Brain Imaging Does Not Prove Biological Causation, and, Being LGBT is, in General, More than Sexual Orientation

Despite the involvement of extremely complex brain-recording technology, the design of the 2018 experiment is very simple. Scientists collected a group of people who are gay and another group of people who are straight, positioned them in a brain scanner, and showed them pornography. While the subjects awkwardly looked at naked bodies, researchers collected images of their brain activity, and lo, discovered that some areas of the brain showed differences between groups.

 

However, one big issue is that straight people and gay people don’t differ just in sexuality. There are also, in general, differences in personalities and lifestyles. What if the brain differences seen in this study are really just differences in social-presentation? If being gay is (often) more than sexual preference, we can’t be confident that the neurological differences are strictly about sexuality.

 

This confound is not unique just to studies dealing with sexuality. The way we conduct brain-imaging today struggles to prove causation in a traditional scientific sense. Before scientists are willing to adopt the term “causation,” they want to see that the manipulation of some variable has an impact on another. In other words, changing X reliably changes Y. Sure, we can compare brain activity between groups; however, we can’t intervene in a way that truly mimics what we’re recording. 

 

The problem is two-fold. For one, commonly-used brain-recording technologies like EEG and fMRI don’t offer very precise resolution. Instead, they record from large swaths of brain tissue. With these technologies, we can evaluate whether a large population of cells are more of less active—but not what any individual cell is doing.

 

The second half of the problem lies with the difficulty with brain stimulation. Non-invasive stimulation technologies (like transcranial magnetic stimulation) can be done pretty easily, but they also lack precise resolution. In this case, even if our recording technologies provide un-ambiguous data, we could not intentionally produce that same activity pattern.

 

If we could reproducibly induce gay or straight preferences, we’d know with real confidence that we’ve discovered the biological basis of homosexuality. Tangentially, if we had the technical capacity to change a person’s sexual orientation, it would open up a pandora’s box of ethical dilemmas (should a parent have the right to convert a kid?). Fortunately, this horror scenario—or Mike Pence’s conversion-camp fantasy—is well beyond our technical capabilities.

 

A Bigger Problem; Neurosciences Persistent Fallacy

Perhaps, though, a thought experiment. Let’s say it’s a little bit in the future, and a son just announced to his father that he is, in fact, gay. The father decides that he needs some verification, and, therefore, takes his son to see the local scientist. The scientist explains that long ago, researchers identified the neural correlates to being gay, as described above, using the round-up and scan method. The scientist then tells the father that he can place the son in the scanner, and, after a short while, determine whether his brain has the characteristics that make his brain gay.

 

Neuroscientists have long hoped that a person’s mental state could be inferred based on the findings of a brain scan. What Russell Poldrack and many other neuroscientists have argued, however, is that this approach relies on questionable reasoning. If we understand a person’s psychology, the argument goes, we can also identify the underlying neurology. Just throw the person in a brain-scanner, and there’s your answer. However, going one step further—taking that newly discovered neurology—and inferring that same psychology in a different person is something of a logical leap. 

 

X → Y does not imply Y → X, because sometimes, maybe, Z → Y. Also, some X’s are Y’s does not imply that all X’s are Y’s.

 

It’s pretty simple. Scientists might be able to observe that gay people, on average, have one sort of brain. But not every gay person’s brain is going to appear gay. Furthermore, some non-gay people may have brains that appear gay, even if they are not gay. The differences that scientists observe in the brain are based on group averages; they almost never perfectly distinguish between two groups of people, and, in the case of the study linked here, they did not appear to. The concept is called “reverse inference”; it’s both neuroscience’s greatest ambition, and the origin of its most frustratingly breathless over-statements.

 

However, enlightened neuroscientists do note that reverse inference is not necessarily wrong, and, at times, it may be useful. Even if we can’t be 100% sure that a particular brain region underlies a particular trait, maybe we can be 95% sure. Oftentimes, correlations we find with brain imaging research are suggestive. Nevertheless, especially in situations where there is some variability in the neurobiology (which, is basically, every brain scan study), people need to be very cautious in making that final reverse inference.

 

To Politics

Neuroscience can’t tell us much about psychology without relying on current psychological measures. In order to conduct research, we have to have some operational definitions. In this case—if we want to identify the neural correlates of being gay—we have to rely on whether people say they’re gay. Self-report is a premise of the argument, which means that science is not well-prepared to transcend self-report. If a person states that he or she is gay, neuroscience is generally not in a position to elaborate.

 

As a scientist, I believe in the importance of science-advocacy, and I agree with the sentiment that much evil originates from humankind’s attempts to define and divide our species into various categories. I also believe that sexuality does not have to be a rigid unchanging quality defined at birth.

 

However, in this case, we seem to be placing solidarity-signalling over neutral scientific reasoning. Confidently asserting the existence of inevitably-gay-brains might make for the ultimate alliance with the LGBTQ community, but it may overstate the confidence of our science. We ally with the LGBTQ community certainly not because of political identity, no, but because it’s rational to do so, because it’s science to do so. 

 

But some political questions transcend objective reality. Whether climate change is happening is science, whether we should do something about it isn’t. Whether or not we believe that a society ought to embrace homosexuality, or a government ought to protect LGBTQ rights, is a moral, not scientific question. 

 

There is an answer to the question of whether homosexuality is fundamental to who a person is, or whether instead, it’s a dishonest corruption of a person’s true nature. The underlying scientific reality can inform our position on whether we support gay rights, but it’s only part of the equation.

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About the Author: Andrew Neff lectures psychology at Rochester University and runs this blog.