Intentional suppression of unwanted memories grows more difficult as we age

Verbal and visuospatial executive functions in healthy elderly: The impact of education and frequency of reading and writing

Objective

To assess the predictive role of education and frequency of reading and writing habits (FRWH) on the cognitive flexibility, inhibition and planning abilities of healthy elderly individuals.

Methods

Fifty-seven healthy adults aged between 60 and 75 years with 2 to 23 years of formal education were assessed as to the frequency with which they read and wrote different types of text, as well as their number of years of formal education. Executive functions were evaluated using the Hayling Test and the Modified Wisconsin Card Sorting Test (MWCST).

Results

Weak to moderate positive correlations were found between education, FRWH and the number of categories completed in the MWCST, while negative correlations were identified between these variables and the number of perseverative and non-perseverative errors on the task. Only the FRWH was significantly correlated with the number of failures to maintain set. Speed and accuracy on the Hayling Test were only correlated with participant education. Both education and FRWH significantly predicted performance on the MWCST, and the combination of these two variables had a greater predictive impact on performance on this task than either of the two variables alone. Variability in scores on the Hayling Test was best accounted for by participant education.

Conclusion

In this sample of elderly subjects, cognitive flexibility was sufficiently preserved to allow for adequate performance on verbal tasks, but may have benefitted from the additional stimulation provided by regular reading and writing habits and by formal education in the performance of more complex non-verbal tasks.

The cognitive control of memory: age differences in the neural correlates of successful remembering and intentional forgetting

Successful memory encoding depends on the ability to intentionally encode relevant information (via differential encoding) and intentionally forget that which is irrelevant (via inhibition). Both cognitive processes have been shown to decline in aging and are theorized to underlie age-related deficits in the cognitive control of memory. The current study uses the Directed Forgetting paradigm in conjunction with fMRI to investigate age-related differences in both cognitive processes, with the specific aim of elucidating neural evidence supporting these theorized deficits. Results indicate relatively preserved differential encoding, with age differences consistent with previous models of age-related compensation (i.e., increased frontal and bilateral recruitment). Older adults did display noticeable differences in the recruitment of brain regions related to intentional forgetting, specifically exhibiting reduced activity in the right superior prefrontal cortex, a region shown to be critical to inhibitory processing. However, older adults exhibited increased reliance on processing in right inferior parietal lobe associated with successful forgetting. Activity in this region was negatively correlated with activity in the medial temporal lobe, suggesting a shift in the locus of inhibition compared to the frontally mediated inhibition observed in younger adults. Finally, while previous studies found intentional and incidental forgetting to be dissociable in younger adults, this differentiation appears to be reduced in older adults. The current results are the first to provide neural evidence for an age-related reduction in processes that support intentional forgetting.

Emotions shape memory suppression in trait anxiety

The question that motivated this study was to investigate the relation between trait anxiety, emotions and memory control. To this aim, memory suppression was explored in high and low trait anxiety individuals with the Think/No-think paradigm. After learning associations between neutral words and emotional scenes (negative, positive, and neutral), participants were shown a word and were requested either to think about the associated scene or to block it out from mind. Finally, in a test phase, participants were again shown each word and asked to recall the paired scene. The results show that memory control is influenced by high trait anxiety and emotions. Low trait anxiety individuals showed a memory suppression effect, whereas there was a lack of memory suppression in high trait anxious individuals, especially for emotionally negative scenes. Thus, we suggest that individuals with anxiety may have difficulty exerting cognitive control over memories with a negative valence. These findings provide evidence that memory suppression can be impaired by anxiety thus highlighting the crucial relation between cognitive control, emotions, and individual differences in regulating emotions.

To think or not to think, that is the question: individual differences in suppression and rebound effects in autobiographical memory

Two studies explored the effects of forget instructions on autobiographical memory at immediate test and following delays of either 12-13 months, or 3-4 months. Using the Autobiographical Think/No-Think procedure (cf., Noreen & MacLeod, 2013), 24 never-depressed participants (Study 1) first generated 12 positive and 12 negative autobiographical memories and associated cues. Participants were then asked to recall the memory associated with some of the cues (i.e., 'think' condition), or to avoid saying or thinking about the memory associated with other cues (i.e., 'no-think' condition). Participants were then asked to recall the memories associated with all the cues at immediate test and following a delay of 12-13 months. Participants were found to be successful at forgetting both positive and negative autobiographical memories following 'no-think' instructions at immediate test but this forgetting effect did not persist following a 12-13 month delay. This pattern of remembering and forgetting was replicated in a second study (using 27 never-depressed participants) following a 3-4 month delay. Participants who had been less successful at forgetting 'no-think' memories at immediate test, were more likely to show rebound effects for those memories following a delay compared to memories which received neither 'think' nor 'no-think' instructions. Individual differences in inhibitory control and the efficacy of potential therapeutic interventions of 'no-think' instructions are considered.

Heart Rate Variability Predicts Control Over Memory Retrieval

Stopping retrieval of unwanted memories has been characterized as a process that requires inhibition. However, little research has examined the relationship between control over memory retrieval and individual differences in inhibitory control. Higher levels of resting heart rate variability (HRV) are associated with greater inhibitory control, as indicated by better performance on a number of cognitive, affective, and motor tasks. Therefore, we tested the hypothesis that higher levels of resting HRV predict enhanced memory inhibition as indexed by performance on the think/no-think task. Efforts to suppress no-think word pairs resulted in impaired recall for those items, as in past studies. Moreover, higher levels of resting HRV were associated with more successful suppression, as indicated by lower recall of the to-be-avoided stimuli relative to baseline stimuli. These findings are among the first to suggest that physiological markers of inhibitory control can be used to index a person’s capacity to control unwanted memories.

Below-baseline suppression of competitors during interference resolution by younger but not older adults

Resolving interference from competing memories is a critical factor in efficient memory retrieval, and several accounts of cognitive aging suggest that difficulty resolving interference may underlie memory deficits such as those seen in the elderly. Although many researchers have suggested that the ability to suppress competitors is a key factor in resolving interference, the evidence supporting this claim has been the subject of debate. Here, we present a new paradigm and results demonstrating that for younger adults, a single retrieval attempt is sufficient to suppress competitors to below-baseline levels of accessibility even though the competitors are never explicitly presented. The extent to which individual younger adults suppressed competitors predicted their performance on a memory span task. In a second experiment, older adults showed no evidence of suppression, which supports the theory that older adults' memory deficits are related to impaired suppression.

Semantically- and Phonologically-Related Primes Improve Name Retrieval in Young and Older Adults

Word and name retrieval failures increase with age, and this study investigated how priming impacts young and older adults' ability to produce proper names. The transmission deficit hypothesis predicts facilitation from related prime names, whereas the blocking and inhibition deficit hypotheses predict interference from related names, especially for older adults. On half of our experimental trials, we exposed participants to a prime name that is phonologically- and semantically-related to a target name. Related names facilitated production of targets overall, with older adults' naming ability improved at least as much as young adults'. Results are contrary to predictions of the blocking and inhibitory deficit hypotheses, and suggest that an activation-based model of memory and language better accounts for retrieval and production of well-known names.

Moderate levels of activation lead to forgetting in the think/no-think paradigm

Using the think/no-think paradigm (Anderson & Green, 2001), researchers have found that suppressing retrieval of a memory (in the presence of a strong retrieval cue) can make it harder to retrieve that memory on a subsequent test. This effect has been replicated numerous times, but the size of the effect is highly variable. Also, it is unclear from a neural mechanistic standpoint why preventing recall of a memory now should impair your ability to recall that memory later. Here, we address both of these puzzles using the idea, derived from computational modeling and studies of synaptic plasticity, that the function relating memory activation to learning is U-shaped, such that moderate levels of memory activation lead to weakening of the memory and higher levels of activation lead to strengthening. According to this view, forgetting effects in the think/no-think paradigm occur when the suppressed item activates moderately during the suppression attempt, leading to weakening; the effect is variable because sometimes the suppressed item activates strongly (leading to strengthening) and sometimes it does not activate at all (in which case no learning takes place). To test this hypothesis, we ran a think/no-think experiment where participants learned word-picture pairs; we used pattern classifiers, applied to fMRI data, to measure how strongly the picture associates were activating when participants were trying not to retrieve these associates, and we used a novel Bayesian curve-fitting procedure to relate this covert neural measure of retrieval to performance on a later memory test. In keeping with our hypothesis, the curve-fitting procedure revealed a nonmonotonic relationship between memory activation (as measured by the classifier) and subsequent memory, whereby moderate levels of activation of the to-be-suppressed item led to diminished performance on the final memory test, and higher levels of activation led to enhanced performance on the final test.

Strength of Coupling within a mnemonic control network differentiates those who can and cannot suppress memory retrieval

The ability to direct our thought processes influences not only what we do, but also what we remember later. Here we sought to identify the brain network that supports the ability to control memory retrieval and to understand the neural basis of age-related changes and individual differences in the capacity for mnemonic control. To this end, we collected functional MRI data from 43 children and young adults while they attempted to retrieve or suppress retrieval of previously learned associations. Seed-based functional connectivity analyses revealed a largely right-lateralized dorsolateral prefrontal cortex-cingulate-parietal-hippocampal network that exhibited strongly correlated activity during retrieval suppression. Regardless of age, individuals who were able to suppress memory retrieval exhibited tighter coupling between key nodes in this dorsolateral prefrontal cortex-cingulate-parietal-hippocampal network than individuals who did not. Further, only those capable of mnemonic control exhibited tighter coupling during successful retrieval suppression (intentional forgetting) than during unsuccessful retrieval (unintentional forgetting). Across both children and adults, individual differences in retrieval suppression were best explained by the strength of these network interactions.

Emotional and non-emotional memories are suppressible under direct suppression instructions

Research on retrieval suppression has produced varying results concerning whether negatively valenced memories are more or less suppressible than neutral memories. This variability may arise if, across studies, participants adopt different approaches to memory control. Cognitive and neurobiological research points to two mechanisms that achieve retrieval suppression: thought-substitution and direct suppression (Benoit & Anderson, 2012; Bergström, de Fockert, & Richardson-Klavehn, 2009). Using the Think/No-think paradigm, this study examined whether participants can inhibit neutral and negatively valenced memories, using a uniform direct suppression strategy. Importantly, when strategy was controlled, negative and neutral items were comparably inhibited. Participants reported high compliance with direct suppression instructions, and success at controlling awareness predicted forgetting. These findings provide the first evidence that direct suppression can impair negatively valenced events, and suggest that variability in forgetting negative memories in prior studies is unlikely to arise from difficulty using direct suppression to control emotionally negative experiences.

Suppressing the encoding of new information in memory: a behavioral study derived from principles of hippocampal function

Cognitive processes do not occur in isolation. Interactions between cognitive processes can be observed as a cost in performance following a switch between tasks, a cost that is greatest when the cognitive requirements of the sequential tasks compete. Interestingly, the long-term mnemonic goals associated with specific cognitive tasks can also directly compete. For example, encoding the sequential order in which stimuli are presented in the commonly-utilised 2-Back working memory (WM) tasks is counter-productive to task performance, as this task requires the continual updating of the contents of one's current mental set. Performance of this task consistently results in reduced activity within the medial temporal lobe (MTL), and this response is believed to reflect the inhibitory mnemonic component of the task. Conversely, there are numerous cognitive paradigms in which participants are explicitly instructed to encode incoming information and performance of these tasks reliably increases MTL activity. Here, we explore the behavioural cost of sequentially performing two tasks with conflicting long-term mnemonic goals and contrasting neural profiles within the MTL. We hypothesised that performing the 2-Back WM prior to a hippocampal-dependent memory task would impair performance on the latter task. We found that participants who performed the 2-Back WM task, prior to the encoding of novel verbal/face-name stimuli, recollected significantly fewer of these stimuli, compared to those who had performed a 0-Back control task. Memory processes believed to be independent of the MTL were unaffected. Our results suggest that the inhibition of MTL-dependent mnemonic function persists beyond the cessation of the 2-Back WM task and can alter performance on entirely separate and subsequently performed memory tasks. Furthermore, they indicate that performance of such tasks may induce a temporarily-sustained, virtual lesion of the hippocampus, which could be used as a probe to explore cognitive processes in the absence of hippocampal involvement.

Forgetting in context: the effects of age, emotion, and social factors on retrieval-induced forgetting

Retrieval-induced forgetting (RIF) refers to the finding that selectively retrieving some information impairs subsequent memory for related but nonretrieved information. This occurs both for the individual doing the remembering (i.e., within-individual retrieval-induced forgetting: WI-RIF), as well as for individuals merely listening to those recollections (i.e., socially shared retrieval-induced forgetting: SS-RIF). In the present study, we examined how the contextual factors of age and emotion independently and interactively affect both WI-RIF and SS-RIF. The results indicated that both WI-RIF and SS-RIF occurred at equivalent levels, both for younger and older adults and for neutral and emotional information. However, we identified a boundary condition to this effect: People only exhibited SS-RIF when the speaker that they were listening to was of the same sex as themselves. Given that participants reported feeling closer to same-sex speakers, this suggests that people co-retrieve more, and therefore exhibit increased SS-RIF, with close others. In everyday life, these RIF effects should influence what information is remembered versus forgotten in individual and collective memories.

The hypercorrection effect in younger and older adults

ABSTRACT The hypercorrection effect, which refers to the finding that errors committed with high confidence are more likely to be corrected than are low confidence errors, has been replicated many times, and with both young adults and children. In the present study, we contrasted older with younger adults. Participants answered general-information questions, made confidence ratings about their answers, were given corrective feedback, and then were retested on questions that they had gotten wrong. While younger adults showed the hypercorrection effect, older adults, despite higher overall accuracy on the general-information questions and excellent basic metacognitive ability, showed a diminished hypercorrection effect. Indeed, the correspondence between their confidence in their errors and the probability of correction was not significantly greater than zero, showing, for the first time, that a particular participant population is selectively impaired on this error correction task. These results potentially offer leverage both on the mechanisms underlying the hypercorrection effect and on reasons for older adults' memory impairments, as well as on memory functions that are spared.

Partially overlapping mechanisms of language and task control in young and older bilinguals

The current study tested the hypothesis that bilinguals rely on domain-general mechanisms of executive control to achieve language control by asking if linguistic and nonlinguistic switching tasks exhibit similar patterns of aging-related decline. Thirty young and 30 aging bilinguals completed a cued language-switching task and a cued color-shape switching task. Both tasks demonstrated significant aging effects, but aging-related slowing and the aging-related increase in errors were significantly larger on the color-shape than on the language task. In the language task, aging increased language-switching costs in both response times and errors, and language-mixing costs only in response times. In contrast, the color-shape task exhibited an aging-related increase in costs only in mixing errors. Additionally, a subset of the older bilinguals could not do the color-shape task, but were able to do the language task, and exhibited significantly larger language-switching costs than matched controls. These differences, and some subtle similarities, in aging effects observed across tasks imply that mechanisms of nonlinguistic task and language control are only partly shared and demonstrate relatively preserved language control in aging. More broadly, these data suggest that age deficits in switching and mixing costs may depend on task expertise, with mixing deficits emerging for less-practiced tasks and switching deficits for highly practiced, possibly "expert" tasks (i.e., language).

Towards solving the riddle of forgetting in functional amnesia: recent advances and current opinions

Remembering the past is a core feature of human beings, enabling them to maintain a sense of wholeness and identity and preparing them for the demands of the future. Forgetting operates in a dynamic neural connection with remembering, allowing the elimination of unnecessary or irrelevant information overload and decreasing interference. Stress and traumatic experiences could affect this connection, resulting in memory disturbances, such as functional amnesia. An overview of clinical, epidemiological, neuropsychological, and neurobiological aspects of functional amnesia is presented, by preponderantly resorting to own data from patients with functional amnesia. Patients were investigated medically, neuropsychologically, and neuroradiologically. A detailed report of a new case is included to illustrate the challenges posed by making an accurate differential diagnosis of functional amnesia, a condition that may encroach on the boundaries between psychiatry and neurology. Several mechanisms may play a role in "forgetting" in functional amnesia, such as retrieval impairments, consolidating defects, motivated forgetting, deficits in binding and reassembling details of the past, deficits in establishing a first person autonoetic connection with personal events, and loss of information. In a substantial number of patients, we observed a synchronization abnormality between a frontal lobe system, important for autonoetic consciousness, and a temporo-amygdalar system, important for evaluation and emotions, which provides empirical support for an underlying mechanism of dissociation (a failure of integration between cognition and emotion). This observation suggests a mnestic blockade in functional amnesia that is triggered by psychological or environmental stress and is underpinned by a stress hormone mediated synchronization abnormality during retrieval between processing of affect-laden events and fact-processing.

Electrophysiological correlates of adult age differences in attentional control of auditory processing

In addition to sensory decline, age-related losses in auditory perception also reflect impairments in attentional modulation of perceptual saliency. Using an attention and intensity-modulated dichotic listening paradigm, we investigated electrophysiological correlates of processing conflicts between attentional focus and perceptual saliency in 25 younger and 26 older adults. Participants were instructed to attend to the right or left ear, and perceptual saliency was manipulated by varying the intensities of both ears. Attentional control demand was higher in conditions when attentional focus and perceptual saliency favored opposing ears than in conditions without such conflicts. Relative to younger adults, older adults modulated their attention less flexibly and were more influenced by perceptual saliency. Our results show, for the first time, that in younger adults a late negativity in the event-related potential (ERP) at fronto-central and parietal electrodes was sensitive to perceptual-attentional conflicts during auditory processing (N450 modulation effect). Crucially, the magnitude of the N450 modulation effect correlated positively with task performance. In line with lower attentional flexibility, the ERP waveforms of older adults showed absence of the late negativity and the modulation effect. This suggests that aging compromises the activation of the fronto-parietal attentional network when processing the competing and conflicting auditory information.

The remains of the day in dissociative amnesia

Memory is not a unity, but is divided along a content axis and a time axis, respectively. Along the content dimension, five long-term memory systems are described, according to their hierarchical ontogenetic and phylogenetic organization. These memory systems are assumed to be accompanied by different levels of consciousness. While encoding is based on a hierarchical arrangement of memory systems from procedural to episodic-autobiographical memory, retrieval allows independence in the sense that no matter how information is encoded, it can be retrieved in any memory system. Thus, we illustrate the relations between various long-term memory systems by reviewing the spectrum of abnormalities in mnemonic processing that may arise in the dissociative amnesia—a condition that is usually characterized by a retrieval blockade of episodic-autobiographical memories and occurs in the context of psychological trauma, without evidence of brain damage on conventional structural imaging. Furthermore, we comment on the functions of implicit memories in guiding and even adaptively molding the behavior of patients with dissociative amnesia and preserving, in the absence of autonoetic consciousness, the so-called “internal coherence of life”.

Searching for interference effects in learning new face-name associations

In three experiments we attempted to increase interference using experimental manipulations in a face-name learning paradigm. All experiments included young and older adult participants because ageing is associated with increases in both susceptibility to interference and difficulty in learning face-name associations. None of the experiments produced interference for either age group: The inclusion of confusable (i.e., ambiguous) names and occupations, having to learn an additional piece of information in association with each face, and requiring participants to guess when uncertain all failed to negatively impact name learning. Interference does not appear to be the critical mechanism underlying the difficulty of learning proper names, and it cannot account for older adults' disproportionate decline in name-learning ability.

Towards a cognitive and neurobiological model of motivated forgetting

Historically, research on forgetting has been dominated by the assumption that forgetting is passive, reflecting decay, interference, and changes in context. This emphasis arises from the pervasive assumption that forgetting is a negative outcome. Here, we present a functional view of forgetting in which the fate of experience in memory is determined as much by motivational forces that dictate the focus of attention as it is by passive factors. A central tool of motivated forgetting is retrieval suppression, a process whereby people shut down episodic retrieval to control awareness. We review behavioral, neurobiological, and clinical research and show that retrieval suppression leads us to forget suppressed experiences. We discuss key questions necessary to address to develop this model, relationships to other forgetting phenomena, and the implications of this research for understanding recovered memories. This work provides a foundation for understanding how motivational forces influence what we remember of life experience.