Event-related alpha and theta responses in a visuo-spatial working memory task.
OBJECTIVE
To explore the reactivity of the theta and alpha rhythms during visuo-spatial working memory.


METHODS
One hundred and seventy-four subjects performed a delayed response task. They had to remember the spatial location of a target stimulus on a computer screen for a 1 or a 4s retention interval. The target either remained visible throughout the entire interval (sensory trials) or disappeared after 150ms (memory trials). Changes in induced band power (IBP) in the electroencephalogram (EEG) were analyzed in 4 narrow, individually adjusted frequency bands between 4 and 12Hz.


RESULTS
After presentation of the target stimulus, a phasic power increase was found, irrespective of condition and delay interval, in the lower (roughly, 4-8Hz) frequency bands, with a posterior maximum. During the retention interval, sustained occipital-parietal alpha power increase and frontal theta power decrease were found. Most importantly, the memory trials showed larger IBP decreases in the theta band over frontal electrodes than the sensory trials.


CONCLUSIONS
The phasic power increase following target onset is interpreted to reflect encoding of the target location. The sustained theta decrease, which is larger for memory trials, is tentatively interpreted to reflect visuo-spatial working memory processes.
Bastiaansen
Marcel C M
MC
Max Planck Institute for Psycholinguistics, Nijmegen, The Netherlands. marcel.bastiaansen@fcdonders.kun.nl
Posthuma
Danielle
D
Groot
Paul F C
PF
de Geus
Eco J C
EJ
D000328:Adult; D000513:Alpha Rhythm / Q000379:methods*; D000704:Analysis of Variance; D004569:Electroencephalography / Q000379:methods; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008568:Memory / Q000502:physiology*; D008875:Middle Aged; D013826:Theta Rhythm / Q000379:methods*