Dynamic Memory Process Research Articles

Representational integration and differentiation in the human hippocampus following goal-directed navigation.

As we learn, dynamic memory processes build structured knowledge across our experiences. Such knowledge enables the formation of internal models of the world that we use to plan, make decisions, and act. Recent theorizing posits that mnemonic mechanisms of differentiation and integration - which at one level may seem to be at odds - both contribute to the emergence of structured knowledge. We tested this possibility using fMRI as human participants learned to navigate within local and global virtual environments over the course of 3 days. Pattern similarity analyses on entorhinal cortical and hippocampal patterns revealed evidence that differentiation and integration work concurrently to build local and global environmental representations, and that variability in integration relates to differences in navigation efficiency. These results offer new insights into the neural machinery and the underlying mechanisms that translate experiences into structured knowledge that allows us to navigate to achieve goals.

Has the concept of systems consolidation outlived its usefulness? Identification and evaluation of premises underlying systems consolidation.

Systems consolidation has mostly been treated as a neural construct defined by the time-dependent change in memory representation from the hippocampus (HPC) to other structures, primarily the neocortex. Here, we identify and evaluate the explicit and implicit premises that underlie traditional or standard models and theories of systems consolidation based on evidence from research on humans and other animals. We use the principle that changes in neural representation over time and experience are accompanied by corresponding changes in psychological representations, and vice versa, to argue that each of the premises underlying traditional or standard models and theories of systems consolidation is found wanting. One solution is to modify or abandon the premises or theories and models. This is reflected in moderated models of systems consolidation that emphasize the early role of the HPC in training neocortical memories until they stabilize. The fault, however, may lie in the very concept of systems consolidation and its defining feature. We propose that the concept be replaced by one of memory systems reorganization, which does not carry the theoretical baggage of systems consolidation and is flexible enough to capture the dynamic nature of memory from inception to very long-term retention and retrieval at a psychological and neural level. The term "memory system reorganization" implies that memory traces are not fixed, even after they are presumably consolidated. Memories can continue to change as a result of experience and interactions among memory systems across the lifetime. As will become clear, hippocampal training of neocortical memories is only one type of such interaction, and not always the most important one, even at inception. We end by suggesting some principles of memory reorganization that can help guide research on dynamic memory processes that capture corresponding changes in memory at the psychological and neural levels.

Differential effects of unipolar versus bipolar depression on episodic memory updating.

Episodic memories, when reactivated, can be modified or updated by new learning. Since such dynamic memory processes remain largely unexplored in psychiatric disorders, we examined the impact of depression on episodic memory updating. Unipolar and bipolar depression patients, and age/education matched controls, first learned a set of objects (List-1). Two days later, participants in all three groups were either reminded of the first learning session or not followed by the learning of a new set of objects (List-2). Forty-eight hours later, List-1 recall was impaired in unipolar and bipolar patients compared to control participants. Further, as expected, control participants who received a reminder spontaneously recalled items from List-2 during recall of List-1, indicative of an updated List-1 memory. Such spontaneous intrusions were also seen in the unipolar and bipolar patients that received the reminder, suggesting that memory updating was unaffected in these two patient groups despite impaired recall of List 1. Unexpectedly, we observed a trend towards higher intrusions, albeit statistically insignificant, not only in the reminder but also in the no-reminder subgroups of bipolar patients. We probed this further in a second cohort by testing recall of List-2, which was also impaired in both depression groups. Again bipolar patients showed intrusions, but this time in the reverse order from List-1 into List-2, independent of a reminder. Taken together, despite impaired recall, updating of episodic memories was intact and unidirectional in unipolar depression. In contrast, indiscriminate updating, as evidenced by bidirectional interference between episodic memories, was seen in bipolar depression. These findings reveal a novel distinction between unipolar versus bipolar depression using a reactivation-dependent memory updating paradigm.

The Baka symbolic landscape as a memory process

In the Jengi ceremony of the Baka (southern Cameroon), words used as names for spirits or with reference to the sound of a hunting amulet, the performance of the Jengi mask and its dance steps evoke a symbolic landscape. This landscape is made up of ‘anthropological places’ that, referring to more or less precise geographical locations, can be identified owing to their ecosystemic and sonorous aspects and to regional distinctions through toponyms as well as dialectal, ethnoecological variants. The variable degree of precision assigned to these anthropological places reflects the intensity of the relationships between ritual specialists who come from various regions to take part in a ceremony. A dynamic process is at work among the open anthropological places. This place-making occurs in an abstract manner as a dynamic memory process in contrast with the principle of commemorations or memorials that take the form of visible, stable, shrines, steles or sacred groves.

Hypothalamic and other connections with dorsal CA2 area of the mouse hippocampus

The CA2 area is an important, although relatively unexplored, component of the hippocampus. We used various tracers to provide a comprehensive analysis of CA2 connections in C57BL/6J mice. Using various adeno-associated viruses that express fluorescent proteins, we found a vasopressinergic projection from the paraventricular nuclei of the hypothalamus (PVN) to the CA2 as well as a projection from pyramidal neurons of the CA2 to the supramammillary nuclei. These projections were confirmed by retrograde tracing. As expected, we observed CA2 afferent projections from neurons in ipsilateral entorhinal cortical layer II as well as from bilateral dorsal CA2 and CA3 using retrograde tracers. Additionally, we saw CA2 neuronal input from bilateral medial septal nuclei, vertical and horizontal limbs of the nucleus of diagonal band of Broca, supramammillary nuclei (SUM), and median raphe nucleus. Dorsal CA2 injections of adeno-associated virus expressing green fluorescent protein revealed axonal projections primarily to dorsal CA1, CA2, and CA3 bilaterally. No projection was detected to the entorhinal cortex from the dorsal CA2. These results are consistent with recent observations that the dorsal CA2 forms disynaptic connections with the entorhinal cortex to influence dynamic memory processing. Mouse dorsal CA2 neurons send bilateral projections to the medial and lateral septal nuclei, vertical and horizontal limbs of the diagonal band of Broca, and SUM. Novel connections from the PVN and to the SUM suggest important regulatory roles for CA2 in mediating social and emotional input for memory processing.

Hippocampal alpha7 nicotinic receptors modulate memory reconsolidation of an inhibitory avoidance task in mice

CF-1 male mice were trained in an inhibitory avoidance (IA) task using either a mild or a high footshock (0.8 or 1.2 mA, 50 Hz, 1 s). A retention test was given 48 h later. Immediately after the retention test, mice were given intra-dorsal hippocampus infusions of either choline (Ch, an α7 nicotinic acetylcholine receptor (α7nAChR) agonist, 0.08–1.30 μg/hippocampus), or methyllycaconitine (MLA, an α7nAChR antagonist, 1.0–30.0 μg/hippocampus). Memory retention was tested again 24 h later. Methyllycaconitine impaired retention performance regardless of footshock intensity and its effects were long lasting. Ch impaired retention performance only in those mice trained with a high footshock. On the contrary, Ch enhanced retention performance when mice were trained with a mild footshock. These effects were long lasting and dose- and time-dependent. Retention performance was not affected in drug-treated mice that were not subjected to memory reactivation, suggesting that the performance effects could not be attributable to non-specific effects of the drugs. Methyllycaconitine effects were dose-dependently reversed by choline, suggesting that MLA and Ch interact at the α7nAChR. Altogether, results suggest that hippocampal α7nAChRs play a critical role in reconsolidation of an IA response in mice, and may also have important implications for dynamic memory processes. This is the first presentation, to our knowledge, indicating that a specific receptor (α7nAChR) is able to modulate consolidated memories after retrieval.

A Bridge Over Troubled Water: Reconsolidation as a Link Between Cognitive and Neuroscientific Memory Research Traditions

There are two research traditions on dynamic memory processes. In cognitive psychology, the malleable nature of long-term memory has been extensively documented. Distortions, such as the misinformation effect or hindsight bias, illustrate that memories can be easily changed, often without their owner taking notice. On the other hand, effects like hypermnesia demonstrate that memory might be more reliable than these distortions suggest. In the neuroscience field, similar observations were obtained mostly from animal studies. Research on memory consolidation suggested that memories become progressively resistant to amnesic treatments over time, but the reconsolidation phenomenon showed that this stability can be transiently lifted when these memories are reactivated, i.e., retrieved. Surprisingly, both research traditions have not taken much notice of each others' advances in understanding memory dynamics. We apply concepts developed in neuroscience to phenomena revealed in cognitive psychology to illustrate how these twins separated at birth may be reunited again.

Dynamic memory networks: dissecting molecular mechanisms underlying associative memory in the temporal domain.

The molecular mechanisms underlying the induction and maintenance of memory are highly dynamic and comprise distinct phases covering a time window from seconds to even a lifetime. Neuronal networks, which contribute to these processes, have been extensively characterized on various levels of analysis, and imaging techniques allow monitoring of both gross brain activity as well as functional changes in defined brain areas during the time course of memory formation. New techniques developed in honeybees and fruit flies even allow for manipulation of neuronal networks and molecular cascades in a short temporal domain while a living animal under observation acquires new associative memories. These advantages make honeybees and flies ideal organisms to study transient molecular events underlying dynamic memory processing in vivo. In this review we will focus on the temporal features of molecular processes in learning and memory formation, summarize recent knowledge and present an outlook on future developments.

Dynamic memory processes in retrieving answers to questions: Recall failures, judgments of knowing, and acquisition of information.

Dynamic memory processes in retrieving answers to questions: Recall failures, judgments of knowing, and acquisition of information.

Dynamic memory processes in retrieving answers to questions: Recall failures, judgments of knowing, and acquisition of information.

Dynamic memory processes in retrieving answers to questions: Recall failures, judgments of knowing, and acquisition of information.

Cognitive correlates of general intelligence: Toward a process theory of g

The cognitive correlates literature suggests that a general ability, probably Spearman's g, underlies most information processing/intelligence relationships. In the present paper we suggest that the nature of g is clarified by the following patterns: (a) response consistency has better predictive and convergent validity than does response speed, and (b) tasks which demand dynamic memory processing predict intelligence better than do tasks which require only stimulus encoding and simple stimulus/response translations. Accordingly, g appears related to the ability to flexibly and consistently reconfigure the contents of working memory. A possible physiological basis of this ability is the recruitment of the transient neural assemblies which underly thought (after Hebb, 1949).

Memory facilitation by posttrial hypothalamic stimulation and other reinforcers: A central theory of reinforcement

A central theory of reinforcement is presented, which is based on the assumption that reinforcers act directly on dynamic memory processes. One prediction from the model is that learning of various tasks should be improved as a result of reinforcement presented during the period of short-term memory. To test this hypothesis the reinforcers food, water or electrical stimulation of the lateral hypothalamus were presented posttrial in diverse learning situations. Posttrial food reinforcement facilitated passive avoidance learning in mice. In rats 30 sec of posttrial reinforcing brain stimulation facilitated learning of a shuttle-box avoidance, step-down avoidance, and small box avoidance. Appetitive T-maze learning was improved with posttrial reinforcing brain stimulation contingent on errors. Learning of a conditioned taste aversion was not influenced by reinforcing brain stimulation presented during the CS - UCS interval.