Experimental Brain Research最新文献

Transcutaneous auricular vagus nerve stimulation (taVNS) is attracting attention as a new neuromodulation technique to improve cognitive function. The effects of this neuromodulation technique on associative memory and its mechanisms have not been fully investigated. This crossover, single-blind, active-versus-sham design experiment examined the effects of taVNS on associative memory performance and the event-related potential P300 or P600. The experiment consisted of an associative memory task with encoding and retrieval as a set, performed three timepoints with a 10 min rest period, on 14 healthy adults. Participants received taVNS or sham during the 10 min rest between the time 1 and time 2. Event-related potentials were measured at each time of the associative memory task. The washout for this experiment was set at one week. We analyzed the effects of taVNS by means of a general linear mixed model with performance on three associative memory tasks and peak amplitude of event-related potential P300 or P600 as dependent variables. The results presented an interaction effect of taVNS and timepoints on associative memory performance. Conversely, no effects on the event-related potentials P300 and P600 were observed. This noninvasive neuromodulation technique holds potential for applications in rehabilitation for cognitive function. Further research is needed to generalize the results of this pilot study. Registration: University Hospital Medical Information Network Center (No. UMIN000055911), date: January 24, 2024 "retrospectively registered".

Operant conditioning (OC) evokes behavioral changes and may be useful in pain management. However, it is unknown how alteration of a tonic painful stimulus may affect cognitive performance in an OC learning task and the associated neural activity. To address this, specific event-related potentials (ERPs) and cognitive performance were assessed after an OC task, using altered pain intensity as the operant stimulus. Two OC paradigms were designed using painful tonic pressure pain as the conditioning stimulus. 29 healthy participants received individually set tonic pressure pain corresponding to visual analogue scale 5 (VAS5; pain threshold). Pressure was maintained and a cognitive task performance yielded reward or punishment. Consequences of correct and incorrect answers in the negative reinforcement (NR) condition were pain relief (VAS3) or no pressure change (VAS5), respectively, and no pressure change (VAS5) or increased pressure (VAS7) in the positive punishment (PP) condition, respectively. The initial condition (NR or PP) was randomized, and 120 trials were conducted in three same-day sessions. 64-channel electroencephalography was recorded, and auditory-feedback ERPs (P1N1, P2N2, P3N3) were extracted. Higher ERP peak-to-peak amplitudes were found when participants received feedback that their answer was incorrect. A small OC learning behavior effect was found across trials with no difference between NR and PP. Independent of OC paradigm, learning behavior was induced, and ERP complex amplitudes increased when incorrect answers were given. These novel findings show that higher pain expectancy due to an incorrect answer, facilitated feedback-related ERPs when using pain as a conditioning stimulus.

A substantial body of literature has examined gait during cognitive dual-tasking in younger and older adults. However, it remains unclear how, and to what extent, different cognitive tasks uniquely influence gait. This meta-analysis quantified age-related differences in gait speed during dual-task walking. Importantly, we examined cognitive task as a potential moderator. We searched Web of Science for studies comparing young and older adults during single-task and dual-task walking conditions. Twenty-two studies met the inclusion criteria, representing 544 young adults (mean age range: 20-31 years) and 511 older adults (mean age range: 62-85 years). Studies employed primarily serial subtraction tasks (n = 12) and verbal fluency tasks (n = 8); however, one study used digit vigilance, and another used a texting paradigm during walking. Random-effects meta-analysis using standardized mean differences (Hedges' g) revealed a significant overall effect (g = -0.2612, 95% CI [-0.4914, -0.0310], p = 0.0261), indicating greater dual-task costs in older adults compared to younger adults with a small to medium effect size. Substantial heterogeneity was observed across studies (I² = 66.53%, p < 0.0001). Subgroup analysis demonstrated that verbal fluency tasks produced a larger and statistically significant age-related difference (g = -0.4744, 95% CI [-0.8712, -0.0777], p = 0.0191), while serial subtraction tasks showed smaller, non-significant effects (g = -0.1412, p = 0.3474). These findings suggest that verbal fluency creates unique neural resource competition in older adults, involving prefrontal, cerebellar, and basal ganglia circuits that support both language production and gait control. The task-specific vulnerability to verbal fluency, and not serial subtraction, provides evidence for age-related changes in cognitive-motor integration. Rehabilitation strategies targeting executive functions may be effective for maintaining mobility in aging populations.

We sought to determine if enhancement of postural reflexes occurs specifically in response to instability induced by leaning and the possible neural level at which this may be mediated. Healthy participants (n = 10; 37 ± 15 years) were asked to adopt leaning postures to increase postural instability. Recordings of postural, eye and neck muscles and from over the cerebellum were made during stable upright stance and with the feet plantarflexed or dorsiflexed. The latter postures were used to modulate tonic activity levels in the soleus and tibialis anterior (TA) muscles to a similar degree to leaning. External perturbations were delivered to the trunk [vertebra prominens (C7) and upper sternum] and at the mastoids. C7 stimulation produced larger short latency (SL) reflex amplitudes in soleus during forwards lean than upright stance, when using matched tonic levels, although SL amplitudes in TA in response to sternal stimulation were unaffected when tonic activity was matched. Cerebellar evoked responses were larger during anterior than posterior lean for truncal stimuli. Mastoid stimulation generally evoked larger responses in the legs during lean than during upright stance with matching tonic EMG levels. Vestibular and non-vestibular responses recorded from the sternocleidomastoid muscles were often larger during posterior lean, independent of the direction of mastoid stimulation. Short-latency vestibular evoked cerebellar responses and extraocular responses were unaffected by posture. Facilitation of postural reflexes by instability occurred for axially-evoked postural reflexes in soleus but not TA. We propose that this effect is mediated by modulation of descending brainstem projections.

The hand laterality judgment task requires participants to determine whether a picture of a hand, presented at various rotational angles, depicts a left or right hand. Several strategies have been suggested to be involved in task performance: in particular, palm-view pictures are thought to rely on motor imagery (MI), whereas back-view pictures are thought to rely on 'nonMI' (i.e., without motor imagery) strategies, including visual imagery (VI). However, the influence of repeated task execution on performance strategies remains unclear. This study examined the relationship between self-reported strategies and response time (RT) profiles during a 512-trial hand laterality judgment task in 42 healthy adults. Based on post-task self-reports for palm-view pictures, participants were classified into the MI group, consistently using MI throughout the trials, and the MI-nonMI group, switching from MI to nonMI during the repeated trials. In the MI group, RT profiles consistently showed longer RTs for lateral palm-view pictures (outward-pointing fingers) than for medial orientations (inward-pointing fingers), characteristic of MI use, across both halves of the task. The MI-nonMI group showed similar RT patterns initially, but in the second half, RT differences between lateral and medial orientations diminished, suggesting a shift toward VI-like characteristics. These findings suggest that although both groups may have used MI, RT trends varied according to the participants' self-reported strategies. In the MI group, both explicit self-report and implicit RT profiles indicated sustained MI use, whereas the MI-nonMI group, self-reports indicated a strategy shift to nonMI, and their RT profiles suggest a combined use of MI and nonMI.

Transspinal stimulation with direct current or at intensities and frequencies that produces intermittent depolarization of motoneurons can be an adjunct treatment strategy for spasticity and recovery of movement in persons with spinal cord injury (SCI). The main objective of this study was to assess changes in neurophysiological biomarkers after multiple sessions of transspinal direct current stimulation (tsDCS) in people with and without SCI. Nine SCI and 10 healthy control subjects received daily cathodal tsDCS over the Thoracic 10 vertebra while supine with an average stimulation intensity of 2.28 ± 0.02 mA. SCI and healthy control subjects received an average of 15 and 10 stimulation sessions, respectively. Before and 1-2 days post intervention, we assessed changes in soleus H-reflex recruitment input-output curves, homosynaptic depression and postactivation depression. tsDCS did not alter the strength of homosynaptic depression in any subject group but reversed postactivation depression to facilitation in AIS D subjects. tsDCS resulted in depression of reflex excitability in both subject groups. No significant changes in clinically assessed hyperreflexia were observed in SCI subjects. The results suggest decreased reflex hyperexcitability without recovery of spinal inhibitory control in the injured human spinal cord after multiple sessions of tsDCS. More systematic investigations on reorganization of spinal and cortical interneuronal networks are needed to delineate the tsDCS-induced neuroplasticity in people with SCI to develop effective treatments.