Neonatal lesions of the ventral hippocampus in rats lead to prefrontal cognitive deficits at two maturational stages.

This experiment assessed the effect of neonatal ventral hippocampus lesions in rats, a heuristic approach to model schizophrenia, on continuous delayed alternation and conditional discrimination learning performance before and after complete cerebral maturation. Delays (0, 5, 15, and 30 s) were introduced in the tasks to help dissociate between a hippocampal and a prefrontal cortex dysfunction. At postnatal day (PND) 6 or 7, rats received bilateral microinjections of ibotenic acid or phosphate-buffered saline in the ventral hippocampus. From PND 26 to PND 35, rats were tested on the alternation task in a T-maze; from PND 47 to PND 85, the same rats were tested in the discrimination task where a stimulus and a response location had to be paired. Deficits in ventral hippocampus-lesioned rats were observed in both tasks whether a delay was introduced before a response or not. Impaired performance regardless of delay length, combined with high rates of perseverative errors, suggested a post-lesional prefrontal cortex dysfunction which persisted from the juvenile stage into adulthood. Premature cognitive impairments could not be predicted on the basis of the neurodevelopmental animal model of schizophrenia. Nevertheless, they appear consistent with accounts of premorbidly compromised memory, both immediate and delayed, in subgroups of schizophrenia patients.

Spatial encoding in domestic cats (Felis catus).

Four experiments were performed to identify the spatial information that cats used to encode the position of an object they saw move and disappear. In Experiment 1 and 2, several sources of allocentric spatial information were manipulated. Results indicated that the cats used none of these sources and instead relied primarily on their own spatial coordinates (pure egocentric information) to locate the hidden object. In Experiment 3 and 4, pure egocentric information was made unreliable by a detour task. Results showed that the cats encoded a metric source of allocentric spatial information--the relationship between the walls of the room and the hiding place. Together, these results reveal that cats' encoding of spatial information is flexible and adapted to various kinds of situations that can be encountered in the natural environment.

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.

Computer-automated method to study cardiac conditioning to a chemical cue in young salmon.

An apparatus was designed in which young Atlantic salmon (Salmo salar) are rapidly conditioned to reduce heart rate using a chemical-electric shock conditioning procedure. A chemical calibration system permitting efficient stimulus control is described as well as the electronic systems and computer software used to control all events of an experimental session and to quantify cardiac and chemical data. Efficient stimulus control and computer-automated recording techniques minimize inter-trial intervals and the time required for the measurement and analysis of cardiac responses. Data are presented showing that 15-month-old Atlantic salmon can be trained to reduce by 20% their heart rate to the synthetic chemical morpholine within 5 training trials whereas 10-month-old fish did not do so until 15 training trials.

Components and recognition of facial expression in the communication of emotion by actors.

This article addresses the issue of the communication of emotion by actors. In Study 1, the facial behavior of 6 actors portraying emotions as felt or unfelt were analyzed with the Facial Action Coding System. Results indicated that the portrayals of felt emotions were closer to the expression of genuine emotion than the portrayals of unfelt emotions for 3 of the 6 emotions under investigation. Study 2 examined the decoding of actors' portrayals from facial behavior. Decoders were found to be very accurate in recognizing the emotional category but not in judging the encoding condition.

Cognitive development in kittens (Felis catus): an observational study of object permanence and sensorimotor intelligence.

Spontaneous behavior of kittens (Felis catus) was filmed from birth until the end of Month 5 and coded according to Piagetian criteria of sensorimotor intelligence (SI) and object permanence (OP). Data revealed that Stages 2, 3, and 4 of SI were reached at Days 10, 26, and 45, respectively, whereas Stages 2, 3, and 4 of OP were reached at Days 31, 37, and 41, respectively. Spontaneous search behavior was exhibited both in searching for an object that disappeared and in hiding while moving toward a target object. From Day 45 on, search behavior was integrated into a playful social interaction in the form of hide-and-seek. Hence, kittens' spontaneous activity provided them with contexts in which OP was necessary for activity. Lastly, it is proposed that the mobility of both social and physical objects triggered circular activity in this species.

Search behavior in various breeds of adult dogs (Canis familiaris): object permanence and olfactory cues.

Human analog tests of object permanence were administered to various breeds of adult dogs (Canis familiaris). Experiment 1 showed that the performance of terriers, sporting, and working dogs did not differ. Dogs succeeded in solving invisible displacement problems, but performance was lower than in visible displacement tests. Familiarity with the task had some influence because invisible displacement tests were more successful if they were preceded by visible displacement tests. In Experiment 2, odor cues from the target object and the hiding screens were available or were masked. Results confirmed that success was lower in invisible than in visible displacement tests and that these problems were solved on the basis of representation of visual information rather than on the basis of olfactory cues or of local rule learning. Dogs are compared with other species that display Stage 6 object permanence.

Cross-sectional study of object permanence in domestic puppies (Canis familiaris).

Visual accommodation and object permanence tests were administered to 70 puppies (Canis familiaris), aged 4 weeks to 9 months. The results showed that understanding of visible displacement problems emerged at the 5th weeks and developed rapidly until the 8th week. Although the search behaviors of older puppies were more flexible, no further significant development was observed between 8 weeks and 9 months. The results on invisible displacement tests suggest that understanding of invisible displacement problems appears around the 1st year in dogs' development.

Neurobehavioral changes in mice chronically exposed to methylmercury during fetal and early postnatal development.

Pregnant C57BL/6 mice were chronically treated with 0, 4, 6, or 8 ppm of methylmercury chloride (MeHg) in drinking water during fetal and early postnatal development. Four behavioral functions were analyzed in female and male offspring between the age of 6 and 12 weeks: motor coordination learning on the rotarod; training to spatial alternation in the standard T maze followed by a working memory test with delays; spontaneous locomotion and rearings in the open field; reference and working memory assessment in the modified T maze [Behav. Neurosci. 102 (1988) 635]. Chronic perinatal treatment with MeHg resulted in moderate brain levels of mercury near birth which rapidly decreased during nursing. MeHg exerted an effect on the performance of females, but not of males, on two of the four measurements. All treated females exhibited less locomotion than control mice when the open field was new, but not in the following four sessions when the environment was becoming increasingly familiar. Working memory was impaired in females treated with 6 and 8 ppm of MeHg in the modified T maze, but not on the test with delays in the standard T maze. Taken together, these results show that chronic exposure to MeHg during fetal and postnatal development had sex-dependent effects on horizontal exploration and on working memory in the modified T maze, and no effects on motor coordination learning and reference memory.

Neurobehavioral changes in mice treated with methylmercury at two different stages of fetal development.

Pregnant C57BL/6 mice were orally given daily doses of 4 or 6 mg/kg of methylmercury chloride (MeHg) or vehicle during either gestational days 7-9 (GD7-9) or days 12-14 (GD12-14). Their female offspring were tested between 6 and 16 weeks of age on a variety of behavioral tasks. Motor coordination on the rotarod and visual discrimination learning in the Y maze were not affected by administration of MeHg either at GD7-9 or at GD12-14. In the open field, the total number of square crossings was lower in mice treated with 4 and 6 mg/kg of MeHg at GD12-14 than in control mice whether the environment was new or familiar, but prenatal administration of MeHg at GD7-9 had no effect on this measure. Administration of MeHg either at GD7-9 or at GD12-14 had no effect on the percentage of central square crossings or on the frequency of rearings in the open field. On spatial alternation training in the T maze, both treated groups in Condition GD7-9 and the group treated with 6 mg/kg at GD12-14 required more sessions to reach the learning criterion than their respective vehicle groups. When spatial alternation was tested with delays, treated groups did not differ from their respective control groups. In the radial arm maze, the performance of mice treated at GD7-9 was normal, but reference memory and working memory were impaired by administration of MeHg at GD12-14. In mice treated with 4 mg/kg of MeHg, reference memory was impaired only on the first block of trials, whereas in mice treated with 6 mg/kg, the deficit persisted on all blocks of trials. Overall, these results indicate that prenatal administration of MeHg at GD12-14 had more detrimental effects on behavioral performance than administration at GD7-9. It reduced locomotor activity and impaired reference memory for egocentric and allocentric spatial information as well as working memory for places.

Judgment of facial expressions of emotion as a function of exposure time.

The purpose of this experiment was to study the accuracy of judgment of facial expressions of emotions that were displayed for very brief exposure times. Twenty university students were shown facial stimuli that were presented for durations ranging from 10 to 50 msec. The data showed that accuracy of judgment reached a fairly high level even at very brief exposure times and that human observers are especially competent to process very rapid changes in facial appearance.

Accuracy and latency of judgment of facial expressions of emotions.

The aim of the experiment was to study the relation between accuracy of judgment of facial expressions of emotions and time for judgment. The results for 34 college students confirmed previous data showing high performance in identification of all emotions, although there were some important differences between emotions. Also, times for judgment were longer for the emotions which were more difficult to identify.

Search behaviour of cats (Felis catus) in an invisible displacement test: cognition and experience.

An invisible displacement test was administered to cats in order to test the hypothesis that search behaviour in this species is influenced by their limited capacity for object permanence as well as by their previous experience with the environment. Experiment 1 compared three groups of cats in a five-choice hiding task in which the hiding places could be discriminated by their spatial positions. Two groups received a visible displacement training before the invisible displacement test and one group did not. Experiment 2 compared two groups of trained subjects in the same task, but the hiding places could be discriminated by spatial and visual cues. The results confirmed that cats are unable to solve problems with invisible displacements. The visible displacement training improved their performance, but was not sufficient to make them succeed. Experience with the hiding potential of the covers also gives more persistence to search behaviour. Finally, the distribution of search attempts is not determined by the proximity to the target and is influenced only partially by the subjects' previous experience. Like Stage 5 infants, cats rely mainly on their immediate perception. They search for an object in the last location they have seen it disappear or under the nearest cover from this location.

Selective impairment of fornix-transected rats on a new nonspatial, odor-guided task.

In the present experiment, sham-operated (SH) and fornix-transected (FX) rats were trained on a new nonspatial, odor-guided task. On each session, eight odor pairs were presented twice. On the first occurrence of a pair, rats were reinforced for pushing the container (go response) in which the olfactory stimuli were placed. On the second occurrence, they were not reinforced and had to refrain from responding (no-go response) to be scored as success. Rats were first trained to criterion on odor pairs made of replicates of the same odor (S pairs). Then they were trained to criterion on pairs made of different odors, each member of the pair overlapping with that of another pair (O pairs) and finally, on pairs of different odors with no overlap (NO pairs). The results showed that the number of sessions to reach criterion was significantly higher in FX than in SH rats during training on O pairs, but not during training on S or on NO pairs. These findings are consistent with the configural (Rudy and Sutherland, 1995: Hippocampus 5:375-389) or relational (Eichenbaum et al., 1994: Behav Brain Sci 17:449-518) account of the hippocampal memory function.

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

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.

Activation of locations in working memory in cats.

Cats saw an object appear and disappear at two successive locations; the movement of the object from one location to the other was not perceived but was indicated by indirect cues and the two disappearances were separated by a 0-sec or a 20-sec interval. Performance was poorer with the 0-sec than with the 20-sec interval. With the 0-sec interval, the percentages of search attempts made at the object's initial and final hiding locations did not differ whereas with the 20-sec interval, more search attempts were made at the final than at the initial location. These results provide additional support to Goulet, Doré and Rousseau's (1994) interpretation of cats' search behaviour in terms of activation of spatial locations in working memory.

Selective hippocampal lesions yield nonspatial memory impairments in rhesus monkeys.

Monkeys with removals of medial temporal lobe (MTL) structures are widely recognized as valid models of human global anterograde amnesia, a syndrome that arises consequent to damage to a finite set of brain structures situated in the medial temporal lobe and/or medial diencephalon. However, a comparison of memory deficits in human and nonhuman primates with MTL damage has presented a long-standing puzzle. Whereas amnesic patients are impaired in learning object discrimination problems, monkeys with MTL damage are typically not. One possible explanation for this difference is that object discrimination tasks for humans and monkeys differ in that the former but not the latter requires the use of contextual information. If this analysis is correct, monkeys with MTL damage might be disadvantaged in learning to discriminate similar objects presented in different contexts. To test this possibility, we evaluated the effects of excitotoxic lesions of one of the MTL structures, the hippocampus, on the rate of learning of discrimination problems embedded within unique contexts. Monkeys with hippocampal lesions were impaired relative to controls in learning object discrimination problems of this type. These findings strongly support the idea that the difference in the effect on object memory of MTL damage in human and nonhuman primates is due to a difference in the opportunity to employ contextual cues rather than to a difference in the organization of memory.