March 22, 2005
Stimulaton Of Primate Brains Show Many Complex Behaviors Are Innate

The set of behaviors that are thought to be innate rather than learned continues to expand.

Vanderbilt researchers, writing this week in the Proceedings of the National Academy of Sciences Online Early Edition, report that they can elicit these complex behaviors by stimulating specific areas in the brain of a small nocturnal primate called the Galago or bush baby (Otolemur garnetti). Their results provide significant new support for the proposition that all primate brains, including our own, contain such a repertoire of innate complex behaviors.

"We have now seen this feature in the brain of an Old World monkey and New World prosimian. The fact that it appears in the brains of two such divergent primates suggests that this form of organization evolved very early in the development of primates. That, in turn, suggests that it is characteristic of all primate brains, including the human brain," says Jon Kaas, the head of the research group, Distinguished Professor of Psychology at Vanderbilt University and investigator at the Vanderbilt Kennedy Center for Research on Human Development.

"These results explain why certain behaviors such as defensive and aggressive movements, smiling and grasping food are so similar around the world. It is because the instructions for these movements are built-in and not learned," he adds.

Over the last 20 years, neuroscientists have identified an area called the primary motor cortex, which, when stimulated, triggers simple muscle movements. The fact that they were able to produce only motions by single muscles and other simple movements reinforced the idea that only simple movements were hard-wired into primate brain circuitry.

Then, last year Michael Graziano at Princeton University pointed out that previous stimulation experiments in the motor cortex the area that controls bodily motions had been done using very short electrical pulses that last less than a half-second. He further suggested that longer pulses might stimulate more complicated motions. Working with alert macaques, he and his colleagues found that applying such long-duration signals did in fact elicit several of these complex behaviors, much as they had predicted.

Kaas and his colleagues, research assistant professor Iwona Stepniewska and doctoral student Pei-Chun Fang, decided to follow the Princeton researchers' lead and try long-duration stimuli in the simpler brain of the Galago. When they did, they also found that this type of stimuli triggered complex behaviors. In fact, they were able to stimulate a larger number of complex movements than the Princeton group had reported, including aggressive facial patterns, defensive forelimb movements, and hand-to-mouth and reaching-and-grasping movements.

The Princeton researchers stimulated areas in the motor cortex. The Vanderbilt researchers found that they could also elicit these behaviors by stimulating a nearby area of the brain called the posterior parietal cortex. This area is heavily interconnected with the motor cortex and had previously been associated with transforming data from the eyes and other senses into a spatial map of the surrounding environment. The new findings reveal that this brain area also plays an important role in complex, innate behaviors.

If a behavior is innate then some day it will become genetically reprogrammable. The reprogramming will be easier to do in embryos than in fully developed humans. A lot of the genetic coding that controls behavior does so by controlling development. Just what choices people will make once they can control the genetic coding of their offspring is one of the most important questions of the 21st century.

Even before offspring genetic engineering becomes possible the discoveries of more genetic causes of human behavior is going to lead to massive rethinks in how we approach child rearing, teaching, criminal justice, decisions about reproduction, and many other aspects of human life. Should a person who is genetically prone to violence be seen as morally responsible for his actions? Is that a reason not to imprison him? Or will people put their own safety first (which is what I'm guessing) and demand that if a violent guy can't help himself should he be jailed for a longer period of time? Also, if he can be identified as violent while still in childhood should be he isolated before he first murders or rapes?

Share |      Randall Parker, 2005 March 22 01:20 PM  Brain Innate

toot said at March 22, 2005 5:01 PM:

The issue of blameworthiness gets kicked around a lot in philosophy courses. There are many who take the view that if there is some cause other than the presumed will of the perpetrator of a crime, then the "perp" is not to be blamed. I don't buy this at all. Even if everything we do is innate, those who commit the crime should do the time. Think of it in the less emotional terms of manufactured products. If a car has bad brakes, we want it taken off the road; it doesn't matter whether the brakes are bad because of improper manufacture (i.e., innately) or they are bad because of excessive wear (i.e., experientially). Besides, if our actions are innate or otherwise predestined, who would be to blame for exacting punishment? The punisher's actions would be equally predestined.

Antinomy said at March 22, 2005 8:52 PM:

I'm just an interested layman, so there is a good chance that I don't know what I'm talking about, but from the things I've read over the years, I suspect that there are lots of people who might be "genetically prone to violence" who nevertheless do not commit violent crimes. If that is the case, preemptive action will be unjust, and I hope that most Americans will agree with me about that. As an analogy, there are many people who are genetically prone to alcoholism who nevertheless do not become alcoholics. All that is needed in that case is a personal conviction never to start drinking. Might not a strong sense of ethics, or even a healthy amount of pragmatism, stop those with violent tendencies from being violent?

SteveSC said at March 23, 2005 6:36 AM:

Just because stimulating a brain region creates a complex movement does not mean it is innate. Brain researchers have know for a long time that by moving away from the primary motor cortex you can stimulate more complex movements, complex sensations, or even memories. But the farther you are away from 'hard-wired' areas like the spinal cord and primary motor cortex, the more the location of the stimulation point becomes individualized. In other words, the size and location of the area which can be stimulated to cause me to raise two fingers in a 'V' are in all likelihood different from that area in your brain. Not only that, there is good evidence that these areas change with new experiences. A study in rats showed that the area of the olfactory (sense of smell) region that responded to a certain smell changed in shape when the rat was trained to recognize a different smell. And areas in the human brain that respond to certain stimuli, or cause certain movements, change after an amputation or spinal cord injury. The fine organization of the 'association' areas that are related to complex movements and sensations are almost certainly influenced more by the environment than by genes.

Second, there are already a lot of ways to predict when someone is going to be violent. Psychologists can look at a profile of a sex offender and predict when the risk of his killing a victim is increasing. But our current system doesn't tolerate 'punishing' someone because of increased risk. That is why we have events like the poor Florida girl's murder by a proven sex offender happen. We don't need genetics to reduce the incidence of violence, 'just' a change in the legal system.

Dave Schuler said at March 23, 2005 8:14 AM:

I'm also skeptical about your idea of re-programming behaviors at the genetic level (at least for the foreseeable future). You could re-program your VCR (by changing its chips) but that wouldn't make it into a BMW roadster.

Eli Budischak said at March 23, 2005 9:31 AM:

One point. There are very few true reflexes in humans because of our capacity for thought. Thought enables us to alter our behavior in accordance with our surroundings. As a result, we have the capacity to stimulate or inhibit almost all programmed behavior on some level. For example, even though breathing is a programmed behavior, you can chose not to breath, at least to some extent (try it now). Your frontal lobe can inhibit that programmed behavior, which is almost un-arguably programmed into our genetic code. So saying all our behavior is based on genetics would be foolish. Your environment, IE someone telling you to stop breathing, can alter your behavior. While most areas of the brain are specialized for certain functions, all areas of the brain can be influenced by other areas. Learned behavior may not be written into your genetic code, but it is based just as much on cellular brain structure as genetically derived behaviors. For example, a professional piano player is good at playing the piano because they have programmed their brains for automatic sequences of muscle movements. If you were to stimulate a specific section of their motor cortex, they would likely appear as if they were trying to play the piano. So yes, while it is clear that some behaviors are learned and others are genetic, they both result in neuron structures that program for a behavior. Because of this, it would be difficult to isolate those behaviors that are learned from the ones that are written into the genetic code. This problem is further aggravated by the fact that brain development requires a combination of genetic and environmental factors. For example, sight cannot develop without an environment that delivers visual stimulus. With the example used earlier, you cannot become an alcoholic if your environment does not contain alcohol, even though you are genetically coded for such behavior. The brain is a unified whole. The brain retains much plasticity throughout life (although more when you are younger), so brain structures are constantly changing depending upon environmental factors. It seems presumptuous to state that a behavior is genetic because monkeys respond to electrical stimulus with complex sequences of muscle movements. What is to say that complex behaviors (IE the brain structures that caused them) were not the result of environmental stimulus. Monkeys could all have the same motor response program because they all have similar environments. It would require some sort of control (IE one monkey raised in a sterile environment), but then again, most genetically derived behaviors have an environmental component, so raising the monkey in the sterile environment could prevent manifestation of the genetically coded behavior. Basically, most all behavior has both a genetic and environmental component which are inseparable. Studies like this clearly help us better understand the structures of the brain, but we should avoid jumping to conclusions about genetics as they relate to brain structure, and how this relates to society as a whole.
Peace, Eli

Randall Parker said at March 23, 2005 9:53 AM:


Yes, there will be people who only have very strong tendencies to violence that come short of being 100% certain to physically assault others or to rape or whatever they have a tendency to do. Suppose we can analyze someone's brain and genes and predict that some guy has a 50% chance of attempting murder. Suppose we can predict another guy has a 90% chance of attempting murder. Do we treat these people just like everyone else because their probability of murdering is less than 100%?

Or suppose we know that there are specific environments or influences that will cause a particular category of people to try to kill. Suppose those situations that will set a person off are out there in normal society. Suppose it is chance whether a given person will hit one of those situations. Do we just let all the people like that go roaming around with no restrictions on their movements or activities?

But there will be people whose genetic and developmental influences will make them absolutely violent. What about them?


Yes, exactly. If it isn't the fault of the killer or rapist then it isn't my fault when my environment makes me insist that the criminal goes to jail for the rest of their life. I can't help it. My environment made me do it.

Randall Parker said at March 23, 2005 10:46 AM:


You can hold your breath. But for how long? Eventually your urge to breathe will override your conscious attempts to stop breathing.

Similarly, the recidivism rate among pedophiles is extremely high. The threat of jail is not enough to deter them.

We differ in the extent to which we can control ourselves through conscious choices of the forebrain. Some people have much weaker conscious control in general and others have weak conscious control on particular subjects. Also, we differ in the extent of our control at different stages of life. Sex drive rises and then falls for example.

I do not think the task of identifying genetic influences or controls on behavior is impossible by any means. First off, when DNA sequencing becomes cheap we will be able to do massive comparisons of people for genotypes and behavior. Second, our tools for watching the brain will become ever more sophisticated and powerful.

toot said at March 24, 2005 8:09 AM:

I agree that it seems wrong to take preemptive measures against someone on the basis of genetic markers that predict violence. But that is based on the current state of understanding of how the mind works. If it were to be found that such predictive measures held up in a large fraction of cases, such as the 90% and 50% levels tossed out in some speculation above, it would be difficult to ignore and take no action. At this point, I would give each individual the presumption that his nurture can overcome a violent nature, and would not take any preemptive action. However, at the same time, I think it would be the responsibility of society to provide special nurture (counseling) to those showing a genetic marker that indicates a high likelihood of bad action. I am not familiar with the statistics of recidivism among pedophiles, although I am aware of some of the reported instances. Of course, the blank slaters will have an explanation for such behavior that does not involve innateness, and I guess I am succumbing to the blank slaters argument here by allowing that counseling might serve to overcome a bad innate tendency (though the hardcore blank slater would argue that there is no innate tendency; everything comes from socialization).

This discussion is bordering on a lot of hot button issues that have been in the news lately, but I won't lead the way in going there. Let's keep the discussion friendly.

RichardSharpe said at August 4, 2005 2:10 PM:

Hmmm, if as seems likely, and some have written papers about, Sociopathic behavior is maintained in the population because of balancing selection, then measures such as Randall suggests will drive such genotypes to develop counter measures.

To some extent the range of behaviors that some of us think are "unwelcome" might simply be conditionally expressed phenotypes that are coded for in our own genes, just not expressed because of more favorable circumstances in our cases ... it simply might not be in our genetic interests to try to eliminate such genes (by penalizing such phenotypes). There but for the grace of god ...

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