The participants in Group B will receive tVNS (pulse frequency = 25Hz, pulse duration = 0.3 ms) on the cymba conchae of left outer ear with upper limb exercises.The electrical stimulation will be generated by the neurostimulator (MH8000P; MEDIHIGHTEC MEDICAL CO., LTD., Taiwan). Intensity of tVNS will be individually selected by the participants according to tolerance levels. Previous studies showed that it was effective to improve the upper limb motor function in people with stroke and cognitive function in people with mild cognitive function.

The participants in Group C will receive placebo tSCS and tVNS with upper limb exercises, where the stimulation will be delivered by placebo-TENS device with disconnected electrical circuit.

The Montreal Cognitive Assessment (MoCA) is a screening tool to detect cognitive impairment of an individual with a total score of 30. The MoCA assesses different cognitive domains, including executive functioning, immediate and delayed memory, visuospatial abilities, attention, working memory, language, and orientation to time and place. It can identify dementia from controls with a sensitivity of 92.3% and specificity of 91.8% with a cut-off score of 22.

The Montreal Cognitive Assessment (MoCA) is a screening tool to detect cognitive impairment of an individual with a total score of 30. The MoCA assesses different cognitive domains, including executive functioning, immediate and delayed memory, visuospatial abilities, attention, working memory, language, and orientation to time and place. It can identify dementia from controls with a sensitivity of 92.3% and specificity of 91.8% with a cut-off score of 22.

The Montreal Cognitive Assessment (MoCA) is a screening tool to detect cognitive impairment of an individual with a total score of 30. The MoCA assesses different cognitive domains, including executive functioning, immediate and delayed memory, visuospatial abilities, attention, working memory, language, and orientation to time and place. It can identify dementia from controls with a sensitivity of 92.3% and specificity of 91.8% with a cut-off score of 22.

The Montreal Cognitive Assessment (MoCA) is a screening tool to detect cognitive impairment of an individual with a total score of 30. The MoCA assesses different cognitive domains, including executive functioning, immediate and delayed memory, visuospatial abilities, attention, working memory, language, and orientation to time and place. It can identify dementia from controls with a sensitivity of 92.3% and specificity of 91.8% with a cut-off score of 22.

The Wolf Motor Function Test (WMFT) evaluates the motor ability of upper extremity through timed and functional tasks. It consists of 17 tasks which is rated by 6-point scale which ranges from 0 (no attempt made to use the more affected upper extremity) to 5 (movement appears to be normal). The time for completing each functional task is also recorded, with a maximum of 120 seconds allow for each task. The higher score represents the better functioning level of upper extremity, Excellent test-retest reliability (ICC = 0.92 - 0.99) has been demonstrated in people with stroke.

The Wolf Motor Function Test (WMFT) evaluates the motor ability of upper extremity through timed and functional tasks. It consists of 17 tasks which is rated by 6-point scale which ranges from 0 (no attempt made to use the more affected upper extremity) to 5 (movement appears to be normal). The time for completing each functional task is also recorded, with a maximum of 120 seconds allow for each task. The higher score represents the better functioning level of upper extremity, Excellent test-retest reliability (ICC = 0.92 - 0.99) has been demonstrated in people with stroke.

The Wolf Motor Function Test (WMFT) evaluates the motor ability of upper extremity through timed and functional tasks. It consists of 17 tasks which is rated by 6-point scale which ranges from 0 (no attempt made to use the more affected upper extremity) to 5 (movement appears to be normal). The time for completing each functional task is also recorded, with a maximum of 120 seconds allow for each task. The higher score represents the better functioning level of upper extremity, Excellent test-retest reliability (ICC = 0.92 - 0.99) has been demonstrated in people with stroke.

A hand-held dynamometer (Model 01165; Lafayette Instrument, Indiana, USA) will be used to measure the muscle force generated by biceps brachii and triceps brachii muscles of affected and unaffected sides. The participant will be instructed to perform isometric contraction and resistance will be applied by the examiner to avoid movement of the arm during the measurement. Two trials will be performed for each muscle group and the mean force of two trials will be recorded.

The Digit Span Test (DST) consists of two parts to measure the verbal short-term memory and working memory of an individual, which are digit span forwards and digit span backwards. The participants are presented with a series of numbers. In the digit span forward (DSF), they are required to repeat the numbers in forward order. In the digit span backward (DSB), they are asked to repeat the numbers in reverse order. The length of digits in each string increases from 3 to 9 in DSF and from 2 to 8 in DSB. Two trials are presented at each length. The test is interrupted when participant failed to either trial at equal digit length. If the participants correctly recall the sequence in either first and second trial, 1 point will be scored. The total score of DSF and DSB are 16 and 14 respectively. The intra-rater reliability of DSF and DSB are 0.891 and 0.598 respectively in older adults with neurocognitive disorder.

The Digit Span Test (DST) consists of two parts to measure the verbal short-term memory and working memory of an individual, which are digit span forwards and digit span backwards. The participants are presented with a series of numbers. In the digit span forward (DSF), they are required to repeat the numbers in forward order. In the digit span backward (DSB), they are asked to repeat the numbers in reverse order. The length of digits in each string increases from 3 to 9 in DSF and from 2 to 8 in DSB. Two trials are presented at each length. The test is interrupted when participant failed to either trial at equal digit length. If the participants correctly recall the sequence in either first and second trial, 1 point will be scored. The total score of DSF and DSB are 16 and 14 respectively. The intra-rater reliability of DSF and DSB are 0.891 and 0.598 respectively in older adults with neurocognitive disorder.

The Digit Span Test (DST) consists of two parts to measure the verbal short-term memory and working memory of an individual, which are digit span forwards and digit span backwards. The participants are presented with a series of numbers. In the digit span forward (DSF), they are required to repeat the numbers in forward order. In the digit span backward (DSB), they are asked to repeat the numbers in reverse order. The length of digits in each string increases from 3 to 9 in DSF and from 2 to 8 in DSB. Two trials are presented at each length. The test is interrupted when participant failed to either trial at equal digit length. If the participants correctly recall the sequence in either first and second trial, 1 point will be scored. The total score of DSF and DSB are 16 and 14 respectively. The intra-rater reliability of DSF and DSB are 0.891 and 0.598 respectively in older adults with neurocognitive disorder.

The Digit Span Test (DST) consists of two parts to measure the verbal short-term memory and working memory of an individual, which are digit span forwards and digit span backwards. The participants are presented with a series of numbers. In the digit span forward (DSF), they are required to repeat the numbers in forward order. In the digit span backward (DSB), they are asked to repeat the numbers in reverse order. The length of digits in each string increases from 3 to 9 in DSF and from 2 to 8 in DSB. Two trials are presented at each length. The test is interrupted when participant failed to either trial at equal digit length. If the participants correctly recall the sequence in either first and second trial, 1 point will be scored. The total score of DSF and DSB are 16 and 14 respectively. The intra-rater reliability of DSF and DSB are 0.891 and 0.598 respectively in older adults with neurocognitive disorder.

The Arm Activity Measure (ArmA) is a 20-item questionnaire to assess the difficulties in passive and active upper limb tasks, where section A evaluates the passive function and section B evaluates the active function. It uses a 5-point Likert scale, ranging from 0 (no difficulty) to 4 (unable to do the task). The total score of section A and B are 32 and 52 respectively [59]. The higher score in ArmA indicates more difficulties experienced in activities when using upper limb. Good internal consistency (Cronbach's alpha = 0.85 - 0.96) has been shown in people with upper limb paresis.

The Arm Activity Measure (ArmA) is a 20-item questionnaire to assess the difficulties in passive and active upper limb tasks, where section A evaluates the passive function and section B evaluates the active function. It uses a 5-point Likert scale, ranging from 0 (no difficulty) to 4 (unable to do the task). The total score of section A and B are 32 and 52 respectively [59]. The higher score in ArmA indicates more difficulties experienced in activities when using upper limb. Good internal consistency (Cronbach's alpha = 0.85 - 0.96) has been shown in people with upper limb paresis.

The Arm Activity Measure (ArmA) is a 20-item questionnaire to assess the difficulties in passive and active upper limb tasks, where section A evaluates the passive function and section B evaluates the active function. It uses a 5-point Likert scale, ranging from 0 (no difficulty) to 4 (unable to do the task). The total score of section A and B are 32 and 52 respectively [59]. The higher score in ArmA indicates more difficulties experienced in activities when using upper limb. Good internal consistency (Cronbach's alpha = 0.85 - 0.96) has been shown in people with upper limb paresis.

The Arm Activity Measure (ArmA) is a 20-item questionnaire to assess the difficulties in passive and active upper limb tasks, where section A evaluates the passive function and section B evaluates the active function. It uses a 5-point Likert scale, ranging from 0 (no difficulty) to 4 (unable to do the task). The total score of section A and B are 32 and 52 respectively [59]. The higher score in ArmA indicates more difficulties experienced in activities when using upper limb. Good internal consistency (Cronbach's alpha = 0.85 - 0.96) has been shown in people with upper limb paresis.

The 12-item Short-Form Survey (second version) (SF-12v2) will be used to measure the health-related quality of life of individuals. This instrument contains eight domains: physical functioning, role physical, bodily pain, general health, vitality, social functioning, emotional role, and mental health. The total score ranges from 0 to 100, with a higher score indicating better quality of life. It has good internal consistency (Cronbach's alpha = 0.48 - 0.81) and test-retest reliability (ICC = 0.67 - 0.82) in healthy adults.

The 12-item Short-Form Survey (second version) (SF-12v2) will be used to measure the health-related quality of life of individuals. This instrument contains eight domains: physical functioning, role physical, bodily pain, general health, vitality, social functioning, emotional role, and mental health. The total score ranges from 0 to 100, with a higher score indicating better quality of life. It has good internal consistency (Cronbach's alpha = 0.48 - 0.81) and test-retest reliability (ICC = 0.67 - 0.82) in healthy adults.

The 12-item Short-Form Survey (second version) (SF-12v2) will be used to measure the health-related quality of life of individuals. This instrument contains eight domains: physical functioning, role physical, bodily pain, general health, vitality, social functioning, emotional role, and mental health. The total score ranges from 0 to 100, with a higher score indicating better quality of life. It has good internal consistency (Cronbach's alpha = 0.48 - 0.81) and test-retest reliability (ICC = 0.67 - 0.82) in healthy adults.

The 12-item Short-Form Survey (second version) (SF-12v2) will be used to measure the health-related quality of life of individuals. This instrument contains eight domains: physical functioning, role physical, bodily pain, general health, vitality, social functioning, emotional role, and mental health. The total score ranges from 0 to 100, with a higher score indicating better quality of life. It has good internal consistency (Cronbach's alpha = 0.48 - 0.81) and test-retest reliability (ICC = 0.67 - 0.82) in healthy adults.

The 23-item Oxford Participation and Activities Questionnaire (Ox-PAQ) evaluates participation and activity levels based on the three domains of routine activities, social engagement, and emotional well-being. Each item is measured on a 5-point Likert scale (0 = never; 1 = rarely; 2 = sometimes; 3 = often; 4 = always). The higher scores represent greater difficulties with participation and activities. Good to excellent internal consistency (Cronbach's α = 0.81 - 0.96) and test-retest reliability (ICC = 0.83 - 0.96) have been shown for this instrument in people with motor neuron disease, multiple sclerosis, and Parkinson's disease.

The 23-item Oxford Participation and Activities Questionnaire (Ox-PAQ) evaluates participation and activity levels based on the three domains of routine activities, social engagement, and emotional well-being. Each item is measured on a 5-point Likert scale (0 = never; 1 = rarely; 2 = sometimes; 3 = often; 4 = always). The higher scores represent greater difficulties with participation and activities. Good to excellent internal consistency (Cronbach's α = 0.81 - 0.96) and test-retest reliability (ICC = 0.83 - 0.96) have been shown for this instrument in people with motor neuron disease, multiple sclerosis, and Parkinson's disease.

The 23-item Oxford Participation and Activities Questionnaire (Ox-PAQ) evaluates participation and activity levels based on the three domains of routine activities, social engagement, and emotional well-being. Each item is measured on a 5-point Likert scale (0 = never; 1 = rarely; 2 = sometimes; 3 = often; 4 = always). The higher scores represent greater difficulties with participation and activities. Good to excellent internal consistency (Cronbach's α = 0.81 - 0.96) and test-retest reliability (ICC = 0.83 - 0.96) have been shown for this instrument in people with motor neuron disease, multiple sclerosis, and Parkinson's disease.

The 23-item Oxford Participation and Activities Questionnaire (Ox-PAQ) evaluates participation and activity levels based on the three domains of routine activities, social engagement, and emotional well-being. Each item is measured on a 5-point Likert scale (0 = never; 1 = rarely; 2 = sometimes; 3 = often; 4 = always). The higher scores represent greater difficulties with participation and activities. Good to excellent internal consistency (Cronbach's α = 0.81 - 0.96) and test-retest reliability (ICC = 0.83 - 0.96) have been shown for this instrument in people with motor neuron disease, multiple sclerosis, and Parkinson's disease.

Trail Making Test (TMT) can assess the attention and cognitive flexibility of individuals. The test is divided into part A and part B. In part A, the circle is numbered (i.e., 1 to 25). The subjects should draw lines in numeric order of the listed circle. In part B, the circles include both numbers (i.e., 1 to 13) and words (i.e., A to L). The subjects should draw the lines in a specific sequence between number and word (i.e., 1 to A to 2 to B etc.). A shorter time recorded in the test indicated the better performance. The test-retest reliability has been tested in people with stroke (ICC = 0.94 and 0.86 for Part A and Part B, respectively).

Trail Making Test (TMT) can assess the attention and cognitive flexibility of individuals. The test is divided into part A and part B. In part A, the circle is numbered (i.e., 1 to 25). The subjects should draw lines in numeric order of the listed circle. In part B, the circles include both numbers (i.e., 1 to 13) and words (i.e., A to L). The subjects should draw the lines in a specific sequence between number and word (i.e., 1 to A to 2 to B etc.). A shorter time recorded in the test indicated the better performance. The test-retest reliability has been tested in people with stroke (ICC = 0.94 and 0.86 for Part A and Part B, respectively).

Trail Making Test (TMT) can assess the attention and cognitive flexibility of individuals. The test is divided into part A and part B. In part A, the circle is numbered (i.e., 1 to 25). The subjects should draw lines in numeric order of the listed circle. In part B, the circles include both numbers (i.e., 1 to 13) and words (i.e., A to L). The subjects should draw the lines in a specific sequence between number and word (i.e., 1 to A to 2 to B etc.). A shorter time recorded in the test indicated the better performance. The test-retest reliability has been tested in people with stroke (ICC = 0.94 and 0.86 for Part A and Part B, respectively).

Trail Making Test (TMT) can assess the attention and cognitive flexibility of individuals. The test is divided into part A and part B. In part A, the circle is numbered (i.e., 1 to 25). The subjects should draw lines in numeric order of the listed circle. In part B, the circles include both numbers (i.e., 1 to 13) and words (i.e., A to L). The subjects should draw the lines in a specific sequence between number and word (i.e., 1 to A to 2 to B etc.). A shorter time recorded in the test indicated the better performance. The test-retest reliability has been tested in people with stroke (ICC = 0.94 and 0.86 for Part A and Part B, respectively).

The Rivermead Behavioural Memory Test - Third edition (RBMT-3) examines the everyday memory function with 14 subtests, including the assessment for visual, verbal, recall, recognition, immediate, and delayed memory. The scaled score of each subtest and total scaled score will be computed by converting raw scores based on different age group using the conversion table of original RBMT-3. The minimum and maximum values of scaled scores for every subsets are 1 and 19, respectively. Higher scaled score indicates better memory function. The RBMT-3 has demonstrated excellent inter-rater reliability (ICC = 0.997) and intra-rater reliability (ICC = 0.924) and good internal consistency (Cronbach's alpha = 0.643 - 0.832) in people with dementia, mild cognitive impairment and healthy older adults.

The Rivermead Behavioural Memory Test - Third edition (RBMT-3) examines the everyday memory function with 14 subtests, including the assessment for visual, verbal, recall, recognition, immediate, and delayed memory. The scaled score of each subtest and total scaled score will be computed by converting raw scores based on different age group using the conversion table of original RBMT-3. The minimum and maximum values of scaled scores for every subsets are 1 and 19, respectively. Higher scaled score indicates better memory function. The RBMT-3 has demonstrated excellent inter-rater reliability (ICC = 0.997) and intra-rater reliability (ICC = 0.924) and good internal consistency (Cronbach's alpha = 0.643 - 0.832) in people with dementia, mild cognitive impairment and healthy older adults.

The Rivermead Behavioural Memory Test - Third edition (RBMT-3) examines the everyday memory function with 14 subtests, including the assessment for visual, verbal, recall, recognition, immediate, and delayed memory. The scaled score of each subtest and total scaled score will be computed by converting raw scores based on different age group using the conversion table of original RBMT-3. The minimum and maximum values of scaled scores for every subsets are 1 and 19, respectively. Higher scaled score indicates better memory function. The RBMT-3 has demonstrated excellent inter-rater reliability (ICC = 0.997) and intra-rater reliability (ICC = 0.924) and good internal consistency (Cronbach's alpha = 0.643 - 0.832) in people with dementia, mild cognitive impairment and healthy older adults.

The Rivermead Behavioural Memory Test - Third edition (RBMT-3) examines the everyday memory function with 14 subtests, including the assessment for visual, verbal, recall, recognition, immediate, and delayed memory. The scaled score of each subtest and total scaled score will be computed by converting raw scores based on different age group using the conversion table of original RBMT-3. The minimum and maximum values of scaled scores for every subsets are 1 and 19, respectively. Higher scaled score indicates better memory function. The RBMT-3 has demonstrated excellent inter-rater reliability (ICC = 0.997) and intra-rater reliability (ICC = 0.924) and good internal consistency (Cronbach's alpha = 0.643 - 0.832) in people with dementia, mild cognitive impairment and healthy older adults.

The muscle stiffness of biceps brachii and triceps brachii muscles will be quantified by MyotonPRO device (Myoton AS, Tallinn, Estonia). The MyotonPRO device will be placed perpendicularly to the skin surface and apply mechanical impulses on the muscles to generate damped oscillations of the underlying tissue. The biceps brachii measurements will be performed at the long head of the muscle in the middle of the arm. The triceps brachii measurements will be performed at the medial head of the muscle in the middle of the arm. Muscle stiffness will be described as newton-meter (N/m), where the higher value indicates the higher stiffness of the tissue.

The muscle stiffness of biceps brachii and triceps brachii muscles will be quantified by MyotonPRO device (Myoton AS, Tallinn, Estonia). The MyotonPRO device will be placed perpendicularly to the skin surface and apply mechanical impulses on the muscles to generate damped oscillations of the underlying tissue. The biceps brachii measurements will be performed at the long head of the muscle in the middle of the arm. The triceps brachii measurements will be performed at the medial head of the muscle in the middle of the arm. Muscle stiffness will be described as newton-meter (N/m), where the higher value indicates the higher stiffness of the tissue.

The muscle stiffness of biceps brachii and triceps brachii muscles will be quantified by MyotonPRO device (Myoton AS, Tallinn, Estonia). The MyotonPRO device will be placed perpendicularly to the skin surface and apply mechanical impulses on the muscles to generate damped oscillations of the underlying tissue. The biceps brachii measurements will be performed at the long head of the muscle in the middle of the arm. The triceps brachii measurements will be performed at the medial head of the muscle in the middle of the arm. Muscle stiffness will be described as newton-meter (N/m), where the higher value indicates the higher stiffness of the tissue.

The muscle stiffness of biceps brachii and triceps brachii muscles will be quantified by MyotonPRO device (Myoton AS, Tallinn, Estonia). The MyotonPRO device will be placed perpendicularly to the skin surface and apply mechanical impulses on the muscles to generate damped oscillations of the underlying tissue. The biceps brachii measurements will be performed at the long head of the muscle in the middle of the arm. The triceps brachii measurements will be performed at the medial head of the muscle in the middle of the arm. Muscle stiffness will be described as newton-meter (N/m), where the higher value indicates the higher stiffness of the tissue.

A hand-held dynamometer (Model 01165; Lafayette Instrument, Indiana, USA) will be used to measure the muscle force generated by biceps brachii and triceps brachii muscles of affected and unaffected sides. The participant will be instructed to perform isometric contraction and resistance will be applied by the examiner to avoid movement of the arm during the measurement. Two trials will be performed for each muscle group and the mean force of two trials will be recorded.

A hand-held dynamometer (Model 01165; Lafayette Instrument, Indiana, USA) will be used to measure the muscle force generated by biceps brachii and triceps brachii muscles of affected and unaffected sides. The participant will be instructed to perform isometric contraction and resistance will be applied by the examiner to avoid movement of the arm during the measurement. Two trials will be performed for each muscle group and the mean force of two trials will be recorded.

A hand-held dynamometer (Model 01165; Lafayette Instrument, Indiana, USA) will be used to measure the muscle force generated by biceps brachii and triceps brachii muscles of affected and unaffected sides. The participant will be instructed to perform isometric contraction and resistance will be applied by the examiner to avoid movement of the arm during the measurement. Two trials will be performed for each muscle group and the mean force of two trials will be recorded.