Perirhinal cortex lesions uncover subsidiary systems in the rat for the detection of novel and familiar objects

The present study compared the impact of perirhinal cortex lesions on tests of object recognition. Object recognition was tested directly by looking at the preferential exploration of novel objects over simultaneously presented familiar objects. Object recognition was also tested indirectly by presenting just novel objects or just familiar objects, and recording exploration levels. Rats with perirhinal cortex lesions were severely impaired at discriminating a novel object from a simultaneously presented familiar object (direct test), yet displayed normal levels of exploration to novel objects presented on their own and showed normal declines in exploration times for familiar objects that were repeatedly presented (indirect tests). This effective reduction in the exploration of familiar objects after perirhinal cortex lesions points to the sparing of some recognition mechanisms. This possibility led us to determine whether rats with perirhinal cortex lesions can overcome their preferential exploration deficits when given multiple object familiarisation trials prior to that same (familiar) object being paired with a novel object. It was found that after multiple familiarisation trials, objects could now successfully be recognised as familiar by rats with perirhinal cortex lesions, both following a 90-min delay (the longest delay tested) and when object recognition was tested in the dark after familiarisation trials in the light. These latter findings reveal: (i) the presumed recruitment of other regions to solve recognition memory problems in the absence of perirhinal cortex tissue; and (ii) that these additional recognition mechanisms require more familiarisation trials than perirhinal-based recognition mechanisms.

Interspecific exchange of avian influenza virus genes in Alaska: the influence of trans-hemispheric migratory tendency and breeding ground sympatry

The movement and transmission of avian influenza viral strains via wild migratory birds may vary by host species as a result of migratory tendency and sympatry with other infected individuals. To examine the roles of host migratory tendency and species sympatry on the movement of Eurasian low-pathogenic avian influenza (LPAI) genes into North America, we characterized migratory patterns and LPAI viral genomic variation in mallards (Anas platyrhynchos) of Alaska in comparison with LPAI diversity of northern pintails (Anas acuta). A 50-year band-recovery data set suggests that unlike northern pintails, mallards rarely make trans-hemispheric migrations between Alaska and Eurasia. Concordantly, fewer (14.5%) of 62 LPAI isolates from mallards contained Eurasian gene segments compared to those from 97 northern pintails (35%), a species with greater inter-continental migratory tendency. Aerial survey and banding data suggest that mallards and northern pintails are largely sympatric throughout Alaska during the breeding season, promoting opportunities for interspecific transmission. Comparisons of full-genome isolates confirmed near-complete genetic homology (>99.5%) of seven viruses between mallards and northern pintails. This study found viral segments of Eurasian lineage at a higher frequency in mallards than previous studies, suggesting transmission from other avian species migrating inter-hemispherically or the common occurrence of endemic Alaskan viruses containing segments of Eurasian origin. We conclude that mallards are unlikely to transfer Asian-origin viruses directly to North America via Alaska but that they are likely infected with Asian-origin viruses via interspecific transfer from species with regular migrations to the Eastern Hemisphere.

Two kinds of attention in Pavlovian conditioning: evidence for a hybrid model of learning

Four appetitive Pavlovian conditioning experiments with rats examined the rate at which the discrimination between compounds AY and AX was solved relative to the discrimination between compounds AY and BY. In Experiments 1 and 2, these discriminations were preceded by training in which A and B were continuously reinforced and X and Y were partially reinforced. Consistent with the Pearce and Hall (1980) model, the results showed that the AY/AX discrimination was solved more readily than the AY/BY discrimination. In Experiments 3 and 4, the discriminations were preceded by feature-positive training in which trials with AX and BY signaled food but trials with X and Y did not. Consistent with the Mackintosh (1975) model, the results showed that the AY/BY discrimination was solved more readily than the AY/AX discrimination. These results are discussed with respect to a hybrid model of conditioning and attention.

Conditioned inhibition and superconditioning in an environment with a distinctive shape

In Experiments 1 and 2a rats received an A+/AX- discrimination in a rectangular pool with two submerged platforms in diagonally opposite corners-the correct corners-for A+ trials. For AX- trials, rats were placed in the pool without the platforms but with identical landmarks, X, in the correct corners. Landmark X subsequently passed both a summation and retardation test for inhibition in Experiment 1. Upon completion of the discrimination in Experiment 2a, the platforms were placed near identical landmarks in the correct corners of the rectangle. The landmarks were those used for discrimination training for a superconditioning group (AX+ trials), but for a control group they were novel (AY+ trials). During a final test in the pool without the landmarks and the platforms, the superconditioning group spent more time than the control group searching in the correct corners. This finding, which was replicated in a kite-shaped pool in Experiment 2b, demonstrates successful superconditioning by landmark X of the cues created by the shapes of the pools. The results pose a problem for the theory of Miller and Shettleworth (2007).

Spatial learning based on boundaries in rats is hippocampus-dependent and prone to overshadowing

In three experiments, rats were required to find a submerged platform by referring to the boundaries of a circular swimming pool. In the first experiment, rats with lesions of the hippocampus were impaired at finding the hidden platform, lending support for the proposal that learning to find a goal that is a certain direction and distance from a boundary is dependent upon the hippocampus. Experiments 2 and 3 offered preliminary tests to see if such boundary learning occurred incidentally, irrespective of the presence of a reliable landmark. In contrast to this proposal, a landmark hanging above the platform successfully restricted learning about the location of the platform with respect to the boundary of the arena. The discussion explores the capacity of the hippocampus to encode boundary information, as well as interprets the behavioral results on the basis of an associative learning framework.

Transmission and reassortment of avian influenza viruses at the Asian-North American interface

Twenty avian influenza viruses were isolated from seven wild migratory bird species sampled at St. Lawrence Island, Alaska. We tested predictions based on previous phylogenetic analyses of avian influenza viruses that support spatially dependent trans-hemispheric gene flow and frequent interspecies transmission at a location situated at the Asian-North American interface. Through the application of phylogenetic and genotypic approaches, our data support functional dilution by distance of trans-hemispheric reassortants and interspecific virus transmission. Our study confirms infection of divergent avian taxa with nearly identical avian influenza strains in the wild. Findings also suggest that H16N3 viruses may contain gene segments with unique phylogenetic positions and that further investigation of how host specificity may impact transmission of H13 and H16 viruses is warranted.

Lesions in the anterior thalamic nuclei of rats do not disrupt acquisition of stimulus sequence learning

Sequence learning and spatial alternation were examined in rats with anterior thalamic lesions or sham surgeries. There was a lesion-induced deficit in spatial alternation but not in sequence learning. During sequence learning, rats discriminated between six different sequentially presented compounds (e.g., reinforce A before B, but not B before A), composed of audio-visual elements. The solution required rats to learn both specific stimulus sequences and the reward contingencies associated with these specific temporal relationships. The failure of anterior thalamic lesions to affect the acquisition of this sequential configural task complements the recent finding that anterior thalamic lesions also spare the acquisition of a configural task involving specific stimulus pairings and their spatial relationships. These findings suggest that such "structural" learning is more reliant on cortico-hippocampal than thalamo-hippocampal interactions.

Lesions of the rat perirhinal cortex spare the acquisition of a complex configural visual discrimination yet impair object recognition

Rats with perirhinal cortex lesions were sequentially trained in a rectangular water tank on a series of 3 visual discriminations, each between mirror-imaged stimuli. When these same discriminations were tested concurrently, the rats were forced to use a configural strategy to solve the problems effectively. There was no evidence that lesions of the perirhinal cortex disrupted the ability to learn the concurrent configural discrimination task, which required the rats to learn the precise combination of stimulus identity with stimulus placement (“structural” learning). The same rats with perirhinal cortex lesions were also unimpaired on a test of spatial working memory (reinforced T maze alternation), although they were markedly impaired on a new test of spontaneous object recognition. For the recognition test, rats received multiple trials within a single session in which on every trial, they were allowed to explore 2 objects, 1 familiar, the other novel. On the basis of their differential exploration times, rats with perirhinal cortex lesions showed very poor discrimination of the novel objects, thereby confirming the effectiveness of the surgery. The discovery that bilateral lesions of the perirhinal cortex can leave configural (structural) learning seemingly unaffected points to a need to refine those models of perirhinal cortex function that emphasize its role in representing conjunctions of stimulus features.

Lesions of the perirhinal cortex do not impair integration of visual and geometric information in rats

Rats with lesions of the perirhinal cortex and a control group were required to find a platform in 1 corner of a white rectangle and in the reflection of this corner in a black rectangle. Test trials revealed that these groups were able to integrate information regarding the shape of the pool and the color of its walls (black or white) to identify the correct location of the platform. A clear effect of the perirhinal cortex lesions was, however, revealed using an object recognition task that involved the spontaneous exploration of novel objects. The results challenge the view that the perirhinal cortex enables rats to solve discriminations involving feature ambiguity.

Failure of retrospective revaluation to influence blocking

In the blocking paradigm, subjects receive reinforced presentations of a compound, AX, after reinforced presentations of A alone. Following this training, responding to X is often diminished relative to a control group, which did not receive the prior training with A. Standard associative theories of learning such as the Rescorla-Wagner model (Rescorla & Wagner, 1972) explain this effect by assuming that A and X compete for control over behavior. In contrast, theories such as the comparator hypothesis assume that learning about X is unaffected by the properties of A, but it is the expression of this learning at test that is affected by the blocking manipulation. The aim of the 3 reported experiments was to distinguish between these 2 accounts. According to the comparator hypothesis, devaluing A following blocking should increase subsequent responding to X. In all 3 experiments the blocking effect was found to persist following devaluation of A, providing support for standard associative theories.

Limited evidence of trans-hemispheric movement of avian influenza viruses among contemporary North American shorebird isolates

Migratory routes of gulls, terns, and shorebirds (Charadriiformes) are known to cross hemispheric boundaries and intersect with outbreak areas of highly pathogenic avian influenza (HPAI). Prior assessments of low pathogenic avian influenza (LPAI) among species of this taxonomic order found some evidence for trans-hemispheric movement of virus genes. To specifically clarify the role of shorebird species in the trans-hemispheric movement of influenza viruses, assess the temporal variation of Eurasian lineages observed previously among North American shorebirds, and evaluate the necessity for continued sampling of these birds for HPAI in North America, we conducted a phylogenetic analysis of >700 contemporary sequences isolated between 2000 and 2008. Evidence for trans-hemispheric reassortment among North American shorebird LPAI gene segments was lower (0.88%) than previous assessments and occurred only among eastern North American isolates. Furthermore, half of the reassortment events occurred in just two isolates. Unique phylogenetic placement of these samples suggests secondary infection and or involvement of other migratory species, such as gulls. Eurasian lineages observed in North American shorebirds before 2000 were not detected among contemporary samples, suggesting temporal variation of LPAI lineages. Results suggest that additional bird migration ecology and virus phylogenetics research is needed to determine the exact mechanisms by which shorebirds in eastern North America become infected with LPAI that contain Eurasian lineage genes. Because of the low prevalence of avian influenza in non-eastern North America sites, thousands more shorebirds will need to be sampled to sufficiently examine genetic diversity and trans-hemispheric exchange of LPAI viruses in these areas. Alternatively, other avian taxa with higher virus prevalence could serve as surrogates to shorebirds for optimizing regional surveillance programs for HPAI through the LPAI phylogenetic approach.

Enhancement of responding to A after A+/AX+ training: challenges for a comparator theory of learning

Two appetitive Pavlovian conditioning experiments with rats investigated the associative changes that A undergoes in an A+/AX+ blocking procedure. Conditioned responding to A was enhanced relative to stimulus B, which had been conditioned in isolation (B+). This result was interpreted in terms of the formation of a within-compound association between A and X. The results of Experiment 2 supported this conclusion by demonstrating that X had associative strength of its own and, furthermore, that extinguishing X resulted in a similar level of responding to A and B. These results are considered in terms of retrospective revaluation theories of learning.

Absence of overshadowing between a landmark and geometric cues in a distinctively shaped environment: a test of Miller and Shettleworth (2007)

Rats in the first 2 experiments, which were designed to test predictions from a model of spatial learning by N. Y. Miller and S. J. Shettleworth (2007), had to escape from a triangular pool by swimming to a submerged platform in a geometrically unique corner. A spherical landmark was suspended above the platform for an overshadowing group. A control group was trained with the same arrangement and with a second, identical landmark suspended in another corner. The platform could thus be found by reference to the landmark or the geometric cues in the overshadowing group, whereas the control group had to rely on geometric cues. There was no indication of overshadowing between the geometric cues and the landmark in the overshadowing group. The final 2 experiments revealed that the absence of overshadowing was not a consequence of the landmark being an ineffective cue for overshadowing. The results indicate either that the landmark and geometric cues were not in competition for the control they acquired over behavior or that an additional process compensated for any such competition that might have occurred in the overshadowing group. This additional process could involve between-cues associations or the provision of a stable spatial framework.

The 36th Sir Frederick Bartlett Lecture: An associative analysis of spatial learning

The ability of animals to find important goals in their environment has been said to require a form of learning that is qualitatively different from that normally studied in the conditioning laboratory. Such spatial learning has been said to depend upon the construction of a global representation of the environment, and the acquisition of knowledge about the position of goals with reference to this representation is said to be unaffected by the presence of other cues or landmarks. To evaluate the first of these claims, experiments are described that investigated the extent to which the effects of training in one environment transfer to another. To evaluate the second claim, experiments are described that investigated whether cue competition effects normally found in conditioning studies can be found in spatial tasks. Overall, the results indicate that most of the phenomena of spatial learning can be explained by the principles of associative learning. The implications of the reported results for an understanding of the neural mechanisms of spatial learning are considered.

Avian influenza at both ends of a migratory flyway: characterizing viral genomic diversity to optimize surveillance plans for North America

Although continental populations of avian influenza viruses are genetically distinct, transcontinental reassortment in low pathogenic avian influenza (LPAI) viruses has been detected in migratory birds. Thus, genomic analyses of LPAI viruses could serve as an approach to prioritize species and regions targeted by North American surveillance activities for foreign origin highly pathogenic avian influenza (HPAI). To assess the applicability of this approach, we conducted a phylogenetic and population genetic analysis of 68 viral genomes isolated from the northern pintail (Anas acuta) at opposite ends of the Pacific migratory flyway in North America. We found limited evidence for Asian LPAI lineages on wintering areas used by northern pintails in California in contrast to a higher frequency on breeding locales of Alaska. Our results indicate that the number of Asian LPAI lineages observed in Alaskan northern pintails, and the nucleotide composition of LPAI lineages, is not maintained through fall migration. Accordingly, our data indicate that surveillance of Pacific Flyway northern pintails to detect foreign avian influenza viruses would be most effective in Alaska. North American surveillance plans could be optimized through an analysis of LPAI genomics from species that demonstrate evolutionary linkages with European or Asian lineages and in regions that have overlapping migratory flyways with areas of HPAI outbreaks.

Analysis of an ambiguous-feature discrimination

An autoshaping experiment with pigeons and three appetitive Pavlovian conditioning experiments with rats investigated the course of an ambiguous-feature discrimination in which trials with stimuli A and BC were followed by food, and trials with B and AC were not. The discrimination between A and B was acquired more rapidly than the discrimination between BC and AC in all experiments. Furthermore, the acquisition of conditioned responding with A was faster than that with BC for the three rat experiments. The results of these experiments are discussed in terms of elemental and configural theories of associative learning.

Phospholipid composition of postmortem schizophrenic brain by 31P NMR spectroscopy

Cell membrane abnormalities due to changes in phospholipid (PL) composition and metabolism have been implicated in schizophrenia pathogenesis. That work has generally assessed membrane phospholipids from nonneural tissues such as erythrocytes and platelets. High-resolution (31)P NMR spectroscopy was used to characterize PLs of gray matter in postmortem brain for 20 schizophrenics, 20 controls, and 7 patients with other mental illnesses (psychiatric controls). Tissues from frontal, temporal, and occipital cortices were extracted with hexane-isopropanol, and (31)P NMR spectra were obtained in an organic-solvent system to resolve the major PL classes (based on headgroups) and subclasses (based on linkage at the sn - 1 position). Surprisingly, repeated-measures multivariate analysis of variance revealed no overall differences among the groups. There were no significant differences (P < .05) among the three groups for any individual PL subclass, including lysophospholipids. The sum of all phosphatidylethanolamine headgroups was significantly lower for schizophrenics than for controls or psychiatric controls in the frontal cortex. The present results are minimally correlated with previous results for aqueous PL metabolites on these same samples. The metabolite changes measured by in vivo (31)P MRS in schizophrenia do not appear to reflect PL concentration changes. The present results offer very little support for the phospholipid hypothesis of schizophrenia.

Genetic evidence of intercontinental movement of avian influenza in a migratory bird: the northern pintail (Anas acuta)

The role of migratory birds in the movement of the highly pathogenic (HP) avian influenza H5N1 remains a subject of debate. Testing hypotheses regarding intercontinental movement of low pathogenic avian influenza (LPAI) viruses will help evaluate the potential that wild birds could carry Asian-origin strains of HP avian influenza to North America during migration. Previous North American assessments of LPAI genetic variation have found few Asian reassortment events. Here, we present results from whole-genome analyses of LPAI isolates collected in Alaska from the northern pintail (Anas acuta), a species that migrates between North America and Asia. Phylogenetic analyses confirmed the genetic divergence between Asian and North American strains of LPAI, but also suggested inter-continental virus exchange and at a higher frequency than previously documented. In 38 isolates from Alaska, nearly half (44.7%) had at least one gene segment more closely related to Asian than to North American strains of LPAI. Additionally, sequences of several Asian LPAI isolates from GenBank clustered more closely with North American northern pintail isolates than with other Asian origin viruses. Our data support the role of wild birds in the intercontinental transfer of influenza viruses, and reveal a higher degree of transfer in Alaska than elsewhere in North America.

Prevalence of Influenza A viruses in wild migratory birds in Alaska: patterns of variation in detection at a crossroads of intercontinental flyways

BACKGROUND

The global spread of the highly pathogenic avian influenza H5N1 virus has stimulated interest in a better understanding of the mechanisms of H5N1 dispersal, including the potential role of migratory birds as carriers. Although wild birds have been found dead during H5N1 outbreaks, evidence suggests that others have survived natural infections, and recent studies have shown several species of ducks capable of surviving experimental inoculations of H5N1 and shedding virus. To investigate the possibility of migratory birds as a means of H5N1 dispersal into North America, we monitored for the virus in a surveillance program based on the risk that wild birds may carry the virus from Asia.

RESULTS

Of 16,797 birds sampled in Alaska between May 2006 and March 2007, low pathogenic avian influenza viruses were detected in 1.7% by rRT-PCR but no highly pathogenic viruses were found. Our data suggest that prevalence varied among sampling locations, species (highest in waterfowl, lowest in passerines), ages (juveniles higher than adults), sexes (males higher than females), date (highest in autumn), and analytical technique (rRT-PCR prevalence = 1.7%; virus isolation prevalence = 1.5%).

CONCLUSION

The prevalence of low pathogenic avian influenza viruses isolated from wild birds depends on biological, temporal, and geographical factors, as well as testing methods. Future studies should control for, or sample across, these sources of variation to allow direct comparison of prevalence rates.

31P NMR spectroscopy of phospholipid metabolites in postmortem schizophrenic brain

Evidence has been accumulating that schizophrenia involves abnormalities in the composition and metabolism of cell membrane phospholipids (PLs) in the brain. In vivo 31P MRS has been used to measure the metabolic precursors and degradation products of PL metabolism in schizophrenia. Because in vivo line widths are substantially broader than in solution, only the broad phosphomonoester (PME) and phosphodiester bands, or partly resolved resonances of individual metabolites, are typically measured in vivo in the 31P spectrum. In addition to poor resolution, the relatively low signal-to-noise ratio (SNR) makes precise quantitation difficult. An alternative with substantially better resolution and precision for quantitation is high-resolution NMR spectroscopy of extracts of samples from postmortem brain. Here we determine absolute concentrations of the individual PL metabolites phosphocholine (pc), phosphoethanolamine (pe), glycerophosphocholine (gpc), and glycerophosphoethanolamine in aqueous extracts of tissue from frontal, temporal, and occipital cortex of postmortem brain for schizophrenics, controls, and patients with other mental illnesses (psychiatric controls [PC]) using high-resolution 31P NMR spectroscopy. For the complete groups, which included both males and females, there were no statistically significant differences for schizophrenics vs. controls for any of the four PL metabolites in any of the three brain regions. Trends (0.05 < P < 0.10) were noted for increased gpc in schizophrenia in all three regions. PC differed from both controls and schizophrenics in several measures. When only males were considered, gpc was significantly (P < 0.05) elevated in all three brain regions in schizophrenia.

Impaired processing of local geometric features during navigation in a water maze following hippocampal lesions in rats

Hippocampal damage impairs navigation with respect to information provided by the shape of an arena. Recent evidence has suggested that normal rats use local geometric information, as opposed to a global geometric representation, to navigate to a correct corner. One implication of this pattern of results is that hippocampal lesions may impair processing of 1 or more of the local geometric features of an environment. The authors therefore investigated the effects of hippocampal cell loss in rats on navigation to a hidden goal with respect to a variety of local cues in an environment with a distinctive shape. Rats with lesions of the hippocampus were impaired in discriminating a right-angled corner from its mirror image. However, they were able to use cues provided by an acute-angled corner (Experiment 1) or a local polarizing cue (Experiment 2). In contrast, lesioned rats were impaired in discriminating long versus short walls (Experiment 3). Results indicate that the hippocampus plays a role in disambiguating locations by processing (metric) information related to the distance between corners.

The discrimination of natural movement by budgerigars (Melopsittacus undulates) and pigeons (Columba livia)

Three experiments examined the ability of birds to discriminate between the actions of walking forwards and backwards as demonstrated by video clips of a human walking a dog. Experiment 1 revealed that budgerigars (Melopsittacus undulates) could discriminate between these actions when the demonstrators moved consistently from left to right. Test trials then revealed that the discrimination transferred, without additional training, to clips of the demonstrators moving from right to left. Experiment 2 replicated the findings from Experiment 1 except that the demonstrators walked as if on a treadmill in the center of the display screen. The results from the first 2 experiments were replicated with pigeons in Experiment 3. The results cannot be explained if it is assumed that animals rely on static cues, such as those derived from individual postures, in order to discriminate between the actions of another animal. Instead, this type of discrimination appears to be controlled by dynamic cues derived from changes in the posture of the demonstrators.