Revisiting grandmother cells


Recent work by R. Q. Quiroga’s group, ‘Explicit Encoding of Multimodal Percepts by Single Neurons in the Human Brain’ in Current Biology, has looked at how we remember people, places and categories. The paper’s abstract is below:

“Different pictures of Marilyn Monroe can evoke the same percept, even if greatly modified as in Andy Warhol’s famous portraits. But how does the brain recognize highly variable pictures as the same percept? Various studies have provided insights into how visual information is processed along the “ventral pathway,” via both single-cell recordings in monkeys and and functional imaging in humans and. Interestingly, in humans, the same “concept” of Marilyn Monroe can be evoked with other stimulus modalities, for instance by hearing or reading her name. Brain imaging studies have identified cortical areas selective to voices and and visual word forms and. However, how visual, text, and sound information can elicit a unique percept is still largely unknown. By using presentations of pictures and of spoken and written names, we show that (1) single neurons in the human medial temporal lobe (MTL) respond selectively to representations of the same individual across different sensory modalities; (2) the degree of multimodal invariance increases along the hierarchical structure within the MTL; and (3) such neuronal representations can be generated within less than a day or two. These results demonstrate that single neurons can encode percepts in an explicit, selective, and invariant manner, even if evoked by different sensory modalities.”

This sounds a lot like grandmother cells to me. Here we have pathways starting with different sensory modalities and going through separate perceptual processes leading ultimately to the same cell in the memory apparatus of the hippocampus. Is this not the neural instantiation of our knowing people, places and abstract concepts? Are these not grandmother cells – a neuron that can be activated by any activity the would amount to a definition of my grandmother and in turn activate attributes of my grandmother missing from the original activity? A photograph of her face brings to mind the sound of her singing.

Locked-in consciousness


There is yet another state of conscious for our collection that are not the same as normal active wakefulness. Some people that appear to be in a vegetative state are actually conscious but unable to respond. The BPS Research Digest has a report on diagnosing this condition (here).

“when she was instructed to pay special attention to her own name, the woman’s EEG signal showed an exaggerated P300 response to her name, compared with when she was instructed to just listen passively. The P300 is a spike of activity recorded from the parietal lobe, which is thought to be a marker of consciousness or decision making.”

Brain imaging has been used before but using EEG is much more cheap and convenient. The protocol is also an advantage.

“this active auditory event-related paradigm (requiring explicit comprehension of auditory-verbal instructions) provides an interesting tool for detecting voluntary brain activity in patients that behaviourally would be diagnosed as comatose”

Wikipedia points out the difference between lock-in syndrome and persistent vegetative state.

“Unlike persistent vegetative state, in which the upper portions of the brain are damaged and the lower portions are spared, locked-in syndrome is caused by damage to specific portions of the lower brain and brainstem (ventral part of the pons) with no damage to the upper brain.”

What is this state like? People who have survived describe it as ‘being buried alive’.

Time and space

The mindhacks blog had a posting on the connection between time and space perception. Here is the abstract of the paper discussed, ‘Prismatic Lenses Shift Time Perception’ by F Frassinetti etal.

“Previous studies have demonstrated the involvement of spatial codes in the representation of time and numbers. We took advantage of a well-known spatial modulation (prismatic adaptation) to test the hypothesis that the representation of time is spatially oriented from left to right, with smaller time intervals being represented to the left of larger time intervals. Healthy subjects performed a time-reproduction task and a time-bisection task, before and after leftward and rightward prismatic adaptation. Results showed that prismatic adaptation inducing a rightward orientation of spatial attention produced an overestimation of time intervals, whereas prismatic adaptation inducing a leftward shift of spatial attention produced an underestimation of time intervals. These findings not only confirm that temporal intervals are represented as horizontally arranged in space, but also reveal that spatial modulation of time processing most likely occurs via cuing of spatial attention, and that spatial attention can influence the spatial coding of quantity in different dimensions.”

I have thought it likely that the processes that are used for one type of perception are also used for any others that can be made to ‘fit’. Particularly, the hippocampus is part of a neural system adept at space and place perception/memory and it also seems to be doing the same for time. Why not for any and everything that we can map with location and direction: numbers, music, procedures etc? So high notes are high, low numbers are low (and to the left if that is the way we read), procedures move along a path, we move into the future and leave the past behind. Some postulate that we think this way because of our language, but it seems more likely that we talk this way because of how we perceive.

Eco cells

An article on the Smithsonian website, Brain Cells for Socializing, discusses Eco cells. (here)

“The von Economo neurons are the most striking finding of recent years in comparative brain research, in which scientists tease out fine differences among species. Neuroanatomist Patrick Hof and his colleagues at the Mount Sinai School of Medicine in Manhattan first stumbled across the neurons in human brain specimens in 1995… Most neurons have cone- or star-shaped bodies with several branching projections, called dendrites, that receive signals from neighboring cells. But von Economo neurons are thin and elongated, with just one dendrite at each end. They are four times bigger than most other brain cells, and even in species that have the cells, they are rare…

The spinal shaped cells occur only in the anterior cingulate cortex and the frontal insula. About 100 mammals have been examined of the unusual cells but they are found only in great apes , elephants, humpback whales, sperm whales, fin whales, orcas and bottle-nosed dolphins. The common thread here is that these animals are (1) very social (2) with large brains. Whales and elephants, like people and great apes, have extremely large brains and a prolonged juvenile stage during which they learn from their elders.

In 1999, the scientists reported that all great ape species had von Economo cells, but lesser primates, such as macaques, lemurs and tarsiers, did not. That meant the neurons evolved in a common ancestor of all the great apes about 13 million years ago, after they diverged from other primates but well before the human and chimp lineages diverged about six million years ago…”

William Seeley, a neurologist at the University of California at San Francisco, studies a poorly understood neurodegenerative disease called frontotemporal dementia. Patients suffer a breakdown in their character, losing social graces and empathy, turning insensitive, erratic and irresponsible. Marriages and careers implode. Many patients seem to lack physical self-awareness: when diagnosed with other illnesses, they deny having any problems. Brain imaging studies of patients with the dementia have uncovered damage to frontal areas of the brain….Analyzing brains from deceased patients, the scientists discovered that, in fact, about 70 percent of von Economo neurons in the ACC had been destroyed, whereas neighboring brain cells were largely unaffected. “It is very clear that the original target of the disease is these cells, and when you destroy these cells you get the whole breakdown of social functioning,” says Allman. “That’s a really astounding result that speaks to the function of the cells about as clearly as anything can.”

It is possible that similar cells with a similar function occur in many social animals but that it is only in large brains where extra speed is required that they take on the distinctive spinal shape and large size.

EEG Question


There has recently been discussion of how much the gamma signal is associated with neural activity and how much it is associated with movements of the eye muscles. Below is the abstract of a paper from Yuval-Greenberg’s group, ‘Transient induced gamma-band response in EEG as a manifestation of miniature saccades’.

“The induced gamma-band EEG response (iGBR) recorded on the scalp is widely assumed to reflect synchronous neural oscillation associated with object representation, attention, memory, and consciousness. The most commonly reported EEG iGBR is a broadband transient increase in power at the gamma range approximately 200-300 ms following stimulus onset. A conspicuous feature of this iGBR is the trial-to-trial poststimulus latency variability, which has been insufficiently addressed. Here, we show, using single-trial analysis of concomitant EEG and eye tracking, that this iGBR is tightly time locked to the onset of involuntary miniature eye movements and reflects a saccadic “spike potential.” The time course of the iGBR is related to an increase in the rate of saccades following a period of poststimulus saccadic inhibition. Thus, whereas neuronal gamma-band oscillations were shown conclusively with other methods, the broadband transient iGBR recorded by scalp EEG reflects properties of miniature saccade dynamics rather than neuronal oscillations.”

As far as I can tell, the question is not settled. There is no doubt that there is gamma voltages from neural processing, and there is no doubt that voltages are produced by muscles. Further it is not unreasonable to presume that saccade eye movements are synchronized with processes creating consciousness. What is not clear is what features of the EEG are from muscles or from neurons. A good review is a posting by Chris Chathan’s (here).

Walking like a duck

Howard Eichenbaum’s group has published many papers on the hippocampus. This one, “Episodic recollection in animals: “If it walks like a duck and quacks like a duck…”, here , makes a good case for animal consciousness. The abstract is below:

In humans, episodic memory is most commonly defined as the subjective experience of recollection, presenting a major challenge to the identification of episodic memory in animals. Here we take the position that episodic memory also has several other distinctive qualities that can be assessed objectively in animals, as well as humans, and the examination of these properties provides insights into underlying mechanisms of episodic memory. We focus on recent evidence accumulated in this laboratory indicating that recognition in rats involves a threshold retrieval process, similar to that observed in human episodic recall. Also, rats can remember the temporal order of unique events, characteristic of the replay of vivid episodic memories in humans. Furthermore, rats combine elements of “when” and “where” events occur, as well as the flow of events within a memory, to distinguish memories that share overlapping features, also characteristic of human episodic memory. Finally, all of these capacities are dependent on the hippocampus, which also plays a critical role in human episodic memory. This combination of findings strongly suggests that animals have the same fundamental information processing functions that underlie episodic recall in humans.

The guessing trick


It seems that we are prone to a particular simplification in analyzing the behavior of others and of ourselves. When someone does something differently than we would, our immediate explanation is of the ‘stupid – lazy – or – evil’ type. When we are confronted by having done something differently than others would have, our immediate explanation is almost never ‘stupid – lazy – or – evil’ and often the exact opposite – we thought long a hard about it. Now, most of us know that we are not smarter, more conscientious, and more moral than absolutely everyone else we meet. Either we are deluding ourselves or underestimating others or both on a fairly regular basis.

I remember first thinking about this years ago when I read someone talking about anthropology and how it is a good idea to assume that everyone does what they do for perfectly rational reasons. If you don’t make that assumption, you are not going to be able to understand strange cultures. I was really blown away by that thought. And I used it. When someone surprised me with their actions, I just assumed they had a good reason but I usually didn’t think about what the reason might be unless I was very curious. What started to happen was that a third person would be somewhat exasperated by the strange behaviour and say, “Why did they do that?” Quite often a plausible reason would jump into my head and I would supply it. “Oh, they probably did it because of x.” The whole thing would be a little magical.

Then I learned that in experiments with split-brained subjects, the speaking left hemisphere would make up reasons for the (to it) strange behaviour of the non-speaking right hemisphere. The left hemisphere appeared to be unaware that it was guessing the motivation of the right. I also learned that people doing inappropriate things under hypnotic suggestion would give plausible explanations when asked why they had done those things. This seemed essentially the same trick as my ‘everyone is rational’ one.

There also is a trickle of evidence that our knowledge of our own motivation can be faulty and that we are pretty good at fabricating justification when necessary.

So now comes the realization that we treat ourselves like I have learned to treat others. We just assumed that we are rational (and not stupid-lazy-evil) and then went a motivation is needed, we guess. And given that we are pretty good at this guessing, we are usually right enough. It is when this mechanism is used in unusual circumstances (like hypnosis) or applied to another’s mind, that we can see that it is just a mechanism for making guesses. Nice trick!

A panpsychic theory of consciousness


Christof Koch has a Scientific American article on the ideas of Giulio Tononi (here). Tononi is putting forward a panpsychic idea of consciousness: everything from a hydrogen atom to a human has some degree of consciousness. Well, I suppose that it would depend on your definition of consciousness! He defines consciousness in terms of an elaboration of information theory, integrated information theory (IIT) of consciousness,

IIT is based on two axiomatic pillars.

First, conscious states are highly differentiated; they are informationally very rich. You can be conscious of an uncountable number of things…Think of all the frames from all the movies you have ever seen or that have ever been filmed or that will be filmed! Each frame, each view, is a specific conscious percept.

Second, this information is highly integrated. No matter how hard you try, you cannot force yourself to see the world in black-and-white, nor can you see only the left half of your field of view and not the right. When you’re looking at your friend’s face, you can’t fail to also notice if she is crying. Whatever information you are conscious of is wholly and completely presented to your mind; it cannot be subdivided. Underlying this unity of consciousness is a multitude of causal interactions among the relevant parts of your brain. If areas of the brain start to disconnect or become fragmented and balkanized, as occurs in deep sleep or in anesthesia, consciousness fades and might cease altogether. …

To be conscious, then, you need to be a single, integrated entity with a large repertoire of highly differentiated states. … And the more interconnected, the more meaningful they become. Indeed, Tononi’s IIT postulates that the amount of integrated information that an entity possesses corresponds to its level of consciousness.

These ideas can be precisely expressed in the language of mathematics using notions from information theory such as entropy. Given a particular brain, with its neurons and axons, dendrites and synapses, one can, in principle, accurately compute the extent to which this brain is integrated. From this calculation, the theory derives a single number, fi . Measured in bits, fi denotes the size of the conscious repertoire associated with any network of causally interacting parts. Think of fi as the synergy of the system. The more integrated the system is, the more synergy it has, the more conscious it is. If individual brain regions are too isolated from one another or are interconnected at random, fi will be low. If the organism has many neurons and is richly endowed with specific connections, fi will be high—capturing the quantity of consciousness but not the quality of any one conscious experience. (That value is generated by the informational geometry that is associated with fi but won’t be discussed here.)…

The cortex and its gateway, the thalamus…on the other hand, are essential for consciousness, providing it with its elaborate content. Its circuitry conjoins functional specialization with functional integration thanks to extensive reciprocal connections linking distinct cortical regions and the cortex with the thalamus. This corticothalamic complex is well suited to behave as a single dynamic entity endowed with a large number of discriminable states.

Somehow there is a ‘with-one-almighty-leap’ between the mathematics and the actual awareness and ‘fi’ is almost impossible to calculate for a system of any size. But these are the sort of problems that beset other theories of consciousness too.

Chalmers and epiphenomenalism

This carries on from the last post where I was pondering what David Chalmers really thought about consciousness. Well, I thought, maybe Eliezer Yudkowsky knows. He wrote a posting on zombies and so I looked at the posting again. I am not going to quote all the Yudkowsky’s arguments – (here) is the link. Below is his summing up of why he feels Chalmers is wrong about epiphenomenalism (the technical term for the belief that consciousness is there, but has no effect on the physical world):

Chalmers is one of the most frustrating philosophers I know. … Chalmers does this really sharp analysis and then turns left at the last minute. He lays out everything that’s wrong with the Zombie World scenario, and then, having reduced the whole argument to smithereens, calmly accepts it…

Humanity has accumulated some broad experience with what correct theories of the world look like. This is not what a correct theory looks like.

“Argument from incredulity,” you say. Fine, you want it spelled out? The said Chalmersian theory postulates multiple unexplained complex miracles. This drives down its prior probability, by the conjunction rule of probability and Occam’s Razor. It is therefore dominated by at least two theories which postulate fewer miracles, namely:

  • Substance dualism (Descarte for example):

    • There is a stuff of consciousness which is not yet understood, an extraordinary super-physical stuff that visibly affects our world; and this stuff is what makes us talk about consciousness.

  • Not-quite-faith-based reductionism:

    • That-which-we-name “consciousness” happens within physics, in a way not yet understood, just like what happened the last three thousand times humanity ran into something mysterious.

    • Your intuition that no material substance can possibly add up to consciousness is incorrect. If you actually knew exactly why you talk about consciousness, this would give you new insights, of a form you can’t now anticipate; and afterward you would realize that your arguments about normal physics having no room for consciousness were flawed.

Compare to:

  • Epiphenomenal property dualism:

    • Matter has additional consciousness-properties which are not yet understood. These properties are epiphenomenal with respect to ordinarily observable physics – they make no difference to the motion of particles.

    • Separately, there exists a not-yet-understood reason within normal physics why philosophers talk about consciousness and invent theories of dual properties.

    • Miraculously, when philosophers talk about consciousness, the bridging laws of our world are exactly right to make this talk about consciousness correct, even though it arises from a malfunction (drawing of logically unwarranted conclusions) in the causally closed cognitive system that types philosophy papers.

I know I’m speaking from limited experience, here. But based on my limited experience, the Zombie Argument may be a candidate for the most deranged idea in all of philosophy.

There are times when, as a rationalist, you have to believe things that seem weird to you. Relativity seems weird, quantum mechanics seems weird, natural selection seems weird.

But these weirdnesses are pinned down by massive evidence. There’s a difference between believing something weird because science has confirmed it overwhelmingly -

- versus believing a proposition that seems downright deranged, because of a great big complicated philosophical argument centered around unspecified miracles and giant blank spots not even claimed to be understood -

- in a case where even if you accept everything that has been told to you so far, afterward the phenomenon will still seem like a mystery and still have the same quality of wondrous impenetrability that it had at the start.

The correct thing for a rationalist to say at this point, if all of David Chalmers’s arguments seem individually plausible – which they don’t seem to me – is:

“Okay… I don’t know how consciousness works… I admit that… and maybe I’m approaching the whole problem wrong, or asking the wrong questions… but this zombie business can’t possibly be right. The arguments aren’t nailed down enough to make me believe this – especially when accepting it won’t make me feel any less confused. On a core gut level, this just doesn’t look like the way reality could really really work.”

So, considering this evaluation including what came before the summing up and what I have tried to read of Chalmers work itself, I will stop even trying to follow what Chalmers believes about consciousness. Life is too short.

Chalmers and emergence


My problem with ‘emergence’ has led me to an old post by David Chalmers (here), where he analyzes a number of definitions of the word. I have no quarrel with his various takes on emergence but I was reminded of how I disagree with his take on consciousness. Or at least probably would disagree if I could understand that he was saying about consciousness.

So, in his first definition of emergence which he says is “ deeply implausible”, in the whole universe the one single solitary thing that may not be deduced from the properties of the parts is consciousness.

Emergence as “inexplicable” and “magical”. This would cover high-level properties of a system that are simply not deducible from its low-level properties, no matter how sophisticated the deduction. This view leads easily into mysticism, and there is not the slightest evidence for it (except, perhaps, in the difficult case of consciousness, but let’s leave that aside for now). All material properties seem to follow from low-level physical properties. Very few sophisticated people since the 19th century have actually believed in this kind of “emergence”, and it’s rarely what is referred to by those who invoke the term favourably. But if you mention “emergence”, someone inevitably interprets you as meaning this, causing no end of confusion.

He goes on through other definitions with increasing usefulness until finally he is dealing with a special case that would be fitting only for designed (or metaphorically designed) systems.

Emergence is the phenomenon wherein a system is designed according to certain principles, but interesting properties arise that are not included in the goals of the designer. … We can view evolution as teleological at the level of the gene – as in Dawkins’ theory, for instance. Then the appearance of complex, interesting high-level properties such as intelligence is quite emergent. We also can reconstrue evolution as teleological at the level of the organism (this is perhaps a more straightforward Darwinian view of things). On this construal, the most salient adaptive phenomena like intelligence are no longer emergent, but the goal of the design process. However, this view does open up the possibility of other kinds of emergent phenomena: firstly, non-selected-for byproducts of the evolutionary process (such as Gould and Lewontin’s “Spandrels”); secondly and more intriguingly, it allows an explanation for why “consciousness” (or “subjectivity” or “qualia” or whatever) seems emergent. Raw consciousness doesn’t not seem to have been selected for, as it doesn’t play any direct functional role (though it does have functional counterparts; this is a subtle issue, but remember we’re talking about the way things seem, not the way they are); but it somehow emerges as a byproduct of selection for adaptive process such as intelligence.

Chalmers is tip-toeing around something here. He either believes that consciousness to deducible from the properties of neurons and their connections, in which case why make an exception, or he doesn’t. And does he believe that consciousness has a function and that function can be selected-for or doesn’t he? Who knows! More in next post.