Time-of-day discrimination by pigeons,Columba livia

Measuring honey bee feeding rhythms with the BeeBox, a platform for nectar foraging insects

In honey bees, most studies of circadian rhythms involve a locomotion test performed in a small tube, a tunnel, or at the hive entrance. However, despite feeding playing an important role in honey bee health or fitness, no demonstration of circadian rhythm on feeding has been performed until recently. Here, we present the BeeBox, a new laboratory platform for bees based on the concept of the Skinner box, which dispenses discrete controlled amounts of food (sucrose syrup) following entrance into an artificial flower. We compared caged groups of bees in 12 h-12 h light/dark cycles, constant darkness and constant light and measured average hourly syrup consumption per living bee. Food intake was higher in constant light and lower in constant darkness; mortality increased in constant light. We observed rhythmic consumption with a period longer than 24 h; this is maintained in darkness without environmental cues, but is damped in the constant light condition. The BeeBox offers many new research perspectives and numerous potential applications in the study of nectar foraging animals.

Modeling within-session dynamics of categorical and item-memory mechanisms in pigeons

Past studies have shown that pigeons can learn complex categories and can also remember large numbers of individual objects. In recent work, Cook et al. Psychonomic Bulletin & Review, 28, 548-555, (2021) provided evidence that pigeons may use a dynamic combination of both category-based information and item-specific memorization to solve a categorical variation of the mid-session reversal (MSR) task, which is an influential task for exploring the nature of temporally organized behaviors in animals. To provide greater insight into these pigeons' behaviors, in this article we developed and investigated different computational models and their variations to account for these data. Of these, two models emerged as good candidates. One was a multinomial-processing-tree categorization/memory model, formalizing the two-process mechanism initially proposed by Cook et al. Psychonomic Bulletin & Review, 28, 548-555, (2021). The second was a new object/time-coding model, which posits the storage of object-specific memories with an additional within-session time code and assumes that a basic stimulus generalization process underlies the pigeons' choice behavior. Both provided high-quality fits to the published sets of training and transfer data collected in the categorical MSR task. These computational efforts give deeper insights into the theoretical mechanisms underlying the temporal and sequential structure of behavior in animals and stimulate future empirical research further revealing the organization of the pigeons' cognitive processes.

The ecological significance of time sense in animals

Time is a fundamental dimension of all biological events and it is often assumed that animals have the capacity to track the duration of experienced events (known as interval timing). Animals can potentially use temporal information as a cue during foraging, communication, predator avoidance, or navigation. Interval timing has been traditionally investigated in controlled laboratory conditions but its ecological relevance in natural environments remains unclear. While animals may time events in artificial and highly controlled conditions, they may not necessarily use temporal information in natural environments where they have access to other cues that may have more relevance than temporal information. Herein we critically evaluate the ecological contexts where interval timing has been suggested to provide adaptive value for animals. We further discuss attributes of interval timing that are rarely considered in controlled laboratory studies. Finally, we encourage consideration of ecological relevance when designing future interval-timing studies and propose future directions for such experiments.

Step changes in the intertrial interval in the midsession reversal task: Predicting pigeons' performance with the learning-to-time model

Our goal was to assess the role of timing in pigeons' performance in the midsession reversal task. In discrete-trial sessions, pigeons learned to discriminate between 2 stimuli, S1 and S2. Choices of S1 were reinforced only in the first half of the session and choices of S2 were reinforced only in the second half. Typically, pigeons choose S2 before the contingency reverses (anticipatory errors) and S1 after (perseverative errors), suggesting that they time the interval from the beginning of the session to the contingency reversal. To test this hypothesis, we exposed pigeons to a midsession reversal task and, depending on the group, either increased or decreased the ITI duration. We then contrasted the pigeons' performance with the predictions of the Learning-to-Time (LeT) model: In both conditions, preference was expected to reverse at the same time as in the previous sessions. When the ITI was doubled, pigeons' preference reversal occurred at half the trial number but at the same time as in the previous sessions. When the ITI was halved, pigeons' preference reversal occurred at a later trial but at an earlier time than in the previous sessions. Hence, pigeons' performance was only partially consistent with the predictions of LeT, suggesting that besides timing, other sources of control, such as the outcome of previous trials, seem to influence choice.

Effects of variable durations of food availability on interval time-place learning with pigeons Columba Livia

We assessed the effects of variable durations of food availability on an interval time-place learning task. 3 pigeons were exposed to a task in which food could be obtained for responses in one of four feeders according to an RI 25 s during 3 min, after which, food could be obtained on a different feeder according to the same schedule. The correct feeder changed following a fixed sequence that was repeated four times throughout the session. After 50 training sessions, an Open Hopper Test was conducted, after which, the second training condition ensued. This condition was like the first one with the exception that the availability period could be either 1,2,3, or 6 min long. A second test was conducted after 50 sessions of this training. Another group of 3 birds experienced these conditions in the reverse order. Data suggest that birds solved the task via interval timing under the fixed duration condition, and via ordinal timing when faced with variable durations. Birds learned the fixed sequence involved in the task under both conditions. Although the present data agree with previous research exploring variability in TPL tasks, they do not necessarily support previous claims for an asymmetrical role of spatial and temporal information in these tasks.

Daily Time-Place Learning in Young Children

Pre-school children find it difficult to correctly report if it is morning or afternoon. The present study tested whether children could learn a non-verbal Time-Place Learning (TPL) task that depended on time of day. Twenty-five 4-year-olds were repeatedly asked to find a toy in one of two boxes. Children in the Cued condition were told the toy was in one box in the morning and in another box in the afternoon. Children in the Not Cued condition were told the toy was sometimes in one box and sometimes in the other box. After 80 trials, children were asked if it was morning or afternoon. About 65% of the children learned the TPL task, and about three-quarters of the children verbally identified if it was morning or afternoon. However, the children who learned the TPL task were not necessarily the children who correctly answered whether it was morning or afternoon, and those in the Cued condition were no more likely to solve the task than those in the Not Cued condition. The implication is that children have a sense of time that can be used to solve spatio-temporal contingencies, but does not depend on the verbal understanding of time of day.

Evidence of non-circadian timing in a low response-cost daily Time-Place Learning task with pigeons Columba Livia

Previous research has shown that rats require high response cost in order to display circadian timing in daily Time-Place Learning (TPL) tasks. For many possible reasons, no explicit effort to explore the effects of response cost on the performance of other species in these tasks has been made. Therefore, the present paper explores the effects of response cost on pigeon's performance on a daily TPL task. Head entry responses were reinforced according to a Random Interval schedule of reinforcement on one feeder during morning sessions and on another feeder during afternoon sessions. Feeders were located 8 cm apart for one group of birds (Group Near) and 56 cm apart for another group (Group Far). After 50 training sessions, testing began. Test sessions consisted of skipping either the morning or the afternoon session. Results show that most birds in the near group respond primarily on the opposite feeder during the first 20 s of the test sessions and then they switch to the correct feeder. On the other hand, most birds in Group Far respond at the same rate on both opposite and correct feeders during 20 s, and then they respond primarily on the correct feeder. The possibility of these data revealing non circadian timing for birds in a low response-cost daily TPL task is discussed along with the implications of such a finding for previous literature that claims that this type of performance could be unique to rats.

Consistent meal times improve performance on a daily time-place learning task

The ability of an animal to learn the spatiotemporal variability of stimuli is known as time-place learning (TPL). The present study investigated the role of the food-entrainable oscillator (FEO) in TPL. Rats were trained in an operant conditioning chamber which contained two levers that distributed a food reward, such that one lever provided food rewards in morning sessions, while the other lever provided food rewards in afternoon sessions. We expected that having access to the FEO would provide rats with more accurate depictions of time of day, leading to better performance. Rats received either one meal per day (1M group), which permitted FEO access, or many meals per day (MM group), which prevented FEO access. As predicted, 1M rats had a significantly higher percentage of correct first presses than MM rats. Once rats successfully learned the task, probe tests were conducted to determine the timing strategy used. Of the 10 rats that successfully learned the time-place discrimination, six used a circadian timing strategy. Future research should determine whether the advantage in learning seen in the rats having access to the FEO is specific to the daily TPL task used in this study, or to learning and memory tasks more generally.

Rats in a levered T-maze task show evidence of time-place discriminations in two different measures

It is difficult for rats to learn to go to an arm of a T-maze to receive food that is dependent on the time of day, unless the amount of food in each daily session is different. In the same task, rats show evidence of time-place discriminations if they are required to press levers in the arms of the T-maze, but learning is only evident when the first lever press is considered, and not the first arm visited. These data suggest that rats struggle to use time as a discriminative stimulus unless the rewards/events differ in some dimension, or unless the goal locations can be visited prior to making a response. If both of these conditions are met in the same task, it might be possible to compare time-place learning in two different measures that essentially indicate performance before and after entering the arms of the T-maze. In the present study, we investigated time-place learning in rats with a levered T-maze task in which the amounts of food varied depending on the time of day. The first arm choices and first lever presses both indicated that the rats had acquired time-place discriminations, and both of these measures became significantly different from chance during the same block. However, there were subtle differences between the two measures, which suggest that time-place discrimination is aided by visiting the goal locations.

Circadian time-place (or time-route) learning in rats with hippocampal lesions

Circadian time-place learning (TPL) is the ability to remember both the place and biological time of day that a significant event occurred (e.g., food availability). This ability requires that a circadian clock provide phase information (a time tag) to cognitive systems involved in linking representations of an event with spatial reference memory. To date, it is unclear which neuronal substrates are critical in this process, but one candidate structure is the hippocampus (HPC). The HPC is essential for normal performance on tasks that require allocentric spatial memory and exhibits circadian rhythms of gene expression that are sensitive to meal timing. Using a novel TPL training procedure and enriched, multidimensional environment, we trained rats to locate a food reward that varied between two locations relative to time of day. After rats acquired the task, they received either HPC or SHAM lesions and were re-tested. Rats with HPC lesions were initially impaired on the task relative to SHAM rats, but re-attained high scores with continued testing. Probe tests revealed that the rats were not using an alternation strategy or relying on light-dark transitions to locate the food reward. We hypothesize that transient disruption and recovery reflect a switch from HPC-dependent allocentric navigation (learning places) to dorsal striatum-dependent egocentric spatial navigation (learning routes to a location). Whatever the navigation strategy, these results demonstrate that the HPC is not required for rats to find food in different locations using circadian phase as a discriminative cue.

Effects of variable sequences of food availability on interval time-place learning by pigeons

The effects of within session variability of the sequences of food availability in a 16 period Time Place Learning (TPL) task on the performance of pigeons were assessed. Two groups of birds were exposed to two conditions. For group 1 (N=3), the first condition consisted of a TPL task in which food could be obtained according to a Random Interval (RI) 25s schedule of reinforcement in one of four feeders, the correct feeder changed every 3min. The same sequence was repeated four times within every training session (Fixed Sequence). The second condition was exactly the same as the first one with the exception that the sequence in which the correct feeder changed was randomized, yielding a total of four randomized sequences of food availability each session (Variable Sequence). An Open Hopper Test (OHT) was conducted at the end of each condition. Birds in group 2 (N=3) experienced the same conditions but in the reverse order. Results showed high percent correct responses for both group of birds under both conditions. However, birds were able to time the availability period's duration only under the Fixed Sequence condition, as shown by anticipation, anticipation of depletion and persistence of visiting patterns on the OHT. The implications of these results to Gallistels (1990) tripartite time-place-event memory code model are discussed, pointing out that these results are in line with previous findings about the important role that spatial parameters of a TPL task can play, for accurate timing was precluded when a variable sequence was employed.

Time-place learning over a lifetime: absence of memory loss in trained old mice

Time–place learning (TPL) offers the possibility to study the functional interaction between cognition and the circadian system with aging. With TPL, animals link biological significant events with the location and the time of day. This what–where–when type of memory provides animals with an experience-based daily schedule. Mice were tested for TPL five times throughout their lifespan and showed (re)learning from below chance level at the age of 4, 7, 12, and 18 mo. In contrast, at the age of 22 mo these mice showed preservation of TPL memory (absence of memory loss), together with deficiencies in the ability to update time-of-day information. Conversely, the majority of untrained (naïve) mice at 17 mo of age were unable to acquire TPL, indicating that training had delayed TPL deficiencies in the mice trained over lifespan. Two out of seven naïve mice, however, compensated for correct performance loss by adapting an alternative learning strategy that is independent of the age-deteriorating circadian system and presumably less cognitively demanding. Together, these data show the age-sensitivity of TPL, and the positive effects of repeated training over a lifetime. In addition, these data shed new light on aging-related loss of behavioral flexibility to update time-of-day information.

Human strategies for solving a time-place learning task: the role of counting and following verbal cues

Two experiments were conducted to assess the emergence of time-place learning in humans. In experiment 1, a computer based software was designed in which participants had to choose to enter one of four rooms in an abandoned house search for a zombie every 3-15s. Zombies could be found in only one of these rooms every trial in 3 min periods during the 12 min sessions. After 4 training sessions, participants were exposed to a probe session in which zombies could be found in any room on every trial. Almost all participants behaved as if they were timing the availability intervals: they anticipated the changes in the location of the zombie and they persisted in their performance patterns during the probe session; however, verbal reports revealed that they were counting the number of trials in each period in order to decide when to switch between rooms. In the second experiment, the task was modified in two ways: counting was made harder by using three different intertrial ranges within each session: 2-6s, 2-11s and 2-16s. Second, labels were displaced during the final session to assess whether participants learned to click on a given place or to follow a set of verbal cues. We found that participants did not notice the label changes suggesting that they learned to click on a given place, and that a win/stay-lose/shift strategy was clearly used to decide when to switch rooms in the second experiment. The implications of verbal behavior when assessing time-place learning with humans and the possible differences in this process between humans and animals are discussed.

Neither the SCN nor the adrenals are required for circadian time-place learning in mice

During Time-Place Learning (TPL), animals link biological significant events (e.g. encountering predators, food, mates) with the location and time of occurrence in the environment. This allows animals to anticipate which locations to visit or avoid based on previous experience and knowledge of the current time of day. The TPL task applied in this study consists of three daily sessions in a three-arm maze, with a food reward at the end of each arm. During each session, mice should avoid one specific arm to avoid a foot-shock. We previously demonstrated that, rather than using external cue-based strategies, mice use an internal clock (circadian strategy) for TPL, referred to as circadian TPL (cTPL). It is unknown in which brain region(s) or peripheral organ(s) the consulted clock underlying cTPL resides. Three candidates were examined in this study: (a) the suprachiasmatic nucleus (SCN), a light entrainable oscillator (LEO) and considered the master circadian clock in the brain, (b) the food entrainable oscillator (FEO), entrained by restricted food availability, and (c) the adrenal glands, harboring an important peripheral oscillator. cTPL performance should be affected if the underlying oscillator system is abruptly phase-shifted. Therefore, we first investigated cTPL sensitivity to abrupt light and food shifts. Next we investigated cTPL in SCN-lesioned- and adrenalectomized mice. Abrupt FEO phase-shifts (induced by advancing and delaying feeding time) affected TPL performance in specific test sessions while a LEO phase-shift (induced by a light pulse) more severely affected TPL performance in all three daily test sessions. SCN-lesioned mice showed no TPL deficiencies compared to SHAM-lesioned mice. Moreover, both SHAM- and SCN-lesioned mice showed unaffected cTPL performance when re-tested after bilateral adrenalectomy. We conclude that, although cTPL is sensitive to timing manipulations with light as well as food, neither the SCN nor the adrenals are required for cTPL in mice.

Are separate theories of conditioning and timing necessary?

Conditioning and timing studies have evolved under separate traditions, which is exemplified in both traditional theories (e.g. the Rescorla-Wagner model of conditioning vs. Scalar Timing Theory) and in a dual process model (Gibbon, J., Balsam, P., 1981. In: Autoshaping and Conditioning Theory. Academic Press, New York.). Other lines of theoretical development in both timing and conditioning fields have resulted in the emergence of 'hybrid' theories in which conditioning and timing processes are integrated. Simulations were conducted with a recent hybrid theory of timing (Machado, A., 1997. Psychol. Rev. 104, 241-265). The simulations were of classical conditioning procedures in which the local or global predictability of food was varied by manipulating the variability of the CS-US relationship, variability of the CS duration, and variability of the intertrial interval. The hybrid model provided good qualitative fits to indices of conditioning (discrimination ratios) and timing (local rates of responding), indicating that it may be possible to model both conditioning and timing results with a single process in which an internal representation of time and a strength of association are integrated. However, the failure of the model to provide good quantitative fits of the data indicates the need for a consideration of alternative perceptual representations of time and/or principles of association within the framework of the hybrid model.

Cognitive approach of spatial and temporal information processing in insects

Within the theoretical framework of adaptive significance, it is often claimed that insects learn just what they are genetically programmed to learn. Consequently, because of the alleged lack of plasticity of their behaviour, many learning tests applied to insects are limited to very simple associative Stimulus-Response research paradigms. If the behaviouristic approach can explain most of the behavioural responses of insect species facing very simple situations, behaviour requires other strategies for learning and memorizing environmental information in species confronting complex and variable ecological conditions, as it is the case for many hymenoptera species. Among them, forager ants Cataglyphis cursor can discriminate, select, store and represent spatial information within a few days, allowing them to locate their remote nest in a highly controlled visual environment. They can learn something about the spatial arrangement of the landmarks configuration and accurately home even in the absence of the main visual stimulus associated to this place. Ectatomma ruidum ants are also capable to store jointly spatial and temporal information in order to schedule their feeding behaviour. Thus, the representational format of spatial and temporal memories in some insect species appears to be more subtle than is generally assumed when compared to other animal species.

Field observations of time-place behaviour in scavenging birds

Encoding the spatial location and the time at which significant biological events occur is thought to be a fundamental way in which one form of memory is organized in animals (Gallistel, 1990, The Organization of Learning. MIT Press, Cambridge, MA). If this is true, one would expect to find evidence of this process in a wide variety of animals and in a wide number of situations. We report field observations of scavenging birds at two outdoor locations at which people tend to congregate and eat food, primarily around midday. Scavenging birds appeared to anticipate this peak in food availability and arrived at these locations before the number of people was at a maximum; time of day, not the absolute number of people, was the best predictor of the number of birds at both sites. At a third location where food is not consumed this relationship was not observed. Taken together these observations support the notion that animals represent the spatial and temporal characteristics of biologically important events and use this knowledge to forage efficiently.

Further evidence that rats use ordinal timing in a daily time-place learning task

Rats received morning, midday, and afternoon sessions each day in a chamber located in a room containing distal spatial cues. A lever was mounted on each of the four walls. The rats could work for food on a different lever during each of the three sessions. The rats were able to learn the location of food availability during morning, midday, and afternoon sessions. Results obtained after skipped morning, midday, and afternoon sessions support our contention that rats solve this time-place task using ordinal timing, or knowledge of the daily spatiotemporal sequence of food availability. However, during probe sessions when the predicted location of food availability based on ordinal information conflicted with the predictions based on other types of information, behavioural compromise was evident. It appears that rats use multiple types of information, one of which is ordinal timing, to track the location of food availability in the daily time-place task.

Time-place learning in golden shiners (Pisces: Cyprinidae)

The goal of this study was to determine whether fish can learn to forage in different places at different times of the day, each place being associated with a specific time. Groups of eight golden shiners (Notemigonus crysoleucas) were kept in aquaria equipped with automatic feeders that dropped food on one side in the morning and on the other side in the afternoon, or on one side in the morning, the other side at midday, and back on the first side in the evening. After 3-4 weeks, food was withheld and the position of the fish within the aquaria was noted at 5-min intervals throughout the day. Consistent with time-place learning, most fish were on the correct side at the correct time. However, another experiment with three places instead of two provided only equivocal evidence of time-place learning; this could reflect the fact that, in the lakes they inhabit, golden shiners may need only distinguish between two places: open waters and littoral. Experiments with phase-shifts of the photoperiod showed that temporal discrimination is based on a circadian clock that can be gradually phase-advanced by 6 h in about 3 days.

Rats are reluctant to use circadian timing in a daily time-place task

On daily time-place learning tasks animals can work for food at different spatial locations during sessions at different times of the day. In previous experiments rats tracked this pattern of food availability with ordinal timing-they learned to respond at the locations in the correct order each day. In contrast, pigeons used circadian timing. In this experiment rats received a mixture of morning session only days, afternoon session only days, and morning and afternoon session days. Under these conditions ordinal timing had low predictive ability, but circadian timing was potentially perfectly predictive of the location of food availability. We thought this procedural change might encourage rats to use circadian timing. However, we found little evidence that rats can use time of day information to track this daily spatiotemporal pattern of food availability. These results are suggestive of differences in the use of circadian clock consultation by rats and pigeons.

Interval time-place learning in young children

While previous research has investigated the ability of animals to learn the spatial and temporal contingencies of biologically significant events (known as time-place learning), this ability has not been studied in humans. Children ranging from 5 to 10 years old were tested on a modified interval time-place learning task using a touchscreen computer. Results demonstrate the children were able to quickly learn both the timing and the sequence of this task. Despite a lack of anticipation on baseline trials, the children continued to follow the spatio-temporal contingencies in probe sessions where these contingencies were removed. Performance on the probe sessions provide strong evidence that the children had learned the spatio-temporal contingencies. Future research is needed to determine what age-related changes in iTPL occur. Furthermore, it is argued that this procedure can be used to extend interval timing in research in children, including, but not limited to, investigation of scalar timing with longer durations than have previously been investigated.

Strain differences in a high response-cost daily time-place learning task

Previous research has shown that rats, unlike birds, do not readily demonstrate daily time-place learning (TPL). It has been suggested, however, that rats are more successful at these tasks if the response cost (RC) is increased. Widman et al. (2000) found that female Sprague Dawley (SD) rats learned a daily TPL task in which they were required to climb different towers depending on the time of day to find a food reward. Using a similar apparatus, we found that male SD rats learned the task, while male Long Evans rats did not. While all rats quickly learned to restrict the majority of their searching to the two towers that provided food, only the SD rats learned to go to the correct location at the correct time of day. Thus, there appears to be a strain difference in the effectiveness of a high RC task to promote learning. Tests of the timing strategies used revealed individual differences with one rat using a circadian strategy and another using an ordinal strategy. Post criterion decrements in performance did not allow sufficient testing to determine the timing strategies of the remaining rats. Possible interactions between strain, response cost, species typical behaviors and dependent measures are discussed.

Temporal control of internal states in pigeons

To understand how animals serially organize complex competing behaviors, we tested pigeons in a sequential task-switching procedure. Daily sessions involved two conditional discrimination tasks that were presented in sequence. In Experiment 1, the first half of a session employed a matching-to-sample task, and the second half tested an oddity-from-sample task. Because the same colors were used for both tasks, these tasks could be solved only by employing a modulating sequential cue. The results of the first experiment revealed that the pigeons could learn this task-switching procedure and that an internal clock was the critical modulator between the tasks. In Experiment 2, we tested a three-alternative choice task. By examining the pattern of errors among choices, the results of this experiment revealed that pigeons learned and used different representations of the choice rules for each half of the experiment. This modulation of the pigeons' internal states by time has implications for how animals organize their behavior in different settings and holds clues as to the evolution of the serial organization of behavior.

Rats acquire a low-response-cost daily time-place task with differential amounts of food

Gallistel (1990) theorized that when animals encounter a biologically significant event, they automatically form a tripartite code consisting of the time, place, and nature of the event. Recent research examining such time-place learning (TPL) has shown that rats are reluctant to perform TPL tasks and appear to do so only under high-response-cost situations (Thorpe, Bates, & Wilkie, 2003; Widman, Gordon, & Timberlake, 2000). In the present study, we trained rats on a low-response-cost daily TPL task, in which the amount of food varied with the spatiotemporal contingencies. It was found that rats readily learned this task. We hypothesize that, rather than automatically encoding a tripartite code when faced with a biologically important event, rats instead automatically encode bipartite codes consisting of time-event and event-place information.

Time-space learning in homing pigeons (Columba livia): orientation to an artificial light source

Time-space learning reflects an ability to represent in memory event-stimulus properties together with the place and time of the event; a capacity well developed in birds. Homing pigeons were trained in an indoor octagonal arena to locate one food goal in the morning and a different food goal in the late afternoon. The goals differed with respect to their angular/directional relationship to an artificial light source located outside the arena. Further, the angular difference in reward position approximated the displacement of the sun's azimuth that would occur during the same time period. The experimental birds quickly learned the task, demonstrating the apparent ease with which birds can adopt an artificial light source to discriminate among alternative spatial responses at different times of the day. However, a novel midday probe session following successful learning revealed that the light source was interpreted as a stable landmark and not as a surrogate sun that would support compass orientation. Probe sessions following a phase shift of the light-dark cycle revealed that the mechanism employed to make the temporal discrimination was prevailingly based on an endogenous circadian rhythm and not an interval timing mechanism.

Rats' performance on an interval time-place task: increasing sequence complexity

Rats were trained on an interval time-place learning (TPL) task in which the location of food availability depended on the time since the start of the session. Each of four levers (numbered 1, 2, 3, 4) provided food on an intermittent schedule for two nonconsecutive 3-min periods. The order in which the levers provided food was 1, 2, 4, 3, 2, 3, 1, 4. This order was consistent across sessions. Previous research conducted in our lab has shown that when only four "places" are used, rather than the eight in the present study, rats use a timing strategy to track the location of food. Pizzo and Crystal (2004) recently trained rats on an interval TPL in which each of eight arms of a radial arm maze provided food. They found evidence suggesting that rats used both spatial and temporal information. In the present study, in which a revisiting strategy was used (i.e., each lever provided food on more than one occasion), the rats tracked both the spatial and the temporal availability of food for the first half of the session. Interestingly, in the second half of the sessions, the rats appeared to be timing the availability of food even though they did not know where it would occur. That is, the rats knew the temporal, but not the spatial, contingencies for the second half of the session. It appears that the requirement of revisiting a previously reinforced lever resulted in rats' no longer being able to solve the spatial aspect of the task.

Spatial associative memory: a possible species difference in rats and pigeons

Previous research has shown that pigeons can remember which of four spatially distinct responses was last reinforced, for at least 72 h. The present study sought to replicate this finding using rats. Rats were tested in an operant chamber containing four spatially distinct levers. In each session one lever was randomly selected to provide reinforcement for 15 min. This reinforced period was preceded by a non-reinforced period that was 30s long, on average. During the non-reinforced period the amount the rat pressed on the previously reinforced lever was compared to responding on the other three levers, and was taken as a measure of memory. Sessions were separated either by 17 min, 24 or 72 h. Unlike pigeons, rats responded at chance levels following each of these retention intervals. This finding adds to previous research suggesting differences in cognitive processes in rats and pigeons.

Interval time-place learning by rats: varying reinforcement contingencies

Two experiments with rats were conducted to study interval time-place learning when the spatiotemporal contingencies of food availability were more similar to those likely to be encountered in natural environments, than those employed in prior research. In Experiment 1, food was always available on three levers on a variable ratio (VR) 35 schedule. A VR8 schedule was in effect on Lever 1 for 5 min, then on Lever 2 for 5 min, and so forth. While rats learned to restrict the majority of their responding to the lever that provided the highest density of reinforcement, they seemed to rely on a win-stay/lose-shift strategy rather than a timing strategy. In Experiment 2, the four levers provided food on variable ratios of 15, 8, 15, and 30, each for 3 min. As expected the rats learned these contingencies. A novel finding was that the rats had a spike in response rate immediately following a change from a higher to lower reinforcement density. It is concluded that rats exposed to spatiotemporal contingencies behave so as to maximize the rate of obtained reinforcement.

Time–place learning in the cichlid angelfish, Pterophyllum scalare

The ability of the cichlid angelfish, Pterophyllum scalare, to associate time and place to locate food, provided twice a day in two different places, was tested. Food was delivered daily in one corner of the tank in the morning and in the diagonally opposite corner in the afternoon, for a 3-week period, and the distribution of the fish in the tank was noted prior to and during feeding time. The results indicate that, in a fairly uniform environment and in the absence of external time cues, angelfish can discriminate and associate time and place to obtain a food reward. It is suggested that they do so by means of an endogenous timing mechanism.

Evidence for an alternation strategy in time-place learning

Many different conclusions concerning what type of mechanism rats use to solve a daily time-place task have emerged in the literature. The purpose of this study was to test three competing explanations of time-place discrimination. Rats (n = 10) were tested twice daily in a T-maze, separated by approximately 7 h. Food was available at one location in the morning and another location in the afternoon. After the rats learned to visit each location at the appropriate time, tests were omitted to evaluate whether the rats were utilizing time-of-day (i.e., a circadian oscillator) or an alternation strategy (i.e., visiting a correct location is a cue to visit the next location). Performance on this test was significantly lower than chance, ruling out the use of time-of-day. A phase advance of the light cycle was conducted to test the alternation strategy and timing with respect to the light cycle (i.e., an interval timer). There was no difference between probe and baseline performance. These results suggest that the rats used an alternation strategy to meet the temporal and spatial contingencies in the time-place task.

Evidence for time-place learning in the Morris water maze without food restriction but with increased response cost

Time-place learning is the ability to distinguish between resources that vary in location at different times of day. Only one previous report has demonstrated successful time-place learning without using food as reward. In this experiment, satiated rats failed to form time-place discriminations in a Morris water maze while food deprived rats did, leading to the conclusion that food system activation is necessary for time-place learning. However, in addition to food system activation, response cost was also increased, which previously has been demonstrated to be effective in allowing the formation of time-place discriminations. The purpose of these two experiments is to test whether food system activation or heightened response cost allowed for time-place learning in the Morris water maze. In the first experiment, we replicate the failure to find time-place discriminations in the Morris water maze without food restriction and without increased response cost. In the second experiment, we found that increased response cost without food restriction was effective in allowing the formation of a time-place discrimination. The implications of this result are discussed in light of the timing mechanism used for time-place discriminations, the nature of the response cost, and the event-time-place tripartite association.

Circadian modulation of performance on an aversion-based place learning task in hamsters

In golden hamsters, the expression of a reward-conditioned place preference (CPP) is regulated in a circadian pattern such that the preference is exhibited strongly at the circadian time of prior training but not at other circadian times. We now report that the same "time-stamp" phenomenon is expressed following context conditioning with an aversive stimulus (conditioned place avoidance, CPA). Animals that were trained at a specific circadian time to discriminate between a "safe" context and one paired with foot shock, showed strong avoidance of the paired context at 24 and 48 h following the last training session, and showed no avoidance at 32 and 40 h following training. Circadian time is a feature that is learned during conditioning even though timing itself is not an explicit discriminative cue in these experiments. The results suggest that in hamsters, the emotional valence associated with the place where arousing stimulation (rewarding and aversive) is encountered is highest at the circadian time of occurrence. The golden hamster may be predisposed to anticipate the recurrence of arousing events at circa-24 h intervals.

Time-place learning in the eight-arm radial maze

Rats (n = 4) searched for food on an eight-arm radial maze. Daily 56-min sessions were divided into eight 7-min time zones, during each of which a different location provided food; locations were randomized across subjects before training. The rats obtained multiple pellets within each time zone by leaving and returning to the correct location. Evidence that the rats had knowledge about the temporal and spatial features of the task includes the following. The rats anticipated locations before they became active and anticipated the end of the currently active locations. The rats discriminated currently active locations from earlier and forthcoming active locations in the absence of food transition cues. After the rats had left the previously active location, they visited the next correct location more often than would be expected by chance in the absence of food transition cues. The rats used handling or opening doors as a cue to visit the first location and timed successive 7-min intervals to get to subsequent locations.

Some pitfalls in measuring memory in animals

Because the presence or absence of memories in the brain cannot be directly observed, scientists must rely on indirect measures and use inferential reasoning to make statements about the status of memories. In humans, memories are often accessed through spoken or written language. In animals, memory is accessed through overt behaviours such as running down an arm in a maze, pressing a lever, or visiting a food cache site. Because memory is measured by these indirect methods, errors in the veracity of statements about memory can occur. In this brief paper, we identify three areas that may serve as pitfalls in reasoning about memory in animals: (1) the presence of 'silent associations', (2) intrusions of species-typical behaviours on memory tasks, and (3) improper mapping between human and animals memory tasks. There are undoubtedly other areas in which scientists should act cautiously when reasoning about the status of memory.

Rats have trouble associating all three parts of the time-place-event memory code

The ability of animals to associate an event with predictable time and place information confers a major biological advantage. The current research uses a variety of procedures and paradigms (e.g. place preference, radial arm maze, Morris water maze, T-maze, go no-go) to show that rats, unlike pigeons [e.g. Anim Learn Behav 22 (1994) 143] do not readily make an event-time-place association. They do make associations between event-time and event-place information, however. These findings are in disagreement with Gallistel's (The Organization of Learning, MIT Press, Cambridge, MA ) theory that claims that animals automatically store a memory code that has these three pieces of information. The present research is in line with the work of others who also find that rats do not readily make daily time-place associations [Behav Processes 23 (1997) 232; Behav Processes 52 (2000) 11; Behav Processes 49 (2000) 21; Anim Learn Behav 28 (2000) 298]. An interesting finding that did emerge from the present research was that at least some rats can use a circadian timer to solve a time-of-day discrimination if the task is a go no-go discrimination.

Representation of time in time-place learning

Ordinal, interval, and circadian mechanisms of solving a time-place task were tested. Rats searched for food twice in the morning and once in the afternoon (Group AB-C, n = 5) or once in the morning and twice in the afternoon (Group A-BC, n = 5) in a box with four food troughs. The location of the food depended on the time of day in a 12:12-h light:dark cycle. Acquisition was documented by food-site inspections at the correct locations prior to food availability. On nonrewarded probes, the time of the middle search (B) was shifted late (for Group AB-C) or early (for Group A-BC). The rats visited Location B at chance, contrary to an ordinal mechanism. When the posttesting meal and light-dark transitions were omitted, the rats visited correct locations with impaired performance but at above-chance levels on nonrewarded probes. The results are consistent with interval and circadian representations of time.

The significance of circadian phase for performance on a reward-based learning task in hamsters

In humans and animal models, circadian modulation of learning has been demonstrated on numerous tests. However, it is unclear which aspects of the cognitive process are rhythmically regulated. In these experiments, we used a conditioned place preference task in hamsters to ask whether memory acquisition (hypothesis 1) or memory recall and performance (hypothesis 2) were subject to circadian modulation. In golden hamsters, access to a running wheel has been used as a reward to condition a place preference, but when given unrestricted access to a wheel, animals perform most of their spontaneous running within a few hours each day or circadian cycle. This suggested that either the perceived reward value of the wheel changes through the day or that the response to this reward is temporally restricted. Contrary to the hypotheses, we found that learning was not tied to the time of training nor to the time of testing, but rather animals showed a preference for a reward-paired context only at the circadian time that training had taken place. Timing is not an explicit discriminative cue in these experiments. Hence, the learning mechanism must be predisposed to register circadian time as an attribute during context learning.

Alterations in time-place learning induced by lesions to the rat medial prefrontal cortex

This experiment examined the effect of medial prefrontal lesions on time-place learning in the rat. During the first phase, prior to lesioning, rats received training on an interval time-place task. Food was available on each of four levers for 3 consecutive min of a 12-min session. The levers provided food in the same sequence on all trials. Rats restricted the majority of their presses on each lever to the time in each session when it provided food and were able to anticipate when a lever was going to provide food. During the second phase some rats received lesions that were restricted to the medial prefrontal cortex. Following these very restricted lesions, rats continued pressing a lever after it stopped providing food (i.e. perseverated, as if their internal clock was running slow). The third phase involved changing the order in which the levers provided food. Lesions had no discernable effect on the rats' ability to learn the correct sequence of food availability. However, this change made the rats' timing perseveration even more noticeable. Our results suggest the medial prefrontal cortex is not necessary for acquisition of time-place sequencing information. However, lesions do appear to produce perseveration on components of the sequence.

Unequal interval time-place learning

In time-place learning tasks food availability depends upon both spatial and temporal variables. For example, food might be first available at location one, then location two, then location three, and finally location four. To date, the duration of food availability at each of the locations have been identical (e.g. for 4 min). The major purpose of the present experiment was to determine if rats can successfully learn a time-place task in which four locations provided food for different durations. Lever 1 intermittently produced food for 6 min, then Lever 2 produced food for 4 min. Lever 3 and 4 provided food for 2 and 8 min, respectively. Rats were able to learn this unequal interval time-place task. However, their behavior on this unequal interval time-place task was not in agreement with Scalar Expectancy Theory/Weber's Law.

How rats process spatiotemporal information in the face of distraction

How rats process spatiotemporal information in the face of distraction was assessed. Rats were trained on a time-place learning task in which the location of food availability depended on the amount of time elapsed since the beginning of the training session. In each training session each of four levers provided food pellets for 5 min on an intermittent schedule. In probe sessions interspersed with the final training sessions, the rats were presented with a second highly preferred food source-a piece of cheese-at various times into the session. Rats choose the correct lever after the cheese distraction, but it appeared that their internal clock had stopped during the cheese consumption period. Thus rats' internal clock, like that of pigeons, displays the properties of 'stop', 'reset', and 'restart'. Rat-pigeon differences in timing processes may be restricted to circadian or time of day timing. Present results also suggest that rats process spatial and temporal information separately.