Biology subjects

Limon, P. N.

Publications and source records attributed to Limon, P. N..

3 recordsLinked to original sources

bioRxiv2026

Psychophysical validation of calibrated white-noise and tuned-noise auditory masks for transcranial focused ultrasound

Auditory confounds have proven to be a major hurdle in the elucidation of veridical neuromodulation effects with transcranial ultrasound stimulation (TUS). Auditory noise masks are an essential method to reduce the audibility of TUS and have shown promise in several studies. Here we describe a novel approach for design, calibration, and psychometric validation of auditory noise masks to reduce the perceptibility of TUS. White noise masks and spectrum-tuned masks matched to a TUS protocol that generates highly salient auditory costimulation (487.5 Hz pulse repetition frequency, 10% duty cycle, 68 W/cm2 pulse-peak average intensity, 500 kHz acoustic frequency) were generated, and dB(A) levels were calibrated with an artificial ear. The masker levels needed to reduce TUS detection performance in a two-interval forced choice task were determined with an adaptive QUEST+ staircase in 20 neurotypical participants. Detection performance of this highly salient TUS protocol was driven to near chance performance (<55%) in 17/20 participants with white-noise and 18/20 participants with spectrum-tuned noise. However, high masker levels approaching safety limits were needed to render TUS inaudible for the majority of participants, indicating the need for formal masker calibration for these TUS settings. Additionally, against expectation the spectrum-tuned masker did not significantly outperform the white-noise masker, suggesting that perceptibility of TUS auditory costimulation does not lawfully follow the sound expected from its pulse envelope and the known spectrum of human hearing.

neuroscience↗

bioRxiv2026

Effects of transcranial focused ultrasound stimulation to human lateral geniculate nucleus on visual perception and steady-state visual evoked potentials

Transcranial ultrasound stimulation (TUS) is an emerging tool to non-invasively modulate neural activity in deep brain areas. A key need in accelerating TUS into cognitive neuroscience and neuropsychiatry is to better understand how different sonication parameters relate to neuromodulatory effects. Here we assess the role of pulse repetition frequency (PRF), a key TUS parameter thought to determine the relative contribution of molecular displacement and acoustic radiation force effects on neural tissue using the human subcortical visual pathway as a testbed. We combined frequency-tagged steady-state visual evoked potential (SSVEP) measures of contrast-response with contrast increment detection psychophysics as neural and behavioral readouts of visual pathway function. We used structural MRIs and acoustic simulations to target the lateral geniculate nucleus (LGN). Concurrent with visual stimulus presentation, the left LGN or a more superficial control site were stimulated with a neuronavigated depth-steerable 4-element TUS transducer at a range of PRFs with 68 W/cm2 free-water ISPPA, and a 10% duty cycle. An effective white-noise auditory mask blinded participants to stimulation conditions. Recordings from 25 neurotypical participants failed to detect any impact of TUS on SSVEP response amplitude, SSVEP response latency, or perceptual behavior. Analysis of simulations generated from the measured transducer positions grant reasonably high confidence that the LGN was within the TUS focus in most participants, with no correlation between targeting accuracy and changes in activity during TUS. Our results provide a cautionary note about the effect size of neuronavigated TUS for online causal manipulations in cognitive and clinical neuroscience.

neuroscience↗

bioRxiv2025

Spatial Attention and Session Day Independently Modulate Human Visual Cortical Plasticity

Stimulus-specific response potentiation (SSRP) is a noninvasive form of cortical neuroplasticity elicited by repeated presentation of high-contrast visual stimuli. Analogous to long-term potentiation, SSRP has been proposed to exhibit input specificity, with potentiation confined to neural populations driven by the induction stimulus. In rodent models, SSRP effects accumulate across days; however, it remains unclear whether selective attention influences the magnitude or specificity of potentiation in humans. Here, we examined whether covert spatial attention modulates SSRP strength using high-density electroencephalography (EEG) in neurotypical adults. An established SSRP paradigm was modified to include an attention task during induction. Pre- and post-induction amplitudes were measured using frequency-tagged (6 and 7.5 reversals/s) bilateral hemifield contrast-sweep checkerboard steady-state visual evoked potentials (SSVEPs). The 10-minute, high-contrast, 2 Hz sign-reversing induction stimulus was presented exclusively to the left hemifield, with the right serving as control. Across two experimental sessions, participants attended either toward or away from the potentiated hemifield during induction. SSRP produced increased post-induction amplitudes in both hemifields, challenging the notion of strict input specificity. Potentiation was significantly greater on the second session day, independent of attention condition. Notably, attention enhanced SSRP in naive but not experienced observers, reflecting a significant interaction between attention and session day. Together, these findings suggest that (1) human SSRP may not be strictly stimulus-specific, (2) attention modestly enhances SSRP during initial exposure, and (3) repeated induction produces a robust plasticity effect that occludes attentional modulation.

neuroscience↗