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Re: Do you think music can recruit and sync high-frequency brain waves?
| quote: | Originally posted by Jake Benson
Ok so this is what I start thinking about when I'm at work and my boss is out of the office (well, I'll admit I'm doing homework right now).
So EEG recordings show different overall brain waves depending on awake or sleep states (which are thousands or more neurons firing simultaneously -- though neuroscientists still have no idea what this means cognitively). For example in the waking state EEG shows brain waves to be 15-60Hz.
So if your listening to music, such as trance with a steady 4/4 beat, obviously some set of neurons are firing in your auditory cortex at this same beat (otherwise you do not perceive the beat). If you associate this rhythm with a slew of emotional and cognitive processes (i.e. think about how much you love the song and essentially "trance out" to only think about the song), is it possible to sync even more brain waves in the neocortex as a fraction of the beat? I.e. if the beat is 140 bpm, do you think a large set of your overall brain activity could sync up firing at a steady 35Hz?
This postulate seems pretty nebulous, but it doesn't seem like it would be impossible either.
c0r version: Shawty in my trance! Shawty in my alpha waves! HEY!....you look kinda cute, in that polka dot bikini guuuuurl. |
I know for sure that that brain cells in the cochlea of the ear and the primary auditory cortex (in which the first steps of musical processing occurs) synchronize to the frequency of the sound-waves. So if a pitch frequency is at 500 Hz, the cells will fire 500 times a second. Now of course this poses a problem for higher frequencies since pitches can reach up to 20.000 Hz whereas the maximum neural firing is estimated to be around 1000 times/sec. (maximally and not for all neurons. The typical firing rates are between 10 and 200-400 something which is reflected in the EEG). So this poses a certain question. How are higher frequencies en/de-coded? It seems that "correspondent firings-to sound-waves" is not the only way that the brain encodes pitch, the place of the receiving neurons do seem to play a role as well. So, neurons in the end fo the cochlea tend to fire at higher frequencies (as far as i remember) whereas those at the beginning tend to fire at lower ones. That cochlear structure leads to a topographically organized map in the primary auditory cortex of the brain, with various anatomic areas corresponding to the cochlea in a precise one(cell/place)-to-one(cell/place) manner.
Now, after that point, things start to get really complex. Further processing occurs on various areas of the temporal lobe (memory/recognition) and frontal lobes (expectations/higher cognitive functions/language) ending on various reverberating connections between those structures and the "reptilian limbic system" which is found deep within the brain. The limbic system is comprised by ancient structures which are responsible for emotions. During those steps, music recognition and emotional responses occur. And whilst those stages are the most important for music appreciation and experience, it seems that we know very little about them. During those "more advanced stages and areas of processing", neuronal synchronizations do occur at times,but they emerge in some unknown (phenomenally) chaotinc manner that doesn't correspond (at least in a similarly precise manner to the cells of the primary auditory areas described before) to the frequencies of the sound waves.
Now i realise that you talk about rhythm and not pitch (melody). As far as i know, rhythm is processed first in some ancient parts of the brain that also process motor movement and timing. These are the cerebellum and basan ganglia. As far as i know, it is true that neurons found in those neuronal structures synchronize their firing-rates to the exact tempo and meter. After that point though, the products of those computations end-up to the higher cortical structures described before, and hence, those precise synchronizations seem to get disorganized and more all-over-the-place.
I've recently red a book called "This Is Your Brain On Music" by Ex-rock-musician-and-producer-becoming-music-psychologist-and-cognitive-neuroscientist Daniel Levitin. I'm strongly recommending it (it is an international best-seller as well lol ). An important finding is that neurons synchronize their firing-rates in response to dissonance ("perceived disharmony"-which result from equally divided scales) and de-synchronize in response to consonance ("perceived harmony", resulting from unequally divides scales such as the Western scale of music). Whereas the contribution of the "(de-)synchronization mechanism to the perception of harmony is still unknown (but of major importance), these studies also suggest that there is an evolutionary basis for prefering western-music-type scales, something which can change with development.
Anyway, remember that EEG shows the activity of millions of neurons, giving some mean of the total neuronal firing rates (action potentials). These oscillations can range from 2-4 Hz (Delta waves occuring in deep sleep) to 20-100+Hz (Gamma waves occuring in higher cognitive function and increased alertness). Now music would probably lead to higher frequencies possibly within the broad gamma frequency spectrum. (I think though that the type/genre of music would make a difference e.g. drone-ambient vs. extreme metal. I have the impression that such a study has not yet been done though).
It is highly unlikely though that the oscillations would reflect the precise tempo and meter, since-as i mentioned before- not all areas synchronize their activations in similar ways. Only the first stages of processing located on the primary auditory areas are sensitive and correspond precisely to the sound. Further processing to the higher brain areas are more complex and do not correspond to the sound in a precise manner (since they don't just reflect the structure of the sound, but also the current emotional state, previous memories, expectations and various perceptions of the different aspects of music. Since those aspects are not directly related to the structure of the music per se, it is also highly unlikely that those complex processes would lead to logical rhythmical patterns. Logical at least to our present-day brains/knowledge). The EEG "give-us a taste" of all this activity and hence doesn't probably reflect a cycle-to-bit correspondence. Such a cycle is evident in the brains primitive areas mentioned before though.
Now that is a really long and nerdy answer damn!
Last edited by PETRAN on Nov-30-2009 at 21:47
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