Functional topography of the primary motor cortex during motor execution and motor imagery as revealed by functional MRI.

Controversy exists regarding the involvement of the primary motor cortex (M1) during motor imagery (MI) and also regarding the differential somatotopic representation of motor execution (ME) and mental simulation of movement, that is, MI within M1. Although some research reported clear M1 involvement during MI without overt motor output, others did not. However, possible somatotopic representation between execution and imagery has not been clearly investigated to date. The aim of the present study was to aid in the resolution of this controversy by investigating the possible involvement of M1 during MI, and the differential, within M1, somatotopic representation between execution and imagery by quantitatively assessing different location markers such as activation peak and center of mass as well as intensity differences between the two tasks in case of with and without the overlap between the two representations. Forty-one healthy volunteers participated in two functional MRI runs of mouth-stretching ME and MI tasks. Our findings suggest the clear involvement of M1 (BA 4) during MI with lower signal intensity compared with ME, and further showed distinct centers for each representation along the y-axis (anteroposterior plane), with MI showing more involvement of the anterior sector of M1 (BA 4a), whereas ME recruited more of the posterior sector (BA 4p). These results parallel the pioneering findings of a functional distinction between BA 4a and BA 4p, where BA 4a is more involved in the cognitive aspects of MI, whereas BA 4p is more related to executive function, promoting the idea of distinctive somatotopic mapping between execution and imagery within M1 sectors.

Brain correlates to facial motor imagery and its somatotopy in the primary motor cortex.

Motor imagery (MI) has attracted increased interest for motor rehabilitation as many studies have shown that MI shares the same neural networks as motor execution (ME). Nevertheless, MI in terms of facial movement has not been studied extensively; thus, in the present study, we investigated shared neural networks between facial motor imagery (FMI) and facial motor execution (FME). In addition, FMI somatotopy within-face was investigated between the forehead and the mouth. Functional MRI was used to examine 34 healthy individuals with ME and MI paradigms for the forehead and the mouth. The general linear model and a paired t-test were performed to define the facial area in the primary motor cortex (M1) and this area has been used to investigate somatotopy between the forehead and mouth FMI. FMI recruited similar brain motor areas as FME, but showed less neural activity in all activated regions. The facial areas in M1 were distinguishable from other body movements such as finger movement. Further investigation of this area showed that forehead and mouth imagery tended to lack a somatotopic representation for position on M1, and yet had distinct characteristics in terms of neural activity level. FMI showed different characteristics from general MI as the former exclusively activated facial processing areas. In addition, FME and FMI showed different characteristics in terms of BOLD signal level, while sharing the same neural areas. The results imply a potential usefulness of MI training for rehabilitation of facial motor disease considering that forehead and mouth somatotopy showed no clear position difference, and yet showed a significant BOLD signal intensity variation.