Intelligence and the neurosciences: First installment.
Why these two blogs?
As of early 2012 enthusiasm for the neurosciences runs almost as high as enthusiasm for Facebook. This afternoon (May 20, 2012) I googled ‘”neuroscience intelligence“and retrieved 9,820,000 possible references. To be fair, many of these references used “intelligence” in the sense of “cognitive capability” rather than in the narrow sense of “individual differences in cognitive ability,” but nevertheless I think the point is clear. Recent advances in medical technology (especially imaging) have made possible major advances in the study of brain-behavior relations While many of the findings could have been anticipated by earlier research, many other findings are truly novel.
My contention is that these advances have major implications for our study of the biological basis of intelligence, including genetics, but virtually no implications for our understanding of the social conditions that produce intelligence or of the way that intelligence is used in modern society. I will develop this argument in two blogs, of which this is the first. In this blog I describe some of the findings that are relevant to the neuroscience of intelligence, and consider how they should be understood. In the next blog I will describe major issues in the study of intelligence that probably will not be influenced by present or foreseeable advances in the neurosciences.
Ultimately, everything is neuroscience. If you memorize your friend’s telephone number, that act produces a change in your brain. If you decide to root for the Seattle Mariner’s baseball team or to study Stoic philosophy these activities will make physical changes in your brain (and baseball fans will not be surprised if those changes overlap). The statement that some “learning experience” CHANGED PEOPLE’S BRAINS should be reacted to by saying “Well, Duh.” What modern neuroscience has done is let us measure some of the changes that we knew had to be there. In addition, the neurosciences have allowed us to say something about the physical aspects of the brain that facilitate such changes.
While brain mechanisms are far different from computer mechanisms, in the abstract they both fulfill just two functions. One is to interpret the current situation in order to select a response, the other is to store information. The information comes in two forms; information about the world and our experiences in it and programmatic information about how to recognize and solve different types of problems. The interpreting and response selection functions are strongly influenced by the “multitasking” aspect of the world. Talking while walking is actually a pretty complex task; talking while driving a car is also complex but in a different way.
Cognitive psychology has shown that intelligent behavior is closely related to the “working memory” complex, which is a shorthand term for the sort of memory that we need to relate to the here and now problems we face. An important part of working memory is the ability to keep attention focused on those aspects of a situation that are relevant to the current problem. Neuroscience research has identified several structures that support working memory functions. The most important are the dorso-lateral prefrontal cortex (on the upper outside of the frontal lobes), and a link to a structure called the cingulate cortex, which lies roughly toward the upper center of the brain. The cingulate cortex is, in turn, closely linked to subcortical structures associated with emotional responses. In addition, a midbrain structure called the hippocampus (because, with imagination, it looks a little bit like a sea-horse) is very important in establishing memories and also in establishing memories for spaces. Finally, language and long term memory (especially for verbally defined stimuli) depend on structures in posterior frontal and temporal regions on the side of your brain. In most people the language functions are primarily on the left side.
These statements refer to structures that all normal people have. Abnormal behavior can result if one of the structures is injured, and different types of structural damage are associated with different types of abnormal behavior. For instance, impulsive behavior and inabilities to control attention are associated with damage to the prefrontal cortex. (And are you driven mad by impulsive, helter-skelter teen agers? That’s not surprising, nerve growth in the prefrontal cortex is often not completed until the late teen years.) Damage to the hippocampus and related regions can impair the formation of new memories. Two conditions that can lead to this are alcoholism and, alas, ageing…a condition that is associated with fading ability to remember recent events but not, except in the case of the sorts of severe deterioration associated with Alzheimer’s disease, an inability to retrieve established memories.
Individual differences in the structure of the brain do occur. One finding, which I have to admit surprised me, is that there is a modest, but significant (r ~ .3) relation between overall brain size and scores on intelligence tests…bright people do have larger brains! For those of you have read Steven J. Gould’s Mismeasure of Man, where Gould debunked the idea, all I can say is that Gould was wrong! Several independently replicated imaging studies have shown the size-score relation. The extent to which this is a genetically determined property is not known. Genetics probably do contribute something, but there is also work showing that “exercised” brain structures can be enlarged. One particularly catchy finding is that the hippocampus…the area of the brain that (among other things) keeps track of spatial locations is enlarged in London taxicab drivers!
Another important finding is that when people solve problems the more adept problem solvers, i.e. the more intelligent people, show less metabolic activity in relevant brain structures than do people with lower test scores. This suggests that intelligence is associated with more efficient neural computing rather than larger neural structures. Finally, the white matter (myelin) wrapped around the axons of some neurons deteriorates with age, suggesting that one of the characteristics of cognitive ageing is a loss in the efficiency of the neural tracts between different regions of the brain.
All these findings, and more, provide important information about the biological basis of intelligence. It is reasonable to expect that within the next twenty to fifty years neuroscientific findings will enable us to trace the genetic basis of intelligence, diagnose abnormalities in cognition, such as autism, very early so that they may be treated, and quite possibly provide a way of tracing the influence of pharmacological, disease, and nutritional effects upon the brain. These discoveries will represent major advances both in our understanding of what it is to be human and in our ability to deal with mental disorders. However I do not think that all studies of intelligence will be reduced to studies of neuroscience. The neurosciences will tells more and more about the structures and processes that the brain uses to process information in the abstract. However they will only tell us a little bit about how the content of that information influences our behavior.
Let me illustrate with an example. Just before I wrote this blog I read two newspaper articles. One was about how the US intelligence establishment had used computer virus programs to mount cyberattacks on opponents. The other article discussed the role of unregulated financing of US political campaigns. I had the thought that I had one friend with whom I would like to discuss the first article, and a second friend who would like to discuss the second article. My decisions about matching person to article were determined both by my knowledge of the articles and of my friends’ interests.
Intelligent people make decisions like this every day, choosing what message to direct to whom is an important part of communicating in society. In order to understand this process a social or cognitive psychologist has to deal with the implications of a person’s knowledge, both to understand discourse comprehension (reading the articles) and to understand the cognitive decisions required in social communication. As I said at the start, ultimately all thinking is in the brain. However offering a neural level explanation of things like discourse comprehension and social communication will often be as useful as using subatomic physics to explain how an automobile works.