Theta-modulated transcranial electrical stimulation for targeting Associative memory: A cross-modal integration of EEG and behavioral indicators

Associative memory (AM) represents an ability to bind unrelated information into meaningful units and encode them as distinct memories. AM has been the function of interest in many non-invasive transcranial electrical stimulation (tES) studies aiming to maximize the potential for memory modulation by varying stimulation loci, frequency, and amplitude. In the current study, we aimed to capture modulation potential of AM performance when tailoring the stimulation protocols to the individual brain rhythms. By matching the stimulation frequency to the frequency of each subject’s AM task-induced electrophysiological (EEG) activity in theta spectrum (4-8 Hz), we developed two types of personalized oscillatory protocols: theta-modulated transcranial direct current stimulation (otDCS) and transcranial alternating current stimulation (tACS), which we administered alongside the constant tDCS and a sham condition in the single-blind cross-over experiment. To comparatively assess the effects of different tES protocols delivered over the posterior parietal cortex, we tested the recognition and recall ability of the 42 healthy young adults on paired-associate paradigms after each of four conditions. During AM assessment participant’s EEG activity was recorded. Group-level comparisons of each active tES condition against sham did not show differences in AM task performance either on recognition or cued-recall. However, data showed variability in performance depending on the task and the outcome measures precluding straightforward comparison between the conditions. To explore the potential sources of variability in effect expression, we propose a methodology for isolating different aspects of the function-relevant neurophysiological markers that could depict the modulatory tES effect, setting the groundwork for further analysis. Apart from introducing a novel approach to probing AM with personalized tES, this well-powered, multi-protocol, multi-task, and multi-measure study produced a comprehensive dataset for the exploration of factors that could uncover patterns in responsiveness to tES, as well as the insight into the relationship between neurophysiological and behavioral indicators

Results of investigating the macroinvertebrate community of the Danube River on the sector upstream from the Iron Gate (km 1083-1071)

The present work cites results of investigating aquatic macroinvertebrates of the Danube River on the sector upstream from the Iron Gate (KM 1083-1071). The investigated part is interesting from the hydrobiological standpoint above all due to differences of faunal composition in relation to higher sections that could be expected in view of differences in overall characteristics of the river. A rich macroinvertebrate community (84 taxa) was observed. The diversity of taxa is primarily a result of habitat diversity within the given stretch. Oligochaeta and Mollusca were the principal components

Results of investigating the macroinvertebrate community of the Danube River on the sector upstream from the Iron Gate (km 1083-1071)

The present work cites results of investigating aquatic macroinvertebrates of the Danube River on the sector upstream from the Iron Gate (KM 1083-1071). The investigated part is interesting from the hydrobiological standpoint above all due to differences of faunal composition in relation to higher sections that could be expected in view of differences in overall characteristics of the river. A rich macroinvertebrate community (84 taxa) was observed. The diversity of taxa is primarily a result of habitat diversity within the given stretch. Oligochaeta and Mollusca were the principal components.Cilj rada je da se prikažu rezultati istraživanja vodenih makroinvertebrata u sektoru uzvodno od Đerdapa (1083-1071 km). Istraživano područje interesantno je za hidrobiološka istraživanja, pre svega, zbog promena u strukturi faune u odnosu na gornji deo toka, što je i očekivano ako se uzmu u obzir promene opštih karakteristika reke u sektoru. Zabeleženo je raznovrsno naselje makroinvertebrata (84 taksona). Raznovrsnost faune posledica je, pre svega, diverziteta staništa u okviru istraživanog područja. Grupe Oligochaeta i Mollusca bile su najznačajnije komponente proučavane zajednice makro invertebrata.Part of the material originated from the Joint Danube Survey, a national progra

Theta-modulated oscillatory transcranial direct current stimulation over posterior parietal cortex improves associative memory

Associative memory (AM) reflects the ability to remember and retrieve multiple pieces of information bound together thus enabling complex episodic experiences. Despite growing interest in the use of transcranial direct current stimulation (tDCS) for the modulation of AM, there are inconsistent evidence regarding its benefits. An alternative to standard constant tDCS could be the application of frequency-modulated tDCS protocols, that mimic natural function-relevant brain rhythms. Here, we show the effects of anodal tDCS oscillating in theta rhythm (5 Hz; 1.5 ± 0.1 mA) versus constant anodal tDCS and sham over left posterior parietal cortex on cued recall of face-word associations. In a crossover design, each participant completed AM assessment immediately following 20-min theta-oscillatory, constant, and sham tDCS, as well as 1 and 5 days after. Theta oscillatory tDCS increased initial AM performance in comparison to sham, and so did constant tDCS. On the group level, no differences between oscillatory and constant tDCS were observed, but individual-level analysis revealed that some participants responded to theta-oscillatory but not to constant tDCS, and vice versa, which could be attributed to their different physiological modes of action. This study shows the potential of oscillatory tDCS protocols for memory enhancement to produce strong and reliable memory-modulating effects which deserve to be investigated further

Trophic relations between macroinvertebrates in the Vlasina river (Serbia)

The aim of the study presented was to define trophic relationships within the benthic community according to functional feeding groups (FFG) in the Vlasina River (Southeast Serbia), with an attempt to use those results to describe the watercourse. In an investigation performed during 1996, a total of 125 macrozoobenthic taxa were identified, 95 of which were included in FFG analyses. Although the investigated part of the river, in its physical and chemical characteristics, as well as characteristics of the benthofauna, generally corresponds to what could be expected, certain variations of faunal composition were observed along the river. Two groups of sites were separated by FFG analysis - sites on the upper section of the river and on a tributary (the Gradska River) comprised one group, while the remaining sites made up the other.Cilj nam je da ovim radom prikažemo trofičke odnose u zajednici makroinvertebrata prema funkcionalnim grupama u ishrani (FGI) u reci Vlasini (jugo-istočna Srbija) i te rezultate upotrebimo za opisivanje vodotoka. U okviru istraživanja obavljenih tokom 1996. godine, od ukupno 125 identifikovanih taksona makrozoobentosa, 95 taksona korišćeno je u FGI analizi. Iako istraživani deo reke, sa njegovim fizičkim i hemijskim karaktristikama, kao i karakteristikama bentofaune uopšte, odgovara srednjem toku reka, istraživane su fine promene u distribuciji bentofaune duž toka. Izdvojile su se dve grupe lokaliteta prema FFG analizi - grupisali su se lokaliteti gornjeg sektora reke kao i pritoka Gradska reka, dok su ostali lokaliteti formirali drugu grupu.nul

Personalized Frequency Modulated Transcranial Electrical Stimulation for Associative Memory Enhancement

Associative memory (AM) is the ability to remember the relationship between previously unrelated items. AM is significantly affected by normal aging and neurodegenerative conditions, thus there is a growing interest in applying non-invasive brain stimulation (NIBS) techniques for AM enhancement. A growing body of studies identifies posterior parietal cortex (PPC) as the most promising cortical target for both transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (tES) to modulate a cortico-hippocampal network that underlines AM. In that sense, theta frequency oscillatory tES protocols, targeted towards the hallmark oscillatory activity within the cortico-hippocampal network, are increasingly coming to prominence. To increase precision and effectiveness, the need for EEG guided individualization of the tES protocols is proposed. Here, we present the study protocol in which two types of personalized oscillatory tES–transcranial alternating current stimulation (tACS) and oscillatory transcranial direct current stimulation (otDCS), both frequency-modulated to the individual theta-band frequency (ITF), are compared to the non-oscillatory transcranial direct current stimulation (tDCS) and to the sham stimulation. The study has cross-over design with four tES conditions (tACS, otDCS, tDCS, sham), and the comprehensive set of neurophysiological (resting state EEG and AM-evoked EEG) and behavioral outcomes, including AM tasks (short-term associative memory, face–word, face–object, object-location), as well as measures of other cognitive functions (cognitive control, verbal fluency, and working memory)

Determining the Individual Theta Frequency for Associative Memory Targeted Personalized Transcranial Brain Stimulation

Non-invasive brain stimulation (NIBS) methods have gained increased interest in research and therapy of associative memory (AM) and its impairments. However, the one-size-fits-all approach yields inconsistent findings, thus putting forward the need for electroencephalography (EEG)-guided personalized frequency-modulated NIBS protocols to increase the focality and the effectiveness of the interventions. Still, extraction of individual frequency, especially in the theta band, turned out to be a challenging task. Here we present an approach to extracting the individual theta-band frequency (ITF) from EEG signals recorded during the AM task. The method showed a 93% success rate, good reliability, and the full range of variability of the extracted ITFs. This paper provides a rationale behind the adopted approach and critically evaluates it in comparison to the alternative methods that have been reported in the literature. Finally, we discuss how it could be used as an input parameter for personalized frequency-modulated NIBS approaches—transcranial alternating current stimulation (tACS) and transcranial oscillatory current stimulation (otDCS) directed at AM neuromodulation

Extraction of individual associative memory related dominant theta frequency for personalized transcranial brain stimulation

Non-invasive brain stimulation (NIBS) has gained increased interest in research and therapy of associative memory (AM) and its impairments. However, the one-size-fits-all approach yields inconsistent findings, thus putting forward the need for the development of personalized frequency-modulated NIBS protocols to increase the focality and the effectiveness of the interventions. There have been only a few attempts to deliver theta frequency-personalized tES. The current study explores the feasibility of determining dominant individual theta-band frequency (ITF) based on AM task evoked EEG activity. In a sample of 42 healthy young adults, we extracted the frequencies (2-15 Hz, in 0.5 Hz steps) with the highest event-related spectral perturbation from the EEG recorded during successful encoding in the AM task. The developed method for extraction of the dominant theta-band frequency based on the AM-evoked EEG changes is able to reliably determine the AM-related ITF and can be used for personalization of the oscillatory NIBS techniques.Preprint:[https://www.biorxiv.org/content/10.1101/2022.03.07.483124v2

Results of investigating the macroinvertebrate community of the Danube River on the sector upstream from the Iron Gate (km 1083-1071)

The present work cites results of investigating aquatic macroinvertebrates of the Danube River on the sector upstream from the Iron Gate (KM 1083-1071). The investigated part is interesting from the hydrobiological standpoint above all due to differences of faunal composition in relation to higher sections that could be expected in view of differences in overall characteristics of the river. A rich macroinvertebrate community (84 taxa) was observed. The diversity of taxa is primarily a result of habitat diversity within the given stretch. Oligochaeta and Mollusca were the principal components.Cilj rada je da se prikažu rezultati istraživanja vodenih makroinvertebrata u sektoru uzvodno od Đerdapa (1083-1071 km). Istraživano područje interesantno je za hidrobiološka istraživanja, pre svega, zbog promena u strukturi faune u odnosu na gornji deo toka, što je i očekivano ako se uzmu u obzir promene opštih karakteristika reke u sektoru. Zabeleženo je raznovrsno naselje makroinvertebrata (84 taksona). Raznovrsnost faune posledica je, pre svega, diverziteta staništa u okviru istraživanog područja. Grupe Oligochaeta i Mollusca bile su najznačajnije komponente proučavane zajednice makro invertebrata.Part of the material originated from the Joint Danube Survey, a national progra

On the importance of hippocampal segmentation for the neural mapping of memory: Evidence from a large-scale study of neural architecture in healthy adults

The hippocampus (HC) is traditionally considered the key neuroanatomical hub responsible for memory. However, previous MRI studies that aimed to relate volumetric hippocampal measures to associative memory (AM) performance have yielded mixed results. In the current study, we aimed to reevaluate these findings in a large sample of young healthy participants (N = 246; age M = 24.95, SD = 4.58; 56% female). Participants were scanned with 3T MAGNETOM Prisma using a 64-channel head coil, followed by the AM assessment in the lab setting. To maximize the scope of AM assessment, we employed four paired-associate tasks of various stimuli modalities (faces, words, scenes) and outcome measure types (recognition, recall). Synthetic T1-weighted images were produced out of relaxometry parameter maps, after which volumetric measures were calculated using FreeSurfer. The whole HC volume showed no correlation with any of the memory measures. However, further segmentation of HC into its functional and anatomical subfields (Parasubiculum, Presubiculum, Subiculum, CA1, CA2/3, CA4, GC-DG, HATA, Fimbria, Molecular layer, Hippocampal fissure, Hippocampal tail) showed scattered yet consistent patterns of significant correlations between different subfield volumes and memory outcomes. The results suggest that distinctive contributions of HC subfields may lead to a null effect when the whole HC volume is considered, thus demonstrating that drawing conclusions based on the volumetric measures of neural macrostructures can be misleading. The results highlight the importance of in-depth segmentation for neural mapping