Serge Dumoulin

Symposium: Population receptive field dynamics in the human brain.

The Guest Speakers:
PhD candidates of the Spinozacentre Computational Cognitive
Neuroscience and Neuroimaging unit.
Sumiya Abdirashid, Marco Aqil & Kathi Eickhoff.

Title: Attraction of population receptive fields is determined by precision of attention
Sumiya Abdirashid

Spatial attention enhances perception at attended locations. We investigated the effect of attentional precision on population receptive field (pRF) properties. We used 7T MRI to measure pRFs while participants performed a color discrimination task. Two attention conditions were compared: attention narrowed on fixation and attention maximally distributed across the entire screen. As predicted by the attention field model, pRF properties were altered as a function of attentional precision.

Title: The involvement of serotonin and GABA receptors in visuospatial divisive normalization
Marco Aqil

We recently introduced a new pRF model based on Divisive Normalization (DN) that unifies and outperforms existing pRF models. Specific DN model parameters modulate distinct response properties. A key question concerns the identification of biological correlates for the DN computation. We hypothesize that serotonin and GABA receptors provide a biological
implementation for different modulations in the DN pRF model. To test this hypothesis, we compared 7T fMRI DN model parameters with Positron Emission Tomography receptor density maps. We find a striking alignment between the DN model parameters and receptor densities. We propose that variations in receptor densities implement modulations of DN, allowing the brain to fulfil a variety of information-processing requirements with a single computation.

Title: Population receptive field properties change dynamically within milliseconds
Kathi Eickhoff

FMRI lacks the temporal resolution to study human pRF properties on the neuronal timescale. We combine pRF modeling and magnetoencephalography (MEG) to measure pRF dynamics in the human visual cortex. We find that pRFs measured by 7T fMRI explain up to 81% of the MEG stimulus-evoked responses. Systematically varying the pRF properties revealed that different pRF sizes explain the MEG signal at different timepoints. pRF sizes were smaller at 100 ms than at 200 ms, speculatively reflecting different contributions of feedforward and feedback processing. These results highlight the feasibility to study spatiotemporal dynamics on a millisecond timescale in the human brain.