Sleeping
with a brain that dissociates
Abhijit Chaudhuri
SMJ
2003 49(2): 42-43
“THERE
IS no delusion more damaging than to get the idea in your head that you
understand the functioning of your own brain”, wrote Lewis Thomas in his essay
The Attic of the Brain,1 “the human mind is not meant to be governed, certainly not by any book
of rules yet written; it is supposed to run itself, and we are obliged to follow
it along, trying to keep up with it as best we can.”
I
was sitting in my neurology clinic across from a 64 year old lady. She was
referred to me by the Ophthalmology Senior House Officer (SHO). Mrs. C, as we
shall call her, was in the busy eye clinic earlier for her poor vision due to
the cataracts. She was hoping to get an idea of the waiting time before the
surgery.
“You
know”, she told the SHO softly, “I see animals and flying birds; green
gardens and waterfalls springing up in front of my eyes: I know they are not
real but I just love to see them”.
“Complex
visual hallucinations”, wrote the SHO, “Get a neurology check and they’ll
arrange a CT scan for you”. So,
there was Mrs. C, waiting in front of me as I finished my neurology
examination.
“You
are perfectly all right Madam”, I reassured her, “You don’t need a CT
scan, either. Just go ahead with the surgery for your eyes”.
She
asked nervously, “But Doctor, surely there is something wrong in
my head or why should I see these pictures?”. It was then that I thought of
Lewis Thomas.
Even before examination, I knew Mrs. C had Charles Bonnet Syndrome (CBS) that is characterised by visual hallucinations with preserved insight in a person who is visually handicapped, usually due to the cataracts or macular degeneration. It is common in elderly people. I still find that some physician colleagues are unaware of this syndrome and they suspect hysteria as the cause of CBS. Most practitioners do not recognise CBS and many have not even have heard of it. This is not be wondered at. CBS is not be found in the index of recent editions of Cecil’s or Harrison’s textbooks of medicine, nor it is to be discovered in the new Oxford Textbook of Psychiatry - two
volumes of some 2,400 pages.
It is possible that CBS may be ignored or underestimatedas a clinical problem because visual hallucination in a personwith poor vision is not taken seriously. Indeed, Ramachandran wrote in his essay on CBS, The Secret Life of James Thurber,2 “When Grandma, sitting in her wheelchair in the nursing home, says: What are those water lilies doing on the floor? . . her family is likely to think she’s lost her mind”.
The
mechanism of CBS is unknown. I have recently proposed that CBS may be an example
of cortical dissociation syndrome for visual function .3
Historically, the
concept of dissociation in the integrated bi-hemispheric cortical function
(“disconnection syndromes”) came from the work of Geschwind and was
developed from his model of language function. These syndromes were caused by
focal lesions in the cerebral white matter that separated different parts of the
same hemisphere (intra-hemispheric disconnection) or one hemisphere from another
(interhemispheric or commissural).
Anterior cerebral artery occlusion and surgical section of the anterior four-fifths of the corpus callosum provide some of the best examples of the inter-hemispheric disconnection. In these conditions, the language and the perceptual areas of the left hemisphere are isolated from those of the right because of the vascular or surgical lesion. If blindfolded, an affected patient is not able to match an object held in one hand with that in the other, nor can he match an object seen in the right half of his visual field with the one in the left half. If given verbal commands, he performs correctly with his right hand but not with his left. Without vision, objects placed in the right hand are named correctly but not those in the left.4
Some
of the intra-hemispheric dissociations may be quite subtle. I still remember Mr.
R, a gentleman in his late 40s. He
presented to his general practitioner (GP) with a problem: he did not understand
any of the words spoken to him. However, he could correctly interpret the
jingles of his doorbells, barking of dogs and the rustling of the autumn leaves
in his garden; he could comprehend everything given to him in writing. He
enjoyed the music played by his favourite radio station but could not understand
what was announced before or after; nor could he follow the newsreader and the
weatherman. Mr. R was equally perplexed when his GP asked him, in writing, if he
had any recentstress or was abused verbally by someone he knew well. “I do not
know what he has”, wrote his GP in his referral letter, “I found both his
ears were normal. I wondered if it could be hysteria”.
The
diagnosis of pure word deafness was obvious without examination, but a brain
scan was necessary to confirm the
clinical
suspicion.
But
what happens if the cortical dissociation was functional rather than anatomic,
as in CBS? Sleepwalking patients provide a very interesting example. Sometime
back, Claudio Bassetti and colleagues described the results of a remarkable
experiment in which they obtained SPECT images of a young man’s brain while he
was sleepwalking.5 They noticed activation of the thalamo-cingulate pathways and persisting
deactivation of other thalamo-cortical arousal systems.
Bassetti explained sleepwalking as a dissociation of what they termed as
body sleep and mind sleep. I have little doubt that dissociation between
“body” and “mind” occurs in other conditions, too. The neurobiology of
the cortical dissociative processes has never been explored by scientific
research. Anterior cingulate cortex
is an important area for integrating affective response to the previously learnt
experience. Activation of the thalamo-cingulate pathways occurs in
“unconsciously” performed physical tasks, as in the man who was sleepwalking
in Bassetti’s study5. However, during any consciously performed task, rythmic bursts of the
thalamo-cortical activity sweeps the entire frontal lobe and both the primary
and the supplementary motor cortices must be activated if voluntary movement is
intended.
I
began with the example of CBS as one of the clinical syndromes that, to me,
suggest that within the brain, functional dissociation does occur, perhaps more
often than what we normally recognise. My daughter used to sleepwalk as a child,
and rather than feeling anxious about it like my wife, I took it as an example
of functional dissociation occurring in a developing brain. In Hindu philosophy,
Nirvana provides the highest level of spiritual attainment where the mind can
function independently of the bodily needs, perhaps exemplifying the highest
level of dissociative brain function attainable in life.
“If after all, as seems to be true, we are endowed with unconscious minds in our brains, these should be regarded as normal structures, installed wherever they are for a purpose”, wrote Lewis Thomas in The Attic of the Brain.1
I
could not agree more.
A
Chaudhuri
Consultant
Neurologist
Institute
of Neurological Sciences
Southern
General Hospital
1345
Govan Road
Glasgow
G51 4TF
ACKNOWLEDGEMENT: AC is supported by the David & Frederick Barclay
Foundation.
REFERENCES
Thomas
L. The attic of the brain. In: Late Night Thoughts on listening to
Mahler’s Ninth Symphony. Penguin 1983.
Ramachandran
VS, Blakeslee S. The secret life of James Thurbar. In:Phantoms in the Brain.
Fourth Estate, 1998.
Chaudhuri
A. Charles Bonnet Syndrome: an example of cortical dissociation syndrome
affecting vision? J Neurol Neurosurg Psychiatry,2000; 69: 704-5.
Adams
RD, Victor M, Ropper AH. Disorders of Speech and Language. In:Principles of
Neurology (6th edition), New York: McGraw Hill 1997; pp 472-93.
Bassetti
C, Vella S, Donati F, Wielapp P, Weder B. SPECT during sleepwalking.Lancet
2000, 356; 484-5.