Experience-Related Differences on Attentional Control in Cognitive Ageing: An Investigation of Bilingualism Effects on Flanker Conflicts in TFRs

Bilingualism has been argued to help maintain cognitive functioning in ageing by contributing to the cognitive reserve, the brain’s functional adaptability and resilience against cognitive decline. Within this, the constant engagement with bilingual mechanisms to monitor multiple languages arguably leads to neurocognitive adaptations of attentional systems. Examining bilingual experience as a spectrum, and how these potentially link to variable individual outcomes in cognitive ageing remains understudied. Therefore, this study investigates the effect of individual differences in bilingual experiences on neurocognition in middle-aged adults and seniors. In the study, a non-linguistic flanker task was implemented while measures of both indices of brain activity through EEG and behavioral data were collected. In looking at the relation between differences in bilingual experiences and ageing, the study found that more balanced bilinguals were able to maintain their reliance on alpha activity in ageing, associated to the efficiency of attentional resources to focus on task relevant stimuli. Furthermore, the study found indications of a post stimulus increase in theta power related to cognitive control recruitment. The behavioral findings however, showed the opposite pattern as to what was expected, as subjects with more engagement in bilingual experiences showed a bigger effect of age on flanker task reaction times. Overall, these findings indicate that individual differences in bilingual experiences have a modulatory effect on neurocognition in ageing, potentially leading to better maintained cognitive functioning in cognitive decline

A neurophysiological examination of voluntary isometric contractions: modulations in sensorimotor oscillatory dynamics with contraction force and physical fatigue, and peripheral contributions to maximal force production

Human motor control is a complex process involving both central and peripheral components of the nervous system. Type Ia afferent input contributes to both motor unit recruitment and firing frequency, however, whether maximal force production is dependent on this input is unclear. Therefore, chapter 2 examined maximal and explosive force production of the knee extensors following prolonged infrapatellar tendon vibration; designed to attenuate the efficacy of the homonymous Ia afferent-α-motoneuron pathway. Despite a marked decrease in H-reflex amplitude, indicating an attenuated efficacy of the Ia afferent-α-motoneuron pathway, both maximal and explosive force production were unaffected after vibration. This suggested that maximal and explosive isometric quadriceps force production was not dependent upon Ia afferent input to the homonymous motor unit pool. Voluntary movements are linked with various modulations in ongoing neural oscillations within the supraspinal sensorimotor system. Despite considerable interest in the oscillatory responses to movements per se, the influence of the motor parameters that define these movements is poorly understood. Subsequently, chapters 3 and 4 investigated how the motor parameters of voluntary contractions modulated the oscillatory amplitude. Chapter 3 recorded electroencephalography from the leg area of the primary sensorimotor cortex in order to investigate the oscillatory responses to isometric unilateral contractions of the knee-extensors at four torque levels (15, 30, 45 and 60% max.). An increase in movement-related gamma (30-50 Hz) activity was observed with increments in knee-extension torque, whereas oscillatory power within the delta (0.5-3 Hz), theta (3-7 Hz), alpha (7-13 Hz) and beta (13-30 Hz) bands were unaffected. Chapter 4 examined the link between the motor parameters of voluntary contraction and modulations in beta (15-30 Hz) oscillations; specifically, movement-related beta decrease (MRBD) and post-movement beta rebound (PMBR). Magnetoencephalography (MEG) was recorded during isometric ramp and constant-force wrist-flexor contractions at distinct rates of force development (10.4, 28.9 and 86.7% max./s) and force output (5, 15, 35 and 60%max.), respectively. MRBD was unaffected by RFD or force output, whereas systematic modulation of PMBR by both contraction force and RFD was identified for the first time. Specifically, increments in isometric contraction force increased PMBR amplitude, and increments in RFD increased PMBR amplitude but decreased PMBR duration. Physical fatigue arises not only from peripheral processes within the active skeletal muscles but also from supraspinal mechanisms within the brain. However, exactly how cortical activity is modulated during fatigue has received a paucity of attention. Chapter 5 investigated whether oscillatory activity within the primary sensorimotor cortex was modulated when contractions were performed in a state of physical fatigue. MEG was recorded during submaximal isometric contractions of the wrist-flexors performed both before and after a fatiguing series of isometric wrist-flexions or a time matched control intervention. Physical fatigue offset the attenuation in MRBD observed during the control trial, whereas PMBR was increased when submaximal contractions were performed in a fatigued state

Transcranial direct current stimulation (tDCS) over the left prefrontal cortex does not affect time-trial self-paced cycling performance: Evidence from oscillatory brain activity and power output

To test the hypothesis that transcranial direct current stimulation (tDCS) over the left dorsolateral prefrontal cortex (DLPFC) influences performance in a 20-min time-trial self-paced exercise and electroencephalographic (EEG) oscillatory brain activity in a group of trained male cyclists. There were no differences (F = 0.31, p > 0.05) in power output between the stimulation conditions: anodal (235W[95%CI 222–249 W]; cathodal (235W[95%CI 222–248 W] and sham (234W[95%CI 220–248 W]. Neither heart rate, sRPE nor EEG activity were affected by tDCS (all Ps > 0.05). tDCS over the left DLFC did not affect self-paced exercise performance in trained cyclists. Moreover, tDCS did not elicit any change on oscillatory brain activity either at baseline or during exercise. Our data suggest that the effects of tDCS on endurance performance should be taken with caution.This project was supported by grants from from the Spanish Ministerio de Economía, Industria y Competitividad-PSI2016-75956-P to D. S. and M.Z., a predoctoral grant from the Spanish Ministerio de Economía, Industria y Competitividad (BES-2014-069050) to L.F.C., and a Spanish “Ministerio de Educación, Cultura y Deporte” predoctoral grant (FPU14/06229) to D.H. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Scalp Eeg and Tms Based Electrophysiological Study of Brain Function of Motor Control in Aging

Voluntary movements of human body are controlled by the brain through corticomuscular pathways. Although neuromuscular control mechanisms of voluntary movements have been studied extensively, many remain to be learned, especially neuromuscular adaptations related to clinical conditions such as neurological disorders and aging. This research aims at a better understanding of functional connection between the brain and muscle during voluntary motor activities in aging and the extent to which this connection can be changed by training the neuromuscular system. Three research projects were conducted to achieve this aim. The analyses in the first two projects are based on comparisons of non-invasive electroencephalographic (EEG) and electromyographic (EMG) signals recorded in young and elderly individuals performing voluntary muscle contractions whereas the third project is based on transcranial magnetic stimulation (TMS). The first project examines the relationship between EEG frequency power and muscle force to identify an EEG or brain signal parameter directly related to voluntary motor action. The second project investigates further the strength of functional brain-muscle connectivity by quantifying EEG-EMG coherence and effects of aging on the connectivity. The third project identifies the representation of the biceps brachii muscle in primary motor cortex with TMS examine its excitability of corticospinal tracts, intra-cortical excitability reflecting activity of both inhibitory and facilitatory inter-neurons and inter-hemispheric inhibition. This research reveals that aging brain has impaired coupling between the central and peripheral neuromuscular systems and also significantly different intra-cortical excitability both may have an influence for weakened muscle output in the elderly. This research will contribute to a better understanding of neural mechanisms underlying voluntary movement deficit in aging and its recovery following training the neuromuscular syste

A review of acute aerobic exercise and transcranial direct current stimulation effects on cognitive functions and their potential synergies

Today, several pharmaceutic and non-pharmaceutic approaches exist to treat psychiatric and neurological diseases. Because of the lack of treatment procedures that are medication free and the lack of severe side effects, transcranial direct current stimulation (tDCS) and aerobic exercise (AE) have been tested to explore the potential for initiating and modulating neuroplasticity in the human brain. Both tDCS and AE could support cognition and behavior in the clinical and non-clinical context to improve the recovery process within neurological or psychiatric conditions or to increase performance. As these techniques still lack meaningful effects, although they provide multiple beneficial opportunities within disease and health applications, there is emerging interest to find improved tDCS and AE protocols. Since multimodal approaches could provoke synergetic effects, several recent studies have begun to combine tDCS and AE within different settings such as in cognitive training in health or for treatment purposes within clinical settings, all of which show superior effects compared to single technique applications. The beneficial outcomes of both techniques depend on several parameters and the understanding of neural mechanisms that are not yet fully understood. Recent studies have begun to directly combine tDCS and AE within one session, although their interactions on the behavioral, neurophysiological and neurochemical levels are entirely unclear. Therefore, this review a) provides an overview of acute behavioral, neurophysiological, and neurochemical effects that both techniques provoke within only one single application in isolation; b) gives an overview regarding the mechanistic pathways; and c) discusses potential interactions and synergies between tDCS and AE that might be provoked when directly combining both techniques. From this literature review focusing primarily on the cognitive domain in term of specific executive functions (inhibition, updating, and switching), it is concluded that a direct combination of tDCS and AE provides multiple beneficial opportunities for synergistic effects. A combination could be useful within non-clinical settings in health and for treating several psychiatric and neurologic conditions. However, there is a lack of research and there are several possibly interacting moderating parameters that must be considered and more importantly must be systematically investigated in the future