Different Behaviors, Different Brains?


Individual Variation

domestic cats
bird song
human development
hermaphroditic fish
crayfish aggression


& Sexual Orientation

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Can we relate this thought process back to humans?

All of these examples of individual variation are interesting in and of themselves, right? We've seen that:

  • wild cats and domestic cats have specific structural and functional brain differences (and, of course, behavioral differences);
  • male and female songbird behave differently, due to gradual changes of brain structure;
  • the human brain develops such that behavior changes are associated with brain changes;
  • certain types of fish can change sex according to the social group around them;
  • and a change in an crayfish' social status has an effect on how the brain uses a neurochemical.

With that foundation, we can consider earlier questions. Now let's again look return to humans. We can begin to make further inferences about our brains and behavior using the knowledge we now have from previous examples.

For example, consider this: a few human individuals are in a park. Individual A is participating aggressively in a wrestling match with a competitor. Individual B is coddling an infant in its lap, fearing the potential for harm that Individual A is enduring. What could we say about these two individuals, without knowing anything about them other than our observations? Do the behavior differences that we observe indicate anything about the structure or function of their brain? Well, given what we have learned so far-- probably. But the differences might be quite small and we might not know where to look. What if I told you that the two individuals were of different gender . . . does that help us start asking questions about brain differences between individuals?

Here's another example: Patient A is has a fully functional ability to communicate. Patient B has no memory of past or understanding of the present. Patient A is able to construct full sentences and tell us what was for dinner yesterday. Patient B finds it difficult to identify himself. Can you tell me anything about similarities or differences of these patients' brains? Perhaps not exactly, but you at least can guess that SOMETHING about their brains is different. And what if I told you that Patient A is 30 years old and Patient B is 90 years old? Does that give us somewhere to start looking?

Do you see where I'm going with this? Even in humans there are definite behavior differences between individuals that may be correlated with differences in the brain. Let's start with some cases where the differences might be large or we may have a better idea of where to look:

Extreme Brain Changes and Behavior: Alzheimer's disease

Gender and Sexual Orientation