Elizabeth Dao

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.

Role of the primary somatosensory cortex in motor learning: An rTMS study

Somatosensation is thought to play an important role in skilled motor learning. The present study investigated how healthy adults learn a continuous implicit motor task when somatosensation is altered by 1 Hz repetitive transcranial magnetic stimulation (rTMS) delivered over the primary somatosensory cortex (S1). Twenty-seven right-handed participants enrolled in a two-part experiment. In Experiment 1, we verified that 20 min of 1 Hz rTMS over S1 disrupted cutaneous somatosensation (indexed by two-point discrimination) in the wrist/hand; the impact of 1 Hz rTMS on wrist proprioception (tested by limb-position matching) was variable. Sham rTMS had no effect on either measure. We exploited these effects in Experiment 2 by pairing either 1 Hz or sham rTMS with practice of a continuous tracking task over two separate sessions on different days. Implicit motor learning was indexed on a third, separate retention test day when no rTMS was delivered. Across practice in Experiment 2, both the 1 Hz and sham rTMS groups showed improved tracking performance; however, 1 Hz rTMS was associated with less accurate tracking and smaller improvements in performance. Importantly, at the no rTMS retention test the effects of altering sensation with stimulation over S1 were still evident in the persistently less accurate tracking behavior of the 1 Hz rTMS group. The current study shows that disruption of somatosensation during task practice impairs the magnitude of change associated with motor learning, perhaps through the development of an inaccurate internal model.

Continuous theta burst stimulation over the contralesional sensory and motor cortex enhances motor learning post-stroke

The current study investigated the contributions of contralesional primary somatosensory cortex (S1c) to motor learning deficits post-stroke. For three days, continuous theta burst (cTBS) was delivered over the contralesional hemisphere prior to practicing a serial targeting task. cTBS was delivered over either S1c, contralesional primary motor cortex (M1c) or as control stimulation (n=4/group). Change in motor ability was assessed from initial performance to a delayed retention test using a serial targeting task and a subset of items from the Wolf Motor Function Test. Practice preceded by cTBS over either M1c or S1c resulted in large decreases in movement time compared to practice preceded by control stimulation. M1c cTBS resulted in larger decreases in peak velocity and peak acceleration compared to control and S1c cTBS. In contrast, S1c cTBS resulted in larger reductions in time to initiate movement and time to complete the WMFT compared to control and M1c cTBS. These preliminary findings suggest that stimulation of either M1c or S1c can enhance the benefits of practice. However, changes in M1c and S1c excitability may contribute to different aspects of post-stroke motor deficits that may differentially impact rehabilitation.

Mind wandering and motor control: off-task thinking disrupts the online adjustment of behavior

Mind wandering episodes have been construed as periods of “stimulus-independent” thought, where our minds are decoupled from the external sensory environment. In two experiments, we used behavioral and event-related potential (ERP) measures to determine whether mind wandering episodes can also be considered as periods of “response-independent” thought, with our minds disengaged from adjusting our behavioral outputs. In the first experiment, participants performed a motor tracking task and were occasionally prompted to report whether their attention was “on-task” or “mind wandering.” We found greater tracking error in periods prior to mind wandering vs. on-task reports. To ascertain whether this finding was due to attenuation in visual perception per se vs. a disruptive effect of mind wandering on performance monitoring, we conducted a second experiment in which participants completed a time-estimation task. They were given feedback on the accuracy of their estimations while we recorded their EEG, and were also occasionally asked to report their attention state. We found that the sensitivity of behavior and the P3 ERP component to feedback signals were significantly reduced just prior to mind wandering vs. on-task attentional reports. Moreover, these effects co-occurred with decreases in the error-related negativity elicited by feedback signals (fERN), a direct measure of behavioral feedback assessment in cortex. Our findings suggest that the functional consequences of mind wandering are not limited to just the processing of incoming stimulation per se, but extend as well to the control and adjustment of behavior.

Mind wandering and the adaptive control of attentional resources

Mind wandering is a natural, transient state wherein our neurocognitive systems become temporarily decoupled from the external sensory environment as our thoughts drift away from the current task at hand. Yet despite the ubiquity of mind wandering in everyday human life, we rarely seem impaired in our ability to adaptively respond to the external environment when mind wandering. This suggests that despite widespread neurocognitive decoupling during mind wandering states, we may nevertheless retain some capacity to attentionally monitor external events. But what specific capacities? In Experiment 1, using traditional performance measures, we found that both volitional and automatic forms of visual–spatial attentional orienting were significantly attenuated when mind wandering. In Experiment 2, however, ERPs revealed that, during mind wandering states, there was a relative preservation of sensitivity to deviant or unexpected sensory events, as measured via the auditory N1 component. Taken together, our findings suggest that, although some selective attentional processes may be subject to down-regulation during mind wandering, we may adaptively compensate for these neurocognitively decoupled states by maintaining automatic deviance–detection functions.

Resistance Training and White Matter Lesion Progression in Older Women: Exploratory Analysis of a 12‐Month Randomized Controlled Trial

To assess whether resistance training (RT) slows the progression of white matter lesions (WMLs) in older women.

One hertz repetitive transcranial magnetic stimulation over dorsal premotor cortex enhances offline motor memory consolidation for sequence-specific implicit learning.

Consolidation of motor memories associated with skilled practice can occur both online, concurrent with practice, and offline, after practice has ended. The current study investigated the role of dorsal premotor cortex (PMd) in early offline motor memory consolidation of implicit sequence‐specific learning. Thirty‐three participants were assigned to one of three groups of repetitive transcranial magnetic stimulation (rTMS) over left PMd (5 Hz, 1 Hz or control) immediately following practice of a novel continuous tracking task. There was no additional practice following rTMS. This procedure was repeated for 4 days. The continuous tracking task contained a repeated sequence that could be learned implicitly and random sequences that could not. On a separate fifth day, a retention test was performed to assess implicit sequence‐specific motor learning of the task. Tracking error was decreased for the group who received 1 Hz rTMS over the PMd during the early consolidation period immediately following practice compared with control or 5 Hz rTMS. Enhanced sequence‐specific learning with 1 Hz rTMS following practice was due to greater offline consolidation, not differences in online learning between the groups within practice days. A follow‐up experiment revealed that stimulation of PMd following practice did not differentially change motor cortical excitability, suggesting that changes in offline consolidation can be largely attributed to stimulation‐induced changes in PMd. These findings support a differential role for the PMd in support of online and offline sequence‐specific learning of a visuomotor task and offer converging evidence for competing memory systems.

Examining the effect of the relationship between falls and mild cognitive impairment on mobility and executive functions in community-dwelling older adults

Cognitive impairment and falls are geriatric “giants” that significantly increase morbidity and mortality in older adults. Even mild cognitive impairment (MCI) is a significant risk factor for falls.1 Clinical gait abnormalities including slow gait and falls are early biomarkers of cognitive impairment,2 suggesting that impaired cognitive function and mobility share common underlying pathophysiology.

Change in body fat mass is independently associated with executive functions in older women: a secondary analysis of a 12-month randomized controlled trial.

Objectives To investigate the independent contribution of change in sub-total body fat and lean mass to cognitive performance, specifically the executive processes of selective attention and conflict resolution, in community-dwelling older women. Methods This secondary analysis included 114 women aged 65 to 75 years old. Participants were randomly allocated to once-weekly resistance training, twice-weekly resistance training, or twice-weekly balance and tone training. The primary outcome measure was the executive processes of selective attention and conflict resolution as assessed by the Stroop Test. Sub-total body fat and lean mass were measured by dual-energy x-ray absorptiometry (DXA) to determine the independent association of change in both sub-total body fat and sub-total body lean mass with Stroop Test performance at trial completion. Results A multiple linear regression model showed reductions in sub-total body fat mass to be independently associated with better performance on the Stroop Test at trial completion after accounting for baseline Stroop performance, age, baseline global cognitive state, baseline number of comorbidities, baseline depression, and experimental group. The total variance explained was 39.5%; change in sub-total body fat mass explained 3.9% of the variance. Change in sub-total body lean mass was not independently associated with Stroop Test performance (P>0.05). Conclusion Our findings suggest that reductions in sub-total body fat mass – not sub-total lean mass – is associated with better performance of selective attention and conflict resolution.

Aerobic exercise increases cortical white matter volume in older adults with vascular cognitive impairment: A 6-month randomized controlled trial

Age at Baseline M 1⁄4 23.67 M 1⁄4 24.43 M 1⁄4 22.97 Estimated IQ (WTAR) M 1⁄4 110.19 M 1⁄4 110.73 M 1⁄4 109.69 MMSE Score M 1⁄4 29.48 M 1⁄4 29.50 M 1⁄4 29.45 Gender % (n) % (n) % (n) Male 44.4 (28) 46.7 (14) 42.4 (14) Female 55.6 (35) 53.3 (16) 57.6 (19) Level of Education Less then High School 3.2 (2) 6.7 (2) 0.0 (0) High School 19.0 (12) 20.0 (6) 18.2 (6) Associates Degree 7.9 (5) 13.3 (4) 3.0 (1) Current College Student 50.8 (32) 40.0 (12) 60.6 (20) Bachelors Degree 15.9 (2) 20.0 (6) 12.1 (4) Graduate Degree 3.2 (2) 0.0 (0) 2(6.1) Race / Ethnicity White (Not Hispanic) 69.8 (44) 63.3 (19) 75.8 (25) Black / African American 4.8 (3) 6.7 (2) 3.0 (1) Hispanic 11.1 (7) 6.7 (2) 15.2 (5) Asian / Pacific Islander 7.9 (5) 10.0 (3) 6.1 (2) American Indian 1.6 (1) 3.3 (1) 0.0 (0) Mixed / Multiple 4.8 (3) 10.0 (3) 0.0 (0)