Ex 21 Artlabeling Activity Figure 111 Integration Sensory Input Motor Input

Highlights

• Awareness may persist in fully disconnected cortical islands.

• We identify both natural and artificial examples of potential islands of awareness.

• Detecting islands of awareness poses difficult but often addressable challenges.

• The possibility of islands of awareness raises important ethical and legal issues.

• The discovery of islands of sensation would accept of import implications for debates about the nature of consciousness.

Ordinary human feel is embedded in a spider web of causal relations that link the brain to the torso and the wider environs. However, there might be conditions in which encephalon activeness supports consciousness even when that activity is fully causally isolated from the body and its environs. Such cases would involve what we phone call islands of awareness: conscious states that are neither shaped by sensory input nor able to be expressed by motor output. This Opinion paper considers conditions in which such islands might occur, including ex cranio brains, hemispherotomy, and in cognitive organoids. We examine possible methods for detecting islands of sensation, and consider their implications for ethics and for the nature of consciousness.

Keywords

• cerebral organoids
• ex cranio brains
• dreaming
• disorders of consciousness
• Guillain-Barré syndrome
• hemispherotomy
• measures of consciousness
• neuroethics

The Challenge of Islands of Sensation

Consciousness is first and foremost a holding of living organisms – organisms that are embodied and embedded in environments. The contents of consciousness are shaped by the sensory stimuli received by the brain, and those contents in plow give ascent to behaviours that prompt the states to attribute consciousness to an organism. However, at that place are conscious states in which the transfer of information betwixt the world and the brain is massively reduced, with the result that the brain (or parts thereof) becomes asunder from its surroundings. In some conditions, disconnection is partial, and then that some form of either input and/or output is retained. In other conditions, the disconnection is complete, and so that the encephalon (or parts thereof) becomes fully isolated from its environs.

What happens to consciousness when the encephalon becomes disconnected from its environment? Can information technology support islands of awareness (encounter Glossary), or does consciousness require the presence of (high bandwidth?) interaction between the encephalon and its environment? This question has long fascinated philosophers, just contempo developments in neuroscience, neurosurgery, and neuroengineering now extend the scope of this discussion beyond the philosopher's armchair and out into the laboratory and dispensary.

Nosotros address 3 issues raised by the possibility of islands of awareness. The first concerns their nature and distribution. Under what conditions might such islands arise? What forms might they take? How mutual might they be? A second result concerns the detection of islands of awareness. Might current methods for detecting consciousness be applicative to islands of awareness, or will nosotros demand new tools for identifying consciousness in disconnected brains? A third issue concerns the implications of islands of awareness. What upstanding implications might such islands take, and what might they tell the states near the nature of consciousness?

We accost these problems by considering three atmospheric condition in which islands of sensation might be idea to occur: ex cranio brains; the neurosurgical process of hemispherotomy; and cerebral organoids. Although these three cases are by no ways the merely cases that could be considered here – for case, i might besides consider whether islands of awareness could occur in utero [

] – nosotros focus on them here because they highlight the bug raised by islands of awareness with particular force and urgency.

From Fractional Disconnection to Complete Disconnection

Before we turn to genuine islands of awareness, we brainstorm with cases of merely fractional disconnection. Clinical neurology offers a rich repertoire of cases to consider here, for structural lesions tin cause the encephalon to go disconnected on either the input or the output side without loss of consciousness.

Starting from the input side, we know that consciousness can be preserved in the absence of afferent activity from peripheral receptors and fretfulness. For example, acquired blindness is a condition in which patients lose sight but retain the capacity for imagery, visual dreaming, and brilliant hallucination [

]. A corresponding dissociation tin also occur in audition [

]. We also know that direct cortical stimulation within the appropriate parameters can elicit visual, auditory, tactile, and interoceptive experiences while bypassing subcortical sensory pathways [

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] (see also [

] for a recent study in which perceptual discrimination was induced in rodents through optogenetic stimulation of visual cortex). Although we are not aware of any case in which all sensory pathways have been structurally severed without concurrent motor nerve impairment, approximations to a severe multimodal disconnection can occur in the late stages of multiple sclerosis or mitochondrial disorders [

].

On the motor side, a archetype example of partial disconnection is locked in syndrome (LIS), which can occur as the result of a ventral pontine lesion severing of all motor fibres except for the tertiary cranial nervus (which drives vertical eye movements and blinking). Despite almost complete motor disconnection, LIS patients can be fully communicative and are undoubtedly conscious. However, in some patients the neurons of the third cranial nerve are as well impaired and the patient is unable to produce any detectable motor output [

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,

]. In such patients the brain is completely disconnected on the output side, only at that place is every reason to think that consciousness has been retained despite the loss of even the final channel of motor output.

In that location are as well cases in which the brain becomes disconnected from its environment in both input and output terms, although the disconnection is non always absolute and is oftentimes reversible. I form of disconnection occurs in dreaming, when changes in neuromodulation issue in cortical gating of sensory inputs and in inhibition of motor neurons [

]. More comprehensive disconnection can occur under the influence of the dissociative anaesthetic ketamine, for at certain doses ketamine blocks both exteroceptive and interoceptive input, allowing patients to undergo invasive surgical procedures. But despite disconnection and profound unresponsiveness ketamine does not ever extinguish consciousness, and can instead induce vivid and sometimes terrifying experiences [

].

Although dreaming and ketamine involve consciousness in the context of sensory and motor disconnection, in both cases the disconnection is functional rather than structural. However, reversible disconnection tin can as well consequence from structural factors. The rare case of a conscious patient in whom concurrent atmospheric condition resulted in complete sensory (visual, auditory, and tactile modalities) and motor disconnection was recently reported [

]. Sensory–motor disconnection with preserved awareness tin also be observed in extreme cases within the spectrum of astute inflammatory polyneuropathy, such as fulminant Guillain–Barré syndrome (GBS) [

]. In some GBS patients, a complete paralysis extending to cranial nerves can exist accompanied by a severe (albeit not consummate) blockage of multiple sensory fretfulness [

,

,

]. In the initial stages of the condition patients are clearly conscious and can communicate through residual movements. Many report brilliant dreams and intense hallucinations, some of which resemble the hallucinations that are induced past weightlessness in astronauts or experienced by those in sensory deprivation tanks [

]. However, all movements are quickly lost and advice becomes impossible. Unresponsiveness can be so deep, fifty-fifty extending to absence of cranial reflexes, that the condition can mimic brain death. Notwithstanding, magnetic resonance imaging (MRI) shows no amending in the central nervous organisation and the limited electroencephalography (EEG) available in this condition shows either normal wakeful patterns or mild slowing [

]. In some cases, patient awareness can as well be demonstrated past preserved EEG and metabolic responses to auditory stimulation [

] and verbal commands [

]. Equally the condition persists, the slumber–wake wheel breaks downwardly and the EEG becomes more difficult to interpret. Patients who gradually recover motor command and functional communication tend to be dislocated and amnestic but some recall having been vividly conscious, albeit in an contradistinct state, while completely paralysed in their acute affliction [

,

].

Islands of Awareness

Although dreaming, ketamine and GBS can each involve (relatively) consummate disconnection from the environment, in each case the brain retains some capacity for being reintegrated into its surroundings. Indeed, it is this capacity that enables the retrospective reports which – together with neuroimaging data – supports the inference that consciousness has been retained. However, it is interesting to ask whether consciousness might also occur fifty-fifty in systems that lack any sensory or motor connections to the body or environment. We phone call such centres of consciousness 'islands of awareness'. An island of sensation can exist thought of as a limiting case of the kinds of sensory and motor disconnections that we have considered in a higher place (Effigy 1). In each of those cases disconnection is merely partial, for at least some sensorimotor pathways between the brain and its environment are retained. A genuine island of awareness, withal, has no sensorimotor interaction with the body that supports it, nor with the environment that surrounds it. It is also important to distinguish islands of awareness from instances of covert consciousness, in which consciousness is not manifested in outward behaviour, and for which there is now significant prove in at to the lowest degree some behaviourally unresponsive patients who have emerged from coma [

,

]. Islands of awareness are more profoundly isolated: their experiences are causally isolated from both the body and the environment, and in both motor and sensory respects.

Figure 1 Schematic Representation of Some Possible Instances of Islands of Sensation in Relation to Other Atmospheric condition of Consciousness.

Prove total caption

The graph represents different atmospheric condition as a function of their approximate level of sensory and motor connectedness. The black purlieus defines the high level of connexion typical of healthy awake humans. The blue boundaries include conscious states characterised by forms of disconnection that are functional and reversible (due east.g., dreaming, and hallucinations during ketamine anaesthesia). The xanthous boundaries include pathological conditions in which consciousness might be preserved in spite of various degrees of structural disconnection. They encompass cases of pure motor disconnection (e.g., locked in syndrome); cases of pure sensory disconnection (e.thou., multiple concurrent lesions of sensory systems); cases in which multifocal encephalon injury may affect both motor and sensory systems to a variable extent (e.k., the large gray area of the minimally conscious country, MCS); and situations that approximate complete, albeit reversible, sensory and motor disconnection (e.g., Guillain –Barré syndrome). The ruddy boundaries identify atmospheric condition of complete, irreversible structural disconnection. As depicted in the inset below, they include ex cranio brains, disconnected hemispheres post-hemispherotomy and cerebral organoids. Ex cranio brains [

], hemispherotomy [

26

• Ribaupierre de S.
• Delalande O.

Hemispherotomy and other disconnective techniques.

• Google Scholar

], cognitive organoids [

]; reproduced with permission. Abbreviation: R-ICA, right internal carotid artery.

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In what kinds of situations might islands of awareness occur? It is certainly possible that they might occur in the context of severe multifocal brain injury (Box 1). All the same, we will focus hither on weather that have not previously been considered in connection with islands of sensation – weather condition that take been made possible past advances in neurosurgery and neuroengineering.

Box 1

Islands of Sensation in Disorders of Consciousness

Following their emergence from the comatose state, many patients who have suffered from serious encephalon injury spend a flow of time in the vegetative state (also known as the unresponsiveness wakefulness syndrome), in which they fail to produce whatsoever behavioural signs of consciousness. However, neuroimaging and EEG active paradigms suggest that roughly 15% of these patients can attune their brain action to exact command, which is indicative of (covert) consciousness [

].

It is possible, however, that these figures misrepresent the true prevalence of covert consciousness in behaviourally nonresponsive patients, for the multifocal nature of traumatic brain injury often results non just in motor and sensory impairments, but too in cerebral and attentional impairments. A significant proportion of these patients might fail both overt and covert tests of consciousness not considering they are unconscious, simply just because they are unable to process or cognitively appoint with sensory stimuli [

,

]. Such cases highlight the fact that intensive care medicine is likely already creating instances of disconnected consciousness, with the precise nature of the disconnection in any i case due to both structural and functional factors. It is besides possible that the behavioural fragments that are sometimes seen in these weather – such as the utterance of a unmarried word [

,

,

] – are manifestations of transient witting experiences, rather than merely being the products of unconscious motor routines. Addressing the challenges posed by genuine islands of awareness, in which the presence of consciousness must be inferred without reliance on any intact sensory or motor pathway, might therefore facilitate the development of increasingly sensitive methods for detecting covert consciousness in postal service-comatose patients.

We begin with a study past Vrselja and colleagues [

], in which intact pig brains were extracted up to 4 h postmortem and then connected to a organisation called BrainEx, which delivered nutrients and oxygen to brain cells. Vrselja and colleagues were able to restore and maintain microcirculation as well as molecular and cellular functions of neurons under ex vivo weather for several hours, and without whatever sensory input or motor output. Significantly, they observed spontaneous synaptic action in these ex cranio brains. Although there was no prove of global brain activity and no EEG response, that fact might be explained past their use of a preservative solution that inhibited neural activity. Previous research in which guinea squealer brains were isolated and perfused in vitro in hypothermic conditions but without pharmacological blocking agents has demonstrated preservation of electrical responses beyond multisynaptic circuits [

] as well every bit synaptic plasticity [

25

• de Curtis Thousand.
• Llinas R.R.

Entorhinal cortex long-term potentiation evoked by theta-patterned stimulation of associative fibers in the isolated in vitro guinea squealer brain.

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].

While these data do non provide direct evidence for awareness in a 'naked brain', [

], they certainly enhance that possibility. Suppose that the experiment conducted by Vrselja and colleagues were to be repeated without an explicit neural inhibitor and under normothermic weather. If organised patterns of spontaneous neural activity were to be observed in this situation, the question of whether an island of awareness was present would immediately ascend (just as it immediately arises in the case of fully disconnected brains in some GBS patients).

Might islands of awareness occur even in an isolated cortical hemisphere? The relatively rare neurosurgical procedure of hemispherotomy, our second example, involves the disconnection of a damaged hemisphere in order to treat children with severe cases of refractory epilepsy [

26

• Ribaupierre de S.
• Delalande O.

Hemispherotomy and other disconnective techniques.

• Google Scholar

]. Hemispherotomy aims at maximal disconnection of white matter pathways linking the pathological hemisphere to the brainstem, thalamus, and contralateral hemisphere. The damaged hemisphere is, however, left within the cranial crenel with vascular connectivity intact. In the related procedure of hemispherectomy, the damaged hemisphere is showtime disconnected and and so removed from the brain entirely. Typical peri-insular hemispherotomy involves severing the corona radiata, resection of the temporal lobe, consummate section of the corpus callosum, subfrontal and temporal stem disconnection, and undercutting or resection of the insular cortex [

]. While neural disconnection is ordinarily assumed to be complete, some residual commissural and primal connections via the hypothalamus and optic chiasm may remain (Michael Carter, personal communication). It is clear that the intact and properly continued hemisphere supports sensation (for patients are clearly witting), but could the disconnected hemisphere also support awareness? If so, so there would exist an island of awareness in the disconnected hemisphere.

Niggling is known about the consequence of this radical deafferentation on neural activity in the disconnected hemisphere. One recent report performed intraoperative electrocorticography and found reduced broadband spectral power in regions of disconnected cortex surrounding the pathological tissue [

]. This study as well institute increased local functional connectivity in this apparently preserved cortex, using mutual information assay approaches. Intriguingly, an earlier functional MRI (fMRI) written report reported surprising and unexplained task-related blood oxygenation level dependent (BOLD) activations in a disconnected left hemisphere, following left hemispherotomy in a child with Rasmussen's syndrome [

].

Boosted prove about electrophysiological action in isolated cortex has been provided by recordings in cortical volumes of various sizes (cortical slabs), which are deafferented from the rest of the brain through a white matter undercut. Timofeev and colleagues [

] showed that small isolated cortical volumes (10 × 6 mm) can sustain sporadic depolarizing events at a frequency of 0.03–0.ane Hz. Notably, the design evolves toward a sleep-like slow oscillation in the delta range (∼one Hz) if the volume of the cortical slab is larger (xxx × 20 mm, roughly corresponding to a cortical gyrus), allowing for more recurrent excitatory action.

This stereotypical pattern resembles the slow oscillations normally observed in intact brains during dreamless sleep and may result from a lack of input from the thalamus and subcortical activating systems to the isolated cortex. This raises the possibility that replacing that input – for example, by direct electrochemical stimulation of cortical neurons or long-term homeostatic processes – might restore adequate levels of cortical excitability, and with this possibly besides some form of consciousness (Box ii).

Box 2

What Is an Enabling Factor?

An of import effect raised by many disconnection scenarios concerns the role that subcortical systems places in the generation of consciousness. These systems are often described equally enabling factors for consciousness, but that phrase can be understood in two ways: causally or constitutively. In the causal sense, an enabling factor makes a causal contribution to the target procedure in the manner in which a lightning strike might cause a forest fire, such that its causal contribution could in principle exist provided by some other process (say, a burning cigarette). If subcortical systems are enabling factors in this sense and so it is at least possible that their causal role could be replaced by some other gene (say, electrochemical stimulation), and cortical processes alone might suffice for consciousness. In the constitutive sense, an enabling factor is a crucial component of the minimal neural substrate of consciousness. Its part is non to crusade cortical systems to enter a land in which they generate consciousness – rather, subcortical activation is itself a component of the neural footing of consciousness. On ane version of this account, subcortical activity does non explain why consciousness has the detail contents that it does (it is non function of the differentiating neural correlates of consciousness), but it does play an essential role in explaining why consciousness of any kind occurs (information technology is a nondifferentiating correlate of consciousness). If subcortical systems turn out to be enabling factors in the constitutive sense, then islands of awareness would not exist possible in a disconnected cortical hemisphere, but would still occur in the context of an ex cranio brain in which cortical activeness was accordingly integrated with subcortical activity. Alternatively, different subcortical structures might plow out to exist enabling factors of different kinds. For example, brainstem activating systems and midline thalamic nuclei, modulating the excitability of cortical neurons, might have a casual role, whereas high-order thalamic nuclei and (say) the claustrum, granting tight structural integration among distant cortical areas, might be constitutive.

The third example in which islands of awareness might occur involves cerebral organoids. These are laboratory-made 3D structures derived from stem cells that display various features of the developing human brain [

]. Cerebral organoids are sometimes called 'mini brains', although it is arguable that this overstates their similarity to normal brains. The primary use of cognitive organoids has been as laboratory models of neurodevelopmental disorders such as Zika-virus-induced microcephaly, just prospective applications could encompass a broad range of neurological weather [

]. Progress in cerebral organoid development has been rapid, with recent organoids demonstrating mature neurons and established network structures. Assessment of neural activity using calcium imaging and high-density silicon microelectrodes has revealed spiking activity [

] and circuitous oscillatory waves resembling some features of homo pre-term EEG [

34

• Trujillo C.A.
• et al.

Nested oscillatory dynamics in cortical organoids model early on human brain network development.

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]. While cerebral organoids still lack a well-defined neuroanatomical axis, every bit well as vascular and food-delivery systems, it is not unreasonable to suppose that near- or mid-term developments will evangelize organoids displaying substantial structural and functional similarities to developing human brains.

Assessing the possibility of consciousness in cerebral organoids faces challenges that do not utilize to the other cases we have discussed. On the one paw, organoids develop as intact wholes, without having ever had whatever causal interaction with the external world. This might be idea to mitigate against consciousness if such connectivity is constitutively necessary for developing consciousness (Box 3). At the same time, the fact that organoids develop 'naturally' and do not endure from radical disruption to their neural structure (in the way that ex cranio brains and hemispherotomy patients do) might be thought to fence in favour of the possibility of conscious organoids. In brusque, the question of consciousness in cerebral organoids remains open up. Figure 1 summarises the various cases that nosotros have examined thus far, including both cases of asunder consciousness (in which connection can sometimes be regained) and what we term islands of sensation, in which neither sensory input nor motor output can be accomplished.

Box 3

Validating Measures of Consciousness

Validating novel measures of consciousness that can be used to detect consciousness in difficult cases – such equally those involving putative islands of awareness – raises deep methodological challenges [

,

,

]. The standard approach to validating a novel measure is to correlate the presence/absence of that mensurate with a given pretheoretical measure of consciousness, such as behavioural responsiveness. However, this approach faces problems when making inferences in cases where the pretheoretical measure by definition cannot exist obtained, such equally in disconnected patients. To address this problem, a measure'due south validation tin be extended to fit too cases of disconnection; for example, by relying on delayed report upon awakening from dreaming and ketamine dissociation. This validation strategy has already been utilised to allow for improved inference in brain-injured patients with sensory and motor disconnection [

]. More more often than not, confidence in novel measures can be gained on the ground of their overall convergence with multiple pretheoretical and previously validated measures of consciousness [

,

,

]. Confidence is further increased when such measures can be demonstrated to operationalise a particular theory of consciousness, to the extent that that theory shows general explanatory and predictive power.

A second claiming is that measures of consciousness validated or otherwise applied in adult human being beings might not transfer to (say) infants or nonhuman animals. This worry applies with particular force to cerebral organoids, considering the kinds of neural activeness that support consciousness in an organoid might differ in important respects from those that support consciousness in man brains. Relying on similarities betwixt organoid activeness and human brain activeness might pb both to the overattribution of conscious states to organoids (false positives; [

]) and, simultaneously, to the underattribution of witting states (false negatives) given that organoid consciousness might involve very dissimilar kinds of activity patterns. Having said this, if theoretically grounded and empirically robust measures applicable in humans are applied with like results in nonhuman cases, this should be taken as highly suggestive of consciousness in such cases.

The history of scientific discipline has repeatedly encountered the trouble of validating measures of incompletely understood phenomena, when accurate measurement is in turn essential for reaching a satisfying scientific understanding of the target phenomenon. For example, the development of reliable thermometers faced and overcame these problems in catalysing a concrete explanation of heat [

]. Similarly, careful and incremental extension of novel measures of consciousness to difficult cases could similarly catalyse a deeper physical understanding of the nature of consciousness that could and so in plough further validate these novel measures.

Detecting Islands of Awareness

Our capacity to tell whether some other animate being is conscious ordinarily relies on inferences from behaviour, and past definition islands of awareness accept no motor output. Although methods have been developed for detecting consciousness in behaviourally nonresponsive patients [

,

,

], most of these methods crave intact sensory pathways and thus they cannot be applied to the cases that we are considering here. How and then might genuine islands of awareness exist detected?

One interesting possibility is that consciousness tin can be detected by assessing causal interactions inside the brain, even when reciprocal interactions with its surrounding surroundings are completely interrupted. A practical way of probing the internal causal construction of the encephalon involves a perturb-and-measure approach through a combination of cortical stimulation and neuroimaging [

]. An example of this method is provided past the perturbational complexity alphabetize (PCI) in which the cerebral cortex is first stimulated by transcranial magnetic stimulation (TMS) and then EEG is used to measure the complexity of the cause–outcome concatenation of neural activations triggered within the brain [

]. PCI has proven effective in detecting disconnected awareness during dreaming and ketamine anaesthesia [

] and proven able to place conscious patients who are minimally responsive, or fully unresponsive, following severe encephalon injury [

]. In spite of its loftier accuracy, the general applicability of PCI presents practical challenges, including (for hemispherotomy) the risks posed past electrical stimulation of an epilepsy-decumbent encephalon.

There are, still, ways to guess the complication of neural dynamics without applying cortical perturbations. For case, measures of the algorithmic complication of spontaneous EEG tin track loss of consciousness beyond sleep and anaesthesia in humans [

,

,

]. Indeed, multivariate design analysis has shown that amidst all EEG features those that contribute most to the correct discrimination between conscious and unconscious patients are long-range connectivity and fourth dimension-series complexity [

]. Further evidence that the dynamic complication of intrinsic encephalon networks represents a reliable marking of consciousness has been provided by Demertzi and colleagues [

].

Given the sensitivity of network complexity measures in detecting a capacity for consciousness in challenging cases such equally ketamine dreams and minimally conscious [

] and massively disconnected patients [

], they might exist usefully applied to the fifty-fifty more challenging cases involving total disconnection. In principle, i could ask whether isolating, disconnecting, or growing encephalon islands allows for complication levels comparable with the ones found in dreaming subjects, or in the injured brains of minimally conscious patients. Clearly, the thresholds and classifiers that currently let accurate detection of consciousness in salubrious subjects and neurological patients may become less reliable as nosotros movement toward singular neural structures (Box 3). Nonetheless, these techniques would enable us to ask primal questions. Is information technology possible for ex cranio brains to display levels of complexity that are comparable with those displayed by the in cranio brains of conscious subjects? If so, for how long might that complexity exist sustained? Could the disconnected hemisphere of a hemispherotomy patient host network dynamics that are every bit complex as the ones seen in the contralateral hemisphere, or does it plunge irreversibly into a deep sleep land due to lack of ascending neuromodulation (Box ii)? Are there conditions in which cerebral organoids develop patterns of internal interactions that go progressively richer, or practice such rich dynamics require a history of interaction with the environment? Addressing these questions would tell u.s. much about the neural basis of consciousness.

Methods similar PCI and other complication measures may exist able to detect an unsuspected capacity for consciousness in asunder brains, but they cannot shed whatsoever calorie-free on the potential conscious contents that might occur in these islands. Ane in-principle approach would be to use stimulus-free neural decoding methods, such as those developed by [

] to decode the contents of dream experiences. Conspicuously, however, decoding conscious contents from within putative islands of awareness will be challenging. Although at that place is some evidence of robust mappings from neural activeness to perceptual content in neurotypical subjects [

], information technology is hundred-to-one that these mappings will also apply to atypical brains. Thus, the question of what kinds of contents might occur in islands of awareness is likely to present some of the deepest challenges hereabouts. We might exist able to tell that there is something it is like to be a disconnected brain without being able to tell merely what it is like.

Last Remarks

Suppose that we were to discover evidence of islands of awareness in ex cranio brains, hemispherotomy patients or cerebral organoids: what implications might such findings have (see Outstanding Questions)?

Let united states begin with implications for accounts of consciousness (Box 4). The discovery of consciousness in a reanimated brain would indicate that ongoing dynamic interaction with the external world is not a necessary condition for consciousness. Although this finding would be in line with some accounts of consciousness, other accounts hold that neural systems are conscious but insofar as they are in ongoing dynamic interaction with their environs. Of course, even if a reanimated encephalon were able to sustain an island of awareness for a brusque period of time, information technology is entirely possible that external input (entrainment) would be needed for consciousness to be sustained in the longer term. The theoretical questions raised by cerebral organoids likewise concern the role that the environment plays in consciousness, although now the question is not only whether consciousness requires ongoing dynamic interaction with the environment, but whether information technology also requires a history of such interaction. Among the theoretical questions raised by hemispherotomy is whether consciousness requires subcortical input, or whether cortical activity solitary might be sufficient to sustain consciousness. In brusk, the discovery of islands of awareness in any one of these three cases would reveal something important about the nature of consciousness, although different things would be revealed in each instance.

Box iv

Theories of Consciousness

One contrast betwixt unlike theories of consciousness concerns the predictions that they brand about when islands of awareness will (and will not) occur. Indeed, there is a more fundamental distinction betwixt those theories of consciousness that permit for the possibility of islands of awareness and those that practise non.

Those who are sympathetic to externalist accounts of consciousness are unlikely to hold that islands of awareness are possible, for externalists debate that the constitutive physical ground of consciousness extends beyond the brain and loops out into the body and environs [

,

]. If the existence of islands of awareness can be established, and so that would identify force per unit area on externalism.

Well-nigh theories of consciousness presuppose some version of internalism, and hold that the constitutive ground of consciousness is exclusively brain-spring. On this view, the trunk and the wider environment are only causally relevant to consciousness (run into Box 2 for more on causality in this context). All internalist accounts concord that islands of awareness are possible, but different internalist theories make dissimilar predictions virtually the conditions under which islands of awareness might arise. For case, higher-guild theories of consciousness predict that islands of sensation volition ascend when and just when a system for generating the appropriate kinds of higher-order representations is active [

]; global neuronal workspace accounts predict that islands of awareness require nonlinear global ignitions of activeness involving (functional equivalents of) both parietal and frontal circuits [

]; and the Integrated Data theory predicts that brain islands will be conscious in a graded manner depending on their intrinsic cause–result ability as measured by Φ [

]. In principle, then, the investigation of islands of awareness provides an important and informative constraint on theories of consciousness.

A unlike ready of implications that the discovery of islands of awareness would have is upstanding and legal. The reanimation of ex cranio brains raises questions about personal identity and the nature of decease. Suppose that whole brain reanimation were to occur in a homo rather than a pig, and that pharmacological agents were non used to preclude organised neural activity. Would complex neural activity in such a brain, indicative of consciousness, ensure the connected existence of a particular individual, or does personal survival require (for example) a sense of bodily identity or agency? These questions are also raised by other conditions (such as dementia and serious brain injury), simply they would be prompted in a particularly vivid fashion by the prospect of whole brain reanimation [

]. The discovery of an island of sensation in a hemispherotomy patient would likewise raise questions of personal identity. Would the experiences associated with the island of awareness belong to a separate bailiwick of experience – a subject whose interests might diverge from those of the communicating subject area – or should we think of the patient as a unmarried subject area of experience who happens to accept 2 streams of awareness (ane of which is isolated and one of which is not) [

,

].

The upstanding challenges raised past the prospect of conscious organoids do non turn on questions of personal identity simply on questions of moral status and standing [

,

,

]. How should conscious organoids exist treated? What would it be to respect their well-existence and interests? Should their treatment be governed by animal welfare laws, or would it require a new legal framework? Would it be permissible to engineer conscious organoids for research purposes, or would that violate their dignity? These questions should occupy a central place in the calendar of consciousness science.

In summary, advances in neurosurgery and neurotechnology may soon generate the capacity to create islands of sensation. Information technology is not incommunicable that they may already take done and then. Information technology is imperative that the scientific and ethical consequences of these developments are subjected to careful consideration, alongside development of methods tuned to the detection of islands of awareness in the various different contexts in which they might arise.

Outstanding Questions

• •

  Might (reversible) islands of awareness occur in contexts other than the ones that we have considered, such as epileptic absence seizures, or local islands of sensation in an otherwise sleeping encephalon?

• •

  What other methods might there be for detecting islands of awareness?

• •

  What animal models can exist developed for investigating islands of sensation? For example, could animal hemispherotomy preparations be studied, with and without preservation of visual input to the otherwise disconnected hemisphere?

• •

  What methods are in that location for interacting or communicating with an island of consciousness?

• •

  Are islands of awareness possible for only short intervals, or could the disconnected brain sustain consciousness for prolonged periods of time?

• •

  Are there some kinds of conscious contents that cannot occur in the asunder brain, or that could simply occur in such situations?

• •

  Does the nature and distribution of islands of awareness discriminate between competing theories of consciousness?

Acknowledgments

T.B. is grateful to the Australian Research Council; A.M.Southward. is grateful to the Dr Mortimer and Theresa Sackler Foundation, which supports the Sackler Centre for Consciousness Science ; Yard.M. is grateful to the European Union Horizon 2022 Framework Programme for its back up through Grant Agreement No.785907 (Homo Brain Project SGA2) and FETOPEN 2014-2015-RIA No. 686764 (Luminous); and all three authors are grateful for the support of the Canadian Institute for Advanced Research : Azrieli Program on Encephalon, Heed, and Consciousness. For helpful comments we thank Michael Carter and Adrian Owen.

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Glossary

Hemispherectomy/otomy

procedure used for the treatment of certain astringent cases of epilepsy in which an entire brain hemisphere is either surgically removed from the cranium and discarded (hemispherectomy), or the connections betwixt the hemisphere and the residue of the brain are cut but the hemisphere itself is left in situ (hemispherotomy).

Islands of awareness

conscious stream (or system) whose contents are not shaped by sensory input from either the external globe or the trunk and which cannot be expressed via motor output.

Cerebral organoids

stem-cell-derived laboratory-grown structures that self-organise into three dimensions with cellular and network features resembling certain aspects of the developing human brain.

Perturbational complication index (PCI)

technique in which TMS is used to perturb the cortex, and EEG is then used to measure the electrocortical responses to that perturbation. The algorithmic complexity (information) inherent in that electrocortical response is taken to be an indicator of consciousness.

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• Islands of Awareness or Cortical Complexity?

  Trends in Neurosciences July 1, 2020

  • In Brief

    Bayne et al. (2020) [i] envision the fascinating possibility that disconnected hemispheres (through hemispherotomy), ex cranio brains, and cognitive organoids may be islands of awareness (IOAs). They divers IOAs as systems fully asunder from the external surrounding, both in terms of input (i.e., sensory information) and output (i.e., motor responses), yet capable of conscious feel (i.due east., aware). In order to test whether these islands are effectively enlightened, the authors propose to use measures of human/fauna consciousness that take been well validated in human being/animate being settings by correlation with pretheoretical measures of consciousness (east.g., behavioural reports) or subjective reports (in the instance of humans).

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• From Complexity to Consciousness

  Trends in Neurosciences July 1, 2020

  • In Cursory

    Nosotros give thanks Cecconi and colleagues for their probing questions about our opinion article 'Are In that location Islands of Awareness?' [one], and we are grateful for the opportunity to return to these important issues.

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