174 BIRREN
explored the role of the mitochondria in the cells of aging rats. This topic
is still in the forefront of research on the physiology of aging since the
mitochondria are the sources of energy for an organism.
Jack Botwinick, a psychologist, introduced the study of the role of
mental set in learning. He found that older adults had a lower anticipa
tory set or expectancy for a stimulus.^8 In another of his studies he found
that in conditioning and extinction of the galvanic skin response, older
subjects conditioned less readily but also extinguished more quickly than
young subjects.^9 This suggests a lower level of arousal in the older subjects.
Edward Jerome conducted a series of learning experiments in an attempt
to identify differences in human learning behavior with aging.^10
One of the four main interests of the section’s research program was
investigating the slowing of behavior widely observed in older persons.
Early investigators tended to attribute the slowing to either sensory input
deficiency or to motor output mechanisms. Such views tended to mini
mize the role of changes in the central nervous system itself as a source
of the slowing. Summarizing a large amount of research conducted in
the Section on Aging, findings showed that the major source of the
slowness was in the nervous system itself and not in the peripheral nerve
conduction velocity or in sensory or perceptual input. The research came
to be recognized as a major contribution to the understanding of the
behavioral changes of aging and the linking of brain function with spe
cific intellectual and psychomotor behaviors.
One of the technical developments was the design and construction
of an instrument in the then pre-computer age for measuring the diff
erence in the speed of response to the complexity of stimuli. The instru
ment was designed and built within the NIMH facilities. It was called
the Psychomet and it made it possible to hold constant the response con
ditions while altering the complexity of the stimuli to which the subject
had to react. Based on the use of the Psychomet, experiments by myself,
Klaus Riegel and Donald Morrison^11 added to the growing recognition
that there was a general psychophysiological factor of speed in the
functioning of the central nervous system that became slower with
advancing age. From the viewpoint of the neurophysiology of the aging
nervous system, it suggested that a property of the brain was changed
resulting in a generalized slowing that was involuntary and not under