Desynchronization of cortical rhythms following cutaneous stimulation: effects of stimulus repetition and intensity, and of the size of corpus callosum
Abstract
Objective: Event-related desynchronization (ERD) and synchronization (ERS) of the Rolandic electroencephalographic (EEG) rhythms following brief, innocuous electrocutaneous stimulation were studied with respect to stimulus intensity and repetition and the size of corpus callosum (CC). Methods: EEG was recorded using 82 closely spaced electrodes in 13 right-handed subjects.
The subjects received 650 brief electrical stimuli to the right index finger at irregular intervals (6-12 s) in 5 blocks. The intensities of the stimuli varied randomly at 20, 30, 50, 65 and 80% of pain threshold.
Results: Mu- and beta-ERD of 0.3-0.6 s latency over the contra- and ipsilateral S1/M1 area was observed in all subjects. Post-stimulus beta-ERS over the contra- and ipsilateral frontal cortices with a peak latency of 0.6-0.8 s was found in 9 subjects.
Stimuli presented in the second half of the experiment were followed by a smaller ipsilateral mu-ERD and smaller contra- and ipsilateral beta-ERD than stimuli applied in the first block. Mu- and beta-ERD and beta-ERS distinguished weak (20%) from intermediate and strong stimuli (>35%) but not the intermediate from strong stimuli.
The amplitude of ipsilateral beta-ERS correlated positively with the size of intermediate truncus of CC (r(9)=0.71, P<0.05). In contrast, ipsilateral ERD showed no significant correlations with the size of CC.
Conclusions: Habituation of ipsilateral mu-ERD and bilateral beta-ERD and beta-ERS suggests that these cortical responses are parts of the orienting response, and fail to disentangle fine intensity gradations. Ipsilateral beta-ERS appears to be mediated by the transcallosal fiber system.