IndiaBioscience - Exploring Science from 2017

How do we actually “pay” attention?

2017-07-25T19:02:00+05:30

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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Embracing the debate

2017-04-21T12:28:00+05:30

A recent paper by scientists from the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Bangalore, has contributed to a hotly contested debate in evolutionary biology—about a phenomenon called niche construction (NC). The paper is due to be published in a special issue on evolution in Journal of Genetics this July.

NC is a process in which an organism modifies its environment in ways that increase its own or other species’ chance of survival. The term was first coined by John Odling-Smee in 1988. A very good example of NC would be “the change in the earth's atmosphere over 2.3 billion years ago by cyanobacteria or blue green algae, the first photosynthesisers. They had the ability to turn carbon dioxide and water into carbon-based tissues and energy, and release oxygen as a waste product in quantities that could not be absorbed. So, oxygen is now about 21 percent of our atmosphere”, says Joan E. Strassmann, Charles Rebstock Professor of Biology at Washington University.

The last decade has seen a lot being written, both for and against niche construction theory (NCT) and its significance in evolution. Evolutionary biologists, however, continue to remain divided over NCT’s role in explaining evolution. The proponents of NC argue that Darwin’s theory of evolution fails to “recognise the full importance of niche construction” and its implications on evolution. They therefore, propose a new evolutionary theory that takes full cognisance of NC and gives it equal “importance as natural selection.” The skeptics are not convinced, however. The disagreement has led to may public debates, such as here and here.

Now, for the first time a group of Indian scientists have made a vocal contribution to the debate on NC’s importance in the evolution. Their paper, which first appeared on BioRxiv, an online repository of pre-publication articles, received an active response on Twitter, including some from the stalwarts of the field. Based on the amount of discussion it has generated, Altimetric has rated it among the top five percent papers on its database

The authors of the paper have critiqued niche construction theory (NCT) on three counts. They say there is no doubt that NC as a phenomenon exists and is evolutionarily and ecologically significant. However to say that it has been neglected in Darwin’s standard evolutionary theory (SET) is incorrect. “Darwin wrote extensively about how earthworms alter their own living conditions and thereby affect their own selection pressures”, said Amitabh Joshi, one of the authors of the paper and professor at Evolutionary and Organismal Biology Unit, JNCASR. “We marshall a lot evidence and arguments (in the paper) to show that in any aspect of work done under the aegis of SET, from the time of Darwin onwards—the perspective that organisms can affect the environment and that can feedback on the evolutionary trajectory—is all pervasive”, he added.

The second objection, authors have is to a call for new evolutionary theory. Since SET's population genetics models can “accommodate NC and its evolutionary dynamics with minor adjustments, then what exactly is the basis of saying that you need a new theory,” wonders Joshi.

Their third objection is about treating NC at par with natural selection. “At most, it (NC) can constrain or facilitate some parts along which evolutionary change proceeds. It is not equivalent to natural selection itself, said TNC Vidya, another author on the paper and faculty fellow at Evolutionary and Organismal Biology unit, JNCASR. “Natural selection can have evolutionary consequences without NC but NC cannot have evolutionary consequences without natural selection”, she added.

Apart from raising objections to the theory of Niche construction, the authors have also raised questions about the way some of the proponents of NC have been pushing this work. “Kevin Laland, John Odlings and Marcus Feldman wrote a book on NC in 2003. From 2003 to 2016 they have published several papers per year on NC without actually saying much new that was not already said in the book. The single major point that has really been added, is an argument to claim that NC and the so called developmental bias are equally important as natural selection”, said Joshi. “We see this as an unfortunate, but perhaps inevitable, nascent post-truth tendency within science, they write in their paper.

Strassmann, who has written previously about NCs and its significance said, “what we have and use (Darwin’s SET) is simple and elegant. So I agree with the authors on this general point, but am more optimistic on theory and evolution overall. I still think the ideas supported by evidence prevail and that science is still enormous fun”.

She draws attention to a paper by John Welch, Department of Genetics, University of Cambridge; that provides some clarity on how to figure out whether a phenomenon has significant evolutionary consequences or not. To quote from the paper, "“red things’’ are common in many ecosystems, and are little discussed as a class in the biological literature. However, removing red things, doubling their number, or changing their colour would change the outcomes of evolution in many cases. In this sense, it is easy to show that ‘‘Red Things are an important and neglected factor in evolution’’. Similar arguments could be made for ‘‘gravity’’, ‘‘burrowing’’, ‘‘oxidative damage’’, ‘‘noses’’, ‘‘histone modification’’, etc."

Kevin Laland, Professor of Behavioural and Evolutionary Biology at the University of St Andrews, who is one of the most vocal proponents of NCT and whose work this paper has criticised, has expressed displeasure over the paper. He says NCT has “never made the claim that niche construction is neglected” and that NCTs strong claims are not based on its “formal theory”, rather its “conceptual framework inspires experimental and theoretical work.”

Laland and his colleagues have now submitted a rebuttal to the paper in the Journal of Genetics. The critique and its rebuttal are going to be published together. It looks like the debate is going to get even hotter. But, isn’t that a good thing? Isn’t a healthy debate is conducive to good science? How and whether this debate will change perceptions about NC’s significance in evolution remains to be seen.