Reduced Balance Restoration Capacities Following Unilateral Vestibular Insult in Elderly Mice.

Acute vestibular syndrome (AVS) is characterized by severe posturo-locomotor and vestibulo-oculomotor impairment and accompanies several types of peripheral vestibulopathies (PVP). We know very little about its etiology, how its various symptoms are expressed and how it evolves with age. Robust repair capabilities of primary vestibular synapses have recently been shown to restore behavioral functionality. In this study, we used a mouse model of an excitotoxically induced unilateral vestibular lesion to compare the ability to restore balance and posture between old and young adult mice. We compared the temporal evolution of the evoked vestibular syndrome using a battery of behavioral tests to follow the evolution of postural-locomotor alterations and equilibrium. For the first time, we show that young adult (3 months) and elderly (22 months) mice are together able to restore normal postural-locomotor function following transient unilateral excitotoxic vestibular insult, though with different time courses. This animal study paves way for future, more detailed studies of how the early postural and locomotor disturbances following a unilateral insult are compensated for by various plasticity mechanisms, and in particular how age influences these mechanisms.

Age-Related Impairment of Hand Movement Perception Based on Muscle Proprioception and Touch.

Impairment in fine hand motor dexterity is well established in older people, yet little is known, about the impaired perception of hand movement in the elderly. Only an age-related increase in movement detection threshold has been reported. Perception of hand movements relies on multiple sensory information, including touch and muscle proprioception. The present study aims to investigate to what extent aging impacts the ability to perceive hand movements accurately and whether this impairment is from a muscle touch and/or tactile origin. To disentangle proprioception and touch, we used specifically designed stimuli: a mechanical vibration applied to the wrist muscle tendon and a tactile-textured disk rotating under the participant's hand, respectively. These two stimuli elicited illusions of hand rotations in two groups of young (20-30 years) and older (65-75 years) participants. Psychophysical testing showed that velocity discrimination thresholds of tactile and proprioceptive illusions were about twice lower in the young, than the older group. Also, relatively small isometric contractions were involuntarily elicited in wrist muscles during the illusions in both groups, but this motor response was positively correlated with the discrimination performance of the young, but not the older, participants. The present results show that muscle proprioception and touch are both functionally affected in kinesthesia after 65 years old, with a more pronounced alteration for muscle proprioception. This alteration in discriminative ability is likely due to impairment in the accurate encoding of the kinematic properties of hand movements. The possible central vs peripheral origin of these perceptive-motor changes with aging is discussed.

[Interindividual variability of contingent negative variation]. / Etude de la variabilité interindividuelle de la variation contingente négative (VCN).

The use of CNV in clinical practice requires the choice of a standardised protocol, the constitution of reference normative data and the consideration of intra- and interindividual variability. For this purpose, we recorded CNV in 86 control subjects (44 men and 42 women, 18 to 62 years old (mean age = 34 +/- 13 years) during a reaction time paradigm with a warning signal and a 1-second S1-S2 interval. Moreover, the role of inter-stimulation interval was analysed in a group of 12 subjects through the comparison of recordings made with 1- and 3-second intervals. The CNV amplitude, its morphology and topographic distribution as well as its resolution mode and evolution through the recording were studied. The subjects' performances and their interactions with electroencephalographic data were also included in the analyses. Our results underscore the contribution of age and gender and psychological factors to CNV variability. CNV amplitude (both M1 and M2) increased and changed topographic distribution toward more central sites in older. Men had faster reaction times than women and lower post-S1 P300. Moreover, the life events-related stress and the subject's current anxiety level were accompanied by a decreased CNV amplitude.

Flashbulb memories and the underlying mechanisms of their formation: toward an emotional-integrative model.

Flashbulb memories (FBMs) are detailed recollections of the context in which people first heard about important events. The present study investigates three models of the formation and maintenance of FBM. Two models have previously been proposed in the literature (Brown & Kulik, 1977; Conway et al., 1994). A third model of FBM that integrates theories of FBM and recent developments in the field of emotions is proposed. The present study compares these three competing models by investigating the FBMs that Belgian citizens developed upon learning of the unexpected death of their king Baudouin. Structural equation modeling revealed that, as compared to the two previously proposed models, the third model, which takes into account emotional processes, better explains FBM.

Adult timing after preweaning shifts of Zeitgeber in rats: crossed sensitization to time?

Preweaning albino rats were exposed from days 1 to 18 of life to successive 6-h shifts in light and temperature Zeitgebers, (1-18 rats), whereas controls (C) were raised under constant 12:12 L:D and temperature cycles. Cyclic Peak Interval performance at adulthood (100 days) showed that 1-18 rats were more accurate and sensitive to time than C subjects. These effects, which were akin to a crossed senzitization to time, were interpreted within the framework of scalar timing theory and the temporal information-processing model. They seemed not to depend upon changes in the pacemaker rate (lambda) or the memory constant K*, but to a change at the level of the decision process: 1-18 rats used a smaller response threshold than controls.

[Interindividual variability of exogenous and endogenous auditory evoked potentials in a condition of voluntary attention]. / Etude de la variabilité interindividuelle des potentiels évoqués auditifs exogènes et endogènes en condition d'attention volontaire.

The use of P300 in psychopathology raises the important problem of the constitution of reference normative data and of the high variability of auditive ERP's in controls. To handle better this problem, we recorded 86 control subjects, using an auditory oddball paradigm with motor response. We analyzed the successive components of the ERP's evoked by target and standard stimuli (N1, P2, N2, P3a, P3b and slow wave negativity). Our results underlined the role of age, sex and psychological factors on the ERP's interindividual variability: P3 amplitude decreased and its latency increased with age, while its topography was more frontal in the older than in the younger subjects. The P300 occurrence after standard stimuli and P3 amplitude after target stimuli were different according to sex. Moreover, P300 amplitude, latency and topography were related to the subject's anxiety level. Finally, our results also propose new description modes of ERP's relying on P3a and P3b relative peak amplitude (P300 with prominent P3a or P3b), topographical predominance (frontal or parietal P300) and duration of the late positive complex (brief or long-lasting P300). These data will improve the clinical use of P300.