There’s an obvious weakness in the brain’s strategy of tossing out sensory information this way, though—namely, the danger that the jettisoned perceptions might be unexpectedly important. Work by Fiebelkorn suggests that the brain has a way to hedge against those risks.
When people think about the searchlight of attention, Fiebelkorn says, they think of it as a steady, continuously shining beam that illuminates where an animal should direct its cognitive resources. But “what my research shows is that that’s not true,” he says. “Instead, it seems that the spotlight is blinking.”
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According to his findings, the focus of the attentional spotlight seems to get relatively weaker about four times a second, presumably to prevent animals from staying overly focused on a single location or stimulus in their environment. That very brief suppression of what’s important gives other, peripheral stimuli an indirect boost, creating an opportunity for the brain to shift its attention to something else if necessary. “The brain seems to be wired to be periodically distractible,” he says.
Fiebelkorn and his colleagues, like Halassa’s team, are also looking to subcortical regions to explain this wiring. For now they’ve been studying the role of yet another section of the thalamus, but they plan to look into the basal ganglia in the future too.
These studies mark a crucial shift: Attentional processes were once understood to be the province of the cortex alone. But according to Krauzlis, in the past five years “it’s become a little more obvious that there are things that are happening underneath the cortex.”
“Most people want the cerebral cortex to do all the heavy lifting for us, and I don’t think that’s realistic,” says John Maunsell, a neurobiologist at the University of Chicago.
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 part of selective attention. “Fish have this,” Krauzlis says. “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 fish’s neural circuitry may offer hints about how attention evolved.
Halassa is particularly intrigued by what the connection between attention and the basal ganglia might reveal about conditions such as attention deficit hyperactivity disorder and autism, which often manifest as hypersensitivity to certain kinds of inputs.
But perhaps the most profoundly interesting point about the involvement of the basal ganglia is that the structure is usually associated with motor control, although research has increasingly implicated it in reward-based learning, decision making, and other motivation-based types of behavior as well.