This is the final post in a series I’ve been doing on Simona Ginsburg and Eva Jablonka’s book: The Evolution of the Sensitive Soul, a book focused on the evolution of minimal consciousness. This is a large book, and it covers a wide range of ideas. A series of relatively small blog posts can’t do them justice. So by necessity it’s been selective. Similar to Feinberg and Mallatt’s The Ancient Origins of Consciousness, there’s a wealth of material I didn’t get to, and like that other book, I suspect it will inspire numerous additional posts in the future.
This final post focuses on various areas that G&J (Ginsburg and Jablonka) explore that caught my interest. So it’s somewhat of grab bag.
The first has to do with memory. Obviously memory and learning are closely related. The consensus view in neuroscience is that the main way memory works is through the strengthening and weakening of chemical synapses, the connections between neurons. In this view, engrams, the physical traces of memory, reside in circuits of neurons that follow Hebbian theory, often summarized as: neurons that fire together, wire together.
But it’s widely understood that this can’t be the full story. Synapses are complex ecosystems of proteins, vesicles, neurotransmitters, and neuromodulators. Proteins have to be synthesized by intracellular machinery. So the strengthening or weakening of a synapse is thought to involve genetic and epigenetic mechanisms as well as ribosomes and other components.
G&J focus cite a study that shows that if synaptic processing is chemically inhibited, so that the synapses retract, long term memories are still able to recover. In other words, the state of the synapse may be recorded somewhere other than the synapse itself. If so, the synapse could be just an expression of an engram stored intracellularly, perhaps epigenetically, an epigenetic engram, an intriguing possibility that may eventually have clinical implications for Alzheimers and other types of neural degenerative diseases.
G&J note that this may mean that epigenetic factors could have large scale effects on how fast synapses grow or weaken. In their view, it may dramatically expand the computational power involved in memory. They even speculate that it could be a system that operates independently of the synaptic one, transmitting information between neurons using migratory RNAs encapsulated in exosome vesicles.
This intercellular transmission could be the mechanism for some learning behavior, such as Kamin blocking, the phenomenon where if there is already an existing association between two stimuli, and a third concurrent one is introduced, that new one won’t become part of the association. This mechanism is poorly understood at the neural level.
You might have noticed all the occurrences of “may” and “could” above. G&J admit that much of this is speculative. There’s no doubt that synaptic processes are supported by intacellular machinery, and exosome vesicles do exist. But the idea that engram states are maintained epigenetically needs, I think, a lot more fleshing out, not to mention evidence. And while the exosomes could conceivably be carrying molecular level memory type information, it seems more likely they’re much more banal metabolic signaling to surrounding glia.
Still, G&J note that there is intense research going on in this area. And it always pays to remember that life is a molecular phenomenon. So only time will tell.
On the next topic, like many animal researchers, G&J cite the views of Bjorn Merker approvingly, notably the idea that consciousness is a low level process starting in the brainstem. (A view I’ve critiqued before.) This puts them partially on the same page as F&M (Feinberg and Mallatt) in The Ancient Origins of Consciousness. In the last post, I noted that G&J come to similar conclusions as F&M on when consciousness evolved. In reality, they use F&M’s review of the research, as well as Merker’s material, in reaching their conclusions.
But this leads to a problem. G&J have a different definition of consciousness than F&M. F&M divide consciousness into three types: exteroceptive consciousness, interoceptive consciousness, and affective consciousness. G&J’s definition seems to most closely align with F&M’s for affective consciousness.
But F&M’s embrace of brainstem consciousness (at least in pre-mammalian species) seems to hinge on the fact that they see exteroceptive and interoceptive processing as sufficient for consciousness. G&J don’t; for them, affective processing is necessary. But F&M’s data indicate that the type of learning necessary to demonstrate the presence of affects only happens in the forebrain.
The reason why pallial function in anamniotes is such a tough problem is that a fish whose pallium has been removed or destroyed can see, catch prey, and seems to act normally. However, such a fish cannot learn from its experiences or from the consequences of its actions. Nor is it able to learn the locations of objects in space. This is a memory problem, and the medial and dorsal pallia of vertebrates are known to store memories.
Feinberg, Todd E.. The Ancient Origins of Consciousness: How the Brain Created Experience (MIT Press) . The MIT Press. Kindle Edition.
On the one hand, forebrains go back to early vertebrates, so affective consciousness is preserved. But in fish and amphibians, much of the exteroceptive and interoceptive processing is separate from affective processing. This isn’t much of an issue for F&M, but it could be seen as weakening G&J’s conclusion that these early vertebrates had the same unified consciousness as later species.
Third topic: G&J late in the book note the existence of something I’d missed until now, a unicellular organism, warnowiid dinoflagellates, that have something called an “ocelloid”, which appears to be something like a camera style eye, much more sophisticated than the typical light sensors that exist at this level. However, these protists are difficult to study in laboratory conditions. They tend not to survive outside their natural habitat, which makes them difficult to study. So the function of this structure is largely conjecture. Still, if it is an eye, what kind of processing in a unicellular organism might such a complex structure be supporting?
Finally, G&J touch on the topic of machine consciousness. Somewhat refreshingly for people who use the “embodied” language, they don’t rule out technological consciousness. However, they note that it could be very different from evolved consciousness in animals. Importantly, they see UAL as an evolutionary marker for consciousness in biology. Its existence in technological systems may not necessarily indicate the presence of machine consciousness. And they expect machine consciousness to require a body, but they allow it could be a virtual one.
As always, my take on these things is it depends on how we define “consciousness”.
As noted above, there is a lot more in this book, some of which I might touch on later. But I think this is it for now.
Finally, and I should have linked to this in the last post, if you want a condensed version of their thesis, and don’t mind wading through some technical material, their paper on unlimited associative learning is online.
What do you think of the idea of epigenetic engrams? Or the various definitional issues? Or G&J’s approach overall?