Do Gravity-Related Sensory Information Enable the Enhancement of Cortical Proprioceptive Inputs When Planning a Step in Microgravity?

International audienceWe recently found that the cortical response to proprioceptive stimulation was greater when participants were planning a step than when they stood still, and that this sensory facilitation was suppressed in microgravity. The aim of the present study was to test whether the absence of gravity-related sensory afferents during movement planning in microgravity prevented the proprioceptive cortical processing to be enhanced. We reestablished a reference frame in microgravity by providing and translating a horizontal support on which the participants were standing and verified whether this procedure restored the proprioceptive facilitation. The slight translation of the base of support (lateral direction), which occurred prior to step initiation, stimulated at least cutaneous and vestibular receptors. The sensitivity to proprioceptive stimulation was assessed by measuring the amplitude of the cortical somatosensory-evoked potential (SEP, over the Cz electrode) following the vibration of the leg muscle. The vibration lasted 1 s and the participants were asked to either initiate a step at the vibration offset or to remain still. We found that the early SEP (90–160 ms) was smaller when the platform was translated than when it remained stationary, revealing the existence of an interference phenomenon (i.e., when proprioceptive stimulation is preceded by the stimulation of different sensory modalities evoked by the platform translation). By contrast, the late SEP (550 ms post proprioceptive stimulation onset) was greater when the translation preceded the vibration compared to a condition without pre-stimulation (i.e., no translation). This suggests that restoring a body reference system which is impaired in microgravity allowed a greater proprioceptive cortical processing. Importantly, however, the late SEP was similarly increased when participants either produced a step or remained still. We propose that the absence of step-induced facilitation of proprioceptive cortical processing results from a decreased weight of proprioception in the absence of balance constraints in microgravity

Overpressure on fingertips prevents state estimation of the pen grip force and movement accuracy

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Interactions entre contrôle inhibiteur et flexibilité comportementale: impact de la dénervation dopaminergique au niveau du striatum dorsomédian chez la souris

International audienceIn Parkinson's disease, nigrostriatal dopamine (DA) degeneration is commonly associated with motor symptomatology. However, non-motor symptoms affecting cognitive function, such as behavioural flexibility and inhibitory control may also appear early in the disease. Here we addressed the role of DA innervation of the dorsomedial striatum (DMS) in mediating these functions in 6-hydroxydopamine (6-OHDA)-lesioned mice using instrumental conditioning in various tasks. Behavioural flexibility was studied in a simple reversal task (nosepoke discrimination) or in reversal of a two-step sequence of actions (central followed by lateral nose-poke). Our results show that mild DA lesions of the DMS induces behavioural flexibility deficits in the sequential reversal learning only. In the first sessions following reversal of contingency, lesioned mice enhanced perseverative sequence of actions to the initial rewarded side then produced premature responses directly to the correct side omitting the central response, thus disrupting the two-step sequence of actions. These deficits may be linked to increased impulsivity as 6-OHDA-lesioned mice were unable to inhibit a previously learned motor response in a cued response inhibition task assessing proactive inhibitory control. Our findings show that partial DA denervation restricted to DMS impairs behavioural flexibility and proactive response inhibition in mice. Such striatal DA lesion may thus represent a valuable animal model for exploring deficits in executive control documented in early stage of Parkinson's disease

Results of source reconstruction from the grand average EEG data of the 6 participants (Low Resolution Electromagnetic Tomography, sLORETA) displayed on the used source space (Montreal warp brain aligned to the co-ordinate system of Talairach and Tournaux).

<p>sLORETA images depicted the estimated current density strengh corresponding to the effect of translation relative to baseline (Translation minus Stationary) for the Late SEP. The scale of the maps was chosen to maximize identification of the sources and were given a marked threshold to only show source activity that was 18% upper of minimal activation. Note the clearly distinguishable activation above the primary somatosensory cortice (top view) and the right posterior parietal cortex (e.g., VIP) and the Temporoparietal region.</p

SEPs recordings. Grand-Average for 6 participants recorded at electrode Cz for the Stationnary standing condition (Top panel), Translation standing and Translation stepping conditions (Bottom panel).

<p>The vertical dotted lines indicate the vibration onset and offset, the second vertical dotted line also indicates imperative tone stimulus for step execution. For both Translation conditions, the vertical dash-dotted line indicates the translation onset (occurring 500 ms before vibration). The “foot-off” indicates the onset of the stepping movement computed on the foot vertical velocity. The scalp topography was shown at the peak negativity for the participants average in the Sationary and Translation conditions.</p

Mean P1-N1 SEP amplitude of each participant (P1–P6) for the Stationary and Translation platform conditions (upper panel).

<p>Normalized attenuation for the translation condition relative to the Stationary condition (bottom panel). The mean attenuation for the 6 participants was of 21% (±6). <b>B:</b> Mean amplitudes for 6 participants of the P1-N1 early SEP and mean integral of EEG activity (iEEG, late SEP) computed in a time window comprising between early SEP ending until 600 ms (*: p<0.05).</p

Experimental set-up and mean lateral platform acceleration (left scale and red curve) and head acceleration (right scale and black curve) during Translation standing condition for the 6 participants.

<p>The onset and offset of head acceleration and deceleration, respectively, were indicated by the arrows according to the vestibular threshold (horizontal dotted lines). <b>B:</b> Mean platform and head accelerations for each of the 6 participants.</p