hemispheric asymmetry
Research Papers
A New Method for Self-Regulation of Slow Cortical Potentials in a Timed Paradigm
A new method of slow cortical potential (SCP) biofeedback is described, in which subjects were presented with a sequence of two alternating tones. Subjects learned to adjust their SCPs with the 4-s rhythm of presented tones by producing directed SCP changes only in certain inter-tone intervals. Specifically, they learned to simultaneously produce two EEG signals: 1) positive or negative SCP shift at vertex, and 2) SCP asymmetry between the right and the left central area. After one training session, 13 healthy participants were able to differentiate significantly between the negativity and the positivity conditions; this differentiation was achieved within less than 300 ms after the discriminative signal, i.e. much faster than in previous studies employing traditional SCP biofeedback technique. However, these participants did not produce a significant hemispheric asymmetry in the first session. In the second experiment, five subjects participated in prolonged training (6 to 17 sessions). Highly significant control of SCP asymmetry over the precentral cortex was attained in four out of five participants. Advantages and disadvantages of the new method as compared with the “classical” SCP biofeedback technique are discussed.
View Full Paper →Biofeedback-produced hemispheric asymmetry of slow cortical potentials and its behavioural effects
Two studies served to examine behavioural effects of slow cortical potentials (SPs). SPs were manipulated by means of a biofeedback procedure. The ability of human subjects to alter SPs differentially between the two hemispheres - specifically over the lateral aspects of teh central sulcus - was tested by providing feedback ofthe SP difference betwrrn C3 and C4. In Expt. I, 21 of the 45 subjects produced hemispheric asymmetries of more than 2 μV between C3 and C4 on an average after 80 trials of analogue, continuous and immediate feedback. In Expt. II, SP changes were fed back digitally at the end of each trial. Within 120 trials, 20 of the 48 subjects reached the criterion of a minimum 2-μV difference in SPs between C3 and C4 on the average. Average differentiation remained significantly below the SP differentiations achieved for continuous feedback. Trials with feedback were followed by ‘task’ trials without feedback, during which subjects were still requested to produce SP changes but also had to complete a task: Either sensorimotor tasks (Expt. I) or forced choice handedness tasks (Expt. II) were presented to evaluate behavioural consequences of hemispheric SP differences. In subjects achieving the required SP differentiation it affected the behavioural output in agreement with the known functions of the respective cortical area.
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