Senses: What you see is how you feel
EMBL’s Hiroki Asari investigates how our internal state can change the way our eyes work
BY EDWARD DADSWELL AND MARGAUX PHARES
Analogies can be useful things in science, but they can put a straitjacket on our thinking too. Hiroki Asari, a group leader at EMBL’s Monterotondo site, is keen to escape from one analogy in particular: the idea that the eye is a camera. It’s something we all learn at school. Light passes through the lens of the eye and falls on the layer of light-sensitive cells known as the retina. We’re taught that the retina is like a roll of film or a digital sensor – it captures the pattern of light, which is then entirely processed in the brain.
The reality is a little different. “The retina performs a lot of computations,” explains Asari. “They’re usually simple, like detecting motion or processing colours, while more complex computations – like face depiction or object recognition – happen in the brain. But I think the retina plays an important role in identifying certain elements of what we see.”
The retina plays an important role in identifying certain elements of what we see
This idea is not new, but Asari takes it a step further. “I believe these computations in the retina are affected by the internal states of our body. For example, when you see a cookie and you’re feeling hungry, it looks attractive. But when you’re full, it’s less attractive. People assume that this kind of processing is happening in the brain. My hypothesis is that it’s happening right at the very first stages of visual system processing – in other words, in the retina.”
Where to look
Asari aims to investigate this theory in mice. He measures the activity of the retina and optic nerve to see how the retina responds to the same visual stimulus under different states, such as when the mouse is hungry or fed; running or standing still. This is done using a range of experimental neuroscience techniques. One is electrophysiology, in which very fine electrodes are inserted into nerve cells and used to measure the nerve impulses. Another is calcium imaging, in which microscopy equipment is used in combination with special dyes that fluoresce in the presence of calcium ions. These ions play an important role in the transmission of nerve signals, so Asari can use the technique to monitor the activity of individual nerve cells in real time.
Finding a few equations that can explain everything in neural systems is my big goal
His work at EMBL is only just starting, but Asari is clear about what he wants to achieve. He’d like to uncover common principles that can be applied to any neural system – starting with the retina – and create mathematical models to describe them. “It’s like in physics, there are a few equations that can explain everything,” he says. “Finding the same kind of equations in neural systems is the big goal of my research.”