Ancient Egyptians are one of the oldest known civilizations to have studied the brain, providing new information studied by scientists later in time. Specifically, the Ancient Egyptians provided the world with some of the first written accounts of the anatomy of the brain: meninges and cerebrospinal fluid¹. In particular, the Edwin Smith Papyrus contains 48 surgical cases that mention these parts of the brain. The Edwin Smith Papyrus was around 5 metres long when first written by the Ancient Egyptians, but half a meter of the document has since gone missing¹. 

Sources: 
1) https://faculty.washington.edu/chudler/papy.html 

Alcmaeon of Croton was affiliated with Magna Graecia, which was one of the most famous and reputable medical schools during this era¹. Croton was seen as a talented scientist who was masterful in his use of vivisection: the dissection of live animals. Through the use of vivisection, Croton was able to state that the optic nerve is necessary for vision². This finding is still valid to this day and interested philosophers and scientists to find out more about the brain. 

Sources: 
1) https://plato.stanford.edu/entries/alcmaeon/ 
2) https://www.britannica.com/biography/Alcmaeon-Greek-philosopher-and-physiologist

Haller performed many experiments at the University of Gottingen, making an important discovery in the year of 1747. After many trials of experiments, Haller observed that the liquid surrounding the brain would secrete into the ventricles, which were then absorbed by the veins. Haller provided this important detail of the brain which intrigued other philosophers¹. As this discovery was made from an external view of the brain, scientists started to become curious of the brain in a more microscopic manner. 

Sources: 
1) http://www.annclinlabsci.org/content/33/3/334.full

One of his most notable was in regards to nerve cells. During Dieter's time, he was able to create one of the most descriptive observations of the nerve cell in his time. Dieter's noted two parts of the cell: the axon and dendrite. Dieter further emphasized that nerve cells have single axons, while having several dendrites². Dieter's started to somewhat speculate that there was some sort of signal flowing through the neurons, which started to become researched by other philosophers interested in neuroscience. 

Sources: 
1) http://mrcanu.pharm.ox.ac.uk/sites/default/files/pdf_files
/23316_ftp.pdf
2) https://pubmed.ncbi.nlm.nih.gov/23436306/

In Golgi's time there was a limited option of staining techniques available, with carmine staining being the most prominent. However, the quality of carmine staining wasn't the best. Neuroscientists were able to see the neurons under the microscope, but clear distinctions were difficult to identify². Golgi started to experiment with different elements such as gold and mercury. With minimal success, Golgi then tried exposing the nerve cells using silver nitrate¹. The utilization of silver nitrate allowed Golgi to see the neuron in its entirety, which was quite significant to the field of neuroscience. 

Sources: 
1) https://www.nobelprize.org/prizes/medicine/1906/golgi/bi
ographical/
2) https://www.sciencedirect.com/topics/medicine-and-dentistry/carmine

Nissl was a motivated researcher and quite competitive. The medical faculty at Ludwig Maximilian University created a competition in the field of neuroscience for researchers to win a grand prize in the year of 1864. Nissl proceeded to win this competition in 1865 due to his innovative stain allowing different parts of the neuron to be visible². Nissl first took the cerebrum and fixed the organ in alcohol while simultaneously adding varying pigments. With this technique, Nissl was able to identify the endoplasmic reticulum of a nerve cell². This then allowed later scientists to differentiate between neurons and glia, while also revealing another piece of information regarding the structure of the neuron. 

Sources: 
1) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6753910/
2) https://jamanetwork.com/journals/jama/fullarticle/340200

After assisting these great scientists, Weigert was offered a position to become director of a pathological-anatomical institute of the Senckenberg Foundation in Frankfurt, Germany. During his time at this institute, Weigert conducted many experiments, with one of his most notable experiments being in the field of neurohistology. Weigert provided a manner in which scientists could stain myelin sheaths². With this advantageous discovery, many new experiments in neurohistology started to come about. 

Sources: 
1) https://litfl.com/carl-weigert/
2) https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/weigert-carl

Cajal attained his license in medicine at the University of Saragossa and proceeded to work as an army surgeon in the year of 1873. After working as a surgeon for the army, Cajal transitioned to medical work in academia. Cajal was appointed as Professor of Histology and Pathological Anatomy at Barcelona in the year of 1887 and in Madrid in the year of 1892¹.

In the 1880's, Cajal started to publish a lot of his scientific work with the most notable publication in the year of 1890: New Ideas on the Fine Anatomy of the Nervous System. In this publication, Cajal came out with his important theory that heavily influenced the neuron doctrine. This theory being that the neurons are not an intertwined continuous network, but rather discrete building blocks that have gaps between one another. In 1906, Ramón y Cajal was awarded the Nobel Prize for his influential work on understanding the nervous system¹. 

Cajal later passed away in October of 1934 with many achievements accomplished in his lifetime¹. 

Sources:
1) https://www.nobelprize.org/prizes/medicine/1906/cajal/biographical/

A scientist by the name of Santiago Ramón y Cajal took interest in the Golgi stain and worked on improving the technique. Cajal was known for his artsiness, drawing many of his observations through a microscope¹. In the year of 1889, Cajal presented some of his work to the Congress of German Anatomical Society at the University of Berlin. In this meeting, Cajal proposed that there was no direct connection between each nerve cell, drawing his Golgi stain observations¹. 

Sources: 
1) https://www.sciencefocus.com/the-human-body/memory-and-the-brain-the-key-discovery-of-santiago-ramon-y-cajal/

Golgi maintained a reticular view of the nervous system, which was a concept derived from German anatomist Joseph Von Gerlach. The reticular theory stated that the nervous system was one whole continuous network. On the other hand, Cajal believed that each neuron was independent of one another, but established a variety of different connections². Cajal's theory still holds true to this day.

Sources: 
1) https://pubmed.ncbi.nlm.nih.gov/11624298/
2) https://www.frontiersin.org/articles/10.3389/fncel.2019.00187/full

The neuron doctrine contains many important observations that were made throughout time in the field of neuroscience. To further emphasize, work done by Jan Purkinje, Gabriel Valentin, Wilhelm His, and a few other scientists are included within the neuron doctrine¹. To this day, many experiments are heavily influenced by the neuron doctrine.

Sources: 
1) https://www.sciencedirect.com/topics/neuroscience/neuron-doctrine

Scientists today have taken an important step to understanding the brain even more. With innovative technology, scientists have been able to render 3-D models of the cerebrum. For example, a neuroscientist by the name of Tony Zador was able to map out 50,000 neurons in the cerebral cortex of a mouse using brain mapping technology. Within the mapping of the brain, the cell bodies and axon branches of the neurons are able to be seen distinctly, too¹. With the creation of this technology, the opportunities of research in the field of neuroscience can be expanded upon exponentially. 

Sources: 
1) https://www.quantamagazine.org/new-brain-maps-with-unmatched-detail-may-change-neuroscience-20180404/