Modulation of thalamic network connectivity using transcranial direct current stimulation based on resting-state functional magnetic resonance imaging to improve hypoxia-induced cognitive impairments.

Hypoxic conditions at high altitudes severely affect cognitive functions such as vigilance, attention, and memory and reduce cognitive ability. Hence, there is a critical need to investigate methods and associated mechanisms for improving the cognitive ability of workers at high altitudes. This study aimed to use transcranial direct current stimulation (tDCS) to modulate thalamic network functional connectivity to enhance cognitive ability. We recruited 20 healthy participants that underwent hypoxia exposure in a hypoxic chamber at atmospheric pressure to simulate a hypoxic environment at 4,000 m. Participants received both sham and real stimulation. tDCS significantly improved the participants' emotional status, including depression, fatigue, and energy level. These effects were sustained for more than 6 h (P < 0.05 at the second to fifth measurements). In addition, tDCS enhanced vigilance, but this was only effective within 2 h (P < 0.05 at the second and third measurements). Central fatigue was significantly ameliorated, and cerebral blood oxygen saturation was increased within 4 h (P < 0.05 at the second, third, and fourth measurements). Furthermore, functional connectivity results using the thalamus as a seed revealed enhanced connectivity between the thalamus and hippocampus, cingulate gyrus, and amygdala after tDCS. These results indicated that tDCS increased local cerebral blood oxygen saturation and enhanced thalamic network connectivity in a hypoxic environment, thereby improving vigilance, depression, fatigue, and energy levels. These findings suggest that tDCS may partially rescue the cognitive decline caused by hypoxia within a short period. This approach affords a safe and effective cognitive enhancement method for all types of high-altitude workers with a large mental load.

Cathodal Transcranial Direct Current Stimulation Over the Right Temporoparietal Junction Suppresses Its Functional Connectivity and Reduces Contralateral Spatial and Temporal Perception.

The temporoparietal junction plays key roles in vestibular function, motor-sensory ability, and attitude stability. Conventional approaches to studying the temporoparietal junction have drawbacks, and previous studies have focused on self-motion rather than on vestibular spatial perception. Using transcranial direct current stimulation, we explored the temporoparietal junction's effects on vestibular-guided orientation for self-motion and vestibular spatial perception. Twenty participants underwent position, motion, and time tasks, as well as functional magnetic resonance imaging scans. In the position task, cathodal transcranial direct current stimulation yielded a significantly lower response in the -6, -7, -8, -9, -10, -11, and -12 stimulus conditions for leftward rotations (P < 0.05). In the time task, the temporal bias for real transcranial direct current stimulation significantly differed from that for sham stimulation (P < 0.01). Functional magnetic resonance imaging showed that cathodal transcranial direct current stimulation suppressed functional connectivity between the temporoparietal junction, right insular cortex, and right supplementary motor area. Moreover, the change in connectivity between the right temporoparietal junction seed and the right insular cortex was positively correlated with temporal bias under stimulation. The above mentioned results show that cathodal transcranial direct current stimulation induces immediate and extended vestibular effects, which could suppress the functional connectivity of the temporoparietal junction and in turn reduce contralateral spatial and temporal perception. The consistent variation in temporal and spatial bias suggested that the temporoparietal junction may be the cortical temporal integrator for the internal model. Moreover, transcranial direct current stimulation could modulate the integration process and may thus have potential clinical applications in vestibular disorders caused by temporoparietal junction dysfunction.

Transcranial direct current stimulation reconstructs diminished thalamocortical connectivity during prolonged resting wakefulness: a resting-state fMRI pilot study.

Reductions in the alertness and information processing capacity of individuals due to sleep deprivation (SD) were previously thought to be related to dysfunction of the thalamocortical network. Previous studies have shown that transcranial direct current stimulation (tDCS) can restore vigilance and information processing after SD. However, the underlying neural mechanisms of this phenomenon remain unclear. The purpose of this study was to investigate the neurocognitive mechanisms of tDCS following SD, by comparing changes in the brain network, especially the thalamocortical network, after tDCS and sham stimulation following 24 h of SD. Sixteen healthy volunteers were tested in a sham-controlled, randomized crossover design experiment. Resting-state functional magnetic resonance imaging was conducted during resting wakefulness and again after either active tDCS or sham stimulation to the right dorsolateral prefrontal cortex (1.0 mA, 20 min) immediately following 24 h of SD. Seed-based correlations and graph theory analysis were used to determine functional connectivity within the brain thalamocortical network. When tDCS was used, the functional connectivity of the thalamus with the temporal lobe and left caudate was higher than that when the sham stimulation was used. Analysis using graph theory showed that compared with sham stimulation, tDCS administration was associated with a significant improvement in not only the number of connections but also the global efficiency of the thalamus itself. Our study reveals a modulation of the activity of the intrinsic thalamus networks after tDCS. The effects may help explain earlier reports of improvements in the cognitive performance after anodal-tDCS.