Functional dualism in the nervous system

altered poliovirus type 3 in a vaccinated population. Lancet 1986; i 1427-32. 12 Van den Kerkhof H. De polio-epidemie vanuit GGD-perspectief. Bull Infect 1993; 4: 203-06. 13 Wright PF, Kim-Farley RJ, de Quadros CA, et al. Strategies for the global eradication of poliomyelitis by the year 2000. N Engl J Med 1991; 325: 1774-79. 14 Slater P, Orenstein WA, Morag A, et al. Poliomyelitis outbreak in Israel in 1988: a report with two commentaries. Lancet 1990; 335:

17 Centers for Disease Control.

the Gambia following the control of poliomyelitis as an endemic disease. II. Clinical efficiency of trivalent oral polio vaccine. Am J Epidemiol 1992; 135: 393-408. 21 World Health Organization. Expanded programme on immunization, poliomyelitis outbreak, Bulgaria. Wkly Epidemiol Rec 1992; 67: 336-37. 22 World Health Organization. Expanded programme on immunization poliomyelitis outbreak, Malaysia, 1992. Wkly Epidemiol Rec 1993: 68: 297-300.

1192-98. 15 Sutter RW, Patriarca PA, Brogan S, et al. Outbreak of paralytic poliomyelitis in Oman: evidence for widespread transmission among fully vaccinated children. Lancet 1991; 338: 715-20. 16 White FMM, Lacey BA, Constance PDA. An outbreak of poliovirus infection in Alberta—1978. Can J Publ Health 1981; 72: 119-24.

Functional dualism in the

nervous

In their pioneer work on cutaneous superficial sensation, Head, Rivers, and Sherren1 explained their observations by proposing two systems, protopathic (lower) and epicritic

components would necessitate dual structures, with the advantage of plasticity but perhaps with different vulnerabilities and different rates of regeneration after injury. Support for Head’s concept has now emerged from studies on the visual pathway: use of micro-electrodes2 in retinal ganglion cells has revealed dual pathways that remain discrete as far as the visual cortex.3-6 They work in concert, but the fact that they react differently to particular neurotransmitters suggests different structures.4 They have been called on and off channels: on channels respond to increasing light against a dark background and off channels respond to decreasing light

(higher). The

two

against a light background.4,5 Disturbances in the balance of such a paired organisation could account for certain sensory disturbances that are so far unexplained. Migraine is an example. The castellation of the fortification spectrum in migraine could be due to imbalance in the laminated superior colliculo-lateral geniculate nuclei, where the two channels are separate and parallel;7,8and the cutaneous paraesthesiae of migraine could have a similar explanation. More complex neurological symptoms from other causes might be due to imbalance in the cutaneous afferent system-spontaneous pain and itching, post-herpetic neuralgia, the pain of glomus tumours, and causalgia. Hyperaesthesia, hyperalgesia, dysgeusia, and even tinnitus could arise in this manner. Another possible consequence of imbalance in a dual system is epilepsy provoked by sensory stimulation. In photogenic epilepsy, a single flash of light or extinction of light can set off an attack; and in other patients seizures are provoked by a loud noise or music. Behrman9 described

system

epilepsy of vestibular origin and Cushing10 reported epilepsy in association with acoustic neuromas. Stroking a cutaneous scar or even undamaged skin provokes epilepsy in some patients. It is noteworthy that carbamazepine," a drug used for the severe pain of tic doloureux, also has anti-epileptic properties. Tumours of the hemispheres, such as gliomas, can present with epileptic attacks long before there is loss of function such as hemiplegia: again, the tumours may cause epilepsy via "imbalance". How could we test this theory of intrinsic dual sensory channels, their "imbalance", and their putative unification? Three elements need to be characterised. The first is molecular differences in parallel channels. In the visual on and off channels they can be identified by the presence or absence of cytochrome oxidase. 12-14 In animal tissues where metabolic processes have been arrested by immersion in liquid nitrogen within a few minutes of death it should similarly be possible to find enzymatic differences, not necessarily the same, in other pathways. If a whole stimulus is regarded as a sine curve which is then split for transmission, then it should be possible to show that the ascending limb and descending limb of the curve are carried by different fibres. The third element would be to identify the factors determining success or failure of the unification process. Delay or attenuation of signals in one of the two channels might be observable in man by means of very short stimuli designed to activate only one channel at a time. I

670

am

grateful to Prof H

Ikeda for

helpful discussions.

References 1

2

3

Department of Immunology, Rayne Institute, UMDS St Thomas’ Campus, London SE1 7EH, UK (J Colover FRCP)

Follow-up on poliomyelitis-United

States, Canada, Netherlands. MMWR 1979; 28: 345. 18 Laboratory Centre for Disease Control. Genomic analysis of type 3 wild poliovirus isolates in southern Alberta. CCDR 1993; 19: 96-99. 19 Kim-Farley RJ, Rutherford G, Lichfield P, et al. Outbreak of paralytic poliomyelitis, Taiwan. Lancet 1984; ii: 1322-24. 20 Deming MS, Jaiteh KO, Otten MW, et al. Epidemic poliomyelitis in

Head H, Rivers WHR, Sherren J. The afferent nervous system from new aspect. Brain 1905; 28: 99-115. Hartline HK. The response of single optic nerve fibers of the vertebrate eye to illumination of the retina. Am J Physiol 1938; 121:

a

400-15. Ikeda H. Transmitter action at cat retinal cells. In: Osborne N, Chader G, eds. Progressive retinal research. Oxford: Pergamon Press, 1985: vol 4, 1-28.

4

Ikeda H, Robbins J. Development of neurochemical separation of ON and OFF channels at retinal ganglion cells. Doc Ophthalmol 1988; 69:

9 10

175-86.

Schiller PH. The ON and OFF channels in the visual system. Trends Neurosci 1992; 15: 86-92. 6 Ikeda H, Wright MJ. Receptive field organization of "sustained" and "transient" retinal ganglion cells which subserve different functional 5

roles. J Physiol 1972;

11

12

227: 769-800.

7

Behan M, Appel PP. Intrinsic circuitry in the cat superior colliculus. Projection from the superficial layer. J Comp Neurol 1992; 315:

8

McConnell SK, LeVay S. Anatomical organization of the visual systems of the mink Mustela vison. J Comp Neurol 1986; 250: 109-32.

13

230-43. 14

Behrman S. Vestibulogenic seizures. Brain 1958; 89: 529-61. Cushing H. On convulsive seizures of the face produced by cerebellopontine angle tumours. J Nerv Ment Dis 1916; 44: 312-21. Jain KK. Investigation and management of loss of efficacy of an anti-epileptic medication using carbamazepine as an example. J R Soc Med 1993; 86: 133-36. Hubel DH, Livingstone MS. Complex unoriented cells in a sub-region of primate area 18. Nature 1985; 315: 325-27. Shipp S, Zeki S. The segregation of pathways leading from area V2 to area V4 and V5 of macaque monkey cortex. Nature 1985; 316: 322-25. Zeki S. Parallelism and functional specialisation in human visual cortex. Coldspring Harbour Symp Quant Biol 1990; 15: 651-61.

BOOKSHELF

certainly achieves its aims, stated in of foreword, being "an Diagnosis and management.-Gerald M Loughlin and Howard Eigen. Baltimore: text clinical aimed unashamedly Williams & Wilkins. 1994. Pp 870.$162/.E112. ISBN 0-683051903. pointblank at the practitioner facing the problems of children with lung Paediatric respiratory medicine has as noisy breathing, cough, and chest problems", but it falls short of probeen a constantly growing subspecialpain. The tables summarising pos- viding complete coverage of paedifor the 20-30 ty past years, partly sible conditions associated with these atric respiratory medicine and needed because of the increasing prevalence symptoms are extremely helpful, and more precision and careful proofof some common respiratory disorthe diagnostic procedures suggested reading. ders such as asthma. This developfor their evaluation are nicely Christian F Poets ment has not been reflected by the grouped according to some key feaDepartment of Paediatric Pulmonology, Medizlnlsche Hochschule Hannover, number of textbooks in the field. tures (eg, expiratory versus inspirato30623 Hannover,

Respiratory disease in children

Thus the appearance of a new textbook on paediatric particularly one that is concise enough to attract not only the specialist but also any practitioner dealing with children who have respiratory diseases, was overdue. . This new textbook on respiratory disease in children aims to be just thata helpful guide for the practitioner. Therefore it may have been a bit unfair that my first approach to this book was to search the index for two rare diseases I happened to see in patients, namely bronchiolitis obliterans and Jeune syndrome (asphyxiating thoracic dystrophy). I was somewhat disappointed to find only one mention, with a figure showing the typical radiographic findings of bronchiolitis obliterans. Jeune syndrome did not appear at all in the index, although I later discovered that there was an entire paragraph . and a figure on this subject which had not found their way into the index. Fortunately, the book is far more appealing when it comes to more common diseases. The chapters on asthma, acute upper airway obstruction, and pneumonia are especially well written and contain many practical tips on diagnosis and treatment of these disorders. I also enjoyed the

pulmonology,

my

chapters common

the

Germany

chronic stridor). there are some drawalso However, backs. There is no discussion of allerry, and acute

versus

gic bronchopulmonary aspergillosis Immunosuppressive drugs in the chapter on cystic fibrosis, or of Developments in anti-rejection cisapride as the first-line pharmacoby Angus W Thomson logical treatment (at least in Europe) therapy.-Edited and Thomas E Starzl. London: Edward for gastro-oesophageal reflux. : Arnold. 1994. 235..E65.

As with many multiauthor textbooks, there is overlap between cha Pters, and it is unfortunate that the editors failed to check these overlapping parts for consistency. For example, in the chapter on bronchopulmonary dysplasia it is suggested that arterial oxygen saturation should be kept at or above 92-95% when administering home oxygen, whereas in the chapter on home oxygen, saturations of 90% are deemed sufficient for these patients. In addition, some information given in the book is imprecise (eg, the explanation for ventilation-perfusion mismatch as "areas of the lung [that] are perfused but underventilated"), wrong (eg, the statement that trans-cutaneous carbon dioxide electrodes must be heated to 44°C), or contradictory (eg, in a table summarising studies on normal values for respiratory the total number of subjects in one study is given as 4, but to the adjacent column there were 9 female and 7 male infants investi-

diagnostic approaches to gated). In summary, pulmonary symptoms, such

frequency,

according

on

this

new

Pp

ISBN 0-340569514.

In the "modern"

of immunosuppressive drug therapy it is difficult to appreciate that prospects for the success of organ transplantation as a era

therapeutic procedure were regarded so pessimistically such a short time ago. As Thomson and Starzl remind

in the preface to this new book charting developments in anti-rejection therapy, even in the early 1960s views expressed could hardly be described as optimistic. For example, in an article published in the New England Journal of Medicine in 1961, us

F MacFarlane Burnet stated "on the whole, the present outlook is highly The unfavourable to success". progress in clinical transplantation since this statement, particularly with respect to the developments in

immunosuppressive

drug

therapy,

has been dramatic.

Immunosuppressive Drugs provides a comprehensive account of these

The editors have not : neglected to chart the early developments in this area even though they

advances.

textbook

671