Posts Tagged ‘ touch ’

Musical Matchups

Our brains process music via different sensory pathways depending on what we think its source is, a new study finds.

Let me stop ya right there - "Stairway to Heaven" is off-limits.

As our brains organize information from our senses into a coherent representation of the world around us, they’re constantly hard at work associating data from one sense – say, sight – with data from another – say, hearing.

A lot of the time, this process is pretty straightforward – for instance, if we see a man talking and hear a nearby male voice, it’s typically safe for our brains to assume the voice “goes with” the man’s lip movements. But it’s also not too hard for others to trick this association process – as anyone who’s watched a good ventriloquism act knows.

Now, as the journal Proceedings of the National Academy of Sciences (PNAS) reports, a team led by HweeLing Lee and Uta Noppeney at the Max Planck Institute for Biological Cybernetics has discovered a way in which musicians‘ brains are specially tuned to correlate information from different senses when their favorite instruments are involved.

Neuroscientists have known for years that the motor cortex in the brains of well-trained guitar and piano players devotes much more processing power to fingertip touch and finger movement than the same area of a non-musician’s brain does. But what this new study tells us is that the brains of pianists are also much more finely-tuned to detect whether a finger stroke is precisely synchronous with a sound produced by the touch of a piano key.

To figure this out, the team assembled 18 pianists – amateurs who practice on a regular basis – and compared their ability to tell synchronous piano tones and keystrokes from slightly asynchronous ones while they lay in an fMRI scanner (presumably by showing them this video). The researchers also tested the pianists’ ability to tell when lip movements were precisely synchronized with spoken sentences.

The team then compared the musicians’ test results against the results of equivalent tests taken by 19 non-musicians. What they found was pretty striking:

Behaviorally, musicians exhibited a narrower temporal integration window than non-musicians for music but not for speech. At the neural level, musicians showed increased audiovisual asynchrony responses and effective connectivity selectively for music in a superior temporal sulcus-premotor-cerebellar circuitry.

In short, pianists are much more sensitive to a slight asynchrony between a keystroke and a piano tone than non-musicians are – but this sensitivity doesn’t also apply to speech and lip movements. In other words, pianists’ brains are unusually sensitive to asynchrony only when it involves piano keystrokes.

Another important finding is that the researchers could predict how sensitive the musicians would be to asynchrony based on asynchronies the fMRI scanner detected in their motor cortex:

Our results suggest that piano practicing fine tunes an internal forward model mapping from action plans of piano playing onto visible finger movements and sounds.

This means there’s a direct link between inter-neural coordination and ear-eye coordination. I don’t know about you, but I think that’s pretty incredible.

The researchers hope that as they study similar data from musicians who work with other instruments, they’ll come to better understand how our brains learn to associate stimuli from one sense from information from another – and maybe even how they learn when and when not to “sync up” these stimuli in our subjective experience of reality.

It’s too bad we can’t hook up the brain of, say, Mozart or Hendrix to an fMRI scanner – who knows what amazing discoveries we might make. But even so, I’m sure you can think of some living musical geniuses whose brains you’d like to see in action.

I Be Strokin’

Watching another person being softly caressed activates very similar brain regions to those that actually allow us to feel a soft touch, says a new study.

"Aah - gently! I said gently! Good lord, you are one strong baby."

The sensation of gentle touch is conveyed by a specific type of neuron – tactile C (CT) afferents – found only in hairy skin. These neurons respond most strongly to soft touches and “caress-like” speeds, and send signals to a brain region called the posterior insula, which helps interpret bodily sensations like pain, warmth or cold, heartbeat, a full bladder or stomach, and balance – and also, interestingly enough, the physical feelings associated with music, laughter, and empathy.

What this new study explores is the insula’s response when volunteers observe another person being caressed. A team led by India Morrison of the Institute of Neuroscience and Physiology at the University of Gothenburg’s Sahlgrenska Academy began by searching for an optimal stroking speed for triggering CT and insula activity – they found that stroking the subjects’ arms at a speed of about three cm/s provoked the strongest response in the insula:

A speed optimal for eliciting CT discharge (3 cm/s) also gives rise to higher BOLD responses in posterior insula than a nonoptimal speed (30 cm/s).

The next step was to study fMRI scans of the volunteers’ brains as the subjects watched videos of another person’s arm being stroked at various speeds. Again, videos showing a stroking speed of about three cm/s provoked the strongest insular response:

When participants viewed videos of others’ arms being stroked at CT-optimal versus -nonoptimal speeds, the posterior insula showed a similar response as to directly felt touch.

Interestingly, the insula seems to respond most strongly to videos depicting social touch, as opposed to “nonsocial dynamic-touch videos.” (No word yet on what the insula thinks of Facebook pokes.) The authors use this observation about social touch to bring up an intriguing point about why our insula might respond more strongly to some caresses than to others:

Such selective tuning for CT-optimal signals in insula may allow recognition of the hedonic relevance of a merely observed caress.

In short, our neurons and brains may be finely tuned to recognize exactly which caresses “mean” what.

On the whole, these results aren’t particularly shocking – after all, we all know that erotica is popular because (at least on some level) it works. Going by that example, it seems that even reading about a caress, or imagining one, might trigger similar insular responses.

What makes this especially interesting, though, is that even when we’re not physically feeling a sensation of touch, our brains are still tuned to respond most strongly to a specific pressure and stroking speed on certain body parts – or to the idea of that specific pressure and speed on those parts. Writers of erotic fiction, take note.

This discussion also awakens the dragon of the ongoing and fiercely fought mirror neuron debate. Without going too tangential here, the basic idea is that some studies seem to suggest the existence of “mirror neuron” groups, which are activated not only when we perform an action, but also when we see it being performed, or even when we hear it being performed in another room. While the system has been invoked to explain everything from task-learning to language acquisition to empathy, mirror neurons (if they actually exist in human brains at all) don’t seem to be essential for any of those tasks.

It may be that, rather than using a specific “mirror neuron” system to model perceived actions, our brains generally respond to perceived and experienced events in roughly the same way, and make the distinction of “self/other” at some point along that process. This seems, to me to offer a sort of Occam’s razor to explain why movies can seem so real, songs can feel like they’re about us, and stories of another person’s pain or pleasure can give us vicarious sensations – which, nonetheless, never feel quite as real as actual physical ones.

I think it’ll be fun to try some experiments with my friends – they can watch while I gently stoke my own arm, then compare that feeling to the one they experience when I touch theirs. Strokin’ for Science!

Virtual Touch

A new brain-machine interface allows minds to literally feel the texture of computer-generated objects, a recent paper reports.

Only the most cutting-edge CGI was used in the new interface.

This interface not only allows a monkey to remotely control a virtual hand by willing it to move – the system also routes feedback on textures and vibrations to the somatosensory cortex, where that feedback is processed as sensations of touch.

Though mind-controlled robotic hands aren’t exactly breaking news anymore, most of those devices only provide visual feedback – in other words, the users of those robotic hands can’t actually feel the objects the hands touch. One recent project did use vibration feedback to help subjects sense the placement of a cursor, but that’s about as far as the idea had been taken.

But now, as the journal Nature reports, a team led by Duke University’s Miguel Nicolelis has created a brain–machine–brain interface (BMBI) that routes movement impulses from a monkey’s brain directly to a virtual hand, and routes tactile (touch) sensations from that hand directly into touch-processing regions of the monkey’s brain:

Here we report the operation of a brain–machine–brain interface (BMBI) that both controls the exploratory reaching movements of an actuator and allows signalling of artificial tactile feedback through intracortical microstimulation (ICMS) of the primary somatosensory cortex.

At the risk of sounding repetitive (I can’t help it; I’m so awestruck by this) the BMBI doesn’t involve any robotic hands – the entire interface takes place between the monkey’s brain and a virtual world created within a computer:

Monkeys performed an active exploration task in which an actuator (a computer cursor or a virtual-reality arm) was moved using a BMBI that derived motor commands from neuronal ensemble activity recorded in the primary motor cortex. ICMS feedback occurred whenever the actuator touched virtual objects. Temporal patterns of ICMS encoded the artificial tactile properties of each object.

The computer receives movement commands from 50 to 200 neurons in the monkey’s motor cortex, translating them into a variety of movements for a virtual “avatar” hand (which I’m picturing, of course, as huge and blue and stripey). As the virtual hand feels virtual objects, the system sends electrical signals down wires implanted into the monkey’s somatosensory cortex, where those signals are processed as touch sensations.

The researchers rewarded the monkeys for choosing virtual objects with specific textures. In trials, it only took the monkeys a few tries to learn how to feel using the BMBI – one monkey got proficient after nine attempts; another one picked it up in four.

The researchers hope this technology can be used to create touch-sensitive prostheses for people with amputated or paralyzed limbs. Which sounds awesome – but why stop there? Why not create entirely new bodies from computer-generated touch sensations? Why not place our consciousnesses into virtual birds, or fish, or swarms of bees?

Maybe it’s just me, but I feel like Sgt. Pepper’s must be playing on continual repeat in a lot of these neuroscience labs.

 

Pain on the Brain

Men and women experience pain in different ways, a new study shows.

"Aaaagh, my KORs are killing me!"

The behavior of opioids – chemicals that suppress pain – differs between men’s and women’s bodies. This is because the three main types of opioid receptors in the brain and spinal cord interact very differently, depending on whether their owner is a man or a woman.

See, scientists have known for years that certain kinds of narcotic analgesics – a certain class of pain relieving drugs – are much more effective on women then on men. It was hard to understand why, though, because both men and women have mu (MOR), delta (DOR), and kappa (KOR) opiate receptors – the three main kinds – and these receptors work in essentially the same way in either gender.

But now, scientists have found that the spinal cords of female animals have almost five times as many kappa-mu heterodimers – complex molecules formed by combining KORs and MORs (commonly called KOR/MOR heterodimers) – as those of males. And not only that – the number of KOR/MOR heterodimers climbs four times higher when a woman’s body is pumping with estrogen and progesterone – two hormones crucial for regulating female body chemistry:

Spinal synthesis of estrogen is critical to the processes [of forming and using KOR/MOR heterodimers], and blockade of either estrogen receptor (ER) α-, β-, or G-protein-coupled ER1 or progesterone receptor (PR) substantially reduces KOR/MOR and eliminates mediation by KOR of spinal morphine antinociception.

In other words, a squirt of estrogen causes a sharp increase in the number of KOR and MOR receptors that get formed. This is a Big Deal, because some previous research suggests that in men, KORs and the chemicals that activate them may actually promote pain – and that their attachment to a MOR converts them to part of a pain-relieving system:

The research suggests that kappa-mu opioid receptor heterodimers could function as a molecular switch that shifts the action of kappa-opioid receptors and endogenous chemicals that act on them from pain-promoting to pain-alleviating.

To figure out what was going on with all these receptors, a team led by Alan Gintzler, a SUNY biochemist, first did some research to show that KOR and MOR opioid receptors join to form KOR/MOR heterodimers, the Journal of Neuroscience reports. This research was the first step toward understanding how these receptors interacted in the body’s pain system.

For this new study, though, the scientists injected estrogen and progesterone into the spinal cords of test animals, and determined that both chemicals were critical for the formation or KOR/MOR heterodimers, and these heterodimers’ activity in suppressing pain, as opposed to spreading it.

This discovery could go a long way toward explaining why certain pain-suppressant drugs that target MORs and KORs – such as pentazocine and nalbuphine – work well on women, but poorly on men: in spinal cords that lack the KOR/MOR heterodimer, the drugs might be activating the lonely little KORs, which – without their MOR friends, would help promote pain instead of relieving it. How rude of them.

Anyway, this new data looks like it’ll provide some encouraging ideas for future pain relief research:

The activation of the kappa-opioid receptor within the kappa-mu-opioid receptor complex could provide a mechanism for recruiting the pain-relieving functions of spinal kappa-opioid receptors without also activating their pain-promoting functions.

The researchers also point out that doctors should talk with women about where they are in their menstrual cycle before prescribing them medications like these – when estrogen and progesterone levels drop, pain relievers might turn into pain promoters.

So the moral of the story is, if you’re a guy (or a women who’s low on estrogen), some things really are gonna hurt me more than they hurt you.

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