Biology subjects

Chang, K. H.

Publications and source records attributed to Chang, K. H..

6 recordsLinked to original sources

bioRxiv2026

"Spilling-in" versus "Filling-in": Disentangling bottom-up drive from predictive completion in human V1 to V3

It is well established that responses in visual areas are a combination of bottom-up stimulus driven input and top-down input driven by expectation. However, it has been difficult to quantify the differential strength of these components, and how they vary across the visual hierarchy. Here, we introduce a method for dissociating bottom-up and top-down contributions in early retinotopic areas (V1-V3). Using a log-scaled bar stimulus, we measured BOLD responses under full-field vs. central scotoma conditions. Using the full-field stimulus, we estimated pRFs in human visual cortex 17 (V1-V3).

neuroscience↗

bioRxiv2026

Blindness reveals that Heschl's gyrus folding is not altered by auditory experience

Heschls gyrus (HG), which contains the primary auditory cortex, shows marked individual variability in its folding pattern, ranging from a single gyrus to partial or complete duplication. Greater HG duplication has been reported in expert musicians, often interpreted as evidence that auditory experience can shape cortical morphology. However, these structural differences might alternatively indicate a bias for musical careers in individuals whose anatomical predispositions facilitate expertise. Here, we examined HG morphology in blind individuals--a population with extensive auditory experience but without selection based on auditory ability. T1-weighted MRI data from 100 human participants (48 females, 42 males, 10 unknown) across blind and sighted groups were analyzed. HG was manually defined in each hemisphere, and folding was measured using both categorical morphology classification and continuous surface-based metrics. Across all analyses, blindness did not increase HG folding. These results suggest that the morphology of HG is largely predetermined. Significance statementIncreased anatomical folding in the auditory cortex has been reported in professional musicians. Is this structural variability due to experience-dependent plasticity, or is it that individuals with increased anatomical folding are more likely to become musicians? We examined Heschls gyrus (HG), which contains the primary auditory cortex, in blind individuals who rely heavily on auditory input. Despite extensive auditory experience, blindness did not alter HG folding. This finding suggests that the morphology of HG is not strongly influenced by auditory experience.

neuroscience↗

bioRxiv2025

Cortical and white matter T1w/T2w development proceed in concert during early infancy

The infant brain undergoes rapid myelination that is critical for healthy brain function. This development has been characterized for gray and white matter independently, but the link between gray and white matter myelination remains unexplored. To close this knowledge gap, we evaluated two complementary myelin-sensitive imaging metrics: Large-scale (N=273) T1w/T2w and quantitative (N=21) R1 data. Automated software was employed to identify 26 white matter bundles and map their cortical terminations, before evaluating T1w/T2w and R1 development shortly after birth. Here we show that for both metrics mean values as well as developmental slopes are correlated across tissues. The synchrony of brain T1w/T2w is impacted by gestational age and prematurity, whereas inter-individual differences in this synchrony predict motor outcomes at 17 - 25 months of age. As T1w/T2w and R1 are associated with myelin content, our results reveal an intricate relationship between gray and white matter myelination.

neuroscience↗

bioRxiv2024

Free water elimination tractometry for aging brains

Tractometry of diffusion-weighted magnetic resonance imaging (dMRI) non-invasively quantifies tissue properties of brain connections. It is widely used in aging studies but could be less reliable in aging brains due to increased white matter free water. We demonstrate that computational free water elimination (FWE) increases reliability and accuracy of tractometry in a large (n = 339) cohort of older adults (66 - 103 y.o.). We found substantial (up to [~]37%) improvements in reliability in a split-half comparison at every stage of the pipeline: estimation of voxel-level fiber orientation distribution functions, delineation of major pathway trajectories, and assessment of tissue properties along the pathways. FWE also improves inferences from tractometry, producing more accurate cross-validated predictions of clinician Fazekas scores. By sub-sampling a multi-b-value dataset, we demonstrated that these findings generalize to both single-b-value data, which is important for many datasets where only one b-value may be available. Overall, the results highlight the importance of accounting for free water in tractometry studies, especially in aging brains. We provide opensource software for free-water elimination that can be applied to a wide range of clinical and research datasets (https://github.com/nrdg/fwe).

neuroscience↗

bioRxiv2024

Improving the Reliability and Accuracy of Population Receptive Field Measures Using a Logarithmically Warped Stimulus.

The population receptive field method, which measures the region in visual space that elicits a BOLD signal in a voxel in retinotopic cortex, is a powerful tool for investigating the functional organization of human visual cortex with fMRI (Dumoulin & Wandell, 2008). However, recent work has shown that population receptive field (pRF) estimates for early retinotopic visual areas can be biased and unreliable, especially for voxels representing the fovea. Here, we show that a log-bar stimulus that is logarithmically warped along the eccentricity dimension produces more reliable estimates of pRF size and location than the traditional moving bar stimulus. The log-bar stimulus was better able to identify pRFs near the foveal representation, and pRFs were smaller in size, consistent with simulation estimates of receptive field sizes in the fovea.

neuroscience↗

bioRxiv2020

Sensitivity of radio-photoluminescence glass dosimeters to accumulated doses

BackgroundThis study investigated the effect of accumulated doses on radio-photoluminescence glass dosimeters (RPLGDs) from measurements involving mega-voltage photons. MethodsForty-five commercially available RPLGDs were irradiated to estimate their dose responses. Photon beams of 6, 10, and 15 MV were irradiated onto the RPLGDs inside a phantom, which were divided into five groups with different doses and energies. Groups 1 and 2 were irradiated at 1, 5, 10, 50, and 100 Gy in a sequential manner; Group 3 was irradiated 10 times with a dose of 10 Gy; and Groups 4 and 5 followed the same method as that of Group 3, but with doses of 50 Gy and 100 Gy, respectively. ResultsFor the annealed Group 1, RPLGD exhibited a linearity response with variance within 5%. For the non-annealed Group 2, readings demonstrated hyperlinearity at 6 MV and 10 MV, and linearity at 15 MV. Following the 100 Gy irradiation, the readings for Group 2 were 118.7 {+/-} 1.9%, 112.2 {+/-} 2.7%, and 101.5 {+/-} 2.3% at 6, 10, and 15 MV, respectively. For Groups 3, 4, and 5, the responsiveness of the RPLGDs gradually decreased as the number of repeated irradiations increased. The percentage readings for the 10th beam irradiation with respect to the readings for the primary beam irradiation were 84.6 {+/-} 1.9%, 87.5 {+/-} 2.4%, and 93.0 {+/-} 3.0% at 6 MV, 10 MV, and 15 MV, respectively. ConclusionsThe non-annealed RPLGD response to dose was hyperlinear for the 6 MV and 10 MV photon beams but not for the 15 MV photon beam. Additionally, the annealed RPLGD exhibited a fading phenomenon when the measurement was repeated several times and demonstrated a relatively large fading effect at low energies than at high energies.

cancer biology↗