Rambling, 7 – Now hear this

i. Ornette and the others play on, enticingly, but I feel as if I’m still clearing the ground for talking about how their music affects me. And there’s quite a lot of ground to clear when the music, or the as yet unanalysed complex of vibration-as-sound, of these four players reaches the brain. 

You can start thinking about what happens next using external data – reports of stimulus and response compiled in cleverly controlled ways – without necessarily delving into actual brains, as the Dutch scholar Henkjan Honing point out in his recent book Music Cognition: The basics. And that can be intriguingly informative. But the brain is kinda interesting, too, so worth a look first.

Even before getting to that, though, I need a bunch of caveats. Until now, I’ve been merrily declarative. These are the facts, as I understand them. But the facts available about music, mind and brain, don’t sit well with that approach. Outside of the brain, we’re mostly fine. If I say there are three bones between the ear drum and the cochlea, that’s textbook stuff. Inside the brain, which after all is where the interesting stuff happens, notsomuch.

Until fairly recently, there wasn’t much to say at all. But there is now a vast amount of neuroscience, sometimes grandly promoted to “cognitive neuroscience”. And music, as one of the abiding human mysteries and one that plenty of us obsess over, has had lots of attention . In critical mood, I’d say it’s maybe had more attention than the state of the field justifies. Creating musical sensation – making sense, if we can, of what Ornette, Don, Charlie and Billy are doing – is surely one of the most complicated things going on in there. And the human brain, as every book on neuroscience* reminds us, is the most complicated thing in the known universe.

There’s more. A lot of the techniques neuroscientists have used, or even still use, are medium to moderately horrific, when applied to other creatures, so don’t get used in humans. But the other creatures don’t do music (with interesting, often arguable, exceptions), so lines of inference get stretched again, often to breaking point. The invasive methods, removing chunks of brain, say, or recording from electrodes sunk into tissue or, more refined, into single cells, tend to apply to people only through happenstance. An injury can be revealing; an unavoidable operation can give access to a portion of the brain for a bit. But that’s all the ethics committee will allow.

And the non-invasive methods on offer now are great, and often yield stunning data, but lend themselves to hype. In the eighties and nineties, documentaries would show volunteers being slid into CAT scanners, and relay brain images captured while they listened to music on headphones, while a breathless voiceover told us we were “seeing” music. Nah, not really. Later, the power of pretty, false-coloured images means that functional magnetic resonance imaging (fMRI) is constantly used to show bits of the brain “lighting up”, and thus revealing regions of activity. Problem: it’s enormously useful, but the areas highlighted are simply more active, not the only ones doing anything. (The machine registers differential blood flow.) The brain is internally connected to an astonishing degree and most regions are linked in to most activities. And when some small region is identified on a scan it looks impressive, but the resolution – spatial and temporal – of fMRI is still coarse compared with the fine detail of what’s happening down among the cells, and synapses.

Still, over time, logging the effects and defects of injuries, lesions or malformations, mapping connections in other mammals, and compiling scans and other probes, a picture builds up of what happens to the information. First broadcast by the instruments playing, it reaches the ear, the cochlea, and the hair cells that turn vibration into information – encoded as nerve impulses. Then it enters a wondrous network – the enchanted loom of twinkling cells and synapses, as Charles Sherrington called it nearly a century ago. We can try and follow.

image source https://www.thelighterman.co.uk (uncredited)

ii. What began as intentions in the minds of four players, became movement of muscles, and then movement in the air, is now a collection of impulses moving down the listener’s auditory nerve, from ear to brain. Just  as for any other sound. The collection includes signals from inner hair cells, which are tuned to frequency, and the, actually more numerous, outer hair cells which do….  other stuff. Where do those signals travel? Many neural regions, near and far. They go, says my handy 1,000 page neuroscience textbook, to the auditory cortex – the portion of the wrinkly outer layer of the brain that concentrates on sound, but not directly. I am overwhelmed by the detail whenever I look at it even in summary. Brain science will do that. But they mostly pass there via one or more of several “nuclei” in between with elaborately uninformative names, in lower layers of the brain from the brain stem on up. The web of nerve fibres connecting them provides a clutch of alternative routes to the auditory cortex. So there there may be one apparently simple mapping at the cortical level, where the fancy stuff like thinking is generally supposed to happen – there are cells in the cortex that respond to cochlear hair cells tuned, along with the membrane they are attached to, to different frequencies, and whose layout mirrors the variation in frequency response along the length of the tiny organ where the hair cells live. But this so-called isotonic mapping is about the only simple thing to hold on to here. All of these bits of brain are connected among themselves, and to other bits. And there are signals travelling in all directions. Nuclei in the brain stem, for instance, send impulses back down axons that connect to outer hair cells. Connections that modify some signals are themselves modified by other signals – like everything in the brain, neural messages in the auditory pathways are modulated in fiendishly complex ways. And the network has unexpected properties. The cochlea, for instance, can generate sounds in response to signals from higher up in the system, as well as registering incoming vibrations. 

There’s more to be teased out here, no doubt. But current knowledge of the network offers tantalising glimpses of how sounds are processed. So there are cells in the nuclei, for example, that somehow analyse their inputs so they can react to variations in frequency over time. And we know a bit about how sound intensity, and the variations between the ears due to the position of the sound – where the horn players are standing, perhaps – are detected. 

What to take from all this? We know this network has some features that seem to make sense. There are cells in the cortex that respond to the frequency, duration, intensity, and timing of the vibrations coming into the ears, and to changes in all those qualities. Do we know how the whole ensemble works, or even how it is organised, yet? Doesn’t look like it. But we can say some general things, also informed by study of the other sensory channels. Processing begins low down in the system, but continues all the way up, and lower levels are influenced by higher as well as vice-versa. One way that works is that the brain is continually making guesses about what will happen next, creating expectations, and registering whether they are met. That’s one result of a mental organ that has evolved so that perception is attuned to difference. Difference conveys new information. It means there is something going on. It deserves attention. True if you are trying to evade a predator creeping behind you through the undergrowth. True also in music.

All these auditory pathways in the brain also connect extensively to other areas, associated with emotion, action and reward. Add them in and it is even harder to keep the big picture in one’s mind. But it at least seems to be a match in complexity for the richness of the things we can get out of the pulsing, leaping, shimmering spray of vibrations that are set up by instruments in action and come together somehow in this web of neurons, axons and synapses to make the experience of music. Ornette and the others are knocking on a sensory door that opens onto an information processing array with astonishing capabilities. Some have been there since birth, some are learned. Together, they allow even a human who does not make music to appreciate it, to enjoy, over and over. But how does that part work? I need to listen again before trying to fathom that, even a little.

Image source https://hms.harvard.edu/news-events/publications-archive/brain/music-brain (uncredited)

* Including mine…

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