Big brain evolution: filtering for attention (Evolution)

by David Turell @, Tuesday, September 24, 2019, 18:54 (364 days ago) @ David Turell

The general controls of filtering attention have been described:

"We can pick out a conversation in a loud room, amid the rise and fall of other voices or the hum of an air conditioner. We can spot a set of keys in a sea of clutter, or register a raccoon darting into the path of our onrushing car. Somehow, even with massive amounts of information flooding our senses, we’re able to focus on what’s important and act on it.


" It’s become clear that activity in the cortex boosts sensory processing to enhance features of interest.

"But now, some researchers are trying a different approach, studying how the brain suppresses information rather than how it augments it. Perhaps more importantly, they’ve found that this process involves more ancient regions much deeper in the brain — regions not often considered when it comes to attention.

"By doing so, scientists have also inadvertently started to take baby steps toward a better understanding of how body and mind — through automatic sensory experiences, physical movements and higher-level consciousness — are deeply and inextricably intertwined.


"He was drawn to a thin layer of inhibitory neurons called the thalamic reticular nucleus (TRN), which wraps around the rest of the thalamus like a shell. By the time Halassa was a postdoctoral researcher, he had already found a coarse level of gating in that brain area: The TRN seemed to let sensory inputs through when an animal was awake and attentive to something in its environment, but it suppressed them when the animal was asleep.


"In effect, the network was turning the knobs on inhibitory processes, not excitatory ones, with the TRN inhibiting information that the prefrontal cortex deemed distracting. If the mouse needed to prioritize auditory information, the prefrontal cortex told the visual TRN to increase its activity to suppress the visual thalamus — stripping away irrelevant visual data.

"The attentional searchlight metaphor was backward: The brain wasn’t brightening the light on stimuli of interest; it was lowering the lights on everything else.


"...the team probed the functional effects of various brain regions on one another, as well as the neuronal connections between them. The full circuit, they found, goes from the prefrontal cortex to a much deeper structure called the basal ganglia (often associated with motor control and a host of other functions), then to the TRN and the thalamus, before finally going back up to higher cortical regions. So, for instance, as visual information passes from the eye to the visual thalamus, it can get intercepted almost immediately if it’s not relevant to the given task. The basal ganglia can step in and activate the visual TRN to screen out the extraneous stimuli, in keeping with the prefrontal cortex’s directive.
“It’s an interesting feedback pathway, which I don’t think has been described before,” said Richard Krauzlis, a neuroscientist.


"When the mice were cued to pay attention to certain sounds, the TRN helped to suppress irrelevant background noise within the auditory signal. The effects on sensory processing “can be much more precise than just suppressing the whole thalamic region for one sensory modality, which is a rather blunt form of suppression,” said Duje Tadin,


"In fact, Halassa’s discovery of the basal ganglia’s role in attention is particularly fascinating. That’s partly because it is such an ancient area of the brain, one that hasn’t typically been viewed as a part of selective attention. “Fish have this,” Krauzlis said. “Going back to the earliest vertebrates, like the lamprey, which doesn’t have a jaw” — or a neocortex, for that matter — “they have basically a simple form of basal ganglia and some of these same circuits.” The fishes’ neural circuitry may offer hints about how attention evolved.


“'How we learn to perceive the world around us is very much through action.” The high level of interconnection with the cortex suggests that, even beyond attention, “these subcortical structures play a much more important role in higher-order cognition than I think is often considered.”


"Slagter is now studying the role that the basal ganglia might play in consciousness. “We experience the world not just using our bodies, but because of our bodies. And brains represent the world in order to meaningfully act in it,” she said. “Therefore, I would think that conscious experience must be tightly linked to actions,” just like attention. “Consciousness should be action oriented.'”

Comment: all of the brain is necessary for perception and consciousness as this study shows. Our brain was meticulously prepared through an intelligently guided evolution.

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