Extraction of the GVS electrical artifact from EEG recordings of the motor related cortical potential.

BACKGROUND: Galvanic vestibular stimulation (GVS) involves the administration of low-amplitude trans-mastoidal current which induces a dense electrical field across the scalp that is difficult to remove from the EEG record. In two proof-of-concept experiments, we designed a paradigm to evaluate functional limb movement, and tested a method of blind source separation to remove the scalp artifact induced by low-amplitude, alternating current GVS to allow measurement of the motor-related cortical response (MRCP) during voluntary movement. NEW METHOD: Off-line Extended Infomax Independent Component Analysis (ICA) was applied to the concatenated dataset to identify and remove core characteristics of the artifact induced by a trans-mastoidal current (Experiment 1: 0.01 Hz, 0.2-3 mA; Experiment 2: 0.01 Hz, 0.3-0.4 mA) during finger (Experiments 1 and 2) and foot tapping (Experiment 2). RESULTS: In Experiment 1, a GVS-related independent component was identified and successfully removed without compromising measurement of the MRCP. This success was replicated in Experiment 2 which included both finger and foot tapping, and a higher GVS amplitude, which resulted in the identification of additional GVS-related artifacts. COMPARISON WITH EXISTING METHODS: Existing methods of artifact rejection typically use an offline bandpass filter that overlaps with the frequency range of the MRCP. Even when similar ICA-based approaches have been employed, they have been applied during rest rather than active movement, have not been described in sufficient detail to enable replication, and require significant expertise and bespoke software to implement. CONCLUSION: The ICA-based approach described here provides a relatively simple and accessible means by which MRCPs can be measured during alternating current GVS. This provides opportunity to identify new biomarkers associated with the therapeutic effects of GVS in people with Parkinson's disease and other disorders of voluntary movement.

Validation of a multidirectional locomotive dual-task paradigm to evaluate task-related differences in event-related electro-cortical activity.

A fundamental aspect of everyday function is the ability to simultaneously execute both cognitive and motor tasks. The ability to perform such tasks is commonly assessed using a dual-task paradigm that has the capacity to manipulate both cognitive and motor components of an action. Dual-task performance provides an opportunity to obtain an insight into how cognitive and motor function are affected during natural tasks (e.g., locomotion). The following study aimed to determine the effectiveness of using a goal-directed multidirectional locomotor task to measure differences in task-related (tasks of increasing difficulty) electro-cortical activity. In the single-task condition participants walked around a grid-based track, performing directional changes at each intersection in response to a sensory stimulus. In the dual-task condition participants performed the same primary task while performing a simultaneous memory recall task. Behavioural differences in trial completion time and electro-cortical activity were identified in relation to the posterior N2 and P3 component mean amplitudes. The results showed that, while performing a higher-level cognitive task during walking (dual-task), interference arises in a shared system that influences neural mechanisms involved in attention and selection for action, and later cognitive processes recruited in working memory and cognitive control. This study extends previous work and shows that performing a more complex cognitive task while walking, elicits interference effects sensitive to higher-level cognitive processes, and takes the next step towards measurement of electro-cortical activity within naturalistic environments.

Fatigue related impairments in oculomotor control are prevented by caffeine.

Strenuous exercise can result in an inability of the central nervous system to drive skeletal muscle effectively, a phenomenon known as central fatigue. The impact of central fatigue on the oculomotor system is currently unexplored. Fatigue that originates in the central nervous system may be related to perturbations in the synthesis and metabolism of several neurotransmitters. In this study we examine central fatigue in the oculomotor system after prolonged exercise. The involvement of central neurotransmission was explored by administering caffeine during exercise. Within a double-blind, randomized, repeated measures, crossover design, 11 cyclists consumed a placebo or caffeine solution during 180 min of stationary cycling. Saccadic eye movements were measured using infra-red oculography. Exercise decreased saccade velocity by 8% (placebo trial). This effect was reversed by caffeine, whereby velocity was increased by 11% after exercise. A non-oculomotor perceptual task (global motion processing) was unaffected by exercise. The human oculomotor system is impaired by strenuous exercise of the locomotor system. Caffeine exerts a protective effect on oculomotor control, which could be related to up-regulated central neurotransmission. In addition, cortical processes supporting global motion perception appear to be robust to fatigue.