Gravity Cues Embedded in the Kinematics of Human Motion Are Detected in Form-from-Motion Areas of the Visual System and in Motor-Related Areas.

The present study investigated the cortical areas engaged in the perception of graviceptive information embedded in biological motion (BM). To this end, functional magnetic resonance imaging was used to assess the cortical areas active during the observation of human movements performed under normogravity and microgravity (parabolic flight). Movements were defined by motion cues alone using point-light displays. We found that gravity modulated the activation of a restricted set of regions of the network subtending BM perception, including form-from-motion areas of the visual system (kinetic occipital region, lingual gyrus, cuneus) and motor-related areas (primary motor and somatosensory cortices). These findings suggest that compliance of observed movements with normal gravity was carried out by mapping them onto the observer's motor system and by extracting their overall form from local motion of the moving light points. We propose that judgment on graviceptive information embedded in BM can be established based on motor resonance and visual familiarity mechanisms and not necessarily by accessing the internal model of gravitational motion stored in the vestibular cortex.

Neuroprotection by neuropeptide Y in cell and animal models of Parkinson's disease.

This study was aimed to investigate the potential neuroprotective effect of neuropeptide Y (NPY) on the survival of dopaminergic cells in both in vitro and in animal models of Parkinson's disease (PD). NPY protected human SH-SY5Y dopaminergic neuroblastoma cells from 6-hydroxydopamine-induced toxicity. In rat and mice models of PD, striatal injection of NPY preserved the nigrostriatal dopamine pathway from degeneration as evidenced by quantification of (1) tyrosine hydroxylase (TH)-positive cells in the substantia nigra pars compacta, levels of (2) striatal tyrosine hydroxylase and dopamine transporter, (3) dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) as well as (4) rotational behavior. NPY had no neuroprotective effects in mice treated with Y(2) receptor antagonist or in transgenic mice deficient for Y(2) receptor suggesting that NPY effects are mediated through this receptor. Stimulation of Y(2) receptor by NPY triggered the activation of both the ERK1/2 and Akt pathways but did not modify levels of brain derived neurotrophic factor (BDNF) or glial cell line-derived neurotrophic factor. These results open new perspectives in neuroprotective therapies using NPY and suggest potential beneficial effects in PD.

Updating process of internal model of action as assessed from motor and postural strategies in young adults.

Internal models are constantly updated based on the actions and experiences of a person in the world. In the present study, we proposed to assess the updating process of internal models of action by providing new environmental constraints for motor planning, postural control, and execution processes in daily tasks such as STS and BTS. STS and BTS tasks were performed with different inclinations of the support surface on which the participant and the chair were positioned: horizontal support, support tilted 10° to the right, or forward. Twelve healthy adults participated in this experiment. Kinematic characteristics were recorded using an optoelectronic motion analysis system. Movement duration and trunk inclination amplitudes were analyzed for STS and BTS as well as trunk orientation and strategies of head stabilization. Concerning the movement analysis our results showed (1) temporal asymmetry between STS and BTS, attributed mainly to the integration of the mechanical effects of gravity, and (2) a decrease of trunk movements when the support was tilted forward, attesting to an immediate adaptation process. Concerning the postural analysis our study revealed that adults adopted selective head stabilization on space strategy with respect to balance constraints. To conclude, young adults were able to immediately update their internal model of action in order to optimize motor control and vertical body orientation.

Is vertical postural orientation in weightlessness correlated with the subjects' perceptual typology?

It was proposed to investigate whether the central nervous system is able to select the most appropriate reference frame for controlling subjects' vertical orientation in response to severe environmental constraints such as microgravity and support perturbations. The question addressed was whether the subjects, regardless of their perceptual typology, might be able to use the same visual reference frame to control their vertical orientation. Fifteen subjects were asked to perform a sit-to-stand (STS) task under microgravity. Subjects were seated on a chair with their feet fixed to a horizontal or forwards tilted support (20°). When the support was tilted the subjects' ankles were placed at an angle of 110°. Two main findings emerged from this study. First, in all the experimental conditions, the results obtained showed that the subjects' controlled their postural orientation fairly correctly but not very precisely, since a bias was systematically observed in their head and trunk orientation. In other words, changes in their ankle angles and the absence of gravity only slightly disturbed their vertical body orientation, and when these two constraints were applied concomitantly, their effects were not cumulative. Secondly, contrary to our initial hypothesis, the subjects' postural orientation performances were not correlated with the perceptual typology. All the subjects preferentially used the visual reference frame to control their vertical postural orientation. The present findings confirm that the proprioceptive dominance of visual independent (VI) subjects enhances their ability to select the most appropriate reference frame to deal with inter-sensory disturbances such as those consisting here of microgravity combined with proprioceptive perturbations imposed at ankle level.