How do social networks, perception of social isolation, and loneliness affect depressive symptoms among Japanese adults?

OBJECTIVE: This study aims to elucidate the complex relationship among social isolation, loneliness, and perception of social isolation and its influence on depressive symptoms by evaluating a hypothetical model. This understanding is essential for the formulation of effective intervention strategies. METHODS: We conducted an online survey on Japanese adults (N = 3,315) and used the six-item Lubben Social Network Scale to assess the size of their social networks. We employed a single question to gauge their perception of social isolation. Loneliness was assessed using the three-item UCLA Loneliness Scale, and depressive symptoms were examined using the Patient Health Questionnaire-9. Structural equation modeling was employed to test the hypothesized model. RESULTS: The final model demonstrated satisfactory fit with data (χ2 (1) = 3.73; not significant; RMSEA = 0.03; CFI = 1.00; TLI = 1.00). The size of social network demonstrated a weak negative path to loneliness and depressive symptoms (ß = -.13 to -.04). Notably, a strong positive association existed between perception of social isolation and loneliness (ß = .66) and depressive symptoms (ß = .27). Additionally, a significant positive relationship was found between loneliness and depressive symptoms (ß = .40). Mediation analysis indicated that perception of social isolation and loneliness significantly intensified the relationships between social networks and depressive symptoms. CONCLUSIONS: Results indicate that interventions of psychological approaches, such as cognitive-behavioral therapy, are effective in reducing the perception of social isolation and loneliness, which may lead to the prevention of depressive symptoms. Future longitudinal studies are expected to refine and strengthen the proposed model.

Timings of attentional switching to perturbation and postural preparation during transient forward or backward floor translation.

BACKGROUND: Relationships between the timings of attentional switching and postural preparation were investigated using a choice-reaction paradigm with transient floor translation (S2), with the direction indicated by a warning auditory signal (S1). METHODS: Thirteen healthy young adults participated in this study. S2 started 2 s after S1 onset while standing on the platform. The platform moved forward when S1 was a high tone, and backward when S1 was a low tone. In the S1-S2 period, attentional switching was evaluated by P3 component of event-related potential. RESULTS: A shift in the center of pressure in the anteroposterior direction (CoPap) or a continuous increase in postural muscle activation toward S2 was recognized as postural preparation. Changes in postural muscle activation were found just before the CoPap shift. P3 was observed about 250-650 ms after S1. Onset of postural preparation was significantly later (about 200 ms) than latency of P3 (p < 0.001) and correlated strongly with P3 latency (forward: r = 0.81, backward: r = 0.74, p < 0.01). CONCLUSION: Postural preparation for S2 was demonstrated to start after attentional switching from S1 to S2.

Developmental changes in shortening of pro-saccade reaction time while maintaining neck flexion position.

BACKGROUND: We investigated developmental changes in shortening of pro-saccade reaction time while maintaining neck flexion. METHODS: Subjects comprised 135 children (3-14 years) and 29 young adults (19-23 years). Children were divided into six groups in 2-year age strata. Pro-saccade reaction tasks for 30 s were performed in neck rest and flexion positions. Reaction times under each position were averaged in every 10-s period. RESULTS: Under neck rest position, reaction time in the 0-10 s period was significantly longer in the 3- to 4-year-old group than in the 5- to 6-year-old group and above. No significant age effect was found for reaction time in the 0-10 s period in the 5- to 6-year-old group and above. Although a significant effect of neck flexion was not observed until the 9- to 10-year-old group, significant shortening of reaction time with neck flexion was found in the 11- to 12-year-old group and above. Furthermore, this shortening was maintained until the first 20-s period in the 11- to 12-year-old group and during the entire 30 s in the 13- to 14-year-old and above. CONCLUSIONS: These results suggest that brain activation with the maintenance of neck flexion, related to shortening of the pro-saccade reaction time, was found from a later age of approximately 11 years and above, compared with the age at which information-processing function in the pro-saccade was enhanced. In addition, brain activation with the maintenance of neck flexion was sustained longer with age.

Activation timing of postural muscles of lower legs and prediction of postural disturbance during bilateral arm flexion in older adults.

BACKGROUND: Activation timings of postural muscles of lower legs and prediction of postural disturbance were investigated in young and older adults during bilateral arm flexion in a self-timing task and an oddball task with different probabilities of target presentation. Arm flexion was started from a standing posture with hands suspended 10 cm below the horizontal level in front of the body, in which postural control focused on the ankles is important. METHODS: Fourteen young and 14 older adults raised the arms in response to the target sound signal. Three task conditions were used: 15 and 45% probabilities of the target in the oddball task and self-timing. Analysis items were activation timing of postural muscles (erector spinae, biceps femoris, and gastrocnemius) with respect to the anterior deltoid (AD), and latency and amplitude of the P300 component of event-related brain potential. RESULTS: For young adults, all postural muscles were activated significantly earlier than AD under each condition, and time of preceding gastrocnemius activation was significantly longer in the order of the self-timing, 45 and 15% conditions. P300 latency was significantly shorter, and P300 amplitude was significantly smaller under the 45% condition than under the 15% condition. For older adults, although all postural muscles, including gastrocnemius, were activated significantly earlier than AD in the self-timing condition, only activation timing of gastrocnemius was not significantly earlier than that of AD in oddball tasks, regardless of target probability. No significant differences were found between 15 and 45% conditions in onset times of all postural muscles, and latency and amplitude of P300. CONCLUSION: These results suggest that during arm movement, young adults can achieve sufficient postural preparation in proportion to the probability of target presentation in the oddball task. Older adults can achieve postural control using ankle joints in the self-timing task. However, in the oddball task, older adults experience difficulty predicting the timing of target presentation, which could be related to deteriorated cognitive function, resulting in reduced use of the ankle joints for postural control.

Postural control and contingent negative variation during transient floor translation while standing with the ankle fixed.

BACKGROUND: Adaptation changes in postural muscle activity and anticipatory attention were investigated with the ankle joint fixed to change postural control strategies during transient floor translation. METHODS: For 15 healthy young adults, 40 transient floor translations (S2) in the anterior direction were applied 2 s after an auditory warning signal (S1), under conditions with or without fixation of the ankle. Activity of the frontal postural muscles (tibialis anterior (TA), rectus femoris (RF), rectus abdominis) and contingent negative variation (CNV, brain potential) were analyzed for 20 trials each of the early and latter halves under each fixation condition. RESULTS: With fixation, peak amplitude of muscle activity after S2 was significantly decreased in TA and increased in RF. These muscles showed marked adaptive decreases. The early component of CNV reduced with adaptation, particularly under fixation condition. Only in RF, background activity increased just before S2, with adaptation under fixation. A significant correlation was found between timings of CNV peak and RF activation just before S2 only after adaptation under fixation. CONCLUSION: These results suggest that the main activation muscle changes from TA to RF with fixation. Under such condition, attention would be focused on the knee with adaptation, and the need for heightening attention in the early stage may have declined. Correspondingly, the timing to heighten stiffness of the RF became later, and attention would have been paid to RF activation just before S2.

Event-related brain potential and postural muscle activity during standing on an oscillating table while the knee, hip, and trunk are fixed.

BACKGROUND: In this study, a cast brace was used to immobilize the knee, hip, and trunk, and relations between the event-related brain potential (ERP) and postural muscle activity were investigated while standing on an oscillating table. METHODS: Twelve healthy young adults maintained a standing posture for 1 min per trial while oscillating in the anteroposterior direction at 0.5 Hz with a 2.5-cm amplitude. Trials were performed without and with the cast brace (no-fixation and fixation condition, respectively) until the subject had adapted to the floor oscillation. The ERP from the Cz electrode, postural muscle activity, and joint movement range were analyzed for the first and last two trials (before and after adaptation, respectively). RESULTS: Movement range of the hip and knee was lower in the fixation condition than in the no-fixation condition, and postural control was achieved by pivoting at the ankle. Peak muscle activity was largest in the gastrocnemius (GcM) in both conditions. GcM activity significantly increased after fixation and then decreased with adaptation. The time of peak erector spinae (ES) activity in the fixation condition was significantly earlier than in the no-fixation condition and was not significantly different from the time of the anterior reversal and peak of triceps surae activity. The negative ERP peaked approximately 80 ms after the anterior reversal. Significant correlations between the time of the peak negative ERP and the peak GcM, soleus, and ES activity were observed only after the adaptation, and were greater in the fixation condition (r = 0.83, 0.84, and 0.83, respectively) than in the no-fixation condition (r = 0.62, 0.73, and 0.51, respectively). CONCLUSION: All joints of the leg and trunk except for the ankle were rigidly fixed by the cast brace, and the phase differences between body segments were very small in the fixation condition. High correlations between the time of the peak negative ERP and the peak GcM, soleus, and ES activity after adaptation in the fixation condition suggest that attention would be more focused on anticipatory processing of muscle sensory information from the triceps surae and/or ES, particularly GcM, which had the greatest activation.

Effect of time pressure on attentional shift and anticipatory postural control during unilateral shoulder abduction reactions in an oddball-like paradigm.

BACKGROUND: The effect of time pressure on attentional shift and anticipatory postural control was investigated during unilateral shoulder abduction reactions in an oddball-like paradigm. METHODS: A cue signal (S1) - imperative signal (S2) sequence was repeated with various S2-S1 intervals (1.0, 1.5, and 2.0 s). S2 comprised target and non-target stimuli presented at the position (9° to the left or the right) indicated by S1. Right shoulder abduction was performed only in response to target stimuli, which were presented with a 30% probability. The P1, N1, N2, and P3 components of event-related potentials were analyzed, and onset times of postural muscles (electromyographic activity of erector spinae and gluteus medius) were quantified with respect to middle deltoid activation. RESULTS: There was no significant effect of S2-S1 interval on the latency or amplitude of P1, N1, or N2. The percentage of subjects with bimodal P3 peaks was significantly smaller and the slope of the P3 waveform in the 100 ms after the first peak was significantly steeper with a 1.0-s S2-S1 interval than with a 1.5- or 2.0-s S2-S1 interval. The onset of postural muscle activity was significantly later in the shorter interval conditions. CONCLUSIONS: These results suggest that with a shorter S2-S1 interval, that is, higher time pressure, attention was allocated to hasten the latter part of cognitive processing that may relate to attentional shift from S2 to next S1, which led to insufficient postural preparation associated with arm movement and anticipatory attention directed to S2.

Adaptation changes in dynamic postural control and contingent negative variation during repeated transient forward translation in the elderly.

BACKGROUND: Adaptation changes in postural control and contingent negative variation (CNV) for the elderly were investigated during repeated forward floor translation. METHODS: Fifteen healthy elderly persons, living in the suburban area of Kanazawa City, Japan, underwent backward postural disturbance by a forward-floor translation (S2) 2 s after an auditory warning signal (S1). A set with 20 trials was repeated until a negative peak of late CNV was recognized in the 600-ms period before S2, and the last set was defined as the final set. Electroencephalograms, center of foot pressure in the anteroposterior direction (CoPap), and electromyograms of postural muscles were analyzed. RESULTS: CoPap displacement generated by the floor translation was significantly decreased until the twelfth trial in the first set, and mean CoPap displacement was smaller in the second and final sets than in the first set. The mean displacement was significantly smaller in the final set than the previous set. A late CNV with a negative peak was not recognized in the first and second sets. However, most subjects (13/15) showed a negative peak by the fourth set, when the late CNV started to increase negatively from about 1,000 ms after S1 and peaked at about 300 ms before S2. At about 160 ms before the CNV peak, the CoPap forward shift started. The increase in timing of the gastrocnemius activity related to the CoPap shift was significantly correlated with the CNV peak timing (r = 0.64). After S2, peak amplitudes of the anterior postural muscles were significantly decreased in the final set compared to the first set. CONCLUSIONS: It was demonstrated that even for the elderly, with so many repetitions of postural disturbance, a late CNV with a negative peak was recognized, leading to accurate postural preparation. This suggests the improvement of frontal lobe function (e.g., anticipatory attention and motor preparation) in the elderly.

Effects of limiting anterior displacement of the center of foot pressure on anticipatory postural control during bilateral shoulder flexion.

In bilateral shoulder flexion with the arms moving from the sides of the body to the horizontal level while standing, no preceding activation of the triceps surae (TS) with respect to focal muscles has been found. Considering that preceding activation would offer a useful indicator of anticipatory postural control, it was attempted to induce preceding activation by limiting the anterior displacement range of the center of foot pressure in the anteroposterior direction (CoPap). Subjects were 13 healthy young adults. The 50% anterior range of CoPap displacement caused by shoulder flexion was calculated, and the floor inclined by the subject's weight when CoPap extended beyond that range. Subjects were instructed not to incline the floor during shoulder flexion. Under the limitation condition, the ankle and knee joints plantarflexed and extended at 1.1°, respectively, with no hip movement; that is, the whole body inclined backward by pivoting at the ankle. This limitation resulted in preceding muscle activation of TS as well as erector spinae and biceps femoris, and no significant differences in onset time were seen between these muscles. These results demonstrated that by limiting CoPap anterior displacement, preceding activation of TS could be induced with backward inclination of the whole body.

Adaptation changes in dynamic postural control and contingent negative variation during backward disturbance by transient floor translation in the elderly.

BACKGROUND: We investigated adaptation changes in dynamic postural control and contingent negative variation (CNV) in 13 young and 12 elderly adults. Subjects repeatedly underwent backward postural disturbance by a forward floor translation (S2) 2 s after an auditory warning signal (S1). Initial and second sets were conducted, each set with 20 trials. Posterior peak position of the center of pressure in the anteroposterior direction (CoPy) after S2 was identified. Electroencephalograms from Cz were averaged for each set, and the CNV negative peak was identified. RESULTS: Compared with the first trial, the posterior peak position of CoPy changed significantly forward from the 12th trial in the young and from the 19th trial in the elderly during the initial set. The mean of the posterior peak position was more forward in second set than in the initial set for both groups and was significantly backward in the elderly compared to the young for both sets. These findings indicate that subjects in both groups adapted better to the postural disturbance in the second set than in the initial set, and the adaptation was later in the elderly. Late CNV in the young started to increase negatively from the middle of the S1-S2 period and peaked just before S2. Peak CNV amplitude was larger in the second set than in the initial set. In contrast, late CNV in the elderly exhibited no negative increase as in the young and peaked in the middle of the S1-S2 period, which was followed by gradual decreasing toward S2. No adaptive changes were found in late CNV for the elderly. CONCLUSIONS: It is conceivable that reduced activation of the frontal lobe may be one of the factors contributing to the decrease in postural adaptability in the elderly. The elderly may use various brain regions for the adaptation of dynamic postural control compared with the young.

Effects of neck flexion on discriminative and cognitive processing in anticipatory postural control during bilateral arm movement.

We investigated the effect of neck flexion on discriminative and cognitive processing in postural control during bilateral arm movement while standing, using event-related potential (ERP) and electromyogram. Fourteen healthy subjects flexed their arms to the target stimuli with a 20% probability in neck resting and flexion positions. Amplitude and latency of N2 and P3, anterior deltoid (AD) reaction time, onset time of postural muscles with respect to AD activation, and peak amplitude and latency of all muscles were measured. With neck flexion, N2 and P3 amplitudes increased, N2 and P3 latencies and AD reaction time shortened, and onset times of all postural muscles became earlier. No significant differences in peak amplitude and latency of each muscle were found between neck positions. Significant positive correlations were found in changes with neck flexion between P3 latency and AD reaction time, and between N2 latency and onset time of erector spinae. These suggest that with neck flexion, attention allocation to discriminative and cognitive processing increased, and the processing speed increased with shortening of reaction time in focal muscles. In addition, the onset time of postural muscles became earlier without changing the activation pattern, which was associated with the hastened discriminative processing.

Effects of attentional dispersion on sensory-motor processing of anticipatory postural control during unilateral arm abduction.

OBJECTIVE: We investigated effects of attentional dispersion on sensory-motor processing of anticipatory postural control during unilateral arm abduction. METHODS: Thirteen adults performed arm abduction under two types of attentional dispersion conditions. A target stimulus was presented with 30% probability in two- or three-positions. By cue signal presentation, subjects either focused their attention on one position or divided attention for two or three positions and abducted right arm for target stimulus. Event-related potentials and onset time of postural muscles were measured. RESULTS: P1-N1 and N2 amplitudes decreased with attentional dispersion in both conditions, but P3 did not change. With attentional dispersion to three-positions, N2 latency increased and start of late CNV was delayed, and also the onset time of gluteus medius was late in correlation to the late CNV changings, with no changings in two-positions. CONCLUSIONS: With attentional dispersion, brain activation decreased in the area related to the sensory processing and especially in the stimulus discrimination area. With increasing attentional dispersion, the delay in motor preparation or anticipatory attention to target stimuli was related to the delay in stimulus discrimination and onset time of postural muscle activation. SIGNIFICANCE: Effects of attentional dispersion on sensory-motor processing of anticipatory postural control were experimentally demonstrated.

Age-related changes and sex differences in postural control adaptability in children during periodic floor oscillation with eyes closed.

We investigated age-related changes and sex differences in adaptability of anticipatory postural control in children. Subjects comprised 449 children (4-12 years old) and 109 young adults (18-29 years old). Subjects stood with eyes closed on a force-platform fixed to a floor oscillator. We conducted five trials of 1-minute oscillation (0.5 Hz frequency, 2.5 cm amplitude) in the anteroposterior direction. Postural steadiness was quantified as the mean speed of the center of pressure in the anteroposterior direction (CoPy). In young adults, CoPy speed decreased rapidly until the third trial for both sexes. Adaptability was evaluated by changes in steadiness. The adaptability of children was categorized as "good," "moderate," and "poor," compared with a standard variation of the mean CoPy speed regression line between the first and fifth trials in young adults. Results were as follows: (1) anticipatory postural control adaptability starts to develop from age 6 in boys and 5 in girls, and greatly improves at age 7-8 in boys and 6 in girls; (2) the adaptability of children at age 11-12 (74% of boys and 63% of girls were categorized as "good") has not yet reached the same level as for young adults; (3) the adaptability at age 11-12 for girls is temporarily disturbed due to early puberty.

Effects of experimentally induced low back pain on the sit-to-stand movement and electroencephalographic contingent negative variation.

It is becoming increasingly evident that people with chronic, recurrent low back pain (LBP) exhibit changes in cerebrocortical activity that associate with altered postural coordination, suggesting a need for a better understanding of how the experience of LBP alters postural coordination and cerebrocortical activity. To characterize changes in postural coordination and pre-movement cerebrocortical activity related to the experience of acutely induced LBP, 14 healthy participants with no history of LBP performed sit-to-stand movements in 3 sequential conditions: (1) without experimentally induced LBP; NoPain1, (2) with movement-associated LBP induced by electrocutaneous stimulation; Pain, and (3) again without induced LBP; NoPain2. The Pain condition elicited altered muscle activation and redistributed forces under the seat and feet prior to movement, decreased peak vertical force exerted under the feet during weight transfer, longer movement times, as well as decreased and earlier peak hip extension. Stepwise regression models demonstrated that electroencephalographic amplitudes of contingent negative variation during the Pain condition significantly correlated with the participants' change in sit-to-stand measures between the NoPain1 and Pain conditions, as well as with the subsequent difference in sit-to-stand measures between the NoPain1 and NoPain2 conditions. The results, therefore, identify the contingent negative variation as a correlate for the extent of an individual's LBP-related movement modifications and to the subsequent change in movement patterns from before to after the experience of acutely induced LBP, thereby providing a direction for future studies aimed to understand the neural mechanisms underlying the development of altered movement patterns with LBP.

Effects of regular heel-raise training aimed at the soleus muscle on dynamic balance associated with arm movement in elderly women.

The effects of low-intensity muscle training with heel-raises on dynamic balance associated with bilateral arm flexion were investigated in postmenopausal elderly women. Twenty-six elderly women were evenly grouped into training and control groups. Training group subjects performed 100 heel raises per day for 2 months. The training was aimed at hypertrophy of the soleus muscle, which has a relatively high proportion (ca. 90%) of slow-twitch muscle fibers and is one of the main postural muscles. Dynamic balance was measured while arm flexion was performed in response to a visual stimulus (simple-reaction condition) or at the subjects' own pace (own-timing condition). The following parameters were compared before and after the training period: plantar flexion strength, thicknesses of the gastrocnemius and soleus (by ultrasound), reaction time of the anterior deltoid in the simple-reaction condition, activation onset timing of postural muscles with respect to the deltoid, movement angles of ankle and hip joints, and postural fluctuation. In the training group only, the following training-related effects were demonstrated: (a) increase in plantar flexor strength and thickness of the soleus, (b) shortening of the deltoid reaction time, (c) earlier activation of the erector spinae in the simple-reaction condition and the soleus in the own-timing condition, and (d) increase in ankle movement in the own-timing condition and a decrease in postural fluctuation. This heel-raise training in the elderly can increase soleus thickness within the triceps surae and improve postural control modality and stability that are effectively contributed to by the leg muscle. This training consists of a low-intensity exercise that requires neither special machines nor a specific environment and can be performed safely for all old-aged groups.

Activation timing of postural muscles during bilateral arm flexion in self-timing, oddball and simple-reaction tasks.

BACKGROUND: We investigated the effect of time constraint on activation timing of postural muscles during bilateral arm flexion in self-timing, oddball and simple-reaction tasks. METHODS: Thirteen healthy adults flexed their arms from a suspended position with maximum speed and stopped at the shoulder level. For erector spinae-longissimus (ES), biceps femoris (BF), and gastrocnemius (GcM), onset timing of burst activation with respect to the anterior deltoid (AD), and the displacement of the center of pressure in the anteroposterior direction (CoPy) were analyzed. RESULTS: AD reaction time was significantly shorter in the simple-reaction task than oddball task, suggesting that time constraint would be lower in the task order noted above and affected the state of postural preparation. The following properties were found in the onset timing of postural muscle: (1) the onset timing of BF and GcM were earlier in the task order noted above, and (2) the earliest activated distal muscle in the self-timing task was activated later in the simple-reaction task. CoPy displacement was smaller in the same task order as the onset timing. CONCLUSIONS: It appears that with sufficient postural preparation, the focus of postural control is on the reduction of postural disturbance and earlier lower leg muscle activation.

Regular heel-raise training focused on the soleus for the elderly: evaluation of muscle thickness by ultrasound.

The soleus, one of the triceps surae muscles, greatly contributes to standing and walking. Strength training focused on the soleus could be important to prevent age-related deterioration in these functions. We therefore investigated the effects of regular heel-raise training focused on the soleus for the elderly. Forty-nine healthy women aged 60 to 79 years trained for at least 40 days in a period of two months. Training consisted of a set of 100 repetitions per day of heel-raise with both legs in a standing position. The training effect was evaluated by changes in each muscle thickness of the soleus and gastrocnemius medialis, which was measured using an ultrasound scanner, as well as plantar flexor strength. The subjects' ability to perform the training and their subjective opinions of its effects were assessed by a questionnaire survey. Plantar flexor strength and thicknesses of the soleus and gastrocnemius medialis were increased significantly by the training. The percentage increase in thickness was significantly greater for the soleus than for the gastrocnemius medialis (12.7% vs. 6.6%). These improvements did not significantly correlate with age. The questionnaire results suggested that the elderly were able to safely and easily perform the heel-raise training at home. This study demonstrated that regular heel-raise training is an effective muscle training method for the elderly, focused on the soleus.

Changes in muscle thickness of gastrocnemius and soleus associated with age and sex.

BACKGROUND AND AIMS: Gastrocnemius and soleus in the triceps surae have functional and histological differences.We therefore investigated age-related changes in muscle thickness of these two muscles, as well as the difference in these changes between men and women. METHODS: Participants comprised 847 healthy adults aged 20 to 79 years. A B-mode ultrasound scanner, with participants sitting on a chair, was used to measure muscle thickness from the midpoint of the gastrocnemius medialis muscle at the level of maximum girth (target point). The ratio of muscle thickness to height was calculated. The inter-rater and intra-rater reliability of measuring muscle thickness with the ultrasound scanner and the validity of the target point were demonstrated before the examination. RESULTS: Gastrocnemius was significantly thinner in women aged 60 or older and in men aged 50 or older, compared with their counterparts in their 20s. For soleus, no significant differences in thickness were found among the age groups in either sex. Decline in muscle thickness from age 40-79 was greater for gastrocnemius than for soleus. CONCLUSIONS: These results confirm that gastrocnemius starts to deteriorate earlier and atrophies at a faster pace than soleus. A significant sex difference was found only in the onset age of gastrocnemius deterioration, which was earlier in men than in women.