"It refers to the appearance of the primary motor cortex on axial GRE or SWI MRI sequences in patients with amyotrophic lateral sclerosis and some of its clinical variants 1,2,6. On these sequences, and in the axial plane, curvilinear bands of low signal may be appreciated within the cortical gray matter of the primary motor cortex (i.e. 'motor bands' of low signal) 1,2,6. Occasionally, T2/FLAIR sequences may also demonstrate the same low signal 1-4."
"While this signal abnormality is usually seen along the whole primary motor cortex, in the progressive bulbar palsy variant, the signal change may only be seen laterally (i.e. in the faciobulbar region; see homunculus) 6. Furthermore, although this pattern of signal change is usually seen bilaterally, it has been reported to also occur unilaterally 2."