Ketamine Disrupts Frontal and Hippocampal Contribution to Encoding and Retrieval of Episodic Memory: An fMRI Study

Background: Episodic memory (EM) is particularly sensitive to pathological conditions and aging. In a neurocognitive context, the paired-associate learning (PAL) paradigm, which requires participants to learn and recall associations between stimuli, has been used to measure EM. The present study aimed to explore whether functional near-infrared spectroscopy (fNIRS) can be employed to determine cortical activity underlying encoding and retrieval. Moreover, we examined whether and how different aspects of task (i.e., novelty, difficulty) affects those cortical activities. Methods: Twenty-two male college students (age: M = 20.55, SD = 1.62) underwent a face-name PAL paradigm under 40-channel fNIRS covering fronto-parietal and middle occipital regions. Results: A decreased activity during encoding in a broad network encompassing the bilateral frontal cortex (Brodmann areas 9, 11, 45, and 46) was observed during the encoding, while an increased activity in the left orbitofrontal cortex (Brodmann area 11) was observed during the retrieval. Increased HbO concentration in the superior parietal cortices and decreased HbO concentration in the inferior parietal cortices were observed during encoding while dominant activation of left PFC was found during retrieval only. Higher task difficulty was associated with greater neural activity in the bilateral prefrontal cortex and higher task novelty was associated with greater activation in occipital regions. Conclusion: Combining the PAL paradigm with fNIRS provided the means to differentiate neural activity characterising encoding and retrieval. Therefore, the fNIRS may have the potential to complete EM assessments in clinical settings.

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Effects of ketamine on brain function during metacognition of episodic memory

Neuroscience of Consciousness ◽

10.1093/nc/niaa028 ◽

2021 ◽

Vol 2021 (1) ◽

Author(s):

Mirko Lehmann ◽

Claudia Neumann ◽

Sven Wasserthal ◽

Johannes Schultz ◽

Achilles Delis ◽

...

Keyword(s):

Episodic Memory ◽

Parietal Lobe ◽

Memory Task ◽

Reaction Times ◽

Neural Correlates ◽

Double Blind ◽

Lingual Gyrus ◽

States Of Consciousness ◽

Fmri Study ◽

Confidence Ratings

Abstract Only little research has been conducted on the pharmacological underpinnings of metacognition. Here, we tested the modulatory effects of a single intravenous dose (100 ng/ml) of the N-methyl-D-aspartate-glutamate-receptor antagonist ketamine, a compound known to induce altered states of consciousness, on metacognition and its neural correlates. Fifty-three young, healthy adults completed two study phases of an episodic memory task involving both encoding and retrieval in a double-blind, placebo-controlled fMRI study. Trial-by-trial confidence ratings were collected during retrieval. Effects on the subjective state of consciousness were assessed using the 5D-ASC questionnaire. Confirming that the drug elicited a psychedelic state, there were effects of ketamine on all 5D-ASC scales. Acute ketamine administration during retrieval had deleterious effects on metacognitive sensitivity (meta-d′) and led to larger metacognitive bias, with retrieval performance (d′) and reaction times remaining unaffected. However, there was no ketamine effect on metacognitive efficiency (meta-d′/d′). Measures of the BOLD signal revealed that ketamine compared to placebo elicited higher activation of posterior cortical brain areas, including superior and inferior parietal lobe, calcarine gyrus, and lingual gyrus, albeit not specific to metacognitive confidence ratings. Ketamine administered during encoding did not significantly affect performance or brain activation. Overall, our findings suggest that ketamine impacts metacognition, leading to significantly larger metacognitive bias and deterioration of metacognitive sensitivity as well as unspecific activation increases in posterior hot zone areas of the neural correlates of consciousness.

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Effects of division of attention during encoding and retrieval on age differences in episodic memory

Experimental Aging Research ◽

10.1080/03610739708254029 ◽

1997 ◽

Vol 23 (2) ◽

pp. 137-143 ◽

Cited By ~ 29

Author(s):

Lars Nyberg ◽

Lars-Göran Nilsson ◽

Ulrich Olofsson ◽

Lars Bäckman

Keyword(s):

Episodic Memory ◽

Age Differences ◽

Encoding And Retrieval

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The Effect of Divided Attention on Encoding and Retrieval in Episodic Memory Revealed by Positron Emission Tomography

Journal of Cognitive Neuroscience ◽

10.1162/089892900562093 ◽

2000 ◽

Vol 12 (2) ◽

pp. 267-280 ◽

Cited By ~ 89

Author(s):

Tetsuya Iidaka ◽

Nicole D. Anderson ◽

Shitij Kapur ◽

Roberto Cabez ◽

Fergus I. M. Craik

Keyword(s):

Positron Emission Tomography ◽

Prefrontal Cortex ◽

Episodic Memory ◽

Divided Attention ◽

Memory Performance ◽

Memory Task ◽

Anterior Cingulate ◽

Emission Tomography ◽

Positron Emission ◽

Encoding And Retrieval

The effects of divided attention (DA) on episodic memory encoding and retrieval were investigated in 12 normal young subjects by positron emission tomography (PET). Cerebral blood flow was measured while subjects were concurrently performing a memory task (encoding and retrieval of visually presented word pairs) and an auditory tone-discrimination task. The PET data were analyzed using multivariate Partial Least Squares (PLS), and the results revealed three sets of neural correlates related to specific task contrasts. Brain activity, relatively greater under conditions of full attention (FA) than DA, was identified in the occipital-temporal, medial, and ventral-frontal areas, whereas areas showing relatively more activity under DA than FA were found in the cerebellum, temporo-parietal, left anterior-cingulate gyrus, and bilateral dorsolateral-prefrontal areas. Regions more active during encoding than during retrieval were located in the hippocampus, temporal and the prefrontal cortex of the left hemisphere, and regions more active during retrieval than during encoding included areas in the medial and right-prefrontal cortex, basal ganglia, thalamus, and cuneus. DA at encoding was associated with specific decreases in rCBF in the left-prefrontal areas, whereas DA at retrieval was associated with decreased rCBF in a relatively small region in the right-prefrontal cortex. These different patterns of activity are related to the behavioral results, which showed a substantial decrease in memory performance when the DA task was performed at encoding, but no change in memory levels when the DA task was performed at retrieval.

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Context preference-based deep adaptive resonance theory: Integrating user preferences into episodic memory encoding and retrieval

2017 International Joint Conference on Neural Networks (IJCNN) ◽

10.1109/ijcnn.2017.7966079 ◽

2017 ◽

Author(s):

Dick Sigmund ◽

Gyeong-Moon Park ◽

Jong-Hwan Kim

Keyword(s):

Episodic Memory ◽

User Preferences ◽

Adaptive Resonance Theory ◽

Memory Encoding ◽

Resonance Theory ◽

Adaptive Resonance ◽

Encoding And Retrieval

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Effects of amnesia on processing in the hippocampus and default mode network during a naturalistic memory task: a case study

10.31234/osf.io/e9n8c ◽

2018 ◽

Author(s):

Christiane Oedekoven ◽

James L. Keidel ◽

Stuart Anderson ◽

Angus Nisbet ◽

Chris Bird

Keyword(s):

Functional Connectivity ◽

Episodic Memory ◽

Memory Performance ◽

Memory Task ◽

Structural Mri ◽

Brain Regions ◽

Left Hippocampus ◽

Cortical Regions ◽

The Right ◽

Encoding And Retrieval

Despite their severely impaired episodic memory, individuals with amnesia are able to comprehend ongoing events. Online representations of a current event are thought to be supported by a network of regions centred on the posterior midline cortex (PMC). By contrast, episodic memory is widely believed to be supported by interactions between the hippocampus and these cortical regions. In this MRI study, we investigated the encoding and retrieval of lifelike events (video clips) in a patient with severe amnesia likely resulting from a stroke to the right thalamus, and a group of 20 age-matched controls. Structural MRI revealed grey matter reductions in left hippocampus and left thalamus in comparison to controls. We first characterised the regions activated in the controls while they watched and retrieved the videos. There were no differences in activation between the patient and controls in any of the regions. We then identified a widespread network of brain regions, including the hippocampus, that were functionally connected with the PMC in controls. However, in the patient there was a specific reduction in functional connectivity between the PMC and a region of left hippocampus when both watching and attempting to retrieve the videos. A follow up analysis revealed that in controls the functional connectivity between these regions when watching the videos was correlated with memory performance. Taken together, these findings support the view that the interactions between the PMC and the hippocampus enable the encoding and retrieval of multimodal representations of the contents of an event.

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