Biology subjects

Juan, C.-H.

Publications and source records attributed to Juan, C.-H..

4 recordsLinked to original sources

bioRxiv2023

Certain spatial prediction decreases the rhythm of attentional sampling

Recent studies demonstrate that behavioral performance during visual spatial attention fluctuates at theta (4-8 Hz) and alpha (8-16 Hz) frequencies, linked to phase amplitude coupling (PAC) of neural oscillations within the visual and attentional system. Moreover, previous research suggests that attentional sampling rhythms are task-dependent, evidenced by varying behavioral performance at different frequencies. To investigate the role of prior spatial prediction, we employed an adaptive discrimination task with variable cue-target onset asynchronies ranging from 300 ms to 1300 ms in steps of 20 ms, while manipulating spatial prediction via cue validity (100% & 50%), with concurrent Electroencephalography (EEG) recording. We applied adaptive data analytical methods, namely Holo-Hilbert Spectral Analysis (HHSA) and Holo-Hilbert Cross-frequency Phase Clustering (HHCFPC). Our findings indicate that response precision for near-threshold Landolt rings fluctuates at the theta- band (4 Hz) under certain predictions and at alpha & beta bands (15 & 19 Hz) with uncertain predictions. Furthermore, spatial prediction strengthens theta-alpha modulations at parietal- occipital areas, frontal theta phase and parietal-occipital alpha amplitude coupling, and within frontal theta phase/ alpha amplitude coupling. Notably, during the pre-target period, beta- modulated gamma oscillations in parietal-occipital areas predict response precision in spatially uncertain conditions, while frontal theta phase and parietal-occipital alpha amplitude coupling predict response precision in spatially certain conditions. In conclusion, our study not only strengthens the notion that the speed of periodic sampling in perception depends on the task at hand but also highlights the critical role of spatial prediction in attentional sampling rhythms. Significance StatementThis study investigates the temporal dynamics of sustained spatial attention under varying certainty levels, employing behavioral and electrophysiological measures in an adaptive discrimination task. Unveiling the rhythmic nature of sustained attention, our findings showcase substantial effects of spatial certainty on attentional rhythms, witnessing an increased certainty that shifts these rhythms from beta to theta frequencies. Neural oscillations offer insights into the underlying mechanisms, revealing theta-alpha coupling and beta-gamma coupling within the visual system and frontal-parietal network. Significantly, our results challenge conventional notions of attentional rhythms, emphasizing the dynamic complexity of these processes. In a broader context, our study contributes to bridging the gap between task demands and periodic sampling rhythms, offering novel insights into attention allocation during complex tasks.

neuroscience↗

bioRxiv2022

The association between working memory precision and the nonlinear dynamics of frontal and parieto-occipital EEG activity.

Electrophysiological working memory (WM) research has shown that distinct brain areas communicate through macroscopic oscillatory activities across multiple frequency bands. Such cross-frequency interactions generate nonlinear amplitude modulations (AM) in the observed signal. Traditionally, the AM of a signal is expressed as coupling strength between the signal and a pre-specified modulator at a lower frequency. Therefore, the idea of AM and coupling cannot be separately studied. This EEG study shows that the AM of parieto-occipital alpha/beta power and the coupling between frontal theta phase and parieto-occipital alpha/beta AM provide different information on WM processing. Thirty-three participants completed a color recall task with simultaneous EEG recording. The results showed that individual differences in WM precision are associated with frontal theta power enhancement and parieto-occipital alpha/beta power suppression. Furthermore, the AM of parieto-occipital alpha/beta power predicted WM precision after presenting a target-defining probe array. The phase-amplitude coupling (PAC) between frontal theta phase and parieto-occipital alpha/beta AM increased with WM load during the processing of incoming stimuli, but they did not predict the subsequent recall performance. These results indicate that the frontoparietal PAC reflects the executive control for selecting relevant WM representations, but whether the memorized information can be retrieved depends on the subsequent amplitude variation of parieto-occipital alpha/beta power. In conclusion, individuals with higher working memory precision are associated with enhanced frontal theta power and parieto-occipital alpha/beta power suppression.

neuroscience↗

bioRxiv2021

Within-cycle instantaneous frequency profiles report oscillatory waveform dynamics.

Non-sinusoidal waveform is emerging as an important feature of neuronal oscillations. However, the role of single cycle shape dynamics in rapidly unfolding brain activity remains unclear. Here, we develop an analytical framework that isolates oscillatory signals from time-series using masked Empirical Mode Decomposition to quantify dynamical changes in the shape of individual cycles (along with amplitude, frequency and phase) using instantaneous frequency. We show how phase-alignment, a process of projecting cycles into a regularly sampled phase-grid space, makes it possible to compare cycles of different durations and shapes. Normalised shapes can then be constructed with high temporal detail whilst accounting for differences in both duration and amplitude. We find that the instantaneous frequency tracks non-sinusoidal shapes in both simulated and real data. Notably, in local field potential recordings of mouse hippocampal CA1, we find that theta oscillations have a stereotyped slow-descending slope in the cycle-wise average, yet exhibiting high variability on a cycle-by-cycle basis. We show how Principal Components Analysis allows identification of motifs of theta cycle waveform that have distinct associations to cycle amplitude, cycle duration and animal movement speed. By allowing investigation into oscillation shape at high temporal resolution, this analytical framework will open new lines of enquiry into how neuronal oscillations support moment-by-moment information processing and integration in brain networks.

neuroscience↗

bioRxiv2020

Population genetic structure in the insular Ryukyu flying fox, Pteropus dasymallus

Small isolated populations are vulnerable to both stochastic events and the negative consequences of genetic drift. For threatened species, the genetic management of such populations has therefore become a crucial aspect of conservation. Flying foxes (Pteropus spp, Chiroptera) are keystone species with essential roles in pollination and seed dispersal in tropical and subtropical ecosystems. Yet many flying fox species are also of conservation concern, having experienced dramatic population declines driven by habitat loss and hunting. The Ryukyu flying fox (Pteropus dasymallus) ranges from Japan and Taiwan to the northern Philippines, and has undergone precipitous population crashes on several islands in recent decades. To assess population genetic structure and diversity in P. dasymallus, and its likely causes, we analyzed mitochondrial and microsatellite DNA. Both markers showed significant genetic differentiation among most island populations with patterns of isolation-by-distance. However, while mitochondrial haplotypes showed some mixing across the region, likely reflecting historical colonization and/or dispersal events, microsatellites markers showed clear subdivisions corresponding to the position of deep ocean trenches. The current distribution of P. dasymallus and its subspecific diversity therefore appears to have arisen through vicariance coupled with a long history of restricted gene flow across oceanic barriers. We conclude that isolated island subgroups should be managed separately, with efforts directed at reducing further declines.

ecology↗