April 8th

The taste cells have tips that protrude into the _______ __________.

taste pores

People who can taste PTC are described as ___________, and those who cannot are called ____________.

tasters nontasters

The glossopharyngeal nerve is associated with taste cells from...

the back of the tongue - we could suggest that these are dealing with the circumvilliate papillae that are at the back of the tongue and are shaped like mounds surrounded by a trench.

The chorda tympani nerve is associated with taste cells from...

the front and sides of the tongue - we could suggest that these are dealing with the fungiform papillae that are found at the tip and sides of the tongue and shaped as the mushrooms.

What is amiloride?

It blocks the flow of sodium into taste receptors. So amiloride is a chemical that knocks out the flow of sodium - it will ablate the sodium movement.

Research has been unable to confirm whether PROP taster and more or less sensitive to other bitter substances. What has been found of super tasters (i.e. people who are really sensitive to PROP)?

It does appear that people who are especially sensitive to PROP, called supertasters, may actually be more sensitive to most bitter substances, as if the amplification in the bitter taste system is turned up for all bitter compounds

Electrical signals generated in the taste cells are transmitted from the tongue in a number of different nerves. What are these four different ways? (4)

(1) the chorda tympani nerve (from taste cells on the front and sides of the tongue - we could suggest that these are dealing with the fungiform papillae that are found at the tip and sides of the tongue and shaped as the mushrooms); (2) the glossopharyngeal nerve (from the back of the tongue - we could suggest that these are dealing with the circumvilliate papillae that are at the back of the tongue and are shaped like mounds surrounded by a trench); (3) the vagus nerve (from the mouth and throat); and (4) the superficial petronasal nerve (from the soft palette—the top of the mouth).

How have researchers been able to study specific taste receptors in mice?

. You can decide on a taste receptor you want to study and you can somehow knock it out in mice so that it is no longer there and so that they don't have it anymore. If there is one that they don't have, you can genetically put it in. You can take the receptor away or put one in.

There are ___________ taste buds.

10,000

The whole tongue has about __________ taste buds and there are bout _______ cells per taste bud.

10,000 50-100

Applying amiloride to the tongue causes what effect?

Applying amiloride to the tongue causes a decrease in the responding of neurons in the rat's brainstem (nucleus of the solitary tract) that respond best to salt but amiloride has little effect on neurons that respond best to a combination of salty and bitter tastes. Thus, eliminating the flow of sodium across the membrane selectively eliminates responding of salt-best neurons but does not affect the response of neurons that respond best to other tastes.

Not all researchers agree that the picture is so clear-cut. For example, Eugene Delay and coworkers (2006) showed that with different behavioral tests, mice that appeared to have been made insensitive to sugar by eliminating a "sweet" receptor can actually still show a preference for sugar. What does Delay suggest from these results?

Based on this result, Delay suggests that perhaps there are a number of different receptors that respond to specific substances like sugar. This means that we don't only have one sugar receptor - we have more than one sugar receptor. * Maybe that is how we can detect differences in sweetness (i.e. ice cream is different from cake and pie).

In the study of PTC, what did Ken Mueller study?

Because a specific receptor in the family of bitter receptors had been identified as being responsible for the bitter taste of PTC in humans, Mueller decided to see what would happen if he used genetic cloning techniques to create a strain of mice that had this human bitter-PTC receptor.

What is the point of talking about these differences in taste perception (i.e. that cats can't taste sweetness) (i.e. what is the significance of this phenomenon for humans)?

Because it turns out that there are genetic differences that affect people's ability to sense the taste of certain substances.

Because of all these arguments between specificity and distributed coding, how are researchers thinking that neurones are involved in taste?

Because of arguments, some researchers believe that even though there is good evidence for specific taste receptors, distributed coding is involved in determining taste as well, especially at higher levels of the system.

What did Erickson call these patterns of nerve firing that he was seeing?

Erickson called these patterns the across-fiber patterns, which is another name for distributed coding.

After finding that NH4Cl and KCl with give out the same distributed pattern of firing in the nerve and that NaCl gave out a different pattern of firing in the nerves - what did Robert Erikson do next?

Erikson gave the rats shocks for drinking what he didn't want them to drink and wanted to see if they could tell the difference. So if the NH4Cl tasted the same as the KCl, then they wouldn't go back to it if they associated shock with both NH4Cl and KCl. To test this hypothesis, Erickson shocked rats while they were drinking potassium chloride and then gave them a choice between ammonium chloride and sodium chloride.

Give a good example of how we see that we don't all have the same taste experience between both humans and animals.

For example, domestic cats, unlike most mammals, don't prefer the sweetness of sugar, even though they display normal taste behavior to other compounds, such as avoiding compounds that taste bitter or very sour to humans.

Give an example of the different individual perception of smell.

For example, the smell of the steroid androsterone, which is derived from testosterone, is described negatively ("sweaty," "urinous") by some people, positively by some people ("sweet," "floral"), and as having no odor by others. Or consider the fact that after eating asparagus some people's urine takes on a smell that has been described as sulfurous, much like cooked cabbage. Some people, however, can't detect this smell.

Robert Erickson (1963) conducted one of the first experiments that demonstrated this type of distributed coding for taste. Explain his first set of research.

He presented a number of different taste stimuli to a rat's tongue and recording the response of the chorda tympani nerve. We don't know how he has recording these responses because he was recording the output of many nerve fibres, not just one. He looked at how 13 different nerve fibres responded to ammonium chloride (NH4Cl), potassium chloride (KCl), and sodium chloride (NaCl).

What were the results of the electrophysiological study by Erickson?

If potassium chloride and ammonium chloride taste similar, the rats should avoid the ammonium chloride when given a choice. This is exactly what they did. And when the rats were shocked for drinking ammonium chloride, they subsequently avoided the potassium chloride, as predicted by the electrophysiological results.

What were the two main findings of Mueller's study of CYx?

In addition, Cyx no longer caused any firing in nerves receiving signals from the tongue. It was as if the Cyx didn't exist for the mouse anymore. Therefore, when the taste receptor for a substance is eliminated, this is reflected in both nerve firing and the animal's behavior.

The results of an experiment by Jeannine Delwiche and coworkers show that the density of taste buds alone cannot explain high sensitivity to PROP. What did these researchers propose and explain this research.

It's not that some people have more taste buds - it's that some people have PROP taste buds and some do not. After confirming that PROP tasters do have a higher density of papillae than nontasters, they devised a system for stimulating the same number of papillae in tasters and nontasters. They accomplished this by presenting stimuli to smaller areas of the tongue for the tasters. When participants rated the bitterness of PROP, the tasters' ratings were much higher than nontasters' ratings, even when the same number of papillae were stimulated.

How do we know that people have different numbers of taste buds on the tongue - that some people just have more taste buds on the tongue than others?

Linda Bartoshuk used a technique called video microscopy to count the taste buds on people's tongues that contain the receptors for tasting. She found that people who could taste PROP had higher densities of taste buds than those who could not taste PROP. The key result of this study was that people who could taste PROP had higher densities of taste buds than those who couldn't taste it.

What did Mueller study with Cyx and mice?

Mueller created a strain of mice that lacked a bitter receptor that responds to a compound called cyclohexamide (Cyx). Mice normally have this receptor, so they avoid Cyx. But the mice lacking this receptor did not avoid Cyx.

What were the findings of Robert Erickson's research?

NH4Cl and KCl with give out the same distributed pattern of firing in the nerve. NaCl gave out a different pattern of firing in the nerves.

Did adding or eliminating bitter receptors have any effect on neural firing or behavior to sweet, sour, salty, or umami stimuli?

No - these receptors are really specific. You can take them out or put them in and they will not affect the capacity to effect the other receptors. * Other research using similar techniques has identified receptors for sugar and umami.

Is amiloride on the tongue of humans effective as in mice?

No. As it turns out, the sodium channel that is blocked by amiloride is important for determining saltiness in rats and other animals, but not in humans. More recent research has identified another channel that serves the salty taste in humans.

Are the taste worlds of every individual (either human or animal) the same?

No. The "taste worlds" of humans and animals are not necessarily the same. * We know that the animals may have different taste receptors than we do (remember that mice had Cyx receptors).

Does Delay's finding knock out the idea of speciality coding?

No. This doesn't knock out the idea of specificity coding - it just means that the coding is even more specific than we had once thought.

What part of the brain does taste end up in?

Taste ends up in the frontal lobe. So if you damage the frontal lobe, like in a car accident, you can affect your taste system.

It turns out that there are genetic differences that affect people's ability to sense the taste of certain substances. Give an examples of this.

One of the most well-documented effects involves people's ability to taste the bitter substance phenylthiocarbamide (PTC). Some people don't seem to be able to taste PTC.

What causes these differences in people's ability to taste PROP?

One reason is that people have different numbers of taste buds on the tongue - some people just have more taste buds on the tongue than others.

What is one suggestion of how both specificity coding and distributed coding occur in taste perception?

One suggestion is that basic taste qualities might be determined by a specific code, but distributed coding could determine subtle differences between tastes within a category. * So differences between slaty and sweet would be specificity coding but within sweetness or differences in saltiness or differences in sourness would be determined by distributed coding. This would help explain why not all substances in a particular category have the same taste. For example, the taste of all sweet substances is not identical

Researchers have studied how taste stimuli effect individual neurons. What has this method of single cell recording revealed?

Recordings from neurons at the beginning of the taste systems of animals, ranging from rats to monkeys, have revealed neurons that are specialized to respond to specific stimuli, as well as neurons that respond to a number of different types of stimuli.

More recently, additional experiments have been done with a substance called 6-n-propylthiouracil, or PROP, which has properties similar to those of PTC. What have researchers found in regards to taste and PROP?

Researchers have found that about one-third of Americans report that PROP is tasteless and two-thirds can taste it.

What other sense is also found int he frontal lobe with taste?

Smell is also in the frontal lobe.

What other sense has to do with the nsula and the frontal operculum cortex?

Smell. This is where smell and taste meet and that is how we get flavour.

What was different from Susan Schiffman's findings as compared with Erickson's results?

Solutions judged more similar psychophysically had similar patterns of firing, as distributed coding would predict. * But in fact, NaCl tasted very different from KCl. NaCl tasted different from NH4Cl. And the KCl and the NH4Cl tasted the same - so that supported the prediction from the rat work.

In the sequence of our bodies, does distributed coding or specify coding happen first?

Specificity coding comes before the distributed coding. The distributed coding happens at higher levels of the brain.

The study of amiloride supports what kind of coding?

Specificity.

What are the five basic taste qualities?

Sweet, salty, bitter, sour and umami.

What is specificity coding in reference to taste?

That there are receptors that are specifically tuned to sweet, bitter, and umami tastes.

What are the different papillae that are involved in taste and found on the tongue?

The filiform papillae are shaped as cones and make the tongue feel rough. The fungiform papillae are shaped like mushrooms. The foliate papillae and a series of folds along the back of the tongue and along the sides. The circumvilliate papillae and shaped like flat mounds surrounds by a trench and are found at the back of the tongue.

One example of single cell recording looked at three neurons in the rat taste system which respond to sucrose (sweet to humans); sodium chloride (NaCl; salty); hydrochloric acid (HCl; sour in low concentrations); and quinine (QHCl; bitter). What was interesting when looking at these three neurons.

The first was sensitive to sucrose, the second was specific to NaCl, the third was selective to NaCl, HCl and quinine. So two of the neurons are really specific but there is one of these neurons that seems to respond to all three.

When does transaction from the taste cells to the taste pores occur?

The transduction occurs when chemicals contact receptor sites located on the tips of these taste cells.

What two types of neural coding are thought to exist with taste and when are these two different types of neural codes thought to be in play?

There is distributed coding and specificity coding - we will say that there is specificity coding at the low part of the system and is you get higher up in the system we will be dealing with distributed coding.

What accounts for these differences in smell that people experience?

These differences in smell in different people are, like differences in tasting, caused by genetic differences that affect the presence of receptors that respond to different chemicals.

Where are the insula and the frontal operculum cortex located?

They are in the frontal lobe and are partially hidden behind the temporal lobe. * This tells you that when we are dealing with these areas, we are deep in the frontal lobe, not in the prefrontal lobe.

Mice normally have a receptor to Cyx - do they avoid or like Cyx?

They avoid it.

What is unique about the filiform papillae - the ones that are found all over the tongue?

They don't have any taste buds attached to them - we need taste buds to taste because there are taste cells in our taste buds.

How do David Smith and Thomas Scott (2003) illustrate their hypothesis of distributed coding in taste?

They illustrate this by drawing an analogy between taste perception and the mechanism for color vision. Even though presenting a long-wavelength light that appears red may cause the highest activation in the long-wavelength cone pigment our perception of red still depends on the combined response of both the long- and medium-wavelength pigments. Similarly, salt stimuli may cause high firing in neurons that respond best to salt, but other neurons are probably also involved in creating saltiness.

Overall, what does the study of phenomenon of amiloride on the tongue tell us about taste?

This means that some neurons don't just respond to one thing.

What does it mean if distributed coding is used in taste?

This means that the code for taste would be specified by the firing of a number of nerves and their pattern.

What senses do go through the thalamus?

Touch, taste, earing, and vision.

Does this variability in taste what we see for individuals happen in any other senses?

We've seen that this is for smell as well.

What were the results of Ken Mueller's research of PTC?

When he did this, the mice with this receptor avoided high concentrations of PTC.

So is it possible that we think specificity and distributed coding are both at work in taste?

Yes - it just depends on where you're at int he system - if you are early in the system then it's probably specificity coding, then the more specific tastes are higher up in the system by distributed coding.

Did Susan Schiffman's study of distributed coding in humans align with Erickson's finding in rats? Explain.

Yes. When Susan Schiffman and Robert Erickson (1971) asked humans to make similarity judgments between a number of different solutions, they found that substances that were perceived to be similar were related to patterns of firing for these same substances in the rat.

Is distributed coding used for other senses, as well as in taste?

Yes. We've seen distributed pattern coding in vision (remember with the recognition of faces) and we saw it in audition.

The different reactions to PTC were discovered accidentally in 1932 by Arthur L. Fox, a chemist working at the E. I. DuPont deNemours Company. Explain Fox's experience and what this lead to.

`Fox had prepared some PTC, and when he poured the compound into a bottle, some of the dust escaped into the air. One of his colleagues complained about the bitter taste of the dust, but Fox, much closer to the material, noticed nothing. Albert F. Blakeslee, an eminent geneticist of the era, was quick to pursue this observation. At a meeting of the American Association for the Advancement of Science (AAAS) in 1934, Blakeslee prepared an exhibit that dispensed PTC crystals to 2,500 of the conferees. The results: 28 percent of them described it as tasteless, 66 percent as bitter, and 6 percent as having some other taste.

Genetic studies have shown that PROP and PTC tasters have ______________ ____________ that are ____________ in nontasters

absent * They just don't have the receptors that allow you to taste those specific tastes.

David Smith and Thomas Scott (2003) argue for distributed coding based on the finding that...

at more central locations in the taste system, neurons are tuned broadly, with many neurons responding to more than one taste quality. Smith and coworkers (2000) point out that just because there are neurons that respond best to one compound like salty or sour, this doesn't mean that these tastes are signaled by just one type of neuron.

Genetic research has shown that this "sweet blindness" in cats occurs because...

cats lack a functional gene for formation of a sweet receptor and so, lacking a sweet receptor, have no mechanism for detecting sweetness. * Cats have to regulate their blood sugar too - they just don't have attraction to sweets.

Erickson reasoned that if the rat's perception of taste quality depends on the across-fiber pattern, then two substances with similar patterns should taste similar. Thus, the ________________ results would predict that ammonium chloride and potassium chloride should taste similar and that both should taste different from sodium chloride.

electrophysiological

So stimulation of the back and perimeter of the tongue results in...

in a broad range of taste sensation - remember that each taste bud has 50-100 taste cells

Ken Mueller and coworkers (2005) did a series of experiments using a chemical compound called PTC that tastes bitter to humans but is not bitter to mice. The lack of bitter PTC taste in mice is inferred from the fact that...

mice do not avoid even high concentrations of PTC in behavioral tests but humans do avoid it.

Neurons have also been found that respond selectively to sour (HCl) and bitter (quinine) - so there are _______ (more/less) selective and this is also _______________ coding.

more (* these are really really specific because they are taking into account more specific tastes, not just one) specificity

Because the filiform papillae have no taste buds, the stimulation of the central part of the tongue causes...

no taste sensations.

The fibers from the tongue, mouth, and throat make connections in the brain stem in the_________________ __ ___ _______________ ___________.

nucleus of the solitary tract

You'll find that the only sense that doesn't go to the thalamus is...

smell.

The results of the experiments involving cloning, recording from single neurons, and the effect of amiloride seem to be shifting the balance in the distributed versus specificity argument toward ______________ coding.

specificity * However, the issue is still not settled.

The results of these experiments in which adding a receptor makes an animal sensitive to a specific quality and eliminating a receptor makes an animal insensitive to a specific quality have been cited as support for ______________ _______________.

specificity coding

Particular neurons that respond selectively to stimuli associated with sweetness (sucrose) or saltiness (NaCl), provide evidence for _____________ _____________.

specificity coding.

The vagus nerve is associated with taste cells from...

the mouth and throat.

The superficial petronasal nerve is associated with taste cells from...

the soft palette—the top of the mouth`

The fibers from the tongue, mouth, and throat make connections in the brain stem in the nucleus of the solitary tract. From there, signals travel to... (3)

the thalamus and then to two areas in the frontal lobe that are considered to be the primary taste cortex — the insula and the frontal operculum cortex. * We have a lot to think about with our food - it goes to two different tracts in the frontal lobe. So when you mess up patients because you do a frontal lobotomy, that is messing up a lot of things!