Normative Values of the Repetitive Saliva Swallow Test and Clinical Factors Affecting the Test Scores in Healthy Adults.

The Repetitive Saliva Swallow Test (RSST) is a screening test for oropharyngeal dysphagia during which the subject is asked to perform as many empty swallows as possible in 30 s. Previous validation studies found a cutoff value of 3 > swallows as pathological. The aims of this study were to establish the normative values of the RSST and to examine the effect of clinical factors on RSST scores in healthy adults. A cross-sectional study of 280 adults. An equal number of females and males were recruited for each decade of life, ages 20 to 90 years. Patients reporting swallowing difficulties, history of neurologic disorders, or head and neck surgery or radiation were excluded. Data collected included RSST scores, number and type of comorbidities, number of prescribed medications, body mass index, smoking habits, and self-assessment xerostomia questionnaire. The mean RSST score for the entire cohort was 7.01 ± 2.86. Males had a higher RSST score (7.6 ± 3.04 compared to 6.47 ± 2.56, p = 0.001). Age showed an inverse correlation with RSST scores (Pearson's Correlation Coefficient (PCC) = -0.463, p < 0.0001), as well as body mass index, BMI (PCC = -0.2, p < 0.0001), number of co-morbidities (PCC=-0.344, p < 0.0001) and number of prescribed medications (PCC= -0.425, p < 0.0001). Self-reported amount of saliva positively correlated (PCC = 1.05, p = 0.04) with RSST scores. A multivariate logistic regression analysis was performed. Age, sex, BMI, and number of prescribed medications were found as significant independent factors on RSST scores. RSST scores in healthy adults decline with age and are lower in females, individuals taking multiple medications and with higher BMI. Mean RSST for all age groups did not fall beneath the previously established pathological cut-off.

Perinatal outcomes and long-term infectious morbidity of offspring born to mothers with familial Mediterranean fever.

PURPOSE: To investigate perinatal outcomes and long-term infectious morbidity in children of mothers with familial Mediterranean fever (FMF). METHODS: A population-based cohort study comparing perinatal outcomes and long-term infectious morbidity of offspring of mothers with and without FMF was conducted. All singleton deliveries between the years 1991-2021 in a tertiary medical center were included. The study groups were followed until 18 years of age for long-term infectious morbidity. A Kaplan-Meier survival curve was used to compare the cumulative incidence of long-term infectious morbidity, and generalized estimation equation (GEE) models as well as Cox proportional hazards models were constructed to control for confounders. RESULTS: During the study period, 356,356 deliveries met the inclusion criteria. 411 of them were women with FMF. The mean follow-up period interval was 9.7 years (SD = 6.2) in both study groups. Using GEE models, preterm delivery, cesarean delivery, and low birth weight were independently associated with maternal FMF. The total infectious-related hospitalization rate was significantly higher in offspring born to mothers with FMF compared to the comparison group (Kaplan-Meier survival curve, log-rank p < 0.001). Using a Cox proportional hazards model, controlling for gestational age, maternal age, diabetes mellitus, cesarean delivery, and hypertensive disorders, being born to a mother with FMF was found to be an independent risk factor for long-term infection-related hospitalization of the offspring. CONCLUSION: Maternal FMF was found to be independently associated with long-term infection-related hospitalization of the offspring. This positive correlation may reflect an intra-uterine pro-inflammatory environment which may result in the offspring's long-term susceptibility to infection.

Population-based corticospinal interactions in macaques are correlated with visuomotor processing.

Visuomotor transformation is a fundamental process in executing voluntary actions. The final steps of this transformation are presumed to take place in the corticospinal (CS) system, yet the way in which the motor cortex (MC) interacts with spinal circuitry during this process is unclear. We studied neural correlates of visuomotor transformation in the MC and cervical spinal cord while monkeys performed an isometric wrist task. We recorded 2 measures of population activity: local field potential (LFP), reflecting local synaptic inputs and multi-unit activity (MUA), reflecting spiking activity emitted by nearby neurons. We found robust cortical and spinal responses locked to visual and motor events. In motor cortex, LFP responses were predominantly visually related; MUA responses were mostly motor related. Spinal LFP responses were generally weak, yet spinal MUAs showed visual and motor responses with distinctive patterns. For both structures, amplitudes of visual responses were positively correlated with amplitudes of motor responses and negatively correlated with reaction times. The temporal relations of cortical and spinal responses shifted from weak coactivation before movement to increased coupling following torque onset, with cortical leading spinal activity. Thus, ongoing CS interactions may exist at early stages of movement preparation. These interactions are dynamic and may shape the executed motor action.

Correlations between groups of premotor neurons carry information about prehension.

How distinct parameters are bound together in brain activity is unknown. Combination coding by interneuronal interactions is one possibility, but, to coordinate parameters, interactions between neuronal pairs must carry information about them. To address this issue, we recorded neural activity from multiple sites in the premotor cortices of monkeys that memorized reach direction and grasp type followed by actual prehension. We found that correlations between individual spiking neurons are generally weak and carry little information about prehension. In contrast, correlations and synchronous interactions between small groups of neurons, quantified by multiunit activity (MUA), are an order of magnitude stronger. A substantial fraction of the information carried by pairwise interactions between MUAs is about combinations of reach and grasp. This contrasts with the information carried by individual neurons and individual MUAs, which is mainly about reach and/or grasp but much less about their combinations. The main contribution of pairwise interactions to the coding of reach-grasp combinations is when animals memorize prehension parameters, consistent with an internal composite representation. The informative interactions between neuronal groups may facilitate the coordination of reach and grasp into coherent prehension.

Computation in spinal circuitry: lessons from behaving primates.

Performing voluntary motor actions requires the translation of motor commands into a specific set of muscle activation. While it is assumed that this process is carried out via cooperative interactions between supraspinal and spinal neurons, the unique contribution of each of these areas to the process is still unknown. Many studies have focused on the neuronal representation of the motor command, mostly in the motor cortex. Nonetheless, to execute these commands there must be a mechanism that can translate this representation into a sustained drive to the spinal motoneurons (MNs). Here we review different candidate mechanisms for activating MNs and their possible role in voluntary movements. We discuss recent studies which directly estimate the contribution of segmental INs to the transmission of cortical command to MNs, both in terms of functional connectivity and as a computational link. Finally, we suggest a conceptual framework in which the cortical motor command is processed simultaneously via MNs and INs. In this model, the motor cortex provides a transient signal which is important for initiating new patterns of recruited muscles, whereas the INs translate this command into a sustained, amplified and muscle-based signal which is necessary to maintain ongoing muscle activity.

Encoding of reach and grasp by single neurons in premotor cortex is independent of recording site.

Neural activity has been studied during reaching and grasping separately, yet little is known about their combined representation. To study the functional organization of reaching and grasping in the premotor cortex (PM), we trained two monkeys to reach in one of six directions and grasp one of three objects. During prehensile movements, activity of proximal (shoulder and elbow) muscles was mainly modulated by reach direction, whereas distal (finger) muscles were also modulated by grasp type. Using intracortical microstimulation, we identified spatially distinct PM sites from which movements of proximal or distal joints were evoked. In contrast to muscles, modulation of neural activity by reach direction was similar for single units recorded in proximal and distal sites. Similarly, grasp type encoding was the same for units recorded in the different sites. This pattern of encoding reach and grasp irrespective of recoding site was observed throughout the task: before, during, and after prehension movements. Despite the similarities between single units within different sites, we found differences between pairs of units. Pairs of directionally selective units recorded by the same electrode in the same proximal site preferred similar reach directions but not grasp types, whereas pairs of object-selective units recorded in the same distal site tended to prefer the same grasp type but not reach direction. We suggest that the unexpected "mixing neurons" encoding reach and grasp within distal and proximal sites, respectively, provide a neural substrate for coordination between reach and grasp during prehension.

Comparison of direction and object selectivity of local field potentials and single units in macaque posterior parietal cortex during prehension.

Recent studies have shown that the local field potential (LFP) can provide a simple method for obtaining an accurate measure of reaching and saccade behaviors. However, it is not clear whether this signal is equally informative with respect to more complex movements. Here we recorded LFPs and single units (SUs) from different areas in the posterior parietal cortex of macaques during a prehension task and compared LFP selectivity with SU selectivity. We found that parietal LFPs were often selective to target direction or object and that percentages of selective LFPs were similar to percentages of selective SUs. Nevertheless, SUs were more informative than LFPs in several respects. Preferred directions and objects of LFPs usually deviated from a uniform distribution, unlike preferences of SUs. Furthermore, preferences of LFPs did not reflect preferences of SUs even when the two signals were recorded simultaneously via the same electrode. Additionally, selectivity of movement-evoked LFPs appeared only after movement onset, whereas SUs frequently showed premovement selectivity. Spectral analysis revealed a lower signal-to-noise ratio of the LFP signal. Different frequency bands derived from a single LFP site showed inconsistent preferences. Significant relations with target parameters were found for all tested bands of LFP, but effects in the fast (gamma) band exhibited properties that were consistent with contamination of the LFP by residual spiking activity. Taken together, our results suggest that the LFP provides a simple method for extracting ample movement-related information. However, some of its properties make it less adequate for predicting rapidly changing movements.

Distinct movement parameters are represented by different neurons in the motor cortex.

Recent studies suggested that a single motor cortical neuron typically encodes multiple movement parameters, but parameters often display strong temporal interdependencies. To address this issue, we recorded single-unit activity while macaque monkeys made continuous movements and employed an analysis that explicitly considered temporal correlations between several kinematic parameters; hand position, velocity, and acceleration. We found that while the activity of almost all motor cortical neurons was modulated during movement, most neurons were related only to a single dominant parameter. The activity of different neurons covaried with different parameters with similar strength, but neurons related to velocity were far more common than neurons related to any other parameter. These results were obtained for neurons recorded in the primary motor (M1) and dorsal premotor (PMd) cortices. Although neural activity tended to precede movement and PMd activity tended to precede M1 activity, time lags were widely dispersed. Shoulder and elbow muscles had the same properties as neurons, but their activity strictly preceded movement. These results demonstrate single neuron specificity and heterogeneity within a population of neurons with respect to movement parameters and time lags. Our results suggest that distinct subsets of motor cortical neurons are involved in computations related to distinct movement parameters.

Neuronal activity in motor cortical areas reflects the sequential context of movement.

Natural actions can be described as chains of simple elements, whereas individual motion elements are readily concatenated to generate countless movement sequences. Sequence-specific neurons have been described extensively, suggesting that the motor system may implement temporally complex motions by using such neurons to recruit lower-level movement neurons modularly. Here, we set out to investigate whether activity of movement-related neurons is independent of the sequential context of the motion. Two monkeys were trained to perform linear arm movements either individually or as components of double-segment motions. However, comparison of neuronal activity between these conditions is delicate because subtle kinematic variations generally occur within different contexts. We therefore used extensive procedures to identify the contribution of variations in motor execution to differences in neuronal activity. Yet, even after application of these procedures we find that neuronal activity in the motor cortex (PMd and M1) associated with a given motion segment differs between the two contexts. These differences appear during preparation and become even more prominent during motion execution. Interestingly, despite context-related differences on the single-neuron level, the population as a whole still allows a reliable readout of movement direction regardless of the sequential context. Thus the direction of a movement and the sequential context in which it is embedded may be simultaneously and reliably encoded by neurons in the motor cortex.

Dynamical organization of directional tuning in the primate premotor and primary motor cortex.

Although previous studies have shown that activity of neurons in the motor cortex is related to various movement parameters, including the direction of movement, the spatial pattern by which these parameters are represented is still unresolved. The current work was designed to study the pattern of representation of the preferred direction (PD) of hand movement over the cortical surface. By studying pairwise PD differences, and by applying a novel implementation of the circular variance during preparation and movement periods in the context of a center-out task, we demonstrate a nonrandom distribution of PDs over the premotor and motor cortical surface of two monkeys. Our analysis shows that, whereas PDs of units recorded by nonadjacent electrodes are not more similar than expected by chance, PDs of units recorded by adjacent electrodes are. PDs of units recorded by a single electrode display the greatest similarity. Comparison of PD distributions during preparation and movement reveals that PDs of nearby units tend to be more similar during the preparation period. However, even for pairs of units recorded by a single electrode, the mean PD difference is typically large (45 degrees and 75 degrees during preparation and movement, respectively), so that a strictly modular representation of hand movement direction over the cortical surface is not supported by our data.