Training delays reduce the choose-short effect with keylight duration samples in pigeons

Pigeons were trained to matching 2- and 8-s keylight samples. The delay on training trials was either 0s (group 0sF), 2s (group 2sF), or varied between 1 and 3s (M=2s, group 2sV). Testing at delays of 10 and 20s revealed a choose-short tendency in all three groups. The magnitude of this tendency was largest in group 0sF and was highly similar in magnitude in groups 2sF and 2sV. In Experiment 2, the training delay remained at 0s in group 0sF and was increased to 5s in group 2sF (now group 5sF). Group 2sV (now group 5sV) received variable training delays ranging from 2 to 8s (M=5s). Testing at a 20-s delay and at a delay that exceeded the training delay by 15s for each group revealed a robust choose-short effect only in group 0sF. Groups 5sF and 5sV both demonstrated a weak and statistically nonsignificant choose-short tendency. When different durations of keylight are employed as samples, training with a nonzero delay, whether fixed or variable, reduces the magnitude of the choose-short effect, with longer training delays producing a greater reduction in the choose-short effect.     

Rats' memory for event duration in delayed matching-to-sample with nonspatial comparison response alternatives

Previous research has suggested that using stationary and moving levers as nonspatial response alternatives can significantly enhance the speed of acquiring a temporal discrimination in rats. In Experiment 1, rats were trained to discriminate 2 and 8s of magazine light illumination by responding to either a stationary lever or a moving lever with a cue light illuminated above it. Rats learned to discriminate event durations at a high level of accuracy after 25 sessions of training. During subsequent delay tests, rats exhibited a strong choose-long bias, indicating that they were timing from the onset of the magazine light until the entry of levers into the chamber. This occurred regardless of whether intertrial intervals and delay intervals were dark or illuminated. On test trials in which the sample was omitted, rats responded as if the short sample had been presented. In Experiment 2, the rats received extensive training with dark and illuminated variable delay intervals (1-4 s). However, they continued to exhibit a tendency to time from the onset of the magazine light until entry of the levers into the chamber. Although the use of stationary/uncued and moving/cued levers as response alternatives enhanced the speed of acquisition of the event duration discrimination in rats, additional procedural modifications will be necessary to prevent rats from timing during the delay interval.     

Training delays reduce the choose-short effect with keylight, but not with food, duration samples in pigeons

Pigeons were trained to match 2- and 8-s food samples. The delay on training trials was either 0s (group 0sF), 5s (group 5sF), or varied between 2 and 8s (M=5s, group 5sV). Testing at a delay that exceeded the training delay by 15s in each group revealed a robust choose-short effect in each group. The same pigeons then reacquired a previously trained matching task involving 2- and 8-s keylight samples. Different comparison stimuli were used on food-sample and keylight-sample trials. The delay on training trials was the same on both food- and keylight-sample trials. Extended-delay testing revealed a robust choose-short effect in all three groups when the durations were conveyed by food presentations, but only group 0sF revealed a choose-short effect when the durations were conveyed by keylight presentations. Hence, training with a nonzero delay, whether fixed or variable, reduces the choose-short effect with keylight durations but not with food durations. It was concluded that at least some of the psychological processes mediating performance differ as a function of the event that conveys the duration.     

The effect of context change upon long-term memory of CS duration

An experiment with rats investigated forgetting of inhibition of delay in the conditioned suppression paradigm. The combined effects of contextual change and retention interval were tested. After a reliable temporal discrimination was reached, half of the rats received a test in the training context after a retention interval of 3 or 20 days. The other half received it in a different but equally familiar context at either retention interval. The longest retention interval flattened the temporal discrimination gradient and increased suppression to the CS. A similar but weaker pattern was found with the change of context; this effect was independent of the retention interval. The implications for retrieval and interference theory [Bouton, M.E., 1993. Psychol. Bull., 114: 80–99] and hypotheses concerning the forgetting of specific features of stimuli over time [Riccio, D.C., Richardson, R. and Ebner, D.L., 1984. Psychol. Bull., 96: 152–165] are discussed.     

Rats' memory for event duration: differential effects of delaying the discriminative choice cue as opposed to the opportunity to execute the choice response

Rats were trained to discriminate short or long durations of houselight illumination using a choice procedure. During the test phase of each trial, the left and right levers were presented with an auditory cue above one of them on (cued lever) while the other was off (uncued lever). The auditory cue was presented immediately after sample offset and the levers were inserted after the auditory cue had been presented for 2 s. For half of the rats, the correct response following the short sample was to press the cued lever, while following the long sample, it was to press the uncued lever. This was reversed for the remaining rats. Following acquisition of the discrimination, two different types of delay tests were administered. In the first set, the delay between offset of the sample and onset of the auditory cue was manipulated (Cue Delay Test). In the second set, the delay between onset of the auditory cue and entry of the levers into the chamber was manipulated (Response Delay Test). Cue Delay testing resulted in a choose-long bias at the longer delays. Response Delay testing did not result in a systematic response bias and there was little forgetting over the delay interval. These data suggest that the rats did not stop the internal clock when the nominal sample was offset, but allowed it to keep running until the auditory cue was presented. The data from the Response Delay Test indicate that either a response decision was made based on the clock reading as soon as the auditory cue was presented, or the clock reading itself was retained over the delay with no subjective shortening and little forgetting.     

On the optimal duration of memory of losing a conflict--a mathematical model approach

In male broad-horned flour beetles, Gnatocerus cornutus, losers of conflicts avoid fighting at subsequent encounters. The loser effect lasts for 4 days. It is considered that the memory of losing remains for 4 days. The duration of the memory is expected to affect the fitness, and the duration, 4 days, is expected to be optimal. We consider the fitness of a mutant in an homogeneous population to obtain the optimal duration. Here we carry out simulations using an individual-based model. The results suggest that the trade-off of getting mating chances and avoiding damage can cause the optimal duration of the memory, and that the decay in time of the female population is an important factor.     

Nonlinear dynamics of two-dimensional cardiac action potential duration mapping model with memory

The aim of this work is the analysis of the nonlinear dynamics of two-dimensional mapping model of cardiac action potential duration (2D-map APD) with memory derived from one dimensional map (1D-map). Action potential duration (APD) restitution, which relates APD to the preceding diastolic interval (DI), is a useful tool for predicting cardiac arrhythmias. For a constant rate of stimulation the short action potential during alternans is followed by a longer DI and inversely. It has been suggested that these differences in DI are responsible for the occurrence and maintenance of APD alternans. We focus our attention on the observed bifurcations produced by a change in the stimulation period and a fixed value of a particular parameter in the model. This parameter provides new information about the dynamics of the APD with memory, such as the occurrence of bistabilities not previously described in the literature, as well as the fact that synchronization rhythms occur in different ways and in a new fashion as the stimulation frequency increases. Moreover, we show that this model is flexible enough as to accurately reflect the chaotic dynamics properties of the APD: we have highlighted the fractal structure of the strange attractor of the 2D-map APD, and we have characterized chaos by tools such as the calculation of the Lyapunov exponents, the fractal dimension and the Kolmogorov entropy, with the next objective of refining the study of the nonlinear dynamics of the duration of the action potential and to apply methods of controlling chaos.

     

The effective duration of the delay phenomenon in the rat.

In standard skin flaps in the rat, the effect of a delay was undetectable for the first 3 weeks and the maximum benefit was not apparent until the sixth week. At all time intervals the delay phenomenon was not as pronounced in the rat as in other species. The delay phenomenon in the rat lasts at least 30 weeks. The rat does not appear to be an ideal model for the study of skin flaps.     

The neuroprotective effect of tacrine on trimethyltin induced memory and muscarinic receptor dysfunction in the rat

In this study chronic (39 days) tacrine (3 mg/kg i.p.) treatment significantly improved trimethyltin (8 mg/kg i.p.) induced deficits in spatial navigation. Tacrine also reduced trimethyltin induced hyperactivity and passive avoidance deficits but these effects did not reach statistical significance. The effect of trimethyltin on muscarinic (M₁ and M₂) receptor sites was determined by means of quantitative autoradiography using [³H]quinuclidinyl benzilate. A selective pattern of M₁ and M₂ receptor loss was observed mainly affecting the hippocampus and other limbic structures while leaving other brain regions intact. Tacrine successfully prevented the M₁ and M₂ receptor loss in the CA₁ and CA₁ hippocampal subfields. The improvement in trimethyltin behavioural toxicity following tacrine treatment may be related to the protective effect of this compound on muscarinic receptor density in the hippocampal formation and lends support to the hypothesis that cholinergic system dysfunction may be primarily responsible for trimethyltin induced deficits in cognitive function.     

Episodic-like memory in the rat

A fundamental question in comparative cognition is whether animals remember unique, personal past experiences. It has long been argued that memories for specific events (referred to as episodic memory) are unique to humans. Recently, considerable evidence has accumulated to show that food-storing birds possess critical behavioral elements of episodic memory, referred to as episodic-like memory in acknowledgment of the fact that behavioral criteria do not assess subjective experiences. Here we show that rats have a detailed representation of remembered events and meet behavioral criteria for episodic-like memory. We provided rats with access to locations baited with distinctive (e.g., grape and raspberry) or nondistinctive (regular chow) flavors. Locations with a distinctive flavor replenished after a long but not a short delay, and locations with the nondistinctive flavor never replenished. One distinctive flavor was devalued after encoding its location by prefeeding that flavor (satiation) or by pairing it with lithium chloride (acquired taste aversion), while the other distinctive flavor was not devalued. The rats selectively decreased revisits to the devalued distinctive flavor but not to the nondevalued distinctive flavor. The present studies demonstrate that rats selectively encode the content of episodic-like memories.     

The lesion of the rat substantia nigra pars compacta dopaminergic neurons as a model for Parkinson's disease memory disabilities

1. In this article we review the studies of memory disabilities in a rat model o Parkinson's disease (PD).2. Intranigral administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to rats causes a partial lesion in the substantia nigra, compact part (SNc) and a specific loss of dopamine and its metabolites in the striatum of rats.3. These animals present learning and memory deficits but no sensorimotor impairments, thus modeling the early phase of PD when cognitive impairments are observed but the motor symptoms of the disease are barely present.4. The cognitive deficits observed in these animals affect memory tasks proposed to model habit learning (the cued version of the water maze task and the two-way active avoidance task) and working memory (a working memory version of the water maze), but spare long-term spatial memory (the spatial reference version of the Morris water maze).5. The treatment of these animals with levodopa in a dose that restores the striatal level of dopamine does not reverse these memory impairments, probably because this treatment promotes a high level of dopamine in extrastriatal brain regions, such as the prefrontal cortex and the hippocampus.6. On the other hand, the adenosine receptor antagonist, caffeine, partly reverse the memory impairment effect of SNc lesion in these rats. This effect may be due to caffeine action on nigrostriatal neurons, since it induces dopamine release and modulates the interaction between adenosine and dopamine receptor activity.7. These results suggest that the MPTP SNc-lesioned rats are a good model to study memory disabilities related to PD and that caffeine and other selective A(2A) adenosine receptor antagonists are promising drugs to treat this symptoms in PD patients.     

The effect of predictability on subjective duration

Events can sometimes appear longer or shorter in duration than other events of equal length. For example, in a repeated presentation of auditory or visual stimuli, an unexpected object of equivalent duration appears to last longer. Illusions of duration distortion beg an important question of time representation: when durations dilate or contract, does time in general slow down or speed up during that moment? In other words, what entailments do duration distortions have with respect to other timing judgments? We here show that when a sound or visual flicker is presented in conjunction with an unexpected visual stimulus, neither the pitch of the sound nor the frequency of the flicker is affected by the apparent duration dilation. This demonstrates that subjective time in general is not slowed; instead, duration judgments can be manipulated with no concurrent impact on other temporal judgments. Like spatial vision, time perception appears to be underpinned by a collaboration of separate neural mechanisms that usually work in concert but are separable. We further show that the duration dilation of an unexpected stimulus is not enhanced by increasing its saliency, suggesting that the effect is more closely related to prediction violation than enhanced attention. Finally, duration distortions induced by violations of progressive number sequences implicate the involvement of high-level predictability, suggesting the involvement of areas higher than primary visual cortex. We suggest that duration distortions can be understood in terms of repetition suppression, in which neural responses to repeated stimuli are diminished.     

Variability in 5- and 8-year-olds' memory for duration: an interfering task in temporal bisection

The purpose of this experiment was to investigate 5- and 8-year-olds' long-term memory for stimulus duration in a bisection task. Children were trained to discriminate between a short and a long standard duration presented as visual stimulus for 2 and 8 s, respectively. They had then to decide whether an intermediate stimulus duration was more similar to the short or to the long standard in two identical testing phases separated by an interfering task lasting for 15 min (immediate test vs. deferred test). The results showed that the 5- and the 8-year-olds produced orderly psychophysical functions. However, the 8-year-olds produced psychophysical functions, which increased more abruptly with the increasing stimulus duration. Nevertheless, whatever the age of children tested, the psychophysical function curves were flatter in the deferred test than in the immediate test, and more particularly in the 5-year-olds. Furthermore, the 5-year-olds produced fewer 'long' responses in the deferred than in the immediate test. Modeling of the data suggests that the variability of the representation of the standard in long-term memory was higher in the 5- than in the 8-year-olds and that the interfering task increased this memory variability.     

The effect of an intruded event on peak-interval timing in rats: isolation of a postcue effect

The present experiment employed the peak-interval (PI) procedure to study the effect of an intruded cue on timing behavior. Rats were trained on a 30-s PI procedure with a tone cue. Subsequently, a 6-s flashing light was paired off-baseline with foot shock (Experiment 1) or presented alone (Experiment 2). Then, in test trials, the light cue was presented 9s prior to (before) or 3s after (during) the onset of the timing cue, or the light was omitted (probe). Results showed rightward shifts in peak time occurring on both before and during trials in both experiments. Peak shifts on during trials exceeded the reset prediction in Experiment 1. When PI functions for before and probe trials were normalized in peak rate and peak time, they superimposed better than when functions were adjusted additively along the time axis, suggesting that the light cue may engender a decrease in functional clock rate. The findings suggested that the intruded cue produced both intracue and postcue interference with timing that was enhanced by fear conditioning.     

The onset and duration of mobilization affect the regeneration in the rat muscle

The effects of different mobilization protocols for muscle regeneration after myotoxin injury was compared in the rat tibialis anterior (TA) muscle. Adult Wistar rats were divided into control (C); mobilized (M); injury (I); injury + late mobilization (LM) and injury + early mobilization (EM) groups. Muscle injury was induced by intramuscular lidocaine injection. The exercised animals were mobilized for 5 and 8 days during 15 and 45 minutes/session. The swimming started 1 hour or 3 days after injury. All animals were killed 8 days after the injury, together with the control group, when the TA muscles were weighted and excised. Cross sections were obtained by cryostat and submitted to Toluidine Blue stain. Qualitative morphological characterization of muscle regeneration and quantitative analysis of muscle fiber and non-muscle fiber area density were performed. The I and late mobilization groups showed decreased muscle mass when compared to all other groups. All injured animals showed signs of muscle fiber damage, although signs of early regenerated muscle fibers were more evident in injury + mobilization groups. Only the EM groups submitted to 45 minutes of exercise had increased muscle fiber and decreased non-muscle fiber area density values when compared to I group (p<0.05). Conclusion: the regeneration process is related to the onset of exercise, since animals submitted to early mobilization showed improved regeneration when comparted to LM groups. Besides, the length of session is also important for accelerating the regeneration process, as it was observed that 45 minutes was better than 15 minutes duration.     

The effect of cdk-5 overexpression on tau phosphorylation and spatial memory of rat

In Alzheimer’s disease (AD), hyperphosphorylation of tau may be the underlying mechanism for the cytoskeletal abnormalities and neuronal death. It was reported that cyclin-dependent kinase5 (cdk-5) could phosphorylate tau at most AD-related epitopesin vitro. In this study, we investigated the effect of cdk-5 overexpression on tau phosphorylation and spatial memory in rat. We demonstrated that 24 h after transfection into rat hippocampus, cdk-5 was overexpressed and induced a reduced staining with antibody tau-1 and an enhanced staining with antibodies 12e8 and PHF-1, suggesting hyperphosphorylation of tau at Ser199/202, Ser262/356 and Ser396/404 sites. Additionally, the cdk-5 transfected rats showed long latency to find the hidden platform in Morris water maze compared to the control rat. 48 h after transfection, the level of cdk-5 was decreased significantly, and the latency of rats to find the hidden platform was prolonged. It implies thatin vivo overexpression of cdk-5 leads to impairment of spatial memory in rat and tau hyperphosphorylation may be the underlying mechanism.     

胰岛素对AD模型大鼠空间学习记忆能力的影响

目的:探讨胰岛素对阿尔茨海默氏病(AD)模型大鼠学习记忆能力影响及其可能机制。方法:大鼠海马微量注射Okadaic acid(OA),胰岛素侧脑室注射。水迷宫实验检测大鼠学习记忆能力;Western blotting实验检测大鼠海马烟碱型胆碱能受体的表达;免疫组化观察大鼠脑内胶质纤维酸性蛋白(GFAP)的表达。结果:与对照组比较,模型组大鼠学习记忆能力明显下降(P<0.01),烟碱型胆碱能受体表达减少(P<0.05),GFAP免疫阳性星形胶质细胞增多(P<0.05)。与模型组相比,胰岛素组大鼠学习记忆能力明显提高(P<0.01),烟碱型胆碱能受体表达增多(P<0.05),GFAP免疫阳性星形胶质细胞减少(P<0.05)。结论:胰岛素提高AD模型大鼠的学习记忆能力可能与其改善模型鼠胆碱能系统功能及减少星形胶质细胞增生有关。