Imagine a symphony orchestra where each musician has their own specialized set of notes and rhythms. This musical ensemble represents the brain’s tonotopic map, a beautifully organized arrangement of neurons that respond to different frequencies and phases of sound. In our latest research, we have developed a model called the Oscillatory Tonotopic Self-Organizing Map (OTSOM), which simulates this harmonious arrangement using a 2-dimensional array of Hopf oscillators. These oscillators act like individual musicians, capable of decomposing sound signals into distinct frequencies and phases, just like an orchestra performing a Fourier-like decomposition! Unlike previous models, our OTSOM model not only captures the frequency tuning as an abstract parameter but also achieves precise phase tuning by coupling pairs of oscillators. It’s like conducting a symphony where musicians synchronize not only their pitches but also their timing. By training the OTSOM model in two stages, we are able to adapt the frequency and phase tuning processes separately, mimicking how our auditory cortices perceive and process sound. This research opens up exciting possibilities for understanding how mammals, such as echolocating bats, map tonal information in their brains. To explore the intricate world of neural oscillators and learn more about our model, check out the full article!

We present a model of a tonotopic map known as the Oscillatory Tonotopic Self-Organizing Map (OTSOM). It is a 2-dimensional, self-organizing array of Hopf oscillators, capable of performing a Fourier-like decomposition of the input signal. While the rows in the map encode the input phase, the columns encode frequency. Although Hopf oscillators exhibit resonance to a sinusoidal signal when there is a frequency match, there is no obvious way to also achieve phase tuning. We propose a simple method by which a pair of Hopf oscillators, unilaterally coupled through a coupling scheme termed as modified power coupling, can exhibit tuning to the phase offset of sinusoidal forcing input. The training of OTSOM is performed in 2 stages: while the frequency tuning is adapted in Stage 1, phase tuning is adapted in Stage 2. Earlier tonotopic map models have modeled frequency as an abstract parameter unconnected to any oscillation. By contrast, in OTSOM, frequency tuning emerges as a natural outcome of an underlying resonant process. The OTSOM model can possibly be regarded as an approximation of the tonotopic map found in the primary auditory cortices of mammals, particularly exemplified in the studies of echolocating bats.

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