Welcome to the Century of Neuroscience, the Century of the Brain – Part III: The Working Assumption of Modern Neuroscience

“Every aspect of our lives depends on the normal functioning of our brains.  Our education depends on it; the education of our children depends on it; our relationships to our fellow humans depend on it; our hopes and aspirations are all represented in our brain. And all of these human qualities are at risk if something goes wrong with one’s brain.”

─ W. Maxwell Cowan, M.D., Ph.D.
Neuroscientist, Educator
Past President of the Society for Neuroscience

“How the brain works and gives rise to our mental and intellectual lives will be the most exciting and challenging area of science in the 21^st century. As a result of this concerted effort, new technologies will be invented, new industries spawned, and new treatments and even cures discovered for devastating disorders and disease of the brain and nervous system.”

─ Francis S. Collins, M.D., Ph.D.
Former Director, National Institutes of Health (NIH)
Former Director, NIH Human Genome Project
Physician, Geneticist,

I n the above quote, Dr. Cowan reminds us of the centrality of the brain to who we are and to our very existence, a reality confirmed by a moment’s reflection on all the brain does and makes possible. As I tell my neuroscience students, the brain is not just another organ in your body: for example, we can replace your heart and you are still you (likewise your kidneys, liver, etc.). But if you get my brain, and I get your brain, you will become me and I will become you and …well, neither of us is likely to be very happy.

Dr. Collins, director of the National Institutes of Health, oversees billions of dollars’ worth of neuroscientific research, and he reminds us of the very bright future that advances in neuroscience will create as we move further into what has been called the “Century of Neuroscience, the Century of the Brain.” When it comes to understanding the brain, the challenges are great, but the prospects for discovery and further understanding are even greater.

Modern neuroscience operates under the working assumption that every sensation, perception, thought, idea, emotion, decision, action, and behavior involves our brain/nervous system. Take away the brain, and humans lose these features and capabilities.

Most neuroscientists, however, would argue that the word “involves” is too weak; they would say the phrase “are produced or generated by” is more appropriate, i.e., thoughts, ideas, emotions, etc. are produced or generated by the brain. They would claim that this stronger causative/mechanistic wording, as opposed to weaker associative or correlational terminology, is becoming increasingly justified by several lines of evidence.

For example, damage to particular brain areas or structures can produce selective or distributed deficits in each of the entities, capabilities or functions mentioned above. Traumatic brain injury (e.g., war-injured soldiers and accident victims) or a variety of mental or neurological disorders would be examples. Animal studies involving selective lesions/ablations provide strong support for structure/function associations that most neuroscientists believe justify the inference that functional causation, rather than mere correlation, is reasonably attributed to particular brain areas/structures.

Animal brains, and in particular mammalian and especially non-human primate brains, share many structural and functional similarities to human brains, making it reasonable to infer that if we grant that an animal structure produces/causes a particular function in an animal, the homologous structure in the human brain is likely to be producing/causing the same or similar function in us.

In addition, selective chemically or electrically targeted stimulation of appropriate brain regions or structures can either elicit or modify those features which we associate with mental states or functional capabilities, as well as one’s actions/behavior in the world, and often do so in quite predictable ways. In this case, examples include drugs of use (e.g., medications for mental illness, pain, etc.) and abuse (e.g., hallucinogenic agents, alcohol, etc.), as well as various therapeutic techniques currently being used or in clinical trials (e.g., deep brain stimulation for Parkinson’s disease, depression, and other neural dysfunctions, transcranial magnetic stimulation for migraines and depression, etc.).

Again, animal brain structure/function studies using chemical and electrical stimulation are usually inferred to involve causative mechanisms and not merely correlational relationships; we can reasonably infer that homologous human structures are similarly causally and not just correlatively related to functions. Since non-human primate brains seem to be capable of producing at least rudimentary cognitive- and emotive-like states similar to those seen in humans, it is reasonable to infer that humans are using homologous structures to produce or process even higher, more complex, but homologous mental states. In non-human primate studies these include (among others) mental states that seem to be akin to fear, anger, sadness, happiness, deception, and even sense of fairness—although lower primates, lacking language and symbolic representation are not consciously processing or experiencing these mental states the way we as humans can.

Finally, the advent of non-invasive brain imaging techniques which go by an alphabet soup list of acronyms (PET, fMRI, EEG, etc.) are allowing us to both discover and confirm the ever-tightening link between brain sites/structures and select functions. The work of neurosurgeon Wilder Penfield et al. on the sensory and motor homuncular maps, the Broca brain area for language/speech production, the Wernicke brain area for language/speech comprehension, and processing areas for facial recognition are just a few examples of these structure/function linkages. Damage to or manipulation of these areas impairs or influences their respective functions often quite predictably, and brain imaging confirms the locus/function relationship.

When combinations of two or more of the above-mentioned manipulations are tested, the results follow mechanistic predictions congruent with causal explanation and not mere correlation. Thus most modern neuroscientists operate under the working assumption that our mental states and faculties comprise most if not all of our experience as conscious human brains; we are, as persons, to that extent identifiable with our brains—from our lowest, most primitive and rudimentary to our highest, most complex and seemingly unique characteristics and capabilities. All of these are emergent attributes of the functionality produced by and not just correlated with our brains. Many would go so far as to say that such a litany of brain structure/function relationships lead us to the ever-tightening linkage between our brain and our essence as persons. Just as the pumping of blood is what the heart does and the filtering of blood is what the kidneys do, so the mind is what the brain does—the brain produces the mind, and the person emerges from the functionality of the brain.

Of course, the brain does not operate in isolation. We are embodied in a physical body. We are embedded in a multi-faceted environment (physical, social, etc.)—aka “nurture.” There are also the strong constraining influences of genetics—aka “nature”—and epigenetics (chemical, dietary, lifestyle and other factors that influence gene expression). But, the brain plays a central role in mediating/processing all of this internal and external information and unifies it into what we experience as our emergent personhood (see figure below).

Neuroscience is the inter/multi-disciplinary process of working out the details of how the brain produces the mind, personhood, and even what we call “human nature.” This effort is one of the most formidable undertakings of the human species because the brain/nervous system is, as far as we can tell, the most complex physical structure in the known universe.

However, the brain has not always been viewed as the locus, controller, or producer of our personhood or as central to the core of our being. A brief history of the various views will be summarized in the next installment of this series.