What we know about the brain

What can neuroscience tell us about ourselves?

The human brain is the most complex structure in the known universe. There are more than 12 times as many neurons (nerve cells) in our brains than there are people on earth, and these neurons forge an estimated 100 trillion interconnections. In ways that neuroscientists are only faintly beginning to grasp, our brains undergird just about everything that makes us who we are-our personalities, memories, hopes, and most intimate thoughts and feelings.

Moreover, our brains are unmatched in many capacities.

As New York University psychologist Gary Marcus has observed, no computer can rival our brains when it comes to inferring meaning. Marcus describes a Stanford University computer system, Deep Learning, which has been programmed to distinguish positive from negative film reviews. Effective as Deep Learning is for some purposes, it is breathtakingly stupid compared with the human brain. Give the computer a line from a review that reads, “This is a film that cannot afford to be ignored,” and it rates the review as negative. In contrast to humans, who immediately grasp the meaning of the sentence, Deep Learning merely counts the number of negative words it encounters. The computer, well, computes; the person understands.

Discovering how the brain accomplishes this and other mental feats is one of science’s most exciting endeavors. It is also one of the most difficult. As scientist Paul Alivisatos, director of the Lawrence Berkeley National Laboratory in California, noted, “Understanding how the brain works is arguably one of the greatest scientific challenges of our time.”

For many decades, psychology was largely brainless. I did my graduate work in clinical psychology in the 1980s and still vividly recall discussions with psychologists who insisted that mental disorders could be understood without any recourse to the brain. Back then, some prominent scholars contended that autism and schizophrenia, for instance, were merely products of bad upbringing. Today, we know that virtually all mental disorders are partly heritable and that the genes that contribute to these conditions work by influencing the brain’s function and perhaps structure.

Fortunately, brainless psychology is a thing of the past, and the past two decades have been remarkably fruitful for neuroscience. In particular, the advent of functional neuroimaging tools, such as positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and single proton emission computed tomography (SPECT), have allowed scientists to visualize the brain in action. Among other things, these techniques have offered us tantalizing cues regarding the brain correlates of mental disorders, such as schizophrenia, and of social problems, such as prejudice.

In the case of schizophrenia, we now know that this condition is associated with underactivity in the brain’s frontal lobes, which subserve organization, planning and memory. This finding, in turn, may help to account for some of the cognitive deficits of this often devastating condition.

In the case of prejudice, psychologists have discovered that most whites display an immediate bias toward unfamiliar African American faces: Their amygdalas, almond-shaped structures deep within the brain that respond to threat, become activated when they view such faces for about one-thirtieth of a second. Yet, if we show white participants these African American faces for about half of a second, we typically see initial amygdala activation, followed by activation in the anterior cingulate cortex and a region of the brain’s frontal lobes,both of which play roles in the inhibition of impulses.

Hence, neuroscience implies that although many of us harbor reflexive biases against people of other races, most of us learn to override these biases.

Still, the linkages between the brain and human behavior remain poorly understood. We don’t know whether the brain differences between people with and without schizophrenia contribute to this condition or are merely statistically associated with it. Imaging techniques have generally been more successful in providing us with a map of the brain’s functions than in elucidating how these functions connect with psychological experiences. That will surely change, especially with new imaging methods that permit scientists to track the pathways of neural signals as they course through the brain; yet the brain’s staggering complexity reminds us that progress along these lines is likely to be glacial. Recently science journalist David Dobbs asked a group of neuroscientists, “Of what we need to know to fully understand the brain, what percentage do we know now?” Their estimates were all under 10 percent. Part of the problem is that functioning imaging techniques, remarkable as they are, are blunt instruments. The images generated by fMRI, for instance, display “voxels,” little blobs that contain tens of thousands of neurons. As a consequence, a brain scan is a bit like the view of a sprawling city we glean from an airplane at 30,000 feet; we can make out some major landmarks, but we can’t see people, let alone their interactions with each other. This state of affairs may soon improve with the Obama administration’s recently

announced BRAIN (Brain Research Through Advancing Innovative Technologies) Initiative, whose goal is to identify the activity of each of the human brain’s 85 billion or so neurons. If successful, this initiative should permit us to map neuronal activity in a far more fine-grained fashion than we can now.

As exciting as brain imaging technologies have been, we must be vigilant about the dangers of going beyond the data. In our recent book Brainwashed: The Seductive Appeal of Mindless Neuroscience, psychiatrist Sally Satel and I discuss the premature application of brain imaging to marketing, lie detection, criminal responsibility, addiction and other domains. Although we acknowledge the potential of neuroimaging to shed light on all of these areas, we worry that the media, entrepreneurs and even a few exuberant researchers have at times advanced simplistic claims concerning neuroscience.

For instance, over the

years, various teams of neuroimagers have claimed to have pinpointed a “God spot” in the brain’s right parietal lobe, just above the ear. Yet recent work reveals that no such spot exists. Although there are certainly brain correlates of religious belief, such belief draws on multiple brain structures that interact in unfathomably complex ways.

Finally, in our understandable zeal regarding neuroscience’s potential to inform our understanding of ourselves, we must be careful not to lose sight of alternative perspectives. Just as psychology was largely brainless prior to the 1980s, psychology is now at risk of becoming mindless, of forsaking the mental level of analysis. Although thoughts and emotions are ultimately enabled by brain events, they may never be fully reducible to such events. These psychological experiences may be “emergent properties,” phenomena that can’t be decomposed into their lower-order elements. At any rate, these phenomena need to be understood and appreciated in their own right.

The mind is far too complex to be left to either neuroscientists or psychologists alone. To crack the enduring mystery of what makes us human, we will require the insights of experts from both fields.

Scott O. Lilienfeld is professor of psychology at Emory University in Atlanta.