Sunday, 25 September 2016
How Different Parts of the Brain Co-operate
Perhaps one of the hardest things to understand about the brain is the way that it is organized into networks. In this post, I will discuss a 2015 study, on the brain structures involved in delayed gratification, that makes this complex subject a bit easier to grasp.
But first, let’s review the basics of what makes this subject so complex, using the amygdala as an example. Starting in the 1990s, research done on the amygdala in Joseph LeDoux’s laboratory clearly demonstrated this structure’s involvement in an animal’s fear response to a perceived threat. As a result, the amygdala was somewhat hastily labelled the brain’s “alarm system”. But subsequent research showed that the amygdala is also highly active in other, very different situations—such as when someone is very hungry, or sees a loved one suffering. The idea thus developed that the activity of the amygdala produces not simply fear, but rather a form of intense concern with any of a variety of situations that are vital to the organism. Such concern may induce someone to flee a threat, but may also induce them to eat when they are hungry, or to provide care to a loved one who needs it. (Other researchers, such as Luiz Pessoa, have pointed to an even broader range of possible roles for the amygdala.)
Against this background, it is interesting to consider a study published in July 2015 by Andrew R. Abela and his colleagues, entitled “Hippocampal interplay with nucleus accumbens is critical for decisions about time”. Abela is talking about the interplay between two brain structures that have usually been regarded as having very different overall functions: in the case of the hippocampus, memory and planning (you retrieve memories to plan your future actions more effectively), and in the case of the nucleus accumbens, pleasure.
In Abela’s study, the researchers found that when they interrupted the connections between these two structures in rats, they became incapable of waiting a little bit longer to receive a larger reward than they would if they did not wait. The ability to wait for a larger reward, known as delayed gratification, is a phenomenon well known to psychologists, who have observed it in humans as well as in rats. This points to a fairly ancient evolutionary origin involving these two parts of the brain, and possibly other parts as well, especially in human brains, which are substantially more complex. (For full details on this study, follow the two links below.)
What makes this study so interesting is that it shows how an elaborate behaviour that enables an animal to delay gratification requires a dialogue between two brain structures, each of which is involved in a particular aspect of that behaviour: the nucleus accumbens in the experience of pleasure, the hippocampus in planning a delay before enjoying that experience. It is therefore the connections joining these two distinct brain structures that enable the emergence of the behaviour, further demonstrating the importance of a networked conception of the brain. This particular experiment examined the brains of rats, but showed that even in these animals, the brain is already employing a sort of neuronal recycling to accomplish a new, more complex task.
This concept of neuronal recycling also helps us to better understand how various parts of the brain that evolved in response to certain evolutionary pressures long, long ago can be reused now for other purposes, in particular in the human brain, which is now evolving in an entirely different environment. One good example of how productive this approach can be is the development of the hypothesis of a common evolutionary origin for spatial orientation and declarative memory in humans (which again, as it happens, involves the hippocampus).
Wednesday, 7 September 2016
Motor cortex is required for learning but not for executing a motor skill
The motor cortex was long thought to be the part of the brain that controlled the body’s voluntary movements. Given the plasticity of the cortex as a whole, it seemed reasonable to believe that decisive changes in the connectivity of the neurons in the motor cortex might well be associated with motor learning. Although this may indeed be the case, a study published by Risa Kawai and colleagues in the journal Neuron in May 2015 forces us to reconsider the primacy of the motor cortex in learned sequences of movements, at least in rats. (more…)
Monday, 22 August 2016
A good general book on neuroscience
Whenever I give a presentation about the human brain, someone almost always comes up afterward and asks me whether I could recommend a good general book on neuroscience. In fact, there are several such books, but the one that I want to recommend here today offers a special advantage: you can buy a printed copy, but you can also access the entire book on the Internet for free!
The book that I’m talking about is Neuroscience, 2nd edition, edited by Dale Purves et al. and published by Sinauer Associates in 2001. It covers wide areas of modern neuroscience and is chock-full of very informative figures and tables. (more…)
Monday, 8 August 2016
A Nanometric 3D Representation of a Mouse Cortex Cortex
The analogy between a real forest and a “forest of neurons” has been drawn many times, but the images produced most recently by the team of Jeff Lichtman and Narayanan Kasthuri (see the first two links below) make it clear yet again that the complexity of the brain’s connections far surpasses that of the densest forest.
As Lichtman has long said, by going down to the scale of the electron microscope and then reconstructing the slightest contacts between axons, dendrites, and neighbouring glial cells slice by slice, we can detect patterns that escape us at the more “macro” scales previously used to model neuronal connectivity. (more…)
Tuesday, 26 July 2016
Greening Cities Are Good for Your Health and Your Spirits
I live on a street east of Lafontaine Park, in Montreal, and I have always thought that if I weren’t “forced” to cross this large park four to eight times per day either walking or on my bike, I would never be able to stand the city and all of its drawbacks (the main reason for which is that there are just too many cars). A study published recently in the open-access journal Scientific Reports seems to confirm this subjective feeling of mine. (more…)