Cortico-Cortical Connectivity between Right Parietal and Bilateral Primary Motor Cortices during Imagined and Observed Actions: A Combined TMS/tDCS Study

Abstract

Previous transcranial magnetic stimulation (TMS) studies showed functional connections between the parietal cortex (PC) and the primary motor cortex (M1) during tasks of different reaching-to-grasp movements. Here, we tested whether the same network is involved in cognitive processes such as imagined or observed actions. Single pulse TMS of the right and left M1 during rest and during a motor imagery and an action observation task (i.e., an index–thumb pinch grip in both cases) was used to measure corticospinal excitability changes before and after conditioning of the right PC by 10 min of cathodal, anodal, or sham transcranial direct current stimulation (tDCS). Corticospinal excitability was indexed by the size of motor-evoked potentials (MEPs) from the contralateral first dorsal interosseous (FDI; target) and abductor digiti minimi muscle (control) muscles. Results showed selective ipsilateral effects on the M1 excitability, exclusively for motor imagery processes: anodal tDCS enhanced the MEPs’ size from the FDI muscle, whereas cathodal tDCS decreased it. Only cathodal tDCS impacted corticospinal facilitation induced by action observation. Sham stimulation was always uneffective. These results suggest that motor imagery, differently from action observation, is sustained by a strictly ipsilateral parieto-motor cortex circuits. Results might have implication for neuromodulatory rehabilitative purposes.

Repetition and variation in motor practice: A review of neural correlates

“…The length of time provided for learners to prepare their response was unrestricted in the Cross et al (2007) study, leading to the question of whether the participants would engage in some form of mental practice before movement execution. It has been observed that the M1 participates in mental imagery (Feurra et al, 2011;Lotze et al, 1999). 1 2 3 4 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 18 analysis of these results shows that the structures involved in the planning and execution of skills tend to exhibit greater increases in activity during random practice than during blocked practice.…”

Local and remote effects of transcranial direct current stimulation on the electrical activity of the motor cortical network

“…Indeed, transcranial magnetic stimulation studies (Koch et al ; Koch & Rothwell, ) documented functional connections between parietal cortex and its sub‐regions, such as posterior parietal cortex and different portions of the intra‐parietal sulcus, and the ipsilateral, or even the contralateral primary motor cortex. TDCS of right parietal cortex induces changes of M1 excitability during motor imagery and action observation (Feurra et al, ). Previous task related studies demonstrated a beta band specific functional connection among frontal and somatosensory areas, corresponding to the same cortical areas in which we found an increased coherence (Babiloni et al, ).…”

Mirror training to augment cross-education during resistance training: a hypothesis

“…Comparisons between TMS evoked responses during movement observation and imagery showed increased activation (Cattaneo and Rizzolatti, 2009; Roosink and Zijdewind, 2010), no difference (Patuzzo et al, 2003; Clark et al, 2004; Leonard and Tremblay, 2007), or decreased activation (Fuerra et al, 2011) during movement observation. Part of these differences could be explained by the use of different tasks; task-specific activation, for instance, increases with task complexity.…”