IEET > Rights > Personhood > Contributors > Keith B. Wiley
The Stream of Consciousness and Personal Identity
Keith B. Wiley   Aug 27, 2019  

This article is a shorter version of a paper I wrote in July, 2019, which loosely coincides with the five-year anniversary of the publication of my book, A Taxonomy and Metaphysics of Mind-Uploading. The book presents a wide range of thought experiments about mind uploading and then conveys my preferred model of identity, commonly known as branching identity.


Personal identity is a challenging topic to tackle with any intent of objective truth discovery. Metaphysical truths (if there are such things) are more difficult to pin down than physical truths because much of metaphysics is not amenable to empirical physical experimentation. People often fail to convince one another of their preferred models of personal identity with respect to mind uploading because all conclusions are interpreted as supporting each person's preexisting model. I am personally resistant to proposed models of identity by which people or uploads are regarded in ways that contradict their first-person points of view, or by which multiple people with essentially identical points of view are nevertheless externally assigned differing identity labels. This preference has led me favor a branching model of identity, a conclusion with which others sometimes disagree. Consequently, explaining this theory of identity has become the bulk of my contribution to mind uploading philosophy, if there is such a thing. As I will repeat at the end, please consider this article to be mere invitation to read the full paper, especially wherever the reader may disagree.

The stream of consciousness

A common argument against spatially and/or temporally discontinuous procedures for mind uploading is based on their apparent failure to preserve a proposed stream of consciousness (SoC). If a mind uploading procedure is deemed to lose track of this diachronic (aka across time) stream, then this theory judges the outcome as a death of the original identity with some new identity invoked as a replacement. This new identity is often referred to as a copy in popular vernacular, and in a disparaging way: to be a copy is judged an undesirable fate and indicates a failure to survive the procedure.

One problem with stream of consciousness arguments is delineating the threshold of consciousness required to maintain identity. Forbidding a breakage in explicit awareness, out of concern for loss of identity, is immediately confounded by examples such as sleep, fainting, general anesthesia, etc., sometimes known as the bridge problem. Clearly, that stream breaks on a regular basis without concern that identity is constantly lost and invoked anew, or at least without concern that such a model of identity is in any way disturbing.

Stream of consciousness proponents (SCPs) generally respond to counterexamples such as sleep by either seeking a bridging criterion to handle gaps or redefining the SoC to represent a different concept deemed likely to persist across gaps in waking consciousness: any and all psychological traits, no matter how deeply subconscious. Furthermore, such an abstract stream is widely admitted to arise from some basal neural activity such that we may focus our examination on the physical. The recast claim is that, should we break this foundational stream of neural activity, obviously disabling the purported SoC in the process, then should the neural activity restart at a later time, with all its previous mental features reestablished, the original identity does not reappear or continue. Rather, the original identity remains permanently lost, while a new identity is invoked in its place. Since this outcome is often characterized as a form of death with replacement by a different person, such mind uploading procedures are generally judged as a lack of survival.

SCPs often accept the notion of mind uploading in principle but insist upon a procedure that on some analysis is entrusted to preserve this stream. Consider the two classic mind uploading procedures known as scan-and-copy and gradual in-place replacement. In scan-and-copy, a statically preserved brain is sectioned and imaged, the overall three dimensional structure (aka the connectome) inferred from those images, the brain recreated either in simulation or as a physical artifact, and finally restarted. In gradual in-place replacement mind uploading, each neuron is steadily replaced within the head by a microscopic artificial neural prosthetic. The whole point of my JoCS paper with Koene, unambiguously titled The Fallacy of Favoring Gradual Replacement Mind Uploading Over Scan-and-Copy, is to show that favoring gradual replacement while dismissing scan-and-copy for identity preservation is an irrational preference upon careful analysis. I urge critical readers to read the paper of course.

This article and the full paper from which it was derived consider the SoC claim against discontinuous mind uploading from two approaches. First, I discuss the related proposal that spatial continuity is of importance on the claim that successful preservation of the purported SoC should hinge on body (or at least brain) spatial continuity. I then explore the popular feature of the SoC characterized as its apparent reliance on a never-ending dynamic metaphysical process (cognition) that arises from an underlying never-ending dynamic neurological process (neural firing activity).

Spatial continuity

One argument for why personal identity fails to preserve in a discontinuous mind uploading scenario involves a violation of spatial continuity. How does identity undergo a discontinuous transfer, or literal travel through space, from inside a person's head to the upload's new brain or computer, like some sort of physical object traveling from one place to another? Since it is unclear how such literal spatial travel of this apparent identity object could be accomplished in a discontinuous procedure, the procedure is rejected as a failure to preserve identity. Contrarily, I don't believe metaphysical identities have physical properties in the first place, such as spatial location, so the entire concept of transferring identity through space from a brain to an upload's new substrate feels like a full-blown category error to me, arguably one of the worst philosophical errors one can make (category errors have been famously characterized as "not even wrong"). My book goes into great detail on this issue.

Both my book and my JoCS paper with Koene have already challenged the spatial-continuity argument based on the flawed expectation that gradual in-place replacement mind uploading would not itself involve discontinuous spatial translation of these same psychological traits. Gradual replacement absolutely does involve discontinuous spatial translation. If we replace each neuron with a microscopic prosthetic device that resides nearby, then when the prosthetic eventually takes over the neuron's role, the nonphysical function (and all its metaphysical attachments) will—if one buys the spatial properties of abstractions in the first place—suddenly discontinuously jump over to the prosthetic, a distance on the order of tens to hundreds of microns. Astoundingly, over the span of a procedure involving a hundred billion neurons, this discontinuous spatial translation of neural function accumulates tens to hundreds of kilometers of discontinuous translation of neurological, psychological and metaphysical traits.

One response to this clarification that gradual replacement also involves spatial discontinuities could be to simply dismiss smaller distances of a few microns as unimportant and somehow capable of preserving identity, but what rationale would justify this distinction? It is suspiciously convenient to prescribe that we should overlook translations short enough to escape our daily awareness (microns), yet that we should assign great metaphysical significance to translations on the scale of our daily experience, such as from a brain to a computer across a room. Would aliens considerably smaller or larger than us assign such an arbitrary threshold differently?

Another response to in-place uploading's inherent spatial discontinuities is to simply abandon the terminology of, and requirement for, continuous spatial translation entirely and pivot to a completely different requirement: piecemeal replacement as opposed to whole parcel replacement, with obvious allusions to the Ship of Theseus thought experiment (which never suggests a solution, by the way; it merely poses the identity question). But Koene and I already argued that it is fallacious to believe that gradual replacement is more identity-preserving than scan-and-copy in our paper.

With gradual replacement thoroughly addressed (and we believe adequately refuted), the most likely next response is to require the preservation of a dynamic neurological process that is not permitted to cease. The claim is that continuous neural activity preserves a continuous cognitive experience along with its continuous SoC and persistent identity, and further claims that stopping and restarting this process should be interpreted as a permanent loss of the original identity and an invocation of a new identity instead of a mere restart of a prior process and identity. I show below that this stance is unsubstantiated, and worse, is incompatible with current medicine.

The memory basis for identity

Consider the following question: How are you confident of your identity relative to yourself from:

  • before you went to sleep.
  • before you underwent general anesthesia.
  • before you underwent medically induced hypothermia to protect your brain during a cardiac emergency.
  • before you suffered rapid frigid drowning in which you fell in a freezing cold lake, drowned, remained submerged for an hour, were taken to the hospital, confirmed to have essentially no pulse and absolutely no brain activity, and then finally revived.
  • before undergoing some as-yet-speculative long-term preservation or stasis, such as hibernation or cryonics.

The situations shown above are known as the bridge problem: if our identity depends on a continuous SoC, then how does it bridge gaps in that stream? Even SCPs generally acknowledge that it is their own persistent identity that awakens each morning. We will see below that such a claim is highly problematic. SCPs usually handle this challenge by leaving the SoC claim behind and moving on to other arguments, such as spatial continuity or continuous neural activity. But then why not open on those terms and abandon the SoC claim once and for all?

It is worth briefly remarking that SCPs must presumably reject that cryonics could ever preserve identity. The SoC community should brand revived cryonics patients as dead originals replaced with newly invoked identities. Cryonic preservation surely satisfies their criteria of a broken SoC. Yet in virtually every way imaginable, a revived cryonics patient has undergone a physical process and mental experience almost indistinguishable from general anesthesia or medically induced hypothermia. To assign different identity labels to indistinguishable personal experiences strikes me as entirely unmotivated. We should bring these two situations into alignment, either by rejecting the identity of millions of actual surgical patients, or by accepting the identity of ostensible cryonics patients? But to accept the identity of revived cryonics patients undermines the claim that never-ending process is important. Proponents of a persistent stream of consciousness based on a persistent stream of neural activity face a conundrum in cryonics.

My preferred response to the questions posed above is that we exclusively identify ourselves by the phenomenological experience (i.e., experience in the moment) of our memories of our lives, known as psychological identity. This stance only assigns significance to our awareness and experience of our memories at any instant in time, which can obviously wax and wane without loss of identity, as illustrated by sleep, etc.

The neural threshold of the stream of consciousness

Another common response to the scenarios presented in the list above is that in none of those scenarios does neural activity truly cease. During a fainting spell, or while under general anesthesia, underlying neural activity and associated SoC are argued to have been maintained above some apparent minimum threshold capable of preserving identity. This response comes up repeatedly in debates and articles, so scrutinizing it is central to this article. This counterclaim that some basal dynamic process is preserved is extremely problematic however. The first response is to simply understand rapid frigid drowning in greater detail. People offering the counterargument of basal neural activity must simply not understand what rapid frigid drowning actually involves. In the most extreme cases to date, rapid frigid drowning victims have survived descents to body temperatures around 13.0 to 13.7C degrees.

One might assume that without literally freezing (13C being notably higher than 0C of course) the brain continues enough interneural signal propagation to keep the hallowed SoC tenuously suspended above the chasm of annihilation. However, in such patients there truly is no measurable neurological activity. Action potentials do not propagate along axons and dendrites at 13C degrees. To the contrary, the temperature at which the brain effectively goes mute is much warmer, closer to 21C degrees. This is well established by multiple experiments involving a medical procedure known as medically induced hypothermia, in which a patient's temperature is intentionally lowered, often following a cardiac emergency, specifically as a neuroprotective measure to prevent brain atrophy. The fact that rapid frigid drowning indicates real-world cases in which patients have not been treated as doppelgängers following their ordeals clearly demonstrates that the SoC claim is incompatible with our general concept of reality.

Nevertheless, let us assume that the proposed SoC does exist and is critical to identity. It must be underlied by some correlate of neurological activity. Perhaps the critical temperature is slightly colder than the most extreme medical cases to date, say 12C degrees. The claim then, is that if we were to revive a patient from 12C degrees (or whatever threshold is ultimately discovered) we should brand them a metaphysical copy. They need not display any outward cognitive deviation to earn this fate. Everything could indicate that they survived, yet the claim is that we should label them as a mental duplicate merely for having dropped below the predetermined 12C degree mark and its apparent consciousness stream threshold.

The question is, would we ever actually regard a patient in the described way? Given such a medical revival, would any SCP ever actually point at a patient and say, "I saw her medical chart. She was below 12C degrees, so she's a copy." Real-world cases of rapid frigid drowning suggest that such beliefs and treatment of others are extremely rare.

Assume that the threshold of neural activity associated with an identity status flip from preservation to loss-with-replacement is determined. Given that neural activity is easily correlated with temperature, we could conceivably use temperature to make identity determinations and judgments. Hospitals could include a stream-of-consciousness-verification test when unconscious patients are brought into the ER. Let's say it has been determined that 12C degrees is the critical threshold in question. Two rapid frigid drowning patients arrive at the hospital, Alice and Bob. Alice is revived, but from below 12C degrees. She is branded a copy for the rest of her life. Alice herself, being a strong believer in the SoC claim, accepts her fate as a copy, deeply believing that she was born after the accident and that her own memories are entirely fallacious. Bob, however, arrived at the hospital with a temperature of 13C degrees, much like real-world patients for whom no fictional speculation is required. Bob is clearly granted the status of preserved identity, consistent with contemporary medical cases. Alice and Bob proceed to live their lives for many decades, interacting with numerous people who regard Alice as a copy and Bob as a preserved identity. Only toward the end of their lives does someone investigate their old medical records and discover to their amazement that both measurements were wrong! Alice only descended to 13C degrees while Bob dipped to 12C degrees that fateful day. So Alice was never a copy in the first place, yet everyone believed she was, including herself! And Bob was a copy the whole time, yet not one person ever realized it or regarded him as a copy, including himself.

The scenario of Alice and Bob reveals the following troubling conclusion: the SoC, even if real in some abstract metaphysical sense, clearly has absolutely no objective impact on reality; it is utterly acausal. It is a completely arbitrary, unfalsifiable, and superfluous metaphysical property injected from the outside. Occam's Razor encourages us to dispose of proposed superfluous and extraneous explanatory phenomena. Therefore, I urge the alternative handling of the SoC claim: that it is simply invalid to begin with.


Note the gravity of the consequences if it turns out that SCPs are in error on the metaphysical question of identity. They reject the philosophical preservation of identity by the scan-and-copy procedure, which although currently theoretical, is likely to become technically feasible within some foreseeable future. At the same time, they accept the gradual in-place replacement procedure, which remains so technologically speculative as to be essentially impossible for all practical purposes. If gradual in-place replacement is even possible, it may take centuries longer to develop than scan-and-copy. Rejecting scan-and-copy destines anyone living during that interim period to death.

It is my position that we should reject the SoC claim and any requirement such a purported metaphysical property would impose on mind uploading procedures. At the least, the onus rests on this claim's proponents to prove such a stream exists and to defend the claim that it would not survive certain mind uploading procedures.

This article is only a brief overview of the full paper from which it was derived. Please consider reading the original paper as well, also titled The stream of consciousness and personal identity, available at Thank you.


Dr. Keith B. Wiley is a researcher with experience across numerous fields within computer science. He has been involved in the ongoing discussion of philosophical and practical aspects of mind uploading for twenty years. His first book on the subject, A Taxonomy and Metaphysics of Mind-Uploading, was released in 2014 with support from Humanity+ Press. Dr. Wiley’s articles and papers are available at


What if we thought of our awareness as correlated to a particular subunit of the central nervous system? The rest of the body could be thought of as an appendage to this core correlate of awareness. The actual awareness may not be generated by any sensory pattern that we can access through observations made with our physical bodies. Preserving the correlation between our awareness and this realm of experience (with the collection of individuals it allows us to interact with) is important to human beings. We may never understand the origin of our awareness, but the fact that it is correlated with neurons and body parts connected to this neurons is apparent. Perhaps the brain is an interface to the body and some realm of interaction with similarly configured awarenesses.

What process must occur to de-correlate our awareness with our bodies and this realm of interaction with other aware beings? You mention a cessation of neuron firings. Is that sufficient? How would we know? It may make sense to think of it as awareness being withdrawn from the structures of the brain and the body’s appendages, the awareness itself may not be extinguished.

The brain goes through a process whereby new neurons are added and processes by which old neurons die. Similar things happen throughout the body as nerve endings die and new ones take their place. Somehow our awareness is able to continue to remain correlated with this body and realm of interaction in spite of these changes. How so you feel this relates to the gradual replacement approach or the idea of awareness transferring across a physical distance?

One approach we might consider is maintaining a core portion of the central nervous system that we know is correlated with awareness, however that correlation occurs. We can then care for this minimum amount of biological tissue with processes that require a very small amount of nutrients and damage repair. We could then connect this biological correlate to an artificial set of items for creating experiences. memories and means for communication with other awarenesses. This arrangement might allow us any set of possible sensory experiences and be easy to maintain indefinitely compared to attempting to maintain the entire physical body, all without presenting much challenge to the notion that the same awareness is being maintained indefinitely.

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