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This image demonstrates the seven category system of odors that was created by Carl Linnaeus in 1752¹. This system described the the seven most "important" odors as labeled by Linnaeus and included camphoraceous, musky, floral, pepperminty, ethereal, pungent and putrid¹. This was an important discovery because scents were now able to be labeled when people smelled them. This generalization helped categorize what certain smells were.
This system was created in the 18th century and was one of the first discoveries related to the sense of olfaction¹. Since olfaction is a sense that was not studied much, this somewhat late discovery kick started odor classification which then influenced the research on how the sense of smell worked.
This discovery was created in Sweden, but it was probably beneficial all around the world as everyone was able to label what they were smelling¹. This discovery is relevant today as there has always been a lot of gray area surrounding the sense of smell and this marked an initial finding that lead way for a lot more research. The olfactory nerve is closely connected to the brain, so the categorization created opportunities for research that studied how different scents affected the brain.

Sources:
(1)
https://www.cambridge.org/core/journals/journal-of-laryngology-and-otology/article/brief-history-of-olfaction-and-olfactometry/8BDD5D4C770382CC232AF1F1DD424CEA

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The 9 olfactory categories and the olfactometer

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The 9 olfactory categories and the olfactometer

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About 100 years after Carolus Linnaeus categorized scents into 7 types, Hendrik Zwaardemaker created a new system for scent labeling that consisted of 9 scents. These included ethereal, aromatic, fragrant, ambrosiac, alliaceous, empyreumatic, hircine, foul, and nauseous⁴. The addition of 2 new scents meant that there was even more possibility for labeling now. This meant that more research could be done on the olfactory system and how scents were identified.
Zwaardemaker also created the olfactometer in 1888 at the University of Utrecht which was a device used to measure olfaction¹. An odorant was drawn up into the nose through a tube and the amount of odorant was determined by the length of the tube³.
This creation was beneficial to neuroscience because he used it to determine defects in olfaction and measured things such as absolute threshold, difference threshold, reaction time, and adaptation². This was the start of neuroscience research on the sense of smell. His research on how smell is detected was especially relevant to neuroscience as we now know that thresholds occur because a certain limit has to be reached for neurons to fire.
Sources:
(1)
https://books.google.com/books?id=_GMeW9E1IB4C&pg=PA186&lpg=PA186&dq=Zwaardemaker+olfactometer&source=bl&ots=kpR1IVCZg0&sig=ACfU3U1lBSdaNFhIWgBzGhBB2oo1yA75nA&hl=en&sa=X&ved=2ahUKEwihxayO1qr3AhWYCjQIHUaVA1cQ6AF6BAgZEAM#v=onepage&q=Zwaardemaker%20olfactometer&f=false
(2)
https://en.wikipedia.org/wiki/Hendrik_Zwaardemaker#:~:text=Hendrik%20Zwaardemaker%20(10%20May%201857,Academy%20of%20Arts%20and%20Sciences.
(3)
https://www.oxfordreference.com/view/10.1093/oi/authority.20110803133602425
(4)
https://www.cambridge.org/core/journals/journal-of-laryngology-and-otology/article/brief-history-of-olfaction-and-olfactometry/8BDD5D4C770382CC232AF1F1DD424CEA

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The image above is Bernard Von Gudden's drawing of Unilateral Nostril Occlusion in a young rabbit's brain¹. In 1870, Gudden performed many studies where he was trying to determine how occluding certain components of sense affected the sense. He studied how occluding a nostril affected the olfactory bulb in newborn rabbits and found that occluding a nostril reduced the size of the olfactory bulb six weeks later¹.
This was one of the first studies performed on identifying how the olfactory system worked, especially the olfactory bulb. Gudden studied the senses in great detail, mainly focusing on the eyes, but also dabbled in the other senses. His findings were beneficial for all researchers but many did not know about them until later.
It was impactful on neuroscience because a mechanistic view of olfaction was present.

Sources:
(1)
https://www.hindawi.com/journals/np/2012/351752/

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Soon after the creation of the olfactometer Hans Henning, in 1916, created the Smell Prism². He believed that olfaction would be better represented in a prism and a smell would be present in one of the corners of the prism². Henning also hypothesized that if these odors are mixed in the proper proportions then any smell could be created¹.
He created this in Germany and this was another step in the direction of olfactory research. As more hypotheses were created, more research could be done based on these "guesses". This was revolutionary for the field of neuroscience as the more research that was done outside the nose, the more could be done inside the nose in the future. The study of how scents mixed, meant that there could be differences in how they were perceived. This meant that more research could be done on olfactory sensation and perception.
Sources:
(1)
https://psychologydictionary.org/smell-prism/
(2)
https://www.cambridge.org/core/journals/journal-of-laryngology-and-otology/article/brief-history-of-olfaction-and-olfactometry/8BDD5D4C770382CC232AF1F1DD424CEA

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About 10 years after the creation of the smell prism, Crocker and Henderson created another system for categorizing the four "main" scents in 1927¹. These included fragrant, acid, burnt and caprylic¹. This was probably one of the most organized systems for smell identification and was similar to the Dewey Decimal system, but for odors. This kit was available for commercial purchase which was beneficial for the public. Crocker and Henderson were American Chemists and they created this system to better chemically understand odor interactions¹.
The large variety of hypotheses that were present at this time demonstrated how much there was unknown about the olfactory system. Study into the neuroscience was still very limited at this time, but the study of chemical interactions of odors would be beneficial in determining their chemical interactions in the body and brain.
Sources:
(1)
https://www.cambridge.org/core/journals/journal-of-laryngology-and-otology/article/brief-history-of-olfaction-and-olfactometry/8BDD5D4C770382CC232AF1F1DD424CEA

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The discovery of DNA polymerase occurred around 1956/1957 and it revolutionized the study of DNA and genes². This was discovered by Arthur Kornberg and he identified DNA Polymerase during his studies on the DNA replication mechanism. He also found that the enzyme needed a primer to start copying the template and could only create DNA in one direction¹.
This was founded in the mid 20th century, right before the discovery of PCR. This finding laid the groundwork for how PCR worked and the primers that would be needed to run PCRs. This discovery was made in America, but it was beneficial to everyone¹.
This was beneficial in the field of neuroscience because it allowed more research to be performed on DNA and genes. There is much we didn't know about genes back then, and much we don't know right now, so this discovery allowed for more gene discoveries and neuro-gene discoveries.

Sources:
(1)
https://www.news-medical.net/life-sciences/History-of-Polymerase-Chain-Reaction-(PCR).aspx
(2)
https://www.biomol.com/resources/biomol-blog/the-discovery-of-dna-polymerase#:~:text=On%20April%2016%2C%201956%2C%20about,known%20as%20DNA%20polymerase%20I.

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The Sanger Method of DNA sequence was created in 1977 by Frederick Sanger². He utilized DNA polymerase, a primer, and nucleotide precursors. This method was a precursor to the PCR technique as all of the components used in a PCR were utilized in this technique. Sanger, an English biochemist, won a Nobel Prize for this discovery as it laid the groundwork for the PCR technique¹. This technique was very similar to the PCR technique and it allowed for specific DNA sequences to be identified.
This technique was beneficial to the field of neuroscience because it allowed for the discovery of gene sequencing. Gene sequencing is beneficial for all biological sciences, but since genetic neuroscience research was limited, this technique was an important find.
Sources:
(1)
https://www.news-medical.net/life-sciences/History-of-Polymerase-Chain-Reaction-(PCR).aspx
(2)
https://en.wikipedia.org/wiki/Frederick_Sanger

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The discovery of the PCR by Kary Mullis in 1983 was a profound discovery in the history of genetics and gene mapping¹. Kary Mullis discovered this technique in California and it is now one of the main ways DNA copies are made in laboratory.
During this time, a lot of research was being performed on DNA and genetics. The creation of the PCR allowed for the human genome project to take place a few years down the line. The PCR method was the best method because it was modeled after how a cell actually replicates¹. This way, the provided DNA or gene sequence is able to be amplified in many copies allowing for better research.
This discovery relates to neuroscience because there was a lot of unknown about genes related to neuroscience topics, especially the olfactory system and this machine allowed for that to be changed. More genetics research could be done in the field of neuroscience and the molecular background of neuroscience could be determined.
Sources:
(1)
https://passel2.unl.edu/view/lesson/d81d0eedbada/2

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The University of Pennsylvania Smell Identification Test

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The University of Pennsylvania Smell Identification Test

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The University of Pennsylvania Smell Identification Test was created in 1984 to determine how different people identify smells². The test was created in Pennsylvania and was available to the general public. It was a very simple test that could be self- administered in 10-15 min and was even available in multiple languages¹.
This test determined the intensity that certain people could smell at and categorized people into one of six possible groups. These groups included: normosmia, mild microsmia, moderate microsmia, severe microsmia, anosmia or probable malingering¹. The test also provided an performance percentage depending on age and sex¹.
This test was helpful for neuroscience because certain types of anosmia's could be studied and how the olfactory system differed in these people could be studied. The olfactory system has a large portion relating to neuroscience and this test was beneficial in creating research relating to it.

Sources:
(1)
https://www.cambridge.org/core/journals/journal-of-laryngology-and-otology/article/brief-history-of-olfaction-and-olfactometry/8BDD5D4C770382CC232AF1F1DD424CEA
(2)
https://www.sciencedirect.com/science/article/abs/pii/0031938484902695?via%3Dihub

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The image above is a summary of the findings of Linda B. Buck, the Nobel Prize winner. Buck, an American biologist discovered how the olfactory system worked and how many genes encoded the mechanics of the olfactory system. She conducted research on this between the years 1990-2000 and won her Nobel Prize in 2004¹.
Her research included many components and the PCR technique had an impactful effect. She was able to begin researching genes related to the olfactory system which then influenced her finding how these genes coded for olfactory sensors and receptors. For three years, Buck initially sequenced olfactory genes and this could not have been done without the PCR¹.
Her gene discovery kickstarted her research and she was able to identify the role of GPCR's in the olfactory system and specific components of the sense of smell¹.
Her research was a turning point for the neuroscience of smell because we were finally able to understand this sense after years of confusion and a myriad of theories.
Sources:
(1)
https://www.sciencedirect.com/science/article/pii/S0092867420305055

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The Nobel Prize winner is Linda B. Buck. She won her Nobel Prize in 2004 for detecting how our sense of olfaction works². She, along with Richard Axel, determined how hundreds of genes in our DNA encoded the odorant sensors in the olfactory sensory neurons¹.
Buck conducted her research on olfaction from about 1988-2001. She gained an interest in the brain's cellular activity and the sense of olfaction which inspired her to conduct this research¹.
Buck was not always interested in becoming a scientist and her first attended college to study psychology. She did not enjoy her classes, so she left university to travel and only took classes intermittently¹. Her immunology class sparked her interest in biology, so she continued taking more classes and eventually got a degree in psychology and microbiology¹. She continued her education, receiving a PhD in immunology. She later gained an interest in the brain's cellular activity and the sense of smell, so she conducted research on this and made a life-changing discovery.
Sources:
(1)
https://www.nobelprize.org/womenwhochangedscience/stories/linda-buck
(2)
https://www.nobelprize.org/prizes/medicine/2004/buck/facts/

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Linda B. Buck's findings on how the olfactory system worked inspired further research in olfaction, especially pheromones. There is a lot unknown about pheromones and there is not even certain findings on if pheromones work on humans. However, the knowledge of the workings of the olfactory system has allowed the opportunity for research to be produced relating to pheromones.
The diagram above demonstrates a possible pheromone interaction in females and how that could relate to a sexual response².
A research study conducted in 2013 studied if the molecule androstadienone, largely found in male sweat, affects the female sexual response¹. This molecule was labeled as a possible pheromone and the results indicated that women did perceive men as more attractive when higher levels of androstadienone are present¹.
This research is being conducted in present-day and all over the world, and these findings would be beneficial in understanding what other factors lead to a sexual response in humans and how these alter the brain.
Sources:
(1)
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3987372/
(2)
https://hankeringforhistory.com/the-history-of-pheromones/