Prefrontal and hippocampal contributions to encoding and retrieval of spatial memory

The prefrontal cortex is thought to be critical for goal-directed action and the hippocampus is known to be importantly involved in spatial memory. Several studies have been suggestive of a role for the orbitofrontal cortex (OFC) in spatial navigation. However, the medial prefrontal cortex (mPFC) receives projections directly from the intermediate CA1 (iCA1) region of hippocampus and this link may be critical for spatial navigation. The purpose of the present investigation was to test the performance of rats receiving bilateral or disconnection infusions of lidocaine into OFC, mPFC, or iCA1 to determine the contribution of these structures to encoding and retrieval of spatial memory using the Hebb–Williams maze. A total of 92 male Long-Evans rats received chronic bilateral, contralateral, or ipsilateral implantation of cannulas into OFC, mPFC, or iCA1. Prior to testing on day 1 or day 2, subjects received central infusions of saline or lidocaine. The number of errors committed on the first five trials compared to the second five trials of day 1 was used to determine encoding, whereas retrieval was determined by comparing the second five trials of day 1 with the first five trials of day 2. The present findings suggest that mPFC and iCA1 are necessary and interact during encoding and retrieval; however, the OFC does not appear to be essential for either process. While the nature of the interaction between mPFC and iCA1 during encoding and retrieval is unclear, it may be supported by the integration of goals and spatial cues or strategy switching.     

Parietal lobe contributions to episodic memory retrieval

Although the parietal lobe is not traditionally thought to support declarative memory, recent event-related fMRI studies of episodic retrieval have consistently revealed a range of memory-related influences on activation in lateral posterior parietal cortex (PPC) and precuneus extending into posterior cingulate and retrosplenial cortex. This article surveys the fMRI literature on PPC activation during remembering, a literature that complements earlier electroencephalography data. We consider these recent memory-related fMRI responses within the context of classical ideas about parietal function that emphasize space-based attention and motor intention. We conclude by proposing three hypotheses concerning how parietal cortex might contribute to memory.     

Modes of cognitive control in recognition and source memory: Depth of retrieval

Recognition memory is usually regarded as a judgment based on trace strength or familiarity. But recognition may also be accomplished by constraining retrieval so that only sought after information comes to mind (source-constrained retrieval). We introduce amemory-for-foils paradigm that provides evidence for source-constrained retrieval in recognition memory (Experiment 1) and source memory (Experiment 2). In this paradigm, subjects studied words under deep or shallow encoding conditions and were given a memory test (recognition or source) that required them to discriminate between new items (foils) and either deep or shallow targets. A final recognition test was used to examine memory for the foils. In both experiments, foil memory was superior when subjects attempted to retrieve deep rather than shallow targets on the earlier test. These findings support a sourceconstrained retrieval view of cognitive control by demonstrating qualitative differences in the basis for memory performance.     

Modeling hippocampal and neocortical contributions to recognition memory: a complementary-learning-systems approach

The authors present a computational neural-network model of how the hippocampus and medial temporal lobe cortex (MTLC) contribute to recognition memory. The hippocampal component contributes by recalling studied details. The MTLC component cannot support recall, but one can extract a scalar familiarity signal from MTLC that tracks how well a test item matches studied items. The authors present simulations that establish key differences in the operating characteristics of the hippocampal-recall and MTLC-familiarity signals and identify several manipulations (e.g., target-lure similarity, interference) that differentially affect the 2 signals. They also use the model to address the stochastic relationship between recall and familiarity and the effects of partial versus complete hippocampal lesions on recognition.     

Simple and associative recognition memory in the hippocampal region

Although it is well established that the hippocampal region is involved in the formation of declarative memory, the exact nature of its involvement is unclear. One view is that the hippocampal region is involved only in tasks that require the formation or use of associations. According to this view, the hippocampal region is not involved in traditional tests of recognition memory. An alternative view is that the hippocampal region combines and extends the processing carried out by structures in the parahippocampal gyrus and that it is involved in all forms of declarative memory, including recognition memory. Using event-related functional magnetic resonance imaging (fMRI), we observed hippocampal activity during both traditional and associative recognition memory tasks. Critically, the hippocampal region was no more active in the associative recognition task than in the traditional recognition task.     

The interplay of trait worry and trait anxiety in determining episodic retrieval: The role of cognitive control

Worrying is a key concept in describing the complex relationship between anxiety and cognitive control. On the one hand, cognitive control processes might underlie the specific tendency to engage in worrying (i.e., trait worry), conceptualized as a future-oriented mental problem-solving activity. On the other hand, the general tendency to experience the signs and symptoms of anxiety (i.e., trait anxiety) is suggested to impair cognitive control because worrisome thoughts interfere with task-relevant processing. Based on these opposing tendencies, we predicted that the effect of the two related constructs, trait anxiety and trait worry, might cancel out one another. In statistics, such instances have been termed suppressor situations. In four experiments, we found evidence for such a suppressor situation: When their shared variance was controlled, trait worry was positively whereas trait anxiety was negatively related to performance in a memory task requiring strategic, effortful retrieval. We also showed that these opposing effects are related to temporal context reinstatement. Our results suggest that trait worry and trait anxiety possess unique sources of variance, which differently relate to performance in memory tasks requiring cognitive control.     

Temporal contexts: filling the gap between episodic memory and associative learning

People can create temporal contexts, or episodes, and stimuli that belong to the same context can later be used to retrieve the memory of other events that occurred at the same time. This can occur in the absence of direct contingency and contiguity between the events, which poses a challenge to associative theories of learning and memory. Because this is a learning and memory problem, we propose an integrated approach. Theories of temporal contexts developed in the memory tradition provide interesting predictions that we test using the methods of associative learning to assess their generality and applicability to different settings and dependent variables. In 4 experiments, the integration of these 2 areas allows us to show that (a) participants spontaneously create temporal contexts in the absence of explicit instructions; (b) cues can be used to retrieve an old temporal context and the information associated with other cues that were trained in that context; and (c) the memory of a retrieved temporal context can be updated with information from the current situation that does not fit well with the retrieved memory, thereby helping participants to best adapt their behavior to the future changes of the environment.     

Sensory and meaning features in stimulus recognition and associative retrieval.

Three experiments addressed the problem of isolating the effects of sensory similarity on subprocesses involved in coding paired associates. In the first, the standard recognition-recall procedure was used and stimulus similarity, concreteness, and frequency were varied. However, because of concern with the validity of this recognition procedure as a measure of functional stimulus contact, an alternative was developed. This alternative led to the second study in which only stimulus similarity was manipulated. In the third experiment, similarity was varied, and the pairs were either associatively compatible, unrelated, or incompatible. The results using the new procedure indicated that similarity consistently disrupted functional stimulus contact but not associative retrieval. By contrast, associative relatedness facilitated both subprocesses.     

Infant visual recognition memory: independent contributions of speed and attention

Relations between infant visual recognition memory and later cognition have fueled interest in identifying the underlying cognitive components of this important infant ability. The present large-scale study examined three promising factors in this regard--processing speed, short-term memory capacity, and attention. Two of these factors, attention and processing speed (but, surprisingly, not short-term memory capacity), were related to visual recognition memory: Infants who showed better attention (shorter looks and more shifts) and faster processing had better recognition memory. The contributions of attention and processing speed were independent of one another and were similar at all ages studied--5, 7, and 12 months. Taken together, attention and speed accounted for 6%-9% of the variance in visual recognition memory, leaving a considerable, but not unexpected, portion of the variance unexplained.     

Variation in working memory capacity and episodic recall: The contributions of strategic encoding and contextual retrieval

The present study examined the extent to which differences in strategic encoding and contextual retrieval account for the relation between individual differences in working memory capacity (WMC) and variation in episodic recall. Participants performed a continual distractor task under either incidental- or intentional-encoding conditions. High-WMC individuals outperformed low-WMC individuals across both encoding conditions and, notably, to a greater degree in the intentional-encoding condition. These results suggest that WMC differences in episodic recall are likely due to a combination of differences in both contextual-retrieval and strategic-encoding processes. These findings are consistent with prior work showing that high-WMC individuals are better at engaging in strategic-encoding processes during the presentation of items than are low-WMC individuals and are better at using contextual cues to focus the search on correct items during retrieval.     

The time course of episodic associative retrieval: Electrophysiological correlates of cued recall of unimodal and crossmodal pair-associate learning

Little is known about the time course of processes supporting episodic cued recall. To examine these processes, we recorded event-related scalp electrical potentials during episodic cued recall following pair-associate learning of unimodal object-picture pairs and crossmodal object-picture and sound pairs. Successful cued recall of unimodal associates was characterized by markedly early scalp potential differences over frontal areas, while cued recall of both unimodal and crossmodal associates were reflected by subsequent differences recorded over frontal and parietal areas. Notably, unimodal cued recall success divergences over frontal areas were apparent in a time window generally assumed to reflect the operation of familiarity but not recollection processes, raising the possibility that retrieval success effects in that temporal window may reflect additional mnemonic processes beyond familiarity. Furthermore, parietal scalp potential recall success differences, which did not distinguish between crossmodal and unimodal tasks, seemingly support attentional or buffer accounts of posterior parietal mnemonic function but appear to constrain signal accumulation, expectation, or representational accounts.     

Stereotype priming in face recognition: interactions between semantic and visual information in face encoding

The accuracy with which previously unfamiliar faces are recognised is increased by the presentation of a stereotype-congruent occupation label [Klatzky, R. L., Martin, G. L., & Kane, R. A. (1982a). Semantic interpretation effects on memory for faces. Memory & Cognition, 10, 195-206; Klatzky, R. L., Martin, G. L., & Kane, R. A. (1982b). Influence of social-category activation on processing of visual information. Social Cognition, 1, 95-109]. For example, providing the label 'criminal' both during encoding and test improves recognition for previously unfamiliar faces that look like the stereotypical criminal. Experiments 1 and 2 both replicate this effect and show that the label exerts its influence during the encoding of stereotypical faces and has little influence at test. These findings indicate that semantic information that is congruent with novel stereotypical faces facilitates their encoding.     

Age‐related changes in the control of episodic retrieval: an ERP study of recognition memory in children and adults

We examined developmental aspects of the ability to monitor the temporal context of an item’s previous occurrence while event‐related potentials (ERPs) were recorded. In a continuous recognition task, children between 10 and 12 years and young adults watched a stream of pictures repeated with a lag of 10–15 intervening items and indicated recurrences. In a second run, these already familiar pictures were repeated as non‐targets along with new pictures, while subjects were instructed to indicate only recurrences within the run. Young adults were able to maintain high performance levels in both tasks, whereas children had longer response times and committed a large number of false alarms to non‐targets. ERPs in both age groups showed similar parietal old/new effects for target repetitions within runs. In addition, adults’ ERPs showed similar old/new effects at frontal electrodes for repetitions and non‐targets, presumably reflecting assessments of familiarity, whereas for children repeated relative to first presentations were associated with more negative‐going waveforms at anterior frontal recording sites. Together, these results suggest a continuing maturation of the brain networks assessing novelty or familiarity. Recollection as indexed by parietal old/new effects appeared similar between young adults and children, but the development of controlled episodic retrieval, resulting in recollection of non‐target information, appears to continue well into adolescence.     

Attentional control and competition between episodic representations

The relationship between attentional control and episodic representation was investigated in six experiments that employed a variant of the classic attentional blink paradigm. We introduced a task-irrelevant (unpredictive) color match between the first and second target stimulus in a three-stream rapid serial visual presentation task. When this match was present, the first target reliably elicited a priming benefit to the identification of the second, lateralized target. However, this was only the case when the identities of the targets did not belong to the same category (digits, letters, or symbols). When targets did belong to the same category, interference was observed instead of priming, particularly at Lag 1. Furthermore, when color was the target-defining feature, interference at Lag 1 gave way to priming at longer lags. The interference effect is attributed to partial overlap between competing episodic target representations, which affects the availability of their overlapping features for successive attentional selection in rapid serial visual presentation.     

Lure similarity affects visual episodic recognition: Detailed tests of a noisy exemplar model

Summed-similarity models of visual episodic recognition memory successfully predict the variation in false alarm rates across different test items. With data averaged across subjects, Kahana and Sekuler demonstrated that subjects' performance appears to change along with the mean similarity among study items; with high interstimulus similarity, subjects were less likely to commit false alarms to similar lures. We examined this effect in detail by systematically varying the coordinates of study and test items along a critical stimulus dimension and measuring memory performance at each point. To reduce uncontrolled variance associated with individual differences in vision, the coordinates of study and test items were scaled according to each subject's discrimination threshold. Fitting each of four summed-similarity models to the individual subjects' data demonstrated a clear superiority for models that take account of interitem similarity on a trialwise basis.     

Limbic networks and associative learning: I. Entorhinal contributions to instrumental conditioning

The hippocampal formation is a highly delineated brain structure that is believed to play a prominent role in learning and memory. The present experiment evaluated the contributions of medial and lateral perforant path input to bar press-conditioning under (a) continuous and (b) differential reinforcement of low rates of responding (DRL) schedules, and (c) shuttlebox avoidance conditioning. Bilateral deafferentation of either pathway had no effect on the acquisition of bar press responses or on performance under the DRL schedule. Deafferentation of the medial pathway facilitated acquisition of avoidance responses in a manner much like the effects seen in hippocampectomized animals. It is suggested that the medial perforant path participates in the expression of correlated patterns of neuronal discharge known to develop within the hippocampus and that this “model” serves to modulate the temporal characteristics of simple conditioned reflexes. Loss of the modulatory influence of the model may affect acquisition and extinction rates. Contributions of other hippocampal circuits are discussed in relation to established deficits. Preliminary results of this experiment were presented at the second annual convention of the American Psychological Society, Dallas, Texas, June 1990.     

Limbic networks and associative learning: I. Entorhinal contributions to instrumental conditioning

The hippocampal formation is a highly delineated brain structure that is believed to play a prominent role in learning and memory. The present experiment evaluated the contributions of medial and lateral perforant path input to bar press-conditioning under (a) continuous and (b) differential reinforcement of low rates of responding (DRL) schedules, and (c) shuttlebox avoidance conditioning. Bilateral deafferentation of either pathway had no effect on the acquisition of bar press responses or on performance under the DRL schedule. Deafferentation of the medial pathway facilitated acquisition of avoidance responses in a manner much like the effects seen in hippocampectomized animals. It is suggested that the medial perforant path participates in the expression of correlated patterns of neuronal discharge known to develop within the hippocampus and that this “model” serves to modulate the temporal characteristics of simple conditioned reflexes. Loss of the modulatory influence of the model may affect acquisition and extinction rates. Contributions of other hippocampal circuits are discussed in relation to established deficits. Preliminary results of this experiment were presented at the second annual convention of the American Psychological Society, Dallas, Texas, June 1990.     

Semantic and visual relatedness of distractors impairs episodic retrieval of pictures in a divided attention paradigm

We used a divided attention (DA) paradigm to infer the representational codes needed to support episodic retrieval of pictures, by measuring susceptibility to memory interference from different distracting tasks. Participants made recognition memory decisions to semantically categorized sets of pictures while simultaneously making size judgments to a set of visually-presented distractor pictures. Recognition accuracy was worse and response times were slower under DA conditions relative to full attention (FA), regardless of semantic relatedness of distractors to targets (Experiment 1). Similarly, we found no differential memory interference under DA relative to FA when distractor pictures were either visually (but not semantically), semantically (but not visually), or unrelated to the targets (Experiment 2). In Experiment 3, memory interference was significantly larger under DA at retrieval when distractors were both semantically and visually similar to the targets. Findings suggest episodic memory for pictures requires access to either visually- or semantically-based representations for optimal performance.     

Aging and autobiographical memory: dissociating episodic from semantic retrieval

Cognitive aging research documents reduced access to contextually specific episodic details inolder adults, whereas access to semantic or other nonepisodic information is preserved or facilitated. The present study extended this finding to autobiographical memory by using a new measure; the Autobiographical Interview. Younger and older adults recalled events from 5 life periods. Protocols were scored according to a reliable system for categorizing episodic and nonepisodic information. Whereas younger adults were biased toward episodic details reflecting happenings, locations, perceptions, and thoughts, older adults favored semantic details not connected to a particular time and place. This pattern persisted after additional structured probing for contextual details. The Autobiographical Interview is a useful instrument for quantifying episodic and semantic contributions to personal remote memory.