Scientists have long known that nerves create electromagnetic pulses that electrodes on the scalp detect as brain waves. They include alpha-beta waves at 8-38Hz, theta waves that occur in sleep at 3-8Hz, and gamma waves of intense focus at 38-42Hz, but their general role is unknown.
Nerves must synchronize their firing to produce brain waves. In cat brain studies, cortical neurons synchronize their fire at a high degree of precision to produce beta-gamma waves (Gray, 1989) that relate to the binding problem:
“… 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.
Nearly all neural areas in the brain beat in synchrony, which isn’t easy given nerve synapse, conductance, and propagation time delays. Even distant cortical neural areas achieve zero-phase synchrony, to beat almost perfectly in time, which 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.
Entrainment was discovered when Huygens found that pendulums set in motion would all synchronize by the next day, because out-of-phase oscillations exchange energy that drops to zero when they vibrate in phase. In the same way, playing a note on a violin makes the violin next to it play that note without touching it by resonance. Neuronal entrainment that allows resonances is ubiquitous in a wide variety of brains (Lakatos, 2019).
The encapsulation principle, that different hierarchies can’t exchange data, means that nerves between distant brain areas don’t transmit content data. When a nerve in the visual cortex fires to register a line angle, it doesn’t encode a message like “I saw a 10° angle at location x,y,z”, it just fires. If a camp surrounded by beacon lights sees that one is lit, it means an enemy is coming that way and likewise when a nerve fires, its location implies the rest. In computing, the simplest signal is a ping, like a ping test that sends a no-content message to see if a web site still works. By encapsulation, signals between distant brain areas are pings with no information content at all!
If distant nerve interactions are just pings, there is no thought information to compete for consciousness (Baars, 1988), or to broadcast a global ignition that causes consciousness (Dehaene, 2014). Nerves constantly repeat reciprocal signals between areas but this “chatter” doesn’t exchange data. Instead, it establishes the phase synchronies that give the brain waves we register.
The brain is an neural oscillator network that can explore a vast domain of resonances. Models of oscillator networks with delayed links show that low frequency hubs can enable higher frequency synchronies (Vlasov & Bifone, 2017), so slow brain waves can help faster ones keep time. The brain 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. The neural synchrony evidence is so compelling that some suggest it is an information code, but there is no evidence for that (Uhlhaas, 2009). Others link synchrony to consciousness to conclude that:
“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.
It is now proposed that consciousness relates directly to brain-generated neural synchronies.