Jack P. Solomon

Multiscale entropy (MSE) changes in relation to age, whereby ageing is associated with an increasing bias towards fine scale entropy. This change is thought to represent a shift towards localized information processing in the brain as we age. However, this relationship has not been tested in large sample sizes alongside other demographic factors and cognitive behaviours. This study aimed to replicate previously reported effects of ageing on MSE in an open access database (Cambridge Centre for Ageing and Neuroscience, N = 587) and expand the findings to include an investigation of the effects of sex and a variety of cognitive behaviours. MSE curves and power spectrum densities (PSD) were calculated for each region of interest from the magnetoencephalography data. Multivariate partial least squares analyses were used to assess the relationship between MSE or PSD and five behavioural/demographic factors including age, sex, fluid intelligence, visual short-term memory, and a generalized measure of cognitive function. Age was associated with increased fine scale and decreased coarse scale entropy, as well as complementary spectral changes, including slowing of peak alpha rhythms, increased beta-band activity, and reduced gamma-band activity, which replicates prior MSE and PSD findings. In both domains, these age-related patterns differentiated based on sex with advancing age. Importantly, the unique effects of sex diverged between MSE and PSD. This result indicates that entropy-based measures can isolate aspects of temporal organization that are not clearly summarized by spectral structure alone.

The macroscale signaling of the brain emerges from the integration of connected areas, orchestrated by microscale, regional molecular processes. Despite growing multimodal neuroimaging data resources, the role of cortical chemoarchitecture in shaping inter-regional functional connectivity remains poorly understood. Here, we examine whether brain regions that share a chemoarchitectural signature exhibit strong frequency-resolved functional connectivity, and whether aging moderates this neurochemical-functional alignment. Using magnetoencephalography data from across the healthy adult lifespan (n = 569), we identify a frequency-dependent organization of functional connectivity by slow neuromodulator systems, with low-frequency bands (θ-α) shaped most strongly by noradrenergic systems, and faster (β) alignment dependent on serotonergic chemoarchitecture. Aging strengthens the influence of neurochemistry on inter-regional connectivity, with frequency-specific implications for age-related cognitive performance. Neurochemical influences on θ-band connectivity were associated with worse cognition in older adults, while the opposite was true for the low-γ (γ↓) band. This suggests that neuromodulatory preservation of high-frequency dynamics in older adults may reflect neural resilience. Together, our findings indicate that neurochemical-functional alignment is frequency-dependent, distinguishing between maladaptive and resilient modes of brain organization.

Multiscale entropy (MSE) changes in relation to age, whereby aging is associated with an increasing bias towards fine scale entropy. This change is thought to represent a shift toward localized information processing in the brain as we age. However, this relationship has not been tested in large sample sizes alongside other demographic factors and cognitive behaviours. This study aimed to validate previously reported effects of aging on MSE in a large open access database (Cambridge Centre for Ageing and Neuroscience, N=587) and expand the findings to include an investigation of the effects of sex and a variety of cognitive behaviours. MSE curves and power spectrum densities (PSD) were calculated for each region of interest from the magnetoencephalography data. Multivariate partial least squares analyses were used to assess the relationship between MSE or PSD and 5 behavioural / demographic factors including: age, sex, fluid intelligence, visual short-term memory and a generalized measure of cognitive function. Age was associated with increased fine scale and decreased coarse scale entropy, as well as complementary spectral changes, including slowing of peak alpha rhythms, increased beta-band activity, and reduced gamma-band activity, which replicates prior MSE and PSD findings. In both domains, these age-related patterns differentiated based on sex with advancing age. Importantly, the unique effects of sex diverged between MSE and PSD. This result indicates that entropy-based measures can isolate aspects of temporal organization that are not clearly summarized by spectral structure alone.

Societal Impact Statement: Butternut is yet another North American tree species undergoing rapid mortality due to the globalization of forest pathogens. Pairing tree health surveys and genetic diversity metrics, we captured a 7‐year snapshot of butternut's path to extirpation from its distinct range in New Brunswick, Canada. We recorded substantial mortality and vigour decline in these genetically unique populations, where a major proportion of genetic diversity was contributed by dying trees. We discuss feasible actions on a tight deadline for species under range‐wide pathogen pressure and highlight a blind spot in conservational policy: the risk of substantial genetic depletion far prior to extirpation. Summary: Butternut ( Juglans cinerea ) populations in New Brunswick, Canada, are rapidly declining due to the fungal pathogen Ophiognomonia clavigignenti‐juglandacearum . Mitigation strategies, including tree breeding, rely on access to genetically diverse populations and take time to implement. It is therefore vital to account for the rate of mortality and genetic diversity decline. Two main objectives: (I) characterize the rate of mortality and diversity decline; (II) assess if visually classed symptoms reflect the tree's state of decline towards mortality; and two exploratory objectives: (III) examine the contributions of trees grouped by health to the total allelic richness of the population; and (IV) project the timeline to mortality of the measured trees based on two timepoints (2016 and 2023). We examined tree health and diversity indices (allelic richness and expected heterozygosity) for 428 individuals (6 populations) at 2 time points: 2016 and 2023. Out of 428 butternut trees 22% died between 2016 and 2023, the median vigour declined in all but one population. Where the majority of the total allelic richness was contributed by vigorous trees in 2016, in 2023 this majority is conferred by dying trees. Qualitative phenotyping provided vital context to the rate of decline. Our results highlight the decreasing time window for the genetic conservation of Canadian butternut populations, and the urgency specifically for New Brunswick as a small, marginal population in steep decline.

The degree to which motor imagery engages the motor system or relies on perceptual/cognitive processes is a continuing debate. Here, we used the size weight illusion to create dissociation between perception and action to address the nature of motor imagery. Participants alternated lifting bricks of equal mass but where one brick was larger than the other, resulting in a perceptual illusion. Fifty‐seven participants were divided into three groups differing in the modality used for training (motor imagery, MI; and overt execution, OE) and exposure to the size weight illusion pretraining, one (MI‐2) and five (MI‐10 and OE) lifts of each brick. We hypothesized that the MI groups would use lifting dynamics post‐training consistent with the illusion, whereas the OE group would maintain accurate lifting forces. Contrary to our hypothesis, the OE and MI‐10 groups maintained the effect of the illusion post‐training. In the MI‐2 group, perception of the bricks' weight changed to reflect the participant's belief that large objects are heavy, and they correspondingly adjusted their lifting force post‐training. These results demonstrate that perceptual and motor processes are engaged during motor imagery and that the simulation of the motor component of the movement during motor imagery guides the performed action.

Whether motor imagery (MI) engages the motor system or relies on perceptual/cognitive processes is a matter of debate. Here we used the size weight illusion to create dissociation between perception and action to address the nature of MI. Participants alternated lifting bricks of equal mass but where one brick was larger than the other, resulting in a perceptual illusion. Fifty-seven participants (M=20, F=37, 22.54.4 years; collected 2019-22) were divided into three groups differing in the modality used for training (MI and overt execution; OE) and exposure to the size weight illusion pre-training (one (MI-2) and five (MI-10 and OE) lifts of each brick). We hypothesized that the MI groups would use lifting dynamics post-training consistent with the illusion, whereas the OE group would maintain accurate lifting forces. Contrary to our hypothesis, the OE and MI-10 groups maintained the effect of the illusion post-training. In the MI-2 group, perception of the bricks’ weight reverted to the participant’s prior belief that large objects are heavy and they correspondingly adjusted their lifting force post-training. These results demonstrate that perceptual and motor processes are engaged during MI, and that the simulation of the motor component of the movement during MI guides the performed action.

Here we present a task developed to probe implicit learning of a complex motor skill. This task addresses limitations related to task complexity noted in the literature for methods investigating implicit motor learning, namely the serial reaction time task and continuous tracking task. Specifically, the serial reaction time task is limited by the kinematic simplicity of the required movement and the continuous tracing task faces time-on-task confounds and limitations in the control of task difficulty. The task presented herein addresses these issues by employing a kinematically complex multi-articular movement that controls factors that contribute to task difficulty: stimulus animation velocity and trajectory complexity. Accordingly, our objective was to validate the use of this task in probing implicit motor learning, hypothesizing that participants would learn one of the repeating stimuli implicitly. Participants engaged in six blocks of training whereby they first observed and then reproduced a seemingly random complex trajectory. Repeated trajectories were embedded amongst random trajectories. In line with the hypothesis, error for the repeated trajectories was decreased in comparison to that observed for the random trajectories and 73% of participants were unable to identify one of the repeated trajectories, demonstrating the occurrence of implicit learning. While the task requires minor alteration to optimize learning, ultimately the findings underline the task’s potential to investigate implicit learning of a complex motor skill.

Theories of motor imagery conflict in their account of what happens during an imagined movement, with some suggesting that movement is simulated while others suggest it involves creating and elaborating upon an internal representation of the movement. Here we report evidence that imagery involves the simulation of a movement and that it varies in accuracy. Two groups of participants performed a motor task focused on challenging movement execution either overtly or via motor imagery. Overt performance was used to model expected performance given required movement characteristics (i.e., speed, complexity, familiarity), which was then compared with self-reported accuracy during imagery. Movement characteristics had a large effect on self-reported accuracy compared with a small effect of imagery vividness. Self-reported accuracy improved across trials with familiar movements compared with novel movements in a similar manner for each group. The complexity of the imagined movement did not influence movement time during imagery or overt trials, further suggesting that imagined movements are simulated rather than abstractly represented. Our results therefore support models of motor imagery that involve the simulation of a movement and its viability, which may be the basis of imagery-based motor learning.

Motor learning relies on adjusting the performance of movements via error detection and correction. How motor learning proceeds via motor imagery, the imagination of movement, is not understood. Motor imagery-based learning is thought to rely on comparing the predicted effect of movement, resulting from the forward model, against its intended effect. Whether motor imagery-based learning uses the observed effect of movement, simulated in motor imagery, to make comparisons to the intended effect to permit error detection and correction, is an open question. To address this, transcranial magnetic stimulation was used to inhibit the left inferior parietal lobe (L_IPL) after each trial of a task requiring participants to reproduce complex trajectories via motor imagery. From past work, we speculated the L_IPL was a candidate for integrating simulated feedback about task performance (simulated observed effects), hypothesizing inhibition of the L_IPL would impair learning, suggesting simulated observed effects of movement are used in motor imagery-based learning. Participants received stimulation to the L_IPL or over the vertex of the head after each trial. Learning was defined as reduced error on a repeated trajectory in comparison to randomly generated trajectories. Regardless of group participants learned, a finding countering our hypothesis, suggesting (a) observed effects of movement are not simulated in motor imagery; (b) the L_IPL is not involved in integrating simulated observed effects of movement; or (c) the timing of the stimulation did not align with the speculated role of the L_IPL. Results encourage further research probing simulated feedback in motor imagery and its neural correlates. (PsycInfo Database Record (c) 2022 APA, all rights reserved).