Implicit memory for nonverbal associations

A color-naming priming task was used to examine implicit memory for new nonverbal associations. Implicit memory was observed for associations between words and colors and between abstract shapes and colors. The authors also asked whether nonverbal association priming might occur more readily than verbal association priming. Colored compound nonwords were used as stimuli, and participants were asked to attend either to the 2 syllables of the compound nonword or to the compound nonword and the color in which it was printed. The authors found that the association formed depended on which attributes of the stimuli were attended to and were not more readily formed for nonverbal material. The results demonstrate that tasks that encourage unitization between the elements to be associated facilitate associative priming.     

Involvement of retrosplenial cortex in forming associations between multiple sensory stimuli.

The retrosplenial cortex (RSP) is highly interconnected with medial temporal lobe structures, yet relatively little is known about its specific contributions to learning and memory. One possibility is that RSP is involved in forming associations between multiple sensory stimuli. Indeed, damage to RSP disrupts learning about spatial or contextual cues and also impairs learning about co-occurring conditioned stimuli (CSs). Two experiments were conducted to test this notion more rigorously. In Experiment 1, rats were trained in a serial feature negative discrimination task consisting of reinforced presentations of a tone alone and nonreinforced serial presentations of a light followed by the tone. Thus, in contrast to prior studies, this paradigm involved serial presentation of conditioned stimuli (CS), rather than simultaneous presentation. Rats with damage to RSP failed to acquire the discrimination, indicating that RSP is required for forming associations between sensory stimuli regardless of whether they occur serially or simultaneously. In Experiment 2, a sensory preconditioning task was used to determine if RSP was necessary for forming associations between stimuli even in the absence of reinforcement. During the first phase of this procedure, one auditory stimulus was paired with a light while a second auditory stimulus was presented alone. In the next phase of training, the same light was paired with food. During the final phase of the procedure both auditory stimuli were presented alone during a single session. Control, but not RSP-lesioned rats, exhibited more food cup behavior following presentation of the auditory cue that was previously paired with light compared with the unpaired auditory stimulus, indicating that a stimulus-stimulus association was formed during the first phase of training. These results support the idea that RSP has a fundamental role in forming associations between environmental stimuli. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Hippocampal seizures disrupt working memory performance but not reference memory acquisition.

The effect of hippocampal seizures in rats was assessed in two spatial memory tasks: The reference memory task was a simultaneous two-choice discrimination in a T-maze. The working memory task was a delayed conditional discrimination in a radial arm maze. In each task the hippocampus of each rat was stimulated to seizure after the presentation of the information to be remembered. In the reference memory task, hippocampal seizures did not impair acquisition, whether the stimulation was given immediately after or 4 hr after the presentation of the stimuli to be remembered. In the working memory task, hippocampal seizures did impair performance in a group of the same rats. These results support the distinction between a trial-dependent working memory system that requires hippocampal function and a trial-independent memory system that does not depend on hippocampal function. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of dorsal versus ventral hippocampal, total hippocampal, and parietal cortex lesions on memory for allocentric distance in rats.

To test for the contribution of the parietal cortex and hippocampus to memory for allocentric spatial cues, the authors trained rats on a go/no-go task that required the rat to remember the distance between two visual cues. Total hippocampal lesions impaired working-memory representation for allocentric distance, whereas parietal cortex lesions resulted in only a transient impairment. In a second experiment, neither hippocampal nor parietal cortex lesions impaired allocentric distance discrimination. A third experiment showed that both the dorsal and ventral areas of the hippocampal formation must be destroyed to impair working memory for allocentric distance information. There appears to be a dissociation between the hippocampus and parietal cortex in mediating memory for allocentric distance information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preserved negative patterning and impaired spatial learning in pigeons (Columba livia) with lesions of the hippocampus.

Pigeons (Columba livia) with bilateral electrolytic lesions of the hippocampus and area parahippocampalis were compared with control pigeons on 2 tasks: negative patterning and delayed spatial alternation. Negative patterning demands configural stimulus representations for its successful solution. The only effect of hippocampal lesions on this task was an increased response rift to the rewarded stimuli. On the delayed spatial alternation task, hippocampal birds showed deficits relative to controls. Differences in the results of prior studies on negative patterning appear to be due to different response requirements to the nonreinforced stimuli. These results are consistent with prior work with rats and suggest that the avian hippocampus is essential for spatial memory and response inhibition but is not involved in configural learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Thinking within the box: The relational processing style elicited by counterfactual mind-sets.

By comparing reality to what might have been, counterfactuals promote a relational processing style characterized by a tendency to consider relationships and associations among a set of stimuli. As such, counterfactual mind-sets were expected to improve performance on tasks involving the consideration of relationships and associations but to impair performance on tasks requiring novel ideas that are uninfluenced by salient associations. The authors conducted several experiments to test this hypothesis. In Experiments 1a and 1b, the authors determined that counterfactual mind-sets increase mental states and preferences for thinking styles consistent with relational thought. Experiment 2 demonstrated a facilitative effect of counterfactual mind-sets on an analytic task involving logical relationships; Experiments 3 and 4 demonstrated that counterfactual mind-sets structure thought and imagination around salient associations and therefore impaired performance on creative generation tasks. In Experiment 5, the authors demonstrated that the detrimental effect of counterfactual mind-sets is limited to creative tasks involving novel idea generation; in a creative association task involving the consideration of relationships between task stimuli, counterfactual mind-sets improved performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Associative structure of fear memory after basolateral amygdala lesions in rats.

The authors have recently demonstrated that rats with basolateral amygdala (BLA) lesions acquire Pavlovian fear conditioning after overtraining. However, it is not known whether the associative basis of Pavlovian fear memory acquired by rats with BLA lesions is similar to that of intact rats. Associations are typically formed between the conditional (CS) and unconditional (US) stimuli (stimulus-stimulus; S-S), although it is possible for stimuli to enter into association with the responses they produce (stimulus-response; S-R). Indeed, the central nucleus of the amygdala, which is essential for fear conditioning in rats with BLA lesions, may mediate S-R associations in some Pavlovian tasks. The authors therefore used a postconditioning US inflation procedure (i.e., exposure to intense footshock USs) to assess the contribution of S-S associations to fear conditioning after overtraining in rats with BLA lesions. In Experiment 1, intact rats that were overtrained and later inflated displayed elevated freezing levels when tested, indicating that S-S associations contribute to overtrained fear memories. Interestingly, neither neurotoxic BLA lesions nor temporary inactivation of the BLA during overtraining prevented the inflation effect (Experiment 2 and 3, respectively). These results reveal that S-S associations support Pavlovian fear memories after overtraining in both intact rats and rats with BLA lesions, and imply that the central nucleus of the amygdala encodes CS-US associations during fear conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Critical determinants of nonspatial working memory deficits in rats with conventional lesions of the hippocampus or fornix.

Rats with conventional lesions of the hippocampus or fornix were compared postoperatively with controls on nonspatial memory tasks. Neither lesion impaired delayed matching-to-sample (DMS) performance in a discrete-trial task involving "pseudo-trial-unique" complex stimuli. An impairment emerged if a single pair of complex stimuli was used throughout each day's session, and the greatest impairment was obtained with the use of a single pair of less complex stimuli throughout each day's test. Transfer to continuous DMS task with no explicit intertrial interval produced a different pattern because both lesion and control levels of performance were depressed when 2 complex stimuli were used repeatedly. A final, separate discrimination learning experiment showed that hippocampectomized rats readily discriminated between the stimuli associated with the greatest lesion-induced DMS deficit. Hippocampal dysfunction thus produces clear deficits on nonspatial memory tasks under appropriate test conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of Hippocampus and Medial Caudate Nucleus Lesions on Memory for Direction Information in Rats.

A delayed matching-to-sample task was designed to assess memory for direction information in rats. During the study phase, rats traversed a maze arm oriented in 1 of 3 directions. After a delay period, a test phase was presented that required a choice between the study phase direction and a foil direction. Once rats reached a learning criterion, probe trials suggested that normal rats favor the use of direction, rather than turning response, information and use vestibular feedback. Rats were then given hippocampus, medial caudate nucleus (MCN), or cortical control lesions. Unlike control rats, those with hippocampus and MCN lesions exhibited marked impairments when retested. However, all rats were able to learn a direction discrimination task. These results suggest that the hippocampus and MCN support processes associated with short-term memory for direction information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of selective immunotoxic lesions of medial septal cholinergic cells on spatial working and reference memory.

The effect of injection into the medial septum of a toxin selective for cholinergic neurons, 192 IgG-saporin, was examined in rats trained to perform 2 versions of the radial 8-arm maze task. Rats were first trained to perform a task with varying delays (0, 1, 2 min) imposed between the 4th correct arm choice and access to all 8 arms. Lesioned rats made significantly more errors in the first 4 choices compared with controls and significantly more errors after delays; however, this effect was not delay dependent. Rats were then trained on a different version of this 8-arm maze task in which they learned to avoid 2 arms that were never baited. There was no treatment effect on acquisition of this task. These data are consistent with the hypothesis that the cholinergic projection to the hippocampus facilitates the acquisition of information into the system responsible for short-term memory for locations visited (spatial working memory) but is not involved in retention of this information. It also appears to play no role in either the acquisition or retention of place-nonreward associations (spatial reference memory). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential roles of dorsal hippocampal subregions in spatial working memory with short versus intermediate delay.

In order to determine the role of subregions of the hippocampus in spatial working memory, this study combined selective neurotoxic lesions of the hippocampal subregions with a simple delayed nonmatching-to-place task on a radial maze in rats. Lesions of the dentate gyrus or the CA3, but not the CA1, subregion of the hippocampus induced a deficit in the acquisition of the task with short-term delays (i.e., 10 sec) and impaired performance of the task in a novel environment. All subregional lesions produced sustained impairment in performing the task with intermediate-term delays (i.e., 5 min) when rats were tested in a familiar environment. The results suggest a dynamic interaction among the dorsal hippocampal subregions in processing spatial working memory, with the time window (i.e., delay) of a task recognized as an essential controlling factor. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of familiarity and unitization on new-association priming.

The role of familiarity and stimulus unitization was examined for nonverbal associations. Implicit memory was tested using a color-naming task. In 2 experiments spatially separated words, novel shapes, or nonwords and colors were presented, and the encoding instructions encouraged their unitization. New-association priming occurred between words and colors but not between abstract shapes and colors or between nonwords and colors. The results suggest that new-association priming occurs for familiar stimuli that are not physically integrated. However, when the stimuli are neither familiar nor unitized, new-association priming does not occur. It is possible that during encoding, memory representations are activated. If the stimuli are neither familiar nor unitized, then these processes must be carried out at study at the expense of learning of the associations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Involvement of the retrosplenial cortex in processing multiple conditioned stimuli.

Lesions of retrosplenial cortex (RSP) disrupt spatial and contextual learning, suggesting that RSP may have a fundamental role in processing overlapping, or simultaneously presented stimuli. If so, then RSP lesions might also be expected to disrupt learning that requires the concurrent processing of phasic conditioned stimuli. In Experiment 1, rats were trained in a compound feature negative discrimination task in which a tone was presented and immediately followed by food on some trials, while on other trials a visual stimulus was simultaneously presented along with the tone and not reinforced. Normal rats learned to discriminate between the trials but RSP-lesioned rats exhibited low levels of conditioning on both types of trials. Experiment 2 demonstrated that this effect was not simply due to a general inability to form associations, since RSP-lesioned rats exhibited normal responding when the visual stimulus was presented alone and paired with food. These findings support the view that RSP has an important role in learning that involves the processing of simultaneously presented stimuli and have implications for understanding the functional relationship between the hippocampus and RSP. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Von Restorff effect in visual object recognition memory in humans and monkeys. The role of frontal/perirhinal interaction

This study reports the development of a new, modified delayed matching to sample (DMS) visual recognition memory task that controls the relative novelty of test stimuli and can be used in human and nonhuman primates. We report findings from normal humans and unoperated monkeys, as well as three groups of operated monkeys. In the study phase of this modified paradigm, subjects studied lists of two-dimensional visual object stimuli. In the test phase each studied object was presented again, now paired with a new stimulus (a foil), and the subject had to choose the studied item. In some lists one study item (the novel or isolate item) and its associated foil differed from the others (the homogenous items) along one stimulus dimension (color). The critical experimental measure was the comparison of the visual object recognition error rates for isolate and homogenous test items. This task was initially administered to human subjects and unoperated monkeys. Error rates for both groups were reliably lower for isolate than for homogenous stimuli in the same list position (the von Restorff effect). The task was then administered to three groups of monkeys who had selective brain lesions. Monkeys with bilateral lesions of the amygdata and fornix, two structures that have been proposed to play a role in novelty and memory encoding, were similar to normal monkeys in their performance on this task. Two further groups--with disconnection lesions of the perirhinal cortex and either the prefrontal cortex or the magnocellular mediodorsal thalamus--showed no evidence of a von Restorff effect. These findings are not consistent with previous proposals that the hippocampus and amygdala constitute a general novelty processing network. Instead, the results support an interaction between the perirhinal and frontal cortices in the processing of certain kinds of novel information that support visual object recognition memory.     

Modulation of the Impairment of Hippocampectomized Rats on the Radial-Arm Maze Cue Task by Visual Characteristics and Subicular Damage.

Rats with N-methyl-D-aspartate lesions of the hippocampus that partially damaged the subiculum and controls were trained on 2 versions of the radial-arm maze cue task, with either proximal or distal visual stimuli. In Experiment 1, the relative positions of the stimuli varied across trials. Lesioned rats were impaired when trained on the distal version, as opposed to transiently slowed down when trained on the proximal version. In Experiment 2, the relative positions of the stimuli were fixed throughout training. Lesioned rats were impaired when trained on the distal or the proximal version. Further analyses showed that combined damage to the hippocampus and the subiculum was required to impair performance in the proximal, but not the distal, version. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interference between cognitive skills.

This study used a novel task, clock arithmetic, and a classic A–B/A–Br transfer design to investigate the presence of interference between cognitive skills. The A–B/A–Br design required participants to first learn problem-to-answer associations during training and then to learn new pairings between the same problems and answers during transfer. The associations learned during training interfered with those learned during transfer, as measured by slowed reaction times to emit the correct response, failures to retrieve any response, and intrusion errors. Interference persisted even after a 1-week retention interval and was especially prevalent during the warm-up period at the beginning of the retention test. The use of the A–B/A–Br design indicates that whether an incorrect answer retrieved from memory is emitted as a response depends on whether the intrusion is recognized as inappropriate for the current task. The long-term memory for cognitive skills means that attempts to learn new responses to old stimuli will be plagued by persistent intrusion errors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Eyeblink classical conditioning: Hippocampal formation is for neutral stimulus associations as cerebellum is for association–response.

Extensive evidence has been amassed that the cerebellum, hippocampus, and associated circuitry are activated during classical conditioning of the nictitating membrane/eyeblink response. In this article, the authors argue that the cerebellum is essential to all eyeblink classical conditioning paradigms. In addition, the septohippocampal system plays a critical role when the classical conditioning paradigm requires the formation of associations in addition to the simple association between the conditioned and unconditioned stimuli. When only a simple conditioned stimulus–unconditioned stimulus association is needed, the septohippocampal system has a more limited, modulatory role. The neutral stimulus association versus simple association–response distinction is one of the ways in which declarative or relational memory can be separated from nondeclarative or nonrelational memory in classical conditioning paradigms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Arbitrary associations in animals: What can paired associate recall in rats tell us about the neural basis of episodic memory? Theoretical comment on Kesner, Hunsaker, & Warthen (2008).

Detailed memories for unique episodes from an individual's past can be triggered, often effortlessly, when that individual is exposed to a stimulus that was present during the original event. The aim of Kesner et al. (see record 2008-17011-003) is to understand the neural basis of memory encoding that supports this cued recall of episodic memories. Kesner and colleagues make novel use of an object-place paired-associate task for rats to provide evidence for a critical role of dorsal CA3 in certain aspects of episodic memory encoding. Using one-trial cued recall versions of the task they show that when rats are cued with an object stimulus, they can be trained to revisit the location in which the object appeared previously. Conversely, when rats are cued with a location, they can learn to choose the object with which it was associated. Rats with dorsal CA3 lesions are severely impaired at these tasks. These data are consistent with the theory that the autoassociative network in CA3 supports the rapid formation of novel associations and may allow pattern completion--the phenomenom whereby a subset of the cues present at an encoding event triggers recall of the whole event. Although flexible recall of arbitrary associations is not fully demonstrated, the study contributes 2 novel behavioral tasks to the previously limited repertoire for studying paired associate recall in rats. It also builds on previous data to specify the role of the hippocampal CA3 subregion in cued recall--a critical aspect of episodic memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Role of Perirhinal Cortex in Visual Discrimination Learning for Visual Secondary Reinforcement in Rats.

Perirhinal cortex in monkeys has been thought to be involved in visual associative learning. The authors examined rats' ability to make associations between visual stimuli in a visual secondary reinforcement task. Rats learned 2-choice visual discriminations for secondary visual reinforcement. They showed significant learning of discriminations before any primary reinforcement. Following bilateral perirhinal cortex lesions, rats continued to learn visual discriminations for visual secondary reinforcement at the same rate as before surgery. Thus, this study does not support a critical role of perirhinal cortex in learning for visual secondary reinforcement. Contrasting this result with other positive results, the authors suggest that the role of perirhinal cortex is in "within-object" associations and that it plays a much lesser role in stimulus-stimulus associations between objects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Emotion and working memory: Evidence for domain-specific processes for affective maintenance.

Working memory is comprised of separable subsystems for visual and verbal information, but what if the information is affective? Does the maintenance of affective information rely on the same processes that maintain nonaffective information? The authors address this question using a novel delayed-response task developed to investigate the short-term maintenance of affective memoranda. Using selective interference methods the authors find that a secondary emotion-regulation task impaired affect intensity maintenance, whereas secondary cognitive tasks disrupted brightness intensity maintenance, but facilitated affect maintenance. Additionally, performance on the affect maintenance task depends on the valence of the maintained feeling, further supporting the domain-specific nature of the task. The importance of affect maintenance per se is further supported by demonstrating that the observed valence effects depend on a memory delay and are not evident with simultaneous presentation of stimuli. These findings suggest that the working memory system may include domain-specific components that are specialized for the maintenance of affective memoranda. (PsycINFO Database Record (c) 2010 APA, all rights reserved)