over short distances in response to primarily sensory processes (Bressler and Freeman, 1980; Ohl et al., 2003), whereas, lower frequency oscillations (1-4 Hz) are generated by synchronization of ensembles interacting at longer distances during higher cognitive processing (Kopell et al., 2000; Lubar, 1997). Our data demonstrating that humans, who are responding to the stimuli show more phase locking in the delta frequencies whereas rats, who are not required to respond to the stimuli have more phase locking in the high frequency oscillations. These data further suggest the possibility that humans may possess a greater ability to synchronize neuronal ensembles over longer distances than rodents who are more specialized to respond to primary sensory processes over shorter distances.
