Perception and the cognitive map
The brain integrates our perceptual experiences into stable and unified representations of the world, a cognitive mapping process that manifests in our memories and guides our everyday behavior.
Cognitive maps are thought to reside in the hippocampal formation, a mnemonic brain structure in the mediotemporal lobe (MTL) known to represent space. Many of the processing steps necessary to form cognitive maps however occur much earlier in the cortical hierarchy.
My long term goal is to understand how the brain derives the unified panorama we experience from sensory inputs, how we store it in our memories, and how these in turn affect the way we perceive and interact with the world.
In my PhD work, I combine functional magnetic resonance imaging (3T & 7T-fMRI), eye tracking and computational modeling to examine how human viewing behavior and brain activity along the visual streams relate to mnemonic and cognitive map-like
processing in the MTL. Tightly-controlled psychophysical experiments and naturalistic virtual reality help me to address this question from multiple angles, complemented by encoding models to characterize and map the tuning of neural populations across the brain.
For a stable representation of the world to be formed, the brain must first tease apart whether incoming sensory signals were induced by changes in the environment or self-induced by our own movements.
This processing step is fundamental to transforming visual information into a self-motion invariant code. In a recent study, I found a whole network of regions engaged in this process, including the earliest visual cortices in the brain (Nau et al. 2018, NeuroImage ).
In another study, I examined a related but higher-order mechanism in the MTL, known to map space during navigation. I asked whether the same MTL-mechanism represents visual space as well, hence where we are looking rather than where we are. A critical neural component here are entorhinal grid cells: neurons that fire at different locations tessellating space with a hexagonal grid.
I refined fMRI-proxy measures for grid-cell population activity during navigation, and adapted it to a viewing task, to show that the human entorhinal cortex indeed represents visual space with a grid-cell like code (Nau et al. 2018, Nature Neuroscience ).
These results yield exciting implications, many of which we discussed in a recent review article (Nau et al. 2018, Trends Cogn. Sci ). Most important in this context, it shows that MTL mechanisms support domain-general computations in the brain, not limited to navigation, and that viewing behavior and visual paradigms enable a powerful read-out of these high-level cognitive computations.
Now, I work on several follow-up ideas, both on a methodological level by adapting voxel-wise and multivariate encoding tools from vision science to study visual- and MTL-tuning during active navigation, but also on a conceptual level by probing how visual memory signals emanating from the MTL impact perceptual processing in upstream brain areas.
