How do we integrate information?

Left or right? Apple or orange? Selma or Birdman? One way to make these decisions is precisely what intuition tell us it should be: we weigh up the pros and cons of each choice. Then, when we have sufficient evidence for one over the other then we go ahead and make that choice.

How this is represented in the brain is quite straightforward: the firing of neurons would go up or down as evidence for one choice or another becomes clear and, when the firing had reached some fixed threshold, when the neurons had fired enough, a decision would be made.

The difficulty has been in figuring out precisely where the information is being encoded; in determining which neurons were increasing their activity in line with the evidence. In fact, multiple regions seem to be participating in the process.

So let us say that you are a little rodent who hears sound from the left and the right; little click click clicks. And you need to decide which side the most clicks are coming from. Every click on one side gives you a smidgen of evidence that that side will have the most, while a click on the other side will make it less likely. You don’t know when the clicks will end – so you have to stay ready.

Now there are two interesting areas of the brain that we can look at: the frontal orienting fields (FOF) that probably guide how you will orient your little snout (to the left? to the right?), and the posterior parietal cortex (PPC), which integrates diverse information from throughout the brain. Here is what the activity of these neurons look like if you plot how fast the neurons are firing, separated out by ‘accumulated value’ (how much evidence you have for one side or another;  I will refer to this as left or right but is actually more like ipsilateral or contralateral):

PPC vs FOF

It looks like PPC, the cortical integrator, fires progressively faster the more evidence the animal has to go left, and progressively slower the more evidence it has to go right. In other words, it is exactly the evidence accumulator we had been hoping for. The orienting region (FOF) has a different pattern, though. Its firing is separated into two clusters: low if there is a lot of evidence to go left, and high if there is a lot of evidence to go right. In other words, it is prepared to make a decision any second, like a spring ready to be released.

It is interesting that this is implemented by sharpening how tightly tuned neurons in each region are for the decision, going from something like a linear response to something more like a step function:

value vs firing rate

This is consistent with an idea from Anne Churchland’s lab that the PPC is integrating information from diverse sources to provide evidence for many different decisions. This information can then be easily ‘read out’ by drawing a straight line to separate the left from the right, a task that is trivial for a nervous system to accomplish in one step – say, from PPC to FOF.

And yet – there are mysteries. You could test the idea that FOF provides the information for left or right by removing it or just silencing it. If it was standing ready to make a decision, you would only care about the most recent neural activity. Indeed, ablating the region or just silencing it for a couple hundred milliseconds has the same effect of biasing the decision to the left or right. But it is only a bias – the information for the decision is still in the system somewhere!

Even more baffling is that the FOF begins to respond about 100 milliseconds after hearing a click – but PPC doesn’t start responding until 200 millseconds after a click. So how is FOF getting the information? Is FOF actually sending the information to PPC?

Decisions are hard. It is not a “step 1. hear information, step 2. add up pro/cons, step 3. make decision” kind of process. A linear 1, 2, 3 would be too simple for the real world. There are many different areas of the brain getting information, processing it and adding their own unique twist, sending their evidence to other areas, and processing it again. Again: even simple decisions are hard.

References

Hanks, T., Kopec, C., Brunton, B., Duan, C., Erlich, J., & Brody, C. (2015). Distinct relationships of parietal and prefrontal cortices to evidence accumulation Nature DOI: 10.1038/nature14066

Brunton, B., Botvinick, M., & Brody, C. (2013). Rats and Humans Can Optimally Accumulate Evidence for Decision-Making Science, 340 (6128), 95-98 DOI: 10.1126/science.1233912

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4 thoughts on “How do we integrate information?

  1. There is a lot about the human brain that we have yet to learn. One thing that is clear is that the brain works together as a whole. Even though it can be divided up into different regions, we need all of those parts to be able to function properly. Each part of the brain is important for performing specific functions, so when it receives information it must be processed in all of the different areas of the brain. The frontal lobe is important in controlling fine movement, the parietal lobe specializes in body senses, the temporal lobe is the main area for hearing and vision, and the occipital lobe and specialized in vision. With that being said, I agree that making a decision isn’t just a 1 step process. It has to travel to every area of the brain, so making just one decision can be very complex to the brain.

  2. The exact process of information passing through the brain is a general pattern with everyone. Every part of every brain is used to make a decision in someway or another. It is not the order the brain processes everything but rather the information the brain is processing. One part of the brain cannot be in control over certain information. It just rather depends on what the information is on which part of the brain the information visits first,

  3. When it comes to thinking and making decisions, whether it may be simple or hard, we often don’t think about the difficult process that the brain goes through in order to fulfill such task. Every specific part of the brain has its own distinct function. The prefrontal cortex contributes to many functions such as attention, that is enhancing the response of other brain areas to the most relevant information and decreasing the response to distractions. Another is working memory, which is the ability to remember, such us remembering the simple things like where you placed your keys. The prefrontal cortex is also important for making decisions and planning movements. When you decide whether to do something, you consider the difficulty of the action, the probabilities of success and failure, and how valuable the possible reward would be to you at that moment. Cells in the prefrontal cortex responds to all complex factors, and when there is an unexpected outcome, the cells are aroused and update their response-outcome predictions. When people with prefrontal cortical damage often make decisions that seem impulsive, the reason for that is because they failed to weigh all the likely pros and cons.
    Even though we have studied the brain for many years now, there still many mysteries about it, and the more and more we try to analyze it we learn new facts and information every day.

  4. Pingback: Permission to stare out the window - Next Action Associates

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