A slice of cheesy pizza. Crunchy French fries piled high. Slushy ice cream melting from a cone on a steamy summer day. A new study by MIT neuroscientists reveals that when you look at any of these items, a specific region of your visual cortex lights up.

This new group of neurons that respond to food is in the ventral visual stream, near other groups of neurons that respond to faces, bodies, places, and words. The researchers speculate that the surprising result may be a reflection of the special place that food holds in human civilization.

“Food is central to human social interactions and cultural practices. It’s not just sustenance,” adds Nancy Kanwisher.

So many aspects of our cultural identity, religious beliefs, social connections, and many other human activities revolve around food.

The findings, which are based on an investigation of a huge public database of human brain reactions to a collection of 10,000 photographs, raise numerous new concerns regarding the development of this neural population.

Postdoc at MIT Meenakshi Khosla and MIT research scientist N. Apurva Ratan Murty are the main authors of the paper. The findings of the study were published in the academic journal Current Biology.

Visual classifications

Kanwisher found cortical areas that respond only to faces more than 20 years ago. He was studying the ventral visual stream, which is the part of the brain that recognizes objects. Later, she and other researchers found other areas with selective responses to objects, people, or speech. When researchers actively set out to look for them, they found most of those regions. However, Kanwisher warns that using a hypothesis-driven method can restrict the results you discover.

She explains, “There could be other things that we might not think to look for. And even when we find something, how do we know that that’s actually part of the basic dominant structure of that pathway, and not something we found just because we were looking for it?”

To try to identify the underlying structure of the ventral visual stream, Kanwisher and Khosla opted to study a large, publicly available dataset of full-brain functional magnetic resonance imaging (fMRI) responses from eight human volunteers as they viewed thousands of images.

“We wanted to see when we apply a data-driven, hypothesis-free strategy, what kinds of selectivities pop up, and whether those are consistent with what had been discovered before. A second goal was to see if we could discover novel selectivities that either haven’t been hypothesized before, or that have remained hidden due to the lower spatial resolution of fMRI data,” Khosla adds.

To achieve this, the researchers used a mathematical technique that enables them to identify neuronal populations from non-traditional fMRI data. An fMRI image is made up of many voxels, which are three-dimensional units that represent a cube of brain tissue. The hundreds of thousands of neurons that make up each voxel may be drowned out by other populations in the same voxel if some of those neurons are part of smaller populations that only respond to certain types of visual input.

The novel analytical method can reveal responses of neuronal populations within each voxel of fMRI data, as Kanwisher’s lab has done before with data from the auditory cortex.

Using this method, the authors noted four populations that matched groups of people who respond to faces, places, bodies, and words that had already been found. According to Kanwisher, “That tells us that this method works, and it tells us that the things that we found before are not just obscure properties of that pathway, but major, dominant properties.”

It’s interesting to note that a fifth population also appeared, and this one seemed to like representations of food.

“We were first quite puzzled by this because food is not a visually homogenous category,” adds Khosla. “Things like apples and corn and pasta all look so unlike each other, yet we found a single population that responds similarly to all these diverse food items.”

The food-specific population, termed the ventral food component (VFC) by the researchers, appears to be dispersed throughout two neuronal clusters located on either side of the FFA. According to the researchers, the fact that the food-specific populations are dispersed among other category-specific populations may assist to explain why they haven’t been observed before.

“We think that food selectivity had been harder to characterize before because,” adds Khosla, “the populations that are selective for food are intermingled with other nearby populations that have distinct responses to other stimulus attributes. The low spatial resolution of fMRI prevents us from seeing this selectivity because the responses of different neural population get mixed in a voxel.”

Food vs. other things

Based on earlier models Murty had created for the parts of the brain responsible for face and location identification, the researchers also utilized the data to construct a computational model of the VFC. The researchers were able to conduct further experiments and forecast the responses of the VFC as a result. In one experiment, they fed the model photos that were remarkably similar to each other of both food and non-food items, such as a banana and a yellow crescent moon.

“Those matched stimuli have very similar visual properties, but the main attribute in which they differ is edible versus inedible,” adds the author. “We could feed those arbitrary stimuli through the predictive model and see whether it would still respond more to food than non-food, without having to collect the fMRI data.”

They could also use the computer model to look at much bigger sets of data, like millions of pictures. These simulations assisted in demonstrating the VFC’s extreme food image selection.

The researchers looked at the fMRI data from people and found that in some people, the VFC responded a little bit more to processed foods like pizza than to natural foods like apples. In the future, they want to find out how people’s reactions to a certain food might be affected by things like how familiar they are with it and whether they like or dislike it.

They also want to find out what other regions of the brain this region interacts with and when and how this region becomes specialized during early life. Another concern is whether this food-selective population will be observed in species, such as monkeys, that do not attach the same cultural meaning to food as humans.

Image Credit: Getty

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