Aging being a dynamic, progressive, and physiological process is accompanied by morphological and functional changes¹. Old age causes a reduction in the functional reserve of organs and systems. This decline leads to changes in balance, postural control, depression, anxiety, and mobility. With age, they tend to lose dynamic and static balance control, because of the inability to counteract the external forces. If not managed properly, these destabilizing forces can lead to a fall. Risk of falls is noted mostly in people over 65 years with recurrent and multiple episodes leading to a decline in daily functions further. This may result in reduced social contact, increased dependency and increased mobility impairments. It is, therefore, necessary to tackle balance problems in the elderly. It is important to teach them techniques to manage balance effectively in the event of a fall. For this, effective motor learning is required.²Besides, it is seen that is a relation between age and decline in motor learning and overall motor performance. Some studies have also mentioned about a significant reduction in learning capacities in older adults^{3, 4}.

Motor learning is defined as the study of the acquisition and /or modification of movement for permanent change. While motor control focuses on understanding the control of movement already acquired, motor learning focuses on understanding the acquisition of movement. Forms of learning are the basis of re-acquisition of complex task post injury.⁵. Also, Humans prefer to practice actions which are similar to their habits and behaviour. Habits allow adequate decision making with flexible behaviour, hence forming a stimulus-response pairing. Planning on the other hand warrants more flexible and productive decision making⁶.A study by Jiang and colleagues about Habitual attention in older and young adults suggest that habitual attention in older adults may be used to counter declines in controlled attention⁷. On the other hand, Associative forms of learning involve the association of ideas which helps the person to associate his relationships with stimulus. Procedural learning, a subset of associative learning, requires learning a task like a habit confined to only one specific aspect. Associative form of learning requires knowledge that can be consciously recalled along with awareness, while attention and reflection form the basis of declarative learning ⁵. Moreover, a study by Eli Vakil and Dafna Agmon-Ashkenazi states that the learning rate of both young and old adults on the procedural tasks did not differ consistently, whether the measure was a number of errors/moves or time elapsed. However, there was one exception in the study in which the older group showed a steeper learning rate for procedural learning than the younger group⁸.So while planning a motor learning strategy in older people it should be based on habituation and should be confined to one specific goal. Most common strategies to improve motor learning involve random order practice, mental imagery practice, videotaped based practice, feedback of knowledge over results etc.⁹. From rehabilitation point of view, not only traditional approaches but newer physiotherapeutic interventions should also be undertaken to tackle problems with everyday functioning to attain effective learning. It is always seen that newer modified activities are preferred over the same old daily activities. Also, older adults show a reduce adherence to daily monotonous exercises¹⁰. A new modified and more interactive exercise can get older adults more devoted to a rehabilitation program¹¹.

Word novel refers to new or not resembling something formerly known as used¹².New Motor skills can be learned efficiently if planned and organised. The longer the duration a task is carried out, faster is the acquisition of a new same skill-a phenomenon of learning to learn. This process of motor adaptation by the newer task can be explained by term “structure learning” Structured learning explains the ability of learning to learn ¹³It infers that in spite of memory problems, older adults are able to retain themselves in a newer environment. Similarly, According to, Fitts and Posner (1967), for learning a new motor task, it is believed that an individual needs to follow the Cognitive ,Associative and Autonomous stages of learning¹⁴.Thus for effective motor learning, the planned task should be to which the individual can associate himself easily. Likewise, it has been found that function-oriented exercises minimize the risk of falls in older adults on the whole improving balance, gait parameters, and the muscle strength of the lower limbs¹⁵.

Nowadays, Modern newer interactive forms of training based on virtual reality (VR) are taking role in rehabilitation. VR has also shown to increase the role of motor stimulation during the modified experience, as users can move through and physically interact with virtual objects. Virtual environments can present combinations of stimuli that are not found in the natural world and the therapist can bring about similar changes which are not possible physically .A study by Rosenberg et al which studied the effect of virtual reality in older adults found out that virtual reality has positive effects on depression, mental health-related quality of life and cognitive performance¹⁶. A lab study showed that while energy expenditure was less in Wii balance exergame as compared to walking with a treadmill, enjoyment was rated much higher in older adults^{16, 17} and, enjoyment has been found to be associated with increased adherence to exercise over time¹⁸. Also, virtual environment increases motivation and interaction between sensorimotor model making it more of an exploratory approach thus regaining active participation31. .A wide base of literature support using virtual reality for stroke or for improving pulmonary function in cerebral palsy kids.VR rehabilitation can be implemented through personal computers (PCs), mobile devices, video games, or specialized equipment. The Virtual reality headset is relatively small in size, which means that each patient can have a small virtual rehabilitation room in his or her home. So, to gain effective motor learning, virtual reality games could be used as a novel task to get beneficial changes. In short, VR can also be described in terms of I³: Interaction + Immersion + Imagination¹⁹. Therefore, an intervention to use virtual reality as a novel task to promote motor learning and achieve efficient recovery of function was decided.

Further, motor learning in older adults might also be influenced by sleep architecture. It is seen that Sleep plays a vital role in memory consolidation and motor learning. Sleep dependent memory consolidation requires the co-ordination of both type of memory that is processed and how well it is stored. Memory consolidation refers to the term in which unstable memory representation is converted into a form that is both more stable and effective²⁰.Offline learning refers to memory consolidation which takes place without any active participation of subject itself ²¹. It is described in terms with interference technique in which the consolidation of a primary task is disrupted by the immediate performance of a secondary task. If the period is lengthened then the extent of learning is lengthened as well ²².

However, older people tend to have greater sleep disturbances that can create a negative impact on their quality of life, mood, and alertness. Elderly individuals sleep 36 per cent less than children at age. Even though the ability to sleep becomes more difficult, the need to sleep does not decrease with age. Literature suggests that exposure to partial and total sleep deprivation impairs primarily behavioural alertness and cognitive processing capabilities ²³. States of sleep are further divided into REM and NREM states. It is during these cycle where major metabolic events contain changes in brain electrophysiology²⁴Also, with aging, as sleep disturbances increase impedance to executive functions might also increase²⁵So accordingly, it can be stated that sleep might be considered as a beneficial factor for executive functions which can, in turn, be related to sleep increase cognitive ability.

Research has proved that sleep enhances the learning of both motor adaptation task and motor Sequence task in young adults²⁶51As sleep disturbances increase with age, it may hinder physical and mental abilities of older individuals Older adults also develop behavioural and ecological changes which affect activities of daily living²⁷. Sleep disturbances might also affect the learning capacity of the individual to adhere to a task. There are possibilities that sleep might affect the ability to learn a new task. Hence, this study was be conducted to find out the effect of sleep on performance of novel motor task learning in elderly individuals..

The statistical analysis was done using Wilcoxon Signed Rank W test within the group and Mann-Whitney U test between the two groups.

The estimated sample size for the study was 68 and subjects were divided into two groups- Group A (sleep group)and Group B (no sleep group) After excluding the dropouts, the samples included in each group were 32 and the total samples studied were 64. All elderly individuals were 65 years of age, both males and females healthy elderly individuals were approached according to criteria and divided into groups. All participants were assessed based on SEBT, TWT and DGI scores and analyzed further.

Results

The obtained results after analysis are plotted in the form of tables and graphs

Subject Characteristics- For both the groups there were no differences in respect to age and gender. Both the groups were matched with respect to sleeping conditions and functional mobility.(table and graph-1,2)

Performance characteristics

Primary Outcome

Star Excursion Balance Test

Older adults in sleep condition showed significant improvements in SEBT in all eight direction with greater degree of percentage change as compared to that of participants in no sleep condition(p<0.05).(Table and graph 3-6).

Tandem Walk Test

Participants in sleep group showed increase significance in step length and stride length components of Tandem Walk test as compared to that of no sleep group(p<0.05).Regarding improvements in base of support component there was significant change seen in both the groups, but percentage change seen in sleep group(38%) was more than that of other group(5.8%).).(Table and graph7-12)

Dynamic Gait Index

Participants in both group showed improvement in dynamic gait index scores with increase percentage change seen in sleep group (16.4%) as compared to that of no sleep group (7.1%)).(Table and graph 13,14).

Secondary Outcome

Standford sleepiness scale

The Stanford Sleepiness Scale administered to ensure state of alertness before the sessions cancels out any negative effect of sleepiness which sleeps deprivation might have imposed³⁰.Hence, it can be quoted that continuous sleep before a session might be optimal than small sleep episodes during the day time

Table 1: Age distribution of subjects into groups

Table 2: Gender distribution of subjects

Graph 1: Age wise distribution of subjects

Graph 2: Gender distribution of subjects

Graph 3: SEBT– standing on left values pre and post training in group a and b

Graph 4: SEBT – standing on right values pre and post training in group a and b

T able 3: SEBT– standing on left values pre and post training in group a and b

Table 4: SEBT– standing on right values pre and post training in group a and b

Graph 5: C omparison between group a and group b in SEBT- standing on left

Graph 6: C omparison between group a and group b in SEBT- standing on right

T able 5: C omparison between group a and group b in SEBT- standing on left

Table 6: C omparison between group a and group b in SEBT- standing on right

Graph 7: TWT- step length (left) pre and post values in group a and b

Graph 8: TWT- stride length (left) pre and post values in group a and b

Graph 9: TWT- step length (right) pre and post values in group a and b

Graph 10: TWT- stride length (right) pre and post values in group a and b

T able 7: TWT- step length (left) pre and post values in group a and b

Table 8: TWT - stride length (left) pre and post values in group a and b

Table 9: TWT- step length (right) pre and post values in group a and b

Table 10: TWT - stride length (right) pre and post values in group a and b

Table 11: TWT-base of support: pre and post values in group a and b

Graph 11: TWT-base of support: pre and post values in group a and b

Table 12: C omparison between group a and group b in components of TWT

Graph 12: C omparison between group a and group b in components of TWT

Table 13: DGI score pre and post training in group a and b

Graph 13: DGI score pre and post training in group a and b

Table 14: C omparison between group a and group b in DGI scores

Graph 14: C omparison between group a and group b in DGI scores

The main purpose of the study was to find out the effect of sleep on novel motor task learning in elderly individuals. Findings from SEBT values in no sleep group confirms the result of the study done June J. Pilcher and colleagues that sleep deprivation strongly impairs human functioning. Even previously done studies suggest that exposure to partial and total sleep deprivation impairs primarily behavioural alertness and cognitive processing capabilities ²³

Improvement in BOS component of TWT in no sleep condition can be explained with work of Lowry K A and colleagues, who studied Age-Related Differences in Locomotor Strategies during Adaptive Walking. They stated that adults tend to preserve mediolateral (ML) smoothness at the expense of anteroposterior (AP) smoothness. Study inferred that older adults prioritized ML control over forward progression during adaptive walking challenges³⁴. So accordingly it can be concluded that older adults while performing the TWT in the no sleep group might have preferred managing the BOS component easily rather than resolving the anterior-posterior components.

Also, in no sleep group a significant improvement was seen in DGI scores. DGI includes components which are similar to daily walking. Walking doesn’t require any conscious effort. Also, walking is an automated movement might have been easy to learn for the subjects even in no sleep group. This can be reasoned out with the theory of Ericsson, which states the premature transition to the autonomous stage of learning.³⁵ Even, Anderson’s Adaptive Control of Thought theory, states- as learning occurs, a transition from declarative memory to procedural memory takes place.Fiery Cushman and Adam Morris,quote that humans use habitual control to select a goal. Once selected they can then effectively plan and improve their performance^.36It might be, because of this reason the DGI score improved even in no sleep group. Considering this relevance, we can conclude that as people were priorly used to the components of DGI it might have been possible that they were able to improve their performance in spite being in the no sleep condition.

It can be stated that learning effect was seen in sleep group as they demonstrated a significant change in SEBT values. A study done by Kuriyama and colleagues mentions about complexity theory which states that sleep enhances learning the tasks that are more complex. ³⁷ Therefore, the present study can also confirm that sleep dependent learning is not limited to simple motor tasks but also extends to novel more complex motor tasks, as SEBT scores in no sleep group were not significant. SEBT being a complex activity to perform might have been difficult to perform.

Findings from TWT suggest that Sleep was effective to get the learning effect post novel task training. These results can be supported with findings of AL Sharman and colleagues which states that sleep enhances learning a functional motor task in middle-aged and older adults.²¹ Also, subjects in sleep group subjects showed a significant difference in DGI scores. Hence, it can be concluded that the learning effect was seen in subjects in the sleep group. As mentioned earlier, this change might be because of the premature transition towards the autonomous stage of learning.³⁵Also, Elmar Kal and colleagues in their systemic review concluded that while comparison between implicit and explicit learning, found that comparisons leaned more toward a greater degree of movement automaticity after implicit learning than explicit learning.³⁸

However, the effect seen in sleep group is greater than no sleep group. With reference to gait variability in older adults³⁴, present study findings can be used to quote that sleep improves novel motor skill learning which indirectly can imply that this technique can also be used in a way to improve or modify or manage the coping strategies used by older adults.

Ericsson in his study also proposed that a premature shift to the autonomous stage of learning can lead to arrested development as the performance stabilizes in a nonmaximal state³⁵. From this, we can say that this arrested performance can be overcome by sleep. Hence, it can be concluded that sleep enhances the learning of novel motor tasks in elderly individuals.

The current study also can suggest that sleep quality and sleep dependent motor learning might have a relation with each other. Sleep quality was assessed by the Pittsburgh Sleep Quality Index and subjects were asked to maintain regular sleep for a week prior^21,29. Therefore after ruling out sleep difficulties and ensuring efficient sleep patterns by addressing Pittsburgh Sleep Quality Index, it can be concluded that with better sleep and fewer awakenings there learning over a task can be improved. Also, the Stanford Sleepiness Scale 64administered to ensure state of alertness before the sessions cancel out any negative effect of sleepiness which sleeps deprivation might have imposed.³⁰ It has already been proved that motor performance is not enhanced by day time naps in older adults³⁹ Hence, it can quote that continuous sleep before a session might be optimal than small sleep episodes during the day time. Also, it is found that there is a positive correlation between sleep spindle density and offline motor learning and sleep duration having an association with specific motor task learning but not with nonspecific learning.²² Hence, we can conclude that with enough sleep duration and quality effective novel motor task training can be achieved.

Hence, in the study presented above it can be concluded that sleep enhances the learning of novel motor tasks in elderly individuals.

Present study states that sleep is effective in novel motor task learning in elderly individuals. It should be seen that significant importance is given to adequate sleep before physical therapy sessions to ensure effective motor learning. Even, during rehabilitation, timing of the session should be plan appropriately to facilitate the learning process. Also, it is necessary to address sleep disorders on a priority basis in the diseased population, because if left unnoticed it might cause hindrance in achieving the goal.

Limitations

Lifestyles were not taken into consideration.

Future Scope

A correlation between the quality of sleep and the extent of motor task learning achieved can be found out. A research can be done to find out the effect of sleep on novel motor task learning in different populations, especially following a neurological deficit or in people with neurological disorder. A study can be proposed to compare the effect of sleep on novel motor task learning in physically active older adults versus that in their sedentary counterparts.