Abstract
Attentional dysfunctions constitute core cognitive symptoms in schizophrenia, but the precise underlying neurocognitive mechanisms remain to be elucidated. In this randomized, double-blind, sham-controlled study, we applied, for the first time, a theoretically grounded modeling approach based on Bundesen's Theory of Visual Attention (TVA) to (i) identify specific visual attentional parameters affected in schizophrenia and (ii) assess, as a proof of concept, the potential of single-dose anodal transcranial direct current stimulation (tDCS; 20 min, 2 mA) to the left dorsolateral prefrontal cortex to modulate these attentional parameters. To that end, attentional parameters were measured before (baseline), immediately after, and 24 h after the tDCS intervention in 20 schizophrenia patients and 20 healthy controls. At baseline, analyses revealed significantly reduced visual processing speed and visual short-term memory storage capacity in schizophrenia. A significant stimulation condition × time point interaction in the schizophrenia patient group indicated improved processing speed at the follow-up session only in the sham condition (a practice effect), whereas performance remained stable across the three time points in patients receiving verum stimulation. In healthy controls, anodal tDCS did not result in a significant change in attentional performance. With regard to question (i) above, these findings are indicative of a processing speed and short-term memory deficit as primary sources of attentional deficits in schizophrenia. With regard to question (ii), the efficacy of single-dose anodal tDCS for improving (speed aspects of visual) cognition, it appears that prefrontal tDCS (at the settings used in the present study), rather than ameliorating the processing speed deficit in schizophrenia, actually may interfere with practice-dependent improvements in the rate of visual information uptake. Such potentially unexpected effects of tDCS ought to be taken into consideration when discussing its applicability in psychiatric populations. The study was registered at http://apps.who.int/trialsearch/Trial2.aspx?TrialID=DRKS00011665.
Highlights
Visual attention dysfunctions, ranging from impairments in processing speed and visual short-term memory capacity to deficient top-down control [1,2,3,4,5,6], are commonly reported in schizophrenia and schizophrenia-spectrum disorders
The question of the precise neurocognitive mechanisms underlying the difficulties in attention tasks has not yet been resolved conclusively. It remains elusive whether both processing speed and working memory (WM) functions are affected in schizophrenia [7] or whether slowed encoding processes are responsible for the reduced visual short-term memory (vSTM) storage capacity in the respective attention tasks [2, 8, 9]
To expand our knowledge about the possible efficacy of transcranial direct current stimulation (tDCS) in schizophrenia, in the second step of this proof-of-principle study, we explored whether the modulation of intrinsic networks through single-dose tDCS can have a functional significance for cognitive, and visual attentional processes in schizophrenia [40]
Summary
Visual attention dysfunctions, ranging from impairments in processing speed and visual short-term memory (vSTM) capacity to deficient top-down control [1,2,3,4,5,6], are commonly reported in schizophrenia and schizophrenia-spectrum disorders. The question of the precise neurocognitive mechanisms underlying the difficulties in attention tasks has not yet been resolved conclusively It remains elusive whether both processing speed and working memory (WM) functions are affected in schizophrenia [7] or whether slowed encoding processes are responsible for the reduced vSTM storage capacity in the respective attention tasks [2, 8, 9]. Such an approach is provided by Bundesen’s Theory of Visual Attention [TVA; [15]], which already proved valuable for systematically characterizing cognitive deficits in diverse neuropsychiatric and neurological disorders [16,17,18] By combining this framework theory with simple psychophysical tests of whole- and partial-report of briefly presented letters, it is possible to derive independent estimates of parameters reflecting the individual efficiency of core visual attention functions. Attentional dysfunctions constitute core cognitive symptoms in schizophrenia, but the precise underlying neurocognitive mechanisms remain to be elucidated
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