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Sukyung Park

Publications and source records attributed to Sukyung Park.

8 recordsLinked to original sources
PubMed2006

Roll rotation cues influence roll tilt perception assayed using a somatosensory technique.

We investigated how the nervous system processes ambiguous cues from the otolith organs by measuring roll tilt perception elicited by two motion paradigms. In one paradigm (tilt), eight subjects were sinusoidally tilted in roll with the axis of rotation near ear level. Stimulus frequencies ranged from 0.005 to 0.7 Hz, and the peak amplitude of tilt was 20 degrees . During this paradigm, subjects experienced a sinusoidal variation of interaural gravitational force with a peak of 0.34 g. The second motion paradigm (translation) was designed to yield the same sinusoidal variation in interaural force but did not include a roll canal cue. This was achieved by sinusoidally translating the subjects along their interaural axis. For the 0.7-Hz translation trial, the subjects were simply translated from side to side. A centrifuge was used for the 0.005- to 0.5-Hz translation trials; the subjects were rotated in yaw at 250 degrees /s for 5 min before initiating sinusoidal translations yielding an interaural otolith stimulus composed of both centrifugal and radial acceleration. Using a somatosensory task to measure roll tilt perception, we found substantial differences in tilt perception during the two motion paradigms. Because the primary difference between the two motion paradigms was the presence of roll canal cues during roll tilt trials, these perceptual differences suggest that canal cues influence tilt perception. Specifically, rotational cues provided by the semicircular canals help the CNS resolve ambiguous otolith cues during head tilt, yielding more accurate tilt perception.

Adult↗
PubMed2006

Predominance of the group A killer Ig-like receptor haplotypes in Korean patients with T1D.

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease in which pancreatic beta cells are selectively destroyed. Although autoimmune diseases are driven by inappropriate adaptive immunity, innate immunity may play a role in the development of T1D. To study the potential involvement of innate immunity in the pathogenesis of autoimmune disease, we investigated associations of the genes for 14 different killer Ig-like receptors (KIRs), the well-characterized receptors in natural killer cells, with Korean T1D patients. Genetic association analyses revealed that some of the KIR genes were associated with T1D. KIR2DL5 and 2DS2 genes were present at significantly low frequency in Korean T1D patients (P < 10(-4)). We did not detect any influence of ligand distribution on KIR association. With the haplotype assignments, 53% of the KIR haplotypes in the control are of type A. Compared with the control (P < 10(-3)) and autoantibody-negative patients (P < 10(-2)), the group A haplotype predominates in Korean patients with T1D. The KIR gene is associated with T1D and distribution differences between T1D and controls were not influenced by the HLA genes (DR-DQ-A-C). T1D, at least in Koreans, is associated with KIR genes, especially in the group A KIR haplotypes. There is a close relationship between innate and adaptive immunity.

Adolescent↗
PubMed2005

Vestibular perception and action employ qualitatively different mechanisms. I. Frequency response of VOR and perceptual responses during Translation and Tilt.

To investigate the neural mechanisms that humans use to process the ambiguous force measured by the otolith organs, we measured vestibuloocular reflexes (VORs) and perceptions of tilt and translation. One primary goal was to determine if the same, or different, mechanisms contribute to vestibular perception and action. We used motion paradigms that provided identical sinusoidal inter-aural otolith cues across a broad frequency range. We accomplished this by sinusoidally tilting (20 degrees, 0.005-0.7 Hz) subjects in roll about an earth-horizontal, head-centered, rotation axis ("Tilt") or sinusoidally accelerating (3.3 m/s2, 0.005-0.7 Hz) subjects along their inter-aural axis ("Translation"). While identical inter-aural otolith cues were provided by these motion paradigms, the canal cues were substantially different because roll rotations were present during Tilt but not during Translation. We found that perception was dependent on canal cues because the reported perceptions of both roll tilt and inter-aural translation were substantially different during Translation and Tilt. These findings match internal model predictions that rotational cues from the canals influence the neural processing of otolith cues. We also found horizontal translational VORs at frequencies >0.2 Hz during both Translation and Tilt. These responses were dependent on otolith cues and match simple filtering predictions that translational VORs include contributions via simple high-pass filtering of otolith cues. More generally, these findings demonstrate that internal models govern human vestibular "perception" across a broad range of frequencies and that simple high-pass filters contribute to human horizontal translational VORs ("action") at frequencies above approximately 0.2 Hz.

Adult↗
PubMed2005

Vestibular perception and action employ qualitatively different mechanisms. II. VOR and perceptual responses during combined Tilt&Translation.

To compare and contrast the neural mechanisms that contribute to vestibular perception and action, we measured vestibuloocular reflexes (VOR) and perceptions of tilt and translation. We took advantage of the well-known ambiguity that the otolith organs respond to both linear acceleration and tilt with respect to gravity and investigated the mechanisms by which this ambiguity is resolved. A new motion paradigm that combined roll tilt with inter-aural translation ("Tilt&Translation") was used; subjects were sinusoidally (0.8 Hz) roll tilted but with their ears above or below the rotation axis. This paradigm provided sinusoidal roll canal cues that were the same across trials while providing otolith cues that varied linearly with ear position relative to the earth-horizontal rotation axis. We found that perceived tilt and translation depended on canal cues, with substantial roll tilt and inter-aural translation perceptions reported even when the otolith organs measured no inter-aural force. These findings match internal model predictions that rotational cues from the canals influence the neural processing of otolith cues. We also found horizontal translational VORs that varied linearly with radius; a minimal response was measured when the otolith organs transduced little or no inter-aural force. Hence, the horizontal translational VOR was dependent on otolith cues but independent of canal cues. These findings match predictions that translational VORs are elicited by simple filtering of otolith signals. We conclude that internal models govern human perception of tilt and translation at 0.8 Hz and that high-pass filtering governs the human translational VOR at this same frequency.

Acceleration↗
PubMed2004

Differential expression of nonislet autoimmunity: comparison of Korean and U.S. patients with type 1 diabetes.

Type 1 diabetes (T1D) is frequently associated with other autoimmune diseases. The occurrence of common features of autoimmune diseases and the coassociation of multiple autoimmune diseases in the same individual or family support the notion that there may be common genetic factors. We previously reported that immunogenetic markers of T1D were similar in Korean and U.S. families. We hypothesized that nonislet autoimmunity might be expressed in a similar manner in Korean as well as in Caucasian patients and correlated with the DRB1-DQB1 haplotypes. Twenty-five percent of Korean patients with T1D (32/128) had antithyroid autoantibodies (ATA+), whereas eight percent of age-matched controls were ATA+ [OR = 3.7 (95% CI:1.0-12.0), P < 0.05]. Twenty-three percent (84/369) of age-matched T1D patients from the U.S. had ATA (not statistically different from that in Koreans). None of the Korean patients nor the family members were positive for 21-hydroxylase (21OH) or transglutaminase autoantibodies (TG). In contrast, in U.S. patients, nine T1D patients (2.4%) were 21OH+ (not statistically different from that in Koreans) and 39 T1D patients (10.6%) were TG+ [OR = 30.7 (95% CI: 4.6-111), P < 10(-4) vs. Korean patients]. Nonislet autoimmunity is prevalent in Korean and U.S. patients with T1D and their family members, but specific forms of autoimmunity differ even after matching for their HLA haplotypes. Individuals with T1D and their relatives frequently develop a panel of autoantibodies, perhaps due to other common susceptibility genes that are shared among first-degree relatives.

Adolescent↗
PubMed2004

Association of the polymorphism for Toll-like receptor 2 with type 1 diabetes susceptibility.

Type 1 diabetes mellitus (T1DM) is a T cell-mediated autoimmune disease in which pancreatic beta cells are selectively destroyed. Although autoimmune diseases are driven by inappropriate adaptive immunity, innate immunity may play a role in the development of T1DM. We investigated the association of the genes for toll-like receptor 2 (TLR2), one of the key surface receptors on innate effectors, with T1DM in Korean patients. Genetic association analyses revealed that the genotype composed of the rare allele (CC) of TLR2 1350 showed weak and protective association with T1DM (OR = 1.7, 95% CI: 1.1-2.7; P < .05) irrespective of the duration of disease, age, and autoantibody status. One of the TLR2 SNP haplotypes, TLR2-Ht4, was strongly associated with T1DM in that those subjects having more than one copy of Ht4 showed strong protection from developing T1DM (OR = 90.5; 95% CI: 13.8-235.7; P < 10(-5)). The TLR2 polymorphisms are associated with T1DM, and distribution differences between T1DM versus controls were not influenced by the HLA genes. There is a close relationship between innate and adaptive immunity.

Adult↗
PubMed2003

Postural feedback responses scale with biomechanical constraints in human standing.

We tested whether human postural responses can be described in terms of feedback control gains, and whether these gains are scaled by the central nervous system to accommodate biomechanical constraints. A feedback control model can describe postural responses for a wide range of perturbations, but biomechanical constraints-such as on the torque that can be exerted on the ground-make a single set of feedback gains inappropriate for all perturbations. To observe how postural responses change with perturbation magnitude, we applied fast, backward perturbations of magnitudes 3-15 cm to 13 healthy young volunteers (4 men, 9 women, aged 20-32 years). We used a 3-segment, sagittal-plane biomechanical model and a linear state feedback controller to reproduce the observed postural responses. Optimization was used to identify the best-fit feedback control gains for each trial. Results showed that trajectories of joint angles and joint torques were scaled with perturbation magnitude. This scaling occurred gradually, rather than abruptly changing at magnitudes where biomechanical constraints became active. Feedback gains were found to fit reasonably well with data ( R(2)=0.92) and to be multivariate and heterogenic in character, meaning that the torque produced at any joint is generally a function of motions not only at the same joint, but other joints as well. Hip gains increased and ankle gains decreased nearly linearly with perturbation magnitude, in accordance with biomechanical limitations on ground reaction torque. These results indicate that postural adjustments can be described as a single feedback control scheme, with scalable heterogenic gains that are adjusted according to biomechanical constraints.

Adult↗