One of the many experimental techniques for recording propagation of action potentials is "voltage-sensitive dye technique." Just search in pubmed.gov and you will find thousands of papers on voltage-sensitive dye recordings.
There is the beginning and old work on it via MRI, see my other question https://www.researchgate.net/post/Are_there_micro_MRI_like_biospec_that_can_measure_neuronal_currents_as_in_Ueno_s_work?_tpcectx=qa_overview_asked&_trid=Ux71JWZEbEOjjgjjrgByiMF0_
Recordings done with high density CMOS microelectrode arrays would also be interesting for you; where inter electrode distance can be less than 20 µm. So, it is feasible to record from different sites of a neuronal network and assess extracellular action potential propagation e.g., as response to electrical stimuli. One example: https://www.nature.com/articles/ncomms3181
A good method for the evidentiation of sensory influx propagation in the brain is the analyisis in time of Evoked Potentials evolution on maps recorded in Source Derivation. We showed that every component of sensory Evoked Potentials comes from relay stations situated in line on the sensory pathways.
Psatta DM, Olaru M, Matei M: Visual inflow traveling in the brain evidenced
by photic evoked potentials mapping. Rom J Neurol, 2002, 40, 27-44.
Michel CM et al: EEG source imaging. Clinical Neurophysiology, 2004, 115,
2195-2222.
222. Psatta DM, Olaru M, Matei M: Auditory Evoked Potentials Mapping in