Biology subjects

Scott, M. T. W.

Publications and source records attributed to Scott, M. T. W..

3 recordsLinked to original sources

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↗

bioRxiv2024

Measuring the effects of age on contrast suppression

The apparent contrast of a suprathreshold central stimulus can be reduced by a surrounding stimulus - a phenomenon known as surround suppression. When stimuli are presented at the fovea, this effect reportedly increases in strength with age. The underlying mechanism proposed for this age dependence, a change in the balance of inhibition and excitation in cortex, makes this phenomenon potentially interesting as a biomarker of neurological dysfunction. Here, we attempt to repeat these measurements, but we use stimuli designed to control for untuned overlay masking, a different form of suppression thought to be of pre-cortical origin. We measured contrast matching thresholds in twenty younger (< 30) and seventeen older (>60) observers. Across all observers, we find weak suppression that has little or no orientation tuning and, importantly, no dependence on age. Our findings contradict those from earlier studies and suggest that effects relating to age may be dependent on the temporal parameters of this stimulus, and could arise from effects on other pre-cortical mechanisms.

neuroscience↗

bioRxiv2024

Visual field asymmetries in responses to ON and OFF pathway biasing stimuli

Recent reports suggest the ON and OFF pathways are differentially susceptible to selective vision loss in glaucoma. Thus, perimetric assessment of ON- and OFF-pathway function may serve as a useful diagnostic. However, this necessitates a developed understanding of normal ON/OFF pathway function around the visual field and as a function of input intensity. Here, using electroencephalography, we measured ON- and OFF-pathway biased contrast response functions in the upper and lower visual fields. Using the steady-state visually evoked potential paradigm, we flickered achromatic luminance probes according to a saw-tooth waveform, the fast-phase of which biased responses towards the ON or OFF pathways. Neural responses from the upper and lower visual fields were simultaneously measured using frequency tagging - probes in the upper visual field modulated at 3.75Hz, while those in the lower visual field modulated at 3Hz. We find that responses to OFF/decrements are larger than ON/increments, especially in the lower visual field. In the lower visual field, both ON and OFF responses were well described by a sigmoidal non-linearity. In the upper visual field, the ON pathway function was very similar to that of the lower, but the OFF pathway function showed reduced saturation and more cross-subject variability. Overall, this demonstrates that the relationship between the ON and OFF pathways depends on the visual field location and contrast level, potentially reflective of natural scene statistics.

neuroscience↗