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Reinforcement contrast effects on the rewarding and aversive components of intracranial stimulation
LEAHSING
AND
MOTI\‘.%TIOZI
Reinforcement Aversive
(1973)
4, 397-404
Contrast Components DALE
Department
of Psychology,
Effects on the of Intracranial
Rewarding Stimulation’
and
M. ATRENS,”
University
of Sydney,
Sydney
2006
N.S.W.,
Australia
AND
FRANCISCA VON VIETINGHOFF-RIESCH, AND AGHOP DER-KARARETLAN The
American
University
of Beirut,
Beirut,
Lebanon
Rats performing a free-operant locomotor response in a shuttlebox to initiate and then escape medial diencephalic stimulation were tested daily on a randomized sequence of three stimulation intensities. In spite of a l-hr interval between stimulation intensity changes, substantial and graded reinforcement contrast effects were obtained. “Elation” effects were obtained both on the rewarding (latency to initiate) and the aversive (latency to escape) components of stimulation whereas “depression” effects were found only on the measure of reward. An important determinant of an organism’s response to a given reinforcer is the relationships that reinforcer has with concurrent and/or previous reinforcers (Black, 1968; Crespi, 1942; Dunham, 1968; Hemmes & Eckerman, 1972; Pear & Wilkie, 1971; Premack, 1969; Wilkie, 1972). For example, abrupt increases in magnitude of reward may produce performance levels temporarily higher than those of the same subject maintained on the high magnitude of reward all along (Crespi, 1942). This enhancement of performance is called positive contrast or elation. Conversely, abrupt decreases in magnitude of reward may produce a disproportionate and transient decrement in performance that is called negative contrast or depression ( Crespi, 1942). Since the great majority of the contrast studies involve food-deprived organisms working for food reinforcement, the generality of this phe‘The authors would like to thank Evalyn Segal for her thoughtful criticism of an earlier draft of this paper. ‘Requests for reprints should be sent to Dale M. Atrens, Department of Psychology, Copyright All rights
University
of Sydney,
Sydney
@ 1973 by Academic Press, of reproduction in any form
2006
N.S.W.,
397 Inc. reserved.
Australia.
398
ATRENS,
VIETINCHOFF-RIESCH,
AND
DER-KARABETIAN
nomenon to other reinforcers and to low-drive organisms is largely undetermined. Recent evidence by Panskepp and Trowill (1969, 1970) indicates both positive and negative contrast effects can be obtained in nondeprived animals lever-pressing for direct intracranial stimulation (ICS) of the lateral hypothalamic area. They also noted (1970) that contrast effects were not obtained in a discrete trial situation requiring a locomotor response. In recent investigations in our laboratory (Atrens, 1970; Atrens, 1972; Atrens and Von Vietinghoff-Riesch, 1972) we have used a testing paradigm that may be considered intermediate to the two procedures of Panskepp & Trowill (1969, 1970). This is a free-operant situation requiring a locomotor response to initiate ICS followed by another locomotor response to escape the self-initiated ICS. Using this two-way shuttle-box procedure we have demonstrated that any electrode locus in the diencephalon that will sustain initiation behavior will also sustain escape behavior and that substantial reward effects can be produced by ICS at points well medial to the traditional lateral hypothalamic reward area (Atrens, 1970; Atrens, 1972; Atrens & Von Vietinghoff-Riesch, 1972). In contrast to Panskepp and Trowill (1969, 1970) we have had no difficulty in obtaining reinforcement contrast effects with a locomotor response. Nor were these effects limited to lateral hypothalamic stimulation or to the rewarding component of ICS. In fact, we have esperienced considerable difficulty in getting rid of these effects which were contributing an undesirable amount of variance to our latency-intensity functions. METHOD
Animals The subjects were 23 albino rats derived from the Sprague-Dawley strain by the Animal House at the American University of Beirut (Lebanon), weighing 200-350 g at the time of surgery. The animals were housed individuahy and had free access to lab chow and water. Electrode Implantation and Histology Twisted 0.4%mm diameter bipolar electrodes (Plastic Products, Roanoke, Virginia) were stereotaxically implanted at various medial diencephalic loci under chloral-hydrate anesthesia. At the conclusion of the experiment the formalin-fixed brains were embedded in paraffin and 10 pm serial sections were stained for myelinated fibers and cell bodies using 1~x01 fast-blue and cresyl-violet or thionin.
CONTRAST
399
Apparatus The shuttle-box measured 75 cm (length) X 25 cm (width) X 32 cm (depth) and had a clear glass front wall and a grid floor. Photobeams crossed the width of the box 4.5 cm above the floor, 15 cm from either end. Breaking the ON photobeam initiated a continuous train of constant-current 50-Hz sine-wave ICS that could be terminated only by breaking the OFF photobeam at the opposite end of the chamber. Electronic timers recorded both the latency to initiate ICS and the latency to escape ICS. Procedure Postoperatively the animals were screened for self-stimulation at three current levels in the shuttle-box. Low intensity ICS was the minimum current that would produce stable shuttling. The high intensity ICS value was chosen so that it produced maximally vigorous behavior without any attempt at jumping from the box and without producing convulsive seizures, The middle intensity was the mean of the high and low intensities. In order to minimize possible contrast effects (they were not the original object of this research) the animals were run in three separate test sessionsdaily, once at each of the three current levels. A test session consisted of a 5-min warm-up period during which the data were not recorded followed by a 5-min test period during which both latencies to initiate and escape ICS were recorded. The three test sessionswere separated by 1-hr intervals and the daily order of presentation of the three current intensities was randomized. To evaluate the successof this procedure in eliminating contrast effects the following comparisons were made on both latencies. The baseline or noncontrasted value of each latency was taken as the latency when the particular ICS intensity was the first in a daily sequence. Low positive contrast effects were assessed by comparing a baseline latency with another latency at the same current level that had been preceded (by 1 hr) by a test at the next lower value. For example, low positive contrast would be determined by subtracting the high-intensity latency of the sequence, say, HLM, from the high intensity latency of the sequence, say, MHL. To extend the example, a high positive contrast comparison was that between the high-intensity latency of the sequence, say, HLM, and the high-intensity latency of the series, say, LHM. In other words, high positive contrast was assessedin a situation in which high-intensity ICS followed low intensity ICS and low positive contrast in a situation where high intensity ICS followed medium intensity ICS. By the same reasoning, high nega-
400
ATRENS,
VIETINGHOFF-RIESCH,
AND
DER-KARABETIAN
tive contrast was assessed in a situation where low intensity ICS followed high-intensity ICS and low negative contrast in a situation where low intensity ICS followed medium-intensity ICS. Since it became apparent that this procedure did not eliminate contrast effects we later switched to a fixed sequence of LMH in an attempt to distribute these effects in an approximately even manner. The data reported here are those from the randomized procedure. Since the animals were run only 4-6 days on the randomized procedure, each contrast condition usually occurred only once so there was virtually no opportunity for the experimenter to “select” the data or to evaluate the persistence of these effects over time. In the few cases where an S was run twice on a given contrast condition the first value was employed for purposes of analysis. Because of the heterogeneity of variance in the difference scores, the data were analysed nonparametrically with the Wilcoxon matched-pairs signed ranks test (Bruning & Kintz, 1968). Since we had specific predictions in each case as to the direction of latency changes, all of the probabilities presented herein are one-tailed. RESULTS
The response latencies which are plotted in Figs. 1 and 2 indicate that substantial and graded reinforcement contrast effects did occur. As Fig. 1 shows, the animals took longer to initiate low-intensity ICS when it followed medium-intensity ICS (p < .005) and when it followed highintensity ICS (p < .Ol) as compared to the case when low-intensity ICS was first in the daily sequence. The two negatively contrasted latencies to initiate ICS were not significantly different ( p < .05) from each other, nor were there any significant differences in the latencies to escape lowintensity ICS as a function of the sequence of ICS intensities. As Fig. 2 shows, the animals initiated high-intensity ICS significantly faster when it followed medium-intensity ICS (‘p < .Ol) or low-intensity ICS (p < .025) as compared to when the high-intensity was the first in a daily sequence. The two contrasted latencies to initiate were not significantly different (p < .OS) from each other. Concurrently, these animals escaped high-intensity ICS significantly more slowly when it followed medium-intensity ICS ( p < .05) or low-intensity ICS ( p < .()I) as compared to when the high-intensity ICS was the first in a daily sequence. In addition the two contrasted escape late&es were significantly different (p < .Ol) from each other. Microscopic examination of the stained brain sections revealed that in 18 of the animals the electrodes were located in the medial and paraventricular hypothalamic nuclei. In the remaining five animals the
401
C0STRAS-i
-----_________
a =
ESCAPE
lcs
8 6i 2 d
I NONE
AMOUNT
LOW
OF STIMULUS
HIGH,
CONTRAST
FIG. 1. Negative reinforcement contrast effects (depression) on the rewarding and aversive components of medial diencephalic brain stimulation in 23 rats. The no-contrast data points represent the response latencies to initiate and escape ICS when the low intensity was first in a daily sequence. Low negative contrast was defined as the case where low followed the medium-intensity in a daily sequence. High negative contrast was defined as the case where low followed the high-intensity in a daily sequence.
electrode tips terminated in the ventral thalamus including the nucleus reuniens, zona incerta.
and medial aspects of the nucleus gelatinosus and the
DISCUSSION
If an increase in the latency to initiate ICS is considered to indicate decreased reward and a decrease in the latency to initiate ICS is considered to indicate increased reward, it is apparent that the free-operant shuttle paradigm is sensitive to both positive and negative reward contrast effects. When low-intensity ICS was preceded by either medium or high-intensity ICS the animals responded much less vigorously to obtain it in comparison to the case where it was not contrasted. Conversely, when high-intensity ICS was preceded by either meduim or lowintensity ICS, the animals responded much more vigorously to obtain it, again in comparison with the noncontrasted case.
102
ATRESS,
WETINGHOFF-RIESCH,
AND
DER-KARABETIAN
9i
4 k 1
I NONE
0
AMOUNT
1 LOW OF
1 HIGH
STIMULUS
CONTRAST
FIG. 2. Positive reinforcement contrast effects (elation) on the rewarding and aversive components of medial diencephalic brain stimulation in 23 rats. The nocontrast data points represent the response latencies to initiate and escape ICS when the high intensity was first in a daily sequence. Low positive contrast was defined as the case where high followed the medium intensity in a daily sequence. High positive contrast in a daily sequence.
was
defined
as the case where
high
followed
the
low
intensity
By the same reasoning as above, an increase in the latency to escape ICS may be taken to indicate decreased aversion, whereas a decrease in the latency to escape ICS indicates increased aversion. When highiutensity ICS was preceded by either medium or low-intensity ICS, the animals escaped more slowly in comparison with the noncontrasted case.
However, the aversiveness of low-intensity
ICS was not changed by ICS. Besides constituting a new type of contrast effect, the concurrent aversion data provide a useful control to assessthe specificity of the reward contrast effects. For example, if preceding a high-intensity ICS by low or medium-intensity ICS simply produced a sort of nonspecific activation, one would expect the animals to run faster in both directions. This was clearly not the case since, in the positive contrast situation contrasting
it with
either
high
or medium
intensity
the animals turned the ICS on more quickly, while, at the same time, they escaped ICS more slowly. Similarly, if the negative contrast pro-
CONTRAST
403
cedure produced a general depressive effect one would expect the animal to respond more slowly in both directions. Again, this did not occur. In the negative contrast situation the latencies to initiate ICS showed a large and significant rise while the concurrent escape latencies remained completely unaffected. It should be mentioned that we have previously shown that a significant aversive component accompanies rewarding ICS anywhere in the forebrain and that these two basic components of motivation (reward and aversion) are independent of each other (Atrens, 1970; 1972; Atrens & Von Vietinghoff-Riesch, 1972). The dissociation of diencephalic reward and aversion processes is further supported by the present findings. It is noteworthy that these contrast effects were produced by medial hypothalamic and ventral thalamic stimulation, whereas Panskepp and Trowill (1969, 1970) employed lateral hypothalamic stimulation. This supports our contention (Atrens & Von Vietinghoff-Riesch, 1972) as to the qualitative similarity between lateral and medial diencephalic reward processes. Perhaps the most surprising aspect of the present data is that the contrast effects were produced in spite of a I-hr interval between switching ICS intensities and a 5-min warm-up on the new intensity! Contrast effects are almost always evaluated over much shorter intervals between reinforcement condition changes, although Premack (1969) reported substantial contrast effects in two subjects with a 16-hr inter-test interval. Premack (1969, p. 136’) h as suggested that “Contrast results if and only if there is a change in the aversiveness associated with OIW of the components in the schedule.” The present data show that the avcrsivcness itself may be subject to contrast and that reward contrasts can be obtained even when there is no change in aversion. AS Rolles (1967) has pointed out, the systematic study of reinforcement contrast effects has been greatly complicated by the elusiveness of the basic phenomena involved. While the present study is by no means a parametric study, the technique described herein should make further investigations into the parameters of contrast effects relatively easy. REFERENCES II. RI. Reinforcing and emotional con
404
ATRESS,
VIETIKGHOFF-RIESCH,
AND
DER-KARABETIAN
BLACK, R. H. Shifts in magnitude of reward and contrast effects in instrumental and selective learning: A reinterpretation. Psychological Review, 1968, 75, 11-3-126. CRESPI, L. P. Quantitative variation in incentive and performance in the white rat. American Journal of Psychology, 1942, 55, 467-517. BOLLES, R. C. Theory of Motivation. New York: Harper and Row, 1967. BRUNING, J. L., & KINTZ, B. L. Computational handbook of statistics. Glenview: Scott Foresman, 1968. DUNHAM, P. J. Contrasted conditions of reinforcement: A selective critique. Psychological Bulletin, 1968, 69, 295-325. HEMMES, N. S., & ECKERMAN, D. A. Positive interaction (induction) in multiple variable-interval, differential-reinforcement-of-high-rate schedules. Journal of the Experimental Analysis of Behavior, 1972, 17, 51-57. PANSKEPP, J., & TROWILL, J. Positive and negative contrast effects with hypothalamic reward. Physiology and Behnvim, 1969, 4, 173-175. PAXSKEPP, J., & TROWILL, J. Positive incentive contrast with rewarding electrical stimulation of the brain. Journal of Comparative and Physiological Psychology, 1970, 70, 358-363. PEAR, J. J., & WILKIE, 1). hf. Contrast and induction in rats on multiple schedules. Journal of the Experimel&d An&is of Behavior, 1971, 15, 289-296. PREMACK, D. On some boundary conditions of contrast. In J. T. Tapp (Ed. ), Reinforcement and behavior. New York: Academic Press, 1969. WILKIE, D. M. Variable-time reinforcement in multiple and concurrent schedules. Journal of the Experimental Analysis of Behavior, 1972, 17, 59-66. (Received
June
9, 1972)
AND
MOTI\‘.%TIOZI
Reinforcement Aversive
(1973)
4, 397-404
Contrast Components DALE
Department
of Psychology,
Effects on the of Intracranial
Rewarding Stimulation’
and
M. ATRENS,”
University
of Sydney,
Sydney
2006
N.S.W.,
Australia
AND
FRANCISCA VON VIETINGHOFF-RIESCH, AND AGHOP DER-KARARETLAN The
American
University
of Beirut,
Beirut,
Lebanon
Rats performing a free-operant locomotor response in a shuttlebox to initiate and then escape medial diencephalic stimulation were tested daily on a randomized sequence of three stimulation intensities. In spite of a l-hr interval between stimulation intensity changes, substantial and graded reinforcement contrast effects were obtained. “Elation” effects were obtained both on the rewarding (latency to initiate) and the aversive (latency to escape) components of stimulation whereas “depression” effects were found only on the measure of reward. An important determinant of an organism’s response to a given reinforcer is the relationships that reinforcer has with concurrent and/or previous reinforcers (Black, 1968; Crespi, 1942; Dunham, 1968; Hemmes & Eckerman, 1972; Pear & Wilkie, 1971; Premack, 1969; Wilkie, 1972). For example, abrupt increases in magnitude of reward may produce performance levels temporarily higher than those of the same subject maintained on the high magnitude of reward all along (Crespi, 1942). This enhancement of performance is called positive contrast or elation. Conversely, abrupt decreases in magnitude of reward may produce a disproportionate and transient decrement in performance that is called negative contrast or depression ( Crespi, 1942). Since the great majority of the contrast studies involve food-deprived organisms working for food reinforcement, the generality of this phe‘The authors would like to thank Evalyn Segal for her thoughtful criticism of an earlier draft of this paper. ‘Requests for reprints should be sent to Dale M. Atrens, Department of Psychology, Copyright All rights
University
of Sydney,
Sydney
@ 1973 by Academic Press, of reproduction in any form
2006
N.S.W.,
397 Inc. reserved.
Australia.
398
ATRENS,
VIETINCHOFF-RIESCH,
AND
DER-KARABETIAN
nomenon to other reinforcers and to low-drive organisms is largely undetermined. Recent evidence by Panskepp and Trowill (1969, 1970) indicates both positive and negative contrast effects can be obtained in nondeprived animals lever-pressing for direct intracranial stimulation (ICS) of the lateral hypothalamic area. They also noted (1970) that contrast effects were not obtained in a discrete trial situation requiring a locomotor response. In recent investigations in our laboratory (Atrens, 1970; Atrens, 1972; Atrens and Von Vietinghoff-Riesch, 1972) we have used a testing paradigm that may be considered intermediate to the two procedures of Panskepp & Trowill (1969, 1970). This is a free-operant situation requiring a locomotor response to initiate ICS followed by another locomotor response to escape the self-initiated ICS. Using this two-way shuttle-box procedure we have demonstrated that any electrode locus in the diencephalon that will sustain initiation behavior will also sustain escape behavior and that substantial reward effects can be produced by ICS at points well medial to the traditional lateral hypothalamic reward area (Atrens, 1970; Atrens, 1972; Atrens & Von Vietinghoff-Riesch, 1972). In contrast to Panskepp and Trowill (1969, 1970) we have had no difficulty in obtaining reinforcement contrast effects with a locomotor response. Nor were these effects limited to lateral hypothalamic stimulation or to the rewarding component of ICS. In fact, we have esperienced considerable difficulty in getting rid of these effects which were contributing an undesirable amount of variance to our latency-intensity functions. METHOD
Animals The subjects were 23 albino rats derived from the Sprague-Dawley strain by the Animal House at the American University of Beirut (Lebanon), weighing 200-350 g at the time of surgery. The animals were housed individuahy and had free access to lab chow and water. Electrode Implantation and Histology Twisted 0.4%mm diameter bipolar electrodes (Plastic Products, Roanoke, Virginia) were stereotaxically implanted at various medial diencephalic loci under chloral-hydrate anesthesia. At the conclusion of the experiment the formalin-fixed brains were embedded in paraffin and 10 pm serial sections were stained for myelinated fibers and cell bodies using 1~x01 fast-blue and cresyl-violet or thionin.
CONTRAST
399
Apparatus The shuttle-box measured 75 cm (length) X 25 cm (width) X 32 cm (depth) and had a clear glass front wall and a grid floor. Photobeams crossed the width of the box 4.5 cm above the floor, 15 cm from either end. Breaking the ON photobeam initiated a continuous train of constant-current 50-Hz sine-wave ICS that could be terminated only by breaking the OFF photobeam at the opposite end of the chamber. Electronic timers recorded both the latency to initiate ICS and the latency to escape ICS. Procedure Postoperatively the animals were screened for self-stimulation at three current levels in the shuttle-box. Low intensity ICS was the minimum current that would produce stable shuttling. The high intensity ICS value was chosen so that it produced maximally vigorous behavior without any attempt at jumping from the box and without producing convulsive seizures, The middle intensity was the mean of the high and low intensities. In order to minimize possible contrast effects (they were not the original object of this research) the animals were run in three separate test sessionsdaily, once at each of the three current levels. A test session consisted of a 5-min warm-up period during which the data were not recorded followed by a 5-min test period during which both latencies to initiate and escape ICS were recorded. The three test sessionswere separated by 1-hr intervals and the daily order of presentation of the three current intensities was randomized. To evaluate the successof this procedure in eliminating contrast effects the following comparisons were made on both latencies. The baseline or noncontrasted value of each latency was taken as the latency when the particular ICS intensity was the first in a daily sequence. Low positive contrast effects were assessed by comparing a baseline latency with another latency at the same current level that had been preceded (by 1 hr) by a test at the next lower value. For example, low positive contrast would be determined by subtracting the high-intensity latency of the sequence, say, HLM, from the high intensity latency of the sequence, say, MHL. To extend the example, a high positive contrast comparison was that between the high-intensity latency of the sequence, say, HLM, and the high-intensity latency of the series, say, LHM. In other words, high positive contrast was assessedin a situation in which high-intensity ICS followed low intensity ICS and low positive contrast in a situation where high intensity ICS followed medium intensity ICS. By the same reasoning, high nega-
400
ATRENS,
VIETINGHOFF-RIESCH,
AND
DER-KARABETIAN
tive contrast was assessed in a situation where low intensity ICS followed high-intensity ICS and low negative contrast in a situation where low intensity ICS followed medium-intensity ICS. Since it became apparent that this procedure did not eliminate contrast effects we later switched to a fixed sequence of LMH in an attempt to distribute these effects in an approximately even manner. The data reported here are those from the randomized procedure. Since the animals were run only 4-6 days on the randomized procedure, each contrast condition usually occurred only once so there was virtually no opportunity for the experimenter to “select” the data or to evaluate the persistence of these effects over time. In the few cases where an S was run twice on a given contrast condition the first value was employed for purposes of analysis. Because of the heterogeneity of variance in the difference scores, the data were analysed nonparametrically with the Wilcoxon matched-pairs signed ranks test (Bruning & Kintz, 1968). Since we had specific predictions in each case as to the direction of latency changes, all of the probabilities presented herein are one-tailed. RESULTS
The response latencies which are plotted in Figs. 1 and 2 indicate that substantial and graded reinforcement contrast effects did occur. As Fig. 1 shows, the animals took longer to initiate low-intensity ICS when it followed medium-intensity ICS (p < .005) and when it followed highintensity ICS (p < .Ol) as compared to the case when low-intensity ICS was first in the daily sequence. The two negatively contrasted latencies to initiate ICS were not significantly different ( p < .05) from each other, nor were there any significant differences in the latencies to escape lowintensity ICS as a function of the sequence of ICS intensities. As Fig. 2 shows, the animals initiated high-intensity ICS significantly faster when it followed medium-intensity ICS (‘p < .Ol) or low-intensity ICS (p < .025) as compared to when the high-intensity was the first in a daily sequence. The two contrasted latencies to initiate were not significantly different (p < .OS) from each other. Concurrently, these animals escaped high-intensity ICS significantly more slowly when it followed medium-intensity ICS ( p < .05) or low-intensity ICS ( p < .()I) as compared to when the high-intensity ICS was the first in a daily sequence. In addition the two contrasted escape late&es were significantly different (p < .Ol) from each other. Microscopic examination of the stained brain sections revealed that in 18 of the animals the electrodes were located in the medial and paraventricular hypothalamic nuclei. In the remaining five animals the
401
C0STRAS-i
-----_________
a =
ESCAPE
lcs
8 6i 2 d
I NONE
AMOUNT
LOW
OF STIMULUS
HIGH,
CONTRAST
FIG. 1. Negative reinforcement contrast effects (depression) on the rewarding and aversive components of medial diencephalic brain stimulation in 23 rats. The no-contrast data points represent the response latencies to initiate and escape ICS when the low intensity was first in a daily sequence. Low negative contrast was defined as the case where low followed the medium-intensity in a daily sequence. High negative contrast was defined as the case where low followed the high-intensity in a daily sequence.
electrode tips terminated in the ventral thalamus including the nucleus reuniens, zona incerta.
and medial aspects of the nucleus gelatinosus and the
DISCUSSION
If an increase in the latency to initiate ICS is considered to indicate decreased reward and a decrease in the latency to initiate ICS is considered to indicate increased reward, it is apparent that the free-operant shuttle paradigm is sensitive to both positive and negative reward contrast effects. When low-intensity ICS was preceded by either medium or high-intensity ICS the animals responded much less vigorously to obtain it in comparison to the case where it was not contrasted. Conversely, when high-intensity ICS was preceded by either meduim or lowintensity ICS, the animals responded much more vigorously to obtain it, again in comparison with the noncontrasted case.
102
ATRESS,
WETINGHOFF-RIESCH,
AND
DER-KARABETIAN
9i
4 k 1
I NONE
0
AMOUNT
1 LOW OF
1 HIGH
STIMULUS
CONTRAST
FIG. 2. Positive reinforcement contrast effects (elation) on the rewarding and aversive components of medial diencephalic brain stimulation in 23 rats. The nocontrast data points represent the response latencies to initiate and escape ICS when the high intensity was first in a daily sequence. Low positive contrast was defined as the case where high followed the medium intensity in a daily sequence. High positive contrast in a daily sequence.
was
defined
as the case where
high
followed
the
low
intensity
By the same reasoning as above, an increase in the latency to escape ICS may be taken to indicate decreased aversion, whereas a decrease in the latency to escape ICS indicates increased aversion. When highiutensity ICS was preceded by either medium or low-intensity ICS, the animals escaped more slowly in comparison with the noncontrasted case.
However, the aversiveness of low-intensity
ICS was not changed by ICS. Besides constituting a new type of contrast effect, the concurrent aversion data provide a useful control to assessthe specificity of the reward contrast effects. For example, if preceding a high-intensity ICS by low or medium-intensity ICS simply produced a sort of nonspecific activation, one would expect the animals to run faster in both directions. This was clearly not the case since, in the positive contrast situation contrasting
it with
either
high
or medium
intensity
the animals turned the ICS on more quickly, while, at the same time, they escaped ICS more slowly. Similarly, if the negative contrast pro-
CONTRAST
403
cedure produced a general depressive effect one would expect the animal to respond more slowly in both directions. Again, this did not occur. In the negative contrast situation the latencies to initiate ICS showed a large and significant rise while the concurrent escape latencies remained completely unaffected. It should be mentioned that we have previously shown that a significant aversive component accompanies rewarding ICS anywhere in the forebrain and that these two basic components of motivation (reward and aversion) are independent of each other (Atrens, 1970; 1972; Atrens & Von Vietinghoff-Riesch, 1972). The dissociation of diencephalic reward and aversion processes is further supported by the present findings. It is noteworthy that these contrast effects were produced by medial hypothalamic and ventral thalamic stimulation, whereas Panskepp and Trowill (1969, 1970) employed lateral hypothalamic stimulation. This supports our contention (Atrens & Von Vietinghoff-Riesch, 1972) as to the qualitative similarity between lateral and medial diencephalic reward processes. Perhaps the most surprising aspect of the present data is that the contrast effects were produced in spite of a I-hr interval between switching ICS intensities and a 5-min warm-up on the new intensity! Contrast effects are almost always evaluated over much shorter intervals between reinforcement condition changes, although Premack (1969) reported substantial contrast effects in two subjects with a 16-hr inter-test interval. Premack (1969, p. 136’) h as suggested that “Contrast results if and only if there is a change in the aversiveness associated with OIW of the components in the schedule.” The present data show that the avcrsivcness itself may be subject to contrast and that reward contrasts can be obtained even when there is no change in aversion. AS Rolles (1967) has pointed out, the systematic study of reinforcement contrast effects has been greatly complicated by the elusiveness of the basic phenomena involved. While the present study is by no means a parametric study, the technique described herein should make further investigations into the parameters of contrast effects relatively easy. REFERENCES II. RI. Reinforcing and emotional con
404
ATRESS,
VIETIKGHOFF-RIESCH,
AND
DER-KARABETIAN
BLACK, R. H. Shifts in magnitude of reward and contrast effects in instrumental and selective learning: A reinterpretation. Psychological Review, 1968, 75, 11-3-126. CRESPI, L. P. Quantitative variation in incentive and performance in the white rat. American Journal of Psychology, 1942, 55, 467-517. BOLLES, R. C. Theory of Motivation. New York: Harper and Row, 1967. BRUNING, J. L., & KINTZ, B. L. Computational handbook of statistics. Glenview: Scott Foresman, 1968. DUNHAM, P. J. Contrasted conditions of reinforcement: A selective critique. Psychological Bulletin, 1968, 69, 295-325. HEMMES, N. S., & ECKERMAN, D. A. Positive interaction (induction) in multiple variable-interval, differential-reinforcement-of-high-rate schedules. Journal of the Experimental Analysis of Behavior, 1972, 17, 51-57. PANSKEPP, J., & TROWILL, J. Positive and negative contrast effects with hypothalamic reward. Physiology and Behnvim, 1969, 4, 173-175. PAXSKEPP, J., & TROWILL, J. Positive incentive contrast with rewarding electrical stimulation of the brain. Journal of Comparative and Physiological Psychology, 1970, 70, 358-363. PEAR, J. J., & WILKIE, 1). hf. Contrast and induction in rats on multiple schedules. Journal of the Experimel&d An&is of Behavior, 1971, 15, 289-296. PREMACK, D. On some boundary conditions of contrast. In J. T. Tapp (Ed. ), Reinforcement and behavior. New York: Academic Press, 1969. WILKIE, D. M. Variable-time reinforcement in multiple and concurrent schedules. Journal of the Experimental Analysis of Behavior, 1972, 17, 59-66. (Received
June
9, 1972)