Never underestimate the ability of scientific inquiry...

Today I'm going to blog about something that I actually have some expertise in, for once. This has been a blog a long time in coming, an idea that came from an especially bad argument someone defending the existence of the supernatural: Science can't measure everything therefore it is unreasonable to dismiss the existence of the supernatural. This is backwards logic. Since by definition one can have no knowledge of the supernatural, discussing the topic as if any knowledge about it can be had is irrelevant. One example this person gave me refuting the ability of science to measure everything was in the form of a question: "How can I know that I love my wife?"

There are several things wrong about this example, which underscore the problem with the argument itself. Indeed, Science can't measure everything - at the moment. The implication of the above statement is that if something like emotion can't be quantified by any current method available, then it will never be measureable. A bold statement indeed, especially in light of the second premise behind the above challenge which is itself incorrect. I can indeed demonstrate that I love my wife. In fact, I have access to the equipment needed for the experiment.
A magnetic resonance imaging (MRI) system is an expensive piece of lab equipment, especially the new generation of high-field systems, but man can they do some amazing stuff. I sat in on a General Electric luncheon in Toronto earlier this spring and was floored not just by the quality, but the applications of MRI. So, how does one go about using MRI to investigate what we call love? This is a special application of MRI called functional MRI, or fMRI for short. The ability to detect brain activation comes from a peculiar decoupling of neuron function and blood flow. What I mean by this is that when the inputs to a neuron from other neurons (delivered by connections between neurons called synapses) cause it to activate and transmit a current down the axon and be the input to the next neuron. This activation of a neuron results in membrane depolarization (ion gradients across membranes, which are kept high by ion transport proteins in the cell membrane, equalize, resulting in electrical transmission down an axon) an increase in metabolism, as it tries to recover the electrical potential across cell membranes. That is, glucose and oxygen usage rise sharply upwards. Local blood flow is sensitive to neuronal activation and increases to meet the increased demand for oxygen, but actually overshoots the requirements of tissue.

Oxygen is carried in red blood cells by hemoglobin. When the oxygen molecules are delivered, hemoglobin becomes deoxyhemoglobin. From a MRI perspective, this is an important change. Deoxyhemoglobin has unpaired electrons (supplied by the iron it contains) that, when oxygen is bound, are not normally there. These unpaired electrons cause very strong local fluctuating magnetic fields, which cause the signal from protons in water molecules (which is how we do MRI) to dephase. In essence, these local fluctuating fields cause the signal to dephase, resulting in a decreased signal that is acquired to produce the image.

How does this show us where brain activation is happening? Well, when tissue is running at a higher metabolic rate, more oxygen gets taken up from blood, increasing the local concentration of deoxyhemoglobin. This deoxyhemoglobin would cause a signal drop to to the dephasing phenomenon, but blood flow local to this increase in oxygen uptake increases to meet the added burden. However, since blood flow overshoots what is necessary, it actually clears out more deoxyhemoglobin relative to tissue that is not running at a higher metabolic rate. Thus, what is seen in the image is an increased signal intensity in those regions where the brain is activated. This is known as the blood-oxygen level dependent (BOLD) phenomenon. It's somewhat more complicated than this, but these are the main events which lead to our ability to do fMRI.

When I made my reply to the question "How can I know that I love my wife?", I wasn't up on the literature in the area. But the experiment was quite obvious to me, so I wasn't all that surprised when I was listening to a CBC radio program called "Between You and Me" where the host was discussing with Helen Fisher of Rutgers University some of the fMRI experiments she has done to study the emotion we call love. So I went into the literature earlier and dug out a couple of papers.

One of the trickiest things in science is designing experiments. The answer from an experiment may not be the answer to the question you were interested in asking, but answering another question altogether. For instance, in Blind Faith Richard Sloan describes the results of a study which seemed to show a significant health benefit related to the amount one attends church. The more often subjects went to church seemed to be healthier than those that did not. What the author of the study failed to account for was what is known as a confounder, which is essentially a word used to describe a monkey wrench thrown into the works. The simple fact of the matter is that healthier people are able to attend church more often than those that are not as healthy. Studies of the type Fisher is engaged in are no different and take very careful designing to remove counfounding variables.

What Fisher and others have shown is that people in a state of what is called romantic love (other states being attachment and lust) show brain activation when the name of their beloved partner was mentioned. The paradigm also included giving the subjects names of neutral friends or describing hobbies they were passionate about. Regions of the brain which are recruited are parts of dopaminergic systems (that is, the primary neurotransmitter in these regions is dopamine). Dopaminergic systems are typically involved in reward/motivation and include such regions as the right ventral tegmental area and right caudate nucleus. This suggests that dopaminergic reward pathways are important in the general arousal component of romantic love.

So, it's quite clear that the poser of the question we started with is in error not only in what we can measure now, but also more fundamentally in the process leading up to the erroneous conclusion. Claiming that Science can not know everything is no reason to believe in the supernatural (which by definition lies outside our experience), nor is there any reason to suggest that we can't at some point in the future measure all things within our experience and then some.

Is this reductionist? Absolutely. But those that use the word in derision are simply ignorant. No one is attempting to demean the emotion of love as a whole by trying to understand from whence it arises. And no understanding of the highest level, our experience of love, can come without understanding the next lower level. Indeed, we gain a lot of insight into other behavior. The same dopaminergic pathways are also involved in gambling addiction. The mind as a whole can not be understood without understanding how neurons work, but not a single neuroscientist will say that such emergent phenomena as the mind can be understood by simply looking at its most basic components. By analogy, we can not understand how a clock works without knowing how gears work. By the same token it is difficult to make a clock by simply looking at a gear. We need to understand each level of organization.

I want to say one more thing here about a new phenomonen popping up, a pseudoscience known as neurotheology. I have one word to describe it: nonsense. What those which push neurotheology are trying to suggest comes from a study on nuns in what they subjectively called "a state of union with God". There are those out there that make outrageous claims that this is some kind of "picture of God". Absolute rot. There is nothing in these images which can not be accounted for by a self-induced change in brain function. As Richard Sloan pointed out in a speech to the Freedom From Religion Foundation on the topic, you will see the brain "light up" while eating a piece of cheese. Does that mean that if you acquired images under such tasty circumstances that you are viewing a picture of Gouda? Hardly. What this is is confusing what we feel with what we believe is the source. However, we've known for a long time that the conscious mind can have a profound effect on brain function and the existence of god is utterly unnecessary in explaining what the fMRI data shows with these nuns.

References:

Fisher H, Aron A, Brown LL. Romantic love: An fMRI study of a neural mechanism for mate choice. J Comp Neurol 493:58-62 (2005)

Beauregard M, Paquette V. Neural correlates of a mystical experience in Carmelite nuns, Neurosci Lett 405:186-90 (2006)

Fisher HE, Aron A, Brown LL. Romantic love: a mammalian brain system for mate choice. Phil Trans R Soc B 361:2173-86 (2006)

Ortigue S, Bianchi-Demicheli F, de C Hamilton AF, Grafton ST. The neural basis of love as a subliminal prime: An event-related functional magnetic resonance imaging study. J Cogn Neurosci 19:1218-30 (2007)