Original fromquantamagazine.org , author: Jordana Cepelewicz, Chinese version starting in the micro-channel public number: Neural reality (ID: neureality)< Span class="text-remarks">, translation: Gu Jintao, cover: Jason Lyon
For a long time, scientists who have studied attention have focused on the cerebral cortex. However, some researchers now find that the attention process may also be buried deep in the brain.
We can hear a conversation in the creaking background, find a bunch of keys in the scattered chaos, and notice the raccoon flying in front of the car in the fast-moving landscape. Even if we feel that information is flooding, we can focus on important things and take action.
Attention is like the brain’s searchlight, which is based on the sensory information associated with the present and filters out the rest of the stimulus. The neuroscientist wants to determine the “circuit” behind the searchlight and figure out how it is aimed and illuminated. For decades, their research has revolved around the cerebral cortex, a thin layer of nerve tissue that wraps the rest of the brain, often associated with intelligence and higher-order cognition – and these studies have revealed: The cortical neural activity can emphasize specific information by enhancing specific sensory processing.
But now, some researchers are experimenting with another idea of how the brain suppresses information rather than enhancing it. Perhaps more importantly, they found that the process involved an older area buried deep beneath the cortex and deep in the brain. In the study of attention, these areas were not usually considered in the past.
Through these studies, scientists have inadvertently touched on the ancient mind-body problems—how the body and mind are deeply and inextricably intertwined through automatic sensory experiences, body movements, and higher levels of consciousness. Although on this issue, they just took a small step like a baby.
Search for the searchlight circuit
For a long time, because attention has always been closely linked to complex functions such as consciousness, scientists have concluded that it is a cortical phenomenon. Francis Crick (bridge), but also acts as a gatekeeper (screening) to fix certain data streams to establish a certain degree of focus.
But decades later, scientists have not found a practical mechanism, mainly because animal experiments are not easy to design.
This did not stop the neuroscientist Michael Harassa in the McGovern Institute of Brain Science at the Massachusetts Institute of Technology (Michael Halassa). He wondered how the brain filtered the sensory input before reaching the cortex, and whether it could locate the Crick-predicted gatekeeper in the thalamus.
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Michael Halassa Image Credit: Caitlin Cunningham Photography
He is attracted by a layer of inhibitory neurons called the thalamic reticular nucleus (TRN), which is wrapped like a shell. The rest of the thalamus. When Harassa was a postdoctoral researcher, he had found a rough gating in the brain: TRN seems to allow the sensory input into the cortex when the animal is awake, allowing the animal to pay attention to the surrounding environment and suppressing the animal while sleeping. Feel the input.
In 2015, Harassa and his colleagues discovered another finer gating, which further proves that the circuit Crick is looking for does have something to do and suggests that TRN has a place in it. In this study, animals were chosen to focus on different sensations. The researchers used trained mice to listen to the command and run according to the flashing of the lights and the tones of the sound.
Then, they control the lights and tones, communicate contradictory commands, and tell the mice to ignore the lights or tones in advance. The response of the mice reflects their level of attention. In the course of the mouse’s task, the researchers used existing techniques to shut down activities in different areas of the brain to see which brain regions interfere with animal behavior.
As expected, the prefrontal cortex, which sends high-order commands to other parts of the brain, is indispensable. But the team also observed that if a test requires mice to pay attention to light, stimulating neurons in visual TRN can interfere with mouse performance. And if you silence the visual TRN, the mouse will not be able to complete the auditory task well.
In fact, the knob that the neural network turns controls the suppression, not the excitement process. If the prefrontal cortex believes that a sensation is an interference, then the TRN will suppress it. If the mouse needs to listen to the auditory information first, the prefrontal cortex will tell the visual TRN: Enhance your activity to suppress the visual activity of the thalamus. We don’t need unrelated visual data.
The metaphor of the attention searchlight is reversed.:The brain does not illuminate the light of the target stimulus; it reduces the light of everything else.
Despite the success of the study, they also confirmed Crick’s hunch: the prefrontal cortex controls the filter of incoming sensory information in the thalamus; but the researchers realized a problem: the prefrontal cortex and TRN There is no direct connection to the feeling part. The circuit has not been completed yet.
But that’s just the past, and now Harassa and his colleagues finally found the last wire, connected the circuit, pointing the way for research attention.
The spotlight is blinking
They used animal tasks similar to the 2015 study and focused on functional interactions and neuronal connections between brain regions. They found that the entire loop actually started from the prefrontal cortex and went to the basal ganglion. (The basal ganglia is a group of nuclei deep in the brain, Usually associated with motion control and many other functions), then to TRN and the thalamus, and finally back to the advanced cortex.
Thus, for example, when irrelevant visual information is transmitted from the eye to the visual thalamus, it can be intercepted almost immediately: The basal ganglia can intervene and activate the visual TRN as indicated by the prefrontal cortex to filter out excess Stimulation.
National Institutes of Health (NIH)National Institute of Ophthalmology, Richard Klauzlis (Richard Krauzlis) says: “This is an interesting feedback path, I don’t think anyone has everReported. He was not involved in the study.
In addition, the researchers found that the mechanism not only filters out information from one sense to enhance awareness of another; it also filters information within a sense. When prompted to note certain sounds, the TRN helps to suppress unrelated background noise within the auditory signal. Roger University’s neuroscientist Dujie Tading (Duje Tadin) says that the effect of sensory processing is “only one that is responsible for a sense.” The entire thalamus area is much more accurate.”
He added: “We often don’t think about how we ignore irrelevant things.” He added, “But I think that ignoring irrelevant things is a more effective way of dealing with information.” In a noisy room In order to let others hear their own voices, you can either improve your voice or try to eliminate the noise source. (Tardin is investigating another type of background suppression, but it is faster and more automatic than selective attention.)< /p>
Halassa’s findings suggest that the brain abandoned unrelated perceptions earlier than expected. Prince University Cognitive Neuroscientist Ian Fibel Cohen(Ian Fiebelkorn) says: “Interestingly, in visual processing The first step, even before the information reaches the visual cortex, the filtering begins.”
Multi-electrode array device used by Michael Halassa in experiments Image Source: Leon Chew
However, in this way, sensory information is thrown out of the brain, and the strategy has obvious weaknesses.That is, the perception of being abandoned may be unexpectedly important, and abandoning them can be dangerous. Fibel Cohen’s work shows that the brain has a way to hedge these risks. Fibel Cohen said that when people think of the searchlights of attention, they see it as a steady beam of light, illuminating the direction of cognitive resources. But he said: “My research shows that it is not true. On the contrary, it seems that the spotlight is flashing.”
According to his findings, the focus of the attention spotlight seems to be weakened about four times per second, presumably to prevent animals from paying too much attention to individual locations or stimuli in the environment. Slow suppression of attention allows the brain to have the opportunity to shift attention to other things when necessary. He said: “The brain seems to be distracting periodically.”
Fairbel Cohen and his colleagues, like the team at Harassa, also want to explain this connection through the subcortical brain area. Currently, they have been studying the role of another part of the thalamus, but they plan to study the basal ganglia in the future.
Cognition also occurs under the cortex
These studies mark a key shift: attention was once thought to be controlled only by the cortex.
But according to Klauzlis, in the past five years, “we have gradually understood that there are many activities in the subcortical area.” John Mussell, a neurobiologist at the University of Chicago, said: “Most people want the cerebral cortex to do all the heavy lifting for us.” Work, but I think this is unrealistic.”
In fact, the basal ganglia has the function of controlling attention, and this discovery is particularly fascinating. Part of the reason is because it is such an ancient part of the brain that people usually don’t see it as part of selective attention. “The fish have this,” Krauzlis said. “Back to the earliest vertebrates, such as the Seven Miles, they have no jaws.” There is no new cortex, and it is necessary to say – “They basically have basal ganglia. The simple form is similar to some of the loops.” Perhaps the fish’s neural loop can provide hints about how attention evolves.
Harassa also has attention deficit hyperactivity disorder (ADHD) and autismInterested in diseases such as these, which usually manifest as allergies to certain types of input. The connection between attention and the basal ganglia may give us some inspiration.
However, The most interesting thing about the involvement of the basal ganglia is that the structure is usually associated with motion control. Although research is increasingly involved in reward-based learning, decision making, and other types of motivation-based behavior, these are all about action (action).
As the work at the Harassa Laboratory is completed, the role of the basal ganglia has now expanded to include sensory control (active inference ). The brain does not passively sample information from the environment and then reacts to observed external stimuli. They also reverse the process: make the appropriate actions to sample from the environment. A small body movement like a blink can also guide perception.
Fibell Cohen said that the sensory and motor systems “are not operating independently, but evolve together.” Therefore, the brain area not only helps shape the output (animal behavior); they also help to adjust the input (animal feelings). Harassa’s findings provide further support for the more active (Heleen Slagter) said, “We basically learn how to perceive the surroundings by action.” world. “The high degree of interconnection with the cortex suggests that even without attention control, “the role of these subcortical structures in higher-order cognition is much more important than what everyone thinks.”
In turn, this can also provide ideas for the most elusive subject in neuroscience, consciousness research. As evidenced by Harassa’s research and other research, when we focus on the neural correlates of attention, we are actually looking for perception (ception) neural related matter. Monsell said: “This is part of a broader picture in terms of trying to understand how the brain works.”
Slager is now studying the role that the basal ganglia may play in consciousness. “We not only use our bodies to experience the world, but also the world because of our bodies. The brain represents the world in order to act meaningfully in it.” She said, “So I think that the experience of consciousness must be closely linked to action.” Just like attention, consciousness should also be guided by what to do.
Original fromquantamagazine.org , author: Jordana Cepelewicz, Chinese version starting in the micro-channel public number: Neural reality (ID: neureality), translation: Gu Jintao, Cover: Jason Lyon