The Neuroscience Behind the “Continuity Illusion”

New research study on the connection impression discovers how the brain views smooth movement, stressing the remarkable colliculus’s significance and recommending brand-new methods for neuroscience research study and scientific practice.

A research study by a group at the Champalimaud Foundation (CF) has actually cast a brand-new light on the remarkable colliculus (SC), an ingrained brain structure typically eclipsed by its more popular cortical next-door neighbor. Their discovery discovers how the SC might play a critical function in how animals see the world in movement, and clarifies the “continuity illusion,” a vital affective procedure important to a lot of our day-to-day activities, from driving cars to seeing films.

Understanding the Continuity Illusion

Imagine seeing a movie. The moving images you see are really a series of fixed frames revealed quickly. This is the connection impression at work, where our brain views a series of fast flashes as constant, smooth movement. It’s a phenomenon not simply essential to our pleasure of movies however likewise an essential element of how all mammals, from people to rats, view the vibrant world around them. This research study from the CF’s Shemesh Lab, released today (February 12) in < period class ="glossaryLink" aria-describedby ="tt" data-cmtooltip ="<div class=glossaryItemTitle>Nature Communications</div><div class=glossaryItemBody>&lt;em&gt;Nature Communications&lt;/em&gt; is a peer-reviewed, open-access, multidisciplinary, scientific journal published by Nature Portfolio. It covers the natural sciences, including physics, biology, chemistry, medicine, and earth sciences. It began publishing in 2010 and has editorial offices in London, Berlin, New York City, and Shanghai.&nbsp;</div>" data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]" tabindex ="0" function ="link" >NatureCommunications, looks into how this impression is encoded in the brain.

TheScience ofPerception

The speed at which flashes need to happen for our brain to see them as consistent instead of flickering is called theFlicker(**************************************************************************************************************************** )(***************************************************************************************************************************** )( FFF) limit. This limit differs amongst animals; for example, birds, which require to see quick motions, have a greater limit than people, which indicates they can still view light as flickering, instead of constant, even when it’s blinking really quickly.The FFF limit is likewise essential in nature, such as in predator-prey interactions, and can be impacted by particular illness like liver conditions or eye conditions like cataracts.

Interestingly, various approaches of determining this limit, like observing animal habits or taping electrical activity in the eyes or the cortex( the brain’s external layer that processes what we see), can offer various outcomes.(********************************************************************************* )recommends that other parts of the brain likewise contribute in how we view flickering light.

(******************************************************************************************************************* )this research study, scientists integrated practical MRI (< period class ="glossaryLink" aria-describedby ="tt" data-cmtooltip ="<div class=glossaryItemTitle>fMRI</div><div class=glossaryItemBody>fMRI stands for functional magnetic resonance imaging. It is a non-invasive neuroimaging technique that uses magnetic resonance imaging (MRI) to measure changes in blood flow in the brain, which can indicate neural activity. In simpler terms, fMRI is a tool that allows researchers to see which parts of the brain are active during certain tasks or stimuli, providing insights into brain function and organization.</div>" data-gt-translate-attributes="[{"attribute":"data-cmtooltip", "format":"html"}]" tabindex ="0" function ="link" > fMRI) brain scans, behavioral experiments, and electrical recordings of brain activity to comprehend how this procedure works.Their findings suggest that the SC is essential in the shift from seeing private flashes to smooth movement, which it might be a crucial element in the production of the connection impression.

AThree-Pronged Attack

“This project was really a ground-up endeavor, and began as a conversation between two PhD students at CF,” notesNoamShemesh, senior author of the research study.”RitaGil, a trainee in my laboratory, was checking out the rat brain’s actions to various light frequencies with MRI.Her conversations withMafaldaValente, in the laboratory ofAlfonsoRenart, caused the advancement of a behavioral job in which rats were trained to compare flashes and constant light.

Using the MRI and behavioral information, they likewise taped the brain’s electrical activity throughout light stimulation.This technique allowed them to determine and compare FFF limits utilizing 3 unique approaches: MRI, behavioral experiments, and electrophysiology.(********************************************************************************* )multimodal technique is rather unusual, and is truly what sets this research study apart.We’re likewise grateful to Alfonso Renart for the intriguing conversations that added to this research study.”

Bridging Behavioral and Biological Data

For the fMRI experiments, rats were revealed visual stimuli at frequencies varying from low to high. To decrease motion and make sure steady brain imaging, the animals were gently sedated.

“fMRI is a non-invasive technique that tracks changes in blood flow, which are indicative of neural activity in the brain,” discussesGil “One of the advantages of fMRI is its ability to map brain activity throughout the entire visual pathway, simultaneously capturing activity from multiple regions.”

The objective was to observe how the brain shifts from viewing private flashes of light (fixed vision) to a constant circulation of light (vibrant vision), and to identify the brain areas included.

“When we looked at the SC,” states Gil, “we found markedly different responses based on the frequency of visual stimuli. As the frequency of the visual stimulus increased, moving towards continuous light perception, there was a shift in the SC’s response from positive to negative fMRI signal regimes.”

Positive signals show increased neural activity, while unfavorable signals possibly symbolize the opposite. Based on these observations, a hypothesis started to form: might the shift from fixed to vibrant vision in the connection impression include the suppression of activity in the SC?

To response this concern, they next turned to behavioral experiments. Rats were trained in a specifically developed box, where they discovered to go to one side port if they viewed the light as flickering, and to the other if they viewed it as constant. Correct options were rewarded with water to strengthen the knowing. By differing the light frequencies showed, the group taped at which point the rats viewed the flickering light as constant.

When they compared the behavioral information with the fMRI information, they made an unexpected discovery: the modification from favorable to unfavorable fMRI signals in the SC at particular frequencies matched the frequencies at which rats behaviourally viewed the shift from flickering to constant light.

Given that the SC revealed the greatest connection in between habits and fMRI information compared to other brain locations, the scientists targeted it for electrophysiological recordings, straight determining the electrical activity of its nerve cells. They utilized light sedation to keep consistency with the fMRI conditions. Their goal was to much better comprehend the particular neural systems included when rats view flickering versus constant light. Did the favorable and unfavorable signals spotted in fMRI represent neural activity and suppression, respectively, as they had assumed?

At low light frequencies where rats recognized private flashes, the scientists observed increased neural activity representing each flash. At greater frequencies viewed as constant light, the neural actions to these private flashes lessened, and rather, there were more noticable actions at both the start and completion of the light stimulation. Notably, there was a significant suppression of neural activity in between these preliminary (beginning) and last (balanced out) peaks.

Valente notes, “Our measurements of electrical activity in the SC aligned well with our fMRI data, which exhibited onset and offset peaks surrounding the negative signals at higher frequencies. These electrophysiological recordings support the notion that the positive and negative signals recorded in fMRI do indeed represent neural activity and suppression, respectively. It seems that this suppression happens when animals enter a state of dynamic vision mode, potentially serving as a key contributor to flicker fusion and the continuity illusion.”

Reflecting on the research study, Valente shares, “What really surprised us was how closely the fMRI signals in the SC matched the behavioural data, even more than those in the cortex, which is typically seen as the main visual processing area in mammals. Equally striking was to find the same patterns in the SC even after we had intentionally disabled the cortex, suggesting that these signals originate in the SC itself and are not just a result of activity from the cortex.”

Gil continues, “This points to the SC’s role as a novelty detector. For instance, at lower light frequencies, each flash seems to be processed as a new event by the SC. But as the frequency increases beyond a certain point, the SC appears to decide the stimulus is no longer new or noteworthy, leading to reduced activity. This could account for the pattern of increased activity at the start and end of high-frequency stimulation, with periods of suppression in between.”

Implications and Future Directions

“Our findings provide a roadmap for how neuroscience experiments could be conducted in the future,” concludesShemesh “By initially using fMRI to present stimuli, researchers can efficiently pinpoint which brain regions to focus on for more detailed electrophysiological studies. This approach not only saves time and resources but also capitalizes on fMRI’s strength in reflecting the population activity of brain regions. While it doesn’t offer the granular detail of single-cell activity, fMRI’s ability to show the bigger picture – whether there’s more brain activation or suppression – makes it a valuable first step in guiding subsequent experiments.”

The authors think that their findings hold significance for scientific applications. In cases of people with visual problems, optic nerve illness, or conditions like autism and stroke, this research study uses brand-new opportunities for both evaluation and prospective treatment of visual dysfunctions. By determining and comparing FFF limits in these people versus those in healthy populations, and observing how these limits develop, it might be possible to assess the versatility of particular brain areas. This might result in an understanding of which locations of the brain stay open to treatment, leading the way for the advancement of targeted restorative interventions.

Looking ahead, the scientists intend to recognize which particular cell key ins the SC are accountable for the activities they observed. Their wider goal is to deepen our understanding of the functions of different brain areas within the visual path, integrating speculative strategies such as targeted sores or visual deprivation in addition to MRI research studies.

These techniques guarantee to offer a much deeper insight into the versatility and function of visual areas, improving our existing design of how each location adds to visual understanding. So, the next time you’re seeing a motion picture, experiencing the impression of fluid movement from the fast succession of frames, spare an idea for the complex procedures at play in your brain, and for the continuous research study efforts to unwind them.

Reference: “Rat superior colliculus encodes the transition between static and dynamic vision modes” by Rita Gil, Mafalda Valente and Noam Shemesh, 12 February 2024, Nature Communications
DOI: 10.1038/ s41467-024-44934 -8