“What you’ve got to realize is that every cell in the nervous system is not just sitting there waiting to be told what to do. It’s doing it the whole darn time. If there’s input to the nervous system, fine. It will react to it. But the nervous system is primarily a device for generating action spontaneously. It’s an ongoing affair. The biggest mistake that people make is in thinking of it as an input-output device.” ~ Graham Hoyle, quoted in William Calvin’s The Cerebral Symphony (p. 214)
Tag Archives: neuroscience
I have been hearing a lot of buzz lately about Asim Roy’s newly published paper Connectionism, controllers, and a brain theory. What is all the hype about? Well, Roy claims to be offering a “new theory for the internal mechanisms of the brain.” Sounds exciting doesn’t it? What could Roy be proposing that is so revolutionary? Roy proposes that…wait for it… some parts of the brain control other parts! I suppose most of you aren’t exactly blown away, and I certainly wasn’t either.
Roy’s rhetoric is obviously pretty overblown, but let us give him the benefit of the doubt and move on to his actual arguments. He starts off by claiming that connectionist theory “postulates that the brain does not have controllers in it.” He quotes Rumelhart, Hinton, and McClelland as saying “there is no central executive overseeing the general flow of processing.” Seems pretty non-controversial to me though. They seem to be merely saying that there isn’t a homunculus in the system, controlling everything with a immutable Will. Philosophy 101. So what is Roy actually arguing against? A straw man? Sort of, but not quite. Roy argues that in connectionist models, there is a “controller” in the system that controls the learning algorithms and thus connectionist theories are essentially rooted in control-theoretic modeling.
But, as peter over at conscious entities mentioned, connectionist theorists haven’t exactly gotten to the point where they are proposing a general architectural model of how the brain works. It seems entirely plausible that when connectionist models get to that point of complexity, they wouldn’t hesitate to propose that some modules control other modules. Otherwise, I don’t see how one could get a theory that modeled high-level cognition. The way Roy structured his arguments, I don’t think anyone would argue against the idea that “there are parts of the brain that control other parts.” Furthermore, Roy himself undermines his claim for proposing a “new paradigm” when he says things as trivially obvious as:
It should be pointed out that this theory does not posit that there is a single executive controller in the brain. [b]Instead it envisions “multiple distributed controllers” controlling various subsystems or modules of the brain[/b]. The main argument of the paper that connectionists use “executive controllers” is only pointing out that their algorithms use a “central controller.” But different modules in the brain using connectionist-type learning can have their separate controllers.
I’d also like to point out that Roy was beaten by at least ten years on his emphasis of controllers. In his 1997 book Being There, Andy Clark says:
The idea here is that the brain should not be seen as primarily a locus of inner descriptions of external states of affairs; rather, it should be seen as a locus of inner structures that act as operators upon the world via their role in determining actions…This perspective leads to a rather profound shift in how we think about mind and cognition-a shift I characterize as the transition from models of representation as mirroring or encoding to models of representation as control
So contrary to Roy’s strong rhetoric, people sympathetic to connectionist theory such as Clark have been thinking about the mind and the brain in terms of action-oriented controllers for many years. In conclusion, I agree with Roy’s essential argument that there are parts of the brain that control other parts of the brain, but I don’t think this is a revolutionary of a paradigm as he thinks it is. Roy himself quotes from all over the neuroscience literature showing that it is riddled with control-theoretic terms, and by his own argument, he shows that connectionist theory is also already steeped in control theory. Surely, the connectionists themselves understand this. So who is Roy arguing against here?
The Italian Neuroscience Mafia is at it again: Giacomo Rizzolatti and cohorts recorded the brain activity of macaque monkeys in the F5 and F1 areas while they were grasping with their hands and then when they were grasping with a pair of pliers. Remarkably, the same neurons fired in the same order when they were grasping with their hands as when they were grasping with the tool. Furthermore, the same neurons also fired in the same order when the monkeys used “reverse pliers” that required closing and then opening the hand in order to grasp the food. Because of this, the researchers concluded that “the capacity to use tools is based on an inherently goal-centered functional organization of primate cortical motor areas.”
Their evidence clearly shows that there are cortical neurons in the F5 and F1 area that code for for the goal of motor acts, instead of the motor act itself. These neurons are then connected to neurons that more specifically code for the motor act of opening and closing. Furthermore, the researchers show evidence that amidst the goal-directed neurons in the F5 area, mirror neurons are also involved, which code for goal-directed actions during the observation and execution of an act and are rich in the F5 area.
Basically, Harvard researchers built a machine that slices thin layers of brain tissue and then takes high-resolution pictures with an electron microscope, hoping to form detailed diagrams of the actual circuitry of the brain i.e. “connectomes”. This process stands to generate a huge amount of data on how the brain is actually wired. Exciting times!
I thought this article was an interesting insight into the thought process of those who disregard the relevance of neuroscience for understanding the mind. The terminology Lehrer uses gives him away:
Even our sense of consciousness is explained away with references to some obscure property of the frontal cortex.
[According to reductionism]The mind, in other words, is just a particular trick of matter, reducible to the callous laws of physics.
You are simply an elaborate cognitive illusion, an “epiphenomenon” of the cortex. Our mystery is denied.
All of these quotes highlight a curiosity in Lehrer’s phrasing. Does he really think that if neuroscience succeeds in explaining cognitive phenomena in mechanistic terms, the mind will be “explained away”? Was heat “explained away” when we reduced it to the movement of molecules? Were the properties of water “explained away” when we reduced it to H2O? On the contrary, the phenomena of both are still with us and it is ridiculous to assume that if neuroscience is successful it will reduce the mind to “just a trick”. On the contrary, the mind will be seen as a complicated set of cognitive phenomena not just “reducible to” but explained by mechanisms in the brain/body system.
So, the question isn’t as Lehrer says whether or not neuroscience can move “beyond reductionism”, but rather, what can be successfully explained in mechanistic terms and what can’t? It is clear that there is useful phenomenological data to be had at the higher levels of abstractions that characterize our thoughts about the mind, but it should be said again that these abstractions aren’t “just” tricks, but rather, complicated phenomena in their own right that need explaining. Whether or not that explanation will be in the terms of neuroscience or at the higher level of cognitive psychology has yet to be determined, but it seems clear that the empirical method itself will give us a clearer picture of the mind.
This brings me to my last point, and that is whether or not neuroscience is capable, in principle, of explaining all cognitive phenomena. For me, the answer is a resolute yes, but I want to emphasize the term “in principle”, because explaining all cognitive phenomena at the molecular level may be pragmatically out of reach. We should be grateful that evolution has given us a language capable of discussing cognitive phenomena at a higher abstraction than that of science, but we should also learn to accept the fact that ultimately everything in the universe, including the mind, can be “reduced” to the physical motions of matter. It might seem like I am making a category mistake, but it seems intuitively plausible to me. I am not saying that all cognitive phenomena will be reduced to the physical level, but I think in principle, it can be. But I don’t think that is a very interesting idea. What is more interesting to me is the question of what will be explained in mechanistic terms and what won’t, and that is a pragmatic question of science that we will be continuously working on for what seems like an indefinite period of time.
In this post, I want to discuss a paper entitled the “Breakdown of Cortical Effective Connectivity During Sleep”. In plain English, this paper discusses the theoretical possibility that consciousness fades during the night because the cortex essentially doesn’t talk to itself as much. More specifically, this study focused on NREM sleep, which accounts for roughly 75-80% of our total sleep time. During NREM sleep, people often report no dream experiences, and it is this lack conscious activity that the researchers wanted to investigate. What goes on in our brains during this period of non-consciousness?
In order to answer this question, the researchers used a combination of transcranial magnetic stimulation(TMS) and electroencephalography(EEG). Using TMS was advantageous for the researchers because they could stimulate the cortex directly without activating the subcortical reticular formation and the thalamo gating relay.
The researchers used TMS to stimulate the rostral portion of the right premotor cortex, which has dense connections with the rest of the cortex area, which is heavily correlated to typical wakeful consciousness. Now for the results:
During wakefulness, TMS induced a sustained response made of recurrent waves of activity…With the onset of NREM sleep, the brain response to TMS changed markedly. After [the initial] large wave, no further TMS-locked activity could be detected.
Thus, during wakefulness, the perturbation of the rostral premotor cortex was followed by spatially and temporally differentiated patterns of activation that appeared to propagate along its anatomical connections. In striking contrast, during NREM sleep the location of maximum current density remained confined to the stimulated area.
During wakefulness, the site of maximum activation moved back and forth among premotor and prefrontal areas in both hemispheres and, in some subjects, it also involved the motor and posterior parietal cortex. During NREM sleep, by contrast, the activity evoked by TMS did not propagate in space and time in any of the subjects.
Thus, an impairment in the ability to integrate information among specialized thalamocortical modules—a proposed theoretical requirement for consciousness—may underlie the fading of consciousness in NREM sleep early in the night.
The researcher’s speculation on the potential neural mechanisms behind this decreased cortical activity during NREM sleep is a little beyond the scope of this blog, but it could have something to do with “down states” of depolarization being triggered more easily. Regardless,
Whatever the precise mechanisms, they are most likely engaged by the progressive reduction of the firing of diffuse neuromodulatory systems that occurs when we fall asleep.
For those interested, a good summary article of this research can be found here
This is a painting done by a congenitally blind artist named Esref Armagan.
The most obvious question is how his brain is able to perform such feats of perspective, but as the article mentions, it is well understood that “blind people… understand and can draw in three dimensions”
With that said, I think this particular “how” question is easily answered with modern paradigms of neural plasticity/pruning etc
I believe the more puzzling question to ask is not how he can perform such tasks, but rather, how his developing brain learned to generate high-order representations of three-dimensional space to such a phenomenal degree of accuracy.
Well, “I was taught, he says. Not by any formal teacher, but by casual comments by friends and acquaintances.”
This remark, combined with the fact that “it is impossible to know if he had some vision as an infant”, makes it difficult to extract any conclusive insights about whether his “mind’s eye” is purely mapped out in non-visual sensory-terms (the primary contributors likely being kinesthetic and proprioceptive), and his incredible “accuracy” is simply the result of his early peers subtlety nudging him back and forth until he got it “right”.
An alternative answer is that his brain got some “extra” reinforcement by crude visual data before his eye completely degenerated, thus making his inner conceptual space not in purely non- visual terms as is suggested by the article. This would also explain why his degree of accuracy is greater than most other congenitally blind people.
These are difficult, but fascinating problems in the psychology of perception, but regardless of Mr. Armagan’s unique skills, there seems to be an emerging consensus from all psychological disciplines that whatever “perception” is, it is realizable across many different modalities.