54 Biological Psychology
nature of the reaction itself. I got interested in the physiology of
the reaction and the attempt to trace conditioned reflex paths
through the nervous system started my program of cerebral
work. (Letter of May 14, 1935, K. S. Lashley to E. R. Hilgard,
reproduced with the kind permission of E. R. Hilgard)It was in the previous year, 1913, that Watson published his
initial salvo in an article entitled “Psychology as the Behav-
iorist Views It.” He was elected president of the American
Psychological Association in 1914.
As we noted earlier, localization of function in the cere-
brum was the dominant view of brain organization at the
beginning of the twentieth century. In Watson’s behaviorism,
the learning of a particular response was held to be the
formation of a particular set of connections, a series set. Con-
sequently, Lashley argued, it should be possible to localize
the place in the cerebral cortex where that learned change in
brain organization was stored—the engram. (It was believed
at the time that learning occurred in the cerebral cortex.)
Thus, behaviorism and localization of function were beauti-
fully consistent—they supported the notion of an elaborate
and complex switchboard where specific and localized
changes occurred when specific habits were learned.
Lashley set about systematically to find these learning
locations—the engrams—in a series of studies culminating in
his 1929 monograph, Brain Mechanisms of Intelligence. In
this study, he used mazes differing in difficulty and made
lesions of varying sizes in all different regions of the cerebral
cortex of the rat. The results of this study profoundly altered
Lashley’s view of brain organization and had an extraordi-
nary impact on the young field of physiological psychology.
The locus of the lesions is unimportant; the size is critically
important, particularly for the more difficult mazes. These
findings led to Lashley’s two theoretical notions of equipo-
tentiality and mass action: that is, all areas of the cerebral cor-
tex are equally important (at least in maze learning), and what
is critical is the amount of brain tissue removed.
Lashley’s interpretations stirred vigorous debate in the
field. Walter Hunter, an important figure in physiological-
experimental psychology at Brown University who devel-
oped the delayed response task in 1913, argued that in fact
the rat was using a variety of sensory cues; as more of the
sensory regions of the cortex were destroyed, fewer and
fewer cues became available. Lashley and his associates
countered by showing that removing the eyes has much less
effect on maze learning than removing the visual area of the
cortex. Others argued that Lashley removed more than the vi-
sual cortex. Out of this came a long series of lesion-behavior
studies analyzing behavioral “functions” of the cerebral cor-
tex. Beginning in the 1940s, several laboratories, including
Lashley’s and those of Harry Harlow at the University of
Wisconsin and Karl Pribram at Yale, took up the search for
the more complex functions of association cortex using mon-
keys and humans.
Perhaps the most important single discovery in this field
came from Brenda Milner’s studies with patient H. M. who,
following bilateral temporal lobectomy (removing the hip-
pocampus and other structures), lives forever in the present.
Work on higher brain functions in monkeys and humans is
one of the key roots of modern cognitive neuroscience, to be
treated later. Since Milner’s work with H. M., the hippocam-
pus has been of particular interest in biological psychology.
Another facet of hippocampal study in the context of the
biological psychology of memory is long-term potentiation
(LTP), discovered by Bliss and Lomo (1973). Brief tetanic
stimulation of monosynaptic inputs to the hippocampus
causes a profound increase in synaptic excitability that can
persist for hours or days. Many view it as a leading candidate
for a mechanism of memory storage, although direct evi-
dence is still lacking.
Yet another impetus to study of the hippocampus in the re-
markable discovery of “place cells” by John O’Keefe (1979).
When recording from single neurons in the hippocampus of
the behaving rat, a give neuron may respond only when the
animal is in a particular place in the environment (i.e., in a
box or maze), reliably and repeatedly. There is great interest
now in the possibility that LTP may be the mechanism form-
ing place cells. A number of laboratories are making use of
genetically altered mice to test this possibility.
Lashley’s influence is felt strongly through the many emi-
nent physiological psychologists who worked or had contact
with him. We select two examples here—Austin Riesen and
Donald O. Hebb. We discuss Roger W. Sperry’s work next in
the context of cognitive neuroscience. The basic problem of
the development of perception fascinated Lashley and his
students. How is it that we come to perceive the world as we
do? Do we learn from experience or is it told to us by the
brain? Riesen did pioneering studies in which he raised mon-
keys for periods of time in the dark and then tested their vi-
sual perception. They were clearly deficient.
This important work served as one of the stimuli for Hebb
to develop a new theory of brain organization and function,
which he outlined in The Organization of Behavior (1949).
This book had an immediate and profound impact on the
field. Hebb effectively challenged many traditional notions of
brain organization and attempted to pull together several dis-
cordant themes—mass action and equipotentiality, effects of
dark rearing on perception, the preorganization of sensory
cortex, the lack of serious intellectual effects of removal of an
entire hemisphere of the brain in a human child—into a