Single-session transcranial direct current stimulation induces enduring enhancement of visual processing speed in patients with major depression

Abstract

Attentional deficits are considered key cognitive symptoms in major depressive disorder (MDD) arising from abnormal activation patterns within dorsolateral prefrontal cortex (dlPFC) alertness networks. Altering these activity patterns with transcranial direct current stimulation (tDCS) might thus ameliorate alertness-dependent cognitive deficits in MDD patients. In a double-blind, randomized, sham-controlled study, we investigated the effect of a single session of anodal tDCS (2 mA) applied to the left dlPFC on different parameters of visual attention based on Bundesen's theory of visual attention (Psychol Rev 97(4):523-547, 1990) in a group of 20 patients with MDD and a control group of 20 healthy participants. The parametric attention assessment took place before, immediately after and 24 h after tDCS intervention. It revealed a selective impairment in visual processing speed as a primary functional deficit in MDD at baseline assessment. Furthermore, a significant stimulation condition × time point interaction showed that verum tDCS over the left dlPFC resulted in a processing speed enhancement 24 h post-stimulation in MDD patients. In healthy control participants, we did not find similar tDCS-induced effects. Our results suggest that even a single session of tDCS over the dlPFC can induce enduring neurocognitive benefits that indicate an amelioration of cortical under-arousal in MDD patients in a time frame beyond that of immediate, excitability increases that are directly induced by the current.

Decreased cingulo-opercular network functional connectivity mediates the impact of aging on visual processing speed

“…Furthermore, iFC in the cingulo-opercular network is known to relate not only to cognitive measures, but also to anxiety (Seeley et al, 2007). As anxiety might influence visual processing speed, as indicated, for example, by reduced processing speed C in patients with major depression (Gögler et al, 2017), we analyzed whether anxiety might be a critical confound in our findings.…”

Parameter-Based Evaluation of Attentional Impairments in Schizophrenia and Their Modulation by Prefrontal Transcranial Direct Current Stimulation

“…20 patients with a ICD-10 diagnosis of schizophrenia or schizophrenia-spectrum disorder (F20 = 19; F25 = 1), recruited from the Department of Psychiatry and Psychotherapy (LMU Munich), and the same 20, demographically matched, healthy controls that participated in our previous study ( 18 ), were included in the investigation (see Tables 1 and 2 for demographic and clinical data). The diagnoses, according to the WHO ICD-10 criteria for schizophrenia or schizophrenia-spectrum disorder, were made by two clinical psychiatrists of whom one (Alkomiet Hasan) is a member of this study group.…”

“…Following that, presented stimuli (T = target = red letters; D = distractor = blue letters) are masked for 500 ms. Adapted according to Gögler ( 18 ).…”

“…To determine whether these deficits can be attributed to losses of specific fundamental attention functions, a theoretically grounded modeling approach is required that can isolate and quantify (potentially compromised) core functions in an unconfounded measurement. 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 – 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.…”

“…While short-term tDCS effects are attributed to tonic modulations of the resting membrane potential of cortical neurons affecting their firing rates, prolonged after-effects are presumed to be controlled by protein synthesis-dependent processes at the synaptic level ( 28 – 31 ). Preliminary studies already provided promising results regarding the potential of tDCS to remediate cognitive deficits in psychiatric diseases, for example, in patients with major depression ( 18 , 32 , 33 ) or alcohol dependence ( 34 ). However, with respect to schizophrenia, the available evidence is scarce and mixed ( 35 , 36 ): one study applied 20 min of anodal tDCS with 2 mA to the left dlPFC and could not show that anodal tDCS improves performance on a procedural learning task in the whole sample, but still had a beneficial effect in a subgroup of patients ( 37 ).…”