The hippocampus as a sorter and reverberatory integrator of sensory inputs

In entorhinal-hippocampal networks, the trisynaptic pathway, including the CA3 recurrent circuit, processes episodes of context and space. Recurrent connectivity can generate reverberatory activity, an intrinsic activity pattern of neurons that occurs after sensory inputs have ceased. However, the role of reverberatory activity in memory encoding remains incompletely understood. Here we demonstrate that in mice, synchrony between conditioned stimulus (CS) and unconditioned stimulus (US)-responsible cells occurs during the reverberatory phase, lasting for approximately 15 s, but not during CS and US inputs, in the CA1 and the reverberation is crucial for the linking of CS and US in the encoding of delay-type cued-fear memory. Retrieval-responsive cells developed primarily during the reverberatory phase. Mutant mice lacking N-methyl-D-aspartate receptors (NRs) in CA3 showed a cued-fear memory impairment and a decrease in synchronized reverberatory activities between CS- and US-responsive CA1 cells. Optogenetic CA3 silencing at the reverberatory phase during learning impaired cued-fear memory. Our findings suggest that reverberation recruits future retrieval-responsive cells via synchrony between CS- and US-responsive cells. The hippocampus uses reverberatory activity to link CS and US inputs, and avoid crosstalk during sensory inputs.

Corporate memory dynamics in project-based organizations (PBOs): multiple case study in Brazilian engineering design firms and a framework proposal

Purpose This study aims to investigate how the processes of memory acquisition, retention, retrieval and application occur in project-based organizations (PBOs). In this kind of organization, the nature of corporate memory is influenced by the transience, uniqueness and independence of the project portfolio. Such understanding may help practitioners to mitigate the effects of project transience and promote knowledge sharing among project teams. Design/methodology/approach An empirical and qualitative study was carried out through a multiple case study approach conducted in three Brazilian Engineering Design Firms, which are organized by projects. Document analysis, direct observation and semi-structured interviews with engineers, project managers and executives were conducted. Findings The memory acquisition process takes place in five forms which have different sources and destinations when comparing PBOs with traditional organizational settings. Memory retention in PBOs crosses organizational boundaries and establishes a knowledge network of former employees and third parties. The PBOs project memory can be divided into volatile and perennial memory, where the former can be lost throughout project execution and the latter is internalized, becoming an inseparable part of the corporate memory. Memory retrieval in PBOs is also distinct since it has particular mechanisms depending on whether the knowledge is technical or administrative. Originality/value The research investigates the corporate memory processes within the volatile context of PBOs in a Latin-American developing country whose culture favors tacit knowledge exchange. The paper proposes a framework that unveils different patterns of knowledge acquisition, temporary and perennial retention structures, intensive usage of external knowledge in memory retrieval and particular memory applications in PBOs. The framework may guide scholars, project managers, engineers and practitioners in navigating through the uniqueness of organizational learning flows and structures in PBOs

Optogenetic scrambling of hippocampal theta oscillations alters working memory retrieval but not hippocampal spatiotemporal codes

The precise temporal coordination of activity in the brain is thought to be fundamental for memory encoding and retrieval. The medial septum (MS) provides the largest source of innervation to the hippocampus (HPC), and its inhibitory neurons play a major role in controlling HPC theta (~8 Hz) oscillations. While pharmacological inhibition of the MS is associated with memory impairment, the exact role of MS inhibitory neurons in HPC function and memory is not fully understood. While HPC place cells were previously reported to not depend on MS inputs, the exact role of MS inputs on HPC temporal codes is still a matter of debate. Moreover, pharmacological manipulations do not have the temporal resolution to distinguish the role of MS activity on working memory encoding, retention and retrieval. Here we stimulated the MS with optogenetics to either pace or ablate theta, while recording large hippocampal assemblies over time using calcium imaging along with local field potentials to monitor theta control. Using scrambled light stimulation, we could robustly ablate theta signals, which was associated with direct modulation of a subpopulation of neurons in the HPC. We found that such stimulation led to decreased working memory retrieval, but not encoding in both a delayed non-match to sample task and a novel place object recognition task. Strikingly, scrambled stimulations were not associated with disrupted spatiotemporal codes. Importantly, we show that our opsin did not transfect cholinergic cells and stimulation did not disrupt HPC ripple activity or running speed, suggesting a specific role for MS GABAergic cells in memory maintenance and retrieval that is independent from these other potential confounding mechanisms. Our study suggests that theta signals play a specific and essential role in supporting working memory retrieval and maintenance while not being necessary for hippocampal spatiotemporal codes.

Intention and Monitoring Influence the Content of Memory Reports

Objectives While voluntary memories are intended and expected, involuntary memories are retrieved with no intention and are usually unexpected (when one is not waiting for a memory). The present study investigates the effects of retrieval intentionality ( wanting to retrieve a memory) and monitoring processes ( expecting a memory to appear) on the characteristics of autobiographical memories. Methods To this end, by applying mixed-method analysis of memory descriptions (i.e. combining qualitative with quantitative analyses) we re-analysed the large pool of involuntary and voluntary memories obtained in one previously published study, asking independent judges to rate all the memories on several dimensions reflecting memory accessibility (i.e. the likelihood that a memory can be retrieved). Results When discussing our findings, we speculate that there may be several stages of memory retrieval that might be differently influenced by intention and monitoring. Conclusions We discuss the novel hypothesis that there may be two different types of monitoring that operate independently of each other, before and after retrieval, respectively.

Dementia-Free Older Adults with Subjective Cognitive Impairment Show Lower Mood and No Deficits of Spontaneous Memory Retrieval

The aim of the present study was to investigate whether spontaneous retrieval deficits could be found in individuals with Subjective Cognitive Impairment (SCI). The sample consisted of 52 participants over 65 years of age (mean age = 76.00; SD = 7.48) with 11 males. We asked 26 individuals with SCI and 26 individuals without SCI to perform a prospective memory (PM) task that had previously demonstrated spontaneous retrieval deficits in individuals with Mild Cognitive Impairment. The results did not demonstrate the expected differences in a PM task based on spontaneous retrieval [ t(50) = −.05; p = .964, d = .01]. However, participants’ mood did predict their subjective memory complaints ( β = −.51; p < .001) and their subjective assessment of their future memory performance ( r = −.38; p < .01). The findings are in line with numerous studies which have shown that SCI is more related to mood disturbance than to objective cognitive functioning.