Saturday, March 16th, 2024

Time	Event
8:31a	Prenatal tuning of thalamic spontaneous activity patterns regulates somatosensory map resolution Precise mapping of peripheral inputs onto cortical areas is required for appropriate sensory processing. In the mouse primary somatosensory cortex, mystacial whiskers are represented in large barrels, while upper lip whiskers are in smaller, less defined barrels. Traditionally, barrel size and definition are believed to be determined postnatally by whisker input and peripheral receptor density. However, prenatal thalamic spontaneous activity can influence somatosensory map development independently of whisker input. Thus, the mechanisms defining distinct barrel field territories, including size and definition, remain poorly understood. Here, we show that prenatal ablation of mystacial whiskers enhances the functional and anatomical definition of upper lip whisker barrels. These changes do not result from alterations in receptor density but rather stem from prenatal reconfigurations in the patterns of spontaneous activity within the thalamus. Our results unveil the role of prenatal synchronized thalamic activity in shaping cortical barrel size and functional map definition in the developing somatosensory system. (Comment on this)
8:31a	Antagonistic behavior of brain networks mediated by low-frequency oscillations: electrophysiological dynamics during internal-external attention switching Antagonistic activity of brain networks likely plays a fundamental role in how the brain optimizes its performance by efficient allocation of computational resources. A prominent example involves externally/internally oriented attention tasks, implicating two anticorrelated, intrinsic brain networks: the default mode network (DMN) and the dorsal attention network (DAN). To elucidate electrophysiological underpinnings and causal interplay during attention switching, we recorded intracranial EEG (iEEG) from 25 epilepsy patients with electrode contacts localized in the DMN and DAN. We show antagonistic network dynamics of activation-related changes in high-frequency (> 50 Hz) and low-frequency (< 30 Hz) power. The temporal profile of information flow between the networks estimated by effective connectivity suggests that the activated network inhibits the other one, gating its activity by increasing the amplitude of the low-frequency oscillations. Insights about inter-network communication may have profound implications for various brain disorders in which these dynamics are compromised. (Comment on this)
12:48p	Impact of extracellular current flow on action potential propagation in myelinated axons Myelinated axons conduct action potentials, or spikes, in a saltatory manner. Inward current caused by a spike occurring at one node of Ranvier spreads axially to the next node, which regenerates the spike when depolarized enough for voltage-gated sodium channels to activate, and so on. The rate at which this process progresses dictates the velocity at which the spike is conducted, and depends on several factors including axial resistivity and axon diameter that directly affect axial current. Here we show through computational simulations in modified double-cable axon models that conduction velocity also depends on extracellular factors whose effects can be explained by their indirect influence on axial current. Specifically, we show that a conventional double-cable model, with its outside layer connected to ground, transmits less axial current than a model whose outside layer is less absorptive. A more resistive barrier exists when an axon is packed tightly between other myelinated fibers, for example. We show that realistically resistive boundary conditions can significantly increase the velocity and energy efficiency of spike propagation, while also protecting against propagation failure. Certain factors like myelin thickness may be less important than typically thought if extracellular conditions are more resistive than normally considered. We also show how realistically resistive boundary conditions affect ephaptic interactions. Overall, these results highlight the unappreciated importance of extracellular conditions for axon function. (Comment on this)

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