Comparative Functional Connectivity of Core Brain Regions between Implicit and Explicit Memory Tasks Underlying Negative Emotion in General Anxiety Disorder

The present study investigated (a) whether the pattern of performance on implicit and explicit memory of patients with type 2 diabetes mellitus (DM2) is more similar to those of patients with Alzheimer's disease (AD) or to cognitively normal older adults and (b) whether glycosylated hemoglobin levels (a measure of glucose regulation) are related to performance on the two memory tasks, implicit word-stem completion and "old-new" recognition. The procedures of both memory tasks included encoding and memory test phases separated by a short delay. Three groups of participants (healthy older adults, DM2 patients and AD patients) completed medical and psychological assessments and performed both memory tasks on a computer. The results of the word-stem completion task showed similar implicit memory in the three groups. By contrast, explicit recognition of the three groups differed. Implicit memory was not affected by either normal or pathological aging, but explicit memory deteriorated in the two groups of patients, especially in AD patients, showing a severe impairment compared to the cognitively healthy older adults. Importantly, glycosylated hemoglobin levels were not related to performance on either implicit or explicit memory tasks. These findings revealed a clear dissociation between explicit and implicit memory tasks in normal and pathological aging. Neuropsychologists and clinicians working with TM2 patients should be aware that the decline of voluntary, long-term explicit memory could have a negative impact on their treatment management. By contrast, the intact implicit memory of the two clinical groups could be used in rehabilitation.

Transfer‐appropriate processing theory (Roediger, Weldon, & Challis, 1989) proposes that dissociations between performance on explicit and implicit memory tests arise because these tests often rely on different types of information processing (e.g., perceptual processing vs conceptual processing). This perspective predicts that implicit and explicit memory tasks that rely primarily on conceptual processing should show comparable results, not dissociations. Numerous studies have demonstrated such similarities. It is, however, possible that these results arise from explicit memory contamination of performance on implicit memory tasks. To address this issue, an experiment was conducted in which participants were administered the sedative midazolam prior to study. Midazolam is known to create a temporary, but dense, period of anterograde amnesia. The effects of blocking stimulus materials by semantic category at study and generation at study were investigated on category exemplar production and category‐cued recall. The results of this study demonstrated a dissociation of the effects of midazolam on category exemplar production and category‐cued recall. Specifically, midazolam reduced the effect of blocking stimulus materials in category‐cued recall, but not in category exemplar production. The differential effect of midazolam on explicit and implicit memory is at odds with transfer‐appropriate processing theory and suggests that theories of memory must distinguish the roles of different types of conceptual processing on implicit and explicit memory tests.

How our memory is affected as we age has been given considerable attention over recent decades as we strive to understand the cognitive processes involved. Memory types have been identified as either explicit (declarative - related to episodes or semantics) or implicit (non-declarative – related to procedures, habits, or earlier priming). Studies have identified likely age-related decline in explicit but not implicit memory though there are opposing results suggested from other studies. It is thought cognitive reserve capacities might explain any non-decline as aging individuals use alternative or additional pathways to ‘remember’. This theory might be supported indirectly if older members remember material accurately but take longer to supply answers. In our current study we re-examined whether age-related differences in accuracy and speed of access in memory are present in both implicit and explicit memory processes and we increased the number of experimental age groups (from 2 to 3) - most previous studies have compared just two groups (young, and old). With three groups (young, middle-old, and older aged groups) we can identify trends across the age range towards deterioration or preservation of memory. We examined sixty-six participants (49 females; 17 males) aged 18 to 86 years (M = 50.27, SD = 21.06) from South-Eastern Queensland and divided these into younger (18 to 46 years of age), middle old (50 to 64) and older aged (65+) cohorts. Participants were administered tasks assessing implicit and explicit memory using computer presentations. Consistent with most prior research, no age differences were identified on accuracy in the implicit memory tasks (verbal and non-verbal, including priming), suggesting that memory for implicit material remains preserved. However, on the explicit memory tasks, older adults performed less accurately than the younger adults, indicative of decline in explicit memory as we age. The finding of a decline in explicit memory but no significant decline in implicit memory confirms most earlier research and is consistent with a view of modular decline rather than overall decline in memory with increasing age. In addition, differences found in speed of response in otherwise accurate implicit memory with older respondents significantly slower, suggests possible support for the cognitive reserve hypothesis.

Component cognitive and motor processes contributing to diminished visuomotor procedural learning in HIV infection with comorbid chronic alcoholism (HIV+ALC) include problems with attention and explicit memory processes. The neural correlates associated with this constellation of cognitive and motor processes in HIV infection and alcoholism have yet to be delineated. Frontostriatal regions are affected in HIV infection, frontothalamocerebellar regions are affected in chronic alcoholism, and frontolimbic regions are likely affected in both; all three of these systems have the potential of contributing to both visuomotor procedural learning and explicit memory processes. Here, we examined the neural correlates of implicit memory, explicit memory, attention, and motor tests in 26 HIV+ALC (5 with comorbidity for nonalcohol drug abuse/dependence) and 19 age-range matched healthy control men. Parcellated brain volumes, including cortical, subcortical, and allocortical regions, as well as cortical sulci and ventricles, were derived using the SRI24 brain atlas. Results indicated that smaller thalamic volumes were associated with poorer performance on tests of explicit (immediate and delayed) and implicit (visuomotor procedural) memory in HIV+ALC. By contrast, smaller hippocampal volumes were associated with lower scores on explicit, but not implicit memory. Multiple regression analyses revealed that volumes of both the thalamus and the hippocampus were each unique independent predictors of explicit memory scores. This study provides evidence of a dissociation between implicit and explicit memory tasks in HIV+ALC, with selective relationships observed between hippocampal volume and explicit but not implicit memory, and highlights the relevance of the thalamus to mnemonic processes.

To examine the status of conceptual memory processes in amnesia, a conceptual memory task with implicit or explicit task instructions was given to amnesic and control groups. After studying a list of category exemplars, participants saw category labels and were asked to generate as many exemplars as possible (an implicit memory task) or to generate exemplars that had been in the prior study list (an explicit memory task). After incidental deep or shallow encoding of exemplars, amnesic patients showed normal implicit memory performance (priming), a normal levels-of-processing effect on priming, and impaired explicit memory performance. After intentional encoding of exemplars, amnesic patients showed impaired implicit and explicit memory performance. Results suggest that although amnesic patients can show impairments on implicit and explicit conceptual memory tasks, their deficit does not generalize to all conceptual memory tasks.

Attending to Remember and Remembering to Attend

Purpose – Prescription drug advertisements are commonly seen in magazines and on television. Many drug ads are targeted toward older adults, who tend to use more medications and suffer from more chronic conditions. Nonetheless, the effectiveness of such advertising remains uncertain. The aim of this paper is to compare implicit and explicit memory for drug ads in older and younger adults. Design/methodology/approach – Older adults typically perform more poorly than young adults on explicit memory tasks, but not on implicit memory tasks. The current study measured implicit memory with an incidental ratings exercise and an indirect test of preference; explicit memory was also measured with intentional studying and a direct test of recognition. The study was a 2 x 2 mixed experimental design with one between-participants variable and one within-participants variable. The between-participants variable was age group (older vs younger adults) and the within-participants variable was implicit and explicit memory. The memory test measures were the outcome variables of the study. Findings – The results showed no age difference for implicit memory for drug ads, but an age difference was found for explicit memory for the ads. The implicit memory manipulation succeeded in demonstrating that drug ads are persuasive, suggesting that a complete assessment of advertising effectiveness should include a test of implicit memory. Research limitations/implications – The fact that age differences were not found for implicit memory, but were found for explicit memory, is not surprising. Practical implications – The study is of theoretical significance because it contributes to cognitive aging research and examines memory within an everyday context. The study is of practical significance because pharmaceutical companies spend vast amounts of money on prescription drug advertisements that may or may not be effective with older adults. The component of this study that may be most important is that the results expanded everyday memory research to another applied context using an implicit memory measure, and the indirect test of memory demonstrated that the prescription drug advertising was effective. Originality/value – Although the findings were consistent with previous research, the study focuses on the real-world context of direct-to-consumer advertising for prescription drugs. Given that older adults have poorer explicit memory than younger adults, but not poorer implicit memory, it is particularly important for advertisers to use implicit memory measures when assessing advertisements aimed at older adult consumers. Marketers of pharmaceutical drug companies must remain aware that the memory abilities of their potential customers are extremely variable, and in some cases, limited.

To the Editor:-We read with interest the article by Ripart et al. 1 that provides clinical evidence to conclude that single-injection, high-volume medial canthus episcleral anesthesia is an efficient and safer alternative to peribulbar anesthesia. The salient features of their method are the injection of a relatively high volume (8 -10 ml) of anesthetic solution and the use of adjuncts, such as clonidine premed-

The present research was designed to provide a direct test of the transfer-appropriate processing framework as it applies to performance on two implicit memory tasks and also to identify the component processes that are engaged on these memory tasks. The general strategy involved employing study tasks that mimicked (more so than a standard Read condition) the processing that appears to occur during the memory task. Performance on a stem-- completion task was not consistently enhanced by a study task in which participants selected potential word endings for the three-letter stems. However, inducing participants to engage in a letter-substitution task during encoding enhanced priming on a fragment-completion test, relative to the standard Read condition. Consistent with the transfer-- appropriate processing framework, the letter-substitution task showed evidence of optimizing priming effects, as additional manipulations of similarity had no further effect on performance on the implicit test. The data suggest that the Read condition does not induce maximum processing, as has been suggested previously, whereas a letter-by-letter substitution strategy mimics the processes used to complete word fragments on an implicit test. However, participants may not normally solve word stems by generating possible word endings and then selecting among these alternatives. Implicit memory tasks are operationally defined as memory tests for which the participant is given no instructions to consciously retrieve information from a prior study list, even though performance on the test may be affected by exposure to the prior study list. By contrast, explicit memory tests are defined as those for which the participant is given instructions at test to retrieve previously studied information (e.g., Richardson-Klavehn & Bjork, 1988). Although everyday uses of memory likely establish a predominant role for implicit memory (see also Masson & Graf, 1993), the extensive theoretical and empirical interest in implicit test performance over the last several years appears to have been motivated by two findings in particular. First, it is now well-established that individuals suffering from amnesia show performance on implicit memory tests that often does not differ from that of people with normal memory function (Morris & Kopelman, 1986; Richardson-- Klavehn & Bjork, 1988; Schacter, 1987; Shimamura, 1986, 1993). Although there are a few exceptions to this pattern (e.g., Hamann & Squire, 1996; Hodges, Salmon, & Butters, 1992), the generalization holds across a large number of etiological bases for the amnesia, including most forms of temporary and permanent amnesia. The second reason for interest in implicit memory is the finding that many independent variables have different effects on implicit and explicit memory performance. This research has been summarized in several places (e.g., Roediger & McDermott, 1993). Of primary relevance to the present work is the finding that performance on most tests of implicit memory is driven primarily by processing of the stimulus whereas performance on most tests of explicit memory is driven primarily by conceptual processing. Several aspects of processing have been shown to affect performance on these implicit memory tests, including typographic format (e.g., Clarke & Morton, 1983; Graf & Ryan, 1990; Jacoby & Hayman, 1987) and modality (e.g., Graf, Shimamura, & Squire, 1985; Jacoby & Dallas, 1981; Roediger & Blaxton, 1987). In contrast, conceptual processing yields much larger effects on explicit memory tasks than on implicit memory tasks (e.g., Gellatly, Parker, Blurton, & Woods, 1994). One of the most widely cited examples of this is the manipulation of depth of processing at study: Whereas depth effects are well-established on explicit tasks (e.g., Craik & Tulving, 1975), they are generally much smaller or even nonexistent on standard perceptual implicit tasks (for reviews, see Brown & Mitchell, 1994; Challis & Brodbeck, 1992; see also Hamann & Squire, 1996; Thapar & Greene, 1994). …

Previous experiments have shown that the procedure of questioning subjects retrospectively about the input and output status of information (input and output monitoring) is a useful method for assessing the awareness states of subjects during implicit and explicit memory tasks. The main purpose of the present study was to investigate whether the previous findings could be extended to other implicit and explicit memory tasks. We were especially interested in whether differences in input- and output-monitoring performance can be observed when both the implicit and explicit memory tasks are conceptual ones. In a final tet phase, the target items from the study phase and new distractor items were presented. In a recognition-like situation, subjects had to decide whether an item had been presented in the study phase (input status), as well as whether they had produced the item in the memory-test phase (output status). In all three experiments judgments about the input status-but only for those items that had been produced in the implicit or in the explicit memory test--were more precise after explicit than after implicit memory testings. This finding was not influenced by the distinction between perceptual and conceptual-memory tasks (Exp. 1), and was obtained under conditions in which the implicit and the explicit memory tasks were both conceptual and differed only in test instructions (Exps. 2 and 3). These results suggest that not only subjects performing a perceptual test of implicit memory, but also subjects in a conceptual implicit test were less aware of using information from a previous study episode than subjects who received memory instructions. It is concluded that requiring judgments about the input status of information is a good method for assessing subjects' test awareness and is preferable to the use of a questionnaire (Exp. 3). In contrast, in all three experiments no differences were found with the output-monitoring measure between implicit and explicit test conditions.

Recently, several studies have addressed the question of whether depression affects priming in implicit memory tasks. The main aim of this experiment was to assess the presence of a bias for negative information in explicit memory (free recall) and implicit memory (word-stem completion) tasks among subclinically depressed subjects compared to nondepressed subjects, using the typical levels of processing manipulation. The results of this study show the existence of a mood-congruent memory bias for both implicit and explicit memory in depressed subjects. The theoretical implications of these findings for implicit and explicit memory biases associated with depressed mood are discussed.

Primary objective: To examine implicit and explicit memory outcome in children who had sustained severe traumatic brain injury (TBI) through childhood. Opposite patterns of impairments were expected: (i) impaired implicit memory in children with early TBI (TBI-EC, < 6 years) and (ii) impaired explicit memory in children with late TBI (TBI-LC, ≥ 6 years).Research design: Children who had sustained severe TBI more then 1 year ago were assessed.Methods and procedure: Fourteen children who had sustained severe TBI (TBI-EC, n = 10 and TBI-LC, n = 4) between 8 months and 13 years 7 months of age and 13 non-injured control subjects (NC) participated. Implicit (repetition priming and skill learning) and explicit verbal memory were examined.Results: The TBI group performed worse on implicit (repetition priming) and explicit memory tasks compared to the NC group. Moreover, impairments were found in implicit and explicit memory in the TBI-EC, but not in the TBI-LC group.Conclusions: This study has shown, for the first time, that severe childhood TBI may compromise not only explicit, but also implicit memory. Nevertheless, instead of a selective implicit memory impairment, it was found that children who sustained injuries in early childhood present with impairments in both memory systems.

Neural correlates of explicit and implicit memory at encoding and retrieval: A unified framework and meta-analysis of functional neuroimaging studies

There is a popular hypothesis that performance on implicit and explicit memory tasks reflects 2 distinct memory systems. Explicit memory is said to store those experiences that can be consciously recollected, and implicit memory is said to store experiences and affect subsequent behavior but to be unavailable to conscious awareness. Although this division based on awareness is a useful taxonomy for memory tasks, the authors review the evidence that the unconscious character of implicit memory does not necessitate that it be treated as a separate system of human memory. They also argue that some implicit and explicit memory tasks share the same memory representations and that the important distinction is whether the task (implicit or explicit) requires the formation of a new association. The authors review and critique dissociations from the behavioral, amnesia, and neuroimaging literatures that have been advanced in support of separate explicit and implicit memory systems by highlighting contradictory evidence and by illustrating how the data can be accounted for using a simple computational memory model that assumes the same memory representation for those disparate tasks.

Implicit and explicit olfactory memory in people with and without Down syndrome