Wednesday, September 10, 2008

Movement and perception disorders : a case for dissolution?

I have touched upon the work of Hughlings-Jackson earlier, albeit very obliquely, and readers familiar with with his work will know the immense contributions he has made to the understanding of epilepsy and other neurological disorders. I was recently reading the Croonian Lectures on the Evolution and dissolution of human nervous system and I encourage my readers to read the 3 lectures in their entirety. Let me briefly try to summarize his approach to brain first:

Hughligs Jackson believed that the brain had evolved. Also that the human brain is heterogeneous with three distinct evolutionary distinct components that were perfected in evolutionary dissimilar times: in this sense he sort of laid the groundwork for the Triune Brain theory of Paul MacLean.

He also believed that these three evolutionary distinct (logical) components of the human brain were hierarchical in nature and that all that these centers really did was representation of impressions and movements or re-representation of that initial representation (in successively higher centers). He also proposed that lower centers were more simple, more organized, more automatic and more reflexive in nature; while the highest centers were the least automatic, least organized , but the most complex and the least reflex-like in nature.

As these centers evolved one after the other, each such center has a positive function that only it can provide and it also inhibits some of the functions that were earlier provided by the lower layers; or in other words keeps the lower layers in check.

He also believed in the concept of dissolution: whereby when a higher center is not working properly then this would result in the lower centers asserting their autonomy. The loss of the higher layer/ center would not only result in the loss of function associated with that center (negative symptoms) ; but by freeing the autonomic activity of lower center from higher inhibition, it would also lead to some new functions to be experienced (positive symptoms). Thus a dissolution that affects the third or highest layer , would free the intermediate layer to produce some positive effects, and because of unavailability of the higher layer function would also lead to loss of some functionality.

He most fully developed these ideas in association with epilepsy patients, in which he believed, that the epileptiform seizure or discharge leads to inactivity of higher layers (1, 2 or all 3) and inappropriate activity in lower layers, thereby produce different degrees of negative and positive symptoms/ behaviors. My earlier post did contain references to this.

We find evidence for the truth of most of his ideas in today's neuroscience developments.

This time I will like to touch upon how he himself had, sort of extended the triune brain, to an eight stage brain and how he delineated eight different levels of dissolution, each progressively of a more severe level than the earlier one , while he related the concept of dissolution in the Croonian lectures (lecture 1) with the help of movement disorders.

Before we proceed, it is instructive to note that Jackson believed in two levels of consciousness: subject and object- the former related to awareness of impressions; while the latter to movements. In simpler terms , he believed that we could discuss, movement (and volitional) related stuff separate from perceptual stuff and I'll stick to that distinction in this post.

I'll first quote at length from him (I have reformatted the stuff, so please read the original lecture for a balanced view):

I now come to give examples of dissolution. I confess that I have selected cases which illustrate most definitely, not pretending to be able to show that all the diseases of which we have a large clinical knowledge exemplify the law of dissolution. However, I instance very common cases, or cases in which the pathology has been well worked out; they are cases dependent on disease at various levels from the bottom to the top of the central nervous system. Most of them are examples of local dissolution.
  1. Starting at the bottom of the central nervous system, the first example is the commonest variety of progressive muscular atrophy. We see here that atrophy begins in the most voluntary limb, the arm; it affects first the most voluntary part of that limb, the hand, and first of all the most voluntary part of the hand; it then spreads to the trunk, in general to the more antomatic parts. To speak of a lower level of evolution in this case is almost to state a barren truism. At a stage when the muscles of the hand only are wasted, there is atrophy of the first or second dorsal anterior horn; the lower level of evolution is made up of the higher anterior horns for muscles of the arm. This statement, however, is worth making, for it shows clearly that by higher and lower is meant anatomico-physiologically higher or lower.
  2. Going a stage higher we come to hemiplegia, owing to destruction of part of a plexus in the mid-region of the brain. Choosing the commonest variety of hemiplegia, we say that there is loss of more or fewer of the most voluntary movements of one side of the body; we find that the arm, the more voluntary limb, suffers the more and longer; we find, too, that the most voluntary part of the face suffers more than the rest of the face. Here we must speak particularly of the lower level of evolution remaining; strictly we should say collateral and lower. We note that although unilateral movements (the more voluntary) are lost, the more automatic (the bilateral) are retained. Long ago this was explained by Broadbent. Subsequent clinical researches are in accord with his hypothesis. The point of it is that the bilateral movements escape in cases of hemiplegia in spite of destruction of some of the nervous arrangements representing them; the movements are doubly represented—that is, in each half of the brain. Hemiplegia is a clear case of dissolution, loss of the most voluntary movements of one side of the body with persistence of the more automatic movements.
  3. The next illustration is paralysis agitans. Apart from all speculation as to the seat of this disease, the motorial disorder illustrates dissolution well. In most cases the tremor affects the arm first, begins in the hand, and in the thumb and index-finger. The motorial disorder in this disease becomes bilateral; in an advanced stage paralysis agitans is double hemiplegia with rigidity—is a two-sided dissolution.
  4. Next we speak of epileptiform seizures which are unquestionably owing to disease in the midregion of the brain (middle motor centers). Taking the commonest variety, we see that the spasm mostly begins in the arm, nearly always in the hand, and most frequently in the thumb or index-finger, or both; these two digits are the most voluntary parts of the whole body.
  5. . [The next illustration was by cases of temporary paralysis after epileptiform seizures.]
  6. Cborea is a disease in which the limbs (the most voluntary parts) are affected more than the trunk (the more automatic parts), and the arms (the more voluntary limbs) suffer more than the legs. The localization of this disease has not been made out;symptomatically, however, it illustrates dissolution. Chorea has a special interest for me. The great elaborateness of the movements points to disease “high up" —to disease on a high level of evolution. Twenty years ago, from thinking on its peculiarities, it occurred to me that some convolutions represent movements. A view I have taken ever since.
  7. Aphasia. This well illustrates the doctrine of dissolution, and in several ways. We will consider a case of complete speechlessness. (a) There is loss of intellectual (the more voluntary) language, with persistence of emotional (the more automatic) language. In detail the patient cannot speak, and his pantomime is of a very simple kind; yet, on the other hand, he smiles, frowns, varies the tones of his voice (be may be able to sing), and gesticulates as well as ever. Gesticulation, which is an emotional manifestation, must be distinguished from pantomime, which is part of intellectual language. (b) The frequent persistence of “Yes“ and “No“ in the case of patients who are otherwise entirely speechless is a fact of extreme significance. We see that the patient has lost all speech, with the exception of the two most automatic of all verbal utterances. “Yes“and “No“ are evidently most general, for they assent to or dissent from any statement. In consequence of being frequently used, the correlative nervous arrangements are of necessity highly organized, and, as a further consequence, they are deeply automatic. (c) A more important, though not more significant, illustration is that the patient who cannot get out a word in speech nevertheless understands all that we say to him. Plainly this shows loss of a most voluntary service of words, with persistence of a more automatic service of words. We find illustrations in small corners. (d) There are three degrees of the utterance “No“ by aphasics. A patient may use it emotionally only—a most automatic service; another patient may also be able to reply correctly with it—a less automatic, but still very automatic service. (Here there is some real speech.) There is a still higher use of it, which some aphasics have not got. A patient who can reply “No“ to a question may be unable to say ‘No“ when told to do so. You ask the aphasic, “is your name Jones?“ he replies “No.“ You tell him to say “No,“ he tries and fails. You ask, “Are you a hundred years old ?“ He replies “No.“ You tell him to say “No.“ He cannot. Whilst not asserting that the inability to say “No“ when told is a failure in language, it is asserted that such inability with retention of power to use the word in reply illustrates dissolution. (e) A patient who is speechless may be unable to put out his tongue when told to do so; that he knows what is wanted is sometimes shown by his putting his finger in his mouth to help out the organ. That the tongue is not paralyzed in the ordinary sense is easily proved. The patient swallows well, which he could not do if bis tongue were as much paralysed as "it pretends to be.“ Besides, on other occasions he puts out his tongue, for example, to catch a stray crumb. Here is a reduction to a more automatic condition; there is no movement of the tongue more voluntary than that of putting it out when told. [The lecturer then remarked on swearing and on the utterance of other and innocent ejaculations by aphasics, remarking that some of these utterances had elaborate propositional structure but no propositional value. The patients could not repeat, say, what under excitement they uttered glibly and well. He spoke next of the frequent retention of some recurring utterance by aphasics, such as “Come on to me.“ These were not, from the mouth of the aphasic, of any propositional value, were not speech. He had no explanation to offer of these, but stated the hypothesis that they were the words the patient was uttering, or was about to utter, at the time he was taken ill.]
  8. . So far I have spoken of local dissolution occurring on but one half of the nervous system on different levels. Coming to the highest centers I speak of uniform dissolution—of cases in which all divisions of these centers are subjected to the same evil influence. I choose some cases of insanity. In doing this I am taking up the most difficult of all nervous diseases. I grant that it is not possible to show in detail that they exemplify the principle of dissolution, but choosing the simplest of these most complex cases we rnay show clearly that they illustrate it in general. I take a very common-place example—delirium in acute non-cerebral disease. This, scientifically regarded, is a case of insanity. In this, as in all other cases of insanity, it is imperative to take equally into account not only the dissolution but the lower level of evolution that remains. The patient‘s condition is partIy negative and partly positive. Negatively, he ceases to know that be is in hospital, and ceases to recognise persons about him. In other words, he is lost to his surroundings, or, in equivalent terms, he is defectively conscious. We must not say that he does not know where he is because he is defectively conscious; his not knowing where he is is itself defect of consciousness. The negative mental state signifies, on the physical side, exhaustion, or loss of function, somehow caused, of some highest nervous arrangements of his highest centers. We may conveniently say that it shows loss of function of the topmost layer of his highest centers. No one, of course, believes that the highest centers, or any other centers, are in layers; but the supposition will simplify exposition. The other half of his condition is positive. Besides his not knowings, there are his wrong knowings. He imagines himself to be at home or at work, and acts as far as practicable as if he were; ceasing to recognize the nurse as a nurse, he takes her to be his wife. This, the positive part of his condition, shows activity of the second layer of his highest centers; but which, now that the normal topmost layer is out of function, is the then highest layer; his delirium is the “survival of the fittest states,“ on his then highest evolutionary level. Plainly, he je reduced to a more automatic condition. Being (negatively) lost, from loss of function of the highest, latest developed, and least organized, to his present “real,“ surroundings, he (positively) talks and acts as if adjusted to some former “ideal“ surroundings, necessarily the more organized.

This to me seems very promising: I am a die-hard fan of the eight stage evolutionary/ developmental model whereby the first five stages are more similar, the next two on a qualitatively different level; while the last or eighth one takes one a notch higher up the octave to a different qualitative level altogether, although resembling or analogous to the first stage to an extent.

I keep mapping analogies between the different stages evident in different developmental / evolutionary processes and this piece of puzzle fits in nicely.

I'll now like to speculate a bit. I'll first restrict myself to movement/action planning, execution and control. I believe that the regions of the brain involved in this activity are (in a heirarchichal order) :
  1. Frontal Cortex (supplementary motor area) : decides which action to initiate/ plans and co-ordinates with respect to complex actions involving say both hands. More involvement in 'voluntary' actions
  2. Primary Motor cortex : Actual execution of the intended/ chosen action.
  3. Pre-motor cortex:responsible for motor guidance of movements especially with respect to external cues
  4. Parietal cortex:responsible for transforming visual information into motor commands
  5. Somatosensory cortex: this too is involved in motor circuits ; see this too.(synapses to and from this go to cerebellum/ basal ganglia): probably involved in triggering visual information related to the action. I am tempted to replace this with Thalamus and I just might do that after some more research!!
  6. Basal Ganglia: a set of structures that are involved in gross motor control
  7. Cerebellum: a structure involved in fine motor control
  8. Brain Stem: a structure involve in controlling vital involuntary movements like breathing, heart beat etc. these movements are neither voluntary nor automatic; they are involuntary and thus a notch different.
Now coming back to the disorders of the movement delineated by hughlings-Jackson, we can readily see some correspondences. The Basal Ganglia abnormality leading to Huntington's Chorea is clearly at level 6. The primary motor cortex lesion leading to stage 2 hemiplegia is also well established. The epileptofm seizure related spasms and temporary paralysis just after that may be plausibly related to lesions of parietal and somatosnesory cortices. The lesion of pre-motor area may give rise to alien hand syndrome (to be distinguished from Anarchic hand syndrome), whereby you grab any object in sight compulsively. The hughlinghs-jackson description of Parkinsonisms at level 3 does not really gel here as Parkinsonism is more of a basal ganglia problem. Similarly PMA (progressive muscular atrophy) is no longer a valid diagnosis, so it may not map to SMA lesion or dysfunction. SMA dysfunction or lesion may instead produce syndromes like the mirror hand syndrome , in which both hands are used for the same action, though only one hand would have sufficed. It is interesting to note that this mirror hand syndrome is conceptualized today as freeing of SMA inhibition of PMA, thus allowing parallel planning of the same action. Similarly level 7 lesions of cerebellum may be more related to Ataxia rather than aphaisas.

Despite the above problems with the above conceptualization, I find the efforts of Jackson is the right direction and ahead of hist time.

I'll now end with a teaser of things to come. It is related to disorders of phenomenal consciousness classified by Thomas Metzinger in Being No One, and they are as follows :

Deviant phenomenal models of reality
  1. Agnosia
  2. Neglect
  3. Blindsight
  4. Hallucinations
  5. Dreams
To me they follow the same 5 stage process, with each stage analogous to the movement related disorder.More about that later.

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