This elderly gentleman presented with progressive slurring of speech and difficulty swallowing . Following is the video demonstrating clear evidence of fasciculations .

Tongue fasciculations ( at times mentioned as fibrillations ) should only be diagnosed with tongue at rest in the mouth . Sometimes flickering movements are seen in the tongue during protrusion and these need not be fasciculations. Common causes include
1 Motor Neurone Disease
2 Denervation from any cause i.e. compression and irritation of the hypoglossal nerve from inflammation and tumours
3 Primary brain stem lesions i.e. infarcts , bleeds and tumours
4 Neuro muscular disease causing denervation 
5 Organo phosphate poisoning and muscle relaxants 
The list is by no means complete and other disorders which can cause muscle fasciculations can certainly produce the same phenomenon in the tongue muscles