The amygdala but not the hippocampus is involved in pattern separation based on reward value

A total of 32 male Long-Evans rats were tested on a modified version of Flaherty, Turovsky, and Krauss's (1994) anticipatory contrast paradigm to assess pattern separation for reward value. Prior to testing, each rat received either a control, a hippocampal, or an amygdala lesion. In the home cage, each rat was allowed to drink a water solution containing 2% sucrose for 3 min followed by a water solution containing 32% sucrose for 3 min. Across 10 days of testing, the rats in each lesion group showed significantly increased anticipatory discriminability as a function of days. To assess the operation of a pattern separation mechanism, each rat was then tested using the same procedure except the 2% solution was followed by a 16% solution for 10 days and then by an 8% solution for 10 days. Control and hippocampal-lesioned rats continued to show high discriminability when the 2% solution was followed by a 16% solution; however, the amygdala-lesioned rats showed low anticipatory discriminability. On trials where the 2% sucrose solution was followed by an 8% sucrose solution, all groups showed low discriminability scores, suggesting that when two reward values are very similar even control animals are not able to separate the reward values in memory. However, the results of a preference task revealed that all groups can perceptually discriminate between a 2% and an 8% sucrose solution. The data suggest that the amygdala but not the hippocampus is involved in the separation of patterns based on reward value.     

Rho-associated kinase in the gustatory cortex is involved in conditioned taste aversion memory formation but not in memory retrieval or relearning

Rho-associated kinase (ROCK) is intimately involved in cortical neuronal morphogenesis. The present study explores the roles of ROCK in conditioned taste aversion (CTA) memory formation in gustatory cortex (GC) in adult rat. Microinjection of the ROCK inhibitor Y-27632 into the GC 30 min before CTA training or 10 min after the conditioned stimulus (CS) impaired long-term CTA memory (LTM) formation. ROCK inhibitor had no effect on taste aversion when injected before the first LTM test day and did not alter taste aversion on subsequent test days. Microinjection of ROCK inhibitor into GC 30 min before preexposure to the taste CS had no effect on latent inhibition of CTA learning suggesting that ROCK is involved in CS-US association rather than taste learning per se. Cumulatively, these results show that ROCK is needed for normal CTA memory formation but not retrieval, relearning or incidental taste learning.     

PKA and PKC are required for long-term but not short-term in vivo operant memory in Aplysia

We investigated the involvement of PKA and PKC signaling in a negatively reinforced operant learning paradigm in Aplysia, learning that food is inedible (LFI). In vivo injection of PKA or PKC inhibitors blocked long-term LFI memory formation. Moreover, a persistent phase of PKA activity, although not PKC activity, was necessary for long-term memory. Surprisingly, neither PKA nor PKC activity was required for associative short-term LFI memory. Additionally, PKA and PKC were not required for the retrieval of short- or long-term memory (STM and LTM, respectively). These studies have identified key differences between the mechanisms underlying nonassociative sensitization, operant reward learning, and LFI memory in Aplysia.     

Modulation of working, short- and long-term memory by nicotinic receptors in the basolateral amygdala in rats

Male Wistar rats were exposed to one-trial step-down inhibitory avoidance training using a 0.5 mA footshock. Through bilaterally implanted indwelling cannulae, they received bilateral 0.5 microL infusions of saline, mecamylamine (1.0 or 10.0 microg/side), or nicotine (0.6 or 3.0 microg/side) into the basolateral complex of the amygdaloid nucleus (BLA). Infusions were either 10 min before training (Experiment 1) or 4 min after training (Experiment 2). In Experiment 1, the animals were tested three times: first for working memory (WM) 5 s after training, then for short-term memory (STM) 90 min later, and finally for long-term memory (LTM) 24 h later. Mecamylamine depressed and nicotine enhanced WM, STM, and LTM. In Experiment 2, the treatments were given after WM was presumably over. Again, mecamylamine inhibited and nicotine enhanced STM and LTM. The results indicate that nAChRs in BLA participate in the regulation of WM formation and STM and LTM acquisition and consolidation.     

The real relationship between short-term memory and working memory

Storage-oriented memory span tasks with no explicit concurrent processing are usually referred as short-term memory (STM) tasks, whereas tasks involving storage plus concurrent processing requirements are designated as working memory (WM) tasks. The present study explores a question that remains unsolved: Do STM and WM tasks clearly tap distinguishable theoretical constructs? For that purpose, a large sample of 403 participants was tested through 12 diverse memory span tasks. Half of those tasks are widely accepted as measures of STM, whereas the other half measure WM. The results show that STM and WM share largely overlapping underlying capacity limitations, suggesting that all memory span tasks tap essentially the same construct. Some implications are discussed.     

The real relationship between short-term memory and working memory

Storage-oriented memory span tasks with no explicit concurrent processing are usually referred as short-term memory (STM) tasks, whereas tasks involving storage plus concurrent processing requirements are designated as working memory (WM) tasks. The present study explores a question that remains unsolved: Do STM and WM tasks clearly tap distinguishable theoretical constructs? For that purpose, a large sample of 403 participants was tested through 12 diverse memory span tasks. Half of those tasks are widely accepted as measures of STM, whereas the other half measure WM. The results show that STM and WM share largely overlapping underlying capacity limitations, suggesting that all memory span tasks tap essentially the same construct. Some implications are discussed.     

The reaction-time task-rule congruency effect is not affected by working memory load: further support for the activated long-term memory hypothesis

Previous studies claimed that task representation is carried out by the activated long-term memory portion of working memory (WM; Meiran and Kessler in J Exp Psychol Human Percept Perform 34:137–157, 2008). The present study provides a more direct support for this hypothesis. We used the reaction-time task-rule congruency effect (RT-TRCE) in a task-switching setup, and tested the effects of loading WM with irrelevant task rules on RT-TRCE. Experiment 1 manipulated WM load in a between-subject design. WM participants performed a color/shape task switching, while having 0, 1 or 3 numerical task rules as WM load. Experiment 2 used a similar load manipulation (1 or 3 rules to load WM) in a within-subject design. Experiment 3 extended these results by loading WM with perceptual tasks that were more similar to the shape/color tasks. The results show that RT-TRCE was not affected by WM load supporting the activated long-term memory hypothesis.     

Awareness is necessary for extracting patterns in working memory but not for directing spatial attention

The contents of working memory (WM) have predominantly been viewed as necessarily conscious. However, recent findings suggest otherwise. Here we investigate whether visual WM can represent subliminal stimuli, such that the positions of an invisible moving object can be extrapolated or learned about in terms of their task-relevant predictive power. We presented a moving cue subliminally and measured subjects' performance on an orientation-discrimination task at the naturally anticipated location on the cue's trajectory and at variably predictable off-trajectory locations. Our data show that orientation discriminability at the on-trajectory location was not significantly different from that at a nearby off-trajectory location. However, orientation discriminability at locations near the final position of the cue was significantly better than that at distal locations. This finding suggests that a moving object can still attract attention when presented subliminally. In contrast, the dynamic trajectory of the object and its task-relevant predictive patterns may not be monitored and maintained in visual WM. (PsycINFO Database Record (c) 2012 APA, all rights reserved).     

Assessing the associative deficit of older adults in long-term and short-term/working memory

Older adults exhibit a deficit in associative long-term memory relative to younger adults. However, the literature is inconclusive regarding whether this deficit is attenuated in short-term/working memory. To elucidate the issue, three experiments assessed younger and older adults' item and interitem associative memory and the effects of several variables that might potentially contribute to the inconsistent pattern of results in previous studies. In Experiment 1, participants were tested on item and associative recognition memory with both long-term and short-term retention intervals in a single, continuous recognition paradigm. There was an associative deficit for older adults in the short-term and long-term intervals. Using only short-term intervals, Experiment 2 utilized mixed and blocked test designs to examine the effect of test event salience. Blocking the test did not attenuate the age-related associative deficit seen in the mixed test blocks. Finally, an age-related associative deficit was found in Experiment 3, under both sequential and simultaneous presentation conditions. Even while accounting for some methodological issues, the associative deficit of older adults is evident in short-term/working memory. (PsycINFO Database Record (c) 2012 APA, all rights reserved).     

Visual short-term memory is not improved by training

A critical question in visual working or short-term memory (VSTM) research is whether the ability to remember briefly presented visual stimuli can be increased. Here we test whether VSTM for locations and shapes is improved by training that allows one to utilize another memory system, visual longterm memory (VLTM). Training was done by repeatedly presenting a subset of memory displays, creating long-term memory traces for these displays. Surprisingly, VSTM performance for repeated displays was not higher than for nonrepeated ones, even though participants recognized repeated displays on a forced-choice test given at the end of the experiment. We suggest that the fidelity of information held by VLTM is inferior to that of information held by VSTM and thus provides no additional benefit over what is extracted on the fly by VSTM.     

Spatial working memory load impairs signal enhancement, but not attentional orienting

The present study examined the effect of spatial working memory load on the attentional cuing effect. It is well-known that spatial working memory and spatial attention functionally overlap or share a common resource. Given this functional overlapping, it is possible that spatial working memory would also interact with the attentional cuing effect. Considering the distinction between channel selection and channel enhancement by attention (Prinzmetal, McCool, & Park, 2005), we expected that the interaction between spatial working memory and the cuing effect would differ with attentional processing type. Two experiments conducted with the spatial cuing paradigm showed that the magnitude of the cuing effect as measured by reaction time, reflecting channel selection, was uninfluenced by spatial working memory load. In contrast, spatial working memory load reduced the cuing effect as measured by accuracy, reflecting channel enhancement. These results suggest that spatial working memory load impairs signal enhancement by attention and does not influence attentional orienting per se. The interaction between spatial working memory and visual perception is also discussed.     

The role of short-term working memory in mental arithmetic

A series of experiments explored the role of information storage in working memory in performing mental arithmetic. Experiment 1 assessed the strategies people report for solving auditorily presented multidigit problems such as 325 + 46. As expected, all subjects reported breaking down the problems into a series of elementary stages, though there were considerable individual differences with regard to the order of their execution. Strategies of this type necessitate both the temporary storage of information and the mobilization of long-term knowledge. Experiments 2 and 3 examined the effects of delaying the output of individual partial results on calculation accuracy and showed that interim information is forgotten if it is not utilized immediately. Experiment 4 showed that forgetting the initial information is also a source of error and suggested that forgetting increases as a function of the number of calculation stages intervening between initial presentation and subsequent utilization of information. Two simple quantitative models were derived from a general task analysis, one of which assumed a decay process in working storage and the other no decay. The decay model gave a reasonable fit to data from Experiments 2–4, and in doing so it coped appreciably well with the effects of a large variety of task variables (e.g., carrying, the provision of written notes, calculation strategy, output order). The decay model is a tractable analysis of a complex task, and it is suggested that similar analyses may prove fruitful for other problem-solving activities which involve the use of working memory.     

Spatial working memory load affects counting but not subitizing in enumeration

The present study investigated whether subitizing reflects capacity limitations associated with two types of working memory tasks. Under a dual-task situation, participants performed an enumeration task in conjunction with either a spatial (Experiment 1) or a nonspatial visual (Experiment 2) working memory task. Experiment 1 showed that spatial working memory load affected the slope of a counting function but did not affect subitizing performance or subitizing range. Experiment 2 showed that nonspatial visual working memory load affected neither enumeration efficiency nor subitizing range. Furthermore, in both spatial and nonspatial memory tasks, neither subitizing efficiency nor subitizing range was affected by amount of imposed memory load. In all the experiments, working memory load failed to influence slope, subitizing range, or overall reaction time. These findings suggest that subitizing is performed without either spatial or nonspatial working memory. A possible mechanism of subitizing with independent capacity of working memory is discussed.     

The central amygdala nucleus via corticotropin-releasing factor is necessary for time-limited consolidation processing but not storage of contextual fear memory

The central nucleus of the amygdala (CeA) is traditionally portrayed in fear conditioning as the key neural output that relays conditioned information established in the basolateral amygdala complex to extra-amygdalar brain structures that generate emotional responses. However, several recent studies have questioned this serial processing view of the amygdalar fear conditioning circuit by showing an influence of the CeA on memory consolidation. We previously reported that inhibition of endogenous CeA secretion of corticotropin-releasing factor (CRF) at the time of contextual training effectively impaired fear memory consolidation. However, the time-dependent range of CeA CRF secretion in facilitating consolidation processing has not been examined. Therefore, to address this issue, we performed CeA site-specific microinjections of CRF antisense oligonucleotides (CRF ASO) at several post-training time intervals. Rats microinjected with CRF ASO at post-training intervals up to 24-h subsequently exhibited significant impairments in contextual freezing retention in contrast to animals treated 96-h after training. To further establish the validity of the results, CeA fiber-sparing lesions were made at two distinct post-training periods (24-h and 96-h), corresponding respectively to the temporal intervals when CeA CRF ASO administration disrupted or had no significant effects on memory consolidation. Similar to the CeA CRF ASO results, CeA lesions made 24-h, but not 96-h, after training induced significant freezing deficits in the retention test. In conclusion, the current results demonstrate: (1) an extended involvement of CeA CRF in contextual memory consolidation and (2) that contextual fear memory storage is not dependent on a functional CeA.     

Distinctive shapes benefit short-term memory for color associations, but not for color

In four experiments, we examined the effect of pairing colors with either homogeneous or heterogeneous shapes on a short-term memory task. In Experiment 1, we found no differences in color memory for displays in which colors were each associated with different shapes, paired with individual homogeneous shapes, or paired with heterogeneous shapes. In contrast, in Experiment 2, we found that when participants were asked to remember the specific pairings of colors, memory was improved for heterogeneous-shape displays. The benefit for heterogeneous shapes appears to be memorial, rather than one that occurs at the time of encoding (Experiment 3) or retrieval (Experiment 4). The present study suggests that distinctive shapes can be used to help bind color associations in visual short-term memory.     

Post-acquisition release of glutamate and norepinephrine in the amygdala is involved in taste-aversion memory consolidation

Amygdala activity mediates the acquisition and consolidation of emotional experiences; we have recently shown that post-acquisition reactivation of this structure is necessary for the long-term storage of conditioned taste aversion (CTA). However, the specific neurotransmitters involved in such reactivation are not known. The aim of the present study was to investigate extracellular changes of glutamate, norepinephrine, and dopamine within the rat amygdala using in vivo microdialysis during the acquisition and 1-h post-acquisition of CTA paradigm. Microdialysis monitoring showed a significant norepinephrine increase related to novel taste exposure and a glutamate increase after gastric malaise induction by i.p. LiCl administration. Interestingly, we found a spontaneous concomitant increase of glutamate and norepinephrine, but not dopamine, 45 min after conditioning, suggesting the presence of aversive learning-dependent post-acquisition signals in the amygdala. These signals seem to be involved in CTA consolidation process, since post-trial blockade of N-methyl-D-aspartate or β-adrenergic receptors impaired long- but not short-term memory. These data suggest that CTA long-term storage involves post-acquisition release of glutamate and norepinephrine in the amygdala.     

Perceptual expertise enhances the resolution but not the number of representations in working memory

Despite its central role in cognition, capacity in visual working memory is restricted to about three or four items. Curby and Gauthier (2007) examined whether perceptual expertise can help to overcome this limit by enabling more efficient coding of visual information. In line with this, they observed higher capacity estimates for upright than for inverted faces, suggesting that perceptual expertise enhances visual working memory. In the present work, we examined whether the improved capacity estimates for upright faces indicates an increased number of "slots" in working memory, or improved resolution within the existing slots. Our results suggest that perceptual expertise enhances the resolution but not the number of representations that can be held in working memory. These results clarify the effects of perceptual expertise in working memory and support recent suggestions that number and resolution represent distinct facets of working memory ability.