A simulation of older adults’ associative memory deficit using structural process interference in young adults

Associative memory deficit underlies a part of older adults’ deficient episodic memory due to the reduced ability to bind units of information. In this article we further assess the mechanism underlying this deficit, by assessing the degree to which we can model it in young adults under conditions of divided attention. We shall describe two experiments in this paper; these experiments investigate item and associative recognition in young adults under full- or divided-attention conditions. The secondary tasks employed were N-back like (NBL), which serves as a working memory updating task, and parity judgement and visuospatial (VS) tasks, which serve as non-working memory tasks. The results of both experiments show that only the NBL specifically affected associative recognition, while the other tasks affected item and associative memory to the same degree, indicating a general resource competition. These results presented a convergence of evidence for the associative deficit in older adults by modelling it in young adults.

A multistage retrieval account of associative recognition ROC curves

Despite its name, associative recognition is a paradigm thought to rely on memory recall. However, it remains unclear how associative information may be represented and retrieved from memory and what its relationship to other information, such as item memory, is. Here, we propose a computational model of associative recognition, where relational information is accessed in a generic, multistage retrieval process. The model explains the relative difficulty of associative recognition compared with item recognition, the difference in experimental outcomes when different types of lures are used, as well as the conditions leading to the emergence of associative ROC curves with different shapes.

Encoding and retrieval of associative recognition memory engage different sub-networks within a hippocampal-thalamo-cortical memory circuit

Recognition of previously encountered stimuli and their associated spatial and temporal information depends on neural activity within a brain-wide network in which the CA1 region of the hippocampus, nucleus reuniens of the thalamus (NRe) and medial prefrontal cortex (mPFC) are key nodes. However, the pathways crucial for coordinating activity during memory encoding and/or retrieval phases have been little explored. Here we opto- or chemo associative recognition memory. We discovered that encoding, but not retrieval depended on the CA1 to mPFC and NRe to mPFC projections. In contrast, retrieval depended on the mPFC to NRe projection. Interestingly the NRe to CA1 pathway was required for both memory phases. Our findings therefore reveal that encoding and retrieval engage dissociable sub-networks within a hippocampal-thalamo-cortical recognition memory circuit in order to enable binding of recent and related information, whilst ensuring a separation of processing.

Thalamic bursts modulate cortical synchrony locally to switch between states of global functional connectivity in a cognitive task

Performing a cognitive task requires going through a sequence of functionally diverse stages. Although it is typically assumed that these stages are characterized by distinct states of cortical synchrony that are triggered by sub-cortical events, little reported evidence supports this hypothesis. To test this hypothesis, we first identified cognitive stages in single-trial MEG data of an associative recognition task, showing with a novel method that each stage begins with local modulations of synchrony followed by a state of directed functional connectivity. Second, we developed the first whole-brain model that can simulate cortical synchrony throughout a task. The model suggests that the observed synchrony is caused by thalamocortical bursts at the onset of each stage, targeted at cortical synapses and interacting with the structural anatomical connectivity. These findings confirm that cognitive stages are defined by distinct states of cortical synchrony and explains the network-level mechanisms necessary for reaching stage-dependent synchrony states.

Sources of interference in item and associative recognition memory

A powerful theoretical framework for exploring recognition memory is the global matchingframework, in which a cue’s memory strength reflects the similarity of the retrieval cuesbeing matched against the contents of memory simultaneously. Contributions at retrievalcan be categorized as matches and mismatches to the item and context cues, including theself match (match on item and context), item noise (match on context, mismatch on item),context noise (match on item, mismatch on context), and background noise (mismatch onitem and context). We present a model that directly parameterizes the matches andmismatches to the item and context cues, which enables estimation of the magnitude ofeach interference contribution (item noise, context noise, and background noise). Themodel was fit within a hierarchical Bayesian framework to ten recognition memory datasetsthat employ manipulations of strength, list length, list strength, word frequency, study-testdelay, and stimulus class in item and associative recognition. Estimates of the modelparameters revealed at most a small contribution of item noise that varies by stimulusclass, with virtually no item noise for single words and scenes. Despite the unpopularity ofbackground noise in recognition memory models, background noise estimates dominated atretrieval across nearly all stimulus classes with the exception of high frequency words,which exhibited equivalent levels of context noise and background noise. These parameterestimates suggest that the majority of interference in recognition memory stems fromexperiences acquired prior to the learning episode.

Long-term associative memory in rats: Effects of familiarization period in object-place-context recognition test

Spontaneous recognition tests, which utilize rodents’ innate tendency to explore novelty, can evaluate not only simple non-associative recognition memory but also more complex associative memory in animals. In the present study, we investigated whether the length of the object familiarization period (sample phase) improved subsequent novelty discrimination in the spontaneous object, place, and object-place-context (OPC) recognition tests in rats. In the OPC recognition test, rats showed a significant novelty preference only when the familiarization period was 30 min but not when it was 5 min or 15 min. In addition, repeated 30-min familiarization periods extended the significant novelty preference to 72 hours. However, the rats exhibited a successful discrimination between the stayed and replaced objects under 15 min and 30 min familiarization period conditions in the place recognition test and between the novel and familiar objects under all conditions of 5, 15 and 30 min in the object recognition test. Our results suggest that the extension of the familiarization period improves performance in the spontaneous recognition paradigms, and a longer familiarization period is necessary for long-term associative recognition memory than for non-associative memory.

The Discovery and Interpretation of Evidence Accumulation Stages

To improve the understanding of cognitive processing stages, we combined two prominent traditions in cognitive science: evidence accumulation models and stage discovery methods. While evidence accumulation models have been applied to a wide variety of tasks, they are limited to tasks in which decision-making effects can be attributed to a single processing stage. Here, we propose a new method that first uses machine learning to discover processing stages in EEG data and then applies evidence accumulation models to characterize the duration effects in the identified stages. To evaluate this method, we applied it to a previously published associative recognition task (Application 1) and a previously published random dot motion task with a speed-accuracy trade-off manipulation (Application 2). In both applications, the evidence accumulation models accounted better for the data when we first applied the stage-discovery method, and the resulting parameter estimates where generally in line with psychological theories. In addition, in Application 1 the results shed new light on target-foil effects in associative recognition, while in Application 2 the stage discovery method identified an additional stage in the accuracy-focused condition — challenging standard evidence accumulation accounts. We conclude that the new framework provides a powerful new tool to investigate processing stages.

Developmental decrease of entorhinal gate disrupts prefrontal-hippocampal communication in immune-challenged DISC1 knockdown mice

The prefrontal-hippocampal dysfunction that underlies cognitive deficits in mental disorders emerges during early development. The contribution of the lateral entorhinal cortex (LEC), a gatekeeper of prefrontal cortex (PFC) and hippocampus (HP), to the early dysfunction is fully unknown. Here we show that the poorer LEC-dependent associative recognition memory detectable at pre-juvenile age is preceded by abnormal communication within LEC-HP-PFC networks of neonatal mice mimicking the combined genetic and environmental etiology (GE) of disease. The prominent entorhinal drive to HP is weaker in GE mice as a result of sparser projections from LEC to CA1 and decreased efficiency of axonal terminals to activate the hippocampal circuits. In contrast, the direct entorhinal drive to PFC is not affected in GE mice, yet the PFC is indirectly compromised, as target of the under-activated HP. Thus, already at neonatal age, the entorhinal function gating prefrontal-hippocampal circuits is impaired in a mouse model of disease.