Light-flicker Ganzfeld (LFG) induces a lower to upper-alpha frequency shift. However, it is unclear how this neurophysiological response might relate to LFG-induced pseudohallucinatory phenomena. It is also unknown whether emotional states (e.g., fear) or traits associated with risk for psychosis (e.g., proneness to perceptual anomalies, ability to produce vivid mental imagery) affect such neurophysiological and/or perceptual responses to LFG.The present study investigated alpha sub-bands during LFG across several flicker frequencies, in relation to individual differences in propensity for Ganzfeld-induced imagery (GI), positive schizotypy and trait mental imagery, and in relation to manipulations of affective state. Given previously reported sex differences in risk for psychosis and response to Ganzfeld, the effect of sex on GI was also studied. Forty-six healthy adults (16 men) completed psychometric measures of trait mental imagery and positive schizotypy before undergoing three LFG (20 minutes each) conditions. In each condition, participants wore white-out goggles and listened to either mood-inducing soundscapes (fear, serenity) or pink noise (control) through headphones. Greatest propensity for GI arose between 12-16 Hz flicker, with a peak at 16 Hz flicker. Occipital lower-alpha was reduced for lower flicker frequencies (12-16 Hz) and was inversely associated with GI. Upper-alpha power was not significantly related to GI or to other measures. Fear-induction was associated with reduction in alpha power, but did not significantly affect GI. Men reported more GI than women. Findings support a role for cortical destabilisation, as reflected in reduced lower-alpha, in perceptual anomalies; and, by extension, LFG as an experimental model of liability to psychosis.
Brain plasticity following spinal cord injury (SCI) has been studied by a wide range of neurofunctional techniques, which tend to have low temporal resolution or overlook cognitive preparatory processes. This study tried to overcome both limitations by recording the movement-related brain potentials using an experimental task somewhat similar to the contingent negative variation paradigm. The aim was to look for amplitude or topographic distribution changes at an early stage of the SCI. Hence, the brain electrical activity of patients who had a clinical history of less than 6 months of paraplegia was recorded and compared with that of two groups of healthy volunteers. None of the patients was able to move their toes, but they were asked to prepare to carry out this movement and to try to execute it in the same way as one of the control groups. The other control group was instructed to prepare to conduct the same movement but not to execute it. Results did not show significant differences in the readiness potential between patients with paraplegia and both controls. However, the readiness potential topography observed in patients was more similar to that of healthy participants who conducted the movement, whereas a greater similarity was found in the motor potential between patients and healthy participants who did not carry out the movement. These findings suggest that neurofunctional changes that take place in the brain after a SCI may be shown earlier by the motor potential than by the readiness potential.
Everyday cognitive tasks are frequently performed under dual-task conditions alongside continuous sensorimotor coordinations (CSCs) such as driving, walking, or balancing. Observed interference in these dual-task settings is commonly attributed to demands on executive function or attentional resources, but the time course and reciprocity of interference are not well understood at the level of information-processing components. Here we used electrophysiology to study the detailed chronometry of dual-task interference between a visual oddball task and a continuous visuomanual tracking task. The oddball task's electrophysiological components were linked to underlying cognitive processes, and the tracking task served as a proxy for the continuous cycle of state monitoring and adjustment inherent to CSCs. Dual-tasking interfered with the oddball task's accuracy and attentional processes (attenuated P2 and P3b magnitude and parietal alpha-band event-related desynchronization), but errors in tracking due to dual-tasking accrued at a later timescale and only in trials in which the target stimulus appeared and its tally had to be incremented. Interference between cognitive tasks and CSCs can be asymmetric in terms of timing as well as affected information-processing components. NEW & NOTEWORTHY Interference between cognitive tasks and continuous sensorimotor coordination (CSC) has been widely reported, but this is the first demonstration that the cognitive operation that is impaired by concurrent CSC may not be the one that impairs the CSC. Also demonstrated is that interference between such tasks can be temporally asymmetric. The asynchronicity of this interference has significant implications for understanding and mitigating loss of mobility in old age, and for rehabilitation for neurological impairments.
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