What’s going on in the brain while we do “pay” attention?
Information can come from anywhere in one’s environment. If your brain were to deem all of it as equally important, its performance would be sub-optimal at best. So, it has to triage the information coming in, and infer some of it more important or relevant than other. There are brain regions that decide which incoming signals should be processed, and there are regions that decide which of the processed signals should guide behaviour. Embedded deep in the brain, the superior colliculus is an evolutionarily ancient, midbrain structure that plays a role in deciding which part of the surrounding space is more relevant to pay attention to, and directs eye movements to those locations. For instance when you are driving, the Toyota Etios straight ahead of you is more pertinent rather than the Ford Figo in the opposite lane. But if you were to make a U‑turn, then the Figo becomes important. This decision to change direction that you have just made requires you to switch your attentional priorities to a new object (the Figo); and is possible, courtesy of the superior colliculus in your brain.
Our current knowledge about this brain region comes from studies where scientists inactivated this region in test animals. When the superior colliculus goes offline, very specific kinds of behavioural defects were observed –the ability of these animals to selectively pay attention to one thing in the environment, at the cost of ignoring other competing stimuli, was compromised.
Take the example of two individuals engrossed in a conversation. The listener’s brain must make the decision to pay attention to the speaker and ignore other stimuli, so {s}he can ask a relevant question or give a pertinent comment; just in general to follow the conversation. To pull this off, in the listener’s brain, incoming auditory information that is attended, gets access to working memory — what was just said, what’s been the trajectory of this conversation, etc. Incidentally, compromises in these brain processes is thought to be why people with Alzheimer’s disease are unable to hold down conversations — the disease damages working memory systems in their brains. In a nutshell, to make your way through everyday things, it’s not enough to have access to information, not even for that information to be processed in your brain; it needs to then guide behaviour. That is where the role of the superior colliculus is absolutely crucial.
Many specialised areas of neuroscience are devoted to deciphering the brain, and they each adopt different study methods and tools to probe the brain. One such field, Cognitive Neuroscience, focuses on how the brain manipulates information and how mental representations arise from neural processes in the brain. To this end, cognitive scientists design models to explain neural mechanisms by which the brain produces observed behaviours (output).
In a recent paper, Sridharan Devarajan and colleagues have developed a behavioural model that explains results from four separate, important studies published by leading international groups. “All of these studies turned off the superior colliculus and showed a common pattern of changes in behaviour, a tendency to pay attention to irrelevant alternatives,” says Sridharan, currently a faculty member at Centre for Neuroscience, Indian Institute of Science (IISc), Bangalore.
To understand these deficits better, Sridharan et al. developed a model based on ‘signal detection theory’ originally developed for military applications to detect enemy aircraft with radar; to explain behaviour in attention tasks. Specifically, they built the model to distinguish behavioural changes from visual processing deficits versus those arising from deficits with making decisions. They then applied this model to analyse behavioural data from animals whose superior colliculus was reversibly turned off, as they performed attention tasks.
Curiously, it was not the processing of incoming visual information that changed in animals where the superior colliculus was inactivated. Rather, the test animals were unable to synthesise changes in incoming sensory information to make appropriate changes to their behaviour. For the studies, animals were trained to pay attention to stimuli from a specific part of the screen, based on visual cues (Figure). But when the superior colliculus was turned off, it produced a very specific kind of disruption — false alarms for irrelevant alternatives — that specifically increased.
Why that’s the case is precisely what Sridharan et al’s model explains. “The model shows that, when the colliculus is turned off, the sensory information processing or sensitivity for the cued stimuli was relatively intact. But the animals were simply unable to use incoming sensory information from the cued locations to make behavioural decisions. Rather, their decisions were based on information coming from other, irrelevant locations,” explains Sridharan.
The classic view of brain functioning is more of a “top-down” hierarchy: evolutionarily newer forebrain areas were thought of as being involved in voluntary attention choices, whereas evolutionarily older midbrain areas in the automatic ones. And yet, the results of this modeling work on the midbrain superior colliculus suggest that forebrain and midbrain may have parallel contributions to voluntary attention choices as well.
“To have a model that’s good enough to explain behaviour from brain activity , is the ‘holy grail’ of cognitive science. What we were successfully able to do, through this model, is to develop an overarching framework that integrates about 10 years worth of work in the field,” says Sridharan.
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