. Schematic delineation of the sensor (A) and the onset marking circuit (B) of the stimulus delivery system used for rhesus monkeys.
FIG. 4. Trace of elicited activity ia) of a laterai bypt~thalamic neuron as well as onset marking signal (b) of the co~esponding gustatory stimulus (0.3 M D-glucose). Calibration: I50 pV for evoked responses. 5 V fr>l onset mark, respectively; time scale is IO s.