Introducing the brain: interpreting self motion (Introduction)

by David Turell , Sunday, May 04, 2025, 18:06 (7 hours, 43 minutes ago) @ David Turell

When you turn your head the background doesn't blur:

https://www.the-scientist.com/is-the-world-spinning-or-is-it-me-how-the-brain-distingui...

"In the 1860s, physician Hermann von Helmholtz did a simple experiment to understand how the world stays still during eye movements. With a still head, he closed one eye and swiveled the other to look around. Despite the rapid darting of the open eye, he noticed the image of the surroundings appeared stable rather than blurred. Next, instead of moving the eye naturally, he gently pushed it around in the socket with a finger and noticed the chaotic movement of the view. Why does the world shift when an external force is used to move the eye, but not when it swivels on its own?

"Von Helmholtz proposed that when an animal decides to move its eyes naturally, certain areas of the brain receive a duplicate of this command called the efference copy, which signals that the upcoming motion of the world is a result of eye movement and not actual shifting of the environment.1 This message is absent when an external force moves the visual field. “When the finger hijacks the movement, it takes away the efference copy and we see what happens in a world without one,” said Tomas Vega-Zuniga, a neuroscientist at the Institute of Science and Technology Austria (ISTA). The efference copy plays a crucial role in an animal’s ability to differentiate its own motion from that of the surrounding world, which in turn is essential for coherent perception and behavior.

***

"Now, researchers at ISTA have shown that a region of the thalamus, called the ventral lateral geniculate nucleus (vLGN), serves as an interface between visual and motor neural circuits and is responsible for correcting self-motion-induced blur. These findings in mice, published in Nature Neuroscience, could help researchers better understand how an organism’s senses faithfully represent the world and enable appropriate behavior.

'Visual perception is complex and requires seamless communication between different brain areas. One such region that integrates visual and other sensory perceptions with movement is the superior colliculus.4 This multi-layered structure receives visual information directly from the retina, as well as indirectly via the visual cortex. “The superior colliculus is like a map of the world. It knows where things are in space,” said Vega-Zuniga, a study coauthor. In previous experiments in primates, researchers showed that the superior colliculus sends signals to areas in the cortex that control eye movements. So, Vega-Zuniga and his colleagues hypothesized that neurons that send information to the superior colliculus could serve as a source of the efference copy and correct motion-induced blur.

"An important function of the efference copy is to block certain sensory inputs to maintain coherent perception for the organism. For example, auditory signaling in crickets is diminished during their own chirps, so as not to desensitize hearing at other times. Since this is achieved through suppression or inhibition, the team focused on the vLGN, which forms inhibitory connections with neurons in superior colliculus.

***

"They found that the vLGN neurons only responded to self-motion. Additionally, when the team blocked vLGN activity, the neuronal responses to eye movement in the superior colliculus became longer and more frequent, suggesting that the vLGN shortens the effective time of visual exposure during movement, thus reducing blur.

"To confirm this, Vega-Zuniga and his colleagues tested how well the mice could perceive depth, which not only requires both visual and movement perception, but is detrimentally affected by blurry vision. They observed that mice in which the vLGN output was blocked showed reduced avoidance of a cliff in the behavioral arena, demonstrating difficulty in judging depth. Based on this, the authors suggested that the vLGN is important for visual perception during self-generated movements."

Comment: since rapid movement is essential to survival this mechanism is essential. Assuming the new brain arrived as a blank slate this entire mechanism had to be learned. God designs for facility.