intelligent
design as one could ever hope to find in nature.
Taste works the same way, except that flavor receptors are in your tongue. Taste is simpler since
there are only five basic flavors: salty, sweet, sour, bitter, and umami. (What’s umami, you say? It’s
the savory taste that’s found in cooked meat or mushrooms or in the food additive monosodium
glutamate, MSG. There’s no word for it in English, which is why we use the Japanese term.) Each of
these basic tastes has at least one receptor, sometimes more. Bitterness, for instance, is sensed by
dozens of receptors. As animals evolved, they needed to detect toxic chemicals in their environments.
Because toxic compounds came in many forms, it was necessary to have receptors that could detect
all of them. This is why we have a natural repulsion to bitter flavors. This distaste can be overridden
by experience; look at all the lovers of tonic water and coffee.
Why do we call spicy foods hot? The chemical that gives chili and hot sauce their zest is
capsaicin. Your body also uses capsaicin receptors to detect warm temperatures. This is why you
sweat when you eat spicy food—the receptors have what you might call a “hotline” into your brain to
trigger responses to cool you off. You have capsaicin receptors not only in your tongue, but all over
your body. One way to discover this is by cooking with hot peppers and then putting in your contact
lenses. Ouch!
Did you know? Why mice don’t like Diet Coke
The ingredient that makes Diet Coke sweet is aspartame (NutraSweet). It works by
binding to sweet receptors in your tongue. In humans, the sweet receptor binds not only to
sugar, but also aspartame, saccharin, and sucralose (Splenda). In mice, sweet receptors
bind to sugar and saccharin, but not aspartame. They don’t prefer water with NutraSweet to
plain water, suggesting that to a mouse, Diet Coke wouldn’t taste sweet. (It’s a similar story
for ants, which are not attracted by diet soda.)
Scientists have used genetic technology to replace the mouse’s sweet receptor with the
human sweet receptor. These transgenic mice like aspartame—and presumably Diet Coke.
This proves that they use the same brain pathways to taste sweet things as we do, just with
different receptors.
If you have pets, there’s an experiment you can do at home. See how they like different
kinds of sweet beverages—juice, sugared soda, and diet soda. Put out one dish of each and
see what your pet goes for. You might be surprised at the results!
Minty foods taste cool for a similar reason. A receptor has recently been identified that binds to
menthol. Plants may make menthol for the same reason that they make capsaicin—to make themselves
taste bad to animals.
Smells and tastes often have strong emotional associations: your grandmother’s apple pie, burning
leaves, your lover’s shirt, fresh coffee in the morning. Smells can also have negative associations. On
September 11, 2001, and in the days after, Manhattan was permeated by a bitter, acrid smell that
nobody who was there can ever forget. Some smells may be negative for some and positive for
others. (Think of Kilgore’s favorite smell in Apocalypse Now : “I love the smell of napalm in the
morning … the whole hill smelled like victory.”) These associations may occur because olfactory
information has a direct connection into your limbic system, brain structures that mediate emotional
responses. These structures are able to learn, raising the possibility that they allow you to associate
smells with pleasurable or dangerous events.
Chapter 9
Touching All the Bases: Your Skin’s Senses
Pickpockets may not spend a lot of time talking about how the brain works, but their profession does
require some practical knowledge of the subject. A common technique involves two partners in
crime. One thief bumps into the victim on one side, to distract him from the other thief’s hand
design as one could ever hope to find in nature.
Taste works the same way, except that flavor receptors are in your tongue. Taste is simpler since
there are only five basic flavors: salty, sweet, sour, bitter, and umami. (What’s umami, you say? It’s
the savory taste that’s found in cooked meat or mushrooms or in the food additive monosodium
glutamate, MSG. There’s no word for it in English, which is why we use the Japanese term.) Each of
these basic tastes has at least one receptor, sometimes more. Bitterness, for instance, is sensed by
dozens of receptors. As animals evolved, they needed to detect toxic chemicals in their environments.
Because toxic compounds came in many forms, it was necessary to have receptors that could detect
all of them. This is why we have a natural repulsion to bitter flavors. This distaste can be overridden
by experience; look at all the lovers of tonic water and coffee.
Why do we call spicy foods hot? The chemical that gives chili and hot sauce their zest is
capsaicin. Your body also uses capsaicin receptors to detect warm temperatures. This is why you
sweat when you eat spicy food—the receptors have what you might call a “hotline” into your brain to
trigger responses to cool you off. You have capsaicin receptors not only in your tongue, but all over
your body. One way to discover this is by cooking with hot peppers and then putting in your contact
lenses. Ouch!
Did you know? Why mice don’t like Diet Coke
The ingredient that makes Diet Coke sweet is aspartame (NutraSweet). It works by
binding to sweet receptors in your tongue. In humans, the sweet receptor binds not only to
sugar, but also aspartame, saccharin, and sucralose (Splenda). In mice, sweet receptors
bind to sugar and saccharin, but not aspartame. They don’t prefer water with NutraSweet to
plain water, suggesting that to a mouse, Diet Coke wouldn’t taste sweet. (It’s a similar story
for ants, which are not attracted by diet soda.)
Scientists have used genetic technology to replace the mouse’s sweet receptor with the
human sweet receptor. These transgenic mice like aspartame—and presumably Diet Coke.
This proves that they use the same brain pathways to taste sweet things as we do, just with
different receptors.
If you have pets, there’s an experiment you can do at home. See how they like different
kinds of sweet beverages—juice, sugared soda, and diet soda. Put out one dish of each and
see what your pet goes for. You might be surprised at the results!
Minty foods taste cool for a similar reason. A receptor has recently been identified that binds to
menthol. Plants may make menthol for the same reason that they make capsaicin—to make themselves
taste bad to animals.
Smells and tastes often have strong emotional associations: your grandmother’s apple pie, burning
leaves, your lover’s shirt, fresh coffee in the morning. Smells can also have negative associations. On
September 11, 2001, and in the days after, Manhattan was permeated by a bitter, acrid smell that
nobody who was there can ever forget. Some smells may be negative for some and positive for
others. (Think of Kilgore’s favorite smell in Apocalypse Now : “I love the smell of napalm in the
morning … the whole hill smelled like victory.”) These associations may occur because olfactory
information has a direct connection into your limbic system, brain structures that mediate emotional
responses. These structures are able to learn, raising the possibility that they allow you to associate
smells with pleasurable or dangerous events.
Chapter 9
Touching All the Bases: Your Skin’s Senses
Pickpockets may not spend a lot of time talking about how the brain works, but their profession does
require some practical knowledge of the subject. A common technique involves two partners in
crime. One thief bumps into the victim on one side, to distract him from the other thief’s hand
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