To uncover it, he and his colleagues asked eight adult study participants to look at patterns of dots that varied in number over time, all the while analysing the neural response properties in a numerosity-linked part of their brain using high-field fMRI (functional magnetic resonance imaging). Use of this advanced neuroimaging method allowed them to scan the subjects for far fewer hours per sitting than would have been required with a less powerful scanning technology.
With the fMRI data that resulted, Harvey and his team used population receptive field modelling, which aims to measure neural response as directly and quantitatively as possible. "This was the key to our success," Harvey said. It allowed the researchers to model the human fMRI response properties they observed following results of recordings from macaque neurons, in which numerosity experiments had been conducted more extensively.
Their efforts revealed a topographical layout of numerosity in the human brain; the small quantities of dots the participants observed were encoded by neurons in one part of the brain, and the larger quantities, in another.
This finding demonstrates that topography can emerge not just for lower-level cognitive functions, like the primary senses, but for higher-level cognitive functions, too.
"We are very excited that association cortex can produce emergent topographic structures," Harvey said.
Because scientists know a great deal about topographical maps (and have the tools to probe them), the work of Harvey et al. may help scientists better analyse the neural computation underlying number processing.
"We believe this will lead to a much more complete understanding of humans' unique numerical and mathematical skills," Harvey said.
Having heard from others in the field about the difficulty associated with the hunt for a topographical map of numerosi
|Contact: Natasha Pinol|
American Association for the Advancement of Science