Biology subjects

Dmochowski, J.

Publications and source records attributed to Dmochowski, J..

4 recordsLinked to original sources

bioRxiv2019

HD-tDCS over mIPS causally modulates online reach correction

Brain lesion and stimulation studies have suggested posterior parietal cortex and the medial intraparietal sulcus in particular as a crucial hub for online movement error corrections. However, causal evidence for this is still sparse. Indeed, lesion studies are potentially confounded by compensatory reorganization mechanisms while brain stimulation studies have produced heterogeneous results when employing transcranial magnetic stimulation. Here we designed a new complementary paradigm using fMRI-guided high-definition transcranial direct current stimulation (HD-tDCS) of the left medial intraparietal sulcus (mIPS) together with regression-based mediation analysis to re-examine the causal role of mIPS in online reach corrections to jumping targets. We obtained two independent measures of stimulation-induced changes in brain activity by modeling current flow in the brain and through EEG recordings before and after HD-tDCS stimulation. Third, to quantify behavioral effects of HD-tDCS we computed movement curvature as a measure of online correction. We demonstrate that both of our measurements of brain activity were consistent with a polarity-specific modulation of the online correction for targets jumping to the contralateral side of the stimulation. Importantly, using a mediation analysis of the relationship between stimulation current and movement curvature suggests that the induced current modifies brain activity, which then leads to the observed behavioral changes. This unique combination of methods and analysis thus provides complementary evidence for the crucial role of the posterior parietal cortex in online error correction, while at the same time setting a new methodological standard with respect to the causal influence of transcranial direct current stimulation. New & NoteworthyTranscranial direct current stimulation (tDCS) is an interesting and potentially useful tool for asking causal scientific questions and design clinical treatments. With our unique combination of highly accurate fMRI guided stimulation, current forward modeling, EEG recordings before and after the stimulation and behavioral changes we could unravel the causal structure of tDCS. Our approach naturally deals with the variability of tDCS results, increasing its potential usefulness as a tool for research and clinical applications.

neuroscience↗

bioRxiv2019

Action enhances perception: Visually evoked neural responses are enhanced when engaging in a motor task

While it is well known that vision guides movement, less appreciated is that the motor cortex also provides input to the visual system. Here we asked whether neural processing of visual stimuli is acutely modulated during motor activity, hypothesizing that visual evoked responses are enhanced when engaged in a motor task that depends on the visual stimulus. To test this, we told participants that their brain activity was controlling a video game that was in fact the playback of a prerecorded game. The deception, which was effective in half of participants, aimed to engage the motor system while avoiding evoked responses related to actual movement or somatosensation. In other trials, subjects actively played the game with keyboard control or passively watched a playback. The strength of visually evoked responses was measured as the temporal correlation between the continuous stimulus and the evoked potentials on the scalp. We found reduced correlation during passive viewing, but no difference between active and sham play. Alpha band (8-12 Hz) activity was reduced over central electrodes during sham play, indicating recruitment of motor cortex despite the absence of overt movement. To account for the potential increase of attention during game play, we conducted a second study with subjects counting screen items during viewing. We again found increased correlation during sham play, but no difference between counting and passive viewing. While we cannot fully rule out the involvement of attention, our findings do demonstrate an enhancement of visual evoked responses during active vision.

neuroscience↗

bioRxiv2019

Transcranial photobiomodulation with infrared laser increases power of brain oscillations

Non-invasive transcranial photobiomodulation with a 1064-nm laser (tPBML1064) has been reported to improve human performance on cognitive tasks as well as locally upregulate cerebral oxygen metabolism and hemodynamics. However, it is unknown whether tPBML1064 also modulates electrophysiology, and specifically neural oscillations, in the human brain. The hypothesis guiding this study was that tPBML1064 of the right prefrontal cortex enhances neurophysiological rhythms at specific frequency bands in the human brain under resting conditions. To test this hypothesis, we recorded the 64-channel scalp electroencephalogram (EEG) before, during, and after the application of 11 minutes of 4-cm-diameter tPBML1064 to the right forehead of human subjects (n=20) using a within-subject, sham-controlled design. Time-resolved scalp topographies of EEG power at five frequency bands were computed to examine tPBML1064-induced EEG power changes across the scalp. The results showed time-dependent, significant increases of EEG spectral powers at the alpha (8-13 Hz) and beta (13-30 Hz) bands at broad scalp regions, exhibiting a front-to-back pattern. The findings provide the first sham-controlled topographic mapping that tPBML1064 increases the strength of electrophysiological oscillations (alpha and beta bands), while also shedding light on the mechanisms of tPBM in the human brain.

bioengineering↗

bioRxiv2018

Increased Blood Flow and Oxidative Metabolism in the Human Brain by Transcranial Laser Stimulation

Although techniques for non-invasive brain stimulation are under intense investigation, an approach that has received limited attention is transcranial photobiomodulation (tPBM), the delivery of near-infrared light to the brain with a laser directed at the scalp. Here we employed functional magnetic resonance imaging (fMRI) to measure the Blood-Oxygenation-Level Dependent (BOLD) signal in n = 20 healthy humans while concurrently stimulating their right frontal pole with a near-infrared laser. We failed to detect an evoked BOLD response at illumination. However, functional connectivity with the illuminated region increased by an average of 10% during stimulation, with some connections strengthening by as much as 40%. 23% of connections with the illuminated region experienced a significant acute increase, with the time course of connectivity exhibiting a sharp rise at illumination onset. Brain-wide connectivity increases were also observed, with connections in the stimulated hemisphere showing a significantly larger increase than those in the non-stimulated hemisphere. We subsequently employed MR Thermometry to measure brain temperature during tPBM (separate cohort, n = 20), and found no significant temperature differences between active and sham stimulation. Our findings suggest that near-infrared light synchronizes brain activity with a non-thermal mechanism, underscoring the promise of tPBM as a new technique for stimulating brain function.

neuroscience↗