title: Time-dependent hierarchical organization of spatial working memory: a transcranial magnetic stimulation study.
abstract: The performance of memory-guided saccades with two different delays (3 and 30 s of memorization) was studied in seven healthy subjects. Double-pulse transcranial magnetic stimulation (dTMS) with an interstimulus interval of 100 ms was applied over the right dorsolateral prefrontal cortex (DLPFC) early (1 s after target presentation) and late (28 s after target presentation). Early stimulation significantly increased in both delays the percentage of error in amplitude (PEA) of contralateral memory-guided saccades compared to the control experiment without stimulation. dTMS applied late in the delay had no significant effect on PEA. Furthermore, we found a significantly smaller effect of early stimulation in the long-delay paradigm. These results suggest a time-dependent hierarchical organization of the spatial working memory with a functional dominance of DLPFC during the early memorization, independent from the memorization delay. For a long memorization delay, however, working memory seems to have an additional, DLPFC-independent component.
authors.affiliation: Eye Movement Research Laboratory, Department of Neurology, Bern University, Bern, CH-3010, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Nyffeler
authors.forename: Charles
authors.initials: C
authors.lastname: Pierrot-Deseilligny
authors.forename: Jaques
authors.initials: J
authors.lastname: Felblinger
authors.forename: Urs P
authors.initials: UP
authors.lastname: Mosimann
authors.forename: Christian W
authors.initials: CW
authors.lastname: Hess
authors.forename: René M
authors.initials: RM
authors.lastname: Müri
mesh_terms: D000328:Adult; D004574:Electromagnetic Fields; D004585:Electrooculography; D005260:Female; D006801:Humans; D008297:Male; D008568:Memory / Q000502:physiology*; D017397:Prefrontal Cortex / Q000502:physiology*; D011930:Reaction Time; D012438:Saccades / Q000502:physiology*; D013997:Time Factors