‘Noise’ in the Brain Encodes Surprisingly Important Signals

Activity in the visual cortex and other sensory areas is dominated by signals about body movements, down to little tics and twitches. Scientists are now rethinking how they study and conceive of perception.

Now, by analyzing both the neural activity and the behavior of mice in unprecedented detail, researchers have revealed a surprising explanation for much of that variability: Throughout the brain, even in low-level sensory areas like the visual cortex, neurons encode information about far more than their immediately relevant task. They also babble about whatever other behaviors the animal happens to be engaging in, even trivial ones — the twitch of a whisker, the flick of a hind leg.
Those simple gestures aren’t just present in the neural activity. They dominate it.

At its core, this discovery reflects the fact that fundamentally, the brain evolved for action — that animals have brains to let them move around, and that “perception isn’t just the external input,” Stringer said. “It’s modulated at least to some extent by what you’re doing at any given time.”

“We used to think that the brain analyzed all these things separately and then somehow bound them together,” McCormick said. “Well, we’re starting to learn that the brain does that mixing of multisensory and movement binding [earlier] than we previously imagined.”

“People tend to think of movements as being separate from cognition — as interfering with cognition, even,” Churchland said. “We think that, given this work, it might be time to consider an alternative point of view, that at least for some subjects, movement is really a part of the cognition.”


A system in which each neuron channels information about multiple activities at once might seem unworkably convoluted, but the Cortexlab team found that the brain can cope with all that data more easily than we might think. Their analysis revealed that when a stimulus is shown, the incoming information simply gets added on top of the movement-related signals that were already present. In a single neuron, those signals appear jumbled together, impossible to tell apart. But different neurons might convey the same stimulus but different background behaviors, so that if enough neurons are recorded together, it becomes possible to tease vision and movement apart.

So… SDR?