Week of March 22, 2000
"I reacted on instinct." Dr. Fred Goodwin begins the program by posing the question: "How often do we hear that (in our lives)?"
The word instinct has been part of our everyday language for generations, but how well do we understand it? Dictionaries define "instinct" as an inborn tendency to behave in a way characteristic of a species. But when we act on instinct, is it always involuntary? In other words, are instinctual behaviors totally hard-wired … or do we have some responsibility for our instinctual acts? Can instincts be altered by experience? Can they be taught?
Modern behavioral neuroscience is refining our understanding of this complex and still mysterious area. We each have a range of behavioral responses to a given situation and we are now coming to understand the ways in which genetics and biology determine the boundaries of that range … rather than determining any specific behavior. As we learn more about those biological boundaries, some fascinating questions are emerging: Has the whole notion of in-born basic urges been replaced as we gain a deeper understanding of the brain, behavior and gene science? What complex set of neuro-biological mechanisms helps a pigeon find its way home, a gazelle escape a lion, or a mother care for her newborn child?To explore the primitive world of instincts, we are joined by Dr. Marc Hauser. Dr. Hauser is a professor of psychology at Harvard University where he heads an animal research program. His new book, 
"Wild Minds," is an entertaining and thoughtful look at animal psychology. It also looks at what we can learn about humans from our knowledge of the animal mind. 
Dr. Hauser defines instincts by telling us that instincts are not "something that that is fixed - some basic mechanism in the brain that leads to one kind of output" - but instincts constrain how experience is taken into the system - and how it is used by the system.
Dr. Hauser says there are three instinctual learning patterns that cut across all animals: a basic capacity to recognize objects, count how many objects there are and navigate through space.
With regard to special navigation, Dr. Hauser sites the Tunisian Desert Ant which zig-zags away from its home when looking for food but will make a straight line back to their home after eating. Dr. Hauser explains that this is a process called dead reckoning, which ancient Sea Farers used when they didn't have maps. Sea Farers would watch the stars and by calculating the speed at which they were moving and the distance traveled from one point to another, they could calculate the fastest way to get home. According to Dr. Hauser, all animals use dead reckoning to find their way home.
Dr. Hauser also says that a common assumption is that if a trait shows up early in life, it is evidence that the trait is instinctual, whereas if a trait develops later in life it is assumed that the trait is learned. He refutes that notion citing adolescent sexual development as an example of a trait that develops later in life that is innate and due to genetic factors.
Dr. Hauser continues on to say that the mating instinct is driven by desire to pick symmetrical mates, which should have the best genetic make-up, as opposed to asymmetrical mates, which have genetic discrepancies. This has been documented in insects, birds, mammals, and now humans - where people are shown pictures of asymmetrical and symmetrical faces and asked "how attractive" they find the person. Generally, the more symmetrical the person, the more attractive they are considered by others.
As an example of an instinct: Dr. Hauser sites a study from the 1940's which indicates that altruism is an innate instinct. In the experiment, rhesus monkeys were given a lever which dispensed food but at the same time as dispensing food, it gave the monkey in the next cage an electrical shock. The monkeys with access to the 'shocking' food levers would not pull the lever, foregoing food for many days, rather than give the monkey next door a shock. However, the monkey was less likely to refrain from pulling the lever if another species of animal (a rabbit for example) was being shocked. Scientists deduced that the monkeys were more altruistic toward animals of their own species rather than animals of different species. (Dr. Hauser points out that because of the cruelty of the experiment, it would not be conducted today.)
The Infinite Mind continues with a story by reporter Guy Hand about Professor Reginald Golledge, a geographer at The University of California - Santa Barbara. Professor Golledge specializes in behavioral geography, the study of how humans physically find their way through the world.
His career has drawn him into super markets to study ways people move through stores and into residential neighborhoods to study the movement patterns of the people who live there. Professor Golledge has tried to understand what compels us, for instance, to take a left turn rather than a right, what mental maps we draw to get from point A to point B, and what complex skills we need to simply find our way home for dinner.
Most of us take this ability to navigate for granted. Yet 16 years ago, a personal tragedy reminded Professor Golledge just how important, how precious that ability really is - he suddenly lost his sight.
As a result of his blindness Golledge's research took a new turn. He explains, "We started talking about whether the cognitive maps ... were the same for people without sight as people with sight. With sight so important to spatial activities people without sight had to be sort of disenfranchised and extremely limited in what they could do. The prevailing sentiment was that yes, that without sight they would be terribly limited. We started this research to find out if this was true."
Professor Golledge's research taught him that blind travelers can learn to get around nearly as well as everyone else, that there are indeed important mechanisms other than sight that help people negotiate the physical world. He points to a recent study involving the well-known navigational skills of London cabbies, who find their way to the most obscure destinations without the aid of street maps. The driver's brains have actually grown larger in the zone associated with navigation-the rear hippocampus. It seems that this adaptation helps them store detailed mental maps of the city securely within their own skulls.
Golledge continues by adding that the development of maps has provided us with so much information that most people don't have to tax themselves anymore to remember where everything is. "It appears that much of our navigational instinct is there but we don't use it," says Golledge. "We've substituted other things. One of the most important things is the fact that the world is now full of signs. It would be difficult to move around in our world if we removed the signs. Not just street signs, but the numbers on houses, the names of buildings. It's almost unthinkable. . ." Dr. Golledge hopes that his work will help those without sight to learn to navigate the world better.
Next, at first glance, nothing seems more instinctive than a mother's love and caring for her child. Dr. Mark George, a psychiatrist and researcher at the Medical University of South Carolina, is doing some groundbreaking work using brain scans of new mothers. Dr. George may have actually located the place in the brain where the maternal instinct resides.
First, Dr. George talks about an imaging study that examined new mother's reactions to a baby's cry. New mothers were placed inside a MRI scanner and were exposed to the sound of a baby crying, as well as the sound of a baby crying for which the audio had been scrambled (so it wasn't obvious that the sound was of a baby crying). It was found that activity occurred in a certain areas of the brain (the thalamus) in the brain cortex when the babies cried.
It has been hypothesized that these electrical reactions were a result of the mother's response to her baby crying. They are currently researching whether mothers respond differently to their own baby's crying and someone else's baby's cries.
Dr. George said they are also looking at the relationship between this circuit in the brain and bonding between people in general. He said it may also be at the core of separation anxiety disorders, since the basis of separation anxiety is the fear of separation from one's parents.
Dr. George said these instincts are in the oldest part of the brain, meaning it is part of the oldest mammalian mother's instinct for nursing, care for young and play.
Finally, we hear from Dr. Charles Jennings, editor of the scientific journal Nature Neuroscience. Dr. Jennings, whose own work is in the area of developmental and molecular neurobiology, stops by once a month to share some of the latest news in neuroscience.
Dr. Jennings first talks about the biological basis for the reason that men may often be unwilling to ask for directions.
In a recent study, the ability of men and woman to navigate unfamiliar environments was tested, as men and woman found their way through mazes on computer screen. Men took an average of 140 seconds to navigate the maze, while woman took 190 seconds (40% longer for women). The study also found that during this task, the hippocampus is more active in men, and the right prefrontal cortex is more active in woman - signaling very different brain functioning in men and women.
Next: stress and memory. There is a new Swiss study that has identified the cortical as the hormone secreted from adrenal glands under stress. The Swiss researchers have examined the effect of cortizol on human memory. They found that stress induced cortizol release does not effect the learning of information, but it does effect the ability to recall information from long term memory (retrieval of information). As a result, when you are under stress you can learn, but you may have difficulty in recalling information. In situations such as standardized testing and court testimony the high levels of stress (and cortizol) can impair the memory and recall.
Finally, Dr. Jennings discusses a new study that identified the bitter taste receptors on our tongue. Dr. Jennings points out that we know a lot about other senses (sight, hearing) but little about taste and that this discovery of our bitter taste receptors is one of the first steps in expanding our knowledge on taste. He continues on to explain that bitter tastes can often reflect poisonous foods whereas sweet tastes can reflect nourishing foods.
