Jane Tan

Research suggests that changes in functional connectivity contribute to age-related declines in response inhibition. Through a double-blind crossover study, we investigated the effects of dual-site beta transcranial alternating current stimulation (tACS) over the right inferior frontal gyrus (rIFG) and pre-supplementary motor area (preSMA) on functional connectivity measured with electroencephalography and response inhibition (stop-signal task performance) in 15 older (aged 61-79 years) and 18 young (aged 18-34 years) adults. Two tACS conditions were administered in separate sessions: in-phase tACS, where electrical currents delivered to rIFG and preSMA had a 0° phase difference, and anti-phase tACS, where currents had a 180° phase difference. Resting-state beta band rIFG-preSMA connectivity significantly increased after in-phase tACS for older and young adults, and decreased after anti-phase tACS for older adults. This shows that tACS can modulate rIFG-preSMA connectivity in a phase-specific manner in the aging brain. However, response inhibition significantly improved after both in- and anti-phase tACS for young and older adults, indicating that inhibitory performance might not be directly regulated by resting-state rIFG-preSMA phase connectivity.

Purpose
This study aimed to investigate bilateral motor control and connectivity between supplementary motor area (SMA) and primary motor cortex (M1) in younger, middle-aged, and older healthy adults.

Methods
32 younger (mean age 22.8 ± 5.3 years), 18 middle-aged (47.6 ± 6.5 years), and 23 older (75.8 ± 6.7 years) adults were tested. Bilateral motor control was assessed using the Purdue pegboard. Dual-site transcranial magnetic stimulation (TMS) was used to measure SMA–M1 connectivity at different conditioning stimulation intensities.

Results
Older adults had significantly poorer motor performance than younger and middle-aged in all pegboard subtests. Notably, there were no conclusive differences in motor performance between younger and middle-aged adults. There was no conclusive evidence supporting age-related and intensity-related differences in SMA–M1 connectivity between younger, middle-aged, and older adults. There was also no conclusive evidence to support clear associations between SMA–M1 connectivity and bilateral motor control.

Conclusion
Age-related declines in bilateral motor functioning was found in older, but not middle-aged adults. The bilateral motor functioning of middle-aged adults is more young-like than old-like. The lack of conclusive age- and intensity-related differences in SMA–M1 connectivity, and lack of conclusive association with bilateral motor performance, might be due to high inter-individual variability in SMA–M1 connectivity. Potential factors contributing to this variability include SMA and M1 morphometry, the structural connectivity between these regions, and the localisation of SMA.

Objective
Tremor is one of the most common motor symptoms of Parkinson’s disease (PD), with adverse effects on daily functioning and quality of life. This study investigated the effects of concurrent intermittent theta-burst stimulation and gamma frequency transcranial alternating current stimulation (iTBS-γ-tACS) on neuroplasticity in the motor cortex and resting tremor severity in individuals with tremor-dominant PD.

Methods
Eighteen individuals (mean age 66.8 ± 10.0 years, 6 females) with tremor-dominant PD attended two sessions, one involving iTBS-γ-tACSreal (real iTBS and real tACS), and the other involving iTBS-γ-tACSsham (real iTBS and sham tACS). Measures of neuroplasticity (corticospinal excitability and intracortical inhibition) and tremor severity were measured before and after iTBS-γ-tACS.

Results
Corticospinal excitability in the target muscle increased significantly after iTBS-γ-tACSreal, but not iTBS-γ-tACSsham. Intracortical inhibition and tremor severity were not significantly modulated by either stimulation condition.

Conclusions
iTBS-γ-tACSreal, but not iTBS-γ-tACSsham, elicited long-term potentiation-like neuroplastic changes in the target muscle.

Significance
This is the first study to show iTBS-γ-tACS can induce neuroplasticity in individuals with tremor-dominant PD. Despite no significant changes in tremor severity, future research should explore if targeting neuroplasticity in the cortical representation of the tremor-dominant muscle and/or multi-session administrations of iTBS-γ-tACS can reduce tremor.

Mounting evidence suggests that transcranial alternating current stimulation can enhance response inhibition, a cognitive process crucial for sustained effort and decision-making. However, most studies have focused on within-session effects, with limited investigation into the effects of repeated applications, which are crucial for clinical applications. We examined the effects of repeated bifocal transcranial alternating current stimulation targeting the right inferior frontal gyrus and pre-supplementary motor area on response inhibition, functional connectivity, and simulated driving performance. Thirty young adults (18-35 yr) received either a sham or transcranial alternating current stimulation (20 Hz, 20 min) across 5 sessions over 2 wk. Resting-state electroencephalography assessed functional connectivity between the pre-supplementary motor area and right inferior frontal gyrus at baseline, the final transcranial alternating current stimulation session, and the 7-d follow-up. Response inhibition was measured using a stop-signal task, and driving performance was assessed before and after the intervention. The results showed significant improvements in functional connectivity in the transcranial alternating current stimulation group between sessions, though response inhibition and driving braking performance remained unchanged. However, while not the targeted behavior, general driving performance potentially improved following bifocal transcranial alternating current stimulation, with participants maintaining stable driving behavior alongside increased spare attentional capacity. These findings suggest that repeated bifocal transcranial alternating current stimulation may enhance cortical connectivity and related cognitive-motor processes, supporting its potential for clinical applications.

Blood flow restriction (BFR) combined with low work rate exercise can enhance muscular and cardiovascular fitness. However, whether neural mechanisms mediate these enhancements remains unknown. This study examined changes in corticospinal excitability and motor cortical inhibition following arm cycle ergometry with and without BFR. Twelve healthy males (24 ± 4 years) completed four, randomized 15‐min arm cycling conditions: high work rate (HW: 60% maximal power output), low work rate (LW: 30% maximal power output), low work rate with BFR (LW‐BFR) and BFR without exercise (BFR‐only). For BFR conditions, cuffs were applied around the upper arm and inflated to 70% of arterial occlusion pressure continuously during exercise. Single‐pulse transcranial magnetic stimulation was delivered to left primary motor cortex (M1) to elicit motor‐evoked potentials (MEP) in the right biceps brachii during a low‐level isometric contraction. MEP amplitude and cortical silent period (cSP) duration were measured before and 1, 10 and 15 min post‐exercise. MEP amplitude increased significantly from baseline to Post‐10 and Post‐15 for both the HW (both z  < −7.07, both P  < 0.001) and LW‐BFR conditions (both z  < −5.56, both P  < 0.001). For the LW condition without BFR, MEP amplitude increased significantly from baseline to Post‐10 ( z  = −3.53, P  = 0.003) but not Post‐15 ( z =  −1.85, P  = 0.388). The current findings show that HW arm cycling and LW‐BFR led to longer‐lasting increases in corticospinal excitability than LW arm cycling alone. Future research should examine whether the increased corticospinal excitability is associated with the improvements in muscle strength observed with BFR exercise. A mechanistic understanding of BFR exercise improvement could guide BFR interventions in clinical populations.
What is the central question of this study? Does low work rate arm cycling with blood flow restriction (BFR) lead to an increase in corticospinal excitability and decrease in cortical inhibition that is comparable to high work rate arm cycling and greater than low work rate arm cycling and BFR without exercise? What is the main finding and its importance? Unrestricted high work rate arm cycling and low work rate arm cycling combined with BFR led to longer lasting increases in corticospinal excitability than low work rate arm cycling alone. Future research is needed to examine whether the increased corticospinal excitability is associated with the improvements in muscle strength observed with BFR exercise.

Research suggests that changes in functional connectivity contribute to age-related declines in response inhibition. Through a double-blind crossover study, we investigated the effects of dual-site beta transcranial alternating current stimulation (tACS) over the right inferior frontal gyrus (rIFG) and pre-supplementary motor area (preSMA) on functional connectivity measured with electroencephalography and response inhibition (stop-signal task performance) in 15 older (aged 61-79 years) and 18 young (aged 18-34 years) adults. Two tACS conditions were administered in separate sessions: in-phase tACS, where electrical currents delivered to rIFG and preSMA had a 0° phase difference, and anti-phase tACS, where currents had a 180° phase difference. Resting-state beta band rIFG-preSMA connectivity significantly increased after in-phase tACS for older and young adults and decreased after anti-phase tACS for older adults. Response inhibition significantly improved after both in- and anti-phase tACS for young and older adults. These findings suggest that tACS can potentially modulate rIFG-preSMA connectivity in a phase-specific manner in the aging brain, and that inhibitory performance might not be directly regulated by resting-state rIFG-preSMA phase connectivity. Due to the lack of sham control, placebo effects cannot be ruled out. However, the differing neurophysiological effects from in- and anti-phase tACS suggest that rIFG-preSMA resting-state phase connectivity is unlikely to underpin the changes in inhibitory performance. Future studies incorporating a sham control are required to verify these findings.

Abstract
Resting tremor—involuntary and rhythmic shaking that usually occurs in the limbs—is the most common presenting motor symptom in Parkinson’s disease (PD). Tremor is not associated with the severity of dopamine depletion in the basal ganglia, and dopaminergic medication, which is used primarily to target dopamine depletion in the basal ganglia, has limited efficacy in reducing tremor. This suggests that other brain regions might underpin tremor in PD. Intracortical inhibition within the primary motor cortex (M1) has been implicated in tremor: intracortical inhibition in M1 is lower in PD than controls, higher motor cortex GABA is associated with lower tremor severity in PD, and pharmacological increases in GABA activity reduce tremor severity in PD. A combined intermittent theta-burst stimulation (iTBS)—gamma transcranial alternating current stimulation (tACS) protocol has been shown to increase short-interval intracortical inhibition (SICI) in PD. Therefore, in the current study, we examined M1 excitability, SICI, and resting tremor before and after real and sham iTBS-tACS. In a within-subjects design, we tested 19 participants (13 male; mean age 66 years) with idiopathic, tremor-dominant PD OFF medication. M1 excitability increased after real but not sham iTBS-tACS. There was no change in SICI after either real or sham iTBS-tACS. Resting tremor in the extensor carpi radialis showed a trend to increase after sham but not real iTBS, indicating that real iTBS-tACS might have prevented resumption of tremor activity in PD participants OFF medication. These findings provide preliminary evidence that iTBS-tACS induced long-term potentiation-like plasticity in M1 in tremor-dominant PD, which could influence tremor severity. However, further research is needed to examine the time-course of iTBS-tACS-induced changes in M1 excitability and tremor severity. If iTBS-tACS can reduce tremor, it could offer an alternative, or supplementary, treatment to levodopa medication for people with tremor-dominant PD.

Research Category and Technology and Methods
Clinical Research: 10. Transcranial Magnetic Stimulation (TMS)

Transcranial electrical stimulation (tES) has garnered significant attention as a non-invasive neuromodulation technique with promising therapeutic potential for various neurological and neuropsychiatric conditions. However, considerable variability in response to tES both between and within-individuals is a prevailing issue. This review explored recent advancements in optimising tES through individualised protocols that consider individual head anatomy, neural oscillatory activities and dynamic changes in the neurophysiology of the stimulated brain. Real-time monitoring and closed-loop systems allow adaptive adjustments of stimulation parameters in response to ongoing brain activity, which holds promise for enhancing tES effectiveness and overcoming the challenge of inter-session response variability. Overall, the reviewed literature highlights the emerging trend towards individualised tES protocols as a means to unlock the full potential of tES in research and clinical use. While promising, further research is warranted to establish standardised methodologies and validate the efficacy of individually tailored tES protocols to realise its full potential.

Augmentative alternative communication (AAC) devices or systems are often prescribed to minimally verbal or nonspeaking autistic individuals and other individuals with complex communication needs to facilitate communication or as an alternative to spoken language. AAC use can result in communication gains and improved quality of life for minimally verbal or nonspeaking individuals. Despite this, AAC abandonment is high, limiting societal participation of the individual on the autism spectrum with complex communication needs. Our study is a novel exploration of the barriers of AAC use from a multi-stakeholder perspective, and a qualitative analysis of similarities and differences between stakeholders. We conducted semi-structured interviews and focus groups with 30 parent-carers, educators and clinicians currently supporting AAC users in Western Australia and analysed the data using reflexive thematic analysis. Barriers from each stakeholder group were coded, resulting in 17 subthemes forming five main themes common to all stakeholders: Stakeholder Knowledge, Stakeholder Attitudes and Stigma, Resources, AAC User Engagement, and Device Fit. Contrasting perspectives included actual and perceived stigma associated with AAC use (parent-carers vs clinicians); different struggles with resources and knowledge (parent-carers vs clinicians and educators); and a lack of clinician communication in the processes that determined AAC-fit for school environments (educators only). Findings are discussed in the context of improving inter-stakeholder collaboration and capacity building in Australian health service and practice to better support minimally verbal or nonspeaking autistic individuals and individuals with complex communication needs. Suggestions are also offered for communication partner training.

With dementia incidence projected to escalate significantly within the next 25 years, the United Nations declared 2021-2030 the Decade of Healthy Ageing, emphasising cognition as a crucial element. As a leading discipline in cognition and ageing research, psychology is well-equipped to offer insights for translational research, clinical practice, and policy-making. In this comprehensive review, we discuss the current state of knowledge on age-related changes in cognition and psychological health. We discuss cognitive changes during ageing, including (a) heterogeneity in the rate, trajectory, and characteristics of decline experienced by older adults, (b) the role of cognitive reserve in age-related cognitive decline, and (c) the potential for cognitive training to slow this decline. We also examine ageing and cognition through multiple theoretical perspectives. We highlight critical unresolved issues, such as the disparate implications of subjective versus objective measures of cognitive decline and the insufficient evaluation of cognitive training programs. We suggest future research directions, and emphasise interdisciplinary collaboration to create a more comprehensive understanding of the factors that modulate cognitive ageing.