By Sarika Garg
Neuroscience is the science of the nervous system, the
study of which involves numerous researchers and doctors from different
disciplines, extending from molecular biology and psychology to anatomy,
physiology and pharmacology. The nervous
system comprises of the brain, spinal cord and peripheral nerves. It is made up
of billions of nerve cells, called neurons, and trillions of supporting cells,
called glial cells. The human brain is one of the most splendid organs in the
human body. Thinking, feeling, planning, movements, memory, etc., everything is
developed and controlled by our brain (Link
1). Alongside the most magnificent functions, several mysteries are
associated with it making it the most intricate structure in the universe. Many astonishing facts have been unraveled due
to the tremendous progress made in medical science and technology. In this
scientific era, it will be interesting to know that how much of the human brain
was known in an ancient era and how the significant events occurred thereafter.
Literature reports divulge that ancient Egyptian civilization was the first to have
described 48 cases of brain injuries around the year 1700 B.C. Despite this
creation of first medical document ever in the history of mankind, ancient
Egyptians believed the ‘heart’ as the most important and the ‘brain’, on the
other hand, the most inconsequential organ of the human body (Link 2). Please find below some of the
notable events in the neuroscience world which helped brain garner much
substantial attention.
Brain
stated as the seat of intelligence (460-379 B.C.)
The argument of whether the heart or the brain was the
seat of intelligence remained unconcluded until the end of the 5th
century B.C. It was Hippocrates, a Greek physician, whose work stated that the
brain is involved with sensation and is the seat of intelligence. He is
considered as the founder of medicine and is referred to as the ‘Father of
Western Medicine’. His oft-quoted
statements showed a clear association between the mind and the brain:
‘Men ought to know
that from the brain, and from the brain alone, arise our pleasures, joys,
laughter and jests, as well as our sorrows, pains, griefs and tears. Through
it, in particular, we think, see, hear and distinguish the ugly from the
beautiful, the bad from the good, the pleasant from the unpleasant… I hold that
the brain is the most powerful organ of the human body… wherefore I assert that
the brain is the interpreter of consciousness…’ (Hippocrates: On the sacred
disease. Quoted by Prioreschi [1996]) (Link
3).
Lecture
on the brain anatomical procedures (177 A.D.)
Galen, a Greek physician in the Roman Empire, delivered a
lecture entitled ‘On the brain’ to the Roman medical students in the year 177.
In his lecture, along with the directives for a systematic brain dissection of
an ox brain, he scattered knowledge about the various parts of the brain. He is
credited with the earliest descriptions and speculations about the pineal, a
small gland in the middle of the head which produces a hormone, melatonin.
Melatonin is known to influence sexual development and sleep-wake cycles. He
was a clever spectator and recognized that the brain becomes smaller in old
animals. While Hippocrates set down the cornerstone of Greek medicine, Galen
further developed its postulate and carried medicine to its apex (Link 4).
The
discovery of the cerebrospinal fluid (1536)
Until the 16th century, on the basis of
Hippocrates and Galen findings, “spiritus animalis” with its mental functions
was thought to be located within the cerebral ventricles. It was believed that
blood moves to all parts of the body and no theory hypothesized blood
circulation. The blood enriched by animal spirits was thought to reach the
body’s organs where it gave life. After reverberating through centuries, the
idea of “spiritus animalis” backed off only after 18 years when a Venetian
physician, Nicolo Massa, described a large amount of fluid within cerebral
ventricles. In his work he mentioned that ventricles are always full or semi
full of watery substance. He was the first to notice and report the existence
of the intraventricular fluid intracranially while making an autopsy. . Among several physicians and anatomists who
have laid the foundations of identification of the cerebrospinal fluid’s presence,
Nicola Massa is considered as the first person to have described the
cerebrospinal fluid properly (Link 5).
The theory
of brain function (1823-1824)
Marie Jean Pierre Flourens, a French physician, was
accepted as a pioneer of the experimental methods in neuroanatomy and of the
modern theory of the brain functions. He postulated that the brain-specific
parts control specific functions. He conducted several ablation and stimulation
methods along with many experimental investigations on mammalian species,
especially rabbits and pigeons. Cerebral cortex, cerebellum and brainstem were
shown to be functioned as a whole and in concomitance with every other part. Animal’s
muscular coordination and sense of equilibrium vanished on removal of the cerebellum.
Cerebral hemispheres and medulla were linked with the cognitive functions and
vital functions, respectively. Death of the animal was noticed on desolation of
the medulla oblongata (Link 6). Taking
into account his achievements, he is today recognized as the founder of the
modern field theory of brain function (Link
7).
The
discovery of the neuron (1889)
It won’t be wrong to say that the neuroscience discipline
did not exist until the 19th century pioneers Cajal and Golgi struck
the right chord. Early in 1839, the cell theory was asserted according to which
all tissues in the body are composed of individual cells. Later, ‘every cell
comes from another cell’ theory was postulated. However, due to the dearth of
good histological method to stain nervous structures, brain tissue was not
considered to comply with the cell theory. In 1873 Camillo Golgi, an Italian
physician, published his work on the silver nitrate staining method. This
method was referred to as Golgi method and successfully stained neurons and
neuroglia cells making them visible against the transparent background. In 1887, Santiago Ramón y Cajal, a Spanish pathologist
and neuroscientist confirmed the usefulness of Golgi method by carrying out the
systematic study of the nervous system. He drew his observations quite
accurately where he showed that the terminal and collateral fibres in the grey
matter remained free, establishing simple contacts with the neuronal cell body
and the dendrites of other adjacent nerve cells instead of forming a diffuse
network. All his discoveries showed him the way to formulate the neuronal
doctrine, a concept that the individual cells constitute the nervous system.
Both Golgi and Ramón y Cajal were jointly awarded a Nobel Prize in Physiology
or Medicine in 1906 in recognition of their work on the structure of the
nervous system (Link 8).
The development
of brain mapping (1909)
In the history of neuroscience, there has not been a
single example as persuasive as the cytoarchitectonic map of the human brain. Korbinian
Brodmann, a German neurologist, published his study in 1909 where he describes
the dissociation of the cerebral cortex into 43 areas. He labeled his human map
of the cortical area by a number between 1 and 52. His map is devoid of areas
with the numbers 12-16 and 48-51 which was explained by Brodmann as the areas
unidentifiable in the human cortex but well developed in other mammalian
species. He utilized Nissl substance (cresyl violet) staining to divulge the
distinct areal borders within the cortical sheet. His approach concluded that a
particular anatomical structure corresponds to a particular function. In the 21st
century, Brodmann’s map is still in use for localizing neuroimaging data
obtained in the living human brain (Link
9).
The
discovery of neurotransmitters (1921)
Neurotransmitters are the chemicals that allow
neurotransmission. They are released from one neuron at the synaptic cleft,
where they are accepted by a receptor on the next neuron. Communication between
the neurons is the foundation of brain function and is accomplished by the
movement of neurotransmitters. In 1921, a German scientist Otto Loewi published
his work on frogs describing the chemical transmission. He conducted several
experiments to characterize the substance and concluded it to be Acetylcholine.
He was awarded the Nobel Prize in 1936 for his contributions (Link 10).
The
invention of electroencephalography (1929)
Electroencephalography (EEG) is an electrophysiological
monitoring and recording of the electrical activity of the brain. Hans Berger,
a German psychiatrist, recorded the first human electroencephalograms in 1924.
He published his work in 1929 where he described EEG changes associated with
attention and mental effort, and alterations in the EEG associated with
cerebral injury. His basic observations were later confirmed by other
scientists revealing the dramatic change in humans EEG patterns during a
night’s sleep. This technique provided early insight into diagnoses of sleep
disorders, epilepsy, brain tumours, strokes and encephalopathies and has since
been improved upon by use of modern techniques such as MRI (Link 11).
The
invention of the electron microscope (1931)
By the beginning of the 20th century, with the
advancement of science and technology scientists were able to analyse some
structures inside the cell using light microscopes. However, the limited
resolution of the microscopes restricted the detailed study of the structures
inside the cells. In 1931, German scientists Max Knoll and Ernst Ruska
conquered the barrier by building the electron microscope (Link 12). An electron microscopic study of the Axo-somatic and
axo-dendritic synapses of the cerebral cortex and several other made
significant contributions in the understanding of the nervous system (Link 13). It also won Ernst Ruska the
Nobel Prize in physics in 1986.
The
discovery of optogenetics
This is the latest and most exciting development in the
field of Neuroscience. So far it has been used to identify specific neurons and
networks like those in the amygdala that contribute to fear conditioning, to
stimulate spiral ganglion in deaf mice and restoring auditory activity.
Optogenetics is the use of light sensitive proteins to monitor and control
living neurons which first attracted wide attention in 2005 (Link 14). This technique was
investigated by several researchers but ultimately Karl Deisseroth, Edward
Boyden and Gero Miesenböck have been recognised as pioneers in this field (Link 15). The uses of this technique
could range from curing Parkinson’s disease and epilepsy, restoring vision, to
further understanding and mapping of the brain and the central nervous system.
