NeuroBlog

This is Sam Brusca posting: Let me start off by stating that I, an admitted dork, have never seen a full episode of Star Trek. That being said, I looked on google and immediately recognized the curved "special glasses" (I must have owned a pair in elementary school). First off, it definitely makes intuitive sense that the sensory systems have evolved in a way that has lead them to develop "adequate stimuli." And, in seemingly every case, the adequate stimuli matches up to the stimuli that the sense would experience most often e.g., light for the visual system.

I also think the two ideas that you linked to the video are inherently interconnected. The idea of stimulating a sense in a “non-natural” way and the idea of a basic neocortex-organizing principal go hand in hand. In other words, the reason you can elicit a normal sensory response from a non-normal energy is due to the fact that the neocortex is conservatively organized. Electric current is a great stimuli for somatosensory, and the somatosensory neocortex is very similarly organized to the visual system’s neocortex. So, isn’t the reason you can stimulate the visual system with a non-normal stimuli because, somewhere else in the cortex, a similar sensory organization is processing the current. Like in the video, the brain has “to be trained” to relate the known somatosensory stimuli to the visual system.

Lastly, the idea of conservative organization seems to be very common in biology (and human physiology). In genetics for example, both the genetic code of DNA and the system of twenty amino acids are conservative. A rather limited set of individual deoxy-ribose or polypeptides can be amplified to millions of effects through combinations and orders. I think this is similar to your description of the Neocortex. Us Humans are so efficient!

Right on, Sam. I'll make a couple comments to clarify what you (and I) have said. First, remember to think of adequate stimuli as being immutable. That is, sensory receptors have adapted over evolutionary history so that currently each is most sensitive to a particular energy form. This obviously makes sense, since it would do the organism little good to have receptive organs with high sensitivity to the "wrong" form of environmental energy, unless the receptor functioned as some sort of 'omnisensor' that detected any and all changes in the pattern of environmental energy. One problem with such a system would relate to the organism's ability to discriminate different energy forms from one another and to ignore certain energy forms at times when paying attention to it (or them) would be counterproductive. Now, if you start thinking about how such an omnisensor would be "put together," before too long you find yourself dividing it into sub-sensor systems, i.e., separate sensory systems. It's actually kind of a fun exercise. Think about a novel sensory capability you'd like to have. How would you 'design' it???

The other point I wanted to make concerned the idea about the common architecture of the neocortex lending itself to object identification. In fact, it's not that surprising at all, since we are vey good at identifying objects by touch. That's a function called stereognosis (literally 'to know the solid'). So, I think it's important to emphasize that in the video example the somatosensory cortices are not engaged in visual perception, per se-- the visual stimulus was merely transduced into an energy form that could active the somatosensory system in such a way that identification of the stimulus features were knowable. That said, clearly the subject is experiencing some sort of visual experience, since the locations of the stimuli OUTSIDE the body were detected and, indeed, perceived.

Anyone else think our devotion to the sciences (esp. neuroscience) is amazing; an award given out only once every three years by the National Academy of Sciences gives a grand total of (drumroll, please) 15,000$ Oh well.
I think the coolest thing about this is how it shows the versatility\plasticity of the brain. Learning to interpret tactile sensations in a manner analogous to sight sounds like it would be a nigh impossible task, but apparently not. This reminds me of the way that among the blind much of the visual cortex begins to be used by the brain for other functions; for example, in an older post, I talked about a blind woman, who, after she had a stroke in her visual cortex, lost her ability to read Braille. I have the feeling that this new 'BrainPort' technology probably would\does cause the brain to adapt in the same manner. Also, the organization of the brain into these vertical 'modules' to serve certain cognitive functions does make a great deal of sense to me. After all, this seems like it would make the developmental process much easier and with less room for error if the various cognitive systems tend to be grouped together vertically; it avoids long meandering axons coiling throughout the brain going from one segment of a 'module' to another. This also conserves space, which is clearly an evolutionary positive, as the more efficient we are in the organization of our brain the more brain matter we can fit inside our skulls- other examples of the importance of this conservation of space include the folding of the neocortex and the fact that we use specialized oligodendroglial cells rather than schwann cells to myelinate the cns's axons.
Mostly however, I just think its great that another step has been taken in the process to restore some semblance of vision to those who lack it. The loss of sensory systems is a huge hindrance to those who suffer from it. The other day, the new governor of New York, who himself is blind, mentioned that 60% of the blind were unemployed and over 90% of the deaf. Wow. Clearly, these losses are hugely debilitating, in spite of our brain and bodies ability to adapt, and I am glad to see that progress is being made.

This is Bridget

It seems to me that an incredibly simplistic and yet crucial component of any sensory system is the fact that once transduction has occurred of the type of energy that was detected by the receptors of the system from the stimulus source, all modes of "communication" within the sensory systems are the same. Namely, changes in membrane potential throughout the neurons in appropriate synaptic relationships throughout a particular pathway. Thus the idea of seeing with a "tongue" does not seem all that impossible to me because as long as that transduction of an "experience" somehow can be transferred from the gustation pathway to the visual pathway, the detection and identification of the stimulus seems to follow suit only from electrical communication anyway.
What I think is also possibly evident in this research, though I could be very likely wrong, is the notion that when one of the sensory systems fails and thus that source of input for detecting and understanding, and experiencing the world around is shut down, the other sensory systems "accomodate" accordingly. This is the idea of the "sharpening" of the residual senses. Though I am not sure what the neuroscience is that explains this observed phenomenon of increased functioning, I do know that there are multiple examples of people with certain heightened senses because other senses are missing. Currently, I am studying the history of jazz, and several examples of unbelievable musicians come to mind as I think of sensory deficits that seem to be made up through other methods of processing the world around us. For example, everyone knows Ray Charles was blind and yet mastered the piano as completely and possibly even more so, than many other pianists. Then there is the example of Lennie Tristano, another great, almost completely blind jazz pianists who helped to define the "Cool Jazz" era. Clearly these musicians were handicapped because they could not receive information about their surrounding world through their visual systems, and yet their incredible ability to listen to the harmonies and the melodic unfoldings of new musical lines seemed to show that what lacked in their vision was made up for in their ability to hear, listen, and feel. I know these examples may be only tangentially related to the article brought up at hand, but I am incredibly curious about whether or not there is actually a relationship between the losing of one sense and the sharpening of the others, or if these musicians and people like them with special talents relating to senses are merely that; talented.

I was wondering, could they use that to depict color too? For shapes the camera detects, just the pattern of electric signaling is used, but can slight changes in intensity be used to detect color too?

I think this article clearly shows that most sensory systems are ultimately the same thing, except that they are interpreted by the brain differently.

Can they perceive depth? That would be so cool. What aspects of vision have they mastered and what can't they perceive yet?

David Doobin posting:
Agreeing with Granvil, this common phenomena of neuroplasticity is very intriguing, especially in this case of cortical plasticity. Here it is apparent that the person is able to see because the visual stimulation is translated into touch stimulation on their tongue, which enters the brain through the brain stem and goes to the somatosensory area, but is relayed into the visual cortex. This was demonstrated in one of the diagrams in the story, and it is the last transition between the somatosensory cortex and the visual cortex that is the most important. I'm guessing here that this goes back to what we were discussing in class about the different neocortical layers and the different neurons in each layer. Some of the neurons facilitated vertical communication, while others facilitated lateral. I'd guess that the transmission of information stimuli from the somatosensory cortex in the parietal lobe to the visual cortex in the occipital lobe is due to the horizontal/lateral connections amongst neurons, and this pathway must be developed. Normally somatosensory information is not analyzed directly by the visual neocortex, but in these people it appears that the visual cortex is actually perceiving these stimuli on the tongue as if they were coming from the eye (or at least I think so). Hence, this pathway must be built up and trained so that it can relay stimulatory information in high quantities and at rapid speed, which is why there was a learning curve to using the device. This example of neuroplasticity is what intrigued me the most about this breakthrough, and I wonder what sort of progress has been made on the device since the story first aired.

This article brings up a very creative solution to a very widespread problem. In almost every psychology/neuroscience course I have taken, the idea that the brain is continually adapting has been a main focus. Thus, it is interesting to see the application of this very idea. I once heard the story of a girl who was the valedictorian of her class and clearly graduated with top honors. However, when she was young she had a terrible case of hydrocephalis and her cortex had been reduced to a very thin layer. Her brain was able to reallocate functions as she grew up and she overcame the physical defecits. Just as someone can reallocate cognitive functions, so can they reallocate sensory functions. Just because one cannot see does not mean that the cortex associated with vision is "broken." Thus, if one can create a stimulus other than photons to activate those visual pathways, the cortex can adapt.
The population that this marketing is aimed at seems to have been born blind. To us, learning to see with one's tongue seems almost silly, but if you have never experienced sight, then how different can it be? We all "learn" how to react to certain stimuli in the environment, but do not question it because we were so young when it was taught. If we all learned at a young age to "see" with our tongues, this machine would be commonplace.

Rosemary Hambright:
Wow, that video was amazing! It totally makes sense, too. The "repeating, basic organizational motif" of all the sensory systems can really be attributed to natural selection. If a physical characteristic works, most likely it will continue to be implemented in future generations. It's interesting to note that octupi are considered to have a more "efficient" sight sensory system than humans because they don't have a blind spot and light doesn't have to travel through all the layers of ganglion and bipolar cells before reaching the photorecptor cells, because the photoreceptors are at the front of an octupus' eye.

On a somewhat less related note, I stumbled upon this really interesting article about another sensory system, proprioception, and "phantom pain" in amputees. Some rather experimental treatments for recent Iraqi war victums have shown that theropy involving mirrors can ease the pain that amputees feel at the end of their damaged limb. The cause of phantom pain is not entirely understood, but some neurologists believe that the neurons that used to control the missing apendage become confused and randomly fire action potentials, causing pain or a freezing sensation. Interesting stuff!

This immediately reminded me that as babies we put things into our mouths because, while our eyes are not so hot yet, our tongues rock at feeling things out. (Also, I feel like I read somewhere that, for it's size, the tongue is the strongest muscle in the body. Rock on.) Fortunately for my reputation the my eyes' abilities have significantly developed to the point that I generally look at things to identify them and rarely revert to sloppier, more slobbery techniques.

It seems that this technology is just providing the right translating service such that the ability of the tongue to receive sensory input is used to compensate for the eye's inability. It's funny that our perceptual experience of our surroundings is so dependent on the relatively arbitrary way that it is broken up by our sensory system. As we discussed, the visual experience is broken up into component parts that, while highly significant in our perception, hardly translate to significantly distinct pillars in the unprocessed "real world." Color is a readily accessible example of this phenomenon. I would rank it as an extremely important distinguishing factor and key descriptive characteristic in my everyday life, despite the fact that the entire experience is essentially created by the mind. Object shape, motion and color are all perceived by separate pathways and seem distinct, though really they are all just components of an objects "essense." Furthermore, our five senses only piece together an understanding of the state that we're in, and are ultimately limited to only gesturing around the seemingly infinite information that could be gathered from the environment, given the right instrumentation. They do a pretty good job of translating relevant aspects of our surroundings into chemical and electrical signals that can be read by the brain so that we can stay out of trouble, or get into trouble (if it looks like fun!).

diane:
just to be totally off kilter and respond to bridget - granvil said that 60% of blind people and 90% of deaf people were unemployed. Perhaps the skills are sharpened because of an incredible amount of time they have to devote sharpening a skill? Just a thought. Kind of like the size principle in relation to axon recruitment - perhaps we recruit or use more neurons in response to the need for survival. I think the potential is there for all people.

and in response to tori: my biology teacher told me about this girl who they thought was a permanent comatose patient and so the mother opted to take her daughter off the air supply to die, but when they took her off the air supply, new neurons, by themselves (?) had grown around her lungs and although she was brain-dead, she could breathe on her own. So they took her off food instead and she essentially starved to death.

Okay, before we move on to a new post, I thought I'd spend a little time addressing several points and comments made above. I think it's important to emphasize that the sightless and normally-sighted subjects in the video clip are using their somatosensory cortices to 'see,' and that a visual equivalent of that somatosenroy experience is ultimately belived to be generated in visual cortical areas, presumably through indirect axonal connections the primary ("crude") sensory areas have with one another via higher order, "association areas" (in this case, probably posterior parietal cortices, which is a place where touch and vision information are integrated). Using this 'non-traditional' access to visual areas would obviously require some level of practice, i.e., learning, before one would become good at using the information. One way to imagine how the process might develop with practice is to have a friend select a random assortment of objects for you to identify by tactile means. While engaging in the behavior, try to visualize the items you are handling. With practice, I suspect you will find that your visual impressions of the manipulated objects occur with increasing rapidity and vividness. Much of what Clara noted should be borne in mind here, too. That is, our normally-sighted visual experience is the result of constant learning about how to interpret patterns of environmental energy. Thus, while it is unclear what the visual experience of a Brain Port user (sightless or not) is, it presumably is not the same as the vision of our experience, since their visual learning histories are fundamentally different than those of normally sighted individuals. Hmm, what else?

Oh. In fact the Brain Port technology DOES provide depth cues. It must, since the guy in the video is navigating an obstacle course, which requires 3-d sensorimotor integration. I'd like you to think about how this capability must also depend in some part upon proprioception (joint position sense) and vestibular sensation (sense of head movement and the plane in which the head is moving). That is, part of the way we know where things are in our visual world depends upon the relationship of objects to us, which we determine in large part using proprioceptive information.

A response to Diane's comments: the ability of the brain-dead girl to respire on her own would not necessailry depend on the generation of either new neurons or new synaptic connections among neurons involved in control of respiration. Also, just to be sure you all know, there would certainly not be any new neurons appearing around the lungs (only in the brain and spinal cord, please). As it turns out, the neurons that regulate respiration communicate with the diaphragm via the phrenic nerves, which are spinal nerves that arise from cervical spinal segments 3, 4, and 5. Also, the spinal accesory nerve (cranial nerve 11) sends some general somatic efferents to the diaphragm. It's worth noting that the medullary regions involved in control and maintenance of respiration are in the neighborhood of neurons that help to keep the brain awake and aware (i.e., conscious). This is why it can be the case that a person who suffers an irreversible coma (absence of reflexes, orienting responses, sleep-wake cycles, and the neurophysiological correlates of same) and still be able to breathe spontaneously. Irreversible coma is often considered brain death. This is a little bit different from a persistent vegetative state, which is like a coma, but the subject has numerous intact reflexes and orienting responses and some degree of sleep-wake cycling, but they are non-cognitive. Interstingly, sometime people in a PVS can oreint and have reflexes (e.g., consensual accommodation or vestibulo-occular reflex), but they cannot breathe spontaneously. You might recall the Terry Schiavo case from a few years ago. After a massive heart attack during her mid-20s, she was in a totally non-cognitive PVS for many years, though she showed a diversity of orienting and reflexive behaviors that some interpreted as signs of cognitive and emotional awareness (e.g., smiling and tracking of visual stimuli). However, fMRI images of her brain very clearly revealed massive bilateral neurodegeneration, especially of the diencephalon, inconsistent with cognitive activity. Her case, along with countless others that occur everyday, reveal how the most basic functions of the brain can be virtually completely separated from those that makes us who we are.

I don’t know if this is a relevant comment on the post but anyway it sounded pretty interestin, to me. I was readin' this post and I was thinkin' about the human ear which is obviously responsible for hearing but also maintaining balance. It’s interesting to note that the ear acts much like the visual system in a sense that what ear does with the sound as its main stimuli resembles what eye does with light. The pinna part of the ear collects the sound and then this sound goes through the inner ear. The inner ear contains these “hair cells” which fire action potentials when they are depolarized enough. So they act much like photoreceptors in the eye. The photoreceptor transduces the air and after connecting with the bipolar cells finally ganglion cells fire the action potentials targeted at the CNS. Inner ear contains several organs that are responsible for different tasks. For example cochlea, an inner rear organ, is responsible for hearing while labyrinth is another organ in the inner ear that controls sense of gravity and ultimately motion. Hair cells are also responsible for sensing motion. But the interesting thing is that the stimulus that turns on these hair cells is different for the “hearing” and the “motion”-responsible hair cells. These two kinds of “hair cells” fire their action potential as expectedly to different parts of the cranial nerves which in turn transfer the message to the brain. This shows that the hair cells that are located in the inner ear, depending on where they synapse and what kind of stimulus activates them would be responsible for variety of tasks.

Some of what others talked about, regarding the social implications of being blind, reminded me of the talk by Dr. Morrell about deafness. A portion of his lecture compared the lifestyle and cultural differences of people with congenital deafness compared to people with late-onset deafness. I was thinking about how a parallel could be drawn to prelingual blindness as opposed to late-onset blindness. In people who are born blind, since their visual system is technically still intact, would BrainPort work if they do not have a reference (a memory, in this case)? And why does BrainPort utilize sensors on the tongue, when the fingers and hands are just as, if not more, sensitive to stimuli? It would be more practical to be able to apply a stimulus to a hand than to the tongue, if this technology was to be used on a regular basis. The idea is still the same, I would think. Also, how can depth be reflected through stimuli? Would it be through stimulus intensity? However, just the fact that the brain can reallocate the visual cortex to touch (and other senses) is truly fascinating.

A couple of weeks ago, my music theory teacher was telling us how some people "see" colors when they hear a pitch being played, as opposed to the solfegge or the note name or scale degree. According to him, some people are just born with this ability to "see" notes differently. This is an example of associating sight with sound. Of course, these people are not necessarily blind--they are visual learners who apply sight to enhance their other senses. I wonder if some people are just born with a greater ability to reallocate sensory processes in the brain than others. Could this be related to why some blind peole can "see" their surroundings with greater ease than others? Is the rate at which the brain can adapt to these situations something which is encoded in our genetic code, or is it based on environmental factors?

At some point in my science background, I watched a video about blind people. In the video it discussed how the neurons in a normal (seeing) person are specific for vision...like we said. However, in blind people, the neurons in the visual cortex are not being used for vision so they adapt and then become useful in the touch system. This is why blind people have such sensitive touch systems that they can read Braille (such small dots that to a seeing person would mean nothing). This is also why, the lady in Granvil's post could lose her ability to read brail after a stroke in the visual cortex--less touch sensitvite neurons are available. The scientists in the video also did an experiment with a normal seeing person where they blind folded the person for an extended period of time (around a month, I think), and tested the neurons in the visual system periodically. They found that the neurons in the blind folded person also changed and became more sensitive to touch as the experiment went on. It is very interesting how our brain can adapt like that. Also, although Braille has been moderately affective for blind people, I think it is really cool that they can now use the extreme sensitivity that blind people have to touch, to allow them to essentially “see” objects.

This article just made me think about how incredible the tongue. It is already involved in two somatosensory systems in the human (taste and touch) that it seems natural that it would be able to accomadate another. Snakes can smell with their tongues as well, further indicating that it is a great place to detect external stimuli. This may indicate that the tongue is closely connected to parts of the brain that combine all the senses to motivate actions, and thus can be rewired to adapt to more uses if trained.
This also demonstrates the great plasticity of the brain. Peolple who suffer some sort of physical impairment often are able to physically readapt , such as a blind person developing heightened sense of hearing, so that they can overcome their impairment and their body can function normally.

Ah, so much to say... OK, let me deal with a few things up there. First, in regard to Daria's post. You're on the right track conceptually, but there are a number of things that I should clarify.

As it turn out, the inner ear (which contains the organ of Corti, which contains auditory hair cells) and labyrynths/semi-circular canals (which contain vestibular hair cells) are activated by very similar proximate stimuli, namely movement of the fluid contained in these structures. The fluid movement in each organ causes the hairs (i.e., stereocilia) on the hair cells to be bent. This in turn causes the cells to depolarize (though they don;t fire action potentials-- that is done by their associated primary sensory afferents). It is the WAY that the fluid is made to move that differs. In hearing, pressure waves in air (i.e., sound stimuli) cyclically compress and decompress the fluid in the inner ear (the compression/decompression is due to movement of the bones of the inner ear- the hammer, anvil, and stirrup). This in turn results in bending of the stereocilia. In the vestibular apparatus the stereocilia are bent by movement of the fluid caused by acceleration or deceration of the head (as in the sacculae) or by rotation or tilting of the head (as in the utricle). One reason why sound can't ordinarily cause movement of the fluid in the vestibular apparatus is because it is embedded in bone, far from where the pressure waves of sound could affect it.

About some of Maya's observations... her music teacher refers to a sensory phenomenon termed 'synesthesia,' which is the perception or sensation of stimulation of one sensory modality (e.g., auditory stimulation) in another (e.g., visual system). It's relatively rare, and the understanding of the neural basis of the phenomenon is rudimentary at this point. I refer the readers to Dr. Lorig's courses on Sensation and Perception (PSYC 252) and Cognitive Neuroscience (PSYC 255) for more thorough (and knowledgable) treatment of the topic.

One other thing Maya mentioned is worth noting. One reason why the tongue is used as the site for application of the Brain Port transducer is that the saliva makes the environment good for conducting the tiny currents that are used to activate the somatosensory receptors located there. If fingers were used, either a higher electrical current or conductive gel (or both) would be required to activate the dermal receptors.....

OK, I gotta come teach you guys now, so I'll get back to this later.

Susan Taylor:
This is an amazing news story. The human brain is an impressive thing, that it can adapt so well as to see through the tongue via electrical impulses. I just wondered why they said that they hoped that one day the image would be clearer than it is today...is it that the electrical impulses need to be refined? Or is it that the tongue needs to be trained more? I wonder if this idea would work with other senses as well, like if you lost your sense of audition, you could somehow wire the signal to another part of the brain to comprehend it? Also, it seems like there are some drawbacks with this system. A blind person could see only so long as they didn't have anything to eat, I could only assume. But once they started to eat, they would lose their vision. Although that is a small price to pay for some amount of vision when you're blind.

Upon studying the motor homunculus man the other day, I started thinking about Maya’s comment about preferentially using the fingers as somatosensory tools rather than the tongue for visually-impaired individuals. Like the primary motor cortex (M1), perhaps there is a similar breakdown whereby different organs of the body (fingers, toes, eyes, etc.) are dedicated differential numbers/density of sensory receptors. After all, it makes sense that your fingers are more sensitive to stimuli, a painful prick, for example, than your back. In Biology 111, we did an experiment where we showed that two different pricks on the back could not be perceived separately when the two stimuli were situated at certain distances apart. If the fingers are more sensitive than the tongue, then I see no reason why this site would not be preferential to the tongue. Consider an individual that was born blind. In order to understand and interact with the world around him, he must constantly feel objects placed in his surroundings. He learns to recognize people by feeling their faces. He learns the difference between a toothbrush and a pencil by feeling his way around them and storing away massive amounts of sensory information – temperature, smoothness, complexity of construction, etc. The same goes for an individual that becomes blind during the middle of their life; the feeling of touch becomes more sensitive to compensate (as others have said). Why not tap into this wonderful and time-developed ability when constructing aids for the visually-impaired? It might cut down on the time that is needed to learn the “language” associated with reading stimuli delivered to the tongue…

As it turns out, tactile discrimination on the tongue (especially the tip) is much better than that on the fingers (by about 500 microns in a two-point discrimination test, which is substantial). So, it serves the purpose better. Some of you have commented about "increased" touch sensitivity in sightless people. In fact, unless sightless people generate additional mechanoreceptors in their epidermi, it is not possible for their two-point discrimination, per se, to improve. Think about the fovea. The high density of receptors there (and the very small receptive fields to which they contribute input) is what determines the visual system's ability to resolve two separate stimuli. It's the same way for touch; the higher the density of receptors in skin, the higher the resolving power of that surface. There is no evidence that blindness is related to an increased density of mechanoreceptors in any epidermis.

This said, people who lose the ability to use one sensory system often demonstrate enhanced ability TO USE the remaining ones. This is attributable probably in some part to neocortical changes that allow one sensory modality (e.g., auditory) to "invade" cortical space previously occupied and utilized by the now-missing sense (e.g., vision). However, the major contributions to the sensory "enhancement" come from adapting sensory-guided behaviors to the remaining modalities (i.e., learning occurs); and from changes in the way patients distribute attentional resources to the remaining sensory inputs (also learned). In other words, if I lose my sight, I no longer need to exert sensory attention on visual stimuli (I can't, I'm blind). So, those attentional resources can be dedicated to other sensory modalities.

An simple example of the way that we can intentionally dedicate our finite attentional resources to a particular sensory process is the so-called "Cocktail Party Effect." This is the situation when your are at a party talking to someone right in front of you and out of the "corner of your ear" you hear your name. Immediately, you begin to focus additional auditory attention on the sounds that are coming from the part of the room where you think your name was uttered. At the same time, your friend probably notices that you are no longer listenting to them carefully, might even stop talking, and may even make a face or wave a hand in an attempt to regain your attention. You might not even notice these gestures even though your eyes are fixed on your friend. I imagine this situation sounds familiar to many of you.

Finally, let's take a mooment to consider another reason why using the tongue is superior versus using fingers. In a previous comment I noted that to use the fingers, a higher density of electrical current and/or conductive gel would be necessary to deliver the impulses from the probe because the finger surface is not very conductive. So, at least two of the subject's finger tips would have a layer of goo on them (and they might experience irritation from it in combination with the current, which heats up the tissue). Note that I said finger tipS. That's because in order to have any analog of depth perception, the subject must have the signal applied to both sides of the body (and of the brain...). The tongue is small enough that it is very easy to stimulate both sides of the midline simultaneously with a relatively small probe. To do this with fingers, one would need to stimulate a finger on each hand, which would double the amount of hardware necessary, and would mean that the subject would have to be aware of and adjust for the probes on their finger tips when they use their hands to manipulate objects (use their hands)..... That's far more inconvenient than removing the probe from the mouth to speak, or to take a drink, or to bite a sandwich. And, as it turns out, since eating stimulates the secretion of saliva, it should actually help to enhance or at least maintain the sensitivity of the tongue to the tiny currents that the probe applies.....

After learning that synapses are pruned through apoptosis following our robust development, it seems that all these parallel systems were derived because of their great efficiency. Maybe I’m thinking about this too simply, but it seems that evolutionarily the animal that could sense as many indicators of danger the quickest and most efficient way possible would be most likely to survive and reproduce.

Also, this may not relate and I am sort of embarrassed to say this but my girlfriend recently bought me a Hannah Montana toothbrush as a joke. Interestingly enough, when you are brushing your teeth, it sends a pattern of vibrations through your mouth that allow you to hear “The Best of Both Worlds” in your head. Now I know this is not quite seeing with your tongue, but I still find it pretty amusing. Is the tongue absorbing the vibration waves and processing them itself. Unlikely I assume. I’m guessing the vibrations in my mouth work their way to my ears the way an external sound wave would transmit.

To clarify...does this mean that a visually-impaired individual is not able to compensate for a constant density of mechanoreceptors on the epidermis of the hands with increased occupation of cortical space? Or are you just saying that it is impossible to claim that an individual possesses enhanced sensitivity to stimuli when what really happens is that that individual has LEARNED to cope with what senses he/she may have...which may physically manifest itself in "heightened sensitivity" with other senses? Also, going off the whole fingers vs. tongue argument and the necessitation of "goo" for better conductive purposes on the fingers, I was wondering whether there are stimuli (besides electrical current) which are better suited for the fingers than the tongue? This is, of course, neglecting the fact that the machinery might be cumbersome since both sides of the midline must be accounted for...

To answer Grace, there IS evidence that crossmodal neocortical plasticity in blind subjects may be involved in the enhanced tactile discrimination. To put it simply, in the brains of blind people even V1 is activated by tactile stimulation but ONLY when the subjects are told to engage in a tactile discrimination task. The same is true when blind subjects are asked to engage in an auditory discrimination task (sounds cause activation of V1). It is worth noting as well that sighted subjects who wear blindfolds for a number of days show similar, task-dependent activation of V1. What does the cross-modal activation mean?

I would submit to you that the task-dependence of the cross-modal activation holds the answer. When one is asked to do something in particular, one must focus attention. If you combine this notion with the fact that 'activation' in an fMRI or PET scan could actually represent increased activity in, for example, a bunch of GABA neurons (which would turn "activated areas" OFF), perhaps the cross-modal activation in V1 of blind subjects reveals attentional suppression of visual cortical areas. You might not be able to see that in sighted subjects because their normally functioning visual system "demands" that it be "given some attention," i.e., less attentional suppression.

Finally, when I use the word learning, it should be clear that some learning occurs that the learner doesn't explicitly know about. It's called implicit learning. Put another way, not all learning is effortful or subject to conscious awareness, which, I think, is what Grace implies with the word 'cope.' In fact, a tremedous amount of learning occurs implicitly, that is without our awareness that it has occurred.

And, lastly, to answer Andrew's gripping question: you can hear that Hannah Montana song because the brush is vibrating your teeth; the vibrations are transmitted via the mandibular (lower teeth) or cheek (upper teeth) bones to the cochlea where they activate auditory hair cells, resulting in the sensation (and perception) of whatever that tune is you mentioned. Your favorite tune, no doubt. Hearing aids for people who have conductive hearing loss or "bone deafness," which means the ossicles of the inner ear have been damaged or become fused together so they no longer work, operate the same way, except the vibrations are transmitted by what is basically a small speaker placed behind the ear on the lower part of the temporal bone, which is called the mastoid process (though putting it on the mandible or zygomatic arch works, too, just like your tooth brush, although it looks funny).

OK, read Bridget's post on neuroscience and racism and/or Clara's post on the "Supercomputer Brain." That one is especially interesting because the design and function of the artificial brain relies on the principles of cortical organization to work.....

To the respond to the fingers versus tongue argument as to the best place to apply the electrical stimulus, I guess I had the opposite reaction of most of the people commenting on it-- my thought was that the tongue sounds like a great place to apply the stimulus because it allows you to still have your hands free. That way you can still manipulate, move, or feel things while "seeing" them. It also means you are still able to carry a cane to feel out and confirm the presence and location of objects you "see" in your way. I hadn't even thought about the necessity of stimulating both sides of the midline for depth perception as Stewart mentioned. The fact that the tongue can stimulate both sides at once is a great advantage over some other part of the body. In fact, considering it right now, I can't even think of another place to put the Brain Port that could do the same. Is there another place on the body with such easy stimulation of both sides of the midline? Even the nose is seperated into two nostrils, each projecting tactile stimuli to only side of the midline, right?
And finally, I was also wondering about the part of the news clip that says they hope to increase the "picture" quality that the Brain Port can transmit. Would that just entail having a grid of a greater number of transmitting electrodes? --to create greater resolution, in a sense. And would that mean that thing that goes on your tongue would increase in size... or are they trying to make the electrodes smaller and fit more of them into the same space? Thinking about that, then, isn't the max resolution they can attain essentially limited by both the two-point discrimination capability of the tongue surface (the density of mechanoreceptors in the epidermis of the tongue) and the overall size of the mouth.
That was kind of a longue sentence. But basically, I am trying to say that it seems that the Brain Port resolution can only get better to a certain point. Once the electrodes get so close together that the tongue can no longer discriminate them as two points, adding more in the same square area will not help. So, the only option then would be to make the whole grid bigger, but you can't make it any bigger than would fit into a normal person's mouth.

Having not seen an episode of Star Trek ever, LeVar Burton went right over my head, but the main blind person the video focused on reminded me of the actor Ron Perlman. Anyways, enough with the irrelevant ramblings, time for some slightly more relevant ramblings. I hate myself for bringing up a terrible movie but the video slightly reminded me of the movie “Daredevil.” For those not familiar, a kid goes blind and trains his other senses to substitute for his eyes, so he can fight crime. Great, I know. But the video somewhat confirmed the possibility of such a future for those who have lost their sight. The “car image” that is predicted for about a year and a half down the road was very promising.

But what about people who are born blind? Does this technology still apply to them even if the proper synapses were never formed during prenatal CNS development? I assume that as long as the somatosensory system is intact in its entirety, the functionality should be fine. However, if someone is blind from birth, and they did not use this new technology until later on in life, they would be learning for the first time all things visual. Letters, symbols, colors; everything they have never before seen would be in visible in full force (with the technology a couple years down the road). It would be a long learning experience but seemingly completely worthwhile one.