Showing papers in "Behavioral Neuroscience in 1999"

Repeated restraint stress facilitates fear conditioning independently of causing hippocampal CA3 dendritic atrophy.

Abstract: This study investigated whether 21 days of restraint stress (6 hr/day) and the subsequent hippocampal dendritic atrophy would affect fear conditioning, a memory task with hippocampal-dependent and hippocampal-independent components. Restraint-stressed rats were injected daily (21 days) with tianeptine (10 mg/kg; to prevent hippocampal atrophy) or vehicle then tested on fear conditioning (Days 23-25, with 2 tone-shock pairings) and open field (Day 25). Restraint stress enhanced freezing to context (hippocampal-dependent behavior) and tone (hippocampal-independent) and decreased open-field exploration, irrespective of whether tianeptine was given. Results confirmed that stress produced CA3 dendritic atrophy and tianeptine prevented it. Moreover, CA3 dendritic atrophy was not permanent but reversed to control levels by 10 days after the cessation of restraint stress. These data argue that different neural substrates underlie spatial recognition memory and fear conditioning.

Working memory is more sensitive than declarative memory to the acute effects of corticosteroids: a dose-response study in humans.

Abstract: The effects of various doses (40 microg/kg/hr, 300 microg/kg/hr, 600 microg/kg/hr or placebo) of hydrocortisone on tasks assessing working and declarative memory function were measured in 4 groups of 10 young men. During the infusion, participants were given an item-recognition working memory task, a paired-associate declarative memory task, and a continuous performance task used to control possible concomitant effects of corticosteroids on vigilance. The results revealed significant acute effects of the highest dose of hydrocortisone on working memory function, without any significant effect on declarative memory function or arousal-vigilance performance. These results suggest that working memory is more sensitive than declarative memory to the acute elevations of corticosteroids, which could explain the detrimental effects of corticosteroids on acquisition and consolidation of information, as reported in the literature.

The effects of oxytocin and vasopressin on partner preferences in male and female prairie voles (Microtus ochrogaster).

Abstract: This study compared the effects of centrally administered oxytocin (OT) and arginine vasopressin (AVP) on partner preference formation and social contact in male and female prairie voles (Microtus ochrogaster). After 1 hr of cohabitation and pretreatment with either AVP or OT, both males and females exhibited increased social contact and significant preference for the familiar partner. After pretreatment with either an OT receptor antagonist (OTA) or an AVP (Via) receptor antagonist (AVPA), neither OT nor AVP induced a partner preference. In addition, treatment with OT+OTA or AVP+AVPA was associated with low levels of social contact in both sexes. Either AVP or OT is sufficient to facilitate social contact if either the OT or AVP receptor is available. However, the formation of partner preferences may require access to both AVP and OT receptors. Monogamous social systems are rare among mammals, occurring in less than 3% of mammalian species (Kleiman, 1977). Prairie voles (Microtus ochrogaster) exhibit several traits associated with monogamy, including high levels of social contact and the capacity to form pair bonds (Carter, DeVries, & Getz, 1995; Dewsbury, 1987; Dewsbury, Baumgardner, Evans, & Webster, 1980). In the laboratory, the selection of a familiar partner in preference to a stranger has been used as an index of pair bonding. Partner preferences can form during nonsexual cohabitation, and the onset of partner preferences is facilitated by mating (Williams, Catania, & Carter, 1992; Winslow, Hastings, Carter, Harbaugh, & Insel, 1993).

Double dissociation of function within the hippocampus: a comparison of dorsal, ventral, and complete hippocampal cytotoxic lesions.

Abstract: Rats with complete cytotoxic hippocampal lesions exhibited spatial memory impairments in both the water maze and elevated T maze. They were hyperactive in photocell cages; swam faster in the water maze; and were less efficient on a nonspatial, differential reinforcement of low rates (DRL) task. Performance on both spatial tasks was also impaired by selective dorsal but not ventral lesions; swim speed was increased by ventral but not dorsal lesions. Both partial lesions caused a comparable reduction in DRL efficiency, although these effects were smaller than those of complete lesions. Neither partial lesion induced hyperactivity when rats were tested in photocell cages, although both complete and ventral lesion groups showed increased activity after footshock in other studies (Richmond et al., 1999). These results demonstrate possible functional dissociations along the septotemporal axis of the hippocampus.

Dissociating context and space within the hippocampus: effects of complete, dorsal, and ventral excitotoxic hippocampal lesions on conditioned freezing and spatial learning.

Abstract: Rats with complete excitotoxic hippocampal lesions or selective damage to the dorsal or ventral hippocampus were compared with controls on measures of contextually conditioned freezing in a signaled shock procedure and on a spatial water-maze task. Complete and ventral lesions produced equivalent, significant anterograde deficits in conditioned freezing relative to both dorsal lesions and controls. Complete hippocampal lesions impaired water-maze performance; in contrast, ventral lesions improved performance relative to the dorsal group, which was itself unexpectedly unimpaired relative to controls. Thus, the partial lesion effects seen in the 2 tasks never resembled each other. Anterograde impairments in contextual freezing and spatial learning do not share a common underlying neural basis; complete and ventral lesions may induce anterograde contextual freezing impairments by enhancing locomotor activity under conditions of mild stress.

Contextual fear conditioning, conjunctive representations, pattern completion, and the hippocampus.

Abstract: Impaired contextual fear conditioning produced by damage to the hippocampus has been attributed to the loss of a conjunctive representation of the features of the context. There is, however, no direct evidence that conjunctive representations contribute to contextual fear conditioning. These experiments addressed this issue and found support for the conjunctive representation view. Two results made this point: (a) Preexposure to the conditioning context, but not to its separable features, facilitated contextual fear conditioning, and (b) generalization of fear conditioning to similar contexts was enhanced by preexposure to the context used to test for generalization. These results are interpreted as pattern completion to the preexposed context during the conditioning episode. They support the view that a conjunctive representation of context plays an important role in contextual fear conditioning and that the impairments produced by damage to the hippocampus result from the loss of this conjunctive contribution.

Involvement of rodent prefrontal cortex subregions in strategy switching.

Abstract: The present study examined whether inactivation of the prelimbic-infralimbic areas or the dorsal anterior cingulate area impairs strategy switching in the cheeseboard task. After implantation of a cannula aimed at either the prelimbic-infralimbic or dorsal anterior cingulate areas, all rats were tested in a spatial and a visual-cued version of the task. Some of the rats received the spatial version first, followed by the visual-cued version. The procedure for the other rats was reversed. Infusions of 2% tetracaine into the prelimbic-infralimbic or dorsal anterior cingulate areas did not impair acquisition of the spatial or visual-cued versions. However, inactivation of the prelimbic-infralimbic areas, but not the dorsal anterior cingulate area, impaired learning when rats were switched from one version to the other. These findings suggest that the prelimbic-infralimbic areas are involved in switching to new behavior-guiding strategies.

Behavioral disturbances in transgenic mice overexpressing the V717F beta-amyloid precursor protein.

Abstract: PDAPP transgenic mice have been shown to develop age dependently much of the cerebral histopathology associated with Alzheimer's disease. PDAPP mice (3-10 months old) were tested in a battery of memory tasks to determine whether they develop memory-behavioral deficits and whether these deficits occur before or after amyloid deposition. PDAPP mice manifest robust impairments in a radial-maze spatial discrimination task at all ages tested. Mild deficits were observed in a barpress learning task in 3-month-old PDAPP mice. In contrast, PDAPP mice show an age-dependent decrease in spontaneous object-recognition performance that appears to be severe at ages when amyloid deposition is known to occur. Thus, the PDAPP mouse shows severe deficits in the radial maze well before amyloid plaque deposition, whereas object-recognition performance decreases with age and may be associated with amyloid deposition.

Taste perception in patients with insular cortex lesions.

Abstract: Research on nonhuman primates suggests that the primary taste cortex in humans is located in the rostrodorsal insula. Qualitative and quantitative assessment of taste perception was performed on 6 patients with unilateral damage to the insula, 3 patients with brain damage outside the insula, and 11 age-matched, normal subjects. Each subject identified the quality and intensity of the gustatory stimuli applied separately to the left and right sides of the anterior tongue. Damage to the right insula produced ipsilateral taste recognition and intensity deficits. Damage to the left insula caused an ipsilateral deficit in taste intensity but a bilateral deficit in taste recognition. The unexpected deficit in the left-hemispheric stroke patients for taste recognition on the right side of the tongue suggests that taste information from both sides of the tongue passes through the left insula.

Inhibition of the mesoamygdala dopaminergic pathway impairs the retrieval of conditioned fear associations.

Abstract: Previous findings have demonstrated that systemic dopaminergic manipulations impair the retrieval of Pavlovian conditioned fear. A second-order fear-conditioning paradigm was used to test whether the dopaminergic projection from the ventral tegmental area (VTA) to the lateral and basal amygdala (LBA) can affect conditioned fear. Phase 1 entailed conditioned stimulus-unconditioned stimulus (CS1-US) pairings. In Phase 2, drugs were infused in either the LBA or VTA prior to pairings of CS2 (a second cue) with CS1. In Phase 3, freezing behavior elicited by CS2 was tested without drugs. Infusions of the D2 agonist quinpirole into the VTA or of the D1 antagonist SCH 23390 into the LBA caused a decrease in freezing to CS2. Both manipulations decrease D1 receptor activation in the LBA. Infusions of the D1 agonist SKF 38393 into the LBA had no effect. This pattern of results is consistent with the hypothesis that the VTA-LBA dopaminergic projection modulates the retrieval of an association between a CS and footshock US.

Dopamine D2 receptor-mediated regulation of partner preferences in female prairie voles (Microtus ochrogaster): a mechanism for pair bonding?

Abstract: This study examined the role of dopamine (DA) in partner preference (PP) formation in female prairie voles (Microtus ochrogaster). The nonspecific DA antagonist haloperidol blocked mating-induced PP, whereas the nonspecific DA agonist apomorphine induced PP without mating. The D2 antagonist eticlopride, but not the D1 antagonist SCH23390, blocked PP, whereas the D2 agonist quinpirole, but not the D1 agonist SKF38393, induced PP without mating. Injections of eticlopride before or immediately after mating, but not 24 hr after mating, impaired PP, indicating that DA's effects were not due to an interference with mating or sensory recognition. Finally, intracerebroventricular injections of eticlopride diminished PP. Together, these data suggest that mating-induced PP requires activation of D2 receptors and that social experience may activate dopaminergic pathways, with enduring effects on behavior.

Anxiety, motor activation, and maternal-infant interactions in 5HT1B knockout mice.

Abstract: This study describes the development of anxiety and motor activation in mice lacking the serotonin (5HT) 1B receptor and in wild type controls and characterizes their early mother-infant interactions. In the isolation-induced ultrasonic vocalization paradigm, 5HT1B knockout pups vocalized less and were hyperactive, rearing, jumping, and rolling more often than wild type pups. One week postpartum, 5HT1B knockout mothers spent 20% more of their time outside the nest and were also hyperactive, rearing and climbing to the edge of the cage more often than the wild type mothers. There were no genotype effects on pup retrieval. Knockout adults were less anxious in the elevated plus-maze, defecated less, and head-dipped more, although none of the standard measures of anxiety (time and entries in the open arms) were different. 5HT1B knockout mice of both sexes were hyperactive during both the light and the dark phases of the 24-hr cycle. Thus, 5HT1B knockout mice show reduced anxiety and are hyperactive throughout their life.

Neurotoxic or electrolytic lesions of the ventral subiculum produce deficits in the acquisition and expression of Pavlovian fear conditioning in rats.

Abstract: The effects of neurotoxic or electrolytic ventral subicular (vSUB) lesions on the acquisition and expression of Pavlovian fear conditioning in rats were examined. Conditioning consisted of the delivery of tone-footshock trials in a novel observation chamber, and freezing served as the measure of conditional fear. Pretraining vSUB lesions produced a severe tone freezing deficit and a modest context freezing deficit, whereas posttraining lesions produced severe deficits in freezing to both a tone and a context conditional stimulus (CS). Similar impairments were produced by neurotoxic and electrolytic lesions. Increases in motor activity associated with the lesions could not account for freezing deficits. These results reveal that neurons in the vSUB have an important role in both the acquisition and expression of Pavlovian fear conditioning to contextual and acoustic CSs.

Hippocampectomized rats are capable of homing by path integration.

Abstract: Navigation in rodents is mediated by at least 3 mechanisms: guidance, path integration, and landmark learning. The hippocampus is necessary for spatial learning based on distal landmarks, and it has been suggested that the hippocampal formation performs a form of path integration in updating place cell firing; however, the necessity of the hippocampus for path integration has not been clearly established. Rats with extensive neurotoxin lesions of the hippocampus and control rats were trained on 2 tasks in which they were required to move in total darkness from one location to another and then return to the start point. Hippocampal and control rats both used path integration in solving these tasks and did not differ in terms of the distributions of their arrival points on the return paths. We conclude that neuronal circuits sufficient for computing a homing vector using path integration are located outside the hippocampus.

Acquisition of fear conditioning in rats requires the synthesis of mRNA in the amygdala.

Abstract: In this study, the role of mRNA synthesis in the amygdala was studied during the acquisition of conditional fear. Rats with cannulas placed in the basolateral region of the amygdala were trained with a series of noise-shock pairings in a distinctive observation chamber. One half of the rats were pretreated with the mRNA synthesis inhibitor actinomycin-D (act-D). Responding to the training context and the auditory stimulus in a novel context measured by defensive freezing was assessed. Pretreatment with act-D significantly attenuated fear responses to both stimuli. Animals receiving act-D injections exhibited normal reactions to the conditioned stimulus-unconditioned stimulus pairings in the initial training session and displayed normal learning when retrained 7 days after injections. These results indicate that the transcription of new mRNA and subsequent protein synthesis in the amygdala may be essential for neural plasticity during this form of associative learning.

Feeding induced by GABA(A) receptor stimulation within the nucleus accumbens shell: regional mapping and characterization of macronutrient and taste preference.

Abstract: This study investigated the areas of the nucleus accumbens shell involved in the modulation of feeding behavior by GABAergic stimulation and characterized this response using macronutrient diets as well as saline, sucrose, and saccharin solutions. The GABA agonist muscimol induced a pronounced feeding response when infused in the medial nucleus accumbens shell but not in the ventral or lateral accumbens shell. In the macronutrient preference study, muscimol increased the intake of both high fat and high carbohydrate diets when presented separately. When both diets were available simultaneously, muscimol stimulated feeding of both diets to the same degree. Muscimol elicited a robust increase in the consumption of sucrose solution. However, no effect of muscimol was demonstrated for water, saline, or saccharin intake. These findings provide evidence for a selective role for GABA-sensitive neurons in the medial accumbens shell in the regulation of ingestive behavior and further suggest that GABA A receptors in this region do not modulate palatability, macronutrient selection, or rewarding properties of food.

Serotonin regulation of aggressive behavior in male golden hamsters (Mesocricetus auratus).

Abstract: These studies examined the neurochemistry and neuroanatomy of the serotonin (5-HT) system innervating the anterior hypothalamus (AH) and the interaction of 5-HT receptor agonists with arginine vasopressin (AVP) in the regulation of offensive aggression in golden hamsters. Because specific 5-HT 1A , 5-HT 1B , and AVP V 1A binding sites were observed within the AH by in vitro autoradiography, the hamsters were tested for offensive aggression after microinjections of AVP in combination with either the 5-HT 1A agonist 8-hydroxy-2-(di-n-propylamino) tetraline (DPAT) or the 5-HT 1B agonist CGS-12066A (CGS) directly within the AH. Though treatment with DPAT resulted in a dose-dependent inhibition of AVP-facilitated offensive aggression, CGS was ineffective. In addition, a retrograde tracer was injected within the AH to localize the distribution of 5-HT neurons projecting to the area. Retrogradely labeled 5-HT neurons were found within the dorsal, median, and caudal linear raphe nuclei and are suspected to inhibit AVP-facilitated offensive aggression by an activation of 5-HT 1A receptors in the AH.

Long-lasting consequences of a social conflict in rats: Behavior during the interaction predicts subsequent changes in daily rhythms of heart rate, temperature, and activity

Abstract: This study shows that the long-term consequences of a social conflict in rats do not depend on the physical intensity of the fight in terms of aggression received but, especially, on how the subjects deal with it. Experimental rats were introduced into the cage of an aggressive conspecific for I hr, and the effects on daily rhythms of heart rate, body temperature, and activity thereafter were measured by means of telemetry In some rats, the confrontation caused a strong decrease in the daily rhythm amplitude that lasted up to 3 weeks, whereas other subjects showed only minor changes. The changes in rhythm amplitude did not correlate with the number of attacks received from the territory owner. Contrary to this, the changes showed a clear negative correlation with the aggression of the experimental rats themselves. Subjects fighting back and counterattacking the cage owner subsequently had a smaller reduction in rhythm amplitude.

Intact learning of artificial grammars and intact category learning by patients with Parkinson's disease.

Abstract: Patients with Parkinson's disease (PD) have been shown to be impaired on some nondeclarative memory tasks that require cognitive skill learning (perceptual-motor sequence learning, probabilistic classification). To determine what other skill-based tasks are impaired, 13 patients with PD were tested on artificial grammar learning, artificial grammar learning with transfer to novel lettersets, and prototype learning. Patients with PD performed similarly to controls on all 3 tests. The intact learning exhibited by PD patients on these tests suggests that nondeclarative cognitive skill learning is not a single entity supported by the neostriatum. If learning the regularities among visual stimuli is the principal feature of artificial grammar learning and prototype learning, then these forms of skill learning may be examples of perceptual learning, and they may occur in early visual cortical processing areas.

Pharmacological dissociation between the reinforcing, sensitizing, and response-releasing functions of reward in honeybee classical conditioning.

Abstract: Reserpine depletes biogenic amines from their stores in the honeybee (Apis mellifera carnica) brain and leads to impaired appetitive conditioning using sucrose as a reinforcer. Compensatory injection of octopamine or dopamine directly into the brain restores these behavioral losses. Dopamine rescues the slowing-down effect on motor patterns, but not sensitization or conditioning. Octopamine leaves the motor patterns as well as sensitization unchanged but rescues conditioning. Specifically, octopamine rescues acquisition but not retrieval. Serotonin has no significant effect on sensitization but impairs conditioning. The authors conclude that octopamine is involved in selectively mediating the reinforcing but not the sensitizing or response-releasing function of the sucrose reward, whereas dopamine is selectively involved in the expression of the motor response.

The hippocampus is not necessary for a place response but may be necessary for pliancy.

Abstract: Rats with kainate-colchicine hippocampal lesions (HL) and controls (C) were initially trained in the Morris water maze with procedures that deterred their prepotent thigmotaxic response. Training began with an escape platform that occupied nearly the entire pool. The area to which the rats could escape was made smaller by substituting smaller platforms as training progressed. In contrast to standard procedures, HL rats and C rats showed comparable performance during acquisition and preferentially searched the goal quadrant on probe trials during which the platform was removed. In a follow-up experiment, the platform was moved to a random position along the wall, which required a switch to a thigmotaxic response for most effective escape. HL rats that were thigmotaxic before place training did not switch to a thigmotaxic response as readily as did controls, behavior consistent with the view that hippocampal damage reduces pliancy.

Lesions of the prelimbic-infralimbic cortices in rats do not disrupt response selection processes but induce delay-dependent deficits: evidence for a role in working memory?

Abstract: Effects of neurotoxic lesions of the prelimbic-infralimbic cortex (PL-IL) were examined in rats performing 2 conditional tasks. PL-IL-lesioned rats showed normal acquisition of a visuospatial conditional discrimination in a Y maze as well as a tone-light conditional discrimination in an operant chamber, indicating that the PL-IL is not necessary for response selection processes. When the working memory load was subsequently increased in the tone-light conditional discrimination, rats with PL-IL lesions showed a delay-dependent disruption of performance. This suggests a role of the PL-IL in some working memory processes. However, the present results, considered along with previous studies, suggest that the PL-IL does not seem to be directly involved in the processes necessary to maintain specific items over a delay period but rather in the planning of forthcoming behavioral responses on the basis of previously acquired information.

The dopaminergic modulation of fear: Quinpirole impairs the recall of emotional memories in rats

Abstract: Past studies examining the contributions of dopamine to fear have produced inconsistent results. The present experiments reevaluated this issue. It was found that systemic pretreatment with the D2 agonist quinpirole before pairing 2 conditioned stimuli (CSs; CS2-CS1) dose dependently blocked the acquisition of second-order fear conditioning. Quinpirole's actions were not due to nonspecific impairments in the ability to perceive the CSs, or form and store an association, because the identical drug pretreatment before pairing the same 2 CSs had no effect on the acquisition of sensory preconditioning. In a separate study, rats were given fear conditioning while untreated and then received extinction sessions while under the influence of quinpirole or its vehicle. Quinpirole pretreatment blocked extinction. Findings suggest that quinpirole decreased fear by blocking the retrieval of a learned association between a CS and unconditioned stimulus (US), rather than by devaluing the US, which would have resulted from summation of quinpirole's appetitive properties with the aversive properties of fear.

Lesions centered on the medial amygdala impair scent-marking and sex-odor recognition but spare discrimination of individual odors in female golden hamsters.

Abstract: The medial amygdala (Me) has been implicated in various social behaviors that depend on chemosensory cues, but its precise role in discriminating and learning social odors is not known. Female golden hamsters (Mesocricetus auratus) received electrolytic lesions of the Me or sham surgery and were tested for their ability to (a) discriminate between odors of individual males in a habituation-discrimination task, (b) show preferences for male over female odors in a Y maze, and (c) scent-mark in response to male and female odors. All females discriminated between scents of individual males. In contrast, Me lesions eliminated female preferences for male odors in a Y maze. Females with Me lesions also showed a substantial reduction in vaginal marking and virtually no flank marking in response to odors. Thus, the Me in female hamsters is critical for differential investigation of opposite-sex odors and for scent-marking behavior but is not involved in discrimination between odors of individuals.

Effect of glucose, glucose regulation, and word imagery value on human memory.

Abstract: Changes in memory performance were examined after intake of a glucose (50 g) or saccharin (50 mg) solution in fasted men and women. Glucoregulation was estimated by using a recovery index to categorize participants within each gender as having poor or good recovery. Memory was assessed with word-learning tasks in which the imagery-evoking value of the words was systematically manipulated to yield high- and low-imagery lists. The results showed that men and women characterized as having poor glucose regulation had significantly worse memory performance under the saccharin condition. This decrement was reversed by glucose ingestion. These effects were observed for both low- and high-imagery words. This study supports the hypothesis that poor glucoregulation is associated with poor memory performance even in young healthy participants and that the ingestion of glucose can improve their memory.

Spatial learning and performance in the radial arm maze is impaired after N-methyl-D-aspartate (NMDA) receptor blockade in striatal subregions.

Abstract: These experiments addressed the role of striatal N-methyl-D-aspartate (NMDA) receptors in spatial behavior in the radial arm maze. Rats treated with the NMDA antagonist D-2-amino-5-phosphonopentanoic acid (AP-5) in the nucleus accumbens core, medial caudate, and posterior caudate were all significantly impaired in acquiring the correct spatial responses. In contrast, rats infused with AP-5 in the nucleus accumbens shell showed little impairment. When rats in all groups had learned the maze and were performing at similar levels, AP-5 had relatively little effect except in the posterior caudate group, where errors and trial times were again increased. These findings demonstrate the importance of NMDA receptor-dependent activity within the accumbens and caudate in spatial learning and performance. The neural processes necessary for adaptive spatial learning in complex environments may recruit multiple cortical systems having specialized functions, which in turn are integrated in widespread striatal regions.

Ibotenic acid lesions of the basolateral, but not the central, amygdala interfere with conditioned taste aversion: evidence from a combined behavioral and anatomical tract-tracing investigation.

Abstract: Rats (Rattus norvegicus) with almost complete ibotenic acid lesions (at least 90%) of the basolateral amygdaloid complex (BLA) failed to learn a conditioned taste aversion (CTA; Experiment 1A). In these same BLA rats, the bidirectional parabrachial-insular pathway that courses through the central nucleus of the amygdala (Ce) was shown to be spared (Experiment 1B), indicating that the BLA per se is critical for CTA learning. In contrast to the deleterious effect of BLA lesions on CTA, ibotenic acid lesions of the Ce did not block CTA learning (Experiment 2). Nonreinforced preexposure to the gustatory stimulus attenuated CTA acquisition in normal rats, and, under these conditions, rats with BLA lesions were no longer impaired (Experiment 3). Thus, ibotenic acid lesions centered over the Ce, sparing a considerable extent of the BLA, together with the testing procedure used in previous experiments (e.g., L. T. Dunn & B. J. Everitt, 1988), led to the belief that the CTA deficits reported after electrolytic lesions of the amygdala were the result of incidental damage to fibers of passage.

Effects of regional striatal lesions on motor, motivational, and executive aspects of progressive-ratio performance in rats.

Abstract: The striatum is implicated in response selection and performance, the dorsal striatum in sensorimotor control and habit learning, and the ventral striatum in motivation and rewarded behaviors. Ventral striatal lesions produce performance changes on food-reinforced, progressiveratio (PR) schedules, but the effects of dorsal striatal lesions on this task are not known. In this study, neither medial nor lateral dorsal striatal lesions produced deficits on the main motivational indices of PR performance. In contrast, significant impairments were observed in motoric or "executive" aspects of performance. Motivationally related manipulations of the task (food deprivation and reward magnitude) produced some subtle lesion-specific changes in behavior on these motoric or executive aspects of performance. Findings are discussed in relation to the roles of the dorsal and ventral striatum in reward-related behaviors.

Neuroanatomical basis of maternal memory in postpartum rats: selective role for the nucleus accumbens.

Abstract: The experience of interacting with pups causes long-term changes in mothers' brains that mediate long-term changes in maternal behavior. As little as 1 hr of pup experience postpartum results in enhanced maternal responses to pups 10 days later. This experiment investigated the effects of lesions in multiple neural sites that have been implicated either in the actual expression of maternal behavior or in learning and memory within other behavioral contexts on the initiation and the long-term experience-based retention of maternal behavior. Electrolytic lesions were performed either before or after a 1-hr or 24-hr maternal experience. Rats sustaining lesions of the nucleus accumbens (NACC), whether administered before parturition and experience or immediately after a brief experience, failed to show a maternal experience effect. NACC lesions sustained 24 hr after a maternal experience did not disrupt long-term retention of the maternal behavior.

Mechanisms of reorientation and object localization by children: A comparison with rats

Abstract: Neurophysiological studies show that the firing of place and head-direction (HD) cells in rats can become anchored to features of the perceptible environment, suggesting that those features partially specify the rat's position and heading. In contrast, behavioral studies suggest that disoriented rats and human children rely exclusively on the shape of their surroundings, ignoring much of the information to which place and HD cells respond. This difference is explored in the current study by investigating young children's ability to locate objects in a square chamber after disorientation. Children 18-24 months old used a distinctive geometric cue but not a distinctively colored wall to locate the object, even after they were familiarized with the colored wall. Results suggest that the spatial representations underlying reorientation and object localization are common to humans and other mammals. Together with the neurophysiological findings, these experiments raise questions for the hypothesis that hippocampal place and HD cells serve as a general orientation device for target localization.