How can things taste or feel “cold” or “hot”? FLASHBACK
This sensation is called chemosthesis and refers to the fact that chemicals that you can taste or apply to your skin can cause “touch” feelings (temperature is part of the “touch” sense whereas chemical sensing is either “taste” or “smell” typically). This would be with icy hot where it feels cold or hot, but your skin temperature does not actually change or when you eat mints and they “taste cold” or when you eat some spicy food and it “tastes hot”.
These cold or hot feelings or tastes are not actually related to temperature. Two chemicals in particular can activate the TRP channels we talked about previously. Menthol (found in mint and icy hot) activates TRPM8 channels that typically sense cold temperatures, while capsaicin (found in chili peppers and other “spicy” foods) activates TRPV1 channels that typically respond to heat. These chemicals attach to the TRP channel and cause it to open the same way temperature would, causing the same responses in the neurons- in your mouth and on your skin. This is why the foods or other chemicals containing these compounds really do taste or feel “hot” or “cold”. It is the same neural response.
Coincidentally, this is why drinking water after having some spicy foods will not help- the water will just move the chemicals around and cause them to activate even more TRP channels, making the feeling stronger. Most concentrated fluids, like milk, can help wash away and displace the chemicals, so the TRP channels will stop being activated.
DO WE HAVE FREE WILL?
Had a great #NeuroLoveChat last night on my twitter (@NeuroLoveBlog). Thanks a bunch to the people who participated! I really enjoyed speaking with all of you.
One of the many interesting questions posed was asked by @zfield27: “What is your stance on the free will vs. no free will argument (if you have one)?”
This is actually a pretty fascinating and loaded debate. Quite honestly, I don’t think it’s something easy to design an experiment to conclusively prove or disprove (perhaps because it would be to our psychological detriment to disprove it), and thus, we might never have a “real” answer.
On the one hand, evidence has been growing that free will might be an illusion. For instance, Hallet (2007) found that the volitional control of movement was an illusion- volitional control meaning, for instance, you decide to move your arm, and then you do. Neurons in the brain had already decided that the arm was going to move before the conscious was on board. Other studies have found similar things- that the conscious gets on board after the “decision” has been made by the brain (Soon et al., 2008).
This is not to say that free will does not exist. I myself would love to believe in free will, but I don’t know if it is that belief that clouds a reasoned consideration of its existence. It’s clear that most people believe in free will, and it appears that a belief in free will is necessary for one’s psychological well being (Leotti, Iyengar, & Ochsner, 2010). So then, is it worth breaking the illusion of free will (if it is an illusion) to keep searching for an answer?
If you did want to prove free will, how would you do so conclusively? I think that would be an incredibly difficult question to address. I wanted to lay out argument for you here though, because I think it is absolutely fascinating to consider.
[Image Source; also thanks to @zfield27 for the question!]
Don’t forget!! TONIGHT, 8-10pm Eastern Time, I’ll be taking/answering any questions you might have with the hashtag #NeuroLoveChat on my twitter, @NeuroLoveBlog. Feel free to submit questions beforehand, if you won’t be able to make it, and I will try to answer them all. You are also welcome just to drop in to say hi!
Thanks so much for following, and I hope to chat with some of you tonight!
As promised, I am planning another live chat with a couple days advance notice! This will be Wednesday, December 19, 2012 from 8:00 pm to 10:00 pm Eastern Time! If you don’t already, follow me on twitter @NeuroLoveBlog. I’ll be following the tag #NeuroLoveChat so I can see any questions you ask and will reply using that tag if you want to follow along too! Any questions you’ve got about applications, neuroscience, etc would be happily received and I will answer as many as I can in that two hour window! You can send me questions in advance on twitter if you can’t make it or through the ask feature on here (just tag them #NeuroLoveChat so I will know what they are for). If you want to ask anonymously, you can send questions through the ask feature on tumblr! If I get some good/common questions or questions that take a while to answer, I might post them with my replies on here Thursday! We’ll see how it goes, but I want to make sure I answer any burning questions that you may have! I hope to see many of you on Wednesday!!
This is a video of a patient with Wernicke’s aphasia, also from the Wisconsin Physio Department, found on youtube here.
This is a patient with Broca’s Aphasia from the Wisconsin Physio Dept, found on you tube here. Remember that Broca’s Aphasia results in an inability to formulate words, though patients still have an understanding of language and know what they want to say- they are simply unable to do so with the ease most of us take for granted. You can see this patient struggles to get the words out and settles for just a few to get out the idea of what he wants to say.
Language Areas of the Brain
The main areas of the brain that deal with language are Broca’s and Wernicke’s areas. Broca’s is involved in producing speech, so the formation of the mouth, tongue, etc that goes into the action of speech (someone with damage to this area would be able to understand what others are saying and know what they want to say, but be unable to say it). Wernicke’s is involved in associating words with meaning and so is usually labeled the language comprehension area (someone with damage to this area would be able to speak but not understand or produce speech with meaning, so they might say a sentence that would be words but without cohesion or meaning- like “word salad”).
Impairments in language are known as “aphasia”- so the disorders I described in parentheses are Broca’s Aphasia and Wernicke’s Aphasia respectively.
One amazing thing that we’ve learned from split brain studies is that when the left hemisphere doesn’t understand something, it will come up with a reasonable explanation. For instance, as you can see in this image, the patient saw different pictures with the two sides of the brain, and each hand selected a card appropriate to the corresponding image. However, since only the right visual field and right hand (left hemisphere) have language, the patient is unable to verbalize why the left hand chose a shovel, so you can see the patient saying that the shovel was chosen because “you need to shovel to clean out the chicken shed,” even though the card was chosen in response to the snowy picture in the right hemisphere of the brain.
This really comes into play with other things in healthy individuals- when the brain sees something it can’t explain, it creates a logical explanation for it, whether they are the right ones or not. So, I am sure you can imagine situations from your own life where that may have come into play (for instance, let’s say you arrive at a house that is super-messy… you may decide that they were recently robbed, or that someone had a party and didn’t clean up). This is actually a pretty complex process if you think about it and happens so easily in the brain. From split-brain patients, we now know that this process likely happens in the left hemisphere.
I found this clever little game on split brain experiments. You basically just get to watch an “in action” experiment of your choosing, but it demonstrates what I have been talking about well and explains it in very simple terms! To try it out, go here: http://www.nobelprize.org/educational/medicine/split-brain/splitbrainexp.html (you can also get there by clicking on the picture above)
FYI: I am going to be on hiatus next week for thanksgiving break, so I can spend time with my family. I have been getting a lot of personal questions recently (about school applications and things), which I have not really had time to respond to individually. To make up for it, I’ll be live tweeting on my twitter (@NeuroLoveBlog) tonight from 6-7 pm eastern time (in an hour and a half) so you can ask me any burning questions you might have! I’ll do my best to respond to all of them, so feel free to ask away! If you don’t already, follow me here! I know it’s last minute, so I’ll try to do another one of these after thanksgiving with more notice!
An important thing to keep in mind is that while split brain patients have divided abilities, those are not present in people who have an intact corpus callosum. These split brain studies led to the ideas of left or right brained people, which isn’t really a thing. We use both sides of our brain, all the time, seamlessly. I’m going to direct you to a great article in the Yale Scientific Magazine about this myth: http://www.yalescientific.org/2012/04/left-brain-right-brain-an-outdated-argument/
An excerpt: “I am definitely a left-brained person — I am not very artistic.” How many times have we characterized ourselves as either left-brained and logical people or right-brained and creative people? This popular myth, which conjures up an image of one side of our brains crackling with activity while the other lies dormant, has its roots in outdated findings from the 1970s, and it seems to imply that humans strongly favor using one hemisphere over the other. More recent findings have shown that although there are indeed differences between the hemispheres, they may not be as clear-cut as we once thought.
Our personalities and abilities are not determined by favoring one hemisphere over the other — that much is certain. Many other functions, however, such as response to danger and language generation, are lateralized in the brain. Researchers hypothesize that these differences arose from early vertebrates. Originally, it seems that the right hemisphere began to respond more quickly to danger. In fact, when we are suddenly confronted by a dangerous stimulus, we will respond more quickly with our left hand, which is controlled by the right hemisphere. The left hemisphere, on the other hand, has developed to handle more common, routine tasks, such as feeding and hand control. Since this hemisphere controls the right hand, a strong right-handed preference has arisen in most of us, providing one explanation of why most people are right-hand dominant.
These are examples of drawings done by each hand of a split brain patient. You can see that the right hand (left hemisphere) is clearly lacking in spatial reasoning and the ability to get the depth of the original images, while the left hand (right hemisphere) is clearly better at this type of task. For more information about split brain patients, see this post.
[Image Source, Fig 13.8]
This is another example of a test that can be done with a split brain patient (for more information about this, see this post). They will look at a half picture of a child on the right (left hemisphere) and a woman on the left (right hemisphere). When asked whom they saw, they will only be able to tell you the picture on the right, as the left hemisphere has language. However, when asked to point to the image they saw, their left hand (right hemisphere) can point to the image on the left. This is akin to the word task, but done with facial recognition (which is a specialized process that occurs in the fusiform face area of the temporal lobe).
To continue with the split brain patient information (basic info here), this is an interesting, albeit old, documentary with Gazzaniga and his data. At about 8:43, you can see the block task I had mentioned before. Basically, in this task, a subject is given a few blocks that are half dark and half light. By arranging these blocks in a specific pattern, you can match images and test spatial reasoning. You can see that with the left hand (right hemisphere), the subject is able to arrange the blocks to match the picture very well. However, with the right hand (left hemisphere), the subject cannot get the blocks arranged correctly. The left hand even tries to jump in and help- at this point, with the two hemispheres severed, the hands are working as separate entities governed by separate brains. The right hemisphere can do the task easily and therefore wants to do it- the left hemisphere, which is supposed to be doing the task, cannot do it accurately. Imagine how frustrating it would be to see someone doing a simple task incorrectly- that is how the right hemisphere feels- and without the corpus callosum to connect it to the left, the left hemisphere is incapable at this task and can’t get the basic assistance it needs.