ERP Correlates of Encoding Success and Encoding Selectivity in Attention Switching

Effects of task switching and emotional stimuli on memory selectivity

It is not always easy to attend to task-relevant information and ignore task-irrelevant distractions. We investigated the impact of task switching and emotional stimuli on goal-oriented selective attention and subsequent recognition memory. Results from two experiments with different stimulus materials (words and images) found that the memory advantage of task-relevant information over task-irrelevant information (i.e. memory selectivity) was attenuated on task switch trials and emotional distractor trials. In contrast, task repetitions and emotional targets improved memory selectivity. These results suggest that both task switching and emotional distractors divert limited cognitive resources needed for selective attention and selective encoding. Emotional targets likely supported selective encoding through the process of attentional prioritisation of emotional stimuli. The effects of task switching and emotional stimuli did not interact, suggesting distinct mechanisms, although this conclusion remains tentative.

Observing memory encoding while it unfolds: Functional interpretation and current debates regarding ERP subsequent memory effects

Our ability to remember the past depends on neural processes set in train in the moment an event is experienced. These processes can be studied by segregating brain activity according to whether an event is later remembered or forgotten. The present review integrates a large number of studies examining this differential brain activity, labeled subsequent memory effect (SME), with the ERP technique, into a functional organization and discusses routes for further research. Based on the reviewed literature, we suggest that memory encoding is implemented by multiple processes, typically reflected in three functionally different subcomponents of the ERP SME elicited by study stimuli, which presumably interact with preparatory SME activity preceding the to be encoded event. We argue that ERPs are a valuable method in the SME paradigm because they have a sufficiently high temporal resolution to disclose the subcomponents of encoding-related brain activity. Implications of the proposed functional organization for future studies using the SME procedure in basic and applied settings will be discussed.

A wandering mind is a forgetful mind: A systematic review on the influence of mind wandering on episodic memory encoding

In the last two decades, mind wandering has received increased interest in the field of cognitive neuroscience. Despite the strong links between attention and memory, its effect on episodic memory encoding has only been recently investigated. To date, there is no systematic synthesis on this link. Following the PRISMA guidelines, a systematic review of the literature on mind wandering and episodic memory was conducted. Five online bibliographic databases (PsycNET, Pubmed, ScienceDirect, Web of Science and Taylor & Francis) were searched. Twenty-four studies were eligible for the current review and were compared based on their methodologies and results. Overall, stimulus-independent mind wandering appeared to be a reliable negative factor influencing the encoding of both words and audio-visual stimuli. However, a few studies pointed out a potential positive effect of stimulus-dependent mind wandering on episodic memory encoding. Theoretical explanations of these results, the limits of existing investigations and avenues for potential future research are discussed.

Stimulating the parietal cortex by transcranial direct current stimulation (tDCS): no effects on attention and memory

Selective attention is relevant for goal directed behavior as it allows people to attend to task-relevant target stimuli and to ignore task-irrelevant distractors. Attentional focus at encoding affects subsequent memory for target and distractor stimuli. Remembering selectively more targets than distractors represents memory selectivity. Brain imaging studies suggest that the superior parietal cortex is associated with the dorsal attentional network supporting top-down control of selective attention while the inferior parietal cortex is associated with the ventral attentional network supporting bottom-up attentional orienting. To investigate the roles of the dorsal and ventral networks in the effect of selective attention during encoding on long-term memory, we stimulated the left superior and the right inferior parietal cortex. Building on previous work, we applied transcranial direct current stimulation (tDCS) during a study phase where pictures and words were presented simultaneously and participants had to switch between a picture and a word decision. A subsequent recognition test assessed memory for target and distractor pictures and words. We hypothesized that a relative increase in activity in the dorsal network would boost selective attention while increased activity in the ventral network would impair selective attention. We also expected to find corresponding effects on memory. Enhanced selective attention should lead to higher memory selectivity, while impaired selective attention should lead to lower memory selectivity. Our results replicated that task switching reduced memory selectivity. However, we found no significant effects of tDCS. Thus, the present study questions the effectiveness of the present tDCS protocol for modulating attention during task switching and subsequent memory.

Environmental rhythms orchestrate neural activity at multiple stages of processing during memory encoding: Evidence from event-related potentials

Accumulating evidence suggests that rhythmic temporal structures in the environment influence memory formation. For example, stimuli that appear in synchrony with the beat of background, environmental rhythms are better remembered than stimuli that appear out-of-synchrony with the beat. This rhythmic modulation of memory has been linked to entrained neural oscillations which are proposed to act as a mechanism of selective attention that prioritize processing of events that coincide with the beat. However, it is currently unclear whether rhythm influences memory formation by influencing early (sensory) or late (post-perceptual) processing of stimuli. The current study used stimulus-locked event-related potentials (ERPs) to investigate the locus of stimulus processing at which rhythm temporal cues operate in the service of memory formation. Participants viewed a series of visual objects that either appeared in-synchrony or out-of-synchrony with the beat of background music and made a semantic classification (living/non-living) for each object. Participants’ memory for the objects was then tested (in silence). The timing of stimulus presentation during encoding (in-synchrony or out-of-synchrony with the background beat) influenced later ERPs associated with post-perceptual selection and orienting attention in time rather than earlier ERPs associated with sensory processing. The magnitude of post-perceptual ERPs also differed according to whether or not participants demonstrated a mnemonic benefit for in-synchrony compared to out-of-synchrony stimuli, and was related to the magnitude of the rhythmic modulation of memory performance across participants. These results support two prominent theories in the field, the Dynamic Attending Theory and the Oscillation Selection Hypothesis, which propose that neural responses to rhythm act as a core mechanism of selective attention that optimize processing at specific moments in time. Furthermore, they reveal that in addition to acting as a mechanism of early attentional selection, rhythm influences later, post-perceptual cognitive processes as events are transformed into memory.

Combination of acupuncture and Chinese herbal formula for elderly adults with mild cognitive impairment: protocol for a randomized controlled trial

Background

Mild cognitive impairment (MCI) is known as a transitional status between normal cognitive function and Alzheimer’s disease (AD). Acupuncture and Chinese herbal medicines (CHMs) are considered to be beneficial to patients with cognitive impairment. However, it is still unknown whether the combination of the two therapies could optimize the therapeutic effect for MCI. This trial is aimed to evaluate the therapeutic effects of acupuncture and the herbal formula Yishen Granule (YSG) for elderly patients with MCI.

Methods/design

This is a multi-sited, patient-blinded, randomized controlled trial (RCT). Two hundred and forty eligible patients will be randomly divided into four groups: A. acupuncture with YSG, B. acupuncture with placebo herbal medicine, C. sham acupuncture with YSG or D. sham acupuncture with placebo herbal medicine. Acupuncture treatment will be given twice a week for 8 weeks and then once a week for 4 weeks. The herbal treatment patients will be given granules daily for 12 weeks, 8 weeks of standard-dose followed by 4 weeks of mid-dose. The primary outcome is scored by the Montreal Cognitive Assessment (MoCA). The secondary outcomes will be scored by the Mini-Mental State Examination (MMSE) and event-related potential (ERP). All the assessments will be conducted at baseline, and at the eighth and 12th week after intervention starts. The follow-up assessments will be performed with the MoCA in the 12th, 24th, and 36th weeks after intervention ends. Intention-to-treat (ITT) analysis will be used in this RCT.

Discussion

This RCT will provide us information on the effect of treating MCI patients with only acupuncture, herbal formula as well as the combination of both. The additive effect or synergistic effect of acupuncture and Chinese herbal formula will then be analyzed.

Trial registration

This trial is registered with ChiCTR-INR-17011569 on 5 June 2017, and has been approved by the Ethics Committee of Shanghai Municipal Hospital of Traditional Chinese Medicine (2017SHL-KY-05).

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3212-z) contains supplementary material, which is available to authorized users.