(Warning: neuroscience weeds)
An interesting paper by Tim Bayne, Anil Seth, and Marcello Massimi, which came up in my Twitter stream today, asks whether there can be islands of awareness.
Ordinary consciousness involves ongoing interaction with the environment, receiving sensory information, and producing motor output. It has a functional role, enabling an organism to deal with novel situations, including dangers and opportunities.
However, it is possible, due to injury or pathology, for some or all of this interaction to be lost, for the consciousness to become isolated. The authors start out discussing various medical situations where people can become almost completely disconnected on the output end, only able to communicate with the world by the twitching of an eyelid, or even worse, be completely locked in, unable to communicate at all.
It’s also possible to become disconnected on the input side. Some of these cases are reversible, such as what happens in dreaming. In that state, we’re generally disconnected from the outside world, although with a strong enough stimulus, that can usually quickly be reversed. There is also the anesthesia drug ketamine, which apparently provides the same disconnection, but doesn’t always extinguish consciousness, sometimes leading to vivid and terrifying experiences.
But what the authors are most concerned about here are actual islands of awareness, where the system in question is completely isolated from the environment. They explore three scenarios: ex cranio brains in a nutrient vat, hemispherotomy, and cerebral organoids.
An example of ex cranio brains were the disembodied pig brains which were kept alive in a nutrient delivery system. The nutrient mix included a neural inhibitor to ensure that the brains wouldn’t regain consciousness, but suppose that inhibitor hadn’t been present? Could such brains actually be conscious? A lot of people would say no, that consciousness requires interaction with a body. But if such a brain showed wide scale organized activity, it might “put pressure” on embodied cognition theories.
A hemispherotomy is sometimes performed on a patient with severe epileptic seizures. It involves severing the connections between the damaged hemisphere and the other side, as well as its connections with the brainstem, thalamus, and other subcortical structures. However, a hemispherotomy, unlike a hemispherectomy, leaves the tissue in place, with all of its vascular connections.
Could such a disconnected hemisphere be conscious? The authors note that, under normal circumstances, without the activating signals coming up from the RAS (reticular activating system) in the brainstem, the activity in the disconnected tissue has very low firing rates, equivalent to a deep dreamless sleep. But, they ask, what would happen if electrodes were inserted and used to stimulate the hemisphere? Might it then regain some consciousness?
The authors discuss the role of subcortical regions in consciousness. It’s well established that they provide crucial support, but what is the nature of that support? Are they causal, constitutive, or both? Causal means they just cause awareness in cortical tissue but don’t participate in generating or consuming the content. Constitutive means they do.
Personally, I think with a disconnected thalamus, the question is somewhat moot. Such a hemisphere’s ability to communicate with its disparate regions would be heavily compromised. I tend to doubt any awareness is possible under those conditions. Only if the subcortical connections were kept intact, with only the RAS disconnected, might it be possible to re-stimulate some form of consciousness.
The third scenario is cerebral organoids. I did a post on these a few months ago. The chances that any form of awareness exists in these largely random collection of neural cells is so close to zero that I find worrying about it counter-productive. There’s simply nothing to indicate these small clumps of neural tissue are organized to have any sensory or affective functionality, and without that, it’s hard to call whatever is happening in them consciousness. We might as well worry about whether brain tumors or other excised tissue are conscious.
The authors worry that as organoids continue to be developed, there may eventually be issues. I guess that’s possible, but it only seems to be a significant possibility when enough of the various components of the brain start to be included, which still seems very remote.
The authors mention other possibilities, such as an in utero fetus with some pathology causing it to be completely disconnected. Given how immature the brain is until well into the third trimester, this only becomes a possibility in the last few months of pregnancy, but it is a possibility. Would such a system, with no history of sensory input, be conscious in anything like our understanding of the word?
But the most likely scenario is the ex cranio one, such as the pig brains. It seems inevitable that someone will eventually try that experiment without the inhibitors. What will it mean if the brains in that scenario do show wide scale organized activity? The paper discusses the difficulty of detection in these scenarios, and of avoiding false positive and false negatives.
It’s worth noting that the major cognitive theories: global workspace (GWT), integrated information (IIT), and higher order thought (HOT), are compatible with the ex cranio scenario. But the more fragmented the tissue is, the less compatible these theories are, although IIT may posit even organoids as having some level of consciousness. The theory that might be most compatible with small fragmentary islands is recurrent processing theory (RPT).
The paper finishes up by noting that neuroscientific progress increases the chances of producing these islands, and that they may already exist. They call for careful consideration of the ethical issues involved.
What do you think? Are conscious hemispheres or organoids more likely than I think? Or are there solid reasons to conclude that disembodied cognition is impossible?