+ Human Brain Mapping 1:l-2(1993) +

EDITORIAL

Human Brain Mapping: A Convergence of Disciplines

Human brain mapping-determining the nature and location of the brain’s elementary information- processing modules and modeling their actions and interactions as neural systems that orchestrate human behavior-enjoys an embarrassment of riches after centuries of unrealized ambitions. That the human mind is the highest study of humanlund is a principle stated and restated by philosophers and scientists from the earliest days of recorded history. That the mind is realized through the brain was a doctrine common to Hippocrates, Plato, and Galen. Despite such fundamental insights, not until the 1860s, when Broca (and others) first made clear associations be- tween focal brain lesions and behavioral impairments, was significant progress made in mapping the func- tional organization of the human brain. Even after Broca’s promising start, lack of methodological devel- opment allowed human brain mapping to lose momen- tum and lapse into a scientific backwater. For more than a century, human brain mapping consisted solely of post mortem correlations between lesion location and neurological deficit. Intraoperative cortical stimu- lations by Penfield and colleagues taught us that lesions need not be irreversible experiments of nature. Yet, an invasive method applicable only by a neurosur- geon was an insufficient basis for significant growth in the field. The advent of X-ray computed tomography converted lesion-deficit correlations into ante mortem research, enabling a substantial body of programmatic investigations. Nevertheless, even computed tomogra- phy could not overcome the practical and theoretical limitations of understanding the brain solely by lesion- deficit association. From Broca’s first report of ”Tan” until very recently, human brain mapping was domi- nated by lesion-deficit correlations and, consequently, has been limited in scope. Times have changed.

Over the past two decades a cornucopia of methods for imaging the functiona2 architecture of the human brain has been developed. Xenon-133 blood-flow imag- ing opened the door, providing tantalizing glimpses of the brain in action. As computed tomography

advanced, positron emission tomography (PET) emerged and rapidly evolved into the preeminent technology for functional brain mapping. The enthusi- asm for human brain mapping generated by PET has been enormous, attracting collaborations with leading scientists from a host of neighboring disciplines. Cog- nitive psychologists, single-unit neurophysiologists, mathematicians, neural modelers, and others joined forces with physicists, radiologists, neurologists, and psychiatrists to chart the neural systems of perception, action, cognition, and emotion. Such highly visible successes, in turn, spurred interest in additional brain- mapping technologies. The recording of scalp electri- cal potentials, emerging decades before computed tomography but long underdeveloped, has been com- pletely transformed. With recording channels multiply- ing and source-localization strateges rapidly advanc- ing, event-related potentials now complements its millisecond temporal resolution with greatly im- proved anatomical localization. Magnetoencephalog- raphy, too, has established its value for temporal and spatial mapping. Functional magnetic resonance imag- ing (NRI), invented only two years ago, is the most rapidly evolving method. Coming on the heels of the interest spawned by PET, fMRI has pushed interest in human brain mapping to unprecedented levels. As with PET, fMRI has become a point of convergence for leading scientists from many neighboring disciplines. Never has the field of human brain mapping been more vital!

Despite such rapid technological advances and wide- spread interest, human brain mapping is neither mature nor secure. Each technique has unique advan- tages and serious limitations. No method has achieved a clear supremacy; rather, each offers a different combination of trade offs. In fact, no technique seems willing to stop evolving long enough to be adequately characterized. Many feel that no single technique will ever be sufficient and now focus on synergistic applica- tions of two or more methods. Although continued technical developments attract the lion’s share of

o 1993 Wiley-Liss, Inc.

attention, of far greater importance for the maturation of the field is expanded participation by scientists in adjoining, complementary disciplines. Experiments need to be built on theoretical frameworks already established by neurophysiology and cognitive psychol- ogy. Data analysis strategies need to be informed by our colleagues in mathematics, statistics, physics, and computer science. Computational modeling needs to advance from the level of the local network to that of the neural system and must be applied to the growing body of knowledge. Databases relating experimental conditions, observed activations, and proposed mod- els need to be created and effectively shared. The field will mature only if laboratories privileged to have instruments capable of mapping the human brain perceive the need for human brain mapping to be a convergence of disciplines, rather than a discipline in isolation. Scientists from potentially contributing areas

should be welcomed, even enticed to join in this grand adventure.

Human brain mapping is an emerging discipline. Only the youngest among us have come directly into this field. Most have arrived through more circuitous routes. Habit inclines each of us to publish our brain- mapping efforts in journals to which we were exposed during training. Neurologists will tend to publish in neurology journals; psychologists will gravitate to psychology journals. In times of change, it matters less where we come from than where we are going. Human Bruin Mupping is offered as a meeting place, a common ground, for scientists from diverse backgrounds to share their observations in this convergence of disci- plines-human brain mapping.

Peter T. Fox, M.D.