Publications by authors named "Natasha Talwar"

4 Publications

  • Page 1 of 1

Functional magnetic resonance imaging of the trail-making test in older adults.

PLoS One 2020 12;15(5):e0232469. Epub 2020 May 12.

Keenan Research Centre for Biomedical Science, St. Michael's Hospital, Toronto, Canada.

The trail-making test (TMT) is a popular neuropsychological test, which is used extensively to measure cognitive impairment associated with neurodegenerative disorders in older adults. Behavioural performance on the TMT has been investigated in older populations, but there is limited research on task-related brain activity in older adults. The current study administered a naturalistic version of the TMT to a healthy older-aged population in an MRI environment using a novel, MRI-compatible tablet. Functional MRI was conducted during task completion, allowing characterization of the brain activity associated with the TMT. Performance on the TMT was evaluated using number of errors and seconds per completion of each link. Results are reported for 36 cognitively healthy older adults between the ages of 52 and 85. Task-related activation was observed in extensive regions of the bilateral frontal, parietal, temporal and occipital lobes as well as key motor areas. Increased age was associated with reduced brain activity and worse task performance. Specifically, older age was correlated with decreased task-related activity in the bilateral occipital, temporal and parietal lobes. These results suggest that healthy older aging significantly affects brain function during the TMT, which consequently may result in performance decrements. The current study reveals the brain activation patterns underlying TMT performance in a healthy older aging population, which functions as an important, clinically-relevant control to compare to pathological aging in future investigations.
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July 2020

Functional MRI of Letter Cancellation Task Performance in Older Adults.

Front Hum Neurosci 2019 16;13:97. Epub 2019 Apr 16.

Physical Sciences Platform, Sunnybrook Research Institute (SRI), Toronto, ON, Canada.

The Letter Cancellation Task (LCT) is a widely used pen-and-paper probe of attention in clinical and research settings. Despite its popularity, the neural correlates of the task are not well understood. The present study uses functional magnetic resonance imaging (fMRI) and specialized tablet technology to identify the neural correlates of the LCT in 32 healthy older adults between 50-85 years of age, and further investigates the effect of healthy aging on performance. Subjects performed the LCT in its standard pen-and-paper administration and with the tablet during fMRI. Performance on the tablet was significantly slower than on pen-and-paper, with both response modes showing slower performance as a function of age. Across all ages, bilateral brain activation was observed in the cerebellum, superior temporal lobe, precentral gyrus, frontal gyrus, and occipital and parietal areas. Increasing age correlated with reduced brain activity in the supplementary motor area, middle occipital gyrus, medial and inferior frontal gyrus, cerebellum and putamen. Better LCT performance was correlated with increased activity in the middle frontal gyrus, and reduced activity in the cerebellum. The brain regions activated are associated with visuospatial attention and motor control, and are consistent with the neural correlates of LCT performance previously identified in lesion studies.
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April 2019

The Neural Correlates of the Clock-Drawing Test in Healthy Aging.

Front Hum Neurosci 2019 5;13:25. Epub 2019 Feb 5.

Keenan Research Centre for Biomedical Science, St. Michael's Hospital, Toronto, ON, Canada.

The clock-drawing test (CDT) is an important neurocognitive assessment tool, widely used as a screening test for dementia. Behavioral performance on the test has been studied extensively, but there is scant literature on the underlying neural correlates. To administer the CDT naturalistically to a healthy older aging population in an MRI environment, and characterize the brain activity associated with test completion. Blood-oxygen-level dependent (BOLD) functional MRI was conducted as participants completed the CDT using novel tablet technology. Brain activity during CDT performance was contrasted to rest periods of visual fixation. Performance on the CDT was evaluated using a standardized scoring system (Rouleau score) and time to test completion. To assess convergent validity, performance during fMRI was compared to performance on a standard paper version of the task, administered in a psychometric testing room. Study findings are reported for 33 cognitively healthy older participants aged 52-85. Activation was observed in the bilateral frontal, occipital and parietal lobes as well as the supplementary motor area and precentral gyri. Increased age was significantly correlated with Rouleau scores on the clock number drawing (R2) component (rho = -0.55, < 0.001); the clock hand drawing (R3) component (rho = -0.50, < 0.005); and the total clock (rho = -0.62, < 0.001). Increased age was also associated with decreased activity in the bilateral parietal and occipital lobes as well as the right temporal lobe and right motor areas. This imaging study characterizes the brain activity underlying performance of the CDT in a healthy older aging population using the most naturalistic version of the task to date. The results suggest that the functions of the occipital and parietal lobe are significantly altered by the normal aging process, which may lead to performance decrements.
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February 2019

Midline posterior glossectomy and lingual tonsillectomy in obese and nonobese children with down syndrome: Biomarkers for success.

Laryngoscope 2017 03 27;127(3):757-763. Epub 2016 Jun 27.

Division of Respiratory Medicine, Hospital for Sick Children, Toronto, Canada.

Objectives/hypothesis: To examine outcomes following midline posterior glossectomy (MPG) plus lingual tonsillectomy (LT) for the treatment of significant obstructive sleep apnea (OSA) in children with Down syndrome (DS).

Methods: Patients with DS who had persistent OSA following tonsillectomy and adenoidectomy (TA) and were relatively intolerant of positive airway pressure (PAP) therapy were evaluated by physical examination and sleep/CINE magnetic resonance imaging to determine the etiology of upper airway obstruction. Patients with relative macroglossia underwent MPG plus LT if required. Successful surgical outcome was defined as the resolution of OSA or the ability to tolerate PAP.

Results: Thirteen children (8 male, 5 female), mean (standard deviation) age 14.2 (4.0) years underwent MPG plus LT. Fifty-four percent of patients were obese (Body mass index [BMI] > 95th centile) and 8% were overweight (BMI 85th-95th centile) preoperatively. All patients underwent pre- and postoperative polysomnography. Postoperatively, the obstructive apnea-hypopnea index fell significantly from 47.0/hour to 5.6/hour (P <.05) in normal weight individuals who did not become obese, but not in obese patients or those who became obese postoperatively. Successful surgical outcome was seen in all (N = 6) children who were normal weight or overweight preoperatively compared with none who were obese preoperatively (N = 7).

Conclusion: Midline posterior glossectomy and LT are beneficial in normal weight and overweight children with DS who have persistent OSA following TA and are intolerant of PAP therapy. Obesity pre- or postoperatively portends a worse prognosis following MPG, suggesting that aggressive weight loss initiatives should be considered as an adjunct to surgery in this population.

Level Of Evidence: 4. Laryngoscope, 127:757-763, 2017.
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March 2017