19th Century Science Advocacy

So here’s a quote from a favourite neuroscientist of mine.

“We, too, we labourers in the realm of the natural sciences, to whatever nation we belong, are soldiers and form an army, but an army that knows of no separation into different camps as a result of national or other interests, an army that is united in the one interest, in the search after truth, in the battle against ignorance and against all the hindrances which some men would like to oppose to our endeavour to reach our ideal aims. It may count as an expression of the mutual character of our cause, that I as a foreigner was called to-day to do honour to a scholar of this country, and for this reason also I have discharged this flattering task with joy and pride.” – E Hitzig, 1900

Eduard Hitzig, a German, was giving a lecture on the motor cortex and the work of John Hughlings Jackson, a British neurologist who created a theory of the brain as a sensorimotor processor. It was a very nationalistic time, and Hitzig was pleased at the conviviality in the scientific community, united not by nation or language but by a mutual striving towards truth.

Hitzig, along with Gustav Fritsch, discovered that portions of the cerebral cortex could be electrically excited, something previously thought to be the sole trait of lower parts of the brain. They also showed definitively that there are regions in the cortex that activate muscles in specific parts of the body, creating an early version of the topographic map that would be defined in humans some six decades and more later, by Dr. Wilder Penfield.

This was a pretty big deal. The biggest names of the era had pretty firmly established that the cerebral cortex had no motor role, and that specific functions could not be localized into regions of the cortex. Equipotentiality was the name of the game, and it was thought that cognitive abilities were only impaired as a function of the amount of cortex removed. This strain of thought actually lasted all the way up to the 50s and 60s with Karl Lashley and his disciples; though in a much more moderated form, since they could not deny that some functions were processed in certain regions.

Anyways. Hitzig and Fritsch’s 1870 paper Ueber die elektrische Erregbarkeit des Grosshirns is a masterpiece of 19th century science writing. It mentions all the previous research which had established the non-excitable, non-motor role of the cortex, in a positive and respectful tone, and sets out their initial experimental procedure in some detail. And then out of nowhere, this line:

“Part of the convexity of the dog cerebrum is motor (this expression is used in Schiff’s sense), another part is not motor.”

Bam. A half century of cortical study overturned, to be followed by some of the most important findings in that decade. Among them, the discovery that the anode of their electrode caused excitation, not the cathode, which they consider in relation to recent contemporary findings in neurochemistry; early findings which might be related to short-term potentiation and depression; and speculation regarding whether the excitation is caused in the nerve cells or nerve fibres, quite some time before our current understanding of cellular nervous function.

Dennett and the self

So I thought, being as it’s quarter past four and I’m not asleep, that I’d elaborate a bit on the reference I made a while back to Daniel Dannett’s idea of the self as a narrative center of gravity.

Now, if you’d like to read the entire essay he wrote on the topic, you can find it here.

But for those of you who looked at it and went tl,dr or for some reason want my perspective on it, here goes.

A center of gravity does not exist, physically. It is an abstract object which has physical, tangible, measurable properties, but which does not correspond to a specific object. Instead, it occupies a sort of spatial-temporal conceptual space. We know where it is, because we know that when it crosses the bounds of its base, the object possessing it falls over. As soon as the center of gravity crosses the base of a chair, the chair falls.

This phenomenon of a ‘tipping point’ is fascinating in and of itself, because it represents a class of phenomena which are essentially binary. The chair is not falling before it hits its tipping point; after it crosses the tipping point, it is falling. No gradual shift, just a sharp category boundary.

None of this should be taken as either Dennett or I claiming that the self is a chair, or that it can tip over. The metaphor isn’t being extended that far. What is being argued is that our selves are essentially fictional, a form of narrative.

Historical, real-world people can have yes-or-no questions asked of them. Dennett notes that while it is a yes-or-no question as to whether Aristotle had a mole on his left shoulder (even if no one knows), there is theoretically a correct answer. But the question “Did Sherlock Holmes have a mole on his left shoulder” is ambiguous. Unless one asks Doyle, or infers it somehow from the text, there is no answer. It’s not that the correct answer is unknown, it is that there simply is no answer to the question.

In this way, our selves are like fictional characters. Our histories are the determinate parts of our character’s past. That Holmes was friends with Watson in not ambiguous or indeterminate. So too are many of our own relationships. But we do not know who we will be. In this way we are constantly being written, and our pasts are subject to revision or reappraisal based on these new writings. An act that seemed perfectly natural just now might, in five years’ time and as the novel of YOU is written, seemed foreign, cruel, or to hardly have happened at all.

Dennett comes up with a scenario which appeals to materialistic old me. Imagine a machine, he suggests, that writes novels. It doesn’t have to be an AI, necessarily. But it has been programmed in such a way that it can create continuous narratives describing the activities of fictional characters.

Now imagine that it has been given wheels and a camera, and manipulators. Imagine that the story it writes seems to describe the daily meanderings and activities of a robot, which wheels about and sees things using its camera. When the machine goes up a ramp, the character in the story goes up a ramp shortly thereafter.

If all the events in the story mirror the experiences of the novel-writing machine, does that machine have a ‘self’?

Dennett, and I tend to agree with him here, sees part of the reason for ourselves-as-fiction as being due to the nature of our minds. I’d mentioned his multiple-drafts theory of consciousness, and part of that includes the idea that our selves are narrated by loosely collaborating committees of various neural modules. Sensory modules, motor modules, their sub-modules, attentional modules, left versus right hemispheres, and all of them cross-talking and competing for resources. It’s no wonder we’d a bit muddled, mentally. The self as a story is written out in multiple drafts by these modules, sent around haphazardly for corroboration, edited, and then send ’round again.

Lastly. Like a center of gravity, we could suggest that the self is localized. In our case, in the brain. But it would be a mistake to attempt to be too specific as to where. Dennett says elsewhere that “if you make yourself very small, you can exclude almost everything.” We will not find our selves shrunk down in a single neuron in a specific region of the brain, in the same way that we will never find an atom that is the center of gravity of an object. It is local but abstract, and we would do well to realize this.

Who we tell ourselves we are is only partly determined, and the narratives we write can change that self to be unrecognizable by the future self.

Slight clarification.

I took a pretty strong position in my last post against domain-specific functional localization, and I feel I should point out one of two things.

My point is largely directed towards cognitive and secondary sensory and motor functions. The support for fairly strict localization of primary sensory inputs and motor outputs is quite strong. Vision definitely projects to the superior colliculus and through the lateral geniculate nucleus to area V1 of the occipital lobe, for example. And I’ve posted in the past on the sensory and motor homunculi, where input from specific regions are represented somatotopically along the post-central and pre-central gyri (respectively).

But high-level functions like language, thought, goal direction, mathematics, etc. These are the functions I’m thinking of when I say any localized functions are not domain-specific. Sequencing is sequencing, whether it’s words or objects or numbers.

A view of the brain.

I’m going to give this short post thing a try, without just posting a video.

So there’s a lot of different ideas about the brain. One of the more popular could be called “localized modularity,” and it’s been around since at least the late 70s, and especially since Jerry Fodor published Modularity of Mind. In it he describes the requirements of a modular system, which is how he sees the brain.

1. Domain specificity, modules only operate on certain kinds of inputs—they are specialised
2. Informational encapsulation, modules need not refer to other psychological systems in order to operate
3. Obligatory firing, modules process in a mandatory manner
4. Fast speed, probably due to the fact that they are encapsulated (thereby needing only to consult a restricted database) and mandatory (time need not be wasted in determining whether or not to process incoming input)
5. Shallow outputs, the output of modules is very simple
6. Limited accessibility
7. Characteristic ontogeny, there is a regularity of development
8. Fixed neural architecture.

Now, I have varying views on these. Bear in mind that I’m at a stage where I’d have trouble seriously defending my positions. But I have them none the less, so here goes.

1. This idea seems suspect to me. Why would it make sense for brains to have specific regions devoted only to language, or to tasting only food, or to recognizing faces? The fusiform face area is supposedly specific to facial recognition in normal orientation, but there’s evidence suggesting it’s really involved in processing any categorical visual information on familiar objects.

2. This just sounds like nonsense. Language doesn’t need to be informed by motor systems for producing speech? We don’t integrate multi-sensory information when viewing a scene? We don’t need to reference our motor system when perceiving ballistics? There’s plenty of evidence that many brain functions draw on a variety of functional regions for processing, not just a single encapsulated module. These days we should be thinking about broad, parallel networks, not single processing units.

3. I’m a bit softer on point 3. I think there are a lot of mandatory processes, both low- and high-level. I think the direct realists make a good point when they suggest that while we can choose to attend to proximal stimuli (cool temperature, smoothness, rigidity) we are obliged to attend to distal stimuli (a can of pop).

On the other hand, we can exercise top-down control of perception as well. This means that we may be able to exert conscious control over certain mental processes – whether Fodor would claim that those portions simply aren’t modules is unknown to me.

4. Again, I feel that this is true for some things and not for others. Perceptual functions might be more obligatory than motor functions, but I’d definitely argue they aren’t strictly encapsulated either.

5. I’d actually agree that network outputs tend to be simple, and that more complex effects are due to multiple network outcomes overlapping in time.

6. I do think we have limited access to mental processes, so I’ll let this one stand.

7. Again, I don’t have a huge problem with this, though I’d caution against genetic interpretations of this for neural development. I think the common brain development patterns (in terms of broad functional localization) is due to a combination of genetics, epigenetics, and massed Hebbian connective wiring.

8. No, no, and no. I can’t imagine anyone defends this one these days. While I think it’s still a bit of a buzzword, our current understanding of neuroplasticity really doesn’t allow us to support any model that includes fixed neural architecture. Use it or lose it seems to be the rule of the game, at least within certain broad bounds.

I’ve given some criticisms that might seem to accept the modular model of the brain, so let me explain briefly how I see things.

I think brain functions are conducted from broadly localized functional regions, made up of networks of non-domain-specific computational units. I think Broca’s area is involved in general sequencing functions, not just linguistic syntax. I think the pre-SMA is involved in new action sequencing, and the SMA proper is involved in voluntary execution of learned action sequences. I think the hippocampus is involved in long-term episodic memory storage.

I do not think that there is any true double-dissociation for precise, domain-specific functions. I think anyone who expects to find anything other than broad functional associations, using our current level of technology, is in for disappointment. And I think if we are able to locate domain-specific functional networks, that the neurons involved will be mixed in among neurons involved in other related functions.

But I could be wrong.