scholarly journals Signal complexity of human intracranial EEG tracks successful associative memory formation across individuals

2017 ◽  
Author(s):  
Timothy C. Sheehan ◽  
Vishnu Sreekumar ◽  
Sara K. Inati ◽  
Kareem A. Zaghloul
Keyword(s):  
Verbal Memory ◽  
Memory Performance ◽  
Memory Task ◽  
Low Frequency ◽  
Human Memory ◽  
Memory Formation ◽  
Intracranial Eeg ◽  
Neural Signal ◽  
Signal Complexity ◽  
Successful Recall

AbstractMemory performance is highly variable between individuals. Most studies examining human memory, however, have largely focused on the neural correlates of successful memory formation within individuals, rather than the differences between them. As such, what gives rise to this variability is poorly understood. Here, we examined intracranial EEG (iEEG) recordings captured from 43 participants (23 male) implanted with subdural electrodes for seizure monitoring as they performed a paired-associates verbal memory task. We identified three separate but related signatures of neural activity that tracked differences in successful memory formation across individuals. High performing individuals consistently exhibited less broadband power, flatter power spectral density (PSD) slopes, and greater complexity in their iEEG signals. Furthermore, within individuals across three separate time scales ranging from seconds to days, successful recall was positively associated with these same metrics. Our data therefore suggest that memory ability across individuals can be indexed by increased neural signal complexity.Significance StatementWe show that participants whose intracranial EEG exhibits less low frequency power, flatter power spectrums, and greater sample entropy overall are better able to memorize associations, and that the same metrics track fluctuations in memory performance across time within individuals. These metrics together signify greater neural signal complexity which may index the brain’s ability to flexibly engage with information and generate separable memory representations. Critically, the current set of results provide a unique window into the neural markers of individual differences in memory performance which have hitherto been underexplored.

scholarly journals No evidence for changes in GABA concentration, functional connectivity, or working memory following continuous theta burst stimulation over dorsolateral prefrontal cortex

2021 ◽  
Author(s):  
Tribikram Thapa ◽  
Joshua Hendrikse ◽  
Sarah Thompson ◽  
Chao Suo ◽  
Mana Biabani ◽  
...  
Keyword(s):  
Working Memory ◽  
Functional Connectivity ◽  
Memory Performance ◽  
Memory Task ◽  
Low Frequency ◽  
Theta Burst Stimulation ◽  
Gaba Concentration ◽  
Dorsolateral Prefrontal ◽  
Theta Burst ◽  
Continuous Theta Burst Stimulation

Continuous theta burst stimulation (cTBS) is thought to reduce cortical excitability and modulate functional connectivity, possibly by altering cortical inhibition at the site of stimulation. However, most evidence comes from the motor cortex and it remains unclear whether similar effects occur following stimulation over other brain regions. We assessed whether cTBS over left dorsolateral prefrontal cortex altered gamma aminobutyric acid (GABA) concentration, functional connectivity and brain dynamics at rest, and brain activation and memory performance during a working memory task. Seventeen healthy individuals participated in a randomised, sham-controlled, cross-over experiment. Before and after either real or sham cTBS, magnetic resonance spectroscopy was obtained at rest to measure GABA concentrations, whereas functional magnetic resonance imaging (fMRI) was recorded at rest and during an n-back working memory task to measure functional connectivity, brain dynamics (low-frequency fluctuations), and task-related patterns of brain activity. We could not find evidence for changes in GABA concentration (P=0.66, Bayes factor [BF10]=0.07), resting-state functional connectivity (P(FWE)>0.05), resting-state low-frequency fluctuations (P=0.88, BF10=0.04), blood-oxygen level dependent activity during the n-back task (P(FWE) >0.05), or working memory performance (P=0.13, BF10=0.05) following real or sham cTBS. Our findings add to a growing body of literature suggesting the effects of cTBS are highly variable between individuals and question the notion that cTBS is a universal 'inhibitory' paradigm.

scholarly journals The genomic underpinnings of oscillatory biomarkers supporting successful memory encoding in humans

2019 ◽  
Author(s):  
Stefano Berto ◽  
Miles Fontenot ◽  
Sarah Seger ◽  
Fatma Ayhan ◽  
Emre Caglayan ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Memory Performance ◽  
Temporal Cortex ◽  
Memory Task ◽  
Memory Formation ◽  
Inhibitory Neurons ◽  
Patient Specific ◽  
Memory Encoding ◽  
Brain Oscillations ◽  
Resected Tissue

AbstractIn humans, brain oscillations are thought to support critical features of memory formation such as coordination of activity across regions, consolidation, and temporal ordering of events. However, understanding the molecular mechanisms underlining this activity in humans remains a major challenge. Here, we measured memory-sensitive oscillations using direct intracranial electroencephalography recordings from the temporal cortex of patients performing an episodic memory task. By then employing transcriptomics on the resected tissue from the same patients, we linked gene expression with brain oscillations, identifying genes correlated with oscillatory signatures of memory formation across six frequency bands. A co-expression analysis isolated biomarker-specific modules associated with neuropsychiatric disorders as well as ion channel activity. Using single-nuclei transcriptomic data from this resected tissue, we further revealed that biomarker-specific modules are enriched for both excitatory and inhibitory neurons. This unprecedented dataset of patient-specific brain oscillations coupled to genomics unlocks new insights into the genetic mechanisms that support memory encoding. By linking brain expression of these genes to oscillatory patterns, our data help overcome limitations of phenotypic methods to uncover genetic links to memory performance.

Low frequency traveling waves in the human cortex coordinate neural activity across spatial scales

2020 ◽  
Author(s):  
Vishnu Sreekumar ◽  
John H. Wittig ◽  
Julio Chapeton ◽  
Sara K. Inati ◽  
Kareem A. Zaghloul
Keyword(s):  
Temporal Lobe ◽  
Traveling Waves ◽  
Verbal Memory ◽  
Single Unit ◽  
Spatial Scales ◽  
Memory Task ◽  
Low Frequency ◽  
Oscillatory Activity ◽  
Neural Communication ◽  
Macro Scale

AbstractTraveling waves of oscillatory activity are thought to influence neuronal spiking, providing a spatiotemporal frame-work for neural communication. However, no direct link has been established between traveling waves and single unit spiking in humans. We examined traveling waves in the human lateral temporal lobe by using recordings from intracranial electrodes implanted in twenty participants for seizure monitoring as they performed a paired-associates verbal memory task. We observed ubiquitous low frequency traveling waves across the temporal lobe. While wave occurrence in a broad low frequency range did not differ between successful and unsuccessful memory conditions, in a subset of participants with microelectrode recordings, we found that macro-scale waves co-occurred with micro-scale waves, which in turn were temporally locked to single unit spiking. This temporal coordination between traveling waves at different spatial scales and between waves and neuronal spiking in the human brain suggests a role for traveling waves in neural communication.

An Examination of Study Time Allocation as a Contributor to Sex Differences in Multitrial Verbal Learning Performance

2021 ◽  
pp. 003329412198929
Author(s):  
Lacy E. Krueger
Keyword(s):  
Sex Differences ◽  
Verbal Memory ◽  
Time Allocation ◽  
Memory Performance ◽  
Verbal Learning ◽  
Memory Task ◽  
Study Time ◽  
Learning Performance ◽  
Superiority Effect ◽  
Study Time Allocation

Researchers have noted sex differences in verbal memory performance with females showing a memory superiority effect. Research paradigms have largely incorporated experimenter-timed materials. Therefore, the extent to which self-regulating study time influences this pattern of sex differences is unclear. The researcher reexamined data from a published paper to determine whether sex differences in multitrial verbal learning are minimized when individuals self-regulate their study time, or if sex differences would still remain. The results from this study showed that females outperformed males on subsequent test trials, and they allocated more study time. Controlling for the influence of study time allocation reduced or eliminated sex differences in memory performance, and only study time allocation was related to whether items were gained or lost across trials. These findings suggest the importance of self-regulated learning in reducing sex differences on a verbal memory task and the contribution of study time allocation to memory performance.

scholarly journals The olfactory bulb modulates entorhinal cortex oscillations during spatial working memory

2021 ◽  
Vol 71 (1) ◽  
Author(s):  
Morteza Salimi ◽  
Farhad Tabasi ◽  
Milad Nazari ◽  
Sepideh Ghazvineh ◽  
Alireza Salimi ◽  
...  
Keyword(s):  
Working Memory ◽  
Olfactory Bulb ◽  
Entorhinal Cortex ◽  
Spatial Working Memory ◽  
Memory Performance ◽  
Memory Task ◽  
Low Frequency ◽  
Rhythmic Activity ◽  
Brain Regions ◽  
Simultaneous Recording

AbstractCognitive functions such as working memory require integrated activity among different brain regions. Notably, entorhinal cortex (EC) activity is associated with the successful working memory task. Olfactory bulb (OB) oscillations are known as rhythms that modulate rhythmic activity in widespread brain regions during cognitive tasks. Since the OB is structurally connected to the EC, we hypothesized that OB could modulate EC activity during working memory performance. Herein, we explored OB–EC functional connectivity during spatial working memory performance by simultaneous recording local field potentials when rats performed a Y-maze task. Our results showed that the coherence of delta, theta, and gamma-band oscillations between OB and EC was increased during correct trials compared to wrong trials. Cross-frequency coupling analyses revealed that the modulatory effect of OBs low-frequency phase on EC gamma power and phase was enhanced when animals correctly performed working memory task. The influx of information from OB to EC was also increased at delta and gamma bands within correct trials. These findings indicated that the modulatory influence of OB rhythms on EC oscillations might be necessary for successful working memory performance.

Oscillatory Theta Activity during Memory Formation and Its Impact on Overnight Consolidation: A Missing Link?

2015 ◽  
Vol 27 (8) ◽  
pp. 1648-1658 ◽  
Author(s):  
Dominik P. J. Heib ◽  
Kerstin Hoedlmoser ◽  
Peter Anderer ◽  
Georg Gruber ◽  
Josef Zeitlhofer ◽  
...  
Keyword(s):  
Memory Performance ◽  
Memory Task ◽  
Memory Formation ◽  
Theta Activity ◽  
Sleep Spindles ◽  
Sleep Spindle ◽  
Control Task ◽  
Spindle Activity ◽  
Before And After ◽  
Neuronal Processes

Sleep has been shown to promote memory consolidation driven by certain oscillatory patterns, such as sleep spindles. However, sleep does not consolidate all newly encoded information uniformly but rather “selects” certain memories for consolidation. It is assumed that such selection depends on salience tags attached to the new memories before sleep. However, little is known about the underlying neuronal processes reflecting presleep memory tagging. The current study sought to address the question of whether event-related changes in spectral theta power (theta ERSP) during presleep memory formation could reflect memory tagging that influences subsequent consolidation during sleep. Twenty-four participants memorized 160 word pairs before sleep; in a separate laboratory visit, they performed a nonlearning control task. Memory performance was tested twice, directly before and after 8 hr of sleep. Results indicate that participants who improved their memory performance overnight displayed stronger theta ERSP during the memory task in comparison with the control task. They also displayed stronger memory task-related increases in fast sleep spindle activity. Furthermore, presleep theta activity was directly linked to fast sleep spindle activity, indicating that processes during memory formation might indeed reflect memory tagging that influences subsequent consolidation during sleep. Interestingly, our results further indicate that the suggested relation between sleep spindles and overnight performance change is not as direct as once believed. Rather, it appears to be mediated by processes beginning during presleep memory formation. We conclude that theta ERSP during presleep memory formation reflects cortico-hippocampal interactions that lead to a better long-term accessibility by tagging memories for sleep spindle-related reprocessing.

scholarly journals Abnormal Temporal Lobe Response in Alzheimer's Disease during Cognitive Processing as Measured by 11C-2-Deoxy-D-Glucose and PET

1987 ◽  
Vol 7 (2) ◽  
pp. 248-251 ◽  
Author(s):  
J. D. Miller ◽  
M. J. de Leon ◽  
S. H. Ferris ◽  
A. Kluger ◽  
A. E. George ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Cognitive Processing ◽  
Temporal Lobe ◽  
Verbal Memory ◽  
Right Hemisphere ◽  
Memory Performance ◽  
Memory Task ◽  
Metabolic Rates ◽  
Positron Emission

Elderly controls and probable Alzheimer's disease patients underwent serial positron emission tomography (PET) studies during a baseline condition and while performing a verbal memory task. for the temporal lobes, all 7 Alzheimer patients demonstrated a relative shift in glucose metabolic rates to the right hemisphere during the memory condition relative to baseline, and 5 of 7 controls showed a shift to the left hemisphere. Baseline absolute regional metabolic rates replicate previous findings and were somewhat less useful than the memory challenge in differentiating patients from controls. These results indicate that a temporal lobe abnormality in Alzheimer's disease is related to memory performance.

scholarly journals Slow rTMS to the left DLPFC enhances verbal memory formation

2021 ◽  
Author(s):  
Mircea van der Plas ◽  
Verena Braun ◽  
Benjamin Johannes Stauch ◽  
Simon Hanslmayr
Keyword(s):  
Prefrontal Cortex ◽  
Verbal Memory ◽  
Repetitive Transcranial Magnetic Stimulation ◽  
Incidental Finding ◽  
Memory Performance ◽  
Memory Formation ◽  
Control Group ◽  
Specific Information ◽  
Left Dlpfc ◽  
Beta Power

AbstractEncoding of episodic memories relies on stimulus-specific information processing and involves the left prefrontal cortex. We here present an incidental finding from a simultaneous EEG-TMS experiment as well as a replication of this unexpected effect. Our results reveal that stimulating the left dorsolateral prefrontal cortex (DLPFC) with slow repetitive transcranial magnetic stimulation (rTMS) leads to enhanced word memory performance. 40 healthy human participants engaged in a list learning paradigm. Half of the subjects (N=20) received 1 Hz rTMS to the left DLPFC while the other half (N=20) received 1 Hz rTMS to the vertex and served as a control group. Subjects receiving left DLPFC stimulation demonstrated enhanced memory performance compared to the control group. This effect was replicated in a double-blind within-subjects experiment where 24 participants received 1 Hz rTMS to the left DLPFC and vertex. In this second experiment, DLPFC stimulation also induced better memory performance compared to vertex stimulation. In addition to these behavioural effects, we found that 1 Hz rTMS to DLPFC induced stronger beta power modulation in posterior areas, a state which is known to be beneficial for memory encoding. Further analysis indicated, that beta modulations did not have an oscillatory origin. Instead, the observed beta modulations were a result of a spectral tilt, suggesting inhibition of these parietal regions. These results show that applying 1 Hz rTMS to DLPFC, an area involved in episodic memory formation, improves memory performance via modulating neural activity in parietal regions.

scholarly journals Oscillations support co-firing of neurons in the service of human memory formation

2021 ◽  
Author(s):  
Frédéric Roux ◽  
George Parish ◽  
Ramesh Chelvarajah ◽  
David T. Rollings ◽  
Vijay Sawlani ◽  
...  
Keyword(s):  
Temporal Lobe ◽  
Medial Temporal Lobe ◽  
Information Transfer ◽  
Memory Task ◽  
Human Memory ◽  
Gamma Oscillations ◽  
Memory Formation ◽  
Neural Firing ◽  
Memory Failure

AbstractBrain oscillations have been demonstrated to support information transfer between neurons in animal models of memory. However, direct evidence for a similar role of oscillations in humans has so far remained unclear. Here we show that theta and gamma oscillations in the medial-temporal-lobe synchronize neural firing during a memory task. We observe that faster oscillations at theta- and gamma frequencies correlate with co-firing of neurons at short latencies (~20-30 ms) and occur during successful memory formation. Slower oscillations in these same frequency bands, by contrast, correlate with longer co-firing latencies and occur during memory failure. A computational model supports the present effects and links these findings to synaptic plasticity. Together, the results support the long-standing assumption that correlated neural firing supports human episodic memory formation.One Sentence Summaryheta and gamma oscillations induce co-firing of neurons in the human medial temporal lobe during successful memory formation.

scholarly journals Signal Complexity of Human Intracranial EEG Tracks Successful Associative-Memory Formation across Individuals

2018 ◽  
Vol 38 (7) ◽  
pp. 1744-1755 ◽  
Author(s):  
Timothy C. Sheehan ◽  
Vishnu Sreekumar ◽  
Sara K. Inati ◽  
Kareem A. Zaghloul
Keyword(s):  
Associative Memory ◽  
Memory Formation ◽  
Intracranial Eeg ◽  
Signal Complexity
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