In the debate about the direction of time in physics, the concept of time reversal has been central. Tradition has it that time-reversal invariant laws are sufficient to state that the direction of time is non-fundamental or emergent. In this paper, we review some of the debates that have gravitated around the concept of time reversal and its relation to the direction of time. We also clarify some of the central concepts involved, showing that the very concept of time reversal is more complex than frequently thought.

Of the four interrelated concepts in the title, only symmetry has an exact mathematical definition. In mathematical development, symmetry is a graded variable-in marked contrast with the popular binary conception of symmetry in and out of the laboratory (i.e. an object is either symmetrical or nonsymmetrical). Because the notion does not have a direct graded perceptual counterpart (experimental participants are not asked about the amount of symmetry of an object), students of symmetry have taken various detours to characterize the perceptual effects of symmetry. Current approaches have been informed by information theory, mathematical group theory, randomness research, and complexity. Apart from reviewing the development of the main approaches, for the first time we calculated associations between figural goodness as measured in the Garner tradition and measures of algorithmic complexity and randomness developed in recent research. We offer novel ideas and analyses by way of integrating the various approaches.

Stimulus equivalence (SE) is demonstrated when participants exposed to conditional discrimination training pass tests for reflexivity, symmetry, transitivity, and equivalence (symmetry combined with transitivity). Most theorists attribute the origin of SE to operant processes, but some argue that it results from Pavlovian conditioning. Symmetry is problematic for the latter hypothesis because it seems to require excitatory backward conditioning. However, equivalence tests resemble backward sensory preconditioning (BSP) and backward second-order conditioning (BSOC), two well-established processes. A review of associationistic theories of BSP and BSOC showed that the temporal coding hypothesis (TCH) explains outcomes that other associationistic theories cannot explain (i.e., BSOC and BSP effects after first-order conditioning with delay vs. trace conditioning and forward vs. backward conditioning). The TCH assumes that organisms encode the temporal attributes of stimulus events (e.g., order and interval duration) and this temporal information is integrated across separate phases of training. The TCH seems compatible with a behavioral analysis if direct stimulus control replaces the notion of temporal maps. The TCH perspective does not seem applicable to SE because SE tests are not predictive tasks. This suggests that SE is fundamentally different from BSP and BSOC and a Pavlovian conditioning analysis of SE is inadequate. This conclusion is consistent with previous criticism of a Pavlovian account of SE according to which Pavlovian conditioning cannot be interpreted as stimulus substitution.

Kinetic asymmetries during sit-to-stand have been consistently observed early after total knee arthroplasty; however, the longer-term outcomes are less clear. The purpose of this systematic review and meta-analysis was to analyze the results of studies examining inter-limb kinetic symmetry during sit-to-stand performance among individuals who were at least one-year post unilateral total knee arthroplasty.
PubMed, SPORTDiscus, CINAHL, and Health Source databases were searched. Studies were included if they were published in a peer-reviewed journal, included subjects who had undergone unilateral total knee arthroplasty at least one-year prior, and examined vertical ground reaction forces and/or knee extension moments for the involved and uninvolved limbs during sit-to-stand performance. Data were transformed into a limb symmetry index, which expressed the ratio of the peak forces/moments for the involved limb, relative to the uninvolved limb (1.0 reflects perfect symmetry). These ratios were meta-analyzed using the ratio of means method.
Seven studies were deemed eligible for inclusion. Ground reaction force data was pooled from seven studies and knee extension moment data was pooled from two studies. For the peak vertical ground reaction forces, the pooled limb symmetry index was 0.96 (CI95% = [0.93, 0.99]). For the peak knee extension moments, the pooled limb symmetry index was 0.91 (CI95% = [0.84, 0.98]). In both cases this reflects greater limb/knee loading for the uninvolved limb, relative to the involved limb.
Asymmetries in limb/knee loading persist beyond the one-year post-operative period following total knee arthroplasty, potentially contributing to degenerative changes for the uninvolved limb.

BACKGROUND: Breast reconstruction (BR) is routinely offered to restore symmetry after mastectomy for breast cancer. Not all women, however, may want reconstructive surgery. A contralateral mastectomy (CM) to achieve \"flat symmetry\" can be an excellent alternative, but surgeons are often reluctant to offer this procedure. This systematic review aimed to summarize the available evidence regarding the outcomes of CM as the first step to developing guidelines in this area.
METHODS: PubMed, MEDLINE, CINAHL and PsycINFO were searched to identify primary research studies, published in English between 1 January 2000 and 30 August 2022, evaluating clinical or patient-reported outcomes for women who underwent a CM without reconstruction after a mastectomy for unilateral breast cancer. Simple descriptive statistics summarized quantitative data, and content analysis was used for qualitative data.
RESULTS: The study included 15 studies (13 quantitative, 1 qualitative, and 1 mixed-methods) evaluating outcomes for at least 1954 women who underwent a bilateral mastectomy without reconstruction (BM) after unilateral breast cancer. The risk of surgical complications after BM was higher than after unilateral mastectomy without reconstruction (UM) but significantly less than after BR. Satisfaction with the decision for BM was high in all the studies. Key themes relating to flat denial, stigma, and gender-based assumptions were identified.
CONCLUSIONS: Women electing to undergo BM reported high levels of satisfaction with their decision and complication rates similar to those for UM. Further study is needed to comprehensively explore the outcomes for women seeking BM, but these data should give surgeons confidence to offer the procedure as an alternative option for symmetry after unilateral mastectomy for breast cancer.
BACKGROUND: This systematic review was prospectively registered on the PROSPERO database (CRD42022353689).

The purpose of this study was to evaluate the outcomes of our polyneural, zone-based reanimation approach for patients with neoplasm-induced facial paralysis.
A retrospective review of consecutive patients who underwent facial reanimation surgery using multiple donor nerve transfers was undertaken. In each case, the selection of donor nerves was based on the availability of donor nerve and the viability of the motor endplate on the affected side. Sources of the neural inputs utilized included the remnant facial nerve stump, masseteric nerve, partial hypoglossal nerve, and branches of the contralateral facial nerve. Clinical outcomes were scored by expert raters. Ratings were undertaken using the modified House-Brackmann, eFACE and MEEI FACEgram scoring systems.
Between 2017 and 2020, 12 patients were included in the study (mean age 60 years; range 26-81 years). Eight patients (67%) achieved a grade III outcome on the modified House-Brackmann grading scale. Mean eFACE static and dynamic scores were 76 and 57 respectively, reflecting a high degree of symmetry at rest and moderate restoration of dynamic movement. Mean time to movement was 5.4 months (SD 1.9). Objective FACE-gram measurements confirmed restoration of midface movement with an average improvement in smile excursion and mouth angle excursion of 3.19 mm (SD 3.18) and 4.81° (SD 2.90) respectively.
Facial reanimation using multiple nerve transfers is effective in achieving improvements in facial function and symmetry.

Structural musculoskeletal adaptations following amputation, such as bone mineral density (BMD) or muscle architecture, are often overlooked despite their established contributions to gait rehabilitation and the development of adverse secondary physical conditions. The purpose of this review is to provide a summary of the existing literature investigating musculoskeletal adaptations in individuals with major lower-limb amputations to inform clinical practice and provide directions for future research. Google Scholar, PubMed, and Scopus were searched for original peer-reviewed studies that included individuals with transtibial or transfemoral amputations. Summary data of twenty-seven articles indicated reduced BMD and increased muscle atrophy in amputees compared to controls, and in the amputated limb compared to intact and control limbs. Specifically, BMD was reduced in T-scores and Z-scores, femoral neck, and proximal tibia. Muscle atrophy was evidenced by decreased thigh cross-sectional area, decreased quadriceps thickness, and increased amounts of thigh fat. Overall, amputees have impaired musculoskeletal health. Future studies should include dysvascular etiologies to address their effects on musculoskeletal health and functional mobility. Moreover, clinicians can use these findings to screen increased risks of adverse sequelae such as fractures, osteopenia/porosis, and muscular atrophy, as well as target specific rehabilitation exercises to reduce these risks.

UNASSIGNED: The evolution of healthcare from 18th-century reductionism to 21st-century postgenomic holism has been described in terms of systems medicine, and the impact of the built environment on human health is the focus of investigation and development, leading to the new specialty of evidence-based, therapeutic architecture. The traditional system of Vāstu architecture-a design paradigm for buildings which is proposed to promote mental and physical health-has been applied and studied in the West in the last 20 years, and features elements absent from other approaches. This review critically evaluates the theory and research of a well-developed, standardized form of Vāstu-Maharishi Vastu® architecture (MVA). MVA\'s principles include development of the architect\'s consciousness, universal recommendations for building orientation, siting, and dimensions; placement of key functions; and occupants\' head direction when sleeping or performing tasks. The effects of isolated Vāstu elements included in MVA are presented. However, the full value of MVA, documented as a systematic, globally applicable practice, is in the effect of its complete package, and thus this review of MVA includes evaluating the experience of living and working in MVA buildings.
UNASSIGNED: The published medical and health-related literature was systematically surveyed for research on factors related to isolated principles applied in MVA as well as on the complete system.
UNASSIGNED: Published research suggests that incorporating MVA principles into buildings correlates with significant improvements in occupants\' physical and mental health and quality of life: better sleep, greater happiness of children, and the experience of heightened sense of security and reduced stress. The frequency of burglaries, a social determinant of health, also correlates. Potential neurophysiological mechanisms are described.
UNASSIGNED: Findings suggest that MVA offers an actionable approach for managing a key social determinant of health by using architectural design as preventive medicine and in public health.

To report the clinical phenotype and associated genotype of a European patient cohort with GUCY2D-related autosomal-dominant (AD) cone-/cone-rod dystrophy (COD/CORD), we retrospectively analyzed 25 patients (17 female, range 12-68) with GUCY2D-related AD-COD/CORD from three major academic centers in Europe and reviewed the previously published data of 148 patients (visual acuity (VA), foveal thickness, age of first symptoms, and genetic variant). Considering all the patients, the onset of first symptoms was reported at a median age of 7 years (interquartile range 5-19 years, n = 78), and mainly consisted of reduced VA, photophobia and color vision abnormality. The disease showed a high degree of inter-eye symmetry in terms of VA (n = 165, Spearman\'s ρ = 0.85, p < 0.0001) and foveal thickness (Spearman\'s ρ = 0.96, n = 38, p < 0.0001). Disease progression was assessed by plotting VA as a function of age (n = 170). A linear best-fit analysis suggested a loss of 0.17 logMAR per decade (p < 0.0001). We analyzed the largest cohort described so far (n = 173), and found that the most common mutations were p.(Arg838Cys) and p.(Arg838His). Furthermore, the majority of patients suffered severe vision loss in adulthood, highlighting a window of opportunity for potential intervention. The emerging patterns revealed by this study may aid in designing prospective natural history studies to further define endpoints for future interventional trials.

OBJECTIVE: The aim of this study was to quantify the symmetry of the facial hard tissue structures using three-dimensional radiographic imaging modalities in a normal Caucasian population group.
METHODS: Electronic literature search was conducted in the following databases: PubMed, Embase, Web of Science, and Cochrane Library up to February 2021. The studies assessing symmetry of facial bones using computed tomography (CT) and cone beam CT were included.
RESULTS: The initial search revealed 8811 studies. Full-text analysis was performed on 33 studies. Only 10 studies were found eligible based on the inclusion criteria. The qualitative analysis revealed that a significant variability existed in relation to the methodologies applied for symmetry quantification.
CONCLUSIONS: The current review suggested that the overall relative symmetry of the normal Caucasian population group varied depending on the skeletal structure being assessed; however, majority of the observations showed a symmetry within the range of 1 mm without any significant difference between left and right sides.
CONCLUSIONS: The quantification of facial hard tissue structure symmetry is vital for the diagnosis and treatment planning of orthodontic and/or maxillofacial surgical procedures. Prospero registration number CRD42020169908.