Context specificity of operant discriminative performance in pigeons: II. Necessary and sufficient conditions

Six experiments were performed to explore the necessary and sufficient conditions for producing context specificity of discriminative operant performance in pigeons. In Experiment 1, pigeons learned a successive discrimination (red S+/blue S−) in two chambers that had a particular odor present and between which they were frequently switched. The birds subsequently learned the reversal (blue S+/ red S−) in one of these chambers with a different odor present. When switched to the alternative chamber, although the odor and the reinforcement contingency were still appropriate to the reversal, performance appropriate to the original discrimination recurred in subjects for which the houselights were on during training and testing but not for those for which the houselights were off. This indicated the importance of visual contextual cues in producing context specificity. Experiment 2 showed that the frequent switching between boxes in initial training was of no consequence, presumably because the apparatus cues were highly salient to the subjects. Experiment 3 showed significantly less context specificity when odor cues were omitted. Experiment 4 showed that simply using a different reinforced stimulus in each phase of training was ineffective in producing context specificity. Experiment 5 showed that the generalization test procedure used in Experiment 4 was sensitive to context specificity when discrimination-reversal training was used with different odors in the two training phases. Experiment 6 replicated the results of Experiment 4, but then showed that when different odors accompanied the two training phases, context specificity was obtained with the single-stimulus paradigm. Thus in both single-stimulus and discrimination-reversal paradigms, redundant odor cues potentiated learning about apparatus cues.     

Estrogen and Neural Plasticity

Converging clinical evidence suggests that postmenopausal estrogen therapy in women is associated with improved cognition and a reduced incidence of Alzheimer's disease. In experimental work, investigators have found estrogen to promote changes in synaptic plasticity within the nervous system. In this article, we review both the clinical and the experimental literature, and consider mechanisms of action of estrogen on neurons and synaptic plasticity, and how they might protect against the cognitive impairments of old age.     

Can mismatch negativity be linked to synaptic processes? A glutamatergic approach to deviance detection

This article aims to provide a theoretical framework to elucidate the neurophysiological underpinnings of deviance detection as reflected by mismatch negativity. A six-step model of the information processing necessary for deviance detection is proposed. In this model, predictive coding of learned regularities is realized by means of long-term potentiation with a crucial role for NMDA receptors. Mismatch negativity occurs at the last stage of the model, reflecting the increase in free energy associated with the switching on of silent synapses and the formation of new neural circuits required for adaptation to the environmental deviance. The model is discussed with regard to the pathological states most studied in relation to mismatch negativity: alcohol intoxication, alcohol withdrawal, and schizophrenia.     

The influence of materialism and ideal body internalization on body‐dissatisfaction and body‐shaping behaviors of young men and women: Support for the Consumer Culture Impact Model

Exposure to media images of the ‘body‐perfect’ ideal has been partly blamed for the pursuit of thinness among women and muscularity among men. Research has largely overlooked the materialistic messages frequently associated with these images. We present findings from two studies with Icelandic students aged 18–21, one focusing on young women (n = 303) and one on young men (n = 226), which test associations of materialistic and body‐perfect ideals with body dissatisfaction and excessive body shaping behaviors. In both studies, the internalization of materialistic values is strongly linked to the internalization of body‐perfect ideals: the thin‐ideal for young women, and the muscular‐ideal for young men. A materialist value orientation also predicted body dissatisfaction in both studies, and was linked to body shaping behaviors, albeit differently for young women and men. Thus, the research identifies materialism as a further correlate of both body dissatisfaction and excessive body‐shaping behaviors. The findings support Dittmar's ( 2008 ) Consumer Culture Impact Model, which proposes that the body‐perfect and ‘material good life’ ideals jointly impact well‐being.     

Modulation of motor variability related to experimental muscle pain during elbow-flexion contractions

Experimental muscle pain typically reorganizes the motor control. The pain effects may decrease when the three-dimensional force components are voluntarily adjusted, but it is not known if this could have negative consequences on other structures of the motor system. The present study assessed the effects of acute pain on the force variability during sustained elbow flexion when controlling task-related (one-dimensional) and all (three-dimensional) contraction force components via visual feedback. Experimental muscle pain was induced by bolus injection of hypertonic saline into m. biceps brachii, and isotonic saline was used as control. Twelve subjects performed sustained elbow flexion at different levels of the maximal voluntary contraction (5–30% MVC) before, during, and after the injections. Three-dimensional force components were measured simultaneously with surface electromyography (EMG) from elbow flexors and auxiliary muscles. Results showed that force variability was increased during pain compared to baseline for contractions using one-dimensional feedback (P < .05), but no significant differences were found for three-dimensional feedback. During painful contractions (1) EMG activity from m. trapezius was increased during contractions using both one-dimensional and three-dimensional feedback (P < .05), and (2) the complexity of EMG from m. triceps brachii and m. deltoid was higher for the three-dimensional feedback (P < .05). In conclusion, the three-dimensional feedback reduced the pain-related functional distortion at the cost of a more complex control of synergistic muscles.     

Muscle strength and functional performance is markedly impaired at the recommended time point for sport return after anterior cruciate ligament reconstruction in recreational athletes

PurposeTo examine potential deficits in muscle strength or functional capacity when comparing (1) an ACL reconstructed group to matched healthy controls, (2) the ACL reconstructed leg to the non-injured leg and (3) the non-injured leg to matched healthy controls, at the time-point of recommended sport return 9–12 months post-surgery.MethodsSixteen patients (male-female ratio: 9:7) 9–12 months post ACL reconstruction and sixteen age and sex matched healthy controls were included. Outcome measures included maximal knee extensor (KE) and knee flexor (KF) dynamometry, including measurement of rate of force development, functional capacity (counter movement jump (CMJ) and single distance hop (SDH)) and the Lysholm score.ResultsCompared to the control group, maximal KE and KF muscle strength were impaired in the ACL reconstructed leg by 27–39% and 16–35%, respectively (p < .001). Also, impairments of both CMJ (38%) and SDH (33%) were observed (p < .001). Rate of force development for KE were reduced in the ACL group compared to the control group (p < .001). Similarly, the KE and KF muscle strength, CMJ and SDH of the ACL reconstructed leg were impaired, when compared to the non-injured leg by 15–23%, 8–20%, 23% and 20%, respectively (p < .05).ConclusionMuscle strength and functional capacity are markedly impaired in the ACL reconstructed leg of recreationally active people 9–12 months post-surgery when compared to healthy matched controls and to their non-injured leg. This suggests that objective criteria rather than “time-since-surgery” criteria should guide return to sport.     

Reorganised motor control strategies of trunk muscles due to acute low back pain

This study assessed how the low back motor control strategies were affected by experimental pain. In twelve volunteers the right m. longissimus was injected by hypertonic and isotonic (control) saline. The pain intensity was assessed on a visual analog scale (VAS). Subjects were seated on a custom-designed chair including a 3-dimensional force sensor adjusted to the segmental height of T1. Electromyography (EMG) was recorded bilaterally from longissimus, multifidus, rectus abdominis, and external oblique muscles. Isometric trunk extensions were performed before, during, and after the saline injections at 5%, 10%, and 20% of maximum voluntary contraction force. Visual feedback of the extension force was provided whereas the tangential force components were recorded. Compared with isotonic saline, VAS scores were higher following hypertonic saline injections (P < .01). Experimental low back pain reduced the EMG activity bilaterally of the rectus abdominis muscles during contractions at 10% and 20% MVC (P < .01) although force accuracy and tangential force variability was not affected. Increased variability in the tangential force composition was found during pain compared with the non-painful condition (P < .05). The immediate adaptation to pain was sufficient to maintain the quality of the task performance; however the long-term consequence of such adaptation is unknown and may overload other structures.     

Coping in childhood: A comparative evaluation of different relaxation techniques

Abstract

This paper reports on the evaluation of relaxation trainings to improve the coping of children with stress situations. Over five training sessions, different relaxation techniques were presented to children to evaluate their short-term and long-term effects on different criteria. Included were a sensoric approach to relaxation (the Progressive Muscle Relaxation), an imaginative approach, and an imaginative approach with additional sensoric elements (combined training). Two control conditions were added. One of them presented non-tension producing stories instead of supplying a systematic relaxation training. The children of the second control condition participated at the measurements without any intervention. The participants were 826 children aged 7–14. The results show clear short-term effects on physiological parameters (blood pressure, pulse rate, body temperature) as well as on subjective ratings of the children's mood and somatic condition. In relation to the overall changes, the differences between the training conditions are comparatively small. Moreover, the long-term effects (recorded one week and two months after the five training sessions) were small in relation to the short-term effects.     

Strength Training Effects on Muscle Forces and Contributions to Whole-Body Movement in Cerebral Palsy

Strength training is often prescribed for children with cerebral palsy (CP); however, links between strength gains and mobility are unclear. Nine children (age 14?±?3?years; GMFCS I-III) with spastic CP completed a 6-week strength-training program. Musculoskeletal gait simulations were generated for four children to assess training effects on muscle forces and function. There were increases in isometric joint strength, but no statistical changes in fast-as-possible walking speed or endurance after training. The walking simulations revealed changes in muscle forces and contributions to body center of mass acceleration, with greater forces from the hip muscles during walking most commonly observed. A progressive strength-training program can result in isometric and dynamic strength gains in children with CP, associated with variable mobility outcomes.     

Muscle Damaging Exercise Affects Isometric Force Fluctuation as well as Intraindividual Variability of Cognitive Function

Healthy untrained men (N = 11) were asked to perform 10 series of 12 repetitions of knee eccentric extension (EE) at 160° per second. Quadriceps muscle torques evoked by electrical stimulation at 20 Hz (P20) and 100 Hz (P100), maximal voluntary isometric contraction torque (MVC), maximal isokinetic concentric torque (IT) at 30° per second, voluntary activation index (VA), simple reaction time (RTs), complex reaction time (RTc), and torque variability at 30% of MVC were measured before EE, immediately after EE, and 60 min and 24 hr after EE. MVC, IT, P20, P100, and VA decreased significantly after EE and remained depressed 24 hr later. Torque variability increased significantly after EE. Average RTs and RTc did not change after EE, whereas intraindividual variability in RTs and RTc increased significantly after EE.