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.

Daily rhythms of locomotor and demand-feeding activities in Schizothorax pelzami (Kessler, 1870)

A study was carried out to investigate the daily rhythms of locomotor and feeding activity of Khajoo, Schizothorax pelzami, a candidate species for freshwater aquaculture. Using self-feeder juvenile Khajoo were exposed to a 12/12 LD cycle to determine the rhythms of locomotor and feeding activity. The effects of feeding on locomotor and feeding activity of fish were also examined. Finally, the endogenous rhythmicity under different lighting condition tested. Fish displayed a strictly diurnal feeding and locomotor activities with 98% and 84% of the total activity occurred in the photophase, respectively. In scheduled feeding, both the L-group (fed in light) and the D-group (fed in the dark) showed a diurnal locomotor activity pattern. However, the L-group had a peak of locomotor activity near the feeding time, but the D-group had a scarce locomotor activity in the scatophase with no significant change at the mealtime. Most of the individuals display free-running rhythms when exposed to different lighting condition including, constant darkness, ultradian 45:45 min LD cycle and reversed DL photo cycle. Taken together the results of this study showed that both locomotor and feeding activity have diurnal rhythms in Khajoo S. pelzami, even fish feeding had taken place at night. Additionally, the free-running locomotor activity of the fish in the absence of external light stimuli, suggests the existence of an endogenous timing mechanism in this fish species.

Experimental setting affects the performance of guppies in a numerical discrimination task

A recent study found that guppies (Poecilia reticulata) can be trained to discriminate 4 versus 5 objects, a numerical discrimination typically achieved only by some mammals and birds. In that study, guppies were required to discriminate between two patches of small objects on the bottom of the tank that they could remove to find a food reward. It is not clear whether this species possesses exceptional numerical accuracy compared with the other ectothermic vertebrates or whether its remarkable performance was due to a specific predisposition to discriminate between differences in the quality of patches while foraging. To disentangle these possibilities, we trained guppies to the same numerical discriminations with a more conventional two-choice discrimination task. Stimuli were sets of dots presented on a computer screen, and the subjects received a food reward upon approaching the set with the larger numerosity. Though the cognitive problem was identical in the two experiments, the change in the experimental setting led to a much poorer performance as most fish failed even the 2 versus 3 discrimination. In four additional experiments, we varied the duration of the decision time, the type of stimuli, the length of training, and whether correction was allowed in order to identify the factors responsible for the difference. None of these parameters succeeded in increasing the performance to the level of the previous study, although the group trained with three-dimensional stimuli learned the easiest numerical task. We suggest that the different results with the two experimental settings might be due to constraints on learning and that guppies might be prepared to accurately estimate patch quality during foraging but not to learn an abstract stimulus-reward association.

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.

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.

Fish intelligence, sentience and ethics

Fish are one of the most highly utilised vertebrate taxa by humans; they are harvested from wild stocks as part of global fishing industries, grown under intensive aquaculture conditions, are the most common pet and are widely used for scientific research. But fish are seldom afforded the same level of compassion or welfare as warm-blooded vertebrates. Part of the problem is the large gap between people's perception of fish intelligence and the scientific reality. This is an important issue because public perception guides government policy. The perception of an animal's intelligence often drives our decision whether or not to include them in our moral circle. From a welfare perspective, most researchers would suggest that if an animal is sentient, then it can most likely suffer and should therefore be offered some form of formal protection. There has been a debate about fish welfare for decades which centres on the question of whether they are sentient or conscious. The implications for affording the same level of protection to fish as other vertebrates are great, not least because of fishing-related industries. Here, I review the current state of knowledge of fish cognition starting with their sensory perception and moving on to cognition. The review reveals that fish perception and cognitive abilities often match or exceed other vertebrates. A review of the evidence for pain perception strongly suggests that fish experience pain in a manner similar to the rest of the vertebrates. Although scientists cannot provide a definitive answer on the level of consciousness for any non-human vertebrate, the extensive evidence of fish behavioural and cognitive sophistication and pain perception suggests that best practice would be to lend fish the same level of protection as any other vertebrate.

Time-place learning and leader-follower relationships in Arctic charr Salvelinus alpinus

Feeding activity from a larger refuge site into two visually separated feeding sites with temporally restricted food availability, one in the morning and one in the evening was studied in duplicate groups of Arctic charr Salvelinus alpinus. A passive integrated transponder (PIT) system enabled continuous monitoring of individual movements between the sites. Both groups synchronized their diel pattern of visit activity to the two feeding sites when food was available. One group showed significant anticipatory visit activity into both feeding sites during the hours before the feed was available, suggesting a time and place learning of resource availability. The anticipatory activity of the other group was, however, less pronounced and only occurred into one of the feeding sites. Individual S. alpinus entered the feeding sites independently and no obvious patterns of leaders and followers were identified. All S. alpinus gained mass and moved between a refuge and the feeding sites. Different strategies of how individual S. alpinus utilized the feeding sites were not correlated with growth.

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.

Learning temporal patterns of risk in a predator-diverse environment

Predation plays a major role in shaping prey behaviour. Temporal patterns of predation risk have been shown to drive daily activity and foraging patterns in prey. Yet the ability to respond to temporal patterns of predation risk in environments inhabited by highly diverse predator communities, such as rainforests and coral reefs, has received surprisingly little attention. In this study, we investigated whether juvenile marine fish, Pomacentrus moluccensis (lemon damselfish), have the ability to learn to adjust the intensity of their antipredator response to match the daily temporal patterns of predation risk they experience. Groups of lemon damselfish were exposed to one of two predictable temporal risk patterns for six days. "Morning risk" treatment prey were exposed to the odour of Cephalopholis cyanostigma (rockcod) paired with conspecific chemical alarm cues (simulating a rockcod present and feeding) during the morning, and rockcod odour only in the evening (simulating a rockcod present but not feeding). "Evening risk" treatment prey had the two stimuli presented to them in the opposite order. When tested individually for their response to rockcod odour alone, lemon damselfish from the morning risk treatment responded with a greater antipredator response intensity in the morning than in the evening. In contrast, those lemon damselfish previously exposed to the evening risk treatment subsequently responded with a greater antipredator response when tested in the evening. The results of this experiment demonstrate that P. moluccensis have the ability to learn temporal patterns of predation risk and can adjust their foraging patterns to match the threat posed by predators at a given time of day. Our results provide the first experimental demonstration of a mechanism by which prey in a complex, multi-predator environment can learn and respond to daily patterns of predation risk.

Circadian time-place learning in mice depends on Cry genes

Endogenous biological clocks allow organisms to anticipate daily environmental cycles. The ability to achieve time-place associations is key to the survival and reproductive success of animals. The ability to link the location of a stimulus (usually food) with time of day has been coined time-place learning, but its circadian nature was only shown in honeybees and birds. So far, an unambiguous circadian time-place-learning paradigm for mammals is lacking. We studied whether expression of the clock gene Cryptochrome (Cry), crucial for circadian timing, is a prerequisite for time-place learning. Time-place learning in mice was achieved by developing a novel paradigm in which food reward at specific times of day was counterbalanced by the penalty of receiving a mild footshock. Mice lacking the core clock genes Cry1 and Cry2 (Cry double knockout mice; Cry1(-/-)Cry2(-/-)) learned to avoid unpleasant sensory experiences (mild footshock) and could locate a food reward in a spatial learning task (place preference). These mice failed, however, to learn time-place associations. This specific learning and memory deficit shows that a Cry-gene dependent circadian timing system underlies the utilization of time of day information. These results reveal a new functional role of the mammalian circadian timing system.

Time-place learning in food-restricted Nile tilapia

Time-place learning based on food association was investigated in eight food-restricted Nile tilapias. Each fish was individually housed for 10 days in an experimental tank for adjustments to laboratory conditions, and fed daily in excess. Feeding was then interrupted for 17 days. Training was then started, based on a food-restricted regime in a tank divided into three interconnected compartments. Daily food was offered in one compartment (left or right side) of the tank in the morning and on the opposite side in the afternoon, for a continuous 30-day period. Frequency of choices on the right side was measured on days 10, 20 and 30 (during these test days, fish were not fed). Following this 30-day conditioning period, the Nile tilapias were able to switch sides at the correct period of the day to get food, suggesting that food restriction facilitates time-place learning discrimination.

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.

Evaluating feeding as unconditioned stimulus for conditioning of an endocrine effect in Nile tilapia

This study tested the adequacy of feeding as an unconditioned stimulus (US) to condition an endocrine response (plasma cortisol increase) in the cichlid fish Nile tilapia (Oreochromis niloticus). In a first study, conditioning was confirmed in grouped fish in the only experiment using single-held Nile tilapia. In this test a conditioned stimulus (CS - aeration off) was associated with a stressor (air emersion for 2 min- US). We then assessed whether several events of paired CS-US resulted in a conditioned endocrine response (CR), in this case an increase in plasma cortisol after presentation of the CS only. Before testing feeding as US, the postprandial or social holding condition for feeding effects on cortisol levels was tested. Nile tilapia showed increased cortisol after feeding associated to social context (grouped fish), but not to food only (single-held fish). In a third study, feeding was tested as US in an experiment similar to the first study but an increase in feeding-induced cortisol could not be conditioned. The absence of CR suggests that the stressor affects acquisition of this response, which may be a consequence of stimulus intensity or biological relevance. This study expands the recently reported Pavlovian conditioning paradigm for endocrine response in fish.

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.

Time-place learning in individually reared angelfish, but not in pearl cichlid

Time-place learning based on food association was investigated in the cichlids angelfish (Pterophyllum scalare) and pearl cichlid (Geophagus brasiliensis) reared in isolation, therefore eliminating social influence on foraging. During a 30-day period, food was placed in one side of the aquarium (containing three compartments) in the morning and in the opposite side in the afternoon. Learning was inferred by the number of correct side choices of all fish in each day of test (15th and 30th). During the test day fish were not fed. The angelfish learned to switch sides at the correct day period in order to get food, suggesting this species has time-place learning ability when individually reared. On the other hand, the same was not observed for pearl cichlid.

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 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.

Fish and welfare: do fish have the capacity for pain perception and suffering?

Humans interact with fish in a number of ways and the question of whether fish have the capacity to perceive pain and to suffer has recently attracted considerable attention in both scientific and public fora. Only very recently have neuroanatomical studies revealed that teleost fish possess similar pain-processing receptors to higher vertebrates. Research has also shown that fish neurophysiology and behaviour are altered in response to noxious stimulation. In the light of this evidence, and in combination with work illustrating the cognitive capacities of fish, it seems appropriate to respond to a recently published critique (Rose 2002) in which it is argued that it is not possible for fish to experience fear or pain and that, therefore, they cannot suffer. Whilst we agree with the author that fish are unlikely to perceive pain in the same way that humans do, we believe that currently available evidence indicates that fish have the capacity for pain perception and suffering. As such, it would seem timely to reflect on the implications of fish pain and suffering, and to consider what steps can be taken to ensure the welfare of the fish that we exploit.

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.

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.

Food-anticipatory activity of groups of golden shiners during both day and night

For 12 days, captive groups each containing four golden shiners (Notemigonus crysoleucas) were fed by automatic feeders at two diametrically opposed daily times. These two times could be midday and midnight, late day and late night, or early day and early night. As measured by interruptions of an infrared beam underneath the feeder, golden shiners almost always expressed food-anticipatory activity. Beam interruptions started to increase a few hours before mealtime, reaching a peak within 1.5 h of food delivery. In at least half of the groups tested, food-anticipatory activity developed for both daily times simultaneously. This double anticipation was maintained for at least 5 days after food was withheld. These results show that golden shiner groups (though not necessarily individuals) can express two peaks of food anticipation at widely separated daily times, even if one occurs during the day and the other at night, providing further evidence for the great variability that fishes can display in their activity patterns.