Biology subjects

Ganis, G.

Publications and source records attributed to Ganis, G..

3 recordsLinked to original sources

bioRxiv2026

Barely depictive: Predicting imagery vividness relative to perception with EEGNet

Previous studies suggest that visual mental imagery (VMI) acts as a weaker form of top-down visual perception (VP), with the two becoming more similar as VMI vividness increases. However, this relationship remains ill-defined, and it is unclear precisely how much weaker VMI is relative to VP. Here, we introduce an original probabilistic deep learning approach to quantify vividness at the neural level. Thirty-four participants either imagined or perceived stimuli presented at varying levels of vividness and provided trial-by-trial, picture-based vividness ratings. EEG activity recorded during VP was used to train a convolutional neural network (EEGNet) to predict perceived vividness from eight posterior electrodes located around early visual areas. A leave-one-subject-out cross-validation procedure showed that the model generalised across participants with above-chance accuracy during VP. On VP trials, predictions tracked vividness labels, with reliable interpolation to new vivid labels not included during training. Applied to VMI trials, mean expected VMI vividness remained substantially lower than expected vividness for seen stimuli but slightly higher than baseline, supporting a barely rather than quasi depictive imagery. For 91% of participants, mean expected VMI vividness was also lower than, yet scaled with, mean reported VMI vividness. This framework provides a principled way to quantify and compare VMI and VP on a shared neural-behavioural scale, with implications for studying individual differences and aphantasia.

neuroscience↗

bioRxiv2026

Temporal changes in mechanical pin prick sensitivity following high frequency induced sensitisation of central nociceptive pathways: a test re-test reliability study

High-frequency stimulation (HFS) is a human surrogate model of secondary hyperalgesia and a key experimental tool for understanding the mechanisms and modulation of central nociceptive pathways. An emerging area of research focuses on the role of top-down endogenous analgesic systems during secondary hyperalgesia development. However, the test-retest reliability of the early temporal changes in sensitivity are poorly understood. In the present study, we investigated the between-session reliability of the early temporal dynamics and late-phase expression of HFS-induced changes in mechanical pinprick sensitivity in a heterotopic area on the volar forearm in 28 healthy participants across five time points relative to HFS conditioning: -15, 5, 20, 35, and 50 minutes. Homotopic changes in single-pulse electrically evoked responses were also assessed although no primary hyperalgesia was evident. Baseline conditioned pain modulation (CPM), temporal summation of pain (TSP), and state-trait anxiety (STAI) were also assessed to investigate potential influences on heterotopic and homotopic responses. The present findings demonstrate the consistent induction of mechanical pinprick secondary hyperalgesia by the end of the HFS window (50 minutes) across repeated test session. However, a distinct reduction in the development of sensitivity was present during session 2. Furthermore, pain during HFS conditioning, anxiety, CPM, and TSP demonstrated no influence on secondary hyperalgesia development and were inadequate to explain between-session variance. These results suggest that careful planning around experimental designs, and the counterbalancing of experimental conditions should be considered when investigating modulating factors over the development of secondary hyperalgesia. Further research into factors influencing habituation across sessions is needed. PerspectiveHigh-Frequency Stimulation evokes mechanical secondary hyperalgesia across repeated sessions; however, sensitivity development is diminished, and unexplained by pain intensity during HFS conditioning, anxiety, or cuff algometry CPM and TSP.

physiology↗

bioRxiv2025

Unilateral online ultrasound stimulation of early visual cortex suppresses responses to contralateral visual stimuli

Transcranial ultrasound stimulation (TUS) shows great promise for inducing neuroplastic changes that persist long after stimulation. Evidence of stimulation-locked neural changes would enable closed-loop application of TUS, but such responses have not yet been clearly dissociated from the coincident neural response to auditory and peripheral stimulation associated with TUS. We leveraged the contralateral retinotopic organization of the early visual cortex to isolate online TUS effects from peripheral confounds in 19 subjects. Using a hemifield visual stimulation paradigm combined with high-precision, functional MRI guided TUS, we applied TUS to the left early visual cortex while participants viewed checkerboards presented in the left or right visual field. TUS was delivered randomly on half of the trials, enabling within-subject comparisons of pattern-locked visual evoked potentials (VEPs) across hemispheres and against no stimuli. We observed a reduction in VEPs in the contralateral, but not ipsilateral, hemifield, consistent with genuine online neuromodulatory effects. Furthermore, online suppression was positively correlated with the TUS dose delivered to the target, as estimated by modelling TUS field-target overlap and differential attenuation through heterogeneous skulls. Collectively, these findings provide a robust framework for future studies aiming to map the TUS parameter space in real time by leveraging topographic organization to control for peripheral confounds.

neuroscience↗