Biology subjects

Thompson, L. W.

Publications and source records attributed to Thompson, L. W..

4 recordsLinked to original sources

bioRxiv2026

Limitations of pupil diameter as a proxy for modes of locus coeruleus activity

The locus coeruleus-norepinephrine (LC-NE) system plays multiple roles in higher brain function that are thought to depend on its mode of activation, which reflects relationships between baseline and evoked activation levels. These relationships are evident in both single-unit LC activity and proposed physiological proxies of LC-NE activity, such as pupil size. Here we used measurements in awake monkeys to show that the baseline-evoked relationships evident within these two different measures are unreliably coupled between them: baseline-evoked relationships of the pupil are not predictive of those in the LC, and vice versa. These results imply that pupil modulations, which can reflect LC-NE activity, should be used with caution to make inferences about "phasic" (moderate baseline, high evoked) and "tonic" (high baseline, low evoked) LC-NE activity modes that are thought to support different forms of information processing in the brain.

neuroscience↗

bioRxiv2024

Functional localization of visual motion area FST in humans

The fundus of the superior temporal sulcus (FST) in macaques is implicated in the processing of complex motion signals, yet a human homolog remains elusive. Here we considered potential localizers and evaluated their effectiveness in delineating putative FST (pFST), from hMT and MST, two nearby motion-sensitive areas in humans. Nine healthy participants underwent scanning sessions with 2D and 3D motion localizers, as well as population receptive field (pRF) mapping. We observed consistent anterior and inferior activation relative to hMT and MST in response to stimuli that contained coherent 3D, but not 2D, motion. Motion opponency and myelination measures further validated the functional and structural distinction between pFST and hMT/MST. At the same time, standard pRF mapping techniques that reveal the visual field organization of hMT/MST proved suboptimal for delineating pFST. Our findings provide a robust framework for localizing pFST in humans, and underscore its distinct functional role in motion processing.

neuroscience↗

bioRxiv2022

Parallel processing, hierarchical transformations, and sensorimotor associations along the 'where pathway

Visually guided behaviors require the brain to transform ambiguous retinal images into object-level spatial representations and implement sensorimotor transformations. These processes are supported by the dorsal where pathway. However, the specific functional contributions of areas along this pathway remain elusive due in part to methodological differences across studies. We previously showed that macaque caudal intraparietal (CIP) area neurons possess robust three-dimensional (3D) visual representations, carry choice-related and presaccadic activity, and exhibit experience-dependent sensorimotor associations (Chang et al., 2020b). Here, we used a common experimental design to reveal parallel processing, hierarchical transformations, and the formation of sensorimotor associations along the where pathway by extending the investigation to V3A, a major feedforward input to CIP. Higher-level 3D representations and choice-related activity were more prevalent in CIP than V3A. Both areas contained presaccadic activity that predicted the direction/timing of eye movements. Intriguingly, the time-course of presaccadic activity in CIP aligned with the temporally integrated V3A output. Sensorimotor associations between 3D orientation and saccade direction preferences were strongest in CIP and moderated by choice signals in both areas. Together, the results explicate parallel representations, hierarchical transformations, and functional associations of visual and presaccadic signals at a key juncture in the where pathway.

neuroscience↗

bioRxiv2022

Behavioral signatures of Y-like neuronal responses in human vision

Retinal ganglion cells initiating the magnocellular/Y-cell visual pathways respond nonlinearly to high spatial frequencies (SFs) and temporal frequencies (TFs). This nonlinearity is implicated in the processing of contrast modulation (CM) stimuli in cats and monkeys, but its contribution to human visual perception is not well understood. Here, we evaluate human psychophysical performance for CM stimuli, consisting of a high SF grating carrier whose contrast is modulated by a low SF sinewave envelope. Subjects reported the direction of motion of CM envelopes or luminance modulation (LM) gratings at different eccentricities. The performance on SF (for LMs) or carrier SF (for CMs) was measured for different TFs (LMs) or carrier TFs (CMs). The best performance for LMs was at lower TFs and SFs, decreasing systematically with eccentricity. However, performance with CMs was bandpass with carrier SF, largely independent of carrier TF, and at the highest carrier TF (20 Hz) decreased minimally with eccentricity. Since the nonlinear subunits of Y-cells respond better at higher TFs compared to the linear response components and respond best at higher SFs that are relatively independent of eccentricity, these results suggest that behavioral tasks employing CM stimuli might reveal nonlinear contributions of retinal Y-like cells to human perception.

neuroscience↗