Movimento volontario dell'arto superiore analisi, perturbazione, ottimizzazione Antonio Currà UOS Neurologia Universitaria, Osp. A. Fiorini, Terracina UOC Neuroriabilitazione ICOT, Latina, Dir. Prof. F. Pierelli
Voluntary movement voluntary recruitment of skeletal motor units to generate torque or displacement
To produce a voluntary movement the human nervous system must solve two problems the first is to prepare the movement the second is to execute it
During the motor preparation phase the nervous system has to plan the movement and code the motor programs
During movement execution it transforms the motor commands into action
Central voluntary motor command takes place at various levels, i.e. higher, middle, lower
The higher level can be subdivided into two functional units
The first unit provides the spatial and temporal representation or guidance of the movement it generates the kinematic parameters of the movement required spatial location of origin and end of movement kinematic profile including acceleration, speed, and course
This unit corresponds to activities termed motor imagination, mental representation, movement rehearsal, or spatiotemporal concept Hanakawa et al, 2003
The mental representation of movement is assumed to involve various cortical areas posterior parietal and lateral frontal premotor areas for sensorybased, i.e., externally triggered functions
The mental representation of movement is assumed to involve various cortical areas inferior parietal and prefrontal circuits for well learned skilled actions or internally-based functions, i.e., automatic movements
Patients with lesions of the posterior parietal or lateral prefrontal cortex may show apraxia and deficits in motor memory clinical impression of excessive motor hesitation with a sense of ineluctable inaccuracy during the performance of voluntary movement, and intense patient frustration. These patients are not paretic
The second unit of the higher level of motor command generates the voluntary drive, or motivation to move involves specific limbic pathways, particularly the medial frontalsubcortical (anterior cingulate) circuits, which could interface between deep limbic and neocortical functions Winterer et al, 2002
Anterior cingulate cortex activity is associated with a gain in reaction speed, at the expense of spatial accuracy subjects with short reaction times showed significantly more ACC activation (Brodmann Area 24) and an increased error rate this finding suggests that increased ACC activity is associated with a gain in reaction speed at the expense of correctness Mulert et al, 2005
Patients with lesions of the mesial prefrontal cortex show slow motor performance and reduced MRPs but are not paretic Wiese et al, 2004
The middle level of motor command corresponds to the planning and preparation of the movement the actual programming in time and space of the various muscle contractions and relaxations required to accomplish the movement intended by the higher level s mental representation
Important distinction is made between - the geometry of a movement (kinematics) - the forces needed to generate the movement (dynamics)
Parameters include timing, rapidity of onset, and intensity and duration of each muscle contraction
This level of motor preparation involves the rsma which has reciprocal connections with the prefrontal cortex and the basal ganglia it also involves the cerebellum, which adds this preparatory role to its involvement in monitoring the movement during its execution and in motor learning
Patients with disturbances of movement preparation typically exhibit acceleration deficits patients with disturbances of movement preparation are not paretic
The lower level of central voluntary motor command is the execution of the movement itself motor commands take the complex viscoelastic and inertial properties of multijointed limbs into account so that the appropriate force is applied to generate the desired motion
Refined motor command starts from the primary motor cortex
... through the centrum semiovale they descend in the internal capsule...
enter the cerebral peduncle at the base of the midbrain
run through the base of the pons where they are scattered among the transverse pontine fibers and nuclei of the pontine gray matter
coalescing again on the ventral surface of the medulla
to enter various fascicles of the spinal cord
.. where they reach the lower motor neurons
and through the neuromuscular junction activate the effector
Motor cortex activity signals not only lower level movement parameters (muscle forces) but also higher level parameters related to the trajectory of the hand during reaching
A simplified account of these areas of the motor system would probably state that Rothwell, 2012
Primary motor cortex is a common output path through which a large proportion of the motor command is funnelled to reach the spinal cord Rothwell, 2012
Dorsal premotor cortex is involved in performing movements triggered by arbitrary cues in the environment such as visual shapes, or auditory tones Rothwell, 2012
Ventral premotor cortex is involved in controlling (particularly hand) movements that relate to real objects in the environment within reach of the body Rothwell, 2012
Supplementary motor area is involved in performance of sequences of movement particularly if they have to be made in the absence of any external cues Rothwell, 2012
The modern laboratory can study voluntary movements by analyzing the ongoing electromyographic (EMG) activity and various kinematic variables including reaction time (RT), movement time, velocity and acceleration of the moving limb Prof. Mark Hallett and his fellows at NIH
According to the complexity of motor action or trajectory a voluntary movement can be classified as simple
or complex sequential, simultaneous Benecke et al, 1986 and 1987; Agostino et al, 1992
According to the number of joints activated single or multijoint Benecke et al, 1986 and 1987
According to the speed and accuracy requirements fast and slow
According to the modality of execution self initiated (internally guided) or externally triggered (sensory based)
According to the modality of execution self initiated (internally guided) or externally triggered (sensory based)
According to the modality of execution self initiated (internally guided) or externally triggered (sensory based)
According to the modality of execution self initiated (internally guided) or externally triggered (sensory based)
The usual way of investigating initiation for a voluntary movement is to study the reaction time
Brain processing during the simple reaction time
Sequential simple reaction time paradigm Modality of execution Subject initiates the movement in response to an external signal or cue visual, acoustic, somatosensory Subject initiates the movement at will Currà et al, 2000a and 2000b
Delayed sequential responses in dystonia with predominant impairment of SI sequences
Delayed sequential responses in chorea with similar slowing of SI and ET
Reaction time paradigm may be complex
Brain processing during choice reaction time A = stimulus identification B = stimulus response mapping C = response selection D = response programming E = response initiation
Sequential choice reaction time paradigm Knowledge of the path or modality of execution? Subjects move faster when they know the sequence path in advance Currà et al, 1997
Predominant impairment of known sequences in PD correspond to self-initiated sequeces
The usual way of investigating execution is to study the movement time Wacholder and Altenburger, 1926
Straight paths and bell-shaped velocity profiles also found during the execution of multi-joint movements Morasso, 1981
Reaching trajectories involving one or more joints consistently having invariant kinematic characteristics
This suggest reaching trajectories are planned in advance without initial need to take account of limb dynamics
Perturbation
Perturbing voluntary movements by delivering electrical or magnetic stimuli
Transcranial Magnetic Stimulation
Suprathreshold sptms lengthens RT more marked with stimuli applied closer to the expected onset of EMG Day et al. 1989; Rothwell et al. 1989; Pascual-Leone et al. 1992; Priori et al. 1993; Berardelli et al. 1994; Romaiguere et al. 1997; Ziemann et al. 1997; Leocani et al. 2000; Burle et al. 2002
Sub- or slightly suprathreshold sptms shortens RT when applied together with Go or at a short interval afterward Hallett et al. 1991; Pascual-Leone et al. 1992, 1994; Romaiguere et al. 1997; Terao et al. 1997; Ziemann et al. 1997; Leocani et al. 2000; Molinuevo et al. 2000; Burle et al. 2002; Hashimoto et al. 2004
The inhibitory aspect of motor preparation has received relatively less attention Decrease of SICI precedes increase of cortical excitability in Simple RT paradigm Reynolds and Ashby, 1999
Inhibition in the human motor cortex is reduced just before a voluntary contraction releasing the brakes before pressing the gas pedal Floeter and Rothwell, 1999
At all stimulation time points, both simple and choice reaction time is shorter with pptms than with sptms Difference in SICI during the early phase of srt and crt suggest that inhibitory circuits other than SICI are responsible for setting the level of cortical excitability at earlier parts of the reaction time period
Voluntary movement may be perturbed by interfering with the function of distinct motor areas Schluter et al, 1998
PMC stimulation alone disrupts an early stage of movement selection M1 stimulation disrupts the movements at a later stage of execution Schluter et al, 1998
PMC is important for selecting movements and the left hemisphere is dominant for the rapid selection of action
Optimization
Motor learning
Short practise
Long practise
transcranial Direct Current stimulation
Small electric field crosses the skull and influences the human brain as behavioral changes are recorded
Reversed effects for the two hands anodal stimulation improved RH > LH performance cathodal stimulation improved LH > RH performance
In the motor system, anodal tdcs enhances cortical excitability and cathodal tdcs diminishes it eighteen publications of motor studies 15 publications evaluated the effect of both anodal and cathodal over the target motor areas 3 evaluated the effect of anodal only Lang et al, 2004; Fregni et al, 2006; Furubayashi et al, 2008; Jefferson et al, 2009; Jeffery et al, 2007; Csifcsak et al, 2009; Kirimoto et al, 2009; Stagg et al, 2009
Transcranial Magnetic Stimulation epidural recordings
Low-frequency rtms (1-Hz) decreases the amplitude of the later I-waves with the amplitude of the I1-wave staying relatively constant intracortical circuitry modulated by 1-Hz rtms, and pyramidal cells are not directly modulated intracortical inhibitory activity, and therefore later I-waves, generated in superficial layers of motor cortex play a role in the early stages of skill acquisition rtms reduces cortical excitability, likely through its facilitation of GABA interneuron activity
High-frequency rtms ( 5Hz) increases D-wave amplitude and induces an additional I-wave modulates motor cortex excitability with differing neural mechanisms depending on the frequency and composition of the magnetic pulse trains continuous 5-Hz rtms increases D-wave amplitude and induces an additional I-wave I1-wave amplitude was not changed
Theta Burst stimulation (TBS) TBS consists of a train of pulse triplets delivered at 50 Hz, with sets of triplets delivered at 5 Hz TBS can be delivered as continuoustbs or intermittent TBS itbs uses triplets at the same frequency as ctbs but in bursts every 200 ms ctbs decreases MEP amplitude by decreasing the amplitude of I1- waves itbs increases MEP amplitude by increasing the amplitude of later I- waves [43].
rtms influences both distal
and proximal sequential limb movements
Paoloni, Di Lorenzo et al, 2012
rtms over cm1 influences both motor initiation and motor execution of a ET known, ET unknown, and SI simple upper limb movement Paoloni, Dilorenzo et al, submitted
Grazie