Scientists shoot lasers into brain cells to uncover how illusions work

An illusion is when we see and perceive an object that doesn't match the sensory input that reaches our eyes.

In a new study published in Nature Neuroscience, researchers identified the key neural circuit and cell type that plays a pivotal role in detecting these illusions—more specifically, their outer edges or "contours"—and how this circuit works.

They discovered a special group of cells called IC–encoder neurons that tell the brain to see things that aren't really there as part of a process called recurrent pattern completion.

Because IC–encoder neurons have this unique capacity to drive pattern completion, the researchers think that they might have specialized synaptic output connectivity that allows them to recreate this pattern in a very effective manner.

They also also know that they receive top-down inputs from higher visual areas. The representation of the illusion arises in higher visual areas first and then gets fed back to the primary visual cortex; and when that information is fed back, it's received by these IC–encoders in the primary visual cortex.

 In the context of the brain and vision—using the above shape diagram—higher levels of the brain interpret the image as a square and then tell the lower-level visual cortex to "see a square" even though the visual stimulus consists of four semi-complete black circles.

They made the discovery by observing the electrical brain activity patterns of mice when they were shown illusory images like the Kanizsa triangle. They then shot beams of light at the IC-encoder neurons, in a process called two-photon holographic optogenetics, when there was no illusory image present.

When this happened, they noticed that even in the absence of an illusion, IC-encoder neurons triggered the same brain activity patterns that exist when an illusory image was present. They successfully emulated the same brain activity by stimulating these specialized neurons.

The findings shed light on how the visual system and perception work in the brain and have implications for diseases where this system malfunctions. In certain diseases you have patterns of activity that emerge in your brain that are abnormal, and in schizophrenia these are related to object representations that pop up randomly.

If you don't understand how those objects are formed and a collective set of cells work together to make those representations emerge, you're not going to be able to treat it; so understanding which cells and in which layer this activity occurs is helpful.

Recurrent pattern completion drives the neocortical representation of sensory inference, Nature Neuroscience (2025). DOI: 10.1038/s41593-025-02055-5.

Geologists discover where energy goes during an earthquake

The ground-shaking that an earthquake generates is only a fraction of the total energy that a quake releases. A quake can also generate a flash of heat, along with a domino-like fracturing of underground rocks. But exactly how much energy goes into each of these three processes is exceedingly difficult, if not impossible, to measure in the field.

Earthquakes are driven by energy that is stored up in rocks over millions of years. As tectonic plates slowly grind against each other, stress accumulates through the crust. When rocks are pushed past their material strength, they can suddenly slip along a narrow zone, creating a geologic fault. As rocks slip on either side of the fault, they produce seismic waves that ripple outward and upward.

We perceive an earthquake's energy mainly in the form of ground shaking, which can be measured using seismometers and other ground-based instruments. But the other two major forms of a quake's energy—heat and underground fracturing—are largely inaccessible with current technologies.

Now  geologists have traced the energy that is released by "lab quakes"—miniature analogs of natural earthquakes that are carefully triggered in a controlled laboratory setting. For the first time, they have quantified the complete energy budget of such quakes, in terms of the fraction of energy that goes into heat, shaking, and fracturing.

They found that only about 10% of a lab quake's energy causes physical shaking. An even smaller fraction—less than 1%—goes into breaking up rock and creating new surfaces. The overwhelming portion of a quake's energy—on average 80%—goes into heating up the immediate region around a quake's epicenter. In fact, the researchers observed that a lab quake can produce a temperature spike hot enough to melt surrounding material and turn it briefly into liquid melt.

The geologists also found that a quake's energy budget depends on a region's deformation history—the degree to which rocks have been shifted and disturbed by previous tectonic motions. The fractions of quake energy that produce heat, shaking, and rock fracturing can shift depending on what the region has experienced in the past.

The team's lab quakes are a simplified analog of what occurs during a natural earthquake. Down the road, their results could help seismologists predict the likelihood of earthquakes in regions that are prone to seismic events.

 Daniel Ortega‐Arroyo et al, "Lab‐Quakes": Quantifying the Complete Energy Budget of High‐Pressure Laboratory Failure, AGU Advances (2025). DOI: 10.1029/2025av001683