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Manipulation of the Working Memory Performance in Humans using Transcranial Alternating Current Stimulation over the Frontoparietal Network

Stefanie Corinna Pabel
Doctoral thesis
Date of Examination: 2018-11-15
Date of issue: 2018-11-14
Advisor: Antal, Andrea Prof. Dr.
Referee: Antal, Andrea Prof. Dr.
Referee: Dechent, Peter PD Dr.
Referee: Meyer, Thomas Prof. Dr.

Persistent Address: http://hdl.handle.net/11858/00-1735-0000-002E-E4FF-9

 

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Abstract

English

The working memory (WM) is a key mechanism that ensures complex behavior in humans. It requires the bilateral activation of the fronto-parietal brain network and has been subdivided on the phonological loop, which processes numbers, semantics and auditory-verbal information, with lateralized activation towards the left hemisphere, and the visuo-spatial sketchpad, which mainly operates in the right hemisphere (Baddeley and Hitch 1974; Sauseng et al. 2005; Müller and Knight 2006; Baddeley 2012; Eriksson et al. 2015). This neural system maintains constant long-range communications within itself and with other cognitive systems through neuronal oscillations. This work aimed to show a causal relationship between visuo-spatial WM functions and the mechanism of fronto-parietal oscillatory connectivity – the theta phase coherence. To reach our aim, two experiments were conducted. Our first hypothesis was that the WM network operates by phase connectivity. The results of the electroencephalographic (EEG) experiment demonstrated significant theta coherence during the WM events. Our second hypothesis was that it would be feasible to interfere with the WM through bi-hemispheric transcranial alternating current stimulation (tACS) and thus change phase connectivity. To show causal effects of theta coherence, behavioral changes in subjects under fronto-parietal theta-tACS bi-laterally, were analyzed. We found that desynchronization of theta phase relations in the fronto-parietal network led to an impairment in the WM performance. Synchronization of the fronto-parietal network had no significant effect on the group level, but individual analysis revealed a tendency for improvement of the WM for subjects with low baseline performance. These results show that optimally balanced theta coherence in the fronto-parietal network is a prerequisite for the ideal WM functions in humans.
Keywords: tACS; theta coherence; frontoparietal network; working memory performance; desynchronization; neuronal oscillations
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