Sniffing and motivated behavior in the rat

Physiology and Behavior. Vol. 6, lap. 49-52. Pergamon Press, 1971. Printed in Great Britain

Sniffing and Motivated Behavior in the Rat SAMUEL

CLARKE

A N D J A Y A. T R O W I L L

Department of Psychology, University of Massachusetts, Amherst, Massachusetts 01002, U.S.A. (Received 15 June 1970) S. AND J. A. TROWILL. Sniffing and motivated behavior in the rat. PHYSIOL.BEHAV. 6 (1) 49-52, 1971.--The effect of rewarding brain stimulation on inspiration rate in the rat was investigated using a temporal conditioning and a fixed-interval lever-pressing procedure. In early temporal conditioning trials, inspiration frequency was most pronounced following brain stimulation. With conditioning, inspiration frequency became most pronounced preceding brain stimulation. Inspiration frequency in the sniffing range remained part of the unconditional response to rewarding brain stimulation throughout both experiments of this study. In the fixed-interval procedure, inspiration frequency increased just prior to the first lever-press of an interval, and continued to increase until reinforcement was delivered. These results suggest that measurement of respiration/sniffing frequency may have relevance to classical conditioning interpretations of motivated behavior, CLARKE,

Incentive-motivation

Reinforcement

Sniffing

Brain stimulation

Conditioning

Rats

Apparatus

BOLLES [5] has recently proposed that the principles of motivation can be translated into the principles of reinforcement. The hypothetical processes by which motivated behavior can be derived from reinforcement principles have variously been termed secondary or conditional reinforcement [10], preconsummatory excitement [13], anticipatory invigoration [1, 8], incentive-motivation [2, 16] etc. All of these terms, reduced to their essential experimental operations, involve contiguous pairing of motivationally neutral stimulation with reinforcing stimulation. Bindra and Campbell [3], using rats, have paired an auditory stimulus with half.second trains of positive electrical hypothalamic stimulation. With conditioning, the auditory stimulation came to elicit walking or rearing while sniffing above control levels. This ability of the rewarding brain stimulation to generate positive incentive-motivational effects in previously neutral stimuli was seen as a property common to all positive reinforcers. In the present experiments, the procedures of temporal conditioning and fixed-interval instrumental learning have been used to continue investigation of the relationship between sniffing and motivated or reinforced behavior in the rat.

The experiments were run in a 22 × 33 x 40 cm chamber which, for the instrumental learning sessions, contained a rat lever (Lehigh Valley Electronics 1352) mounted 8 cm from the floor. This lever protruded only 1 cm into the chamber to prevent the probe assembly from becoming entangled. Brain stimulation consisted of 1.0 sec trains of 60-cycle sine waves of a constant current intensity set approximately 10 tzA above that which maintained steady self-stimulation behavior on a continuous reinforcement schedule. Current intensity was monitored with an a.c. microammeter in series with the animal. Respiration and sniffing behavior was measured with a thermocouple probe (manufactured to specification by P. Beckman of High Temperature Instruments Corp., Philadelphia) inserted in the nasal cannula. The probe was conneeted through a swivel to a HiGain preamplifier (E & M Instrument Company). Recordings were made on an E & M physiograph with the chart speed set at 1 cm/see. An upward deflection of the recording pen indicated the inspiration of relatively cool room air; a downward deflection indicated the expiration of air warmed by the body. The response time of the probe was approximately 5 msee; its sensitivity was approximately 50 ~V/degree Centigrade. F o r the temporal conditioning experiment, reinforcement was recorded on the event channel of the physiograph; for the fixed-interval experiment, both lever pressing and reinforcement were recorded on this channel.

METHODS AND MATERIALS

Animals and Surgery F o u r mature male Charles River rats which displayed lever-pressing behavior for stimulation of monopolar electrodes unilaterally aimed at the lateral hypothalamus were selected for these experiments. Stereotaxic coordinates were 1.4 m m posterior to bregrna, 1.6 mm lateral to the midline, and 8.9 m m ventral from skull top [12]. Each rat was implanted with a cannula in one nasal passage so that temperature changes in this airway could be measured with a thermocouple probe during recording sessions [7]. Throughout the experiments, the subjects were maintained on ad lib Purina Lab Chow and water.

Procedure The first experiment (temporal conditioning) was run in three days. On the first day, the animals were given a one-hr session of habituation to the chamber. They then received a single one-see train of brain stimulation every 20 see for 100 presentations on each of the second and third days. Records were made of inspiration rate throughout both conditioning sessions. In the second experiment, the same four rats were trained 49

CLARKI A N D I R t ) ~ I I I

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to lever-press on a fixed-interval 20-sec schedule (FI-20") for one-sec trains of brain stimulation of the intensity used for temporal conditioning. On the first day of this experiment, starting with a continuous reinforcement schedule, intervals of non-reward were gradually increased to 20 sec during a one-hr session. On the second day, the rats were allowed to press on the FI-20" schedule for one-hundred reinforcements. On the third day, inspiration was recorded for another onehundred fixed-interval trials. In the temporal conditioning experiment, the number of inspirations (upward deflections on the recording pen) within four-sec periods of the 20-sec conditioning interval were handcounted and transformed into an inspiration-per-sec score for respective four-sec periods. In the fixed-interval experiment, each of the last ten intervals in which there was at least 9 sec of non-pressing followed by at least 3 sec of pressing before reinforcement was delivered, were hand-scored for inspirations per each of these seconds. (No attention was paid to the often varying amplitude of the respiration/sniffing recordings because temperature changes were recorded in only one nasal passage. The technique is, therefore, primarily useful for measurement of inspiration/expiration frequency.)

It can be seen from Trials 1-10 that initially the inspiration rate was highest immediately following brain stimulation. With conditioning (Trials 90-99 and 190--199), this poststimulus inspiration rate decreased markedly while prestimulation inspiration rate increased as a function of temporal contiguity to the delivery of reinforcement. Sniffing, in the range of 6-9 inspirations per sec, remained a completely consistent part of the unconditional response to brain stimulation in all four animals. Representative physiograph records, taken from Rat SNI9 late in temporal conditioning are presented in Fig. 2A.

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Temporal Conditioning Averaged inspiration-per-sec scores for the first and last ten trials of the first day (Trials 1-10 and 90-99) and for the last ten trials of the second day (Trials 190-199) of temporal conditioning are presented individually for each rat in Fig. 1. ii

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FIG. 2. A. Representative records of Rat SN19 for temporal conditioning (TC) trials 184, 186 and 188. The one-see reinforcement marks correspond to one-see trains of brain stimulation. Inspiration up. B. Representative records of the same rat responding on fixedinterval (FT)Trials 78, 80 and 82. The short marks on the event lines signify non-reinforced lever presses. The longer, one-see marks signify lever presses that were reinforced by one-see trains of brain stimulation.

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FIG. 1. Individuallyplotted inspiration-per-see data of four animals. Each line is the average of ten temporal conditioning intervals. Reinforcement was delivered just before the first 4-see period of the 20-see interval and just after the fifth 4-see period of this interval.

The data from the second experiment are presented in Fig. 3. For rats SN19 and SN22, the last ten intervals in which there was a non-reinforced lever-press, preceded by at least 9 sec without responding, and followed by at least 3 sec of (premature) non-reinforced pressing, are plotted. Rat SN20 pulled the thermocouple probe part way out of its cannula midway in the recording session. Therefore, data for this animal came from the last ten criterion intervals of the first fifty (instead of the entire 99) inter-reinforcement intervals. Rat SN21 developed excessive fluid, in its nasal passages and did not therefore produce a scoreable respiration/ sniffing record. The data in Fig. 3 show that inspiration-rate increased just prior to the first lever-press of a fixed-interval, and continued to increase during the remainder of the interval, that is, until reinforcement was delivered. As a measure of reliability,

SNIFFING AND MOTIVATED BEHAVIOR

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FIG. 3. Individually plotted inspiration-per-sec data of three rats responding on a fixed-interval 20-sec schedule. Each line is the average of ten intervals in which there was at least 9 sec of nonpressing, followed by at least 3 sec of lever pressing before reinforcement was delivered.

each of the ten scores for the second preceding onset of pressing was compared with the mean of the entire 90 pre-pressing scores for each animal. F o r rat SN20, nine of these ten scores were above the pre-pressing mean of that animal. F o r the other two rats in Fig. 3, all ten scores for the second preceding onset of lever-pressing were higher than the respective pre-pressing means of these two animals. Representative inspiration, lever-pressing, and reinforcement recordings for rat SN19 are presented in Fig. 2B. The intervals illustrated in this figure immediately preceded those that were analyzed for this rat. These records were selected in sequence (as were those in Fig. 2A) to emphasize the orderly changes in respiration/sniffing frequency under the conditions imposed by the present experiments.

DISCUSSION

The results of the temporal conditioning experiment can be seen to extend work which has shown that conditional sniffing is elicited by stimuli contiguously paired with positive brain stimulation in non-deprived rats [3, 7], and with water delivery in thirsty rats [4]. Unlike the observational methods used to measure walking or rearing while sniffing in these previous studies, direct measurement of the respiration/

snitfmg response permits an analysis of moment-to-moment changes in terms of rate rather than yes-or-no classifications in terms of occurrence. N o attempt has been made in the present experiments to distinguish between resting respiration and sniffing behavior because the physiograph records do not always show abrupt changes in frequency between these two presumably different modes of response. Welker [17], through a motion picture analysis of the rat sniffing pattern, has determined that sniffing frequency varies between five and eleven cycles per see. This determination was based on the frequency of vibrissae, nares and head movements as well as on the frequency of the inspiration/expiration cycle. As yet unpublished observations in our laboratory have shown that the respiration/sniffing frequency varies from as low as ½ cycle per sec in rats anticipating or receiving strong tail shock, to as high as eleven cycles per see in rats anticipating or receiving positive hypothalamic stimulation. It is therefore possible that respiration/sniffing frequency may be useful as a measurable response across the full spectrum of negative to positive incentive conditions (cf. [2, 4]). The finding that sniffing was part of the unconditional response to the brain stimulation is consistent with previous findings that forward locomotor activity and sniffing are associated with stimulation of reinforcing electrode sites throughout the lateral hypothalamus [6]. The behavior of the rats which was associated with the increase in inspiration rate just before onset of pressing in the fixed-interval experiment (Fig. 3) is worth describing. Quite typically, these rats faced away from the lever and lay down during the initial periods of the non-reinforcement interval. Towards the end of this interval, while still lying down, their vibrissae suddenly began to twitch and their snouts were lifted. With their vibrissae continuing to protract and retract, the rats rose, turned toward, and began to press the lever. Vibrissa protraction and retraction is synchronized with the inspiration/expiration cycle and indicates that the rat is sniffing [9, 17]. If increases in inspiration rate can be generally shown to precede the appearance of instrumental behavior in the rat, then this response system (as a measure of conditioning) may have considerable relevance to theories which attempt to explain instrumental behavior primarily in terms of classical conditioning principles of reinforcement [10, 13-15, 18]. Since sniffing occurs as a conditional response when motivationally neutral stimuli are contiguously paired with reinforcing stimuli [3, 4], respiration/sniffing frequency may, in certain situations, reflect magnitudes of conditional or secondary reinforcement. Komisaruk [9] has recently presented evidence showing that activity of the vibrissae muscles is temporally correlated with theta waves in Limbic System E E G during bouts of exploratory sniffing in the rat. While the relationship between limbic system theta and reinforcement is beyond the scope of this discussion, a recent paper by Paxinos and Bindra [11] may be consulted for important findings and references.

REFERENCES 1. Appley, M. H. Derived motives. Ann. Rev. Psychol. 21: 485518, 1970. 2. Bindra, D. Neuropsychological interpretation of the effects of drive and incentive-motivation on general activity and instrumental behavior. Psychol. Rev. 75: 1-21, 1968.

3. Bindra, D. and J. F. Campbell. Motivational effects of rewarding intracranial stimulation. Nature 215: 375-376, 1967. 4. Bindra, D. and T. Palfai. The nature of positive and negative incentive-motivational effects on general activity. J. comp. physiol. Psychol. 63: 288-297, 1967.

52 5. Bolles, R. C. Theory of Motivation. New York: Harper & Row, 1967. 6. Christopher, Sister Mary and C. M. Butter. Consummatory behaviors and locomotor exploration evoked from selfstimulation sites in rats. J. comp. physiol. Psychol. 66: 335-339, 1968. 7. Clarke, S., J. Panksepp and J. Trowill. A method of recording sniffing in the free-moving rat. Physiol. Behav. 5: 125-126, 1970. 8. Corer, C. N. and M. H. Appley. Motivation: Theory and Research. New York: Wiley, 1964. 9. Komisaruk, B. Synchrony between limbic system theta activity and rhythmical behavior in rats. J. eomp. physiol. Psychol. 70: 482~92, 1970. 10. Mowrer, O. H. Learning Theory and the Symbolic Processes. New York: Wiley, 1960, (cf. chapter 1). I 1. Paxinos, G. and D. Bindra. Rewarding intracranial stimulation, movement and the hippocampal theta rhythm. Physiol. Behav. 5: 227-231, 1970. 12. Pellegrino, L. J. and A. J. Cushman. A Stereotaxic Atlas of the Rat Brain. New York: Appleton-Century-Crofts, 1967.

('IARI~II A N D ' I R O W I t l 13. Sheffield, F. D. New evidence on the drive-inductiot~ theory or reinforcement. In: Current Research hi Motivation, edited by R. N. Haber. New York: Holt, Rinehart & Winston, lt)66, pp. 111-122. 14. Sheffield, F. D. Relation between classical conditilming and instrumental learning. In: Classical Conditioning: i1 Symposium, edited by W. F. Prokasy. New York: AppletonCentury-Crofts, 1965, pp. 302-322. 15. Stein, I.. Reciprocal action of reward and punishment mechanisms. In: The Role of Pleasure in Behavior, edited by R. Heath. New York: Harper, 1964, pp. 113 139. 16. Trowill, J. A., J. Panksepp and R. Gandelman. An incentixc model of rewarding brain stimulation. Psyehol. Rev. 76: 3ful381, 1969. 17. Welker, W. I. Analysis of sniffing in the albino rat. Behavior 22:223 244, 1964. 18. Williams, D. R. Classical conditioning and incentive motivation. In: Classical Conditioning: A 5~vmposium, edited by W. F. Prokasy. New York: Appleton-Century-Crofls, 1964, pp. 340-357.