Working memory in aged rats.

The performances of young and aged rats were compared on a spatial (spatial delayed nonmatching-to-sample) and a nonspatial (object delayed nonmatching-to-sample) test of working memory. Although evidence was found that aging slowed acquisition of both of these tasks, performance over different retention intervals of up to 60 sec was normal once the task was mastered. An impairment was found, however, in the performance of the spatial test when the number of locations to be remembered on each trial was increased from one to two. The conclusions of this study are that under some conditions, the retention capabilities of aged rats may not change and that some acquisition impairments do not reflect alterations in learning or memory per se, but, in common with other studies, deficits in the remembrance of spatial locations may be found. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Social behavior of rats with chronic prefrontal lesions.

Studied the social behavior of adult male Wistar albino rats in 6 experiments following medial frontal (n = 20) or orbital frontal (n = 14) lesions. 34 Ss served as controls. While both lesion groups showed transient increases in emotionality, only the Ss with orbital frontal lesions showed changes in social behavior. They were more aggressive in male-male aggression and shock-induced aggression but failed to differ from controls on tests of gregariousness, territorial aggression, and predatory aggression. Data may provide support for C. M. Leonard's (1969) suggestion that the orbital frontal cortex of rats and monkeys is homologous. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Automatic and effortful processing in depression.

Automatic processes require few attentional resources, but effortful processes use attentional capacity. Research on cognitive processing by depressed individuals is reviewed and the following is concluded: (1) Depression interferes with effortful processing. The degree of interference is determined by the degree of effortfulness of the task, the severity of depression, and the valence of the stimulus material to be processed. (2) Depression interferes only minimally with automatic processes. Hypothetical causal mechanisms for interference in effortful processes by depression, whether interference in effortful processing is unique to depression or characteristic of psychopathology in general, and whether negative automatic thoughts are associated with current depression or depression proneness also are addressed. The effortful–automatic perspective has implications for understanding depressive clinical features, treating depression, and conducting future research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Serial position curves in rats: Automatic versus effortful information processing.

20 male Long-Evans rats were trained to remember lists of 5 arms on an 8-arm radial maze. A forced-choice memory recognition test procedure was used that required the S to choose between an arm previously visited during the study phase of a trial and an arm not visited. To receive additional food reinforcement, 10 Ss were required to return to the previously visited arm (win-stay) and 10 Ss were required to choose the novel, unvisited arm (win-shift). In this way, a direct comparison was made between the serial position curves (SPCs) generated by win-stay trained and win-shift trained Ss. Only win-stay trained Ss produced the classical U-shaped SPC, which included significant primacy and recency effects. Win-shift Ss showed only recency effects. Findings are discussed in terms of differential processing requirements for the 2 procedures. It is suggested that the win-stay rule necessitates relatively more effortful, elaborative processing than does the win-shift rule, which is used automatically. (41 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Normal conditioning inhibition and extinction of freezing and fear-potentiated startle following electrolytic lesions of medial prefrontal cortex in rats.

The authors investigated the role of medial prefrontal cortex (mPFC) in the inhibition of conditioned fear in rats using both Pavlovian extinction and conditioned inhibition paradigms. In Experiment 1, lesions of ventral mPFC did not interfere with conditioned inhibition of the fear-potentiated startle response. In Experiment 2, lesions made after acquisition of fear conditioning did not retard extinction of fear to a visual conditioned stimulus (CS) and did not impair "reinstatement" of fear after unsignaled presentations of the unconditioned stimulus. In Experiment 3, lesions made before fear conditioning did not retard extinction of fear-potentiated startle or freezing to an auditory CS. In both Experiments 2 and 3, extinction of fear to contextual cues was also unaffected by the lesions. These results indicate that ventral mPFC is not essential for the inhibition of fear under a variety of circumstances. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition of conditional associations and operant delayed spatial response alternation: Effects of lesions in the medial prefrontal cortex.

8 male rats received bilateral lesions of the medial prefrontal cortex, another 8 rats were control operated. Three weeks after surgery, they were exposed to an autoshaping procedure in which the insertion of a lever into the experimental chamber (conditioned stimulus) always preceded the delivery of a response-independent food pellet (unconditioned stimulus). Ss with lesions acquired this conditional association faster than control. Ss as evidenced by the fact that they were more likely than control Ss to contact the conditioned stimulus at higher rates. Locomotor activity, observed in a standard open-field preceding autoshaping sessions, decreased for both groups of Ss with repeated exposure to the open-field, whereas differences between groups were not observed. Ss were also exposed to an operant delayed spatial response alternation procedure in which they were required to alternate responding between two levers that were inserted into the experimental chamber after delay intervals of either 5, 10, or 20 s had elapsed. Alternation response accuracy of Ss with lesions and control Ss decreased as a function of the duration of the delay interval, but control-operated Ss responded more accurately at each interval duration. Response accuracy increased with prolonged training for both groups of Ss, but faster for control than for Ss with lesions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some tests of response habituation in rats with discrete lesions to the orbital or medial frontal cortex.

Studied the inter- and intrasession habituation rates of 33 male albino rats with aspiration lesions to the medial frontal or orbital frontal cortex or with no lesions in 2 situations (open field and investigatory head poke). Medial frontal lesions produced impaired intrasession habituation in both test situations, while orbital frontal lesions failed to alter significantly intrasession habituation in either situation, and neither lesion significantly altered intersession habituation rates. Data confirm earlier reports of functional dissociation within the prefrontal cortex of the rat and suggest that only the medial frontal cortex is involved in the habituation process. (French summary) (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Working memory and work with memory: visual-spatial and further components of processing

Empirical and theoretical evidence for the concept of working memory is considered. We argue that the major weakness of this concept is its loose connection with the knowledge about background perceptive and cognitive processes. Results of two relevant experiments are provided. The first study demonstrated the classical chunking effect in a speeded visual search and comparison task, the proper domain of a large-capacity very short term sensory store. Our second study was a kind of extended levels-of-processing experiment. We attempted to manipulate visual, phonological, and (different) executive components of long-term memory in the hope of finding some systematic relationships between these forms of processing. Indeed, the results demonstrated a high degree of systematicity without any apparent need for a concept such as working memory for the explanation. Accordingly, the place for working memory is at all the interfaces where our metacognitive strategies interfere with mostly domain-specific cognitive mechanisms. Working memory is simply our work with memory.     

Place memory is intact in rats with perirhinal cortex lesions.

Two experiments compared the effects of bilateral lesions of the hippocampal formation (HPC) or perirhinal cortex (PRh) on rats' performance of an allocentric spatial working memory task—delayed matching-to-place (DMTP) in a water maze. DMTP trials consisted of paired swims, and the hidden platform was moved to a new location on each trial. Performance was assessed with intervals between the first and second swim (i.e., retention delays) of 4, 30, 120, and 300 s. The rats received extensive presurgery training in Experiment 1 and no presurgery training in Experiment 2. In both experiments, rats with HPC lesions displayed DMTP deficits at all delays, taking longer and swimming farther to find the platform on the second swims than did sham-operated controls. By contrast, rats with PRh lesions displayed normal DMTP acquisition and performance. The results suggest that, unlike the functions of HPC, those of PRh are not critical for allocentric spatial working memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Functional connections between medial prefrontal cortex and caudate-putamen in brain-stimulation reward of rats.

Rats were trained to self-stimulate for trains of cathodal pulses delivered via electrodes placed in the medial prefrontal cortex (MPFC) and caudate-putamen (CPu). When the pulses were delivered via 9 ipsilateral MPFC and CPu sites alternately, summation varied from 13% to 40%. However, the overall summation for 2 contralateral MPFC-CPu pairs was 5%, thus indicating a greater integration of ipsilateral than contralateral reward signals. When the interval between alternate pulses decreased in 4 of the 9 ipsilateral pairs, the summation also decreased, an outcome consistent with collision of action potentials passing between the MPFC and CPu sites. The size of the collision effect ranged from 15% to 33%. Estimates of conduction velocity varied between 0.4 to 5.4 m/sec, with a 1.7 m/sec average. According to these values, the neurons connecting the MPFC and CPu self-stimulation sites appear to be slower than the ones that have been shown to link reward fibers that course between posterior brain regions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Strategic processing and memory for temporal order in patients with frontal lobe lesions.

This study evaluated whether deficits in memory for temporal order in patients with frontal lobe lesions result from impaired automatic encoding of temporal information or are secondary to deficits in effortful processes, such as the use of organizational strategies and control of interference. Patients with lesions in the dorsolateral prefrontal cortex and control participants were tested on temporal order reconstruction of semantically related and unrelated word lists learned under intentional or incidental conditions. Memory for temporal order in patients with frontal lobe lesions was sensitive to semantic relatedness but not to intention to learn. Tests of item free recall and recognition using similar encoding manipulations indicated that order performance in these patients was dissociable from item memory. Results indicate that automatic processing of temporal information is intact in patients with frontal lobe lesions but that strategic processing of this information is impaired. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Medial septal lesions in rats produce permanent deficits for strategy selection in a spatial memory task.

Rats with medial septal (MS) lesions have been shown to consistently use a stereotypic response strategy rather than a nonstereotypic spatial learning strategy when solving a radial maze task. The present study examined the long-term effects of MS lesions on spatial memory performance to determine whether MS lesions permanently impair rats from using a nonstereotypic strategy. Male rats, initially trained on a radial maze, were given either MS or sham surgeries and were subsequently retested on the maze. Consistent with previous studies, all Ss with MS lesions used a stereotypic strategy during the postoperative retest. However, when placed through a series of retraining phases that required the S to use a nonstereotypic strategy to solve the task, none of the MS Ss could solve the task. These results indicate that lesions of the MS produce permanent spatial memory deficits that cannot be restored through extensive behavioral training. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Functional consequences of embryonic neocortex transplanted to rats with prefrontal cortex lesions.

In four experiments, we reexamined the recent report by Labbe, Firl, Mufson, and Stein (1983) that fetal cortical tissue transplanted to an aspirative prefrontal cortical cavity in rats can ameliorate the learning impairments induced by the aspirative lesions. Healthy surviving grafts from young (E16) embryonic donors had no immediate effects on the rats' impairments in T-maze alternation, spatial navigation in the Morris swimming pool task, or locomotor activity, and they produced even greater impairments than the lesions alone when all three tests were conducted after longer (3–5 month) survival periods. Grafts taken from older (E21) donors did produce a short-lasting improvement in the T-maze alternation performance, replicating the previous report. However, this effect was not seen in the other two behavioral tests; the grafts survived poorly, and the beneficial effect was no longer apparent in the long-term tests. It is concluded that (a) functional benefits of embryonic cortical grafts are dependent on a precise combination of conditions rather than being a general phenomenon, and (b) the short-lasting recovery in delayed alternation performance is attributable to diffuse influences of the embryonic tissue on the lesioned host brain rather than to a reconnection of damaged circuitries. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of the medial prefrontal cortex in the play fighting of rats.

Although decorticated rats are able to engage in play, their play is abnormal in three ways. First, decorticates do not display the normal, age-related shifts in defensive strategies during development. Second, decorticates do not modify their defensive tactics in response to the social identity of their partners. Third, decorticates display a global shift in defensive tactics from more complex to less complex strategies. It has been shown that lesions of the motor cortex (MC) selectively produce the abnormal developmental effects on play, and that lesions of the orbitofrontal cortex (OFC) selectively produce the deficits in behavioral discrimination between social partners. In the current set of experiments, we demonstrate that lesions of the medial prefrontal cortex (mPFC) produce the shift from more complex to less complex defensive tactics, while leaving intact the age-related and partner-related modulation of defensive strategies. Thus, we have evidence for a triple dissociation of function between the MC, the OFC, and the mPFC with respect to social play behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of prefrontal cortex and striatal output systems in short-term memory deficits associated with ageing, basal forebrain lesions, and cholinergic-rich grafts.

Reviews studies demonstrating that cholinergic grafts can ameliorate some deficits in aged animals and in animals with basal forebrain or fimbria-fornix lesions. Additional experiments were conducted with 35 male rats in Exp 1 and 26 female rats in Exp 2. Lesions of the motor and parietal zones of dorsolateral neocortex did not affect Ss' performance on a delayed-matching-to-performance task. Transection of the fimbria-fornix disrupted task performance in a delay-dependent manner, suggesting a specific disruption of short-term retention. Data confirm involvement of the medial prefrontal cortex and its ventral striatal outputs in performance of the task and in age-related deficits in short-term memory. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Double dissociation of egocentric and allocentric space following medial prefrontal and parietal cortex lesions in the rat.

Animals with medial prefrontal cortex or parietal cortex lesions and sham-operated and non-operated controls were tested for the acquisition of an adjacent arm task that accentuated the importance of egocentric spatial lateralization and a cheese board task that accentuated the importance of allocentric spatial localization. Results indicated that relative to controls, animals with medial prefrontal cortex lesions are impaired on the adjacent arm task but displayed facilitation on the cheese board task. In contrast, relative to controls, rats with parietal cortex lesions are impaired on the cheese board task but show no impairment on the adjacent arm task. The data suggest a double dissociation of function between medial prefrontal cortex and parietal cortex in terms of coding of egocentric versus allocentric spatial information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sidman avoidance performance and response suppression in rats with septal lesions.

Ran 10 male Long-Evans hooded rats with septal lesions on 3 Sidman avoidance schedules which differed only in length of response-shock (RS) interval. Of the 5 septal Ss run on postoperative acquisition, all emitted responses at lower rates than the 5 controls, maintained shock rates equivalent to those of controls, and distributed their responses more efficiently than controls. Successive reductions in length of the RS interval produced suppression of avoidance responding in all Ss. However, for septal Ss, more sessions and a shorter RS interval were required to suppress avoidance responding. Performance of 5 Ss given preoperative experience was not changed by septal ablation. Both the lower response rate and the difficulty in suppressing avoidance responding are interpreted in terms of a deficit related to acquisition of stimulus control by conditioned aversive stimuli. (15 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex-related differences in cortical function after medial frontal lesions in rats.

The effects of sex on the performance of 4 spatial mazes (Morris water task, landmark task, radial arm maze, and egocentric radial arm maze) were studied in male and female rats given medial frontal lesions. Operated rats from both sexes were impaired at all of the tasks, but the frontal males were much less impaired than frontal females on the Morris task and the radial arm maze, both of which require animals to use multiple visual-spatial cues for their successful solution. Males also performed better on the egocentric maze. In contrast, frontal females performed better than frontal males at the landmark task, which is best solved by using a single spatial cue. The only sex difference in unoperated rats was a small advantage for females on the egocentric task. The sex differences may reflect an underlying difference in cortical organization or a differential response to cortical lesion in males and females. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Habituation of startle response, lick suppression, and exploratory behavior in rats with hippocampal lesions.

34 male albino Holtzman rats with bilateral hippocampal lesions (HLs) and 22 controls with neocortical lesions (NLs) were compared on the habituation of lick suppression and startle response. Ss with HLs showed no consistent differences from controls on any measure within these 2 response systems. Ss with HLs showed significant retention of habituation over periods of 24 hrs and 21 days. Experimental and control differences were not revealed when stimulation was presented on a 1-sec interstimulus interval. None of these results varied with the extent of the HLs, which ranged from relatively small lesions restricted to the dorsal hippocampus to large lesions that damaged the hippocampus in its dorsal, posterior, and ventral aspects. In contrast to the startle response and lick suppression results, HLs significantly disrupted Y-maze exploratory behavior, and the disruption was directly related to the extent of hippocampal damage. Data suggest that the hippocampus is not involved in any important way in the control of either short- or long-term habituation of elicited, reflex-like behaviors but is importantly involved in the control of emitted, exploratory behaviors. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of retroactive interference in the spatial memory of normal rats and rats with hippocampal lesions.

Studied the importance of retroactive interference (RI) in memory for spatial locations by using a 12-arm radial maze and a standard RI paradigm. 26 male albino Sprague-Dawley rats in the RI condition first learned to choose 4 of the 12 arms, followed by training to a 2nd set of 4 arms. In the control condition for interference, Ss learned the 1st set of arms but were not trained to approach the 2nd set. Thereafter, Ss in each interference condition were assigned to groups (hippocampal, cortical control, or unoperated control), the operations were carried out, and then all Ss were tested for retention of the set of arms learned first. Contrary to predictions of the cognitive map theory (J. O'Keefe and L. Nadel, 1978), RI was found in control Ss. The severe memory deficit found in hippocampals was not influenced by the interference variable. In addition to impaired performance early in relearning, Ss with hippocampal lesions continued to make many errors throughout the 10 wks of testing, including choices to unbaited arms and repeated entries into baited arms. However, hippocampals eventually learned not to reenter unbaited arms. Data indicate a deficit in the selection and utilization of sets of responses and are interpreted as implicating the hippocampus in retrieval processes. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)