Population Receptive Field (pRF) mapping during reaching and saccades

To plan and execute directed movements, such as reaching for a cup or looking
at a traffic light, our brain needs to compute the exact location of the target
and transform it into the appropriate movement trajectory. The target position
is initially coded relative to the eyes, and then transformed into the
coordinates system of the effector (eyes or hand) (Andersen and Buneo, 2002).
Numerous topographical maps representing the spatial location of the target
have been reported in human parietal cortex for eye (Sereno et al., 2001; Konen
and Kastner, 2008) and hand movements (Hagler et al., (2007); Levy et al,
2007). The neurons in these maps carry out the transformations necessary to
plan the direction of the movement of the specific effector. However, the
precise role of each map, and the exact computations taking place are not well
understood yet.

This project aims at identifying and characterizing these maps and their
properties and roles in the human brain.
To this end, we will employ pRF mapping (Dumoulin and Wandell 2008) which
provides a biologically plausible means to characterize the spatial and
non-spatial properties of the neuronal populations in each voxel. Recently, the
pRF modelling has been applied to map the selectivity of visual neurons to
orientation contrasts by Prof. Cornelissen*s lab (Yildirim, Carvalho and
Cornelissen 2018).
The pRF modelling approach will allow us to measure the visual field map, the
size of the RF and RF tuning characteristics for both eye and hand movements.
Indeed, a previous study by the applicant found different strengths of
selectivity for the direction of the reaching movements across brain regions,
by comparing the width of their tuning functions (Fabbri et al., 2010). The pRF
approach will allow assessing such properties in much greater details.
Additionally, we will use the connective field modeling (Haak et al. 2013) to
measure the connections between identified maps. Overall, this project will
greatly improve our understanding of the functional contribution of different
cortical (and subcortical) areas to the planning and generation of hand and eye
movements.

The study consists of two fMRI experiments that will be collected in a 3Tesla
MRI scanner. Both experiments will consist in a localizer block, to measure the
retinotopic maps in the brain, and in rapid event related blocks during which
participants are asked to perform the task (saccade task in Experiment 1 and
reaching task in Experiment 2). During both tasks, eye movements will be
recorded using an MR-compatible eye tracker.
During the scanning session, participants are asked to lie as still as possible
to prevent head movements. in between the blocks, an anatomical scan will be
collected, during which participants can close their eyes and rest.

In the MRI scanner, participants will be exposed to a field strength of 3 Testa
and to scanner noise. There is no evidence that suggest that exposing human to
a magnetic field of this strength has negative consequences for participant's
health. The scanner noise will be minimized by providing participants with hear
plugs. Participants will not directly benefit for their participation to the
study, but their participation will contribute to improve the current
understanding of the existence of spatial maps in the human brain.