Does the strength of corticospinal tract input influence the pattern of weakness?

Despite the intense research focus on the molecular and cellular mechanisms of motor neuron degeneration using models based on specific genetic mutations, there are good reasons to consider amyotrophic lateral sclerosis (ALS) as a ‘system degeneration’, which arises through multiple biological triggers. ALS experts generally agree that loss of function has a clinically focal onset and a non-random pattern of spread, which favours the ‘vulnerable network’ hypothesis, in which the degenerative process propagates through compartmentalised anatomical and functional networks.1 Furthermore, evidence from neuropathological studies suggests that the burden of TDP-43 proteinopathy reflects an orderly progression of spread through anatomically contiguous pathways.2 All of which raises the critical question of the nature of the anatomical substrate of …