Continuity. Indivisible systems. One node connected to another connected to another, each pulling and pushing against the weight of its partners. Try to analyze the individual constituents of most systems and what do you get? Data out of context, potentially irrelevant,– perhaps even blatantly false.
Simplification is the backbone of experimental control. But it is also its greatest shortcoming. When we study cells in vitro (or in glass as the Latin denotes), removing tissues from a living organism, plating them and culturing them in a petri dish to study distinct cell populations under given conditions, we take them out of context and deny them many of the nonautonomous factors generally given them. Not only do we alter the biological signals normally available to them from other cell populations, we often don’t consider that we have changed the cell’s normal relation to space. In my field of CNS research what use would studying neocortical neurons plated across a few meager planes in a petri dish be compared to the beautiful radially aligned cell columns that occur in vivo? The relationship of the neurons to one another changes entirely, going from a cortical configuration to a nuclear one. And sometimes, many times, the relationship can be the defining factor. As my partner’s earlier studies have found, it isn’t so much a pathology within any given cell within the brain that has defined his postmortem autistic subjects but changes in the relationship that the neurons have with one another and their relationship to 3-dimensional space .
I know, I know. To many scientists I’m preaching to the choir, which is why in vitro research is often followed by in vivo studies. But even in vivo can be taken out of context and not necessarily reflect true trends in the natural world. For instance, amongst my various projects I am studying the development of myelin in the mouse spinal cord. Specifically I’m looking at soluble signaling factors which may determine the timing of myelination and which may therefore serve as useful targets for treatment of degeneration or injury. At my university, there are various animal housing units, with mice and rats comprising the largest populations. As with American pet mice, my males are sometimes aggressive towards their male siblings once they’ve matured and it’s often necessary to isolate them in different cages to prevent injury. However, this raises another issue that these mice are poorly socialized except during periods of mating. Now in this set of experiments, it’s vitally important that differences are generally controlled for, such that our double transgenic mice have almost identical genetic, prenatal, and early postnatal backgrounds with their littermate controls, excepting of course the targeted mutations. But Liu et al. (2012) have just published a study which suggests that a certain level of myelination is both plastic and directly subject to social interaction . In summary, mice who were exposed to protracted isolation during adulthood showed decreased levels of myelination and changes in chromatin within the prefrontal cortex which subsequently reverted once they were reintroduced. What if aspects of myelination within spinal cord are likewise subject to socialization? What if I didn’t know to keep track of which mice were isolated and which were socialized and simply collected tissues ignorant of the contextual lives of these animals? It could potentially mean the difference between reliable results and false ones.
Granted, the Liu et al. study has its flaws. For instance, how do they assure us that they were able to collect comparable segments of tissue, especially when viewing specimens under an electron microscope? The prefrontal cortex, even in a mouse, is huge and is poorly landmarked. Nevertheless, it is acknowledged that a certain level of plasticity is inherent to mature myelin, and in fact an earlier study found that socialization (as well as gender) plays a role in the size of the corpus callosum, the bundle of white matter fibers that connects the cerebral hemispheres [3, 4].
This is just one example amongst many. And, granted, perhaps I’m drawn towards quality of life issues for the animals we work with because, even before being a scientist, I am an animal lover. But I also know it’s good science to get all your facts straight. When working with biological systems which are so complex, we often assume that minute differences will wash away in the comparison provided the N is large enough. But is that always the case? Is it not reasonable to assume that, with a large enough N, vital details, small but distinct effects are washed away as well?
“Statistical reasoning shows that even with large population studies, it is difficult to identify a small increase in the rate of a commonly occurring event. Subtle effects, long-term delayed effects . . . could easily escape detection” .
As humans, pattern-loving, generalizing, simplifying big-brained organisms, we seek to define cause and effect. An admirable trait. But on the other hand, we are perpetually trapped in the assumption that big effects follow big causes and small effects, small causes. Not an altogether inappropriate rule of thumb. But in the world of chemistry, the tiniest molecules can have incredible effects. The small pill you take for your blood pressure; the teratogenic thalidomide metabolites developing fetuses were exposed to; the billions of bacteria that live in your digestive tract which help to orchestrate both its development and its mature function; and the basic mineral scaffolding which, billions of years ago, may have provided the subtlest of directive cues towards the developing chirality (handedness) of biological molecules:
“For almost 70 years, origin-of-life specialists have focused on demonstrating the phenomenon of chiral molecular [adherence] on a mineral surface– a process that might have jumpstarted the homochirality characteristic of life. . . . The principal challenge here lies in detecting a chiral excess that may be as small as 1% for [adhered] molecular species in concentrations no more than ~1 nanomole cm-2″ .
Less than one nanomole cm-2! Such a small effect to have been such a crucial turning point in the development of life. How many other small effects do we fail to see in our experiments because we’ve removed not only the research itself from biological context but our own theories as well? How many geneticists or molecular biologists envision the genome, RNA, or individual protein products as separable from the larger cellular system? How many neuroscientists still attempt to view the neuron as its own entity?
If Evolution has taught us anything, it is that there is a continuum of relationships across all living organisms at every level of comparison, such that boundaries are a gray area akin to defining “love” or “happiness”. Meanwhile, the continual turnover of accepted paradigms hopefully teaches us that each new paradigm is merely a simplification of sets of occurrences within the natural world but, by nature of generalization, it will never be wholly accurate. All we can hope is that each new paradigm is perhaps a little more accurate than the last.
Note: The title is a quote by Donna Haraway, 2003.