The vestibular, cerebellar, and reticular systems are central in impor
tance, in motion sickness and habituation, to the effects of motion. N
uclear medicine single photon emission computed tomography (SPECT) stu
dies of cerebral blood flow and power spectral electroencephalographic
recordings during motion sickness were used to determine alterations
in the central nervous system. The rotating chair with and without vis
ual stimulation was used to study the rate of habituation and the effe
ct of antimotion sickness medications on this rate. An increase of the
ta waves over the frontal cortex indicated a decreased activation of t
he higher centers during motion sickness. Motion sickness also produce
s an increase of blood flow in the central cerebellum that has connect
ions to the reticular system. This increase in cerebellar activity is
relayed to the reticular system whereby neural recruitment builds up t
o trigger the vomiting center, producing motion sickness. Habituation
may be a conditioned compensatory activation of the reticular neurons
that prevents this disruption of normal activation. The rate of habitu
ation when motion sickness was prevented by scopolamine was slowed, in
dicating that, if the central nervous system is not challenged by disr
uption of normal activation, it does not produce the compensatory reac
tions that result in habituation.