Scanning the Brain

Intensive instruction in reading improves how a kindergartener's brain works. In schizophrenia, key parts of the brain may not communicate so well, making it hard to organize one's thoughts. And the course of true love runs smoother with the neurotransmitter dopamine. How do we know all this? We know from neuroimaging, an increasingly sophisticated toolkit that helps us open up the human brain and look inside.

Through neuroimaging, medical technology and psychological science are coming together to shed light – literally -- on everything from how children learn 2+2=4 to the causes of dementia. Doctors and scientists once had to wait until autopsy to examine the brain and psychologists had to deduce from behavior where the brain was injured. Now they can study live images to spot problems; understand what happens during tasks, thoughts and even emotions; and assess the effectiveness of various kinds of treatment.

Current neuroimaging techniques show both form and function. They depict the brain's anatomy, including the integrity of brain structures and their interconnections; its chemistry, including neurotransmitter levels; and its physiology, or its electrical and metabolic activity. The newest tools check how well the brain's different parts connect and communicate. They can even reveal with split-second timing the sequence of events during a specific process such as reading, watching activity move among different parts of the brain.

Psychologists employ these tools across the range of disciplines, not only to show individual neural traits but the “social brain” as well. Social cognitive neuroscientists are capturing the psychological and neural processes involved in emotion, pain, self regulation, self perception, and person perception. For example, using neuroimaging technology, psychologists have demonstrated how White Americans, even those who report themselves free of prejudice, show differences in brain activity in the amygdala -- a structure involved in emotional learning – when they look at pictures of White or Black people. Positive emotions are also under scrutiny. Psychologists compared functional images snapped when students looked at pictures of their hearts' devotion versus when they looked a pictures of an acquaintance. When students gazed at their beloved, two deep-brain areas that communicate as part of a circuit, showed increased levels of activity. As it turns out, those areas help to regulate the neurotransmitter dopamine, which swishes around the brain when people want or anticipate a reward.

Neuroimaging is helping us to understand how the brain develops from infancy through adulthood. For example, developmental neuroscientists study the neurobiological underpinnings of cognitive development. With functional measures of brain activity as well as behavioral measures, they hope to see how subtle early insults to the nervous system affect cognitive and emotional function later in life – for example, the effects of a diabetic pregnancy on learning, memory and attention later in childhood. Imaging tools can pay off in the classroom, too: Using such tools, literacy experts have shown that a year of intensive, methodical reading instruction makes the brains of high-risk kindergarteners act like those of more skilled youngsters, leaving most of the former kids able to read as well as the latter kids.

To aid clinical treatments, psychologists are using functional imaging to get at the neural mechanisms involved in such difficult problems as post-traumatic stress disorder, phobias and panic disorder. For example, high-tech scans reveal that schizophrenia's diverse symptoms may result not from faults in single neural “components” but rather from differences in webs of neural connections. Scans similarly help researchers follow brain activity to assess whether treatment changes the underlying brain dysfunction, such as patterns of communication or poor regulation of neurotransmitters.

Neuroimaging shows where behavioral events evoke specific responses in the brain.  That doesn't necessarily shed light on the neural mechanisms at work in the spots where there is increased activity, nor the brain's complex web of interactions. Still, patterns of response point arrows at problems and help to map how brain functions correlate to everyday activity. Knowing which areas are more active during certain behaviors confirms that behavior is based in the brain. Yet it's not all mechanistic. Experts caution that despite the helpfulness, intrigue and sheer fun of new discoveries in neuroimaging, they are merely tantalizing clues to the mind's enduring mystery.

CAT scans -- computerized axial tomography – are oblique X-ray slices that show the density of brain structures. MRI – magnetic resonance imaging – uses changes in electrically charged molecules when they are placed in a magnetic field to assess differences in cerebral activity in different regions of the brain. Both technologies are more precise than ordinary X-ray and help find problems when people fall ill. These images also help us “map” the brain regions associated with different behaviors, often by studying people with specific brain injuries. MRI images are clearer than CAT scans and don't use radiation; they show brain atrophy and increased cerebrospinal fluid. But they're not safe for people with electrically powered implants, such as pacemakers, or with metal not anchored to bone, such as artery clips.

Other commonly used tests examine how the brain uses glucose or oxygen, two prime fuel sources; neurotransmitter levels; and electrical activity. PET (positron emission tomography) scans use radioactive tags to show how specific brain areas get more active, metabolizing more glucose, when someone does something. PET scans are good for showing the many brain structures that may be involved in a single cognitive function and help to examine the processing of neurotransmitters. They are also coming into use for the differential diagnosis of Alzheimer's disease.

Functional MRI (fMRI), which tracks the brain's blood flow and oxygen use, two measures of neuron activity, has fostered highly publicized findings. fMRI is precise and can use standard MRI. Doctors often overlay an fMRI on an anatomical MRI to make it easier to assess behavior in terms of brain structure and activity. Another imaging process called diffusion tensor imaging (DTI) uses a regular MRI machine to track how water molecules move in and around the fibers connecting different parts of the brain. DTI gauges the thickness and density of the brain's connections. If they are weak, the result is like an orchestra playing out of synch.

Other measures of brain activity include electroencephalography (EEG), which records the brain's electrical waves to detect abnormal activity such as in seizures and sleep disorders. Event Related Potentials (ERPs) show how the brain responds to single events.

Aron A., Fisher H., Mashek D.J., Strong G., Li H., Brown L.L. (2005). Reward, motivation, and emotion systems associated with early-stage intense romantic love. Journal of Neurophysiology, 94(1), 327-37.

Breier, J. I., Simos, P. G., Fletcher, J. M., Castillo, E. M., Zhang, W., and Papanicolaou, A. C. (2003). Abnormal activation of temperoparietal language areas during phonetic analysis in children with dyslexia. Neuropsychology, 17, 610-621.

Davidson, M. C. Thomas, K. M., & Casey, B. J. (2003).  Imaging the developing brain with fMRI.  Mental Retardation and Developmental Disabilities, 9(3), 161-167.

Fan, J., Flombaum, J. I., McCandliss, B. D., Thomas, K. M., & Posner, M. I. (2003).  Cognitive and brain consequences of conflict.  Neuroimage, 18(1), 42-57.

Fisher, Brown and Aaron study, romantic love

LaBar, K. S. and Cabeza, R. (2006, January). Reviews: Cognitive neuroscience of emotional memory. Nature, 7, 54-?

Ochsner, K. N. & Lieberman, M. D. (2001). The emergence of social cognitive neuroscience. American Psychologist, 56(9), 717-734.

Phelps, E. A., O'Connor, K. J., Cunninghamd, W.A., Funayama, E. S., Gatenby, J. C., Gore, J.C., and Banaji, M. R. (2000). Performance on indirect measures of race evaluation predicts amygdala activation. Journal of Cognitive Neuroscience, 12(5), 729-738.

Simos, P. G., Fletcher, J. M., Sarkari, S., Billingsley, R. L., Castillo, E. M., Pataraia, E., Francis, D. J., Denton, C., Papanicolauo, A. C. (2005). Early development of neurophysiological processes involved in normal reading and reading disability: A magnetic source imaging study. Neuropsychology, 19(6), 787-798.

Spelke, E. S. (2002). Developmental neuroimaging: a developmental psychologist looks ahead. Developmental Science, 5(3), 392-396.

Thomas, K. M. (2003).  Assessing brain development using neurophysiological and behavioral measures.  Journal of Pediatrics, 143, S46-S53.

Zhang, L., Thomas, K. M., Davidson, M. C., Casey, B. J., Heier, L. A., & Ulug, A. M. (2005).  Diffusion and volume changes during brain development.  American Journal of Neuroradiology, 26, 45-49.

American Psychological Association, April 19, 2006