Todd C. Handy

Resistance Training and Executive Functions: A 12-Month Randomized Controlled Trial

BACKGROUND Cognitive decline among seniors is a pressing health care issue. Specific exercise training may combat cognitive decline. We compared the effect of once-weekly and twice-weekly resistance training with that of twice-weekly balance and tone exercise training on the performance of executive cognitive functions in senior women. METHODS In this single-blinded randomized trial, 155 community-dwelling women aged 65 to 75 years living in Vancouver were randomly allocated to once-weekly (n = 54) or twice-weekly (n = 52) resistance training or twice-weekly balance and tone training (control group) (n = 49). The primary outcome measure was performance on the Stroop test, an executive cognitive test of selective attention and conflict resolution. Secondary outcomes of executive cognitive functions included set shifting as measured by the Trail Making Tests (parts A and B) and working memory as assessed by verbal digit span forward and backward tests. Gait speed, muscular function, and whole-brain volume were also secondary outcome measures. RESULTS Both resistance training groups significantly improved their performance on the Stroop test compared with those in the balance and tone group (P < or = .03). Task performance improved by 12.6% and 10.9% in the once-weekly and twice-weekly resistance training groups, respectively; it deteriorated by 0.5% in the balance and tone group. Enhanced selective attention and conflict resolution was significantly associated with increased gait speed. Both resistance training groups demonstrated reductions in whole-brain volume compared with the balance and tone group at the end of the study (P < or = .03). CONCLUSION Twelve months of once-weekly or twice-weekly resistance training benefited the executive cognitive function of selective attention and conflict resolution among senior women. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00426881.

Meta-awareness, perceptual decoupling and the wandering mind

Mind wandering (i.e. engaging in cognitions unrelated to the current demands of the external environment) reflects the cyclic activity of two core processes: the capacity to disengage attention from perception (known as perceptual decoupling) and the ability to take explicit note of the current contents of consciousness (known as meta-awareness). Research on perceptual decoupling demonstrates that mental events that arise without any external precedent (known as stimulus independent thoughts) often interfere with the online processing of sensory information. Findings regarding meta-awareness reveal that the mind is only intermittently aware of engaging in mind wandering. These basic aspects of mind wandering are considered with respect to the activity of the default network, the role of executive processes, the contributions of meta-awareness and the functionality of mind wandering.

Going awol in the brain: Mind wandering reduces cortical analysis of external events

Converging evidence from neuroscience suggests that our attention to the outside world waxes and wanes over time. We examined whether these periods of mind wandering are associated with reduced cortical analysis of the external environment. Participants performed a sustained attention to response task in which they responded to frequent nontargets (digits 09) and withheld responses for infrequent targets (the letter X). Mind wandering was defined both behaviorally, indicated by a failure to withhold a response to a target, and subjectively, via self-report at a thought probe. The P300 event-related potential component for nontargets was reduced prior to both the behavioral and subjective reports of mind wandering, relative to periods of being on-task. Regression analysis of P300 amplitude revealed significant common variance between behavioral and subjective markers of mind wandering, suggesting that both markers reflect a common underlying mental state. Finally, control analysis revealed that the effect of mind wandering on the P300 could not be ascribed to changes in motor activity nor was it associated with general arousal. Our data suggest that when trying to engage attention in a sustained manner, the mind will naturally ebb and flow in the depth of cognitive analysis it applies to events in the external environment.

Resistance training promotes cognitive and functional brain plasticity in seniors with probable mild cognitive impairment.

Lindsay S. Nagamatsu, MA1,2,3, Todd C. Handy, PhD1,2, C. Liang Hsu, BSc2,3,4, Michelle Voss, PhD5, and Teresa Liu-Ambrose, PT, PhD2,3,4 1Department of Psychology, University of British Columbia, Vancouver, BC, Canada 2The Brain Research Centre, Vancouver Coastal Health Research Institute, University of British Columbia, Vancouver, BC, Canada 3The Centre for Hip Health and Mobility, Vancouver Coastal Health Research Institute, University of British Columbia, Vancouver, BC, Canada 4Department of Physical Therapy, University of British Columbia, Vancouver, BC, Canada 5University of Illinois at Urbana-Champaign, The Beckman Institute for Advanced Science and Technology

Attention and spatial selection: Electrophysiological evidence for modulation by perceptual load

Behavioral data have suggested that perceptual load can modulate spatial selection by influencing the allocation of attentional resources at perceptual-level processing stages (Lavie & Tsal, 1994). To directly test this hypothesis, event-related potentials (ERPs) were recorded for both low- and high-perceptual-load targets in a probabilistic spatial cuing paradigm. The results from three experiments showed that, as measured by the lateral occipital P1 and Nl ERP components, the magnitude of spatially selective processing in extrastriate visual cortex increased with perceptual load. Furthermore, these effects on spatial selection were found in the P1 at lower levels of perceptual load than in the N1. The ERP data thus provide direct electrophysiological support for proposals that link perceptual load to early spatial selection in visual processing. However, our findings suggest a relatively broader model—where perceptual load is but one of many factors mediating early selection.

Resistance training and functional plasticity of the aging brain: a 12-month randomized controlled trial

Maintaining functional plasticity of the cortex is essential for healthy aging and aerobic exercise may be an effective behavioral intervention to promote functional plasticity among seniors. Whether resistance training has similar benefits on functional plasticity in seniors has received little investigation. Here we show that 12 months of twice-weekly resistance training led to functional changes in 2 regions of cortex previously associated with response inhibition processes-the anterior portion of the left middle temporal gyrus and the left anterior insula extending into lateral orbital frontal cortex-in community-dwelling senior women. These hemodynamic effects co-occurred with improved task performance. Our data suggest that resistance training improved flanker task performance in 2 ways: (1) an increased engagement of response inhibition processes when needed; and (2) a decreased tendency to prepare response inhibition as a default state. However, we highlight that this effect of resistance training was only observed among those who trained twice weekly; participants of the once-weekly resistance training did not demonstrate comparable response profiles, both in behavioral performance and hemodynamic activity in cortex. In sum, our findings suggest that twice-weekly resistance training in seniors can positively impact functional plasticity of response inhibition processes in cortex, and that it does so in a manner that complements the effects on selective attention that have previously been ascribed to aerobic exercise in seniors.

Promoting Novelty in Vision: Inhibition of Return Modulates Perceptual-Level Processing

To facilitate visual search of complex scenes, information arising from recently attended locations is subject to a selective inhibition in processing known as inhibition of return (IOR). Although the mechanisms of IOR remain unresolved, both motor and perceptual influences have been proposed based on reaction time (RT) studies. Here we report the results of two reflexive cuing studies in which signal detection methodology was employed to directly examine the effects of IOR on perception. IOR was found to be associated with a significant reduction in the accuracy of target discriminations at recently attended locations. Further, these effects of IOR on response accuracy were independent of whether emphasis was placed on the speed of responding. These results provide the first direct evidence that IOR can affect the perceptual quality of visual processing.

Perceptual Load and Visuocortical Processing: Event-Related Potentials Reveal Sensory-Level Selection

Behavioral evidence suggests that the processing of parafoveal stimuli decreases as the perceptual demands of a task at fixation increase. However, it remains unclear whether or not this effect of perceptual load occurs during initial sensory-level processing at early stages of visuocortical analysis. Using event-related potential measures, we found that increasing the perceptual load of foveal targets led to a significant decrease in the sensory-evoked response to parafoveal stimuli. Moreover, these effects were observed using two different operational definitions of perceptual load. This result indicates that perceptual load affects the flow of information during the initial stages of visuocortical processing.

Extensive Individual Differences in Brain Activations Associated with Episodic Retrieval are Reliable Over Time

The localization of brain functions using neuroimaging techniques is commonly dependent on statistical analyses of groups of subjects in order to identify sites of activation, particularly in studies of episodic memory. Exclusive reliance on group analysis may be to the detriment of understanding the true underlying cognitive nature of brain activations. In the present study, we found that the patterns of brain activity associated with episodic retrieval are very distinct for individual subjects from the patterns of brain activity at the group level. These differences go beyond the relatively small variations due to cyctoarchitectonic differences or spatial normalization. We quantify this individual variability by cross-correlating volumes of brain images. We demonstrate that individual patterns of brain activity are reliable over time despite their extensive variability. We suggest that varied but reliable individual patterns of significant brain activity may be indicative of different cognitive strategies used to produce a recognition response. We believe that individual analysis in conjunction with group analysis may be critical to fully understanding the relationship between retrieval processes and underlying brain regions.

Slow fluctuations in attentional control of sensory cortex

Top–down control of visual sensory cortex has long been tied to the orienting of visual spatial attention on a rapid, moment-to-moment basis. Here, we examined whether sensory responses in visual cortex are also modulated by natural and comparatively slower fluctuations in whether or not one is paying attention to the task at hand. Participants performed a simple visual discrimination task at fixation as the ERPs to task-irrelevant probes in the upper visual periphery were recorded. At random intervals, participants were stopped and asked to report on their attentional state at the time of stoppage—either “on-task” or “off-task.” ERPs to the probes immediately preceding these subjective reports were then examined as a function of whether attention was in an on-task versus off-task state. We found that sensory-evoked responses to the probes were significantly attenuated during off-task relative to on-task states, as measured by the visual P1 ERP component. In two additional experiments, we replicated this effect while (1) finding that off-task sensory attenuation extends to the auditory domain, as measured by the auditory N1 ERP component, and (2) eliminating state-dependent shifts in general arousal as a possible explanation for the effects. Collectively, our findings suggest that sensory gain control in cortex is yoked to the natural ebb and flow in how much attention we pay to the current task over time.