Effects of the unilateral dynamic handgrip on resting cortical activity levels: A replication and extension.

Previous studies have linked unilateral hand contractions to subsequent changes in hemispheric asymmetric activity, as reflected in the electroencephalographic alpha (8-12 Hz) range in each hemisphere. However, debate continues regarding the state of asymmetry induced by unilateral contractions. We have previously found a bilateral enhancement of alpha amplitude that occurs after contractions, reflecting cortical downregulation instead of changes in asymmetric activity. To corroborate our observations, we examined the effects of 45 s of unilateral dynamic handgrip contractions on subsequent resting alpha activity. Twenty-two right-handed participants were recruited (M = 25 years, 17 female). The study used a within-subjects design consisting of a pre- and post-test (2 min resting; eyes open) for the intervention (dynamic handgrip; at a self-determined pace of approximately twice a second for 45 s for each hand). Following the handgrip task, an increase in alpha amplitude above the baseline was observed over the entire cortex, which was greater after left-hand squeezing. This observation confirms our previous findings and we have extended them by adding more electrodes to gain further insights into the handgrip exercise as an external brain stimulator. Moreover, we grouped electrodes according to scalp regions to facilitate the visualization of the effects on the frequency spectrum. Our findings can be used to develop targeted interventions aimed at modifying behavioral outcomes affected by alpha activity.

Central theta amplitude as a negative correlate of performance proficiency in a dynamic visuospatial task.

Dynamic visuospatial tasks, requiring continuous engagement of attention over long time periods, have been little studied with the electroencephalogram. Specifically, the role of the theta band in these tasks is unclear, with task-related theta enhancements improving performance in some studies, and hindering it in others. In this study, 30 participants performed the Pong videogame as a dynamic visuospatial task to analyze the influence of theta and alpha amplitude as well as alpha asymmetry on performance. The theta band increased significantly at central-parietal regions and correlated negatively with performance, especially at anterior regions. The alpha band showed a significant decrease, greater at right over left parietal regions, but neither the amplitude nor the asymmetry ratio correlated with performance. With theta being an indicator of top-down cognitive control, it may be concluded that proficient performance in dynamic visuospatial tasks depends on a bottom-up guidance of attention with little top-down intervention.

Unilateral Left-Hand Contractions Produce Widespread Depression of Cortical Activity after Their Execution.

The execution of unilateral hand contractions before performance has been reported to produce behavioral aftereffects in various tasks. These effects have been regularly attributed to an induced shift in activation asymmetry to the contralateral hemisphere produced by the contractions. An alternative explanation proposes a generalized state of reduced bilateral cortical activity following unilateral hand contractions. The current experiment contrasted the above explanation models and tested the state of cortical activity after the termination of unilateral hand contractions. Twenty right-handed participants performed hand contractions in two blocks, one for each hand. Using electroencephalogram (EEG), the broad alpha band and its asymmetry between hemispheres before, during, and after hand contractions were analyzed. During contractions, significant bilateral decrease in alpha amplitudes (indicating cortical activation) emerged for both hands around sensory-motor regions. After contractions, alpha amplitudes increased significantly over the whole scalp when compared to baseline, but only for the left hand. No modulation of hemispheric asymmetry was observed at any phase. The results suggest that unilateral hand contractions produce a state of reduced cortical activity after their termination, which is more pronounced if the left hand was used. Consequently, we propose that the reduced cortical activity (and not the persistent activation asymmetry) may facilitate engagement in subsequent behavior, probably due to preventing interference from other, nonessential cortical regions.

The Speed of Visual Attention and Motor-Response Decisions in Adult Attention-Deficit/Hyperactivity Disorder.

BACKGROUND: Adults with attention-deficit/hyperactivity disorder (ADHD) exhibit slowed reaction times (RTs) in various attention tasks. The exact origins of this slowing, however, have not been established. Potential candidates are early sensory processes mediating the deployment of focal attention, stimulus response translation processes deciding upon the appropriate motor response, and motor processes generating the response. METHODS: We combined mental chronometry (RT) measures of adult ADHD (n = 15) and healthy control (n = 15) participants with their lateralized event-related potentials during the performance of a visual search task to differentiate potential sources of slowing at separable levels of processing: the posterior contralateral negativity (PCN) was used to index focal-attentional selection times, while the lateralized readiness potentials synchronized to stimulus and response events were used to index the times taken for response selection and production, respectively. To assess the clinical relevance of event-related potentials, a correlation analysis between neural measures and subjective current and retrospective ADHD symptom ratings was performed. RESULTS: ADHD patients exhibited slower RTs than control participants, which were accompanied by prolonged PCN and lateralized readiness potentials synchronized to stimulus, but not lateralized readiness potentials synchronized to response events, latencies. Moreover, the PCN timing was positively correlated with ADHD symptom ratings. CONCLUSIONS: The behavioral RT slowing of adult ADHD patients was based on a summation of internal processing delays arising at perceptual and response selection stages; motor response production, by contrast, was not impaired. The correlation between PCN times and ADHD symptom ratings suggests that this brain signal may serve as a potential candidate for a neurocognitive endophenotype of ADHD.