The nervous system in antiquity (Clast)


(BEING CONTINUED FROM  23/06/16)

Neurophysiology Pneuma

Neurophysiological hypotheses largely revolved around concepts regarding the nature and function of pneuma(air) as ‘vital spirit’ essential for life, which entered the body mainly during breathing but also through pores in the skin. Originally postulated by Anaximenes (6th century BC),1 the concept was supported by Democritus who taught that pneuma was transmitted by semen.12 Diogenes’ view (that pneuma was breathed in with air and transmitted through the body in blood vessels as well as other ill-defined passages, enabling cognition and intelligence) became widely accepted.1 The Hippocratic Corpus described pneuma as a major enabling factor in brain function, entering the brain through blood vessels, but also directly via pneumatic channels from the mouth and nose.2 Aristotle stated that, as the central controlling organ of the body, the heart (through ‘innate heat’) converted pneuma (in blood) to ‘connate pneuma’, which was the ‘generative heat’ in semen, but also enabled organs to experience sensation. In view of its considered bloodlessness, the brain was therefore unimportant in this process. Its main role was seen as thermoregulatory – keeping the body cool. Although Praxagoras referred to ‘psychic pneuma’, this important concept was first formulated by Diogenes (4th century BC) who, as promoter of the heart as seat of the hegemonikon, claimed that ‘psychic pneuma’, formed in the heart, spread through the body’s vessels to effect voluntary motion. Interruption of this flow resulted in disease. The Stoics made a major contribution to the pneuma theory by stating that it was a multifaceted changeable force, capable of inter aliabecoming ‘vital pneuma’ (the soul itself) or ‘psychic pneuma’ (responsible for consciousness and intelligence). The brain played no direct role in all this.1

Erasistratus taught that ‘psychic pneuma’, converted from ordinary pneuma in the meninges, was the vital force necessary for nervous function.1 Herophilus apparently believed that ‘psychic pneuma’ was formed in the choroid plexus of the lateral ventricles (out of ‘natural pneuma’) from where it permeated through to the 4th ventricle (command centre) and activated all nerve action (there being a ‘sensory pneuma’ for sensory nerves, and ‘motorpneuma’ for motor nerves). Praxagoras’ hypothesis was that voluntary and involuntary movement, spasms, palpitations and tremors were due to arterial (not nervous) activities. Galen’s views, which remained in vogue for the next millennium, represented a further evolutionary development, which stated that a ‘pneuma-like substance’ absorbed in the lungs reached the heart where, under influence of ‘innate heat’, it converted to ‘vital pneuma’,which passed to all organs via the arteries. On reaching the brain, this was converted to ‘psychic pneuma’ in the retiform plexus or choroid plexus in the lateral ventricles. ‘Psychic pneuma’ could also be formed in the brain ventricles from pneuma absorbed directly through the nose (and cribriform plates). ‘Psychic pneuma’ then permeated the ventricular system and the cerebellum in particular, activating nerves by flowing through them; it also passed via the optic nerve to the eye. The role of pneuma in interaction with the soul or activation of neuro-psychiatric functions was not elaborated on by Galen.6,8

Other mechanisms

The popular hypothesis of antiquity (that health was dependent on an equilibrium between body humours and basic elements) also held for neurophysiology. Scarborough13 suggests that the concept of four humours (blood, phlegm, yellow and black bile) probably originated with Thales (early 6th century BC), while Alcmaeon first stressed the importance of an internal equilibrium of natural phenomena.10 Empedocles added four basic elements (water, fire, earth and air)12 and Philistion ascribed four qualities (hot, cold, dry and moist) to these elements.10Disease would then result from internal imbalances, which in turn could be caused by external factors (such as excessive variation in temperature or humidity, trauma, incorrect diet or physical activity) or the blockage of passages that conveyed the humours and elements. Hippocrates’ consolidation of these theories remained dogma throughout antiquity, although the early Alexandrians disagreed with mainly the humoural theories.14

Aristotle believed that the brain’s main function was that of cooling the body and the hot heart in particular.1Hippocrates stated that the spinal cord was indeed warmer than the brain,1 and Galen confirmed the brain’s supposed cooling function.7 Plato maintained that the brain was the body’s controlling organ, and that the soul consisted of three parts – the main or rational soul was in the brain, but the heart and upper abdomen also housed components.7

Neurological illness

Although the symptoms and signs of disease were often quite well described, ignorance about relevant pathophysiology barred the ancients from prescribing effective therapy. Recognisable neurological illnesses included the following:

Papyri from ancient Egypt mention unilateral facial palsy which could be Bell’s paralysis, unilateral headache possibly compatible with migraine, and a variety of paralyses caused by cranio-spinal injury.3 The Hippocratic Corpus devotes a book to epilepsy (The Sacred Disease), clearly describing variants of the disease.2 Erasistratus recognised apoplexy1 and, 800 years later, Caelius Aurelianus differentiated it from epilepsy, hysterical conditions, ‘paralysis’ and ‘general lethargy’. The latter two conditions clearly represented a hodge-podge of ill-understood neurological problems which, like most illnesses, were blamed on disequilibrium within people or abnormalpneuma.16 Head wounds received prominent attention but there was limited comment on neurological complications, although Hippocrates did describe contralateral convulsions.17 Headache was recognised as a complex symptom associated with many diseases,18 and Hippocrates attributed mental disease to derangement of the brain.2 In the 1st century AD, Celsus19 recognised four kinds of insanity: melancholia, progressive ‘foolishness of the spirit’ (possibly dementia), illusions in an otherwise healthy person, and ‘phrenitis’ (delirium associated with fever). Hydrophobia (rabies), first described in Hellenistic times, was clearly defined by Caelius Aurelianus.16

THE END

NOTES

12. Nutton V. Ancient Medicine. London: Routledge, 2004: 45-55, 92-93, 121-122,179.        

13. Scarborough J. Medical and Biological Terminologies. Norman: University Oklahoma Press, 1992: 216.        

14. Smith WD. Erasistratus’ dietetic medicine. Bull Hist Med 1982; 56: 378-409.     

15. Hippocrates. On Diseases II. p.5.     

16. Caelius Aurelianus. Acute and Chronic Diseases. Drabkin IE (translator). Chicago: University of Chicago Press, 1950: chapters 4-137.

17. Hippocrates. Injuries of the Head, ch. 19, 21.       

18. Caelius Aurelianus. Acute and Chronic Diseases. Drabkin IE (translator). Chicago: University of Chicago Press, 1950: chapters 4-183.

19. Celsus. De medicina III, 18.3-19.   

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