RICERCA ITALIANA     

Research program

Computational and neural mechanisms of sensorimotor learning and control

University Co-ordinator

Università degli Studi di GENOVA - NEUROSCIENZE, OFTALMOLOGIA E GENETICA - GENOVA(GE)

Research Unit Leader

Carlo TROMPETTO

Description

In the present research, an innovative experimental platform for the execution of motor learning paradigms will be developed. Furthermore, the platform will be tested as a tool in motor rehabilitation of neurological patients. The system will consist of a haptic interface (planar handle, impedance controlled) competent to apply interactive motor trials. The subjects enrolled in the study (both healthy control and neurological patients) will be asked to use the experimental platform to perform with the dominant arm (healthy subjects) or the affected arm (patients) reaching movements on the horizontal plane, following trajectories fixed in advance or indicated just before the starting signal. The haptic interface will measure the subject's strength, whose vector will be displayed on a computer screen, positioned in front of the subject, allowing the creation of feedback systems, potentially useful to improve motor control. The handle, during subject's performance, will be set to be fully inert or to exert a strength, in order to facilitate or counteract the movement. The system will be able to generate passive movements, providing the possibility to determine their amplitudes and velocities
In this project, the tasks of the UR UNIGE 2 will be performed in the following two work-packages (WP): WP3 and WP8, and will collaborate with the other partners in WP6, in this case with a reource allocation of 10%.

WP3: Assessment of plastic changes in healthy subjects during motor learning

A complete neurophysiological approach will be used to investigate the neural modifications induced by motor skill learning. Measurements will be obtained before the start of the training (baseline condition) and immediately after each 45 minutes training session. Techniques able to investigate the sensory-motor system as a whole (tonic vibration reflex, long component of the stretch reflex) will be used, as well as techniques designed to assess the plastic changes in specific neural structures, as the sensory system (somato-sensory evoked potentials), the cortico-spinal system (transcranial magnetic stimulation) and the spinal circuitry (short component of the stretch reflex). The measurements will be focused in the biceps and triceps muscles of the dominant arm.
The tonic vibration reflex (TVR) will be elicited in the biceps and triceps muscles through a cylindrical vibrator placed over the muscles' tendons at the elbow, driven at 150-160 Hz with displacements of 1.0 to 2.0 mm by an electrical motor (Dynatronic, Valence, France).
The somatosensory evoked potentials (SEPs) will be elicited by electrical stimulation of the musculocutaneous nerve at the axilla, provoking a twitch of the biceps muscle (Rossini et al., 1987). Electrical activity will be recorded from the contralateral scalp (with respect to the stimulated arm), by means of averaging techniques that allow the detection of the evoked signals from the background electro-encephalographic (EEG) activity (Abbruzzese et al., 1980). Scalp SEPs will be recorded via Ag / AgCL disks attached with collodion, using non-cephalic reference electrodes.
Transcranial magnetic stimulation (TMS) will be delivered with a focal coil connected to a Magstim 200 magnetic stimulator (Magstim, Whitland, UK). Focal TMS will be delivered to the optimal scalp position for the activation of biceps muscle. The coil will be placed tangentially to the scalp, with the handle pointing backwards and rotated away from the midline by 45° degrees. Using this stimulation set, the induced current in the brain will be directed perpendicular to the line of the central sulcus, thus activating the corticospinal elements mainly trans-synaptically (for a review, see Abbruzzese and Trompetto, 2002).
Measures of corticospinal excitability will include resting and active motor thresholds, recruitment curves both at rest and during a mild voluntary contraction of the target muscles.
Stretch reflex responses will be evoked in biceps and triceps muscles during a submaximal tonic contraction. A standard torque perturbation (15 Nm, 170 ms) will be applied to the forearm to induce reflex EMG activity in the two investigated muscles. Totally 40 perturbations will be applied (20 for the biceps and 20 for the triceps). Both short and long latency stretch reflexes will be evaluated.

Percentual resource allocation: 45%
Deliverables:
D3.1: Report on experiments performed with TVR (month 12)
D3.2: Report on experiments performed with SEPs (month 12)
D3.3: Report on experiments performed with TMS (month 15, in cooperation with UR_UniRoma3)

WP8: Neurorehabilitation

This WP is aimed to investigate the rehabilitative potentialities of the experimental platform.
A group of patients will be selected showing an upper limb motor impairment. The clinical signs (weakness, spasticity, bradykinesia, dystonic and ataxic features) will be evaluate quantitatively using the appropriate clinical scales. Exclusion criteria will be concomitant peripheral neuropathies, systemic vasculopathies, dementia or severe aphasia making patients uncooperative, age > 70 years, presence of metallic clips and pacemakers.
In daily sessions performed for an overall period of four weeks, the patients will be asked to use the experimental platform, tuning the handle on the basis of the motor impairment displayed by the single patient.
During the rehabilitative period, patients will be longitudinally evaluated by means of complete neurological examinations.
Before starting the rehabilitation period and immediately after the last session (four weeks later), the patients will be evaluated by means of the neurophysiological approach described in WP1, in order to reveal the modulations of plastic changes and correlate them to the clinical results.

Percentual resource allocation: 45%
Deliverables:
D8.1: Report on rehabilitation experiments focused on patients with upper limb motor impairment (month 24)
D8.3: Report on rehabilitation experiments focused on closed-loop FES (month 24; in cooperation with UR_Polito, UR_UniGE1)