Brief Communication
The Contextual Modulation of Conditioned
Taste Aversions by the Physical Environment
and Time of Day Is Similar
Ignacio Morón,1 Tatiana Manrique,1 Andrés Molero,1 Ma Angeles Ballesteros,1
Milagros Gallo,1,2,5 and Andre Fenton3,4
1
Department of Experimental Psychology and Physiology of Behavior, University of Granada, Campus Cartuja, Granada 18071, Spain;
Institute of Neurosciences F. Oloriz, University of Granada, Spain; 3Institute of Physiology, Czech Academy of Sciences, Prague, Czech
Republic; 4Department of Physiology and Pharmacology, State University of New York, Downstate Medical Center, Brooklyn,
New York 11203, USA
2
In a pair of experiments, we have compared the ability of changes of place (Exp. 1) and changes of time of
day (Exp. 2) to separately modulate learned saline-aversion memory phenomena in rats. Neither a spatial nor a
temporal change disrupted latent inhibition using the present behavioral procedure. However, pre-exposure
to the taste increased the contextual control of the learned aversion expression. The aversion reappeared in
the place or at the time of conditioning after extinction in a different context. The results indicate that
environmental and temporal contexts can independently, but similarly modulate taste aversion learning.
Context is an often loosely defined term, which in neuroscience is becoming more common, especially with the
current interest to investigate the neural bases of episodic
memory in humans (Nadel et al 1985; Schacter and Tulving
1994) and to search for equivalent memory phenomena in
nonhuman animals (Clayton and Dickinson 1998; Aggleton
and Brown 1999). Whereas rats readily associate tastes of
substances with their visceral consequences (García and
Koelling 1966; García et al. 1968; Bures et al. 1998; Bernstein 1999), contextual cues also modulate conditioned
taste aversions (CTA), because the context specificity, both
of the expression (Boakes et al. 1997; Archer et al. 1979,
1980; Jarbe et al. 1986; Puente et al. 1988; Bonardi et al.
1990; Loy et al. 1993) and extinction (Rosas and Bouton
1997; Archer et al. 1979) of a learned aversion, and of the
latent inhibition (LI) of CTA (Rudy et al. 1977; Hall and
Channell 1986) has been reported. In CTA studies, context
frequently refers to a particular place that may combine a
variety of external environmental cues. However, a broad
definition of context may include not only external, but also
internal, background cues and a sense of time (Bouton
1993; Pearce and Bouton 2001). Very few of the above-cited
studies reporting context modulation of CTA have included
the time of day as part of the context, either purposely
(Rosas and Bouton 1997) or as the outcome of applying two
daily drinking sessions (Hall and Channell 1986; Bonardi et
al. 1990). Moreover, although the possibility that the time of
day may itself form a context is supported by a recent report showing a time-of-day-dependent expression of the behavioral sensitization to amphetamine (Arvanitogiannis et
al. 2000), to our knowledge, no study has explored the
ability of the time of day to modulate CTA independently of
the spatial context.
In the present experiments, we specifically examine
whether spatial (Exp. 1) and temporal (Exp. 2) contextual
cues separately modulate learned saline-aversion memory
phenomema. In Experiment 1, two different sized and
shaped cages were used as contexts (Fig. 1). The environments differed in location, geometry, visual, auditory, and
tactile cues. In Experiment 2, two different times during the
illumination cycle were used as temporal contexts. To differentiate them as much as possible, morning (10:00) and
evening (20:00) drinking sessions were used. Except for the
details concerning the specific contexts used (Fig. 1), both
experiments were similarly designed and allowed us to measure the context dependency of LI, the extinction, and the
context-specific expression of extinguished learned saline
aversions. Four groups of rats were used in a 2X2 design
(Table 1). Pre-exposed groups (Pre), but not control groups
(Ctrl), received two nonreinforced saline pre-exposures before conditioning. Animals in each group were further assigned to one of two groups, a group (Same), were preexposed, aversively conditioned to saline, and tested in the
same place or at the same time of day. Another group (Different) were aversively conditioned to saline in a different
context of the pre-exposure and testing. After the saline
aversions had extinguished in all groups, a context-specific
extinction test was given. The context of this test was the
5
Corresponding author.
E-MAIL mgallo@ugr.es; FAX 34-958-246239.
Article and publication are at http://www.learnmem.org/cgi/doi/
10.1101/lm.52202.
LEARNING & MEMORY 9:218–223 © 2002 by Cold Spring Harbor Laboratory Press ISSN1072-0502/02 $5.00
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Physical and Temporal Context Modulation of Learning
Figure 1 Depiction of the experimental conditions. Experiment 1(A,B). Photographs from the side of Context A (e.g., A: Pre-exposure) and
from overhead of Context B (e.g., A: Conditioning). Experiment 2 (C,D) had a similar design. The physical conditions were identical for each
drinking session, only the time of day (phase of the light/dark cycle) differed.
context in which the saline aversion had been conditioned.
This design allowed us to measure (1) the expression of a
learned taste aversion after a change of physical or temporal
context between the conditioning and testing sessions, (2)
the effect of taste familiarity on the magnitude of any context-specific modulation, and (3) whether extinction was
specific to the context.
The volume of consumed saline was compared across
groups and across days. The average values ± SEM are reported. No differences were found among the groups in the
water intake, either during the habituation or before testing. There were no differences between water intake in
both contexts at the end of the context habituation phase.
Prior to conditioning, the only differences between the
groups in both experiments was the expected preference
for saline in the rats of the pre-exposed groups compared
with the water intake by the control nonpre-exposed
groups.
Figure 2A summarizes the results of the conditioning,
testing, and renewal phases in Experiment 1. All of the
groups drank the same amount of saline in the conditioning
session. A 2X2 ANOVA (Pre-exposure X Group) analysis of
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the different groups’ saline intake during the conditioning
session showed no significant effect of pre-exposure
(F1,36 = 0.85; P >0.36), group (F1,36 = 1.34; P <0.25), nor
the interaction pre-exposure X group (F1,36 = 0.11;
P >0.74).
The analysis of saline intake during the testing using
a 2X2X3 (Pre-exposure X Group X Days) mixed ANOVA analysis revealed significant main effects of Group (F1,36 = 6.24;
P <0.02), Days (F1,36 = 112.9; P <0.001), and the interaction Pre-exposure X Days (F1,36 = 6.03; P <0.01). The rats
that were tested in a different environment than the one in
which they were conditioned, had lower saline aversions
(14.1 ± 0.78) than those tested in the context that the aversion was conditioned (11.7 ± 0.87). The saline intake increased on each of the three extinction tests (each
P <0.01).
The Pre-exposure X Days interaction was analyzed by
independent 2X2 (Pre-exposure X Group) ANOVAs of each
test. In the first test, there was a significant effect of Preexposure (F1,36 = 3.31; P = 0.05) and Group (F1,36 = 6.92;
P <0.02), but no effect of the interaction Pre-exposure X
Group (F1,36 = 0.27; P >0.6). Latent inhibition of the
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Morón et al.
Table 1. Behavioral Procedures for the Different Groups in Experiment 1 (A) and Experiment 2 (B)
A
Pre-1 & 2
Pre-Different
Ctrl-Different
Pre-Same
Ctrl-Same
Sal (A)
W (A)
Sal (A)
W (A)
Conditioning
Sal-LiCl (B)
Sal-LiCl (B)
Sal-LiCl (A)
Sal-LiCl (A)
Recovery
Extinction 1–3
W (HC)
W (HC)
W (HC)
W (HC)
Context-specific retention
Sal (A)
Sal (A)
Sal (A)
Sal (A)
Sal (B)
Sal (B)
Sal (A)
Sal (A)
B
Pre-1 & 2
Conditioning
Recovery
Extinction 1–5
Context-specific retention
Sal (pm)
W (pm)
Sal (pm)
W (pm)
Sal-LiCl (am)
Sal-LiCl (am)
Sal-LiCl (pm)
Sal-LiCl (pm)
W (am/pm)
W (am/pm)
W (am/pm)
W (am/pm)
Sal (pm)
Sal (pm)
Sal (pm)
Sal (pm)
Sal (am)
Sal (am)
Sal (am)
Sal (am)
Pre-Different
Ctrl-Different
Pre-Same
Ctrl-Same
For brevity counterbalancing is not represented.
(A/B) Contexts; (HC) Home cage; (LiCl) Lithium Chloride; (Pre-1 and Pre-2) Pre-exposure 1 and 2; (Sal)
Isotonic saline; (W) Water.
Group (F[1,31] = 0.94; P >0.3) or the interaction Pre-exposure X Group (F[1,31] = 0.94; P >0.3). The evening saline
intake over five extinction tests was analyzed using a 2X2X5
(Pre-exposure X Group X Days) ANOVA. There were significant main effects of Pre-exposure (F[1,31] = 10.43;
P <0.01) and Days (F[4,124] = 72.82; P <0.01). No other
effect approached significance, except the interaction Preexposure x Days (F[4,124] = 2.29; P <0.07). There was a
clear latent inhibition effect, as the Pre-exposed groups had
a reduced saline aversion (6.58 ± 0.69) compared with the
nonpre-exposed control groups (3.92 ± 0.68). Saline intake
increased through the first four extinction tests (P <0.01).
The extinction of the aversion stabilized after Day 4, as
there were no differences in saline intake between Test 4
and Test 5 (P >0.36). As the interaction Pre-exposure X
Days approached significance, independent 2 X 2 (Pre-exposure x Group) ANOVAs were performed for each extinction test. In the first test, there was only a significant effect
of Pre-exposure (F[1,31] = 6.55; P = 0.01). In Test 2, there
were significant effects of Pre-exposure (F[1,31] = 23.95;
P <0.01) and the Pre-exposure X Group (F[1,31] = 7.99;
P <0.01), but the main effect of Group did not reach significance (F[1,31] = 3.81; P = 0.06). Post-hoc NewmanKeuls comparisons indicated a higher saline intake in the
group Pre-Different compared with the rest of the groups
(P <0.01), indicating contextual control of the saline-aversion expression only in the pre-exposed groups. In Test 3,
there was only a significant main effect of Pre-exposure
(F[1,31] = 14.23; P <0.01). No effect approached significance in Tests 4 and 5, due to the extinction of the learned
aversions in all of the groups.
The analysis of the morning renewal test using a 2X2
(Pre-exposure X Group) ANOVA showed a significant main
learned saline aversion occurred, because the Pre-exposed
groups had a reduced saline aversion (8.78 ± 1.03) compared with the nonpre-exposed control groups
(6.45 ± 0.83). The modulation of the learned aversion by
context was also evident, as the animals that were tested in
a different context from where they were conditioned had
a weaker saline aversion (9.3 ± 0.89) than the animals that
were tested in the same context as where they were conditioned (5.93 ± 0.91). No effect reached significance in
Test 2 and Test 3, due to the extinction of the learned
aversions in all of the groups.
The renewal of the extinguished saline aversion in the
context that the aversion was learned was examined in the
Context-specific test. The data were analyzed by a 2X2 (Preexposure X Group) ANOVA. There was a significant main
effect of group (F1,36 = 6.43; P <0.02), confirming the
lower saline intake in those groups, which has extinguished
the saline aversion in a different context. No other effect
was significant. A mixed 2X2 (Test-Context X Days) ANOVA
of the saline intake of the different groups on both the last
test and the Context-specific test showed no effect of
group (F1,36 = 0.63; P >0.42) and no effect of Days
(F1,36 = 1.9;P >0.17), but a significant Group X Days
(F1,36 = 9.28; P >0.01) interaction. A repeated measures
ANOVA indicated a reduced saline intake in the renewal test
compared with the last test only in the groups that had
extinguished the aversion in a different context than they
had been conditioned in P <0.02.
Figure 2B summarizes the results of the conditioning,
testing, and renewal phases in Experiment 2. A 2X2 (Preexposure X Group) ANOVA analysis of the different groups’
saline intake in the conditioning session showed no significant effect of Pre-exposure (F[1,31] = 0.94; P >0.3),
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Physical and Temporal Context Modulation of Learning
change in the temporal context have
similar effects on CTA learning phenomena. After learning a saline taste
aversion in a particular physical context
or at a particular time of day, the extinction of the taste aversion was context
specific. Renewal of taste aversions extinguished in a different context has
been reported upon returning to the
conditioning context using both singlebottle tests (Rosas and Bouton 1997)
and two bottle tests (Archer et al.
1979).
Consistent with previous work
(Bonardi et al. 1990; Rosas and Bouton
1997), the present results do not indicate that either the physical or temporal
context has a relevant influence on the
expression of a learned taste aversion after one conditioning trial in the nonpreexposed groups. The previous experience with the taste seemed, however, to
increase the ability to express lower aversions when the conditioning and testing
were in different contexts. This effect
was clear when the physical context was
examined and it reached significance in
the second test after changing the time of
day. An increase of the contextual control
of CTA induced by taste familiarity has
been reported (Puente et al. 1988;
Boakes et al. 1997). Consistent with this
finding, the bulk of the studies reporting
context dependency of CTA expression
have applied several conditioning trials
(Archer et al. 1979, 1980; Jarbe et al.
Figure 2 Mean (± SEM) saline intake of the different groups during the conditioning, ex- 1986; Puente et al. 1988; Loy et al. 1993;
tinction, and the Context-specific retention phases in Experiment 1 (A) and Experiment 2 (B).
(Cond) Conditioning; (D) different Groups; (S) same Groups; (E1–E5) extinction tests 1 to 5; Boakes et al. 1997).
Latent inhibition of CTA was not
(Ret) Context-specific retention test.
affected by changing the physical or
temporal context. Although a context change between preeffect of Group (F[1,31] = 3.87; P = 0.05). No other effect
exposure and conditioning eliminates latent inhibition (LI)
approached significance. To test whether the change to
in a variety of learning tasks (Lubow 1989), evidence is not
saline in the morning altered the amount to saline intake
so clear using CTA. Some studies have found LI indepencompared with the previous day’s intake in the evening, a
dent of the context (Kurz and Levitsk 1982; Best and Mearepeated measure ANOVA was performed on the Test 5 and
chum 1986) and others have reported context-dependent LI
Renewal data. There was a relative increase in saline intake
(Rudy et al. 1977; Hall and Channell 1986).
during the morning renewal test (P <0.01) only in those
To our knowledge, this is the first definitive evidence
groups that had been conditioned and given extinction sesthat rats use the time of day as a context to modulate the
sions during the same evening period. There was no such
expression and extinction of a learned taste-aversion
increase in those groups that were conditioned during the
memory that was acquired in one conditioning trial. Almorning drinking session and extinguished in the evening
though further research on the relevance of procedural fea(Pre-Different, P >0.56; Ctrl-Different, P >0.16).
tures that may be critical for time-dependent latent inhibition
Taken together, the results of Experiments 1 and 2
is required, the phenomenon opens the door for research into
indicate that both a change in the physical context and a
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Morón et al.
the neural mechanisms that underlie how memories are stored
and modulated by a sense of extended time.
Forty naïve male Long-Evans rats (350–450 g) provided
by the breeding colony of the Institute of Physiology (Prague)
were used in Experiment 1 (n = 10 per group). The animals
were housed four per cage in a 22°C temperature and 12:12
light:dark cycle controlled vivarium. Thirty-five naïve male
Wistar rats (280–320 g) from the breeding colony of the
University of Granada were used in Experiment 2 (n = 9 per
group except Ctrl-Different n = 8). They were housed individually in a room with constant temperature and a 12:12 h.
light-dark cycle, with lights on at 9:00 and off at 21:00. Food
was available ad libitum, but water availability depended on
the behavioral procedure. In the first experiment, the animals had a daily 15-min drinking session, and in the second
experiment, two daily 15-min drinking sessions. The procedures were approved by the Institute of Physiology and the
University of Granada Ethics Committees, and were in accordance with both the NIH of the United States guidelines
for the ethical treatment of animals, and the European Communities Council Directive of 24 November 1986 (86/609/
EEC).
The behavioral procedure had five phases as follows:
Context Habituation, Taste Pre-exposure, Conditioning, Extinction, and Context-specific Extinction (Fig. 1). The
amount of fluid ingested was recorded to the nearest 0.1 mL
in all phases. During the Context Habituation phase, all of
the animals drank water during the daily 15-min drinking
period until the water intake in each context was similar. In
Experiment 2, morning and evening intake was equated by
limiting morning water ingestion to 6 mL.
The Pre-exposure phase lasted for 2 d. The pre-exposed groups (Pre-Same and Pre-Different) were allowed to
drink saline (1%) for 15 min, whereas the control nonpreexposed groups (Ctrl-Same and Ctrl-Different) were allowed
to drink water instead. The spatial contexts were counterbalanced in Experiment 1, but saline pre-exposures always
took place during the evening drinking session in Experiment 2.
During the conditioning session, the animals were allowed to drink the saline solution either in the same context
as during the pre-exposure sessions (Pre-Same) or in the
other context (Pre-Different). The nonpre-exposed (Ctrl)
groups drank in the same contexts as their corresponding
pre-exposed group. Immediately after the 15 min of saline
drinking, all of the animals were poisoned with an i.p. injection of lithium chloride (0.15 M; 2% body weight) and
returned to the home cage. The next day, they were allowed to recover from the poisoning with access to water
in the home cage during the daily drinking period.
The extinction phase began the day after recovery. The
rats were allowed to drink the saline solution in the context
they had pre-exposure drinking sessions. The extinction
phase lasted 3 d in Experiment 1 and 5 d in Experiment 2.
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After the learned taste aversion was extinguished, the Context-specific saline aversion was tested. The rats were allowed to drink the saline solution in the context in which
the Different groups had the conditioning session.
ACKNOWLEDGMENTS
This research was supported by the CICYT grants PB98–1309
(Spain). Ignacio Morón and Andrés Molero were recipients of a
predoctoral grant of the Junta de Andalucía (Spain). We thank Geoffrey Hall for an informative discussion on this topic and related
data.
The publication costs of this article were defrayed in part by
payment of page charges. This article must therefore be hereby
marked “advertisement” in accordance with 18 USC section 1734
solely to indicate this fact.
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