Walking and Thinking - Brain Activity During Complex Walking in Stroke

BACKGROUND Stroke is one of the leading causes of mortality and disability in the world and the prevalence of stroke-related disability is expected to increase globally. In Sweden, about 29,000 individuals are affected by stroke every year. Individuals who have suffered a stroke often experience a high incidence of motor and cognitive impairment which are associated with insufficient blood supply and brain oxygenation. One main objective in post-stroke rehabilitation is fostering the capability to walk and navigate the community safely, aiming to uphold independence, facilitate social integration, and encourage active participation in society. Challenges such as impaired balance and compromised turning abilities are often manifested through irregularities in gait and an elevated risk of falls in individual's post-stroke. These difficulties may potentially result in injuries, restrictions in daily activities, and limitations in social engagement for people post stroke.

Complex walking and dual tasking. The achievement of safe and efficient walking relies on a delicate balance between automaticity, involving movements that require minimal attention, and executive control processes, which involve movements requiring attention. The automatic control of walking is essential for ensuring safe ambulation, allowing executive control to be directed towards other crucial aspects of the environment (e.g., navigating in crowded areas) or concurrent tasks (e.g., walking and talking on the phone). Assessment of walking automaticity commonly involves dual-tasking, where two tasks with distinct goals are performed simultaneously, such as walking while engaging in a cognitive task.

Increasing evidence indicates a strong correlation between mobility, and cognitive processes, with people post stroke documented to show the highest level of cognitive-motor interference (i.e., the relative cost of dual-tasking) when performing concurrent working memory and balance tasks. Therefore, developing and establishing robust methods to concurrently assess cortical activity and complex walking hold significant potential to provide insight into cognitive processes driving mobility in people post stroke.

Measurement of cortical activity during complex walking. While functional magnetic resonance imaging (fMRI) is considered the gold standard for functional neuroimaging, its applicability is constrained when studying gait and balance is limited. Functional near-infrared spectroscopy (fNIRS) is a novel and non-invasive imaging method that utilizes the optical properties of neuronal activity to measure changes in the concentration of oxygenated and deoxygenated hemoglobin in cortical regions. This new technology combined with the measurement of behavior (i.e., gait parameters) has the potential to measure real-time cortical activity during ecologically valid states at low costs. This is of importance for health science who often aim to study individuals' capacities to be active and participate in everyday life activities.

This study builds on previous work done by our research team, who developed and tested the feasibility of using fNIRS to measure cortical activity during different complex walking conditions in healthy adults. Promising results were found in the pilot study, and the research team further developed the protocol to include people with Parkinson's and multiple sclerosis. To date few studies have used fNIRS to investigate complex walking in people post stroke and these studies have several limitations which include homogenous and small cohorts.

The investigators are in a strong position to carry out this truly innovative research. The findings of this project will enrich the knowledge of cognitive processes driving mobility and dual tasking in people post stroke, which in turn, could facilitate the development of effective strategies and novel interventions.

PURPOSE AND GOALS The overarching purpose of this project is to clinically assess motor cognitive performance during complex walking and dual-tasking conditions by integrating a non-invasive measure of brain activity i.e. fNIRS and objective assessments of motor behavior in people post stroke. The goals of this project are to 1) validate complex walking protocols developed previously for people with neurological diseases for evaluating motor-cognitive performance and assessing brain activity using fNIRS in individual's post-stroke. 2) investigate differences in cortical activity with walking performance during complex walking tasks and compare it to healthy adults, people with Parkinson's disease and multiple sclerosis; 3) establish correlations between fNIRS-derived cortical activity and walking performance metrics (i.e., gait speed and stride length) to gain insight into the relationship between brain activity, cognitive performance, disease severity and functional outcomes in people post stroke.

MATERIALS AND METHODS Study Participants: A sample of 50 participants post stroke will be recruited through patient organizations, advertisements and established collaborating clinical sites in Stockholm (e.g., Karolinska University Hospital and Stora Sköndal).

Inclusion criteria

Individuals with a stroke ≥ 6 months confirmed by a clinical diagnosis according to established criteria before study enrollment and being able to ambulate continuously indoors with/without a walking aid for ≥5 minutes. Exclusion criteria: Individuals post stroke with cognitive impairment, severe neglect, and global aphasia affecting the ability to provide written informed consent, severe perceptual problems (e.g., spatial neglect) or severe freezing of gait.

Data collection: Prior to data collection, individuals meeting the inclusion criteria will receive written and oral information about the study. All included study participants will attend 2 sessions at the uMOVE core facility, Karolinska University Hospital, Stockholm. The assessment detailed below consists of interviews, clinical tests, gait measures, and cortical activity measurements using fNIRS and will be conducted a week apart.

Session 1 comprises:

• Structured interviews of personal factors (e.g., age, sex, height, weight, educational level and medical history) and environmental factors (e.g., living situation, employment status, use of assistive devices).
• Cognitive performance assessed using the Montreal Cognitive Assessment (MoCA).
• Assessment of cortical brain activity during 3 walking protocols using fNIRS. Cortical brain activity will be measured during three walking protocols with different complex walking conditions using a block design. Each block consists of 20 seconds of stimulus followed by 15 seconds of rest period to allow for baseline measures. Protocol 1 consists of walking straight, standing still while performing an auditory Stroop task, and straight walking while performing the auditory Stroop task. Protocol 2 consists of walking straight and navigated walking. Protocol 3 consists of navigated walking and navigated walking while performing an auditory Stroop task. In the navigation condition, participants will be directed to navigate through a maze featuring a randomized arrangement of turns ranging from 90° to 225° to the left and right. The maze incorporates yellow, red, and blue cones. Participants will be specifically instructed to walk around the cones, alternating between yellow and red cones, while ignoring the blue cones. The auditory Stroop task consists of the two Swedish words for 'high' and 'low', verbally presented in a congruent and incongruent high and low pitch level through headphones.

Cortical brain activity - Changes in oxygenated (HbO) and deoxygenated (HHb) hemoglobin in the prefrontal cortex will be measured using the NIRSPORT 2 (NIRx Medizintechnik, Berlin, Germany) continuous wave fNIRS device. During each protocol, the participants will be fitted with an fNIRS cap with 16 sources and 16 detectors, and a controller box attached to a backpack harness. The source optodes transmit infrared light at 760 and 850 nm and the detector optodes record changes in HbO and HHb at 10 Hz. Optode placement will be arranged according to the international 10-20 system over the prefrontal area.The fNIRS data will be streamed wirelessly to a local computer using the Aurora software.

Measurement of gait and behavioral parameters - Simultaneously gait parameters (e.g., walking speed and cadence) will be measured using 3 inertial measurement units (OPAL APDM inc.) positioned at on top of each foot and around the lumbar. The sensors will continuously stream data to a local computer using the Mobility LabTM software. To measure mistakes during navigational walking the investigators will mount a GoPro camera on the chest of each participant pointing to the feet. Additionally, the auditory Stroop verbal responses will be recorded through headphones using the Audacity software (version 2.4.2).

Session 2 comprises questionnaires and clinical assessments:

• Stroke Severity measured using the National Institutes of Health Stroke Scale (NIHSS).
• Stroke-specific health status measured using the Stroke Impact Scale (SIS).
• Physical impairment measured using the Chedoke McMaster Stroke Assessment.
• Fatigue measured using the Fatigue Severity Scale (FSS).
• Walking ability measured using the Walk-12G.
• Balance performance measured using the Mini-BESTest.
• Anxiety and Depression measured using the Hospital Anxiety and Depression Scale (HADS).
• Cognitive performance will be assessed using the Montreal Cognitive Assessment (MoCA), Trail Making Tests, Ray Auditory Verbal Learning Test (RAVLT) and Color and Word Test from the Delis-Kaplan Function System ( D-KEFS).

Inclusion criteria

• 18 years or older
• with a stroke ≥6 months confirmed by a clinical diagnosis
• with the ability to walk with or without a walking aid for ≥ 5 min

Exclusion criteria

• Individuals post stroke with cognitive impairment
• severe neglect
• global aphasia affecting the ability to provide written informed consent
• severe perceptual problems or severe freezing of gait