José María López-Frutos

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.

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.

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.

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.

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

ABSTRACT 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.

Interference Impacts Working Memory in Mild Cognitive Impairment

Mild cognitive impairment (MCI) is considered a transitional stage between healthy aging and dementia, specifically Alzheimers disease (AD). The most common cognitive impairment of MCI includes episodic memory loss and difficulties in working memory (WM). Interference can deplete WM, and an optimal WM performance requires an effective control of attentional resources between the memoranda and the incoming stimuli. Difficulties in handling interference lead to forgetting. However, the interplay between interference and WM in MCI is not well-understood and needs further investigation. The current study investigated the effect of interference during a WM task in 20 MCIs and 20 healthy elder volunteers. Participants performed a delayed match-to-sample paradigm which consisted in two interference conditions, distraction and interruption, and one control condition without any interference. Results evidenced a disproportionate impact of interference on the WM performance of MCIs, mainly in the presence of interruption. These findings demonstrate that interference, and more precisely interruption, is an important proxy for memory-related deficits in MCI. Thus, the current findings reveal novel evidence regarding the causes of WM forgetting in MCI patients, associated with difficulties in the mechanisms of attentional control.