Author Archives: Ju-Han Yao

This past Friday (June 21^st) is the annual Paris Fete de la Musique, or the Paris music festival.  European countries such as France have a long history of successful musicians creating magnificent masterpieces.  To this day, we often have the opportunity to listen to street musicians perform in the metro station, on the RER, or just by the side of the streets.  Because of the easily available music in pretty much every single metro station of Paris, you might think that the Fete de la Musique is nothing special.  However, it is completely different.

Notre Dame

The party started around 4pm as musicians began to set up their own speakers and instruments on almost every single street and bar of Paris.  We went to Notre Dame as our first stop and we were already welcomed with all different genres of music from classical to folk to choral to bass-thumping club music.  As we wandered around on the side streets near Notre Dame along with hundreds of other people, stopping at different concerts and listening to different street musicians playing, I noticed my ability to focus on the music I want to enjoy despite all these background noises.  Somehow, my brain was able to do a descent job ignoring noises consisting off motorcycles, tourists asking for directions, nearby musicians, and drunk people singing out of tune.  However, the occasional car honking sounds can still distract me from the beautiful music of the Fete de la Musique.

Musicians at Fete de la Musique

Musicians at Fete de la Musique

A little bit a research shows that there is biological basis behind our ability to ignore background noise and focus on the wonderful melodies of music.  A study done by Perez-Gonzalez et al. (2005) found a type of neuron that will respond to novel sounds but not a repetition of sounds; it is located in the inferior colliculus (IC) of rats, part of the midbrain nuclei that receives input from the auditory cortex and peripheral auditory pathway.  Specifically, this type of neuron is named “detector neuron” and shows stimulus-specific adaptation (SSA) in which these neurons are able to detect all frequencies of sound within the rats’ hearing frequency range, but will stop firing if the same pitch of sound is repeated at 0.5 hertz or higher.  However, the firing of these neurons can be brought back when a sound of a different pitch is introduced (Perez-Gonzalez et al., 2005).  Although discovered in a rat model, it is possible that humans also have the same kind of neurons. This would explain why I was able to filter out constant repeated background traffic noise when listening to the changing notes of a classical masterpiece that a violinist was playing.  However, when a car honked, I would get distracted because this type of detector neuron will fire to the sudden change in pitch of the traffic noise caused by the honking sound.

More recently, research on shifting attention between different sound sources further differentiated between a top-down (voluntary) and bottom-up (involuntary) shift of auditory attention.  For example, I made the conscious choice of focusing on the violinist playing music; this is a top-down shift of attention.  However, when a car honking noise surprised me and caught my attention, it is a bottom-up involuntary shift of attention.  To test the difference in brain activation, Huang et al. (2012) used fMRI while testing 19 healthy subjects on hearing tests.  Specifically, in a 10-second trial, the healthy subjects were informed to wait for a “cue” (sound) at the ear where a subsequent  “target” sound is likely to appear.  After the cue sound, the subjects were instructed to pay attention to the ear that received the cue and press a button as fast as possible right after hearing the target sound.  However, in 20% of the trials the “target” sound is replaced by a novel sound opposite to the ear that received the cue in order to trigger involuntary attention shift (Huang et al., 2012).  The fMRI results showed different activation pattern of the brain between voluntary cued attention shift and the involuntary novel sound attention shift.  For voluntary attention shift, superior / posterior intra-parietal sulcus (IPS), located on the surface of the parietal lobe and precentral areas such as Pontine micturition center (PMC), part of the brainstem and frontal eye fields (FEF), a region of the prefrontal cortex, are more activated.  For involuntary attention shift, inferior IPS, posterior superior temporal sulcus (STS), and temporal parietal junction (TPJ) are more activated.

Intraparietal Sulcus (IPS)

Frontal Eye Fields

Temporoparietal Junction (TPJ)

Superior Temporal Sulcus (STS)

While knowing all these different brain regions can be confusing and might not be necessary, it is more important to recognize the idea that this study demonstrated two types of auditory attention shifts supported by the evidence of different brain activations using fMRI.  One potential flaw of this study is the inherent difficulty to distinguish whether the brain areas activated are due to attention shifting or other pathways that happens to be activated by the auditory stimuli.  In addition, a slightly bigger sample size would increase the credibility of this study. Despite these flaws, combining the more macro view of brain area activations of voluntary and involuntary attention shift to the micro view of specific neurons that fire when a novel auditory stimulus is introduced, researchers have gotten closer to understanding the complex auditory system that enables us to filter out sound waves that are not important and only focuses on the sounds that are more important such as the wonderful music at the Fete de la Musique.

-Eric Yao

References:

Huang S, Belliveau JW, Tengshe C, Ahveninen J (2012) Brain networks of novelty-driven involuntary and cued voluntary auditory attention shifting. PLoS One 7:e44062.

Perez-Gonzalez D, Malmierca MS, Covey E (2005) Novelty detector neurons in the mammalian auditory midbrain. The European journal of neuroscience 22:2879-2885.

This afternoon we went to the museum of perfume near the Paris opera house off Metro 8.  The museum is opened by a perfumery called Fragonard Parfumeur.  Fragonard Parfumeur was established shortly after WWI by an entrepreneur named Eugene Fuchs in 1926.  During the tour, we learned about different concentrations of perfume, their making techniques as well as the correct way to put perfume on yourself.  For example, Eau de Toilette is around 10% aromatic compound while the actual perfume is 20%.  Towards the end of the tour, we were given strips of paper scented with different perfumes.  One particular perfume named “Juste un baiser” or “Just a kiss” smelled sweet.  The perfume almost smelled like strawberry and mandarin orange dipped in honey.

Map of the Museum of Perfume

It is interesting how people often use adjectives for taste, or even food items to describe a smell.  We don’t hear people say this flower smells red, or this perfume smells loud.  This must indicate that there are some sort of overlap of brain processing for taste and smell.  This phenomenon is called “synesthesia” in which the stimulation of a sensory pathway leads to involuntary activation of a separate sensory pathway.  There are many different types of synesthesia that are not common to the majority of us.  For example, people with color-graphemic synesthesia view letters and numbers with a specific color (Rich and Mattingley, 2002), and people with number-form synesthesia view numbers in a specific location in space (Sagiv et al., 2006).  Therefore, odor-induced taste might be a universal form of synesthesia that most of us have experienced.

Different types of perfume

If odor-induced tastes are so similar to taste itself that people describe an odor “sweet”, then these odors are probably processed in the same area of the brain as tastes.  Not surprisingly, there are already multiple papers suggesting that the insula, part of the primary gustatory cortex that is responsible for the initial processing of gustatory signals, is also activated by odors that are able to induce taste-like sensations (Stevenson and Miller, 2013).  Instead of looking at the primary taste cortex, Stevenson and Miller (2013) investigated the two secondary gustatory processing areas of the brain: the orbitofrontal cortex (OFC) and the amygdala to see whether odors that induces tastes-like sensation are also processed through similar areas of the brain.  To test their hypothesis, they put 9 patients with brain resections in the anteromedial temporal lobe (AMTL) that included the amygdala, 3 patients with OFC damage, and 42 healthy controls through a series of gustatory and olfactory tests.  All test subjects were presented with 2 sweet-smelling odors (chocolate and plum) and 2 non-sweet-smelling odors (Vegemite and oregano).  An “odor-taste quality score” was based on the test subjects’ ratings of whether a smell is sweet, sour, salty, or bitter compared to the expected taste of the odor (Stevenson and Miller, 2013).  The result of this study shows that AMTL patients, while impaired in gustatory senses, were unimpaired in odor-induced taste tests.  On the other hand, one of the three OFC patients who was severely impaired in gustatory senses, was also impaired in odor-induced taste tests.  The data indicates that one of the two secondary gustatory processing areas, the OFC, is involved in both the processing of tastes, and odor-induced tastes.  Stevenson and Miller (2013) further showed that OFC and insula both have the same type of cells that are more responsible for the discrimination of tastes while the amygdala has cells that supports the recognition of tastes.  This is probably why both the insula and the OFC are needed for the processing of odor-induced tastes while the amygdala is not.

Red part shows the amygdala.

Green part shows the Orbitofrontal cortex (OFC)

This study shows that odor-induced taste is a type of synesthesia that is experienced by the majority of us, which also explains why we often use gustatory adjectives to describe a smell.  However, I think further research is needed to prove this concept because of the low sample size and the fact that only 1 out of 3 OFC patients showed correlation between impairment of taste and odor-induced taste.  In addition, there might be other unknown brain-related problems in these patients, which will affect the interpretation of the data.  Furthermore, an fMRI study of the areas of the brain are active during odor-induced taste tests could potentially provide a more accurate indicator for the overlap of brain processing area of taste and odor-induced taste.  Aside from all the potential flaws of the study, at least now we know that there are biological evidences behind all the taste and food-related description of different kinds of perfume!

-Eric Yao

References:

Rich AN, Mattingley JB (2002) Anomalous perception in synaesthesia: a cognitive neuroscience perspective. Nature reviews Neuroscience 3:43-52.

Sagiv N, Simner J, Collins J, Butterworth B, Ward J (2006) What is the relationship between synaesthesia and visuo-spatial number forms? Cognition 101:114-128.

Stevenson RJ, Miller LA (2013) Taste and odour-induced taste perception following unilateral lesions to the anteromedial temporal lobe and the orbitofrontal cortex. Cognitive neuropsychology 30:41-57.

This past Saturday, we took a three-hour bus ride from Paris to the Loire Valley to visit two famous chateaus:  the Château de Villandry and the Château de Chenonceau.  Château de Villandry especially caught my attention because despite its rather plain exterior compared to other chateaus. It has one of the most beautifully designed gardens.  Château de Villandry have a long history since the 14^th century, but most recently, Joachim Carvallo, a Spanish doctor and researcher, bought the property in 1906. As we stood on the upper levels of the chateau, I was amazed by the geometric designs of the decorative gardens that represented tender, passionate, fickle, and tragic love.  Carvallo renovated the château and designed medicinal gardens to further his research.  In addition to the medicinal herb garden, there are also flower gardens, vegetable gardens, and waters gardens, which are representative of renaissance style chateaus.

Chateau de Villandry

Decorative gardens in Chateau de Villandry

The medicinal herb garden is farther away from the main building because it was built in the 1970s by Carvallo’s grandson according to his original design.  The garden contains various different types of herbs, roots, and leaves that have therapeutic properties.  As I was meandering through the garden slowly, a slight scent of minty lemon caught my attention.  The scent originated from a little bush with green leaves that resembled the shape of mint leaves.  A little web browsing showed that the plant is called lemon balm, or Melissa officinalis.  Lemon balm is usually used to make herbal tea, which I don’t particularly like.  However, since Carvallo chose to have lemon balm planted in his herb garden, I am curious to find out the beneficial effects of this nice smelling plant.

Lemon balm has various therapeutic properties ranging from lowering anxiety to treating Alzheimer’s disease (Maguire et al.).  Lemon balm has such a wide variety of therapeutic uses because of its effects in many neurotransmitters that are important for neuron communication in the body.  Neurotransmitters are molecules secreted by one neuron to another for signaling purposes; most of them can be divided into two categories.  One group of neurotransmitters will increase the activity and electrical firing of the recipient neuron.  The other group of neurotransmitters will decrease the activity and electrical firing in the neuron receiving the molecules.

Lemon Balm (By quinn.anya)

Among many studies investigating possible usages of lemon balm for treating different diseases, a study on lemon balm extract’s ability to induce neurogenesis in dentate gyrus of hippocampus, an area of the brain that is responsible for forming new memories, seems particularly promising for treating many memory related diseases such as Alzheimer’s (Yoo et al., 2011).  Neurogenesis in the dentate gyrus focuses on the formation of granule cells, a cell type that is thought to be responsible for spatial memories (Colicos and Dash, 1996).  The process of neurogenesis starts with the proliferation of granule cell progenitors in the subgranular zone, which then migrate to the granule cell layer where the new granule neuronal cells are made (Yoo et al., 2011).

To see if lemon balm actually promotes neurogenesis, Yoo et al. set up three groups of mice.  The first group was fed with 50mg/kg lemon balm extract, the second group received a higher dose of 200mg/kg, and the last group is a control group in which the mice were fed with distilled water (Yoo et al., 2011).  All three groups were fed once a day for 21 days.  To track the effect of lemon balm on neurogenesis in the dentate gyrus, we have to monitor several proteins that are produced as by-products of neurogenesis.  Ki-67 is a protein that will be present in the cellular nucleus during cell proliferation.  DCX, another protein, is expressed in immature neurons, which is indicative of new neuron formation.  To see if these proteins are made in the dentate gyrus, antibodies that will attach themselves specifically to these two proteins were used.  To quantify how many antibodies are attached to these two proteins, a stain was performed on sections of the dentate gyrus after the antibodies were administered (Yoo et al., 2011).

The results of this study is astonishing in which there is a 7-fold increase in the level of Ki-67 in the mice group that received 200mg/kg lemon balm compared to the control group that received water.  Similarly, there is also significant increase in the level of neurons expressing DCX in the dentate gyrus for the two experimental groups that received lemon balm extract (Yoo et al., 2011).  The combined increases in expression of these two proteins indicate that neurogenesis of granule cells are increased due to the intake of lemon balm extract by the mice.

Although there are still many differences between mice and human, I think it wouldn’t hurt to drink some lemon balm tea once in a while.  If granule cell neurogenesis can be induced by lemon balm extract as suggested by the mouse model, drinking some lemon balm tea might actually improve my spatial memory and help me navigate through the complex RER and metro system in Paris! 

-Eric Yao

References:

Colicos MA, Dash PK (1996) Apoptotic morphology of dentate gyrus granule cells following experimental cortical impact injury in rats: possible role in spatial memory deficits. Brain Research 739:120-131.

Maguire MA, Dvorkin L, Whelan J Boston Healing Landscape Project – Melissa Officinalis. In. Boston University School of Medicine.

Yoo DY, Choi JH, Kim W, Yoo KY, Lee CH, Yoon YS, Won MH, Hwang IK (2011) Effects of Melissa officinalis L. (lemon balm) extract on neurogenesis associated with serum corticosterone and GABA in the mouse dentate gyrus. Neurochemical research 36:250-257.