The brain appears to strengthen perception when it processes sight and sound together, particularly when it detects something in its peripheral vision.
Group leader Flor Iacaruso at the Crick. Credit: Dave Guttridge.
You often react to things before you consciously see them. Think of flinching at a branch, a cyclist or a wasp. This ‘spider sense’ is important, it can stop you walking into something, or even save your life.
The structure responsible for this mild superpower is called the superior colliculus. It’s the size of a pea, sits deep in the midbrain and hasn’t changed much across species for around 500 million years.
The superior colliculus acts as a rapid threat-detection system, triggering instinctive eye movements, head orientation and defensive reflexes, such as dodging looming objects.
Some neurons in the superior colliculus respond to sights, others to sounds and some respond to both, so-called ‘multisensory’ neurons. Flor Iacaruso, a neuroscientist who leads the Crick’s Neuronal Circuits and Behaviour Laboratory, and her team are particularly interested in these multisensory neurons and how they might help the superior colliculus locate threats.
“Our brains use physics to localise targets. Sound and light travel at different speeds. Light is very fast and sound is relatively slow,” says Flor. “Consequently, there will be an audio-visual delay that will change depending on how far the target is from us, and these tiny differences in timing can tell us where objects are.”
To discover how multisensory neurons contribute to target location, Flor’s lab recorded more than 5,000 brain cells in mice, mapping what happens to the neurons in the mouse’s brain when they interpreted sight and sound stimuli.
“We have found multisensory neurons in the superior colliculus that respond strongly and selectively to specific audiovisual delays,” says Flor. “These ‘delay’ neurons can accurately tell us how far away a stimulus is, among other things.”
Flor’s lab found that neurons in the superior colliculus representing the peripheral visual field were more heavily interconnected, and showed more precise delay responses.
“So, this means that there is a better multisensory integration in parts of the visual field where the animal is not directly looking,” says Flor. “Where the animal can’t see as well, it’s making more use of other sensory signals.”
Given the similarities between the neural connections in both humans and mice, Flor thinks her findings probably also apply to our own brains.
In their endeavour to understand how we interpret the world, Flor’s team plans to further explore the behaviour of neurons within this area of the brain through mouse models.
“We will continue to look at how multisensory neurons talk to each other, how they connect and how they communicate with the rest of the brain,” she says.
