Chapter 18 

 MOTION SICKNESS: ITS PSYCHOPHYSIOLOGICAL ASPECTS 



JAMES E. BIRREN 



U. S. Public Health Service 



Introduction 



Most people with sea experience can de- 

 scribe the symptoms of seasickness, but it 

 is less well known that the same symptoms 

 may be produced in other situations involv- 

 ing acceleration. The motion of airplanes, 

 streetcars, automobiles, swings and other 

 sources of movement may cause sweating, 

 nausea and finally vomiting. Marked leth- 

 argy and even headache and dizziness may 

 also occur in some persons. The whole pat- 

 tern of symptoms may be called motion sick- 

 ness, whether produced in an airplane or 

 aboard ship. 



Statistically there is nothing unusual 

 about motion sickness, since more than half 

 of the population may be made seasick and 

 some investigators believe that everyone 

 may be made motion -sick under appropriate 

 conditions. Motion sickness is therefore a 

 common psychophysiological phenomenon. 

 Animals, as well as man, share this predis- 

 position to illness when exposed to periodic 

 motion. As in man, there are individual 

 differences in susceptibility. Some dogs be- 

 come motion-sick after a few minutes in a 

 simple laboratory swing, whereas others 

 will not salivate and vomit even after a 

 half hour of continuous swinging. 



While the primary factor in motion sick- 

 ness is acceleration, there are also secondary 

 factors which may influence the incidence 

 and severity of motion sickness. Although 

 it is unlikely that these secondary factors, 

 such as vision, odors, and the attitudes of 

 the individual, can by themselves produce 

 motion sickness, it is recognized that they 

 may well influence its course given the pri- 

 mary conditions of acceleration. 



Primary Sense Organ in Motion Sickness 



The vestibular apparatus of the inner ear 

 may be regarded as the primary source of 

 sensory stimulation in motion siclaiess. The 

 evidence is as follows: (1) deaf mutes are 

 immune to motion sickness, (2) animals may 

 be immunized by removal of the vestibular 

 apparatus or by severing the eighth cranial 

 nerve, (3) removal of the vestibular portion 

 of the cerebellum eliminates motion sickness 

 in dogs, and (4) head position affects the 

 incidence of motion sickness (19, 55, 82, 102, 

 114). 



Particular sensory receptors of the inner 

 ear that are involved in motion sickness are 

 not yet clearly defined. The inner ear is 

 a relatively complicated structure and the 

 sensory portions consist of the cochlea, sac- 

 cule, utricle and semicircular canals (26) ; of 

 these only the utricle and the semicircular 

 canals are generally considered as being im- 

 portant in the production of motion sickness. 

 Each sensory unit of these receptor organs 

 consists of a mass, gelatinous or calcareous, 

 attached to the hairs of a sensory epithelium. 

 When the body is moved, the suspension 

 medium permits the "mass" to exert a stim- 

 ulating pressure upon the sensory endings. 

 Experiments on nerve fibers from both the 

 semicircular canals and the utricle have dem- 

 onstrated that these organs are excited by 

 acceleration, and in the case of the utricle, 

 by gravity as well. The sensory endings in 

 the semicircular canals appear to be particu- 

 larly affected by angular acceleration, 

 whereas the utricle also is excited by linear 

 acceleration and gravity. Either angular or 

 linear acceleration may lead to motion sick- 

 ness, and in most situations aboard ship it 



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