Working memory retrieval differences between medial temporal lobe epilepsy patients and controls: a three memory layer approach.

Multi-store models of working memory (WM) have given way to more dynamic approaches that conceive WM as an activated subset of long-term memory (LTM). The resulting framework considers that memory representations are governed by a hierarchy of accessibility. The activated part of LTM holds representations in a heightened state of activation, some of which can reach a state of immediate accessibility according to task demands. Recent neuroimaging studies have studied the neural basis of retrieval information with different states of accessibility. It was found that the medial temporal lobe (MTL) was involved in retrieving information within immediate access store and outside this privileged zone. In the current study we further explored the contribution of MTL to WM retrieval by analyzing the consequences of MTL damage to this process considering the state of accessibility of memory representations. The performance of a group of epilepsy patients with left hippocampal sclerosis in a 12-item recognition task was compared with that of a healthy control group. We adopted an embedded model of WM that distinguishes three components: the activated LTM, the region of direct access, and a single-item focus of attention. Groups did not differ when retrieving information from single-item focus, but patients were less accurate retrieving information outside focal attention, either items from LTM or items expected to be in the WM range. Analyses focused on items held in the direct access buffer showed that consequences of MTL damage were modulated by the level of accessibility of memory representations, producing a reduced capacity.

Early prefrontal activation as a mechanism to prevent forgetting in the context of interference.

OBJECTIVE: Recent research has focused on interference resolution deficits as the main cause of short-term memory decreases in aging. To determine whether activation of brain compensatory mechanisms occur during the encoding process in older people. Moreover, two different levels of interference (distraction and interruption) were presented during the maintenance period to examine how they modulate brain activity profiles. DESIGN: A delayed match-to-sample task with two experimental conditions: distraction and interruption. PARTICIPANTS: Twenty-seven young adults from Complutense University of Madrid and 20 healthy older adults from Complutense Elderly University of Madrid. MEASUREMENTS: Magnetoencephalography scans were recorded during the execution of a working memory interference task. Brain activity sources from younger and older adults during the encoding stage were compared in each condition using minimum norm estimation analyses. RESULTS: The elderly showed enhancement of prefrontal activity during early latencies of the encoding process in both conditions. In the distraction condition, enhanced activity was located in left ventrolateral prefrontal regions, whereas in the interruption condition, enhanced activity was observed in the right ventral prefrontal areas and anterior cingulate cortex. CONCLUSION: Increased recruitment of prefrontal regions in the elderly might be related to the processing depth of information, encoding of new information and semantic associations that are successfully recalled, and with interference resolution and preparatory control when the level of interference becomes higher. These prefrontal modulations during early latencies might reflect a higher top-down control of the encoding process in normal aging to prevent forgetting.

Functioning of Cognitive Memory Inhibition Processes in People with Down Syndrome: An Empirical Study.

Cognitive inhibition is part of executive functions. When it exercises control over memory processes, it has the function of regulating the accessibility of memories and allows interference to be resolved. The impairment of its functioning has been related to the presence of forgetfulness of relevant information. In this research, we study the functioning of cognitive memory inhibition processes in people with intellectual disabilities in tasks of delayed visual recognition and analyze the influence of age. For this purpose, 36 people with Down syndrome (mean age = 33.44, standard deviation = 7.54, 50% females) and 36 people with neurotypical development (mean age = 33.55, standard deviation = 7.52, 50% females) participated. The results reflected a lower effectiveness in the group of people with Down syndrome, F(1, 68) = 159.09, p < .001, $ {\upeta}_{\mathrm{p}}^2 $ = .70. The people in the group with Down syndrome had difficulties in interference resolution, both in the subgroup of young people (p = .014, $ \hat{\updelta\ } $= 0.88) and in the subgroup of older people (p = .022, $ \hat{\updelta\ } $= 0.67). The impairment of cognitive inhibition in people with Down syndrome warrants the need to develop specific intervention programs for this process.

Operation of cognitive memory inhibition in adults with Down syndrome: Effects of maintenance load and material.

BACKGROUND: Cognitive inhibition is one of the executive functions; this process over memory plays a fundamental role in recalling relevant information. The aims of this study were to understand the effects of maintenance load and stimuli on the operation of cognitive inhibition over memory in working memory tasks in adults with Down syndrome. METHOD: The study included 36 individuals with Down syndrome (mean age = 33.44 years, standard deviation = 7.54 years, 50% women) and 36 individuals with neurotypical development (mean age = 33.55 years, standard deviation = 7.52 years, 50% women). The participants performed a working memory task in which they had to solve an interference problem during the maintenance phase. RESULTS: The Down syndrome group performed worse on cognitive inhibition over memory than the neurotypical development group. Both groups had lower recall with interference and under high-load conditions. In the neurotypical development group, memory was similar with both materials. The Down syndrome group performed better with non-social stimuli than with social stimuli. CONCLUSIONS: Understanding the variables that influence cognitive inhibition over memory will help in planning effective interventions for people with Down syndrome. Considering the results, special importance should be placed on work with social stimuli, at least in individuals with Down syndrome.

The effects of aging on the working memory processes of multimodal information.

Normal aging is associated with deficits in working memory processes. However, the majority of research has focused on storage or inhibitory processes using unimodal paradigms, without addressing their relationships using different sensory modalities. Hence, we pursued two objectives. First, was to examine the effects of aging on storage and inhibitory processes. Second, was to evaluate aging effects on multisensory integration of visual and auditory stimuli. To this end, young and older participants performed a multimodal task for visual and auditory pairs of stimuli with increasing memory load at encoding and interference during retention. Our results showed an age-related increased vulnerability to interrupting and distracting interference reflecting inhibitory deficits related to the off-line reactivation and on-line suppression of relevant and irrelevant information, respectively. Storage capacity was impaired with increasing task demands in both age groups. Additionally, older adults showed a deficit in multisensory integration, with poorer performance for new visual compared to new auditory information.

Age-related effects in working memory recognition modulated by retroactive interference.

One of the main causes for age-related declines in working memory is a higher vulnerability to retroactive interference due to a reduced ability to suppress irrelevant information. However, the underlying neural correlates remain to be established. Magnetoencephalography was used to investigate differential neural patterns in young and older adults performing an interference-based memory task with two experimental conditions, interrupting and distracting, during successful recognition. Behaviorally, both types of retroactive interference significantly impaired accuracy at recognition more in older adults than in young adults with the latter exhibiting greater disruptions by interrupters. Magnetoencephalography revealed the presence of differential age-related neural patterns. Specifically, time-modulated activations in temporo-occipital and superior parietal regions were higher in young adults compared with older adults for the interrupting condition. These results suggest that age-related deficits in inhibitory mechanisms that increase vulnerability to retroactive interference may be associated with neural under-recruitments in a high-interference task.

Age effects on retroactive interference during working memory maintenance.

The present study uses magnetoencephalography (MEG) to examine brain magnetic patterns in young and older adults who perform an interference-based working memory (WM) task with two experimental conditions; interrupting and distracting. Behaviourally, both types of retroactive interference significantly impair WM accuracy at recognition more in older adults than in young adults with the latter exhibiting greater disruptions by interruptors. MEG results revealed the presence of differential age-related and interference-related neural patterns. Specifically, time-modulated activations in posterior-frontal regions were increased in young compared to older adults characterising each condition. Additionally, young adults exhibited greater posterior-frontal activations for the interrupting compared to the distracting condition. These results suggest that age-related deficits in inhibitory mechanisms that increase vulnerability to interference are associated with under-recruitments in posterior-frontal regions. On the other hand, the absence of differential interference-related neural recruitments reflects that both types of interference affect WM equally in the elderly.

Retroactive interference in normal aging: a magnetoencephalography study.

Biomagnetic responses were recorded from healthy elderly subjects (55-67 years) performing a working memory task during recognition. The objective was to identify differential spatio-temporal brain activity patterns with magnetoencephalography by the presentation of two types of retroactive interference, active and passive. We obtained increased activity in the left medial temporal lobe and the left anterior ventral prefrontal cortex at early (100-200 ms) and medium latencies (300-400 ms) for the active interference group, and left anterior ventral prefrontal cortex showed greater activity at late latencies (700-800 ms) for the passive interference group. A time-modulated ventral prefrontal activation was shown for the active and passive interference conditions indicating that executive control mechanisms were necessary in both groups.