Piggybacking on Vaughan Bell's account of how the word "neuroplasticity" is abused in the public sphere, here's one specific example from to show how fuzzy the picture really is. This particular study by Minerbi et al, available via open access here, measures the structural changes to synapses over a fairly long time frame (~ 5 days) in the presence and absence of electrical input.
The researchers cultured rat neurons in dishes and tethered the genetic expression of a common post synaptic protein (PSD-95) to the expression of green fluorescent protein, in order to measure changes in synapse size over time.
At the population level, increases in electrical network activity (i.e., more action potentials) correlate with increases in post synaptic size, as expected. And at the population level, blocking electrical action potentials with the tetrodotoxin stops the increase in post synaptic size.
But when researchers looked at individual synapses, their simple relationship breaks down. The fluorescence of the post synaptic protein, a measure of the size and thus strength of the synapse, varies somewhat randomly over time. This is true even when the activity blocker tetrodotoxin was applied to the neurons.
If the structure of synapses were constant, there would be little change in the flourescence of the post synaptic protein over time. In the following 8 second video, each circle represents one synaptic puncta, the Y-intercept shows fluorescence, and as you can see, the fluorescence is definitely not constant:
Bottom Line: When marketers and pundits claim that "[something] changes the brain!", what they are saying is technically true. But the connotations are misleading, because any sort of stimulation changes your brain in some way. And moreover, even with no electrical at all stimulation individual synapses are constantly changing their size and configurations and exhibiting "neuroplasticity."