Conditioned inhibition in taste aversion learning: Testing methodology and empirical status

Transcription

1 Animal Learning & Behavior (1) Conditioned inhibition in taste aversion learning: Testing methodology and empirial status ANDREW R. DELAMATER, JOHN M. KRUSE, STUART MARLIN, and VINCENT M. LoLORDO Dalhousie University. Halifax. Nova Sotia, Canada Several assays were used in assessing onditioned inhibition within a taste aversion proedure. Following Pavlovian onditioned inhibition training, in whih one taste was followed by an injetion of LiCI on A+ trials, but was followed by aess to a seond flavored solution on AXtrials, retardation-of-aquisition and summation tests failed to indiate that the X stimulus (NaCl) had beome inhibitory. Nor was the X stimulus onsistently preferred to water or dilute quinine in two-bottle tests, ontrary to an earlier report (Best, 1975). Most assessments of Pavlovian onditioned inhibition have used either the retardation-of-aquisition test or the summation test (Resorla, 1969). In the retardation test, the putative inhibitor is paired with the unonditioned stimulus (UCS) and the rate of aquisition of an exitatory onditioned response (CR) is ompared with the rate of aquisition in a group that has previously been administered some ontrol treatment. In the summation test, the putative inhibitor is presented in ompound with a known exitor, and the response to this ompound is ompared with the response to the exitor alone. Resorla (1969) asserted that when the organism is less responsive to the ompound than to the exitor alone in the summation test, and the putative inhibitor is relatively slow to beome an exitatory CS in the retardation-of-aquisition test, then there is good evidene for onditioned inhibition. Although relatively few studies of inhibition have inluded both test proedures, many experiments using one test or the other have provided evidene for inhibition in diverse onditioning preparations, inluding rabbit eyeblink onditioning (Marhant, Mis, & Moore, 197), autoshaping in pigeons (Resorla, 198; Wasserman, Franklin, & Hearst, 1974), and the onditioned emotional response and related proedures in rats and dogs (Hammond, 1967; Resorla & LoLordo, 1965). This researh has been guided by the notion (Konorski, 1948, 1967; Resorla & Wagner, 197) that onditioned inhibition is in some sense the opposite of onditioned exitation, for example, that it involves the formation of an inhibitory assoiation between CS and UCS enters (Konorski, 1948). Furthermore, these disussions of inhibition have enouraged the belief that onditioned inhibition will be manifested only in the presene of exitation. This researh was supported by an operating grant from the Natural Sienes and Engineering Researh Counil of Canada to V.M.L. During the ourse of this researh 1.K. and A.D. were supported by I. W. Killam postdotoral and predotoral fellowships, respetively. The authors' mailing address is: Department of Psyhology, Dalhousie University, Halifax, NS, Canada B3H 411. One exeption to the standard assays of inhibition has been provided by Best (1975) and Batson and Best (1981), using the onditioned taste aversion paradigm. They reported that a taste that had signaled the absene of illness was more aeptable in a two-bottle test of preferene than was the same taste in ontrol onditions. In the ontext of prior work on the problem of onditioned inhibition, an assertion that a taste prediting the nonourrene of illness will be preferred to water provides a novel approah to the detetion of onditioned inhibition. From suh demonstrations one ould onlude that onditioned inhibitors an exert an effet upon behavior even in the absene of an exitatory ontext (see Resorla, 1976, 1979). Additionally, these proedures seem to offer a new test for onditioned inhibition whih is neither a retardation-of-aquisition nor a summation test. Beause the goal of the present researh was to ompare the outome of the test used by Best (1975) with the outome of summation and retardation tests for inhibition, using a preparation very similar to that of Best (1975), a brief desription of that study is appropriate at this point. A Pavlovian onditioned inhibition proedure was used. The taste ofsaharin was rendered exitatory by pairing it with apomorphine injetions in the experimental group; the ontrol groups did not learn an aversion to saharin. The inhibition trial, of whih there was only one, onsisted of min of aess to saharin followed immediately by min of aess to a saline solution but no illness. Apparently the nonourrene of the apomorphine injetion on the day that the saline solution was onsumed rendered the salt taste inhibitory. In a subsequent two-bottle test, this saline solution was preferred to water in the experimental group, but not in either of the ontrol groups. In other experiments, Best showed that asein hydrolysate also ould serve as the CS-, and that a latent inhibition manipulation prevented his proedure from rendering the CS- inhibitory. This final demonstration distinguished the assoiatively based preferene for the CS- from the inreased aeptane of a flavor gener- Copyright 1986 Psyhonomi Soiety, In. 6

2 ated by learned safety or latent inhibition proedures (Kalat & Rozin, 1973; Rozin & Kalat, 1971). There seem to be no other studies in whih a taste was used as an inhibitor in the onditioned taste aversion (CTA) paradigm. One additional study, whih used odor stimuli (Taukulis & Revusky, 1975), mayor may not be diretly omparable to studies that used only tastes (f. Bouton & Whiting, 198; Rusiniak, Hankins, Garia, & Brett, 1979). Beause there has been a history of debate over the degree to whih CTA learning parallels other Pavlovian paradigms (e.g., Domjan, 1980; Garia & Koelling, 1966; Kalat & Rozin, 197; Palmerino, Rusiniak, & Garia, 1980; Rozin & Kalat, 1971), this report provides further evidene onerning the empirial status of Pavlovian onditioned inhibition in the CTA paradigm. EXPERIMENT 1 The training proedure used here, like Best's, is a variant on the ommon A+, AX- proedure, whih generally endows the X stimulus with onditioned inhibitory properties. The most ommon way of administering this type of training entails simultaneous presentation of the two stimuli on ompound trials. However, in the ase of taste aversion learning, our pilot work (see also Resorla & Cunningham, 1978) suggests that mixing the two flavors tends to result in within-ompound assoiations and, therefore, exitation rather than inhibition. Consequently, we followed Best and presented the two ues, A and X, sequentially, with X following A. Four different assessmentproedures were used to detet onditioned inhibition. One was the retardation test reommended by Resorla (1969), in whih the putative inhibitor was paired with illness several times. Another was a modified summation test: A new taste was paired with illness and then subjets were offered a hoie between this taste and a mixture of this taste and the inhibitor. The other two tests were preferene tests, in whih the inhibitor served as an alternative to either water or dilute quinine in a two-bottle test. Method Subjets. Seventy-two male albino rats of the Sprague-Dawley strain were obtained from Charles River Canada, Ltd., to serve as subjets. The subjets of Repliation 1 were experimentallynaive, whereas the 36 rats used in Repliation had previously served in a onditionedsuppression study; the latter were assigned to groups in the present study orthogonally to their previous experiene. All subjets were individually aged and had ontinuous aess to food and water until 9 days prior to the start of the experiment, when liquid intake was restrited to min/day. Conditioning manipulations took plae during the early part of the dark phase of the 1-h light-dark yle. Proedure. The experiment was onduted in two sequentialrepliations. The proedures used in the two repliations were idential. There were 36 subjets in eah repliation, assigned randomly to six groups (three pairs, inhibition and ontrol), with one exeption, as noted below. The subjets were given min of aess to water eah day for 8 days prior to the start of the experiment INHIBITION IN CTA 7 as well as on all "reovery" days during the ourse of the experiment. There were three onditioning yles, eah 7 days long and eah inluding one exitatory onditioning trial, two inhibitory onditioning trials, and intervening reovery days. Conditioned inhibition treatments and disriminative onditioning ontrol treatments differed from eah other only on inhibitory onditioning days. Eah yle started with an exitatory trial: Instead of the usual water, a.1 % (w/v) solution of sodium saharin was made available to the subjets for min, and immediately after this drinking session eah subjet was injeted intraperitoneally (ip) with 1.8 meq of a.15-m lithium hloride (LiCI) solution. Injetions and almost-daily weighings ourred in a room adjaent to the olony. On injetion days, eah subjet was arried into this room, injeted, and returned immediately to its home age. Two water reovery days followed an exitatory onditioning (injetion) day. These, in turn, were followed by an inhibitory onditioning trial, a reovery day, another inhibitory trial, and another reovery day. On inhibitory onditioning days, members of the inhibitory onditioning groups were given min of aess to the.1 % saharin solution, followed immediately by min ofaess to a 0.9% (w/v) solution of sodium hloride (NaCI). Members of the ontrol groups were given min of aess to the NaCI solution with no exposure to the saharin solution. No injetions ourred on these inhibitory onditioning days. Following onditioning, two groups, water inhibition (WI) and water ontrol (WC), first reeived a IO-min two-bottle pratie test with both bottles full of water to habituate them to the two-bottle testing proedure. On the following day, these subjets reeived a -min test of preferene between water and the salt solution; the positions of the bottles were swithed midway through this test. Two additional groups, quinine inhibition (QI) and quinine ontrol (Q), reeived one exposure to a.005% solution of quinine sulfate; this was followed, after a water day, by two separate twobottle tests of preferene between the quinine sulfate solution and the NaCI solution. The position of the bottles was swithed midway through eah IO-min test. Two further groups, retardation inhibitory (RI) and retardation ontrol (RC), were administered a retardation test: Groups RI and RC were administered three trials onsisting of IO-min aess to the NaCI solution followed immediately by an injetion of LiCI (I.8 meq). Two water reovery days intervened between suessive onditioning trials. Finally, the subjets of Groups WI and WC were administered a summation test. They were given IO-min aess to a.1 % (v/v) vanilla (Club House, London, Canada) solution followed immediately by an injetion oflici. Following reovery days, they were given two separate two-bottle tests of preferene between vanilla and a mixture of vanilla and NaC!. Results Aquisitionofan aversionto saharinwas substantial after three trials in all groups (trials, F = 5lO.9). The nonreinfored presentations of saharin on inhibition days apparently attenuated the aversion, as the members ofthe inhibition groups drank slightly more saharin on Trials and 3 than did the ontrol group members [groups X trials, F(lO,) =.15, p=.05]. However, there was no overall effet of groups [F(5,60) = 1.91, p >.lo]. Subjets in Repliation onsumed less saharin than those in Repliation 1 [F(1,60) = lo.67, p=.oo], and they also aquiredan aversion more quikly and/or ompletely [repliation x trials, F(,) 17.59, P <.001]. On the last onditioning trial, subjets of Repliation 1 drank a mean of.9 ml of saharin, whereas subjets of Repliation drank only 0.4 ml, The

3 8 DELAMATER, KRUSE, MARLIN, AND LoLORDO three-way interation was not signifiant (F < 1). Within eah repliation, differenes among the inhibition groups and among the ontrol groups were negligible. The patterns ofsaharin onsumption during the -min inhibition trials were also analyzed. As was the ase on exitatory onditioning trials, subjets of Repliation onsumed less saharin during Trials and 3 than did subjets ofrepliation 1. On Trial 3, group means (n=6) for onsumption of saharin ranged from 1.5 to 0 mi. Consumption of the saline solution in Repliation 1 averaged 16.8 mi on Trial 1 and.4 mi on Trial 6. Consumption of saline in Repliation started at 17.4 mi on Trial 1 and rose to 3.9 mi on Trial 6. Consumption inreased similarly in all groups. Following onditioning, one pair of groups was initially administered a two-bottle test of preferene between saline and water. As inspetion of Figure 1 shows, the inhibition group drank a higher perentage of the putative inhibitorthan did the ontrol group. An ANOVA (groups x repliations) indiated a signifiant effet of groups [F(I,0) = 4.99,p=.035] but no othersignifiant effets or interations (Fs < 1). The results of two-bottle tests of preferene between the quinine solution and an NaCI solution administered to another pair of groups appear in Figure, whih suggests that on one test the inhibition group showed a greater preferene for the NaCI solution than did the ontrol group. An ANOV A revealed that there was a signifiant effet ofrepliations [F(l,0) = 7.15, p=.014], indiating that subjets drank a signifiantly higher perentage ofnaci in the seond repliation than in the first, but this did not interat with either groups or tests at onventional. levels of signifiane (Fs < 1). There was a signifiant groups X tests interation [F(I,0) = 6.35, p=.oi9]. Further tests indiated that the two groups, ombined over 50 I" 40,... - Figure 1. Perentage of NaCI onsumed (NaCI/(NaCI + water» when NaCI was presented in a two-bottle test with water as the alternative. I"" C;C z _ 30 :; i 0 Trial: I'".1 C Figure. Perentage of NaCI onsumed when NaCI was presented in a two-bottle test with.005% quinine as the alternative. repliations, differed from eah other only on the seond test [F(l,0) = 5.46; F < 1 for first test). No other main effets or interations were statistially signifiant. The retardation-of-aquisition test administered to another pair ofgroups yielded rather equivoal evidene for onditioned inhibition. Figure 3 suggests that the inhibition group was retarded relative to the ontrol group only in the seond repliation. An ANOVA indiated a nonsignifiant main effet of groups [F(I,0) = 1.37], a nonsignifiant groups x trials interation [F(,40) = 1.9], but a signifiant groups X repliation x trials interation [F(,40) = 8.61, p=.001]. Further analyses of this interation (Kirk, 1%8) revealed that in Repliation, on Trial, the inhibition group onsumed signifiantly more saline than the ontrol group [F(l,40) = 18.96). This indiates that in Repliation aquisition of an aversion was slower, but eventually as omplete, in the inhibition group as in the ontrol group. The inhibition and ontrol groups did not differ from eah other at any other point in testing, and the only other signifiant effet indiated by the analysis was that of trials [F(,40) = 57.4], indiating that pairing the saline solution with LiCI injetions resulted in redued intake of the saline solution. The subjets that were initially administered a watersaline preferene test were subsequently administered two tests of preferene between vanilla and a vanilla-nacl mixture. Figure 4 suggests that the inhibition group drank I'"

4 INHIBITION IN CTA D-C 0... V 0Z 15 5 Trial: 3 3 Rep 1 (n =6) Rep (n =6 ) Figure 3. Absolute onsumption of NaCI when it was paired with an LiCI injetion over three trials in Experiment 1. a higher perentage of the vanilla-nacl mixture than did the ontrol group (means = 47.8 and 30.8, respetively), but an ANDVA (groups X repliations x trials) indiated that the effet of groups was nonsignifiant [F(I,0) =.91, p=.], as were the interations involving groups. The repliation X trial interation was signifiant [F(1,0) = 6.71, p=.016], but this is uninformative with respet to onditioned inhibition. No other effets or interations were signifiant (ps >.0). Disussion These results provide some evidene of onditioned inhibition. Some of the tests for onditioned inhibition suggested that the saline solution had beome inhibitory, whereas others did not. Even in the positive tests, the differenes between the inhibition and ontrol groups were not very large. It might be argued that, in fat, the disriminative ontrol proedure produed weak. onditioned inhibition in the ontrol groups, and that omparison of the experimental and ontrol groups led to underestimation of the amount ofinhibition in the former. However, pilot work immediately preeding the present experiments had suggested that this ontrol proedure generated the same aeptability value for the saline solution as did a proedure in whih the saharin was not paired with illness but did preede the saline solution on inhibitory trials. Although some experimenters have found that the disriminative onditioning proedure oasionally generates some inhibition (e.g., Resorla, 198), otherstudies have used this proedure as a baseline against whih the effets of inhibitory proedures have been ompared (e.g., Resorla & Holland, 1977). Although, in the present instane, the disriminative onditioning ontrol proedure seemed to be appropriate, the disriminative onditioning proedure was ompared with another ontrol treatment in Experiment 3. The NaCl-water two-bottle test provided the most straightforward evidene for onditioned inhibition, in terms of statistial reliability, inasmuh as the effet of the experimental manipulation was observed when both repliations were ombined. This finding onfirms those.. II :)-Ie 'e 30 u II 0 (n=1) Figure 4. Perentage of vanilla-naci mixture onsumed when the mixture was presented in a two-bottle test with a previously poisoned vanilla solution as the alternative. C

5 DELAMATER, KRUSE, MARLIN, AND LoLORDO of Best (1975) and Batson and Best (1981). It is interesting that this test should provide the strongest evidene of inhibition, sine the theoretial understanding of inhibitors has been that they in some sense ounterat the tendenies evoked by onditioned exitors, rather than aquiring ontrol over behaviorof their own (see Resorla, 1969). In the present test there was no obvious exitatory stimulus present. The observation that the preferene for NaCI over quinine was only about 60% is onsistent with the idea that NaCI aquired aversive properties as a result of its unonditional effets upon the organism. Devenport (1973) has demonstrated that the postingestive onsequenes of isotoni saline an result in a mild aversion to the taste ofthe saline solution. Even the preferene for saline when pitted against water (Figure 1) was not very high; in the inhibition group, saline intake was approximately 48 %. This salt preferene sore is less than that obtained by Devenport (1973) and Wong (1977), but it is onsistent with unonditioned salt preferene values obtained in this laboratory with Charles River rats (Kruse & LoLordo, 1986; also see Wiener & Deutsh, 1967). The observation that only the seond NaCl-quinine test resulted in evidene for a NaCI preferene may be due to some general effet of familiarity with the two-bottle testing proedure. In any event, the results ofthis test were similar to the results of the water-naci test. In both ases, the inhibition group exhibited a stronger preferene for the taste that had predited the nonourrene of illness than did the ontrol group. The retardation-of-aquisition and vanilla versus NaCIvanilla tests are more like the traditional tests for onditioned inhibition. The evidene yielded by these tests must be taken as equivoal, sine the inhibition group was retarded in aquisition in only one of the repliations. Moreover, our summation test, whih pitted vanilla against a vanilla-naci mixture, provided no evidene for onditioned inhibition. Perhaps responses to saline were altered by prior experiene with the saline-water test. In summary, several onventional assays failed to produe strong evidene for onditioned inhibition. In ontrast, results of the test in whih saline and water served as alternatives most strongly indiated that saline had beome inhibitory. EXPERIMENT This experiment was originally intended to be a repliation and extension of Experiment 1. The saline-water test for onditioned inhibition seemed to provide the most stable results in Experiment 1; onsequently, it was hosen as the assay for Experiment. Zimmer-Hart and Resorla (1974) reported that repeated presentation of onditioned inhibitors in isolation following training did not redue their inhibitory effet in subsequent tests. In the present ase, their effet was sought in the ontext of CTA learning. Confirmation of the findings of Zimmer-Hart and Resorla (1974) would strengthen our onvition that the target taste had truly been rendered inhibitory. After the first test for inhibition was onduted, the remaining animals in this experiment were subjeted to a modified summation test for onditioned inhibition, to be desribed below. Method Subjets. Fifty-two experimentally naive male albino rats, obtained and housed as in Experiment I, served as subjets. They were assigned randomly to groups of 13. Proedure. The subjets were divided among four groups; three inhibitory onditioning groups and one ontrol group. The training proedures were the same as in the first experiment. That is, there were three training yles, eah onsisting of an exitatory trial and two inhibitory onditioning trials and all followed by water reovery days. As before, an exitatory trial onsisted of lo-rnin aessto saharin followed by an ip injetionof 1.8 meq ofo.15-m LiCl. The inhibitory trials onsisted of min of saharin followed by min of NaCI for the inhibitory groups, and min of NaCI (not preeded by saharin) for the ontrol group. One of the inhibitory groups and the ontrol group were tested with a two-bottle preferene test, as in Experiment 1. They were first given a two-bottle test with water in both bottles, to habituate them to the proedure. They were then given two tests (separated by reovery days) of preferene between NaCI and water. Given the results of the two-bottle tests administered to the first pair of groups in this experiment, the remaining subjets were not used for the originally intended purpose. They had all had the same inhibitory training, and for this test they were split into two groups and administered another type of test for the existene of onditioned inhibition. This test an be onsidered a variant of the summation test (Resorla, 1969), exept that the elements, exitatory and inhibitory, were presented sequentially, rather than simultaneously. Half of the subjets were administered min of aess to the saline solution followed immediately by min of aess to the saharin solution. The remainder of the subjets were administered min of aess to water, followed immediately by min of aess to saharin. There were three suh trials altogether, onduted on separate days and followedby reovery days. For all subjets, a day of min of aess to saharin intervened between Trials and 3 of this test, in an attempt to attenuate a possible floor effet resulting from strong saharin aversions. Results As in the first experiment, the aquisition of an aversion to saharin proeeded slightly more slowly in the inhibition groups than in the ontrol group. On the last 1O-min training trial, rats in the ontrol group drank a mean of0.4 ml ofsaharin solution, whereas the means for the three inhibition groups were 1.1, 1.6, and 1.8 ml. The animals drank approximately.5 ml of the saline solution on the last inhibition trial. The two groups given the two-bottle test with NaCI and water as the alternatives drank approximately the same preentage of NaCI, as Figure 1 shows. An ANOVA indiated that these values did not differ signifiantly from eah other [F(1,4) =.16] and that none of the other effets or interations were signifiant (ps >.30). In the sequential summation test, rats appeared to onsume slightly more saharin after onsuming NaCI than after onsuming water (Figure 5), but the statistial analysis indiated that the effet was not reliable. The only signifiant effet in the sequential tests was that of trials [F(,48) = 7.3, p=.oo], indiating that the subjets

6 INHIBITION IN CTA =.... ụ.. en Trial: EXPERIMENT 3 In 13 ) Figure 5. Consumption of saharin during eah to-min one-bottle test when aess to NaCI (inhibition group) or water (ontrol group) had preeded it for min. drank inreasing amounts of saharin over trials. The main effet of groups was nonsignifiant (F < 1), as was the interation between groups and trials (F < 1). During the immediately prior -min exposure to saline or water, the onsumption ofsaline by the inhibitory onditioning group was slightly greater than the onsumption of water by the ontrol group (mean saline onsumed = 4.86 ml for the inhibition group, and mean water onsumed = 3.88 ml for the ontrol group). Suh a differene ould tend to mask an inhibitory onditioning effet of saharin intake if enhaned fluid onsumption during this -min period were to alleviate thirst motivation. However, there was also a slight positive orrelation between the amount of fluid onsumed during this period and the amount of saharin onsumed during the subsequent lo-min exposure (r=.4), indiating that no suh masking had ourred. In the l O-min exposure to saharin between Trials and 3 of this phase, the two groups onsumed equal amounts of saharin (F < 1). Disussion The subjets in this experiment were trained in exatly the same manner as those of the first experiment. Following this, the saline-water test used in Experiment 1 was onduted. In ontrast to the results of the first experiment, the present results gave no indiation that exposure to the onditioned inhibition proedure had inreased the preferene for the saline solution. In light of these negative results, we turned to yet another attempt to detet onditioned inhibition. The sequential summation test is similar in logi to more onventional summation tests. However, the results of this test provided no evidene that the saline solution had beome inhibitory. This experiment was a further attempt to demonstrate onditioned inhibition using summation and retardation- 3 of-aquisition tests. In Experiment 1 there was the possibility of greater generalization derement from nonreinfored onditioning trials to retardation-of-aquisition test trials in the onditioned inhibition group than in the differential onditioning ontrol. Suh differential generalization derement would have opposed the demonstration of onditioned inhibition. To ontrol for this possibility, the differential onditioning ontrol was replaed by a ontrol group whih reeived the same saharinsaline sequene as the experimental group on nonreinfored trials, but reeived unpaired, rather than paired, presentations of saharin and LiCl. This ontrol group, whih was used by Best (1975), was also added for rats whih were to reeive the summation test. In Experiment 1, the summation test, whih pitted a vanilla exitor against a mixture of vanilla and saline, was administered to rats that had already been given a test of preferene for saline versus water. To ontrol for the possibility that the inhibitory effet ofthe saline extinguished as a result of the first test, and thus was not revealed in the summation test, in the present experiment the saline versus water test was omitted and replaed by a two-bottle test of water versus water to familiarize the rats with the two-bottle test proedure. The vanilla used as the new exitatory flavor in the summation test of Experiment 1 might have had an aversive odor as well as an aversive taste. Ifthis was the ase, then the odor might have kept the rats away from the spouts so that they failed to sample the saline enough to form a preferene. To ontrol for this possibility, a "pure" taste, HCI, was substituted for vanilla. Method Subjets. Sixty experimentally naive male albino rats, obtained and housed as in Experiment 1, served as subjets. They were assigned randomly to groups of 1. Proedure. The subjets were divided among three groups during the onditioning phase of the experiment. The onditioned inhibition (N=4) and differential onditioning ontrol (N= 1) groups were treated exatly like their ounterparts of the first two experiments. The unpaired ontrol (N=4) group reeived lo-min aess to saharin on one oasion during eah onditioning yle and -min aess to saharin followed by lo-min aess to saline on two oasions during eah yle, just as the onditioned inhibition group did. However, the rats in the unpaired ontrol group reeived LiCI injetions following water onsumption, 4 h after exposure to saharin. Twelveof the rats in the onditioned inhibition and unpaired ontrol groups were given a retardation-of-aquisition test for inhibition. The proedure of Experiment 1 was repeated, exept that there were four, rather than three, pairings of saline and LiC!. The remaining 1 rats in eah of the onditioned inhibition and unpaired ontrol groups, along with the 1 rats in the differential onditioning ontrol group, reeived a summation test for inhibition. Following the onditioning phase, these rats reeived a single pairing of -min aess to a 1.5 % normal solution of HCI with an ip injetion of 1.8 meq of O.15-M LiC!. Following waterreovery days, the rats reeived lo-min two-bottle tests with water in both bottles on suessive days. The positions of the two bottles were swithed 5 min into the tests. This proedure was designed to adapt the rats to the two-bottle testing proedure. Then the rats reeived two summation tests pitting HCI against a mixture of HCI and saline; these tests were separated by a water-reovery day. The starting position for the HCI and saline mixture was ounterbalaned

7 1 DELAMATER, KRUSE, MARLIN, AND LoLORDO 80 Q) x Uas 40 Z I U :::I: oe. 0 r- - r- - r- - - r- r- 0 - f0- -E - : 18 0-Co E r- (J) : 16 0 U,... CiS- 0 14r- - r- I- CI UPDC CI UPDC CI UPDC CI UP DC Test 1 Test Test 1 Test Figure 6. The left panel illustrates perentage of HCI-NaCI mixture onsumed when the mixture was presented in a two-bottle test with a previously poisoned HCI solution as the alternative. The right panel illustrates the total intake from both bottles during this test. differential onditioning ontrol groups; the unpaired ontrol group maintained its onsumption of saharin (groups X trials, F = 67.36). As in Experiment 1, members of the inhibition groups drank slightly more saharin on Trials and 3 than did rats in the differential onditioning ontrol groups. Saline onsumption inreased aross trials, as in Experiment 1, and again the groups did not differ in this respet. Figure 6 illustrates the total fluid onsumed during eah summation test and the perentage ofhc1-nacl mixture onsumed during eah test. The three groups failed to differ on either measure during either test [all Fs(,33) < 1]. However, there was an inrease in total onsumption from the first to the seond summation test [F(1,33) = 58.3], suggesting that the failure of the groups to differ on the preferene measure during the first test was not the result of a eiling effet on onsumption. In the subsequent test of preferene for NaCl alone versus NaCl mixed with HCl, virtually all rats preferred NaCI alone. The effet of flavor was signifiant [F(1,33) = 177], whereas the effet of groups and the group X flavor interation were not signifiant [Fs(,33) < 1.13]. Figure 7 illustrates the results of the retardation-ofaquisition test. The unpaired ontrol group aquired an aversion to saline more slowly than did the onditioned inhibition group. Statistial analysis supported this asseraross subjets. Finally, the rats underwent a treatment designed to show that they ould disriminate 1.5% HCI when it was mixed with the saline. Following a water-reovery day, all rats from the summation testing proedure reeived lo-min aess to HCI followed by an injetion of a 3-mEq dose of LiCl. After waterreovery days, NaCI was pitted against HCI mixed with NaCI in a two-bottle test. Results Aquisition ofan aversion to saharin was substantial after three trials for the onditioned inhibition and tion. Although the effet of groups was not signifiant [F(l,) =.96], the effet of trials [F(3,66) = 166] and the group X trial interation [F(3,66) = 3.18] were signifiant. Disussion Neither the summation nor the retardation-of-aquisition test provided any evidene for onditioned inhibition. In - E - : o -Co E (J) : o U o as Z Figure 7. Absolute onsumption of NaCI when it was paired with an LiCI injetion over four trials in Experiment. 3 Trials 4 5

8 INHIBITION IN CT A 13 the ase ofthe summation test, the onditioned inhibition group failed to differ from either a differential onditioning ontrol group, like that of Experiment I, or an unpaired ontrol group, like that used by Best (1975). Moreover, the effets ofthe two ontrol proedures were similar. In the retardation test, the unpaired ontrol group, whih should have suffered as muh generalization derement as the experimental group, aquired a taste aversion more slowly than the onditioned inhibition group, a result opposite that expeted on the basis ofonditioned inhibition. GENERAL DISCUSSION The general patternofresults from all the present work on onditioned inhibition in the CTA paradigm suggests that this is an elusive phenomenon. Data from several assays do not onverge upon the existene of suh a phenomenon. This onlusion ontrasts sharply with that drawn by Best (1975), who obtained a robust effet in several experiments. There are several differenes between the present work and Best's. One differene is that we used LiCI as the unonditioned stimulus (DCS) and Best used apomorphine. This ould be an important differene, sine reent evidene suggests that onditioned taste aversions indued by apomorphine and LiCI are based on different physiologial mehanisms (Pratt & Stolerman, 1984). However, Batson and Best reported onditioned inhibition in an experiment with LiCI as the DCS. Generating onditioned inhibition might be expeted to require a large number of training trials, relative to the number required to generate onditioned exitation (e.g., Wagner & Resorla, 197), and it is ertainly the ase that more trials are used for inhibitory onditioning than for exitatory onditioning in most preparations. However, empirially, the rate of aquisition ofondi tioned inhibition is not well understood. The present experiments involved more trials than Best's experiments, and approximately the same number as were presented by Batson and Best. The present proedure seems reasonable in the ontext of our goals-to repliate and extend previous work. Another differene between the present manipulations and those used by Best is that we administered repeated yles ofexitatory trials and inhibitory trials, rather than administering two exitatory trials and then one inhibitory trial as he did. However, the present training proedures are more similar to ommon praties (see Marhant & Moore, 1974; Resorla, 198; Resorla & LoLordo, 1965), as are those ofbatson and Best (1981). Historially, there has been onsiderable interest in the differenesbetween onditioned taste aversions and other onditioned responses (see, e.g., Garia & Koelling, 1966; Rozin & Kalat, 1971; Rusiniak et al., 1979). Kalat and Rozin (197) speulated that CTAs might be formed by some mehanism more "primitive" and less ognitive than those underlying the aquisition ofother onditioned responses; they based their suggestion on their failure to observe bloking in a CTA preparation (but see Gillan & Domjan, 1977; Revusky, 1971). Garia, Hankins, and Rusiniak (1974) suggested that in aquiring a taste aversion, unlike in say the CER proedure, the rat "does not at as if it were aquiring an 'if-then' strategy. It ats as if a hedoni shift, or a hange in the inentive value ofthe flavor were taking plae" (p. 831). Ifthe A+, AX-proedure typially renders stimulus X inhibitory beause X is nonreinfored at a time when A evokes an expetation of the DCS, then the suggestion made by Garia and his olleagues would imply that the A+, AX-proedure used in the present experiments should not generate onditioned inhibition, beause A, a taste, evokes no expetation of illness to be violated in the presene of X. Why then should Best (1975) and Batson and Best (1981) have established onditioned inhibition? In both of those studies, unlike the present ones, the A ue onsisted not only of aess to a taste but also of being plaed in a distintive environment. Perhaps the set of ontextual ues evoked an expetation of illness, and thus permitted the AX-trials to establish X as a onditioned inhibitor. Consistent with this suggestion, Best, Dunn, Batson, Meahum, and Nash (1985) reported the finding, in three experiments, of an enhaned preferene for a flavor trained as an inhibitor in a ontext that otherwise reliably preeded illness. On exitatory onditioning trials, the rats were exposed to the novel ontext for min (the last 5 min of whih water was made available in Experiments and 3) and then injeted with LiCL On inhibitory onditioning trials, a vinegar solution was presented during the last 5 min ofexposure to this ontext. In ontrast to a proedure that uses a taste exitor, this proedure should espeially enourage the development of inhibition not only beause the ontextual stimuli might evoke an expetation of the DCS, but also beause the presumed expetation is evoked at a time when the putative inhibitor is simultaneously present (Konorski, 1948; Pavlov, 197). Proedures in whih a taste is paired with reovery from the illness indued by poisoning (e.g., Hasegawa, 1981) or thiamine defiieny (Zahorik, Maier, & Pies, 1974) an be onsidered formally similar to bakward and essation onditioning proedures, whih often result in onditioned inhibition (see LoLordo & Fairless, 1985). Tastes paired with reovery from illness in these proedures do beome preferred to familiar tastes (Zahorik et al., 1974), an effet analogous to the inhibitory effet we sought. However, it should be noted that the ourrene of this so-alled "mediine effet" does not imply that the A+, AX- proedure used in the present experiments should also yield inhibitory effets, for the mehanism of the mediine effets and other inhibitory onditioned effets of bakward and essation onditioning proedures may be very different from the mehanism ofinhibition in the A+, AX- proedure. Presumably, the former involve no violation of expetations. Thus, our results are plausible despite the ourrene of mediine effets.

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