Introduction 
tively minor allergic disorders continue to pose 
problems both for the practicing physician and 
for the patients who suffer from them. Many of 
Investigators in the Immunology Program 
Alt, Frederick W., Ph.D. 
Atkinson, John P., M.D. 
Bevan, Michael J., Ph.D. 
Bjorkman, Pamela J., Ph.D. 
Bloom, Barry R., Ph.D. 
Bothwell, Alfred L. M., Ph.D. 
Bottomly, H. Kim, Ph.D. 
Chaplin, David D., M.D., Ph.D. 
Cooper, Max D., M.D. 
Davis, C. Geoffrey, Ph.D. 
Davis, Mark M., Ph.D. 
Fischer Lindahl, Kirsten, Ph.D. 
Goodnow, Christopher C, Ph.D. 
Greene, Warner C, M.D., Ph.D. 
Grosschedl, Rudolf, Ph.D. 
Holers, V. Michael, M.D. 
Jacobs, William R., Jr., Ph.D. 
Janeway, Charles A., Jr., M.D. 
Kappler, John W., Ph.D. 
Korsmeyer, Stanley J., M.D. 
Leiden, Jeffrey M., M.D., Ph.D. 
Neuroscience Program 
Among the most challenging problems in bio- 
medical research are those posed by the human 
brain. How do we perceive the world around us? 
How do we learn from past experiences? How do 
we store and recall information derived from 
those experiences? How do we determine when 
to act and what actions to carry out? What is 
thought? And what are the neural mechanisms 
that underlie language? In a word, how are all 
those aspects of our lives that most specifically 
define our humanity instantiated in the function- 
ing of our brains? The answers to these questions 
still lie far in the future, but in the past two de- 
cades considerable progress has been made in our 
understanding of some of the cellular and molec- 
ular mechanisms involved in brain function. Rec- 
ognizing this, in 1983 the Institute initiated its 
Neuroscience Program, which, until recently, 
has been largely focused on the ways in which 
nerve cells conduct signals and communicate 
with each other and with the effector tissues of 
the body (such as muscle and gland cells) and on 
the cellular mechanisms involved in the develop- 
ment of the nervous system. 
Modern neuroscience is founded on two funda- 
mental concepts that derive from the late nine- 
the reports in this volume indicate how these and 
other problems associated with the immune sys- 
tem are currently being addressed. 
Liftman, Dan R., M.D., Ph.D. 
Loh, Dennis Y.-D., M.D. 
Marrack, Philippa, Ph.D. 
Nussenzweig, Michel C, M.D., Ph.D. 
Pay an, Donald G., M.D. 
Perlmutter, Roger M., M.D., Ph.D. 
Peterlin, B. Matija, M.D. 
Rich, Robert R., M.D. 
Schatz, David G., Ph.D.' 
Schwartz, Benjamin D., M.D., Ph.D. 
Smale, Stephen T., Ph.D. 
Thompson, Craig B., M.D. 
Tonegawa, Susumu, Ph.D. 
Weiss, Arthur, M.D., Ph.D. 
Weissman, Irving L., M.D. 
Witte, Owen N., M.D. 
This investigator was appointed after manuscripts 
were submitted for 1991. His research will be de- 
scribed in the next volume. 
teenth and the early years of the twentieth cen- 
tury. The first of these, commonly referred to as 
the neuron doctrine, is that the fundamental 
functioning units of the nervous system are nerve 
cells, or neurons. Among the cells of the body, 
neurons are distinguished anatomically by the 
fact that they all extend processes (some of con- 
siderable length) that are of two general types: 
shorter tapering processes (dendrites) that 
mainly serve to receive information from other 
cells, and longer processes (axons), of more uni- 
form diameter, that serve to transmit information 
to other parts of the nervous system or to the body 
at large. The second basic concept is that infor- 
mation in the nervous system is principally en- 
coded in a series of signals called nerve im- 
pulses, or action potentials. These are brief, 
usually all-or-nothing electrical changes in the 
nerve cell membrane that are propagated along 
the axons at rates between about 3 and 300 feet 
per second. A necessary corollary of this concept 
is the notion that nerve cells communicate this 
encoded information to each other at specific 
sites called synapses, where the axon of one cell 
functionally interacts with the dendrites or the 
bodies of other neurons. 
