Biology subjects

Newton, T. H.

Publications and source records attributed to Newton, T. H..

4 recordsLinked to original sources

bioRxiv2025

SpIC3D imaging: Spinal In-situ Contrast 3D imaging

High-definition visualization techniques are critical for understanding the neuroanatomy of the spinal cord, an essential structure for sensorimotor and autonomic functions, in both healthy and pathological conditions. Magnetic resonance imaging (MRI) is a common method for visualizing neural structures in 3D. However, techniques for spinal cord MRI have historically achieved limited visualization of rootlets and nerves, especially at lower spinal levels, due to their highly complex and compact organization. Here we developed a spinal in-situ contrast 3D imaging (SpIC3D) method that allows visualization of spinal compartments in fixed animal and human specimens with ultra-high resolution at various spinal levels. Using SpIC3D, we achieved quantification of neuronal cell density in dorsal root ganglia, multi-segment identification of individual rootlets and roots, and volumetric reconstruction of multiple spinal structures for computational modeling. SpIC3D provides a basis for accelerated spinal pathology characterization and personalized spinal cord stimulation treatments.

neuroscience↗

bioRxiv2022

Safety Recommendations for Temporal Interference Stimulation in the Brain

Temporal interference stimulation (TIS) is a new form of transcranial electrical stimulation (tES) that has been proposed as a method for targeted, non-invasive stimulation of deep brain structures. While TIS holds promise for a variety of clinical and non-clinical applications, little data is yet available regarding its effects in humans. To inform the design and approval of experiments involving TIS, researchers require quantitative guidance regarding exposure limits and other safety concerns. To this end, we sought to delineate a safe range of exposure parameters (voltages and currents applied via external scalp electrodes) for TIS in humans through comparisons with well-established but related brain stimulation modalities. Specifically, we surveyed the literature for adverse events (AEs) associated with transcranial alternating/direct current stimulation (tACS/tDCS), deep brain stimulation (DBS), and TIS to establish known boundaries for safe operating conditions. Drawing on the biophysical mechanisms associated with the identified AEs, we determined appropriate exposure metrics for each stimulation modality. Using these metrics, we conducted an in silico comparison of various exposure scenarios for tACS, DBS, and TIS using multiphysics simulations in an anatomically detailed head model with realistic current strengths. By matching stimulation scenarios in terms of biophysical impact, we inferred the frequency-dependent TIS stimulation parameters that resulted in exposure magnitudes known to be safe for tACS and DBS. Based on the results of our simulations and existing knowledge regarding tES and DBS safety, we propose frequency-dependent thresholds below which TIS voltages and currents are unlikely to pose a risk to humans. Safety-related data from ongoing and future human studies are required to verify and refine the thresholds proposed here.

neuroscience↗

bioRxiv2019

Voltage-sensitive dye imaging reveals inhibitory modulation of ongoing cortical activity

Voltage-sensitive dye imaging (VSDI) is a powerful technique for interrogating membrane potential dynamics in assemblies of cortical neurons, but with effective resolution limits that confound interpretation. In particular, it is unclear how VSDI signals relate to population firing rates. To address this limitation, we developed an in silico model of VSDI in a biologically faithful digital reconstruction of rodent neocortical microcircuitry. Using this model, we extend previous experimental observations regarding the cellular origins of VSDI, finding that the signal is driven primarily by neurons in layers 2/3 and 5. We proceed by exploring experimentally inaccessible circuit properties to show that during periods of spontaneous activity, membrane potential fluctuations are anticorrelated with population firing rates. Furthermore, we manipulate network connections to show that this effect depends on recurrent connectivity and is modulated by external input. We conclude that VSDI primarily reflects inhibitory responses to ongoing excitatory dynamics.

neuroscience↗

bioRxiv2019

Epidemiology of human culture: parietal rock art requires high population density

Demographic models of human cultural evolution have high explanatory potential but weak empirical support. Here we use a global dataset of rock art sites and climate and genetics-based estimates of ancient population densities to test a new model based on epidemiological principles. The model focuses on the process whereby a cultural innovation becomes endemic in a population. It predicts that this cannot occur unless population density exceeds a critical value. Analysis of the data, using a Bayesian statistical framework, shows that the model has stronger empirical support than a null model, where rock art detection rates and population density are independent, or a proportional model where detection is directly proportional to population density. Comparisons between results for different geographical areas and periods yield qualitatively similar results, supporting the robustness of the model. Re-analysis of the rock art data, using a second set of independent population estimates, yields similar results. We conclude that population density above a critical threshold is a necessary condition for the maintenance of rock art as a stable part of a populations cultural repertoire. Methods similar to those described can be used to test the model for other classes of archaeological artifact and to compare it against other models.

paleontology↗