Sonia Goulet

Search behavior in cats and dogs: Interspecific differences in working memory and spatial cognition

Cats’ and dogs’ search behavior was compared in different problems where an object was visibly moved behind a screen that was then visibly moved to a new position. In Experiments 1 (cats) and 2 (dogs), one group was tested with identical screens and the other group was tested with dissimilar screens. Results showed that in both species, search behavior was based on processing of spatial information rather than on recognition of the visual features of the target screen. Cats and dogs were unable to find the object by inferring its invisible movement. They reached a high level of success only if there was direct perceptual evidence that the object could not be at its initial position. When the position change was indicated by an indirect cue, cats searched more at the object’s initial than final position, whereas dogs searched equally at both positions. Interspecific similarities and differences are interpreted in terms of the requirements for resetting working memory.

Aspiration lesions of the amygdala disrupt the rhinal corticothalamic projection system in rhesus monkeys

Abstract In macaque monkeys, aspiration but not excitotoxic lesions of the medial temporal lobe limbic structures, the amygdala and hippocampus, produce a severe impairment in visual recognition memory. Furthermore, certain ventromedial cortical regions, namely the rhinal (i.e., entorhinal and perirhinal) cortex, are now known to be critical for visual recognition memory. Because the route taken by temporal cortical efferent fibers, especially perirhinal efferents, passes nearby the amygdala, it is possible that inadvertent damage to these fibers is produced by the aspirative but not the excitotoxic process, thereby accounting at least in part for the different behavioral outcomes of the two types of lesion. To test this idea, we assessed the integrity of the rhinal corticothalamic projection system after aspiration lesions of the amygdala. Three rhesus monkeys with unilateral amygdala removals received bilaterally symmetrical injections of a retrograde fluorescent tracer into the medial portion of the mediodorsal nucleus of the thalamus. Retrogradely labeled cells were identified using conventional fluorescence microscopy techniques. In all three cases, the rhinal cortex of the intact hemispheres contained moderate numbers of retrogradely labeled cells. By contrast, the rhinal cortex of the amygdalectomized hemispheres consistently contained few retrogradely labeled cells, and a direct comparison of the two hemispheres showed this difference to be statistically significant. A similar asymmetric pattern was observed for area TE but not for the cortex lining the dorsal bank of the superior temporal sulcus, nor for the rostral cingulate motor area, which was examined as a control. The results indicate that aspiration lesions of the amygdala not only remove the cell bodies of the amygdala, as intended, but also inadvertently disrupt projection fibers arising from cells in the rhinal cortex and area TE that pass nearby or through the amygdala en route to the thalamus. Behavioral studies examining the effects of aspiration lesions of the amygdala in nonhuman primates need to take these findings into consideration.

Neonatal ventral hippocampus lesions disrupt extra-dimensional shift and alter dendritic spine density in the medial prefrontal cortex of juvenile rats

Recent data showed that neonatal ventral hippocampus (VH) lesions, an approach used to model schizophrenia symptoms in rodents, produce premature deficits of working memory believed to be associated with early medial prefrontal cortex (mPFC) maldevelopment. This experiment expands the investigation of mPFC integrity in juvenile rats with neonatal VH lesions by assessing behavioral flexibility and dendritic spine density. Sixteen Sprague-Dawley male pups received bilateral microinjections of ibotenic acid in the VH or SHAM surgery on postnatal day (PND) 6. On PND 29 and 30, rats were subjected to a spatial shift task in a cross-maze; an attentional set-shifting task was then administered on two consecutive days, between PND 33 and PND 35. Rats were sacrificed at PND 36 and dendritic spine density in the mPFC was assessed using Golgi-Cox staining procedure. Results revealed impaired extra-dimensional shift in VH-lesioned rats and inconsistent reversal discrimination outcomes. Although lesioned animals displayed intact performance in the spatial shift, rates of perseverative responses were higher than normal in this task. Neonatal VH damage resulted in lower dendritic spine density in the mPFC than measured in control brains; however, no significant correlation was found between this outcome and behavioral data. Juvenile morphological and cognitive perturbations are consistent with the early emergence of mPFC anomalies following neonatal VH lesions. Results are discussed in relation with potential common mechanisms linking pre- and post-pubertal onsets of behavioral dysfunction.

Potential benefits of mindfulness-based interventions in mild cognitive impairment and Alzheimer's disease: an interdisciplinary perspective.

The present article is based on the premise that the risk of developing Alzheimers disease (AD) from its prodromal phase (mild cognitive impairment; MCI) is higher when adverse factors (e.g., stress, depression, and metabolic syndrome) are present and accumulate. Such factors augment the likelihood of hippocampal damage central in MCI/AD aetiology, as well as compensatory mechanisms failure triggering a switch toward neurodegeneration. Because of the devastating consequences of AD, there is a need for early interventions that can delay, perhaps prevent, the transition from MCI to AD. We hypothesize that mindfulness-based interventions (MBI) show promise with regard to this goal. The present review discusses the associations between modifiable adverse factors and MCI/AD decline, MBIs impacts on adverse factors, and the mechanisms that could underlie the benefits of MBI. A schematic model is proposed to illustrate the course of neurodegeneration specific to MCI/AD, as well as the possible preventive mechanisms of MBI. Whereas regulation of glucocorticosteroids, inflammation, and serotonin could mediate MBIs effects on stress and depression, resolution of the metabolic syndrome might happen through a reduction of inflammation and white matter hyperintensities, and normalization of insulin and oxidation. The literature reviewed in this paper suggests that the main reach of MBI over MCI/AD development involves the management of stress, depressive symptoms, and inflammation. Future research must focus on achieving deeper understanding of MBIs mechanisms of action in the context of MCI and AD. This necessitates bridging the gap between neuroscientific subfields and a cross-domain integration between basic and clinical knowledge.

Object permanence and working memory in cats (Felis catus).

Cats (Felis catus) find an object when it is visibly moved behind a succession of screens. However, when the object is moved behind a container and is invisibly transferred from the container to the back of a screen, cats try to find the object at or near the container rather than at the true hiding place. Four experiments were conducted to study search behavior and working memory in visible and invisible displacement tests of object permanence. Experiment 1 compared performance in single and in double visible displacement trials. Experiment 2 analyzed search behavior in invisible displacement tests and in analogs using a transparent container. Experiments 3 and 4 tested predictions made from Experiment 1 and 2 in a new situation of object permanence. Results showed that only the position changes that cats have directly perceived are encoded and activated in working memory, because they are unable to represent or infer invisible movements.

Delayed alternation performance following subchronic phencyclidine administration in rats depends on task parameters

The cognitive effects of subchronic phencyclidine administration in rats are still unsettled in the literature. Possible causes of discrepancies are different drug treatment regimens and task parameters. The current experiment tested whether variations in procedures of the delayed T-maze alternation task result in performance differences following identical PCP treatments. Sixteen rats were trained on a continuous version of the T-maze task where they alternated between successive free-choice runs. Another sixteen were trained on a discrete trials version where each trial started with a forced run followed by a free choice test. After training, half of the rats submitted to each task version were treated daily for 14 days with i.p. injections of PCP (10 mg/kg) and the remaining half received a saline solution. At 48 h after the last injection, the subjects were tested for 10 days in their respective task version. Results showed that rats treated with PCP were impaired relative to controls in the continuous alternation task whereas performance of PCP and Saline groups did not differ in the discrete trials version. Cognitive control from prefrontal cortex and/or striatal response-related processes could have been damaged by PCP exposure. The systematic study of differences in tasks parameters may help reconcile discordant findings on PCPs functional outcomes.

Impaired social motivation and increased aggression in rats subchronically exposed to phencyclidine

Phencyclidine (PCP) treatment induces social withdrawal in the rat model of schizophrenia but little is known about the qualitative adequacy of behaviors displayed during interactions. Affiliative, avoidance, and aggressive behaviors were examined in rats 20 h after the 1st, the 8th, and the 15th injection of 10 mg/kg of PCP or of a saline vehicle. PCP treatment reduced the initiation of affiliative contacts with a control congener and increased aggressive responses, in the absence of drug outcomes on time spent in social interaction. These results suggest that subchronic PCP administration in rats affects perception and appraisal of social situations as well as motivation to interact. Such pathological behaviors are consistent with the social impairments characteristic of human schizophrenia.

Contributions of the dorsal hippocampus and the dorsal subiculum to processing of idiothetic information and spatial memory

It is well established that the dorsal hippocampal formation is crucial for spatial memory in rats. However, little is known about the distinct functions of the dorsal hippocampus and the dorsal subiculum. To examine the role of the dorsal hippocampus and the dorsal subiculum, Long-Evans rats with excitotoxic lesions (NMDA) of the dorsal hippocampus (DH), the dorsal subiculum (DS), or both (DHDS), and controls were trained on a nonmatching-to-place task. Then, to identify the strategy used by each group, they were tested on the same task in the dark with the T-maze being rotated between the sample and the test runs. In the light, rats with combined lesions were impaired. In the dark, groups DH, DS, and controls performed near chance level except in trials without rotation, suggesting the use of a sense of direction. The same rats were trained on a radial-arm maze task. In the light, where proximal visual cues were accessible, combined lesions affected performance whereas in the dark, it was impaired by all lesions. This experiment demonstrated that the dorsal subiculum and the dorsal hippocampus play a crucial role in processing idiothetic information and/or in maintenance of this information in memory.

Schizophrenia-like syndrome inducing agent phencyclidine failed to impair memory for temporal order in rats

Although subchronic phencyclidine (PCP) administration is recognized as a probative method to model schizophrenia-like symptoms in animals, only a few sets of data support the hypothesis of a cognitive prefrontal cortex (PFc) dysfunction in PCP-treated monkeys and rodents. Two experiments were here conducted to further test the integrity of prefrontal function in two versions of a memory for temporal order (MTO) task administered to rats. Original versions of this task elaborated by Kesner repeatedly yielded moderate to severe performance deficits in PFc lesioned rats. MTO assessment in an eight-arm radial maze consisted in a recency discrimination between two arms previously explored in the context of sequential forced choices. In Experiment 1, 16 naive Long-Evans rats were pre-trained on a variable version of the MTO task involving randomly re-mixed sequences until they reached a group criterion. Then, rats were treated daily for 21 days with PCP (10mg/kg) or saline vehicle and were tested on the same task approximately 20 h after an injection. The performance of the groups did not differ. In Experiment 2, 16 naive Long-Evans rats untrained prior to treatment received 27 daily injections of either PCP (10mg/kg) or saline vehicle and were tested, 20 h after each injection, on a constant version of the MTO task. This time, a fixed set of four sequences of successive arm entries was repeated within each daily session as well as across days. Again, prolonged PCP exposure failed to impair discrimination of temporal order despite the stability of sequential information over time. These negative results are not consistent with long-lasting hypofrontality, a major landmark of human schizophrenia, in the PCP rat model.

Dorsal, ventral, and complete excitotoxic lesions of the hippocampus in rats failed to impair appetitive trace conditioning

Three experiments examined appetitive trace and delay conditioning of the licking response (LR). In Experiment 1, normal rats were trained in trace conditioning using different trace intervals (2, 4, or 8s) and in delay conditioning (i.e., with a 0-s trace) in order to determine an appropriate trace interval for the following lesion experiments. Only the rats trained with a 2-s trace interval ultimately reached the same level of learning as rats trained in delay conditioning. In Experiments 2A and 2B, the performance of rats with dorsal, ventral, and complete excitotoxic hippocampal lesions was compared to that of sham-operated rats in LR conditioning with a 2-s trace. In Experiment 2B, the performance of rats in trace LR conditioning was also compared to that of rats tested in the delay paradigm. In both experiments, acquisition did not differ in lesioned and sham-operated rats and, in Experiment 2B, it was faster in the delay than in the trace paradigm. These results contrast with those showing that aversive trace conditioning is impaired after hippocampal damage. Experiment 3 examined whether the differential effects of hippocampal lesions on aversive and appetitive trace conditioning could be related to a parametric difference, that is, the relative durations of the conditional stimulus and of the trace interval. Again, hippocampal damage failed to produce a learning impairment. It is suggested that the procedure of aversive, but not of appetitive, trace conditioning is context-specific and that an intact hippocampus is required only in these situations.