Biology subjects

Chung, C. K.

Publications and source records attributed to Chung, C. K..

7 recordsLinked to original sources

bioRxiv2025

Figure--ground relationship of voices in musical structure modulates reciprocal frontotemporal connectivity

When listening to polyphonic music, we often perceive a melody as the figure against the ground of accompanying sounds. However, with repeated exposure, this figure-ground relationship may naturally shift, allowing the melody to recede into the ground. In a previous study, we found the consistent pattern of frontotemporal connectivity for the "Twinkle, Twinkle, Little Star" (TTLS) melody in the headings of two variations (II and IV) in Mozarts 12 Variations, K. 265, indicating that the TTLS melody, but not the different lower voices, was the figure. However, the frontotemporal connectivity pattern may change in the same phrases repeating in the two variations. In the current study, we examined how frontotemporal connectivity changes in the repeated phrases. In the results, the frontotemporal connectivity pattern between the two variations changed in the final phrase after repeated passages. This suggests that the shift in the figure-ground relationship persists, with the TTLS melody becoming less prominent while the lower voices become relatively more prominent. Additionally, frontotemporal connectivity was strongly correlated with temporofrontal connectivity in the opposite direction. Finally, our data indicate that TTLS melody-based and sensory-based processes in response to a switched figure-ground relationship, are incorporated into the bidirectional connections between frontotemporal and temporofrontal connectivity. Our study highlights the brains ability to reconfigure figure- ground relationships in the processing of musical voices.

neuroscience↗

bioRxiv2024

Frontotemporal connectivity changes reflect figure-ground reversal in multivoiced music

When listening to multivoiced music, it is possible to perceive distinct voices in differing pitch ranges independently. The melody that one focuses on becomes the figure, and other voices form the background. Shifting focus from one voice to another causes a figure-ground reversal, which may easily occur as a result of anticipation within repeated passages in a musical structure. We previously found that frontotemporal connectivity reflects changes in the melody of "Twinkle, Twinkle, Little Star" (TTLS) in Mozarts 12 Variations K. 265. We hypothesized that if frontotemporal connectivity remains unchanged in repeated passages, the melody of TTLS remains the figure; however, if connectivity changes, the melody shifts toward the background. Our findings show that frontotemporal connectivity only changed during the final, fourth repetition. This was accompanied by a bidirectional correlation in frontotemporal regions, implying both top-down and bottom-up processes. We captured a momentary figure-ground reversal in the multivoiced texture of continuously changing and developing music.

neuroscience↗

bioRxiv2024

Distinct Functional Roles of Narrow and Broadband High-Gamma Activities in Human Primary Somatosensory Cortex

In previous studies, higher (broadband) and lower (narrowband) components of high-gamma (HG) activity (approximately from 50 to 150 Hz) have different functions and origins in the primary visual cortex (V1). However, in the primary somatosensory cortex (S1), it is unknown whether those are similarly segregated. Furthermore, the origin and functional role of S1 HG activity still remain unclear. Here, we investigate their roles by measuring neural activity during vibrotactile and texture stimuli in humans. Also, to estimate their origins, S1 layer-specific HG activity was measured in rats during somatosensory stimulation. In the human experiment, with texture stimulation, the lower HG activity (LHG, 50-70 Hz) in S1 represents the intensity of the sustained mechanical stimulus. In the vibrotactile experiment, the higher HG (HHG, 70 -150 Hz) activity in S1 depended on the ratio of low and high mechanical frequencies with its pattern being a mixture of neural activity for low and high mechanical frequencies. Furthermore, 8 texture types could be classified using power values of HHG activity, while the classification using LHG activity showed poor performance. In the rat experiment, we found that both HHG and LHG activities are highest in the somatosensory input layer (layer IV), similar to previous visual cortex studies. Interestingly, analysis of spike-triggered LFP (stLFP) revealed significant HG oscillations during pressure stimulation with the stLFP HG power most significant in layer IV, suggesting that both LHG and HHG activities are closely related to the neuronal firing in layer IV. In summary, LHG activity represents the intensity of tactile sensation, while HHG activity represents the detail of the surface geometry of objects interacting with skin. Additionally, low and high mechanical frequencies are processed in parallel in S1. Finally, both HHG and LHG originated in layer IV of S1.

neuroscience↗

bioRxiv2024

Single and Multi-Site Cortical Stimulation Related to Human Sensorimotor Function

Somatosensory feedback is crucial for precise control of our body and thereby affects various sensorimotor-related brain areas for movement control. Electrical stimulation on the primary somatosensory cortex (S1) elicits various artificial somatosensations. However, replicating the spatiotemporal dynamics of somatosensory feedback and fine control of elicited somatosensation are still challenging. Furthermore, how and where the somatosensory feedback interacts with neural activity for sensorimotor processing is unclear. Here, we replicate the spatiotemporal dynamics of somatosensory feedback and control the quality of elicited somatosensation using multi-site direct cortical stimulation (DCS). We also investigate how and where the neural feedback activity interacts with neural activity for motor processing by stimulating the downstream areas of the S1. We found that multi-site DCS on the S1 elicits different sensations simultaneously. Using the artificial feedback, blindfolded patients could efficiently perform a DCS-guided reach-and-grasp task successfully. Interestingly, we also found that multi-site DCS close to each other elicits different qualities of somatosensation in the same body part. Additionally, we found that DCS on the ventral premotor area (vPM) can affect hand grasping with eliciting artificial sensation of the hand. Throughout this study, we showed that semi-invasive, macro-level, and multi-site DCS can precisely elicit/modulate somatosensations in human. We suggest that activation of multiple cortical areas elicits simultaneous and independent somatosensations and that interplay among the stimulated sites can change the somatosensation quality. Finally, the results of vPM stimulation indicate that vPM has a critical role in function-specific sensorimotor interactions, such as hand grasping.

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bioRxiv2021

Temporal changes in resting state networks induced by propofol anesthesia.

The cerebral cortical changes associated with propofol-induced unconsciousness remain unknown. While the anesthetic agent affects the entire cerebral cortices, there might be spatiotemporal differences in cortical changes. In particular, we hypothesized that there might be spatiotemporal differences in cortical changes with propofol-anesthesia. To address this hypothesis, we investigated power spectrum changes in electrocorticography (ECoG) signals obtained during the induction phase from awake state to unconsciousness. We found that, 1) the power increased in the range of frequencies < 46 Hz (delta to low gamma), and decreased in the range (62-150) Hz (high gamma), in global channels during the induction phase. 2) The power in the frontoparietal network (FPN), specifically the superior parietal lobule and prefrontal cortex, started to change early, but took a long time to completely change. However, the power in the default mode network (DMN) started to change late, but took a short time to completely change. 3) The power change ({Delta}Power) in the DMN was more conspicuous than that of the dorsal attention network (DAN) in high gamma frequency. Considering that the FPN is involved in communication with the external world and that DMN is involved in communication with self, loss of consciousness induced by general anesthesia results from first, disrupted communication between self and external world, and is then followed by disrupted communication within self, with decreased activity of the FPN, and later, attenuated activity of the DMN. Significance StatementWe investigated the spatiotemporal changes of power spectrum in human electrocorticography (ECoG) during the induction phase from awake state to unconsciousness. We found that from delta to low gamma frequency, the power increased, while in high gamma frequency, the power decreased over all channels. The power in the frontoparietal network (FPN) preferentially changed, then the power in the DMN changed later. The power in DMN decreased more than those in other RSNs in high gamma frequency. Loss of consciousness induced by general anesthesia results from first, disrupted communication between self and external world, followed by disrupted communication within self, with decreased activity of the FPN, and later, attenuated activity of the DMN.

neuroscience↗

bioRxiv2020

Dissociation of connectivity for syntactic irregularity and perceptual ambiguity in musical chord stimuli

Previously syntactic irregularity has been most studied with chord sequences. However, the same chord may be interpreted as having different harmonic functions, implying perceptual ambiguity. Hence, syntactic irregularity and perceptual ambiguity may be processed simultaneously. We devised 3 different 5-chord sequences in which the ending chord differed with the tonic (T), submediant (SM), and supertonic (ST). In terms of syntactic regularity, T is most regular, ST is most irregular. However, in terms of perceptual ambiguity, the most irregular ST had the salient highest voice. Therefore, the SM was the most ambiguous condition. We investigated how the human brain separates syntactic irregularity and perceptual ambiguity in terms of effective connectivity in bilateral inferior frontal gyri (IFGs) and superior temporal gyri (STGs) with magnetoencephalography in 19 subjects. Correct rate was lower for the most ambiguous chord (SM) (P = 0.020) as expected. Connectivity from the right to the left IFG was enhanced for the most irregular chord (ST) (P = 0.024, false discovery rate (FDR) corrected), whereas connectivity from the right to the left STG was enhanced for the most ambiguous chord (SM) (P < 0.001, FDR corrected). The correct rate was negatively correlated with connectivity in the STG, further reflecting perceptual ambiguity (P = 0.026). We found that syntactic irregularity and perceptual ambiguity in music are dissociated in connectivity between bilateral IFGs and STGs, respectively. Significance StatementWe provide the first neurophysiological evidence of the processing of perceptual ambiguity, other than syntactic irregularity, implied in musical chords. We found that the notion of "perceptually ambiguity" is applicable to musical chord stimuli different in syntactic irregularity, and that perceptual ambiguity is separate from syntactic irregularity. Our data demonstrate that the brain interprets the three conditions of musical chords as both "from regular to irregular" and "from ambiguous to unambiguous" conditions simultaneously. This study is the first to unveil dissociation of connectivity by syntactic irregularity and perceptual ambiguity involved in musical chord stimuli.

neuroscience↗

bioRxiv2020

Increased fronto-temporal connectivity by modified melody in real music

In real music, the original melody may appear intact, with little elaboration only, or significantly modified. Since a melody is most easily perceived in music, hearing significantly modified melody may change a brain connectivity. Mozart KV 265 is comprised of a theme with an original melody of "Twinkle Twinkle Little Star" and its significant variations. We studied whether effective connectivity changes with significantly modified melody, between bilateral inferior frontal gyri (IFGs) and Heschls gyri (HGs) using magnetoencephalography (MEG). Among the 12 connectivities, the connectivity from the left IFG to the right HG was consistently increased with significantly modified melody compared to the original melody in 2 separate sets of the same rhythmic pattern with different melody (p = 0.005 and 0.034, Bonferroni corrected). Our findings show that the modification of an original melody in a real music changes the brain connectivity.

neuroscience↗