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About the Authors:
Nina Wolinski
Roles Formal analysis, Investigation, Methodology, Writing - original draft, Writing - review & editing
Affiliation: Centre for Brain Science, Department of Psychology, University of Essex, Colchester, United Kingdom
Nicholas R. Cooper
Roles Methodology, Resources, Supervision, Writing - review & editing
Affiliation: Centre for Brain Science, Department of Psychology, University of Essex, Colchester, United Kingdom
Paul Sauseng
Roles Formal analysis, Funding acquisition, Methodology, Resources, Software, Writing - review & editing
Affiliation: Department Psychologie, Ludwig-Maximilians-Universität München, München, Germany
Vincenzo Romei
Roles Conceptualization, Data curation, Formal analysis, Methodology, Resources, Supervision, Writing - original draft, Writing - review & editing
* E-mail: [email protected]
Affiliations Centre for Brain Science, Department of Psychology, University of Essex, Colchester, United Kingdom, Centro studi e ricerche in Neuroscienze Cognitive, Dipartimento di Psicologia, Università di Bologna, Campus di Cesena, Viale Europa, Cesena, Italy
ORCID http://orcid.org/0000-0003-1214-2316Abstract
The speed of theta brain oscillatory activity is thought to play a key role in determining working memory (WM) capacity. Individual differences in the length of a theta cycle (ranging between 4 and 7 Hz) might determine how many gamma cycles (>30 Hz) can be nested into a theta wave. Gamma cycles are thought to represent single memory items; therefore, this interplay could determine individual memory capacity. We directly tested this hypothesis by means of parietal transcranial alternating current stimulation (tACS) set at slower (4 Hz) and faster (7 Hz) theta frequencies during a visuospatial WM paradigm. Accordingly, we found that 4-Hz tACS enhanced WM capacity, while 7-Hz tACS reduced WM capacity. Notably, these effects were found only for items presented to the hemifield contralateral to the stimulation site. This provides causal evidence for a frequency-dependent and spatially specific organization of WM storage, supporting the theta-gamma phase coupling theory of WM capacity.
Author summary
Our ability to temporarily retain sensory information is limited to a handful of items and is referred to as working memory capacity. Such memory capacity has been shown to vary across the general population, with some people retaining a higher number of items than others. An influential theory suggests that this individual capacity might be determined by the speed of slow brain waves (so-called theta waves) that range in frequency between four and seven cycles per second. It is hypothesized that...