Does gravity influence the timing of motion? A project study on isochronous repetitive movements in human healthy subjects

The ability to perform isochronous repetitive movements while listening to a paced auditory stimulus requires a flexible process that integrates timing information with movement. Our group has developed and studied an audio-motor and recall-motor integration paradigm in which sets of repeated isochronous wrist"s flexion-extensions (IWFEs) are performed under different sensory conditions while minimizing visual and tactile information. Data indicate that the listening alone to paced auditory stimuli does not improve the precision of an isochronous performance (Modulation of isochronous movements in a flexible environment: links between motion and auditory experience. Bravi et al., 2014, Exp Brain Res, DOI 10.1007/s00221-014-3845-9). Recently, using the same paradigm, we tried to get further insights into the domain of repetitive timed movements by introduction of an external perturbation of the motor peripheral (kinesiotaping), thus showing how the precision of isochronous performance is subject to peripheral contribution. In line with our previous studies we are investigating, by means of a synchronization-continuation paradigm under different audio conditions, whether and how the gravity vector influences the production of IWFEs. First, sets of IWFEs are performed with the forearm, supported on armrest, in pronated position. Second, sets of IWFEs are performed with the forearm internally rotated by 90 degrees. Kinematic parameters were evaluated during each session and temporal parameters of movements were analyzed. Preliminary results suggest that the gravity vector influences isochronous movements by altering their durations. Results provide further evidence for an adaptable control of timing in the audio-motor coupling for isochronous movements

Do different musics interfere differently with the timing of repetitive isochronic movements? A project study on human healthy subjects

Our group has previously developed an experimental paradigm based on performance of repetitive isochronous wrist flexion-extensions (IWFEs) not requiring explicit time representation. IWFEs have been coupled to time-based audio stimuli. We found that timed auditory stimuli, expecially those in the high range of bpm, influence the timing of IWFEs in conditions of recall. Recalls of previously listened music reduce the rate of isochronous movements while recalls of clicks result in an increased rate of movements. At present we are investigating the ability of different timed musics - acknowledged being familiar vs unfamiliar - to shape perception of time and, consequently, to influence subsequent production of IWFEs. Selected subject are neither musically-trained nor listeners of classical music repertoire. We tested the differential behaviour of IWFEs in the conditions of listening of auditory stimuli, both metronome clicks and timed musical excerpts (as familiar, from contemporary entertainment music; as unfamiliar, from classical repertoire), and in recall conditions. Preliminary results suggest that music aknowledged being familiar univocally influences the timing of IWFEs in the conditions of recall whereas unfamiliar music evokes an assorted palette of results, veritably reflecting the listening biography of the single subjects or their attitude toward the unknown music message. Specific influence of music on movement tends to vanish with unfamiliarity, merging eventually with the one elicited by listening to simple clicks

THE COURSE OF PARVALBUMIN-POSITIVE GABAERGIC INTERNEURONS IN THE DORSAL HIPPOCAMPUS OF SOD1 MUTANT MICE

Cognitive impairments have been recently described in the amyotrophic lateral sclerosis (ALS), a progressive and fatal neurodegenerative disease. However, limited attention has been yet devoted to the study of cortical and hippocampal damages in the mouse model of ALS, SOD1 (G93A). We hypothesized possible association between cognitive impairment and changes of hippocampal GABAergic system in SOD1 mice. We analyzed SOD1 mice at presymptomatic (n=6, aged 13 weeks) and symptomatic (n=6, aged 18 weeks) states, and wild-type mice (n=6, aged 8-12 weeks). Animals were anaesthetized and perfused transcardially by 4% paraformaldehyde. Brain sections were immunohistochemically processed to visualize the largest class of interneurons of the hippocampal formation, the parvalbumin-immunopositive (PVi) GABAergic interneurons. After image acquisition, the hippocampus was reconstructed and analyzed with ImageJ (NIH). In SOD1 mice of both groups the number of PVi neurons was reduced by onethird to two-third. The decrease of PVi cells involved all hippocampal subregions. Interestingly, the PVi cell population was reduced already at presymptomatic stage, well before evidences for impairment of motor behaviors. Our findings situate hippocampus changes in SOD1 as starting point of the pathological chain of events, with potential implications on diagnosis and treatment of ALS

Isochronous sounds for isochronous movements: The multiplex control of timing in human subjects

The ability to perform isochronous movements when listening to rhythmic auditory input requires a foremost and flexible process to manage timing information. We tested whether isochronic movement is result of a multifaceted control process of timing whose individual elements are sensitive or variously resistant to auditory input. We recorded kinematic parameters of movement while participants, free from visual and touch information, performed repeated isochronous wrist's flexion-extensions in silence, driven by streams of beats or excerpts of music, and during auditory recall. Our study on the temporal behavior of isochronous wrist movements reveals composite interrelations between auditory input and motor performance. Some elements of timing are insensitive to auditory information. Other elements of timing are sensitive to auditory input, but only as regarding rhythmic information. Interestingly, the nature of the auditory input is not real-time influential, comes into play only during recall, and for a comprehensive characteristic of rhythmic motor performance: the tempo. Our results provide evidence of a multiplex control of timing in audio-motor coupling for isochronous movements. This intricate framework to control movement offers unique opportunities for the functional exploration of then normal and diseased human brain

Alterations of the cortico-cortical network in sensori-motor areas of dystrophin deficient mice.

The dystrophin defective mdx mouse, acknowledged model of Duchenne Muscular Dystrophy (DMD), bears outstanding alterations of the cortical architecture, that could be responsible for the cognitive impairment often accompanying this pathological condition. Using a retrograde tract tracing technique to label neurons in Golgi-like fashion, we investigated the fine anatomical organization of associative cortico-cortical projections in mdx mice. While the absolute number of associative pyramidal neurons was significantly higher in mdx than in control animals, the ratio between the number of supra- and infragranular cortico-cortical cells was substantially unmodified. Basal dendrites of layer 2/3 pyramidal neurons displayed longer terminal branches in mdx compared to controls. Finally, the density of dendritic spines was significantly lower in mdx animals. The anomalies of associative cortico-cortical projections provide potential groundwork on the neurobiological bases of cognitive involvement in DMD and value the role of cortical microcircuitry alterations as possible source of interference with peripheral motor impairment