Excitability changes in human corticospinal projections to muscles moving hand and fingers while viewing a reaching and grasping action

Abstract

Excitability of the H-reflex in the relaxed flexor digitorum superficialis (FDS) muscle was tested in five subjects observing a reaching and grasping action. The amplitude of the FDS H-reflex was modulated with a peak occurring during the hand-opening phase of the observed movement. When the H-reflex was facilitated by subliminal transcranial magnetic stimulation (TMS), the modulation was larger than for an unconditioned reflex of similar size. This suggests that the primary motor cortex excitability is modulated by action viewing and reasonably causes the motoneuronal excitability changes. Moreover, motor evoked potentials (MEPs) were elicited by supraliminal TMS in FDS, flexor carpi radialis (FCR) and first dorsal interosseus (FDI) when observing the same movement. MEP amplitude was modulated in FDS with the same time-course as the H-reflex, the peak excitability occurring during hand opening. In FDI, however, the maximal excitability occurred during finger closing while in FCR no correlation was found with the movement phases. Finally the EMG activity of FCR, FDS and FDI was recorded while the subjects were actually performing a grasping movement similar to the one observed. In all subjects and for each muscle there was a clear-cut correspondence between the time-course of the excitability modulation of MEPs and the temporal pattern of EMG recruitment. In conclusion, the present study suggests that 'motor resonance' subliminally activates the same motor pathways that would be overtly recruited in each observer when actually performing the observed movement, reproducing the personal strategy adopted in the same task.

Emotional stimuli modulate readiness for action: A transcranial magnetic stimulation study

“…This observation is in line with the findings of previous studies (Leocani et al, 2000;Nikolova et al, 2006;Rossini et al, 1988;van den Wildenberg et al, 2010). However, our main interest was in the possible effect of emotional processing on the dynamics of corticospinal excitability and in extending previous results that showed a tonic effect of emotion on the action system.…”

“…Neutral stimuli mostly depict static objects, whereas pleasant and unpleasant pictures mostly show humans involved in dynamic situations-that is, engaged in some mouth/facial or hand/arm activity or operating an object such as a gun or a knife. Observation of others' (emotionally neutral) actions increases the MEP amplitude (Fadiga, Fogassi, Pavesi, & Rizzolatti, 1995;Montagna, Cerri, Borroni, & Baldissera, 2005), as does observation of implied motion stimuli (Urgesi, Moro, Candidi, & Aglioti, 2006). As a result, the present MEP patterns might also be explained by the difference in action content of the stimuli.…”

“…Using single-pulse TMS applied over M1 at various time intervals between the presentation of the stimulus and the execution of the response in a simple reaction time (RT) protocol, several motor-TMS studies described a gradual increase in corticospinal excitability, starting 80-120 msec prior to movement onset and rising to a maximum just prior to the time of overt responding (e.g., Leocani, Cohen, Wassermann, Ikoma, & Hallett, 2000;Nikolova, Pondev, Christova, Wolf, & Kossev, 2006;Rossini, Zarola, Stalberg, & Caramia, 1988). Building on this paradigmatic approach, our present aim was to examine how this dynamic buildup of corticospinal…”

The multiform motor cortical output: Kinematic, predictive and response coding

“…The aim of this study was to disentangle the relative contribution and combination of different 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 14 person being observed and the observer's ones (Avenanti, Bolognini, Maravita, & Aglioti, 2007;Borroni et al, 2005;Borroni & Baldissera, 2008;Fadiga et al, 1995;Gangitano et al, 2001;Montagna et al, 2005;Strafella & Paus, 2000;Urgesi et al, 2006) and an anticipatory modulation of motor activations according to the final end of the perceived movement. While the video in which the soccer player suddenly stopped after kicking the ball ('still' condition) determined a decrease in CS excitability -signaling a transition to the motor profile designated by the action seen, observing the videos in which the player continued to run extended CS activity until the final phase of the action sequence.…”

Corticospinal Excitability Modulation During Action Observation

“…Those investigators considered the effect an expression of a mechanism blocking the overt execution of observed actions. Modulation of motor potentials evoked by TMS during action observation 3,20,21 appears to be specific, then, for the muscles involved in executing an action 3 and follows, in an anticipatory fashion 22 , the same temporal activation pattern 17,23 . Along these lines, Urgesi and colleagues 24,25 recently found that observation of start and middle phases of grasp actions engendered a significantly higher motor facilitation than observing their final postures.…”