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  • Writer's picturemattfaw

06 What about H.M. (and other patients like him)?

From the published paper:

A male epileptic patient from Connecticut, commonly known as H.M., was the most famous patient with adult-onset bilateral complete hippocampal damage (AOCBHD). Most of his HC was removed surgically to save him from the overwhelming epilepsy that was focused there.

Patients like H.M. are unable to form detailed or coherent intrinsic simulations, like mental navigation, future projection, vivid imagination, and social rehearsal. These patients are afflicted with anterograde amnesia, the inability to form new episodic memories, and retrograde amnesia, the inability to replay previous episodic memories.

In the model we are proposing, such patients cannot have NSE, which may sound implausible. Specialists who work with AOCBHD patients describe the patients’ responsiveness to the outside world, their personality, sense of (short-lived) continuity, an ability to respond to queries about one’s inside state, and even some limited ability to learn procedural skills and semantic information. This is what we mean from the third-person view when we describe someone else as ‘conscious,’ and indeed, H.M. was that, when awake. These are all part of the usual working definition of consciousness, but none of them are part of how we are defining NSE.

We are neither saying that H.M. lacked subjectivity nor that he lacked experience. What he was missing was the specific phenomenon that the phrase ‘Subjective Experience’ refers to (among those of us with working hippocampi), which is cortical activation by a specific type of neural information. According to our theory, NSE is caused by inter-network information (the engram), which helps to expedite processing and which may be stored for future recall.

It subjectively represents processes like responsiveness, personality, etc., but it should not be confused with them. All of the processes that are represented in the hippocampal simulation are only news reports of the actual processes in the EN and DMN, and patients like H.M. still have access to those original processes (see section 3.3: Memory Generation as

Simulation on boundary extension).

Unlike the Cartesian model (Figure 2), we believe that NSE is not necessary to engage with the outside world. All immediate interaction with the world is handled by pre-memory EN departments. We could not survive otherwise because the ~500 ms it takes to revise a new memory to account for unpredictable activity would leave us a half-second behind reality. We could never drive, for example, if we were always a half-second behind changing


Figure 2:

‘Driving Mind’ as Insight into H.M.’s Processes

The ability of the EN to act independent of the HC representation is probably not uncommon, but we tend to notice it only in extreme cases, like ‘driving mind.’ Most of us who drive have probably experienced the phenomenon of driving someplace (usually on a familiar route) and then upon arrival, realizing that we have no memory, whatsoever, of the drive. In fact, it seems as if I was not involved in the drive at all.

The explanation that is usually given for ‘driving mind’ is that the driving is done ‘automatically,’ but we see that as a highly problematic, dualistic explanation. The body and brain are checking the mirrors, braking and accelerating, changing lanes. All the functions of sensation, evaluation, decision, and action are clearly being employed in the drive or the car would crash. The driving functions are performed by the same EN departments as usual, so the behavior is only ‘automatic’ if it is missing oversight from sort of ‘I,’ some ‘self’ that is distinct from the brain. This would imply that the brain is somehow an unconscious vehicle, driven by a non-brain conscious self, which puts us in dualism (i.e., Descartes’ notion that ‘mind’ is a nonmaterial intelligent essence), and back into the Cartesian Theater.

But what is startling about ‘driving mind’ is precisely the lack of memory of the drive. So we think it much more likely that the exact same brain departments as usual are conducting the drive; however, there is just no memory formed of it. That lack of memory can be explained by the fact that the HC serves very different purposes for the EN versus the DMN. As we have seen in section 3: The Hippocampal Complex as Experience Simulator, the DMN uses the ‘Holodeck’ features of the HC as a virtual workspace in which to manipulate representations. The DMN runs predictive simulations, imagining a conversation or exploring scenarios before trying them on the world. It examines, and tries to make sense of, previous memories. It is even tasked with daydreaming/fantasy, in which we get to simulate our wish fulfillment.

In the case of ‘driving mind,’ we see it likely that the EN is performing all the driving tasks, as it always does. However, the reports from the sensory and motor cortices do not make it into memory because the HC is already fully occupied with a DMN simulation, like daydream, memory recall, or social rehearsal. Because episodic memory only contains what was processed in the HC, the DMN simulation is all that is remembered, leaving the brain with no memory of the drive, and because NSE is due to the broadcast of episodic memory, I had no NSE of the drive, although my EN was fully engaged during it.

In the case of driving mind, my ‘inner H.M.’ is doing the driving, and the resultant NSE is only of the DMN/hippocampal simulation.

Was H.M. a Zombie?

Philosophers have invented a rhetorical being, which they call a zombie, that behaves and self-reports exactly like a conscious human but who somehow lacks any kind of inner awareness or experience. As we are proposing that AOCBHD patients lack the

phenomenon that those of us with working hippocampi know as Subjective Experience, it may sound like we are claiming that H.M. and similar patients fit that zombie category.

However, as we have seen in section 3.3 (Memory Generation as Simulation on boundary extension), AOCBHD patients are aware of the photo they see and can report based on that awareness. The neural information that they report, however, is from an EN pre-memory buffer that those of us with working hippocampi have no direct access to. Despite the fact that we have the same functional pre-memory buffers as AOCBHD patients, those of us with working hippocampi (according to our theory) only experience the HC output, and that output obscures the pre-memory awareness. In section 7.3: The Causal Power of NSE, we more fully explore the possible reasons why pre-memory processes are left out of awareness.

Based on his work with another AOCBHD patient D., Antonio Damasio wrote that the patient D. does not have ‘an elaborate sense of self ... at a point in individual historical time, richly aware of the lived past and of the anticipated future’ (p. 16). Endel Tulving essentially wrote the same about AOCBHD patient N.N. What is missing in patients D. and N.N. is the context and expanded sense of self that is provided by memory. They are NOT zombies, because they have inner lives, albeit transient ones. We hypothesize that their EN experience is probably substantially different than the NSE of those of us with working HCs.

This is where we think H.M. lived: he sensed and interacted with the outside world, could rely

upon his short-term visual and auditory buffers, and could report body states and a few details about his self-identity. What he could not do was benefit from the HC’s newscast. He could not use the gestalt from a moment ago to expedite his processing. He could

not place himself within a broader sense of what came before and what is likely to happen next.

Unfortunately, it is impossible to guess, from our perspective, precisely what H.M.’s, N.N.’s, or D.’s non-memory experience is like, as our own normal pre-memory experience is not available to our subjective view. It is like asking ourselves to describe the unremembered act of driving during ‘driving mind’; there is nothing to remember and thus no way to report. Nor can we expect patients with AOCBHD to reliably know how their perceptions have changed post-morbidity because, missing their HC, they can no longer evoke the vivid memories of previous experience to compare to their current way of seeing the world.

Some evidence from the literature does exist, however, and suggests that perception does change for such patients. Graham et al. quoted one patient with limited hippocampal damage, who could still remember fairly well, but whose perception lacked qualities that the HC usually provides. She could form and remember snapshot images of her environment but still had a very difficult time navigating through the world because “whichever angle I look, everything looks the same” (p. 832). The patient continued: “I would prefer not to call my experiences ‘memory problems,’ they are not. This is a total misrepresentation of the damage I have. What I experience are ‘orientational problems.’” Her perception of the world is missing some of the context of the allocentric environmental information from the PHC and hippocampus, elements that those of us with fully working hippocampi take for granted. NSE reflects a simplified, but much more contextualized, representation of events than the pre-memory reports in the EN.

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