A film comprising an i-carbon is formed by converting a reactive gas containing a carbon compound gas into plasma by a resonance using a microwave and a magnetic field. In particular, the invention concerns a method of promoting the growth or regeneration of neurons, and treating disease or conditions associated with the loss, loss of function or dysfunction of nerve cells, in particular thalamic nerve cells, by administering a polypeptide having a high degree of sequence identity with a native sequence Netrin G1 or an agonist thereof. In this way, a high-resolution image always can be obtained regardless of the subject distance.