779 research outputs found

    Oscillations and Episodic Memory: Addressing the Synchronization/Desynchronization Conundrum

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    Brain oscillations are one of the core mechanisms underlying episodic memory. However, while some studies highlight the role of synchronized oscillatory activity, others highlight the role of desynchronized activity. We here describe a framework to resolve this conundrum and integrate these two opposing oscillatory behaviors. Specifically, we argue that the synchronization and desynchronization reflect a division of labor between a hippocampal and a neocortical system, respectively. We describe a novel oscillatory framework that integrates synchronization and desynchronization mechanisms to explain how the two systems interact in the service of episodic memory

    Sleep-Dependent Memory Consolidation and Incremental Sentence Comprehension : Computational Dependencies during Language Learning as Revealed by Neuronal Oscillations

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    We hypothesize a beneficial influence of sleep on the consolidation of the combinatorial mechanisms underlying incremental sentence comprehension. These predictions are grounded in recent work examining the effect of sleep on the consolidation of linguistic information, which demonstrate that sleep-dependent neurophysiological activity consolidates the meaning of novel words and simple grammatical rules. However, the sleep-dependent consolidation of sentence-level combinatorics has not been studied to date. Here, we propose that dissociable aspects of sleep neurophysiology consolidate two different types of combinatory mechanisms in human language: sequence-based (order-sensitive) and dependency-based (order-insensitive) combinatorics. The distinction between the two types of combinatorics is motivated both by cross-linguistic considerations and the neurobiological underpinnings of human language. Unifying this perspective with principles of sleep-dependent memory consolidation, we posit that a function of sleep is to optimize the consolidation of sequence-based knowledge (thewhen) and the establishment of semantic schemas of unordered items (thewhat) that underpin cross-linguistic variations in sentence comprehension. This hypothesis builds on the proposal that sleep is involved in the construction of predictive codes, a unified principle of brain function that supports incremental sentence comprehension. Finally, we discuss neurophysiological measures (EEG/MEG) that could be used to test these claims, such as the quantification of neuronal oscillations, which reflect basic mechanisms of information processing in the brain

    The ongoing search for the neuronal correlate of consciousness

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    A few decades ago the search for the neuronal correlates of consciousness was considered both technically intractable and philosophically questionable. Searching for a material substrate of phenomena accessible only from the first-person perspective appeared to be epistemically problematic. But the development of non-invasive imaging technologies and the availability of intracranial recordings from patients alleviated the imminent technical problems. Progress in the analysis of the connectome of the brain, and the introduction of multisite recordings from the cerebral cortex of animals led to a revision of concepts in the field of cognitive neuroscience, emphasizing principles of distributed processing in recurrent networks with non-linear dynamics, self-organization, and coding in high-dimensional-state space. These advances, together with the growing evidence for epigenetic shaping of brain functions by socio-cultural influences, pave the way for novel theories that attempt to bridge the gap between neuronal processes and subjective states

    A review of neurobiological factors underlying the selective enhancement of memory at encoding, consolidation, and retrieval

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    How is the strength of a memory determined? This review discusses three main factors that contribute to memory enhancement - 1) emotion, 2) targeted memory reactivation, and 3) neural reinstatement. Whilst the mechanisms through which memories become enhanced vary, this review demonstrates that activation of the basolateral amygdala and hippocampal formation are crucial for facilitating encoding, consolidation, and retrieval. Here we suggest methodological factors to consider in future studies, and discuss several unanswered questions that should be pursued in order to clarify selective memory enhancement

    Long-term memory encoding of facial information in humans: an EEG and tACS study

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    In recent years, the investigation of memory formation and retrieval has attracted increasing interest. As oscillatory activity plays a crucial role in neuroplastic processes, episodic memory is to a considerable extent attributable to synaptic changes, synchronization, and neurophysiological alterations through oscillating electric fields. Perception processes are part of episodic memory encoding. Human face perception and encoding arouse particular interest due to their fundamental relevance in social behavior. This study aimed to determine the causal role of brain dynamics in the encoding of facial episodic memory in humans. As recent studies revealed an enhancement in cognitive processes by the entrainment of internal brain oscillations, tACS stepped up as a new method of non-invasive brain stimulation to induce neuroplasticity (Antal et al. 2008; Antal and Herrmann 2016). It is a promising tool to test the role of brain oscillations on episodic memory encoding in humans and the potential for memory improvement. For the entire study, we developed a memory task that includes encoding, a Short-Term Memory Retrieval Part, maintenance, and a Long-Term Memory Retrieval Part. In the longterm face recognition, we assessed both the performance and the choice confidence on the 3-point scale. Two consecutive experiments were performed. For the first experiment (20 participants), we used 128-channel EEG to identify the region of the brain that is exclusively responsible for the long-term face encoding and the frequency of the brain rhythm that is associated with the successful subsequent recognition. Then, we conducted the tACS experiment (25 participants) based on the frequency and spatial data from the EEG experiment. We implemented a double-blinded, randomized, counterbalanced, crossover, and placebo-controlled study design. 20 minutes of 4 Hz-tACS at 3 mA peak-to-peak were applied during the encoding task to the identified right or to the left TPO area for active control. One more session included sham stimulation to one or the other area. The EEG study revealed a significant synchronization of brain oscillations during successful long-term facial memory encoding in the right TPO area at the low theta range (4 Hz). In complete agreement, the placebo-controlled tACS study showed a significant enhancement of long-term memory recognition performance after the low theta-stimulation of the right but not the left TPO area. The results indicate that low theta oscillations in the right TPO area are vital for successful episodic long-term memory encoding of facial stimuli. Secondly, we confirm that active low theta-tACS applied on this area during encoding improves the subsequent memory recognition performance. This supports the concept of lateralization for face processing in the right posterior brain region; moreover it puts forward this area as a crucial neocortical node in communication with the hippocampus for the long-term memory encoding (Pitcher et al. 2011; Geib et al. 2017). The results are in agreement with other studies that revealed a positive correlation between theta power and memory performance (Pahor and Jaušovec 2014; Clouter et al. 2017). However, the present work reveals a causal link between the empowered low theta in the right TPO area and enhanced subsequent long-term memory recognition. In summary, tACS is a highly suitable non-invasive tool to entrain local neocortical low theta activity and enhance long-term memory encoding, which is important in the clinical context for revealing novel therapeutic strategies in prosopagnosia and prosopamnesia.2021-09-1

    The influence of typeface fluency on simple sentence encoding as measured through spectral power analysis

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    This item is only available electronically.Previous research has shown that typeface fluency has an impact on the encoding and processing of written texts. Specifically, less fluent letters and words appear to be processed more deeply and remembered more accurately. To date, there is limited research regarding the mechanisms by which typeface fluency impacts on the encoding of full sentences. Therefore, this study aimed to expand on this research by focusing on the way it can be applied to the encoding of full sentences. Participants were asked to memorise simple sentences presented in either a fluent or disfluent typeface. Electroencephalography was used to record the changes in spectral power during the learning phase in order to determine the level of encoding success. Following a period of distraction, an audio-presented recall task was used to assess recall accuracy. Fluency was found to be associated with changes in alpha power at learning. Further, alpha power significantly differed between the parietal and occipital regions of the brain but did not show any reaction with fluency. Due to performance ceiling effects, these findings could not be associated with memory outcomes. This research is especially relevant to education, as much of the information presented in schooling is digitally presented text. Keywords: electroencephalography, spectral power, typeface fluency, language encoding, typographyThesis (B.PsychSc(Hons)) -- University of Adelaide, School of Psychology, 201

    Alpha Oscillations during Incidental Encoding Predict Subsequent Memory for New "Foil" Information.

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    People can employ adaptive strategies to increase the likelihood that previously encoded information will be successfully retrieved. One such strategy is to constrain retrieval toward relevant information by reimplementing the neurocognitive processes that were engaged during encoding. Using EEG, we examined the temporal dynamics with which constraining retrieval toward semantic versus nonsemantic information affects the processing of new "foil" information encountered during a memory test. Time-frequency analysis of EEG data acquired during an initial study phase revealed that semantic compared with nonsemantic processing was associated with alpha decreases in a left frontal electrode cluster from around 600 msec after stimulus onset. Successful encoding of semantic versus nonsemantic foils during a subsequent memory test was related to decreases in alpha oscillatory activity in the same left frontal electrode cluster, which emerged relatively late in the trial at around 1000-1600 msec after stimulus onset. Across participants, left frontal alpha power elicited by semantic processing during the study phase correlated significantly with left frontal alpha power associated with semantic foil encoding during the memory test. Furthermore, larger left frontal alpha power decreases elicited by semantic foil encoding during the memory test predicted better subsequent semantic foil recognition in an additional surprise foil memory test, although this effect did not reach significance. These findings indicate that constraining retrieval toward semantic information involves reimplementing semantic encoding operations that are mediated by alpha oscillations and that such reimplementation occurs at a late stage of memory retrieval, perhaps reflecting additional monitoring processes
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