Involuntary and voluntary memory retrieval relies on distinct neural representations and oscillatory processes.

Involuntary memory retrieval is a hallmark symptom of posttraumatic stress disorder and a frequent phenomenon in everyday autobiographical memory. However, the neural mechanisms that drive involuntary retrieval remain unclear. This study aims to elucidate how involuntary retrieval spontaneously initiates memory reactivation and how the reactivated neural representations differ in their content, distinctiveness and temporal compression from voluntary retrieval.

Representational dynamics during extinction of fear memories in the human brain.

Extinction learning-the suppression of a previously acquired fear response-is critical for adaptive behaviour and core for understanding the aetiology and treatment of anxiety disorders. Electrophysiological studies in rodents have revealed critical roles of theta (4-12 Hz) oscillations in amygdala and hippocampus during both fear learning and extinction, and engram research has shown that extinction relies on the formation of novel, highly context-dependent memory traces that suppress the initial fear memories. Whether similar processes occur in humans and how they relate to previously described neural mechanisms of episodic memory formation and retrieval remains unknown.

Reinstatement and transformation of memory traces for recognition.

Episodic memory relies on the formation and retrieval of content-specific memory traces. In addition to their veridical reactivation, previous studies have indicated that traces may undergo substantial transformations. However, the exact time course and regional distribution of reinstatement and transformation during recognition memory have remained unclear.

Maintenance and transformation of representational formats during working memory prioritization.

Visual working memory depends on both material-specific brain areas in the ventral visual stream (VVS) that support the maintenance of stimulus representations and on regions in the prefrontal cortex (PFC) that control these representations. How executive control prioritizes working memory contents and whether this affects their representational formats remains an open question, however. Here, we analyzed intracranial EEG (iEEG) recordings in epilepsy patients with electrodes in VVS and PFC who performed a multi-item working memory task involving a retro-cue.

The memory trace of a stressful episode.

Stress influences episodic memory formation via noradrenaline and glucocorticoid effects on amygdala and hippocampus. A common finding is the improvement of memory for central aspects of a stressful episode. This is putatively related to changes in the neural representations of specific experiences, i.

Tracking Selective Rehearsal and Active Inhibition of Memory Traces in Directed Forgetting.

Selectively remembering or forgetting newly encountered information is essential for goal-directed behavior. It is still an open question, however, whether intentional forgetting is an active process based on the inhibition of unwanted memory traces or whether it occurs passively through reduced recruitment of selective rehearsal [1, 2]. Here, we show that intentional control of memory encoding relies on both, enhanced active inhibition and decreased selective rehearsal, and that these two processes can be separated in time and space.

Spectral fingerprints or spectral tilt? Evidence for distinct oscillatory signatures of memory formation.

Decreases in low-frequency power (2-30 Hz) alongside high-frequency power increases (>40 Hz) have been demonstrated to predict successful memory formation. Parsimoniously, this change in the frequency spectrum can be explained by one factor, a change in the tilt of the power spectrum (from steep to flat) indicating engaged brain regions. A competing view is that the change in the power spectrum contains several distinct brain oscillatory fingerprints, each serving different computations.

Stress Elevates Frontal Midline Theta in Feedback-based Category Learning of Exceptions.

Adapting behavior based on category knowledge is a fundamental cognitive function, which can be achieved via different learning strategies relying on different systems in the brain. Whereas the learning of typical category members has been linked to implicit, prototype abstraction learning, which relies predominantly on prefrontal areas, the learning of exceptions is associated with explicit, exemplar-based learning, which has been linked to the hippocampus. Stress is known to foster implicit learning strategies at the expense of explicit learning.

Spatial Mnemonic Encoding: Theta Power Decreases and Medial Temporal Lobe BOLD Increases Co-Occur during the Usage of the Method of Loci.

The method of loci is one, if not the most, efficient mnemonic encoding strategy. This spatial mnemonic combines the core cognitive processes commonly linked to medial temporal lobe (MTL) activity: spatial and associative memory processes. During such processes, fMRI studies consistently demonstrate MTL activity, while electrophysiological studies have emphasized the important role of theta oscillations (3-8 Hz) in the MTL.

Entrainment of prefrontal beta oscillations induces an endogenous echo and impairs memory formation.

Brain oscillations across all frequency bands play a key role for memory formation. Specifically, desynchronization of local neuronal assemblies in the left inferior prefrontal cortex (PFC) in the beta frequency (∼18 Hz) has been shown to be central for encoding of verbal memories. However, it remains elusive whether prefrontal beta desynchronization is causally relevant for memory formation and whether these endogenous beta oscillations can be entrained by external stimulation.

Brain oscillatory subsequent memory effects differ in power and long-range synchronization between semantic and survival processing.

Memory crucially depends on the way information is processed during encoding. Differences in processes during encoding not only lead to differences in memory performance but also rely on different brain networks. Although these assumptions are corroborated by several previous fMRI and ERP studies, little is known about how brain oscillations dissociate between different memory encoding tasks.

Oscillatory power decreases and long-term memory: the information via desynchronization hypothesis.

The traditional belief is that brain oscillations are important for human long-term memory, because they induce synchronized firing between cell assemblies which shapes synaptic plasticity. Therefore, most prior studies focused on the role of synchronization for episodic memory, as reflected in theta (∼5 Hz) and gamma (>40 Hz) power increases. These studies, however, neglect the role that is played by neural desynchronization, which is usually reflected in power decreases in the alpha and beta frequency band (8-30 Hz).