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Two new apps will enable blind people to navigate indoor buildings with spoken directions from a smartphone app, providing a safe method of wayfinding where GPS doesn’t work.  UC Santa […]

Human echolocation repurposes parts of the brain’s visual cortex for sound, even in sighted people

I offered students in Introduction To Epidemic Modeling For Infectious Diseases some general guidance on using AI this week, and I thought I’d share it more broadly. We are going to get into …

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Layer 6 corticothalamic (L6CT) neurons are an excitatory neuron class with projections to both cortex and thalamus. L6CT neurons have been reported to induce multiple effects, including the up- and down-modulation of cortical and thalamic firing rates, and the enhancement of high gamma oscillations in the local field potential (LFP) of the surrounding cortex. These recently reported oscillations offer a neuronal substrate to link recurrent thalamocortical interactions, a critical connection hinging on L6CT neurons, to high frequency oscillations, that have been implicated in several cognitive and pathological conditions. We hypothesize that the high gamma oscillations induced by L6CT neurons in the cortex depend on the dynamic engagement of intracortical and cortico-thalamo-cortical circuits. To test this hypothesis, we optogenetically activated L6CT neurons in NTSR1-cre mice selectively expressing channelrhodopsin-2 in L6CT neurons. Leveraging the vibrissal pathway of awake, head-fixed mice, we presented LED ramp-and-hold inputs of different intensities while recording neuronal activity in the primary somatosensory barrel cortex (S1), the ventral posteromedial nucleus (VPm), and the reticular nucleus (TRN) of thalamus using silicon probes. First, we confirmed that the activation of L6CT neurons induces high-frequency oscillation of S1 local field potential. These oscillations are modulated in frequency, but not in amplitude, across LED intensities and over time. To identify which neuronal classes contribute to these oscillations, we examined the evolution over time of the firing rate of cortical neurons across layers and electrophysiologic cell classes, VPm, and TRN. While the firing rate of most cortical and TRN neurons was steadily suppressed over time, the firing rate of VPm and Layer 4 fast spiking (L4 FS) neurons evolved from being suppressed to being facilitated within 500 ms. Using dimensionality reduction, we found that this pattern reflects two underlying components: one stable component that is represented across all units, and one evolving component that is mainly represented in VPm and in L4 FS neurons, suggestive of differential recruitment of the cortico-cortical vs cortico-thalamo-cortical pathways. Finally, we related the firing rate of each unit to the amplitude and frequency of S1 LFP, finding that the evolution of S1 LFP amplitude weakly correlates with all neurons, while its frequency selectively correlates with VPm firing rate. Taken together, our data suggests that L6CT neurons generate high gamma oscillations in S1 LFP through a combination of intracortical and cortico-thalamo-cortical pathways and can sculpt its oscillation frequency through the cortico-thalamo-cortical pathway. Our findings provide a neuronal substrate for linking recurrent interactions, mediated by L6CT neurons, to the modulations of high gamma oscillations observed in several brain states and pathological conditions. ### Competing Interest Statement S.R. is the Chief Scientific Officer of Manava Plus. The other authors declare no competing interests.

Transcranial ultrasound stimulation (TUS) has emerged as a promising technique for non-invasive neuromodulation, but current systems lack the precision to target deep brain structures effectively. Here, we introduce an advanced TUS system that achieves unprecedented precision in deep brain neuromodulation. The system features a 256-element, helmet-shaped transducer array operating at 555 kHz, coupled with a stereotactic positioning system, individualised treatment planning, and real-time monitoring using functional MRI. In a series of experiments, we demonstrate the system's ability to selectively modulate the activity of the lateral geniculate nucleus (LGN) and its functionally connected regions in the visual cortex. Participants exhibited significantly increased visual cortex activity during concurrent TUS and visual stimulation, with high reproducibility across individuals. Moreover, a theta-burst TUS protocol induced robust neuromodulatory effects, with decreased visual cortex activity observed for at least 40 minutes post-stimulation. These neuromodulatory effects were specific to the targeted LGN, as confirmed by control experiments. Our findings highlight the potential of this advanced TUS system to non-invasively modulate deep brain circuits with high precision and specificity, offering new avenues for studying brain function and developing targeted therapies for neurological and psychiatric disorders. The unprecedented spatial resolution and prolonged neuromodulatory effects demonstrate the transformative potential of this technology for both research and clinical applications, paving the way for a new era of non-invasive deep brain neuromodulation. ### Competing Interest Statement BET, EM, OW, and MR are authors of or have a financial interest in patent filings related to the technology described in this study. BET is a developer of the commercially available k-Plan treatment planning software used in this study and BET and BTC hold a financial interest in the software. The remaining authors declare no competing interests.

While there are already apps that guide blind users to a bus stop's approximate GPS coordinates, those people may unknowingly end up standing too far away from the actual stop. A new app addresses that shortcoming, by letting the smartphone's camera in on the act.