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Spatial performance correlates with long-term potentiation of the dentate gyrus but not of the CA1 region in rats with fimbria-fornix lesions.
Although hippocampal long-term potentiation (LTP) is generally assumed to be a cellular mechanism of learning and memory, there has not been definitive evidence for this hypothesis. In the present study, therefore, we addressed the possible relationship between spatial learning ability and LTP by using rats with bilateral fimbria-fornix lesions. The animals were tested for spatial performance in spontaneous alternation behaviors with further in vivo investigation of LTP. The behavioral parameters of spatial memory showed a significant correlation with LTP in the dentate gyrus, but we found no evidence for a linkage with LTP in the CA1 region. Thus, LTP in the dentate gyrus may be important for spatial cognitive ability.
Visuospatial impairments in aged canines (Canis familiaris): the role of cognitive-behavioral flexibility.
This study used a novel delayed nonmatching-to-position task to compare visuospatial learning and memory in young and aged beagle dogs (Canis familiaris). The task used 3, rather than 2, spatial locations, which markedly increased difficulty. There were striking age differences in acquisition. Most of the aged canines did not learn the task, and those that did showed impaired learning when compared with the young canines. The aged canines also showed reduced maximal working memory capacity compared with the young canines. Analysis of the response patterns of individual canines indicated that the deficits were related to the use of ineffective strategies and inflexibility in strategy modification.
Differential effects of a small, unilateral, 6-hydroxydopamine-induced nigral lesion on behavior in high and low responders to novelty.
The goal of this study was to develop an animal model that evaluates striatal-specific behavior after partial, unilateral destruction of nigrostriatal neurons. 6-OHDA (1 microg) was injected intranigrally (day 0) to reduce dopaminergic innervation of the dorsal striatum (DS); 6-OHDA (5 microg) was injected to reduce innervation of DS and nucleus accumbens (ACC). We analyzed changes in (a) behavior regulated by dopamine (DA) release in the DS (hindpaw preference from day 5 to day 19, every other day) and the ACC (novelty-induced locomotion on day 16) and (b) apomorphine-induced rotation (on day 21). We used two types of rat that show differences in structure and function of the dopaminergic neurons, namely high (HR) and low (LR) responders to novelty. 6-OHDA (1 microg) significantly decreased TH immunoreactivity (TH-ir) in the DS and increased preference for the hindpaw controlled by the nonlesioned side in HRs and LRs in time. Only in LRs was the significant increase of novelty-induced locomotion accompanied by a significant increase in TH-ir density in the ACC: this suggests a lesion-induced shift in nigrostriatal/mesolimbic balance toward a dominance of the mesolimbic system. The higher 6-OHDA dose significantly decreased TH-ir in the DS and the ACC and increased preference for the hindpaw controlled by the nonlesioned side in HRs and LRs in time. However, this increase occurred significantly earlier in LRs than in HRs. Apomorphine elicited contralateral rotations solely in LRs, and not in HRs, indicating development of supersensitive dopamine receptors in the DS of LRs, but not HRs. The data show that LRs are more susceptible to 6-OHDA than HRs. The relevance of the present data for Parkinson's disease is discussed.
Saccade-related and visual activities in the pulvinar nuclei of the behaving rhesus monkey.
We studied three subdivisions of the pulvinar: a retinotopically organized inferior area (PI), a retinotopically mapped region of the lateral pulvinar (PL), and a separate, visually responsive component of the lateral pulvinar (Pdm). Single neurons were recorded in these regions from awake, trained rhesus monkeys, and we correlated the discharge patterns of the cells with eye movements. About 60% of the neurons discharged after saccadic eye movements in an illuminated environment and had either excitatory, inhibitory, or biphasic (inhibitory-excitatory) response patterns. These responses were most often transient in nature. Neurons with excitatory activity had a mean onset latency of 72 ms after the termination of the eye movement. Latencies for cells with inhibitory responses averaged 58 ms. In sharp contrast, the cells with biphasic response patterns became active before the termination of the eye movement. A unique set of these neurons termed saccade cells, were active with visually guided eye movements in the light, with the same eye movements made to a briefly pulsed target in the dark, and for similar eye movements made spontaneously in total darkness. The activity was present with the appropriate saccade, independent of the beginning eye position. Biphasic response patterns were typical of these saccade cells. Saccade cells were most common in Pdm and PI. About half of the saccade cells also had some visual response that was independent of eye movement. A second group of cells was active with saccadic eye movements in the light but not in the dark. Some of these cells had clear visual responses that could account for their activity following eye movements; others had no clear visual receptive field.(ABSTRACT TRUNCATED AT 250 WORDS)
Intra-prefrontal 8-OH-DPAT and M100907 improve visuospatial attention and decrease impulsivity on the five-choice serial reaction time task in rats.
RATIONALE: The central serotonergic systems are a major target for drugs used to treat neuropsychiatric disorders such as depression and schizophrenia in which disruption of frontal cortex function has been implicated. However, it is not known precisely how serotonin (5-HT) modulates the medial prefrontal cortex (mPFC) to affect cognitive function and behaviour. OBJECTIVE: To investigate the roles of 5-HT(1A) and 5-HT(2A) receptors in mPFC on performance of the five-choice serial reaction time task (5CSRT), which assesses visuospatial attention, impulsivity and motivational processes. METHODS: Following training on the 5CSRT, rats were implanted with bilateral guide cannulae aimed at the mPFC. Rats received intra-mPFC infusions of either 8-OH-DPAT (10, 30 and 100 ng) or M100907 (30, 100 and 300 ng) according to a Latin square design. RESULTS: Both 8-OH-DPAT and M100907 selectively enhanced accuracy of target detection. When the stimulus duration was shortened, infusions of 8-OH-DPAT continued to improve accuracy, whereas M100907 decreased premature responding and omissions, thus partly dissociating the effects of these two compounds. Similar effects were obtained following systemic administration of M100907 and 8-OH-DPAT. The effects of 8-OH-DPAT were blocked by the 5-HT(1A) antagonist WAY 100635, at a dose that itself had no significant effects on behaviour. CONCLUSIONS: These results indicate that modulation of 5-HT function within the mPFC via distinct receptors can enhance performance on the 5CSRT. These findings suggest a mechanism by which serotonergic agents improve cognitive function, which may be relevant to their therapeutic benefit in the treatment of neuropsychiatric disorders.
Psychology and epistemology: the place versus response controversy.
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Behavioral effects of sequential and one-stage ablations of orbital prefrontal cortex in the monkey.
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Geometry for the selfish herd.
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Some relationships between adrenal function and the effectiveness of a period of isolation in inducing intermale aggression in albino mice.
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The experimenter as an independent variable in studies of animal hypnosis in chickens (Gallus gallus).
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Movement-related activity in the premotor cortex of rhesus macaques.
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A novel, direct spatio-temporal approach for analyzing fMRI experiments.
We introduce a novel approach to couple temporal similarity with spatial neighborhood information. This is achieved by concatenating the K nearest, spatially contiguous neighbors of a pixel time-course (TC) of T time-instances. This produces a new TC of (K+1)T time instances. Depending on how "nearest" is defined, we have various options. Strictly spatial nearness means augmenting a given TC by its K nearest neighbors in some canonical spatial order. A more powerful and flexible option is to order the TCs to be concatenated according to their temporal similarity to the central voxel TC. For this study, we have chosen Pearson's cross-correlation coefficient as the measure of similarity. For more than a single neighbor, two concatenation options are possible. The direct ordering option requires that the TCs to be concatenated be spatially contiguous to the central pixel. The more flexible indirect option merely demands that one of a chain of temporally similar TCs be spatially connected to the central pixel. We also apply the temporal similarity criterion to the more conventional spatial (median) filtering, and show that it gives superior result to a strict spatial filtering. The method is tested and verified on a null fMRI dataset onto which we superposed two types of "activations" with known temporal behavior and spatial location. It is also applied to a real dataset containing visual activation. We also propose a strategy, based on the flexibility of the method, to determine a consensus, "core" set of activations.
Effects of localized septal lesions on hippocampal EEG activity and behavior in rats.
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Choosing a safe place to cross the road: the relationship between attention and identification of safe and dangerous road-crossing sites.
BACKGROUND: Safe pedestrian behaviour relies on cognitive skills, including the ability to focus attention on the traffic environment and ignore irrelevant stimuli. An important pedestrian skill that young children find difficult is the ability to find a safe place to cross the road. The aim of this study was to examine the relationship between attention and children's ability to identify safe and dangerous road-crossing sites. METHODS: Participants were 95 children (aged 6.5 years, 8.6 years and 10.4 years) and 33 adults. Ability to identify safe and dangerous road-crossing sites was assessed using computer presentations of five safe and five dangerous sites. Attention was assessed using the Stroop test for resistance to interference. Correlations were calculated between Stroop test measures and pedestrian task measures (accuracy and speed of identifying safe and dangerous road-crossing sites) for each age group separately. RESULTS: The ability to identify safe and dangerous road-crossing sites and the ability to resist interference increased with age. Significant correlations were observed between identification of safe and dangerous road-crossing sites and performance on the Stroop test for children but not for adults. DISCUSSION: The results indicated that attention is required for identifying road-crossing sites quickly and accurately, especially for younger children. Road safety training programmes for children may need to take into account the development of children's attention.
On human symbiosis and the vicissitudes of individuation.
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Individual differences in road crossing ability in young children and adults.
Young children are more at risk of traffic pedestrian accidents than adults. Previous experiments have failed to show large differences between adults and children in crossing behaviour. The reasons for this are not clear, but it could be that some children are more at risk than others, because of individual differences. These differences have been difficult to investigate in the past. This paper examines a double video technique developed to solve the problems. Two groups of participants, children and adults (mean age 7 years 2 months and 20 years 6 months respectively), were presented with the video and asked to indicate by pressing a button when they would choose to cross the road. Variables measured included the total number of crossings made and the percentage of those that were safe, number of missed opportunities and unsafe gaps chosen, the mean starting delay and gap size chosen, and the correlation between the delay and the gap chosen for each individual. Results showed that, although there were large and significant differences between adults and children on total crossings, percentage safe crossings, mean starting delay and gap size chosen, the structure of the road crossing behaviour was very similar. Children make decisions in the same way as adults, but are less good at it. There were large individual differences, suggesting that some children were more at risk than others, with possible factors being impulsivity and fine motor coordination. It is suggested that the video technique may, with some refinements, make a useful tool to screen children at risk and to use in remedial training.
Choice with delayed and probabilistic reinforcers: effects of variability, time between trials, and conditioned reinforcers.
In a discrete-trials procedure with pigeons, a response on a green key led to a 4-s delay (during which green houselights were lit) and then a reinforcer might or might not be delivered. A response on a red key led to a delay of adjustable duration (during which red houselights were lit) and then a certain reinforcer. The delay was adjusted so as to estimate an indifference point--a duration for which the two alternatives were equally preferred. Once the green key was chosen, a subject had to continue to respond on the green key until a reinforcer was delivered. Each response on the green key, plus the 4-s delay that followed every response, was called one "link" of the green-key schedule. Subjects showed much greater preference for the green key when the number of links before reinforcement was variable (averaging four) than when it was fixed (always exactly four). These findings are consistent with the view that probabilistic reinforcers are analogous to reinforcers delivered after variable delays. When successive links were separated by 4-s or 8-s "interlink intervals" with white houselights, preference for the probabilistic alternative decreased somewhat for 2 subjects but was unaffected for the other 2 subjects. When the interlink intervals had the same green houselights that were present during the 4-s delays, preference for the green key decreased substantially for all subjects. These results provided mixed support for the view that preference for a probabilistic reinforcer is inversely related to the duration of conditioned reinforcers that precede the delivery of food.