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There are some basic cases of stimuli that are typically experienced either as pleasant or unpleasant, e.g. the major third as opposed to the tritone.

Assuming that there are different processes going on in my brain while listening to these two intervals, I'd like to know: What are the qualitative differences between these processes that would allow to understand that the first is experienced as pleasant and the other is experienced as unpleasant.

Just by thinking about it, there seem to be three possibilities:

  1. The same regions/areals/neuron groups are active but in different characteristic modes, exhibiting different spatio-temporal patterns of neural activity.

  2. Different regions are active in different modes.

  3. Different regions are active but in somehow similar modes.

Assuming that the difference is mainly due to different activity modes (cases 1 and 2), I would like to know which characteristics might correlate with the pleasantness and unpleasantness of the expericence, e.g. some kind of "harmony".

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Simply put, pleasant/unpleasant sensations are associated with the activation of certain brain regions:

Many affective stimuli are hedonically complex mixtures containing both pleasant and unpleasant components. To investigate whether the brain represents the overall affective value of such complex stimuli, or the affective value of the different components simultaneously, we used functional magnetic resonance imaging to measure brain activations to a pleasant odor (jasmine), an unpleasant odor (indole), and a mixture of the two that was pleasant. In brain regions that represented the pleasantness of the odors such as the medial orbitofrontal cortex (as shown by activations that correlated with the pleasantness ratings), the mixture produced activations of similar magnitude to the pleasant jasmine, but very different from the unpleasant indole. These regions thus emphasize the pleasant aspects of the mixture. In contrast, in regions representing the unpleasantness of odors such as the dorsal anterior cingulate and midorbitofrontal cortex the mixture produced activations that were relatively further from the pleasant component jasmine and closer to the indole. (The Journal of Neuro Science)

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  • $\begingroup$ Your answer is in favour of case 3, right? The most mysterious one, in my opinion: How can somehow similar modes of (mere) activity of just different regions give rise to such different experiences? $\endgroup$ – Hans-Peter Stricker Jan 7 at 17:13
  • $\begingroup$ I would consider all 3 possibilities you mentioned, for example, a certain neurotransmitter in a certain amount acting on a certain receptor can stimulate, but in a larger amount it can inhibit a process, so the difference can occur literally on the level on a single neuron. But the case I presented is in favour of your 3rd option, I think. $\endgroup$ – Jan Jan 7 at 17:16
  • $\begingroup$ @Hans-PeterStricker, A sound may be perceived as pleasant due to a different activity of a single neuron, a combination of activities in a single brain cortex area or a combination of activities in different areas. $\endgroup$ – Jan Jan 7 at 17:25
  • $\begingroup$ Is this true: "due to a different activity of a single neuron"? Is there evidence for this? $\endgroup$ – Hans-Peter Stricker Jan 7 at 17:35
  • $\begingroup$ @Hans-PeterStricker, I can't say strictly for pleasantness and unpleasantness of music, but, for example, regular caffeine use can result in resistance to the caffeine effects due to downregulation of receptors, as in this study in mice: "a downregulation of A2A receptor mRNA after both acute and repeated intraperitoneal injections with caffeine was found." Receptors are on a level of a single neuron, but of course, downregulation occurs in many neurons in a certain area at the same time. $\endgroup$ – Jan Jan 7 at 17:56

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