It is an odd fact that out-of-phase metronomes synchronize overnight if left side-by-side on a wooden board. Huygens called this entrainment, and it occurs because out-of-phase vibrations exchange energy that drops to zero when they vibrate in phase. Playing a note on a violin also evokes the same note in the violin next to it without touching it by resonance. Hence when neuroscientists discovered that brain waves are ubiquitous in a wide variety of species, they attributed it to neuronal entrainment creating resonances (Lakatos, 2019).
For example, electrodes on the human scalp detect electromagnetic pulses, such as alpha-beta waves (8-38Hz), theta waves of sleep (3-8Hz), and gamma waves of intense focus (38-42Hz). These waves require nerves to synchronize their firing, so cortical neurons in a cat brain must synchronize their fire very precisely to produce beta waves (Gray, 1989).
Given nerve synapse, conductance, and propagation time lags, for distant cortical areas to beat almost perfectly together in zero-phase synchrony is an extraordinary feat:
“Early studies showed that zero-phase lag synchronization can occur even between distant neuronal assemblies,… This is particularly relevant as the conduction delays in the cortex make the occurrence of zero-phase lag synchronization difficult to accomplish.” (Uhlhaas, 2009), p3.
Neurons are then electro-magnetic oscillators that entrain to produce resonances, but how is unclear, and why is even less so. Regarding how, nerves connecting distant neural assemblies can’t exchange data by the encapsulation principle, so their purpose isn’t to transmit content. Computer networks use no-content signals called pings to measure the time taken for a web site to respond, so brains could do the same, as distant brain areas linked by reciprocal pings could establish the same pulse frequency to create a resonance. Note that if distant nerve signals are pings not chatter that exchanges data, there is no information to compete for consciousness (Baars, 1988), or to broadcast a global ignition that causes consciousness (Dehaene, 2014). The evidence for neural synchrony is compelling but it is unlikely to be an information exchange code (Uhlhaas, 2009).
The brain is then a neural oscillator network that explores a domain of resonances using pings. Models of oscillator networks with delayed links show that low frequency hubs can enable higher frequency synchronies (Vlasov & Bifone, 2017), so slow brain waves could keep fast ones in time.
But why might regions that respond to different features synchronize their neurons, then use neuron pings to other regions to also synchronize with them? Brains evolved many long-range and precise lag-free synchronies, so it must serve a key function, and the exquisite time sensitivity of neural spikes implies that timing is critical. Neuroscience concludes that these synchronies somehow solve the brain’s binding problem, as studies:
“… have demonstrated that response synchronization is a ubiquitous phenomenon in cortical networks and is likely to serve a variety of different functions in addition to feature binding at early levels of sensory processing.” (Uhlhaas, 2009), p1.
Neural synchronies are ubiquitous in animal and human brains, so it is possible that as regions specialized to observe different features, synchrony acted to bind them into a unified observation. This then has implications for the unity of observation experience we call consciousness, as:
“The central issue is how coherent, informational activity in multiple cortical areas is welded into a seamless unity that becomes aware of itself.” (John, 2005), p160.