Phys.org has a great overview of two issues from Royal Society Publishing on the origins of nervous systems. One great thing about the issues is it seems so far at least that almost every article in the two issues seems to be freely and easily available to anyone. The direct links to the issues are here and here.
The Phys.org article by John Hewitt Where did brains come from? focuses especially on the origins of nervous systems with neurotransmitters. “Jékely’s chemical brain hypothesis postulates that neurotransmitters came before synapses and neurites, as opposed to the other way around. In other words, transmitters make nervous systems”. However, the coverage of the two issues is much broader than the Phys.org article suggests. It includes, among others, papers on learning in slime molds, origin of self, and transitions in learning and cognition by Simona Ginsburg and Eva Jablonka.
However, what has more immediately attracted my attention is a paper by Alison Hanson Spontaneous electrical low-frequency oscillations: a possible role in Hydra and all living systems. I would like to quote some major excerpts from it. Here is its abstract. Bolding is mine.
As one of the first model systems in biology, the basal metazoan Hydra has been revealing fundamental features of living systems since it was first discovered by Antonie van Leeuwenhoek in the early eighteenth century. While it has become well-established within cell and developmental biology, this tiny freshwater polyp is only now being re-introduced to modern neuroscience where it has already produced a curious finding: the presence of low-frequency spontaneous neural oscillations at the same frequency as those found in the default mode network in the human brain. Surprisingly, increasing evidence suggests such spontaneous electrical low-frequency oscillations (SELFOs) are found across the wide diversity of life on Earth, from bacteria to humans. This paper reviews the evidence for SELFOs in diverse phyla, beginning with the importance of their discovery in Hydra, and hypothesizes a potential role as electrical organism organizers, which supports a growing literature on the role of bioelectricity as a ‘template’ for developmental memory in organism regeneration.
And here is where the paper points to similarities between oscillations in the Hydra and the Default Mode Network in the human brain.
Sherrington’s still-influential proposal of the nervous system as effectively a ‘reflex organ’ waiting for environmental stimuli to push the organism to behavioural response —the foundational proposition of the input–output view of information processing —cannot account for spontaneous neural activity that seemingly has no effect on behaviour. As we have seen, however, such ‘cryptic’, non-behaviour-inducing spontaneous activity has been recognized in Cnidaria for more than half a century. Although speculated to play a role in coordinating animal behaviour at the time, the function of this activity was left to ‘future work’, which was never done. While poorly understood, findings across diverse Cnidaria were essentially the same: endogenously active nervous systems produced rhythmic, low-frequency pulses even in an unchanging environment and even when organisms were at rest. Why? Why would energetically expensive nervous systems be perpetually active in the absence of a stimulus and in the absence of any discernible behaviour? A clue about the potential role of this low-frequency spontaneous neural activity in comparatively simple organisms comes from an unexpected place: the human brain.
This is tied back to theories by Buszáki.
Another way to think about the potential role of the DMN in human self-construction is as the top layer of the hierarchical predictive coding ‘self-model’ as put forth by Friston. Like Buszáki’s theory, which predicts the need for an ultimate brain integrator or ‘reader’ (i.e. a ‘self’), a hierarchical predictive coding model also implies the need for an ultimate brain integrator or ‘predictor’ (also a ‘self’) at the top of the hierarchy. According to predictive coding brain models, prediction error is passed up the hierarchy from the low-level primary, unimodal sensory areas to the ultimate, multi-modal ‘predictor’ at the top of the hierarchy, which contains a high-level abstract representation (of the ‘self’) that then passes predictions back down to the lower levels. In this way, the DMN, oscillating at the lowest frequency in the brain, might act as the brain’s ultimate information integrator, receiving input from all the lower-level, otherwise isolated units (oscillating at higher frequencies), and passing on one unified ‘self’ prediction back down to generate coherent, adaptive behaviour
In conclusion, the author Hanson conjectures “that SELFOs may be the ultimate organism-wide electrical information integrators and communicators in all biological systems at all levels of scale, making them critical for maintenance of organism unity and coherent, adaptive behaviour”.
McFadden in his EM field theories emphasizes the noticeable synchronous firing of neurons during cognition, however, seems to pay little attention to the so-called “background noise” of the brain. These noticeable firings (frequently shown in red on brain images) are frequently used as proxy representations of consciousness in many cognition studies. I would suggest this might be a mistake. Base consciousness might be found in the EM fields generated by regular, even somewhat non-descript, firings of the DMN whereas the noticeable firings found on MRIs may, in fact, represent the integration of new information into the base consciousness.
Whatever the case may be Hanson provides some interesting thoughts in line with the Cellular Basis of Consciousness theory of Reber..