Some time ago I commented cells move around inside by 'walking on stilts . . . ,'
filopodia and lamellipodia are reflective of the stilt like structures facilitating the moment of new cells possibly into the space prior cells failed.

This paper reviews the processes in great detail . . . :

The Growth Cone Cytoskeleton in Axon Outgrowth and Guidance
The growth cone cytoskeleton in axon outgrowth and guidance - PubMed

I would not be surprised many non-biologists would find this paper (and some of the others) more difficult to follow.

A key point however, is why are the DiPALS results of 31 moons not seen as very different from the RespiStimALS result of 56 moons? A twenty-five moon difference ought not be overlooked. One big difference between the RespiStimALS study and the DiPALS study is the DiPALS study is the only one not 'blinded,' rather the study was open . . . exposed. The primary point of double blind placebo controlled studies is the prevention of tampering . . . no one can tamper with such studies because no one knows who is getting what. Such was not true in the DiPALS study.