Dear Mr. Kopfermann,
Due to your close friendship with my parents from our early childhood, my sister and I both benefited a great deal from being acquainted with you. I am very grateful to my parents that they convinced you to become our music teacher. I can only call it an extraordinary privilege to have had a music teacher of such eminent standing. Unfortunately, the pupil did not quite match the teacher, as I must admit that I could and should have learnt more from you than what I actually did. Yet nevertheless, your teaching had a great impact on me and my conception of what music is, or should be. Above all, the idea that there is a “true” music that must be clearly distinguished from all other kinds of man-made acoustical phenomena. But what is the nature of such “true” music? A person of a far less deep understanding of music like me, might find himself somewhat like Parzival in search of the Holy Grail. What distinguishes “true” music from the rest? While the answer to this question of course resides within the realm of music itself, as a neurobiologist one may see some interesting analogies between how a musical work is composed and neuronal circuits operate.
Naïvely, music can be considered as being comprised of essentially two aspects, i.e. its material (the Töne, which were the famous and hotly-debated subject of so many discussions between you and my father that from my childhood on accompanied me with unfailing intensity over the years) and its arrangement within a composition. Now, in the nervous system we also deal with two such elements, namely (i) the neurons and (ii) their interconnectivity. Neurons may then be seen as analogous to the “Töne” in as much as they occur in different functional flavours. First of all, they may be either excitatory or inhibitory meaning that they may increase or decrease the activity in other neurons to which they are connected. Secondly, they differ in their intrinsic discharge properties, so that some neurons are called “regular spiking” because they discharge their action potentials at regular temporal intervals when stimulated, while others fire in bursts, thus exhibiting an intrinsic dynamic temporal structure in their discharge properties. Finally, the so-called “fast spiking neurons” fire at extremely high frequencies. Within some limits, these features can be considered stable. The particular firing types are due to the equipment with different sets of ion channels that endow these cells with distinct response patterns to the very same stimulus.
While thus considering the neurons as the underlying material from which nervous activity can be composed, the way they are interconnected within the circuitry may be analogous to the composition itself. Due to their specific intrinsic properties, not all possible combinations of connectivity may result in a stable circuit, thereby exerting a selection among all possible combinations. For instance, certain connections may be “prohibited” such as strong feedback excitation that may however occur under pathological conditions such as epilepsy. Here recurrent connections between excitatory neurons result in widespread synchronisation that interferes with the proper functioning of the circuit. In a naïve analogy, such epileptic seizure activity may share some features with synchronisation of musical sound via constant percussion thus disabling a finer temporal dynamic structure.
These considerations about the neurons and their functional assembly may thus be an analogy to the way Töne become assembled in music. Semir Zeki has stated in his book Inner Vision: An exploration of Art and the Brain that in a certain sense painters may be conceived as neurobiologists of vision. Painting would be a process by which we attempt to understand the process of seeing, against a neurological background. He derived this idea from the observation that certain works of art would be tailor-made to optimally activate specific neurons within the path of visual processing. Thus, these paintings may be said to reveal something about the nature of visual processing, as they provide a kind of mirror image of the neuronal circuitry. Likewise, the musician may be seen as a neurobiologist of the acoustical sense and the process of hearing, but possibly also of neuronal processing in a more general way. By means of arranging Töne distinctly combined in a time does he not create a model or mirror image of the temporal structure of neuronal activity?
Remarkably, auditory and visual cortices differ in their micro-architecture. Work from Mriganka-Sur and colleagues revealed that the respective micro-architectures are dependent on “instructions” that the visual and the auditory cortices receive from their corresponding thalamic input structure that relay sensory input [1]. For instance, the redirecting of visual thalamic fibres into the territory of the auditory cortex at certain developmental stages, results in a reorganisation of horizontal connections within this cortical area, hence resembling a visual area. Moreover, animals that underwent such rewiring interpreted the processing of such visual stimuli, even though “perceived” by a piece of auditory cortex, indeed as seeing, not hearing. Thus, in a certain way, the cortex may be thought of as a kind of tabula rasa that can adopt different micro-architectures depending on the temporal structure of the input it receives [2]. This temporal structure may in part be due to some inherent physical properties of the stimuli themselves and will certainly also be dependent on the intrinsic properties of the neuronal elements that are involved in the processing of the stimulus prior to reaching the cortex. But it will also be dependent on the temporal structure of the stimuli upon arrival at the senses. Thus, one may also ask whether some aspects of the cortical micro-architecture may be modifiable by music. A more complex musical composition may also induce a more complex neuronal micro-architecture. If so, one may wonder whether the development of music was accompanied by a development of the brain areas involved in its processing. If so, the term experimental music may gain the additional meaning of experimenting with our own brain.
With this I will finish, not without wishing you all the best for your 70th birthday.
With great affection,
Benedikt Berninger
References:
1. von Melchner, L., Pallas, S.L., and Sur, M. (2000). Visual behaviour mediated by retinal projections directed to the auditory pathway. Nature 404, 871-876.
2. Kalisman, N., Silberberg, G., and Markram, H. (2005). The neocortical microcircuit as a tabula rasa. Proc Natl Acad Sci U S A 102, 880-885.
