Lateralized ultradian rhythms in time and space: A chronobiological field study in Kenyan Maasai

Lateralized ultradian rhythms oscillating separately in the right and left hemispheres of the human brain can be monitored by variations in the tactil e discrimination of either hand. A previous study in male German subjects h as shown that the tactile error rates determined for the right and left han ds oscillate with significantly different periodicities. In the present stu dy, a group of Kenyan Maasai shepherds was tested while the subjects were l eading herds on daily feeding routes. The Maasai exhibit considerable ultra dian rhythms of about 2 hours in tactile error rates of either hand, but in contrast to the German subjects there is no significant difference between the right and left side. While an individual is en route, his hemispheres proceed through alternating states in matching segments of the path. Ultrad ian rhythms thus 'scan' not only the time of day but also the space, and mi ght provide an intrinsic time-frame for neuronal processes of cognitive map ping.