Effects of acute transcranial direct current stimulation in hot and cold working memory tasks in healthy and depressed subjects

Abstract

Dorsolateral prefrontal cortex (DLPFC) hypoactivity and subcortical hyperactivity have been associated to cognitive impairment for non-emotional ("cold") and emotional ("hot") working memory tasks in major depressive disorder (MDD). We investigated whether an increase of DLPFC activity using transcranial direct current stimulation (tDCS) would differently influence the performance in working memory tasks in depressed and healthy subjects. Forty young adult participants (20 with MDD and 20 healthy controls) were randomized to a single, sham-controlled, bifrontal (left anodal / right cathodal), 2mA, 30-min tDCS session in a parallel design. The n-back and the Internal Shift Task (IST) were used as proxies of cold and hot working memory performance, respectively. Active tDCS compared to sham promoted more accurate and faster responses to the n-back task for both patients and controls.Conversely, only patients presented an improvement in response times for the IST task. Our findings suggest that the mechanisms of tDCS in MDD involve modulation of both cold and hot working memory. We discuss these findings considering the modulatory top-down effects of tDCS on subcortical structures via prefrontal activation, and how spreading of activation might be different for healthy volunteers versus depressed patients. We also discuss the role of tDCS in cognitive amelioration for depressed patients. Finally, the distinct effects of tDCS in the "hot" cognition task for healthy and depressed participants are indicative that tDCS outcomes are also regulated by differences in baseline activity of the stimulated network. KeywordsTranscranial direct current stimulation; major depressive disorder; working memory; cognition. 4 List of abbreviationsMajor depressive disorder (MDD); dorsolateral prefrontal cortex (DLPFC); transcranial direct current stimulation (tDCS); Internal Shift Task (IST); Mini International Neuropsychiatric Interview (MINI); Hamilton Depression Rating Scale (HDRS); analyses of variance (ANOVAs); response times (RTs); standard deviation (SD). HighlightsMDD patients present non-emotional and emotional working memory impairment.The DLPFC is associated with MDD and cognitive deficits.We used tDCS to acutely increase DLPFC activity in MDD and controls.MDD patients presented improvement in emotional and non-emotional cognition.We discuss pathophysiological mechanisms and clinical implications of our findings. 5

Balanced bifrontal transcranial direct current stimulation enhances working memory in adults with high-functioning autism: a sham-controlled crossover study

“…Finally, our participants received active tDCS at a current density of 0.06 mA/cm 2 for 40 min. This is twice as long as it has been typical of behavioral studies, although periods of 30 min and longer [ 32 , 38 , 40 , 41 , 79 – 83 ] are becoming common in recent years, especially in studies of cognition. Longer stimulation periods seem to more effectively modulate WM [ 62 ], current density greater than 0.029 mA/cm 2 is positively correlated with greater effects on WM [ 62 ], and total charge delivered is positively correlated with effect size in studies of cognition [ 78 ].…”

Neurocognitive effects of transcranial direct current stimulation (tDCS) in unipolar and bipolar depression: Findings from an international randomized controlled trial

“…In addition to antidepressant properties, some research has suggested that tDCS may have beneficial neurocognitive effects in both healthy participants and patients with neuropsychiatric disorders, including unipolar and bipolar depression (Martin et al, 2015; Minchino et al, 2015; Moreno et al, 2015; Oliveira et al, 2013; Pope, Brenton, & Miall, 2015). Specific effects include improvement in neurocognitive functions such as attention, processing speed, learning and memory, and working memory.…”

Prefrontal cortex regulates amygdala response to threat in trait anxiety

“…Induced changes in tissue excitability can persist over minutes to hours after stimulation (depending on stimulation current, duration and number of sessions), effects that are N-methyl-D-aspartate (NMDA) receptor-dependant, and presumed to reflect changes in synaptic efficacy and plasticity (15,16). Initially used as a tool to induce changes in motor evoked potentials, tDCS has more recently been used to modulate cognition, such as attentional control (17) and working memory (18). Neuroimaging indicates that prefrontal tDCS alters functional activation and connectivity in brain regions that support cognitive function, including regions distal from the stimulating electrodes (19,20) (21).…”