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At least 1,063 records · Page 59Linked to original sources
PubMed2004

Maintenance in working memory or response selection? Functions of NMDA receptors in the pigeon "prefrontal cortex".

The prefrontal cortex is involved in various aspects of working memory like stimulus maintenance and response selection functions. Neurobehavioral studies and neurocomputational models assume a role for NMDA receptors in prefrontal cortex for maintenance processes, while our previous studies on NMDA receptors in the avian prefrontal cortex-analogue, the nidopallium caudolaterale (NCL), showed them to be involved in response selection functions. Various tasks used in PFC-related research address in fact both functions, so they cannot disambiguate their separate contributions to performance. In order to investigate the role of NMDA receptors in avian NCL for stimulus maintenance and response selection, we trained pigeons in a delayed matching-to sample (DMTS) task, requiring both functions, and a simultaneous matching to sample (SMTS) task, requiring only response selection. After reaching criterion, pigeons had to perform the tasks alternately under local NMDA receptor blockade in NCL (DL-AP5) and after infusion of vehicle (saline solution). Blockade of NCL-based NMDA receptors led to significant increases in error rates in both DMTS and SMTS--compared with the same subjects' performance during training and in the control condition. However, there was no additional increase in errors due to the additional maintenance component, so the impairment appears to be due to deficits in adequate selection of responses, the function necessary for both tasks. We conclude that NMDA receptors in the pigeon NCL participate in response selection rather than stimulus maintenance in tasks requiring the processing of context information.

Animals↗
PubMed2005

The role of the hippocampus in object recognition in rats: examination of the influence of task parameters and lesion size.

Studies examining the effects of hippocampal lesions on object recognition memory in rats have produced conflicting results. The present study investigated how methodological differences and lesion size may have contributed to these discrepancies. In Experiment 1 we compared rats with complete, partial (septal) and sham hippocampal lesions on a spontaneous object recognition task, using a protocol previously reported to result in deficits following large hippocampal lesions . Rats with complete and partial hippocampal lesions were unimpaired, suggesting the hippocampus is not required for object recognition memory. However, rats with partial lesions showed relatively poor performance raising the possibility that floor effects masked a deficit on this group. In Experiment 2, we used a second spontaneous object recognition protocol similar to that used by the two other studies that have reported deficits following hippocampal lesions . Rats with complete hippocampal lesions were significantly impaired, whereas rats with partial lesions were unimpaired. However, the complete lesion group showed less object exploration during the sample phase. Thus, the apparent recognition memory deficit in Experiment 2 may be attributable to differential encoding. Together, these findings suggest that the hippocampus is not required for intact spontaneous object recognition memory. These findings suggest that levels of object exploration during the sample phase may be a critical issue, and raise the possibility that previous reports of object recognition deficits may be due to differences in object exploration rather than deficits in object recognition per se.

Analysis of Variance↗
PubMed2006

The pre-movement component of motor cortical local field potentials reflects the level of expectancy.

Cortical local field potentials (LFPs) are modulated in parallel with single neuron discharge, but the information they carry is often unclear. Multi-electrode recordings of both LFPs and single neuron activities were made in motor cortex as monkeys performed a delayed pointing task in which the probability of the moment of signal occurrence, and thus movement execution, was manipulated. A large positive LFP component (P1) appeared immediately preceding movement onset only under conditions of low probability, that is, when a response signal was weakly expected. The amplitude of P1 was much smaller when probability of signal occurrence was high, or when the same movement was self-paced. Although P1 has been described as being linked to the descending motor signal, we found that it was more closely associated with the processing of movement-related information than with the ultimate motor command. Its timing did not bear a fixed relationship with movement onset and its frequency of occurrence in each monkey varied in parallel with each animal's overall performance and the percentage of context-related "pre-processing" neurons encountered.

Action Potentials↗
PubMed2004

Tool-use and tool-making by captive, group-living orangutans (Pongo pygmaeus abelii) at an artificial termite mound.

The present study examined the use and making of tools to obtain foodstuffs in artificial-mound holes by five captive, group-living Sumatran orangutans (Pongo pygmaeus abelii). Three adult orangutans frequently stripped leaves and twigs from a branch provided (tool-making), and then inserted the tool into a hole to obtain foodstuffs (tool-using). A 5-year-old female juvenile usually used the tools that adult orangutans had previously used, but rarely made tools herself. A 2-year-old male infant did not use any tools. The adult orangutans tend to leave one to several leaves at the top of the branch than to leave many leaves on the branch or to strip all leaves. It seemed likely that tools with appropriate leaves are easier to insert into holes and obtain more foodstuffs, compared with branches with many leaves or sticks without any leaves. When the orangutans were unable to insert a tool into a hole, they usually modified the tool and/or changed their tool-using technique, such as changing how they grasped the tool. These findings are discussed from the perspectives of the orangutan's behavioral flexibility regarding tool-use skills and hierarchical organization in food-processing techniques.

Animals↗
PubMed2006

A pharmacological model for psychosis based on N-methyl-D-aspartate receptor hypofunction: molecular, cellular, functional and behavioral abnormalities.

BACKGROUND: The psychotomimetic effects of N-methyl-D-aspartate (NMDA) receptor antagonists such as phencyclidine (PCP) in healthy humans and their ability to exacerbate psychotic symptoms in schizophrenic patients have promoted a view of schizophrenia as being related to altered glutamatergic neurotransmission. METHODS: This prompted us and others to develop animal models for psychosis based on a glutamatergic approach. Pharmacological induction of a state of impaired glutamatergic neurotransmission based on chronic, low-dose application of MK-801, a highly selective noncompetitive NMDA antagonist, revealed marked parallels between schizophrenia and our animal model. RESULTS: MK-801 altered the expression of NR1 splice variants and NR2 subunits of the NMDA receptor in a pattern partially resembling the alterations detected in schizophrenia. Ultrastructurally, the number of gamma-aminobutyric-acid (GABA)ergic parvalbumin-positive interneurons was relatively decreased, a finding which again parallels observations in post mortem brain from schizophrenic patients. As a functional consequence, local inhibition of pyramidal cells which is largely mediated by recurrent axon collaterals, originating from GABAergic interneurons, was altered. Not unexpectedly, these animals showed cognitive deficits resembling findings in schizophrenic humans. CONCLUSIONS: These convergent lines of evidence suggest that our approach has a significant potential of serving as a model of the pathobiology of several aspects of psychosis and consequently could contribute to the development of new therapeutic strategies.

Animals↗
PubMed2004

Perirhinal N-methyl-D-aspartate and muscarinic systems participate in object recognition in rats.

To determine the possible involvement of N-methyl-d-aspartate (NMDA) and muscarinic activation of the perirhinal cortex in object recognition, an NMDA antagonist (d,l-2-amino-5-phosphonopentanoic acid (AP5)) and a muscarinic antagonist (scopolamine) were injected into the perirhinal cortex of rats. A high dose of AP5 (60 mM) and two doses of scopolamine (20 and 80 mM), but not a low dose of AP5 (30 mM) alone, significantly impaired discrimination between novel and familiar objects in a spontaneous object recognition task, which is one of the recognition memory tasks. These results suggest that activation of both NMDA and muscarinic receptors in the perirhinal cortex contributes to object recognition.

2-Amino-5-phosphonovalerate↗
PubMed2006

Encoding of time-discounted rewards in orbitofrontal cortex is independent of value representation.

We monitored single-neuron activity in the orbitofrontal cortex of rats performing a time-discounting task in which the spatial location of the reward predicted whether the delay preceding reward delivery would be short or long. We found that rewards delivered after a short delay elicited a stronger neuronal response than those delivered after a long delay in most neurons. Activity in these neurons was not influenced by reward size when delays were held constant. This was also true for a minority of neurons that exhibited sustained increases in firing in anticipation of delayed reward. Thus, encoding of time-discounted rewards in orbitofrontal cortex is independent of the encoding of absolute reward value. These results are contrary to the proposal that orbitofrontal neurons signal the value of delayed rewards in a common currency and instead suggest alternative proposals for the role this region plays in guiding responses for delayed versus immediate rewards.

Action Potentials↗
PubMed2006

The odour span task: a novel paradigm for assessing working memory in mice.

Impoverished odour recognition and memory are amongst the earliest symptoms observed in mild cognitive impairment, Alzheimer's disease and schizophrenia, and have been advocated as early disease bio-markers. Although transgenic animals modelling disease pathologies continually emerge, there remains a paucity of tasks to examine olfactory working memory in mice. The present studies describe a mouse odour span task, which assesses the ability to remember increasing numbers of odours. Since caspase-3 is highly expressed throughout the olfactory system, we postulated that mice over-expressing this apoptogenic protein would exhibit impaired performance in the odour span task. Mice over-expressing human caspase-3 (Tg) exhibited age-independent deficits in olfactory working memory (6-18 months) compared with wild-type littermates, requiring longer for task acquisition and exhibiting impaired asymptotic performance, with reduced span lengths, lower accuracy and increased error rates. These impairments appeared to be selective for working memory, as Tg mice had no deficits in odour discriminatory ability or in locomotor measures. Importantly, nicotine, which improves working memory span in man, reversed the deficits exhibited by Tg mice. In conclusion, the mouse odour span task can detect subtle changes in olfactory working memory induced by genetic manipulation and drug administration and therefore should be applied to animal models of neurological disease.

Analysis of Variance↗
PubMed2005

The primate amygdala and reinforcement: a dissociation between rule-based and associatively-mediated memory revealed in neuronal activity.

To investigate the role of the primate amygdala in stimulus-reinforcement association learning, the activity of single amygdala neurons was recorded in macaques during two memory tasks. In a visual discrimination task, a population of neurons (17/659) was analyzed which responded differentially to a visual stimulus which always indicated that the primary reinforcer fruit juice could be obtain if the monkey licked, and a different visual stimulus that indicated that the primary reinforcer aversive saline would be obtained if the monkey licked. Most (16/17) of these neurons responded more to the reward-related than the aversive visual stimulus. In a recognition memory task, the majority (12/14 analyzed) of these neurons responded equally well to the trial unique stimuli when they were shown as novel and the monkey had to not lick in order to avoid saline, and when they were shown a second time as familiar and the monkey used the rule that if he licked, fruit juice would be obtained. The responses of these amygdala neurons thus reflect the direct associations of stimuli with reinforcement, but do not reflect the reward value of the stimuli when this must be assessed based on a rule (in the recognition memory task, that a stimulus will be punished the first time it is shown, and rewarded the second). This finding also shows that these amygdala neurons respond to relatively novel stimuli in the same way as they do to stimuli that have become rewarding by stimulus-reinforcement association learning. This provides a neural basis for relatively novel stimuli to be treated as rewarding, and approached.

Acoustic Stimulation↗
PubMed2006

Refuge use: a conflict between avoiding predation and losing mass in lizards.

Prey often respond to predation risk by increasing refuge use, but this strategy may entail a loss of body condition. Factors responsible for this loss of body condition remain unclear. Also how prey deal with refuge use to cope with predation risk without incurring costs of body condition, and how initial body condition affects refuge use remain barely known. We analyzed in the field whether adult Iberolacerta cyreni lizards modify their escape strategies and refuge use in areas with different levels of habitat deterioration and ecotourism pressure, which represent different levels of predation risk, and the consequences of changes in antipredator behavior to body condition. Lizards inhabiting deteriorated areas, where risk is higher, remained closer to refuges, but decreased time spent hidden in refuges after attacks, probably to maintain similar body condition than lizards inhabiting natural areas. We performed two laboratory experiments to isolate potential costs of refuge use that might affect the body condition of male lizards: a) a decrease of the efficiency of digestion due to low temperatures inside refuges and/or b) a reduction in food intake. Results suggest that refuge use is costly in terms of body condition due to reduced food intake, but the loss of efficiency of digestion seems unimportant. Lizards modified refuge use in relation to their body condition, with lizards with worse condition decreasing time hidden after predatory attacks. We concluded that lizards compensated for increased predation risk with flexible antipredatory strategies, coping with risk without incurring costs for body condition.

Adaptation, Physiological↗
PubMed1999

Memory and socioemotional behavior in monkeys after hippocampal damage incurred in infancy or in adulthood.

The present study reviews the long-term effects of neonatal hippocampal damage in monkeys on the development of memory functions and socioemotional behavior. The results showed that neonatal damage to the hippocampal formation impairs specific memory processes, such as those subserving automatic (as opposed to effortful) recognition memory and relational learning, while sparing the abilities to acquire skills, such as object discriminations. Furthermore, the neonatal hippocampectomy led to a progressive loss of social affiliation and a protracted emergence of locomotor stereotypies. While the memory losses following neonatal hippocampal lesions resemble those found after similar lesions acquired in adulthood, only the neonatal lesions resulted in a protracted emergence of abnormal behaviors. These later findings suggested that, presumably, the neonatal lesions impacted on neural systems remote from the site of damage. This was confirmed by our more recent neurobiological studies, demonstrating that neonatal, but not late, lesions of the medial temporal lobe region, disrupt the normal behavioral and cognitive processes subserved by the prefrontal cortex and the caudate nucleus. All together the data support the neurodevelopmental hypothesis viewing early insult to the medial temporal region as the origin of developmental psychosis in humans, such as schizophrenia.

Age Factors↗
PubMed2000

Sucrose intake as a function of its cost and the cost of chow.

The avid consumption of pure carbohydrate solutions, which often results in a distortion of nutrient balance, is generally presumed to be driven by their taste. In the first of two experiments, we examined the effect of consumption cost on rats' intake of three concentrations of sucrose solution (8%, 16%, and 32%) when a nutritionally complete chow was concurrently freely available. In the second experiment, we examined the intake of 24% sucrose solution and chow as the consumption costs of both were varied. Increasing the cost of sucrose resulted in a reduction in the percent calories taken from sucrose; the steepness of the decline in intake with price was inversely related to the sucrose concentration and to the cost of chow. Chow calories were substituted for relatively expensive sucrose calories. An increase in the cost of chow resulted in a reduction in the percent of calories taken from chow and a protein-poor diet. The cost of sucrose did not affect the slope of the chow intake curve, presumably because, despite its sweet taste, sucrose was not a substitute for the protein, fat, and micronutrients in chow. Total caloric intake was conserved in all cases.Thus, the avid consumption of sucrose solution is curtailed when it is costly; but the degree of change in intake with cost depends on the cost of an alternative food. These results suggest that diet selection involves a comparison not only of the taste and post-ingestive consequences of available foods, but also of the cost of calories and nutrients in the foods. Selection appears to be guided first by caloric requirements and the relative cost of calories, then by nutrient requirements and the relative cost of nutrients, and finally by taste.

Animals↗
PubMed1997

Nesting material as environmental enrichment has no adverse effects on behavior and physiology of laboratory mice.

Environmental enrichment may improve the quality of life of captive animals by altering the environment of animals so that they are able to perform more of the behavior that is within the range of the animal's species-specific repertoire. When enrichment is introduced into an animal's environment, it is important to evaluate the effect of the enrichment program and to assess whether the animal continues to use the enrichment in the long-term. Groups of mice were housed under either standard or enriched conditions for several weeks. Nesting material which was highly preferred in previous studies was used as enrichment. During the period of differential housing several behavioral parameters (behavioral tests and handling) and physiological parameters (urine and plasma corticosterone, food and water intake, body and adrenal weight) were monitored to determine the impact of environmental enrichment. Observations were made to determine whether or not the mice continued to use the enrichment. The results indicated that throughout the study all mice used the nesting material to build nests and that mice from enriched conditions weighed more than mice housed under standard conditions, although the latter consumed more food. No major differences for behavioral and physiological parameters were found between the groups of mice housed under different conditions. Therefore it is not likely that supply of nesting material will jeopardize the outcome of experiments.

Adrenal Glands↗
PubMed2003

Effects of chronic cocaine on impulsivity: relation to cortical serotonin mechanisms.

Drug addiction can be considered an impulse control disorder in that addicts exhibit increased impulsivity on both behavioural and self-report measures. We investigated whether chronic cocaine affects delay of gratification and/or behavioural disinhibition in rats using the delayed reinforcement and Go/No-go paradigms. Animals were treated with saline or cocaine (15 mg/kg) three times per day for 14 days; all behavioural tests occurred prior to daily injections. To assess the effectiveness of the cocaine treatment, sucrose intake, behavioural sensitization and serotonin (5-HT)-dependent (dorsal raphe-stimulated) cortical activation were also measured. Chronic cocaine caused a transient (days 7-8) increase in impulsivity in the delayed reinforcement paradigm, but did not influence behaviour in the Go/No-go paradigm. As expected, chronic cocaine increased behavioural sensitization scores, although it did not affect sucrose consumption. Although, cocaine treatment did not affect dorsal raphe-stimulated electrocorticographic activation, the serotonergic receptor antagonist methiothepin (0.1 mg/kg) was more effective in blocking cortical activation in cocaine- than in saline-treated animals. The electrocorticographic changes may be the result of a pre-synaptic 5-HT deficit and the compensatory supersensitivity of post-synaptic 5-HT receptors. Given the differential time courses of the behavioural and electrocorticographic data, however, this change probably does not mediate the effects of chronic cocaine in the delayed reinforcement paradigm.

Analysis of Variance↗
PubMed2002

The lesser shame: abortion among educated women in southern Cameroon.

Educated women in southern Cameroon both condemn abortion and practice it with some regularity. This apparent paradox arises because educated Cameroonian women use abortion as one of a set of strategies to manage the timing and social context of entry into motherhood. This paper is based on a body of research which included a demographic life history survey (N = 184), open-ended narrative interviews (N = 37), and participant observation over 10 months. The survey data included 61 reported abortions, giving a lower-bound estimate of the crude abortion rate of 19 per thousand woman-years of life. In southern Cameroon, sexual activity is socially tolerated in a wide variety of non-marital relationships, while childbearing is not. Thus, most of my informants, including those who reported having aborted, say that abortion is shameful; however, they view its moral and social consequences as less grave than those of a severely mistimed entry into socially recognized motherhood. That is, abortion persists in southern Cameroon because it is the lesser shame.

Abortion, Illegal↗
PubMed1998

Altered ambient temperature and ethanol-induced conditioned place preference in mice.

Previous studies with rats exposed to altered ambient temperature (Ta) or with mice selectively bred for their thermal response to ethanol have shown that a reduced hypothermic response is correlated with decreased place aversion and greater place preference, respectively. The present experiment was designed to test whether alterations in Ta would alter ethanol's ability to produce conditioned place preference in genetically heterogeneous mice. Three groups of mice underwent a differential conditioning procedure that paired one distinctive floor texture with ethanol (2.25 g/kg, i.p.) and a different floor texture with saline. During conditioning, each group was exposed to a different Ta: cold (10 degrees C), normal (21 degrees C), or warm (34 degrees C). Each group was further divided and subgroups were tested for preference at either the conditioning temperature or a different temperature. Consistent with previous findings, mice conditioned and tested at normal Ta developed a conditioned preference for the ethanol-paired floor. In contrast, mice exposed to a warm or cold Ta during conditioning or testing failed to show place conditioning. Although exposure to either warm or cold Ta interfered with place conditioning, only the warm Ta had an effect on hypothermia. These findings suggest that altered Ta produced stimuli that may have interfered with the association between floor cues and ethanol during conditioning or interfered with expression of this association during testing.

Animals↗
PubMed2000

Understanding atypical emotions among children with autism.

Children with autism are said to be poor mind readers: They have a limited understanding of the role that mental states play in determining emotions and behavior. In this research, 23 high-functioning children from the autistic spectrum (M age 9 years 3 months), 42 6-year-old controls, and 43 10-year-old controls were presented with six emotion-evoking stories and they were asked to explain protagonists' typical and atypical emotions. In the case of typical emotions, as expected on the basis of the mindblind hypothesis, children from the autistic spectrum gave few mental state explanations, referring to fewer than even the 6-year-old control group. However, in the case of atypical emotions, the autistic group performed as well as the 10-year-old controls. Their explanations for the atypical emotions demonstrate that children from the autistic spectrum indeed have the capacity to mind read (with respect to both desires and beliefs), although they do not always use this capacity in the same way as normally developing children. It is argued that the mind-reading capacity of high-functioning children from the autistic spectrum might be basically intact; unused in everyday circumstances but not necessarily defective.

Affect↗