Lateralized ultradian rhythms of the right and left brain: Temporal variations of tactile discrimination tested in German subjects

Endogenous ultradian rhythms with a periodicity of 2-3 hours operate separa tely in the right and left hemispheres of the human brain and modulate phys iological functions, perception and cognition. Since sensory pathways from either hand terminate in the contralateral hemisphere, ultradian rhythms of the right and left brain can be monitored by variations in the tactile dis crimination of the left and right hand, respectively. Thirteen right-handed German males were tested every 15 minutes for 8 hours. Time series of the tactile error rate determined for the right and left hands oscillate with s ignificantly different ultradian periodicities. Whereas cycles in tactile d iscrimination of the right hand (left hemisphere) have a periodicity of abo ut 2 hours, tactile discrimination of the left hand (right hemisphere) is m odulated by longer periods of about 3 hours. This is interpreted in terms o f the overall functional asymmetry of the human brain. Since the left brain is the specialized locus for verbal processing and the right brain for vis ual-spatial processing, lateralized ultradian rhythms operating in the hemi spheres may provide a distinct frame for long-term timing of neuronal proce sses underlying semantic and spatial mapping of the environment. This is pa rticularly important for interpreting biosocial behavioural rhythms seen in humans living under natural conditions.