Saturday, June 29, 2013

Sweaty, smelly Saturday - review of odor processing from the nose

It's Saturday, and the heat has reached Orange County. MOH and I went out for our weekly trip to the farmer's market and it was blistering hot. It's not normally too hot in the OC, so when it spikes above 80, things get sweaty real quick. Needless to say, this week we will not be eating my favorite summer soups - no malabar spinach, no amaranth soup. It's stir fry and pasta this week!

This week my baby sister is visiting us and my parents have sent us some great homecooked viet food that's always a treat. My parents sent along dried fish, a gallon of honey (so good - it's really pure, granulated honey that tastes great with ANYTHING), tom kho tau (sauteed prawns cooked in its roe - sounds weird, but really delicious), and finally..... drumroll..... lemongrass tofu! After reading this list, you're probably thinking.. of everything listed, you're most happy about lemongrass tofu?!?! No, this tofu is amazing. It's very simple in principle - get tofu packed in water, pat tofu dry and slice thick squares of tofu. Then, deep fry tofu to a crisp (don't use tofu that's already been deep fried - frying tofu that's been sitting in water is more effort, but tastes far superior, trust me) and fill with stuffing of your choice. For me, I love a garlic-lemongrass sautee mixture, but tofu will go great with any type of filling (eggplant shallot mixture would taste just as good!).



This dish is very aromatic and lends to the fragrance of the lemongrass and garlic filling. To get the filling, my mom simply sautees garlic, lemongrass, and thai chilis, seasoning with a bit of salt. Then, when the tofu crisps are cool, you can split the tofu in halves and place filling. It's a very sharp, spicy smell, and it catches your interest right away. 
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So, how is smell accounted for in our brain? How does our brain tease apart the difference between the suffocating B.O. in a crowded gym versus the sweet smell of blueberry shortbread cookies? Extreme examples of two types of smells, but you get the picture.

Our ability to discriminate between various odors is dependent upon the different odorant receptors, or sensors in our nose that are sensitive to specific odor molecules (more comprehensive review in Mori et al., 1999). Mammals are equipped with as much as 1000 odorant receptors. Each receptor is specific for sensing a particular odor molecule. 


The odor molecules come in through our nose and bind onto different odor sensors on cells called olfactory sensory neurons (OSNs) along our olfactory epithelium in our nose. 
Each OSN is specialized to be specific to a particular odor molecule, whether it's the scent of a ripe habanero pepper or fresh-out-of-the-oven chocolate chip cookies. Furthermore, each OSN only has one receptor that codes for a particular odor. So what exactly happens with a complex odor, like what you'd experience at a bakery? BTW, there's this awesome bakery in Huntington Beach, the Donuttery, that has the BEST red velvet donuts. I would pass up a red velvet cupcake for one of their donuts. If you're stuck with the late night munchies, or just need to satisfy that sweet tooth, run here. They're open pretty late.

Lots of great concoctions, but red velvet (right hand side, fourth from back) is the best!
Imagine that you're actually at a bakery -  you have wafting scents of flavors (blueberry, strawberry, maple, and chocolate),  pastry varieties (donuts, bagels, croissants), and beverages (coffee, tea, milk). The different odor molecules (like blueberry versus coffee) bind onto their specific receptors on the OSNs. In turn, the odor signal received by the OSN travels to the first "smell" region of your brain, the olfactory bulb, where it terminates on the glomerulus, a specific cell structure that is responsible for acting as a gatekeeper for all the odor-information processed by your nose. The glomerulus acts as a relay center where it receives all the signals from your OSNs, bundles this information, and sends it up to the olfactory cortex, where all the information comes together for you to perceive particular smells. 


(this Science cover features staining of the olfactory bulb - the dots in blue are the individual glomerulus. The long lines stained are the connections that originate from the OSNs.The lines represent where odor information travels before it hits the glomerulus.)

While the actual storage and synthesis of olfaction-mediated memories are performed in higher brain regions like the orbitofrontal cortex and amygdala (see previous posting), our brain dissociates different odors by what combination of OSNs are activated in our noses. So the next time you're at your local bakery or hitting up your favorite food truck scene and you get a whiff of all your favorite scents, think back on how precisely your nose receptors can parse out different scents. Amazing, right?

Happy dining all! 

PS. Be on the lookout for my next posting: culinary experiment 1 - quinoa sliders > meat sliders? Stay tuned for the results! Granted, the poll will be conducted with an n of 3, results will be reported nonetheless!



References:
Mori et al., 1999. The olfactory bulb: coding and processing of odor molecule information. Science. 286 (5440): 711-5. 

Costanzo RM. 2005. Regeneration and rewiring the olfactory bulb. Chemical Senses. 133-4.

Friday, June 21, 2013

Smelly ode to HM

Hey, it's Saturday! Saturday has officially become the farmer's market trip day, bake kale chips, eat all said kale chips, and then eat what my other half (MOH) decides to bake. MOH's been really into baking lately.


My my, what beautiful feet you have my lovelies!

It started off real innocent with trying to master macarons, which after several batches, not wearing a belt anymore, and now sporting a maca-belly, the final product was ah-mazing. I figured after getting macarons down, MOH was going to hang up his apron, but the cookies, brownies, custards, and cupcakes keep coming.

This weekend MOH's decided to make the best of our last quinoa batch (I made the stupid mistake of buying quinoa in bulk), and he decided to make almond cranberry quinoa cookies (bon apetit inspired recipe). Absolutely delicious - the cookies taste like scones with a great bite from the crunchy quinoa. Seriously, if you like quinoa, or have lots of it to use, I'd strongly suggest trying to use your leftover quinoa for making a savory dessert. And this cookie tastes great with tea! These cookies smell good, too. Really good. There's that great lingering aroma of baked goodness and the cranberry/almond mixture is so tantalizing.



It's funny how much better things taste when they smell good. It sounds so DUH, but it's really amazing how much smell contributes to our perception of good food. For me, nothing beats scarfing down a cookie hot out of the oven (burns my fingers, but so good going down). That smell of molten chocolate chips can brighten up any day for me. Then there's the opposite, when food smells too alien that any interest in trying it is lost. Case in point: durian. The foot-like smell of durian is too much for some people to enjoy this exotic fruit - if you're really daring, I'd strongly suggest durian ice cream!

Thinking about how much smell affects our ability to appreciate food, I thought about if there were any documented cases of individuals with brain deficits that also had any problems with discriminating smell. Doing a quick search, I came across a really famous patient named HM who was well known for having an inability to create new memories. If you've taken any neurobiology or learning/memory classes, you're probably familiar with the famous HM. HM was a male who suffered with cerebral seizures for many years before finally getting a surgery at age 25 to treat his epilepsy.


The surgery removed HM's medial temporal lobe, including the brain regions called the amygdala, parahippocampal gyrus, and hippocampus (Scoville et al., 1953). While the amygdala was already documented as being important for emotion, the parahippocampal gyrus and hippocampus were relatively unexplored in terms of memory.



While the seizures were gone, HM's ability to form new, declarative memories was affected. Declarative memory is the ability to remember facts or knowledge. Non-declarative memory refers to unconscious memories and skills (like riding a bike). His working, non-declarative memory was intact, as he could do several motor tasks just as good as any normal subject. While he faced severe anterograde amnesia, or the ability to form new memories, his childhood memories as well as most past memories (retrograde amnesia) were relatively intact (Scoville et al., 1957). HM's unique case really opened the field of neuroscience in providing insight into different memory types as well as demonstrated how different brain functions are localized within the brain. What I didn't find out until recently though was his memory deficits also included olfactory deficits, or the ability to identify aromas  (Eichenbaum et al., 1983). 

In HM's case, HM was able to tell different concentrations of food, but couldn't tell the difference between different odors. He described several common odors incorrectly, oftentimes giving descriptions of the odors that had no relation to the odor itself. Some examples included describing raspberries as smelling like "carrion, like a squirrel," or vanilla like "freshly made paper." He could still smell, and was able to identify the odors when given a visual cue, but his ability to discriminate odors was severely impaired (Eichenbaum et al, 1983). 

Beautiful photo of canh chua, courtesy of Jason Hutchens

Imagine if you had to go about your everyday life with the inability to smell. It's something that we take for granted, and sometimes we even wish we didn't have (you know those times). But without the ability to smell, the enjoyment of food drastically changes. Probably half the enjoyment behind having great food is taking in the variety of different aromas that culminate together to create this cohesive dish. Think about how much food sucks when you're sick - I personally feel that everything I eat tastes like salted water when I'm not feeling great. I think the best part of eating things like a really good pasta dish is the fragrant basil, or pesto topping, or the deep aromatic tomato sauce. 

So the next time you're out and about town, maybe hanging at your favorite food truck, or dining at that cute hole-in-the-wall lunch joint, take a moment to smell all the different food aromas that are surrounding you. We don't even consider how much smell can affect our interest and desire to take in that additional cake slice, or that additional helping of sour tamarind soup (canh chua) on a cool day. 


Happy dining all! 

PS. If you were interested in learning more about how sensory information like smell and taste is processed in the brain, tune in for next week's posting! 


References:

Scoville et al., 1953. Observations on medial temporal lobotomy and uncotomy in the treatment of psychotic states. Research publications - Association for Research in Nervous and Mental Disease. 31: 347-73.

Scoville et al., 1957. Loss of recent memory after bilateral hippocampal lesions. Journal of Neurology, Neurosurgery and Neuropsychiatry. Feb; 20(1):11-21.  

Eichenbaum et al., 1983. Selective olfactory deficits in H.M. Brain. 106: 459-72.



Saturday, June 15, 2013

Behind the title

Welcome to Amygdaleats! First off, thanks for tuning into this blog - I hope you find it entertaining and informational (or at least enjoy my random ramblings).

I'm a third year graduate student studying how the brain develops specific connections
in both development and following injury to the system. When I'm not at the lab running my experiments, I'm normally at my apartment running culinary experiments from recipes that I either get from friends, other food blogs, or online (I regularly troll Epicurious and allrecipes). While I've always been interested in biology, my love for food and experiencing good, unique foods, ocurred during my undergraduate years where I took up cooking as a hobby and as a stress-reliever. This hobby has turned into an ongoing love-affair that has transformed into trying various recipes at home, to sampling different cuisines while out and about southern
California. My love for all things science and food has been the spearhead of this blog.

And who wouldn't love food?!

Food has so many dimensions, especially in terms of how it relates to science.

1. Food and health: certain foods are great for increasing our well being in preventing disease progression. Think about how many studies are out there about the benefits of red wine, dark chocolate, blueberries or other antioxidant-rich "superfoods" that are published every year (one review of many: Parletta et al., 2013, Journal of Nutritional Biochemistry). We eat certain foods to gain more muscle, be healthier. Then, there's the flip side - how diets rich in saturated fat increase cholesterol and are linked to increased risk of heart disease.



2. Food and emotion: probably one of my best childhood memories was Saturday mornings catching up with my family on daily news over a warm bowl of hu tieu. My mom would make a large vat of delicious pork broth and serve rice noodles over seafood and fresh scallions, bean sprouts and herbs. Now, whenever I have hu tieu at a restaurant, or make it at my apartment, I'm always thinking back on being with my family, comforted by loved ones. Whether it's remembering an important personal event, or remembering an important person, food can illicit some of the strongest emotions. We eat because we're sad, happy, angry, or even just bored. Emotions ranging from extreme pleasure to intense rage are all processed in a subcortical region called the amygdala. Even though the amygdala is most well known for encoding fearful memories, strong emotions can activate the amygdala. Food can even evoke some of the best pleasures known to life - ever experience a "foodgasm?" Whether it's reflecting back on the nostalgic feelings of having hu tieu (seafood noodle soup) crafted by my mom, or enjoying an omakase meal for your birthday, emotional memories of all kinds, even food-related, are encoded in some part by the amygdala.



3. Food and the brain: how exactly is food encoded in our brain? The basis of food relies on the different flavors that come together to make things like a sweet bread pudding, tangy tartare, or savory pesto. Taste itself follows a one cell to one tasting code in order for the information to be neurally processed in our primary taste cortex, the insula. Researchers have even discovered a "map" that has different flavor profiles mapped out in the insula (Chen et al., 2011, Science). The insula isn't the only brain region that's responsible for encoding our perception of food - other parts of the neocortex like the orbitofrontal cortex and subcortical areas like the nucleus accumbens and amygdala are important for our perception of food and pleasure behind scarfing down that umpteenth cookie (reviewed in Berridge et al., 2010, Brain Research - neural regions important for taste reviewed, not why I ate that extra few cookies). All these brain regions collectively compute together all our sensory food information and are responsible for generating that immense pleasure behind digging into a decadent tiramisu after dinner.



Long rant, I know. I promise that this is the last time I ramble about why I love food (hopefully). But you get the general idea behind this blog, and hopefully, you can see the rationale behind the title "amygdaleats." Tune in for more posts ranging from fun recipes to try, interesting reviews on science articles pertaining to food science, or just random postings related to foods!

References:

Parletta et al., 2013. Nutritional modulation of cognitive function and mental health. Journal of Nutritional Biochemistry. May 2; 24 (5): 725-43.

Chen et al., 2011. A gustotopic map of taste qualities in the mammalian brain. Science. Sep 2; 333 (6047): 1262-6.

Berridge et al., 2010. The tempted brain eats: pleasure and desire circuits in obesity and eating disorders. Brain Research. Sep 2; 1350: 43-64.