The talk will provide an informal approach to tensors
from a
physicist's viewpoint. I will start, as it was the case historically,
with early examples taken from continuum mechanics, will follow
describing the essential role tensors have had in Electromagnetism
and Relativity as well as in Quantum Mechanics, and at the end I will
be briefly mentioning spinors, which are a close yet rather eccentric
relatives of tensors and seem to be required also to describe the
world as it is.
The more dry aspects of the mathematical formalism,
index gymnastics,
etc. will be left out, in favour of a deliberate emphasis in the
geometrical meaning and in the more descriptive traits.
A review of some of the major developments in the
genesis of neurosurgery and its evolution from prehistory to the
present suggests that the development can be considered marked by
several milestones: 1) the first tools and skills to allow invasive
manipulation of the cranium, 2) definition of the anatomic substrate
and cerebral localization and the concept of the functional nervous
system, 3) development of anesthesia, 4) development of concepts of
antisepsis and asepsis, 5) development of imaging devices, 6) the
introduction of magnification and the operating microscope, 7)
expansion of the arsenal of tools with the introduction of the computer
and a multiplicity of anatomic and neurophysiological imaging and
monitoring modes.
From the initial Neolithic settings to modern times,
the metamorphosis of the neurosurgical discipline has been guided by a
singular goal: the execution of safe and beneficial surgical
manipulation of the nervous system. The practice of surgical
manipulation of the cranium has been evident for more than 12,000
years. The history of the development of this practice is rich in
details, events, and personalities.
The formative time for the development of modern
neurosurgery encompasses the four decades from 1879 to 1919. In 1879,
William Macewen in Glasgow combined the three critical technologies of
anesthesia, antisepsis, and cerebral localization to perform the first
modern neurosurgical operations. However, by the later 1890s there was
widespread discouragement about surgery for “brain
cases,” because mortality and morbidity rates were
forbidding. Harvey Cushing (1869–1939) was the single most
important individual in neurosurgery’s development during the
latter two decades of its gestational period (1901– 1920),
because he was able to develop techniques that led to major
improvements in mortality rates. In 1919, he presented a paper on
improved statistics in brain tumor surgery at a meeting of the American
College of Surgeons. It was the enthusiastic reception of that
presentation that marked the medical profession’s recognition
of neurological surgery as a distinct specialty.
In 1957, at the University of Southern California,
Theodore Kurze used an operating microscope for the first time in
neurosurgery. It can be assumed that the advent of modern neurosurgery
was with the introduction of the operating microscope. During the
critical period 1965–1990, there was a refinement of the
preoperative definition of the structural substrate, a minimization of
operative corridors, a reduction of operative trauma, increased
effectiveness at the target site, and incorporation of improved
technical tools. All these effects produced an evolution in
neurosurgery, which offered a precision of orientation and manipulation
expressed as progressive minimalism.
During the decade of the 1990s, there was a great
escalation in capabilities for neuroscience in general and neurosurgery
in particular. During this period of evolution, there was a clear
progression related to the more sophisticated use of the microscope,
the introduction of more refined imaging modes including magnetic
resonance imaging and positron emission tomography, the acceptance of
the computer as a neurosurgical tool, and new monitoring modes for
intraoperative assessment of neurological function. The entire
specialty accepted the notion of minimal invasion of anatomy but
maximum beneficial impact on the disease process. This is clearly
apparent in the technical enterprises of endoscopy, endovascular
surgery, and cellular/molecular neurosurgery with restoration of
function. However, it is most practically apparent in the field of
imaging-guided stereotactic neurosurgery and so-called neuronavigation.
During the past 2 decades, these developments have served as a platform
for the further emergence of concepts to be applied within the
neurosurgical field, including voice control, holography in real time,
robotics, virtual reality systems for simulation and training, and
telesurgical systems.
History has proved that neurosurgeons have
assimilated and adapted the most effective tools of modernity into
their operative environment and they will probably continue to do so.
There is a push-pull relationship between clinical and other sciences
that is critical in neurosurgery: for example, molecular biologists and
engineering scientists "pushing" ideas for the prevention, alleviation
or cure of sickness, while clinical scientists need to continually
"pull" ideas and solutions to the patient. Technology transfer is the
result of this successful interaction of scientists from many
disciplines working together around the same problem. Essential factors
are thorough comprehension of one's own scientific discipline, teamwork
and a common scientific language.