John Hughlings Jackson was one of the founding fathers of neurology, and he got there they way you had to get there in the 1800s and now; by careful clinical observation and by the deployment of keen inductive powers.
This post is developed in three parts. First, I’ll discuss the observations that led to Hughlings Jackson’s firm belief in the primacy of the brain as a sensoimotor machine; that is his characterization of epilepsy. Next, I’ll cover his writings on the evolution of the brain, which led to key neurological insights such as “positive” and “negative” signs and more generally to an organizational scheme that allows predictions of the consequences of brain damage that we may see at bedside. Finally, I’ll briefly describe a whole host of work, some from much earlier writing in this blog and supplemented by a variety of scientific findings and very recent popular science writing, all of which show that Hughlings Jackson was a total intellectual badass. At the end of this piece, I’ll lament the science writers who can’t apply his work and who can’t even ask the people they interview about it knowledgeably.
Can there be a better illustration of Kantian inference to best explanation (the so-called Transcendental Method) – or a more romantic one – than the following?
Jackson’s beloved wife was epileptic. She died too young, in part because of complications of the disease. One of Hughlings Jackson’s major discoveries was of Jacksonian seizures, the tendency for some types of motor activity such as twitches to “march” from the distal portion of a limb (the arm) toward the face, with no loss or alteration of consciousness. Hughlings Jackson was able to infer the topographic representation of the motor cortex by his observations! Somatotopy is fundamental and found in every introductory textbook, usually accompanied by a graphic such as this, taken from McGill University:
The way I was taught this idea in my graduate Neuropsychology courses was lovely; he was consistently distraught over his wife’s symptoms and driven to think about her problems, watching her seizures with a total inability to help her. And so his complex sets of ideas grew from watching the harm suffered by his wife.
II. Representation and rerepresentation; the evolution of the brain.
One other major contribution that Hughlings Jackson made was to think of the brain as an evolved organ over time; inner “core” areas of the brain were responsible for functions that would – in phylogenetically-later developing areas – be duplicated. There was an ordinal re-representation of lower areas by higher areas. York and Steinberg have written extensively about Hughlings Jackson, and I quote them here from a 2011 Brain article:
Hughlings Jackson assumed that the cortex was the highest evolutionary level of the nervous system. As such, it controlled and inhibited the function of lower levels so that cortical disease led to two sets of symptoms, ‘negative’ from loss of the controlling cortex and ‘positive’ from the emergence of the lower centre (Spencer, 1855; Russsell Reynolds, 1861; Pearce, 2004). This implied an anatomical and physiological hierarchy of higher and lower centres, with the higher ones suppressing the function of the lower ones. He expresses the physiological relationship between higher and lower functions in Spencer’s evolutionary principles:
The higher the centre the more numerous, different, and more complex, and more special movements it represents, and the wider region it represents-evolution. The highest centres represent innumerable, most complex and most special movements of the organism, and … each unit of them represents the organism differently. In consequence, the higher the centre the more numerous, complex and special movements of a wider region are lost from a negative lesion of equal volume-dissolution. (Hughlings Jackson, 1882)
Two common terms used to denote what Hughlings Jackson is talking about here are disinhibition and “unmasking.” Because of the inherent, evolutionarily-derived redundancy of the brain and higher control over lower areas, when higher areas are damaged residual function of lower areas can be revealed.
Unmasking is a useful lens by which to view the operations of the brain. Take blindsight, for example. In blindsight, damage to visual cortex results in blindness in parts of the visual world; these holes are called scotomas. The explanation of residual visual capability in blindsight is that some basic visual information can be processed by an evolutionarily older pathway – the superior colliculus to MT pathway. Ramachandran talks about this and we see the behavior of famous patient GY here:
III. Recent work relevant to unmasking; my previous blogging, the science of learning and memory, and recent popular science missed opportunities.
I’ve already written about this stuff! Here
and also here (although, I apparently didn’t fully finish my thoughts)
In a large scale review of memory formation during sleep, Walker (2005) discusses procedural memory formation by the blockage of GABA inhibitory activity. In several sensorimotor systems, it appears, blocking inhibitory suppression allows latent connections to come to the fore. See page 54 here:
But frankly, I was upset after reading this article in Popsci by Adam Piore. http://www.popsci.com/science/article/2013-02/when-brain-damage-unlocks-genius-within.
The article is all about how brain damage has “unleashed” the power of visual and musical artists is such a way that comparisons should be made to savantism. I don’t have a problem with this characterization per se, but I have a problem with not properly grounding these ideas historically, and not realizing scientifically the large-scale context within which we should interpret behavioral effects after brain damage. And I take severe objection with the radical incompleteness in saying the following: “Savants can access raw sensory information, normally off-limits to the conscious mind, because the brain’s perceptual region isn’t functioning.” What?
Unmasking doesn’t require brain damage to be visualized, but perhaps just an extraordinary, intense single experience which can exercise dormant pathways. Again, in a recent gee-whiz kind of science article with little background, we understand that there is a release of stereo depth processing in stereoblind people after exposure. This article by the BBC of course mentions plasticity and even briefly mentions that there may be long-dormant withered pathways that can be reawakened, so in that respect it is much better than the article above.