The neural binding hypothesis proposed decades ago (Crick & Kock, 1990) is that if some nerves represent a trunk and others its leaves, they represent a tree when they fire in synchrony, so synchrony combines information, but why isn’t clear as synchronizing physical oscillators doesn’t unify their information. Yet neural synchronies seem to unify cognitive outputs as they:
a. Accompany face recognition. Face recognition occurs when distant nerves synchronize with no phase lag (Rodriguez et al., 1999).
b. Accompany object recognition. In the visual cortex, the “… selection of responses for further processing is associated with enhanced synchronization rather than increased firing.” (Singer, 1999), p62, so synchrony could let one object direct responses.
c. Represent odors. Different smells produced odor-specific synchronies in locust olfactory nerves for different smells but not for the same smell (Laurent et al., 1996), so the observation of odors could depend on nerve synchrony.
d. Are transient. Neural synchronies are often brief and hard to detect (Singer et al., 1997), just as sensory experiences are often fleeting moments.
e. Accompany cognitions. Beta/gamma brain waves correlate with cognitive functions like attention, recall, sense integration, and motor coordination (Uhlhaas, 2009), p8, so synchrony could provide the binding of neural functions they require.
Studies from insects, cats, monkeys, and humans then support the theory that neural synchronization binds neural groups with different functions (Fries, 2015), p220. The result is a mood of optimism that our consciousness experience is coming within the realm of science:
“Beliefs about the basis of subjective experience have slowly evolved, from mystical notions of the soul and a disembodied mind to acceptance of the proposal that consciousness must derive from neurobiological processes.” (John, 2005) p143.
But if our consciousness derives from a brain-wide neural synchrony that binds brain functions, it isn’t unique to us. For example, locusts exhibit neural synchrony so they must experience as we do to some degree. Human consciousness as the ability to unify brain functions then began in other animals, like a bright light that evolved from dimmer ones. And if our brain evolved many synchronies, as brain waves suggest, some may occur outside the global synchrony we experience, to allow for example subconscious effects. This implies that the degree of consciousness depends on the synchrony size generating it, so people under anesthetic, sleeping, or sleepwalking have less consciousness not none at all.
Brain synchronies also build-up in a time-frame that reflects the chronology of a conscious experience (John, 2005):
1. 50 milliseconds: P1 waves occur as nerve synchronies in primary sensory cortex areas that register input features.
2. 130 milliseconds: N1 wave synchronies link the cortex to the thalamus/limbic system.
3. 210 milliseconds: P2 waves link higher cortex layers to the thalamus/limbic system.
4. 300 milliseconds: Sustained P300 gamma oscillations synchronize the frontal and parietal lobes with zero-delay in what is considered the basis of human perception itself.
Sense input triggers local synchronies in sensory areas, then long-range synchronies add emotions, memory, and language to give a global conscious experience. There is agreement that neural synchrony relates to consciousness, but how it does so is unclear.