The Sanskrit vowels are placed in such manner that speaking them vocally enhances and activates the entire mouth and the organs involved in producing the sound.
the neurological benefit of some vowels is true, take OM for an example
It is a combination of 3 vowels "A + U + M", when spoken as a singularity, A activates lower abdominal and stomach ...
"Upashishye" means "I am worshipping" Or "I'm performing the Upasana". "Sandhyamupashishye" means "I'm worshipping Sandhya" or "I'm performing Sandhya worship".
You can get a Sankalpa Mantra from the book "Essence of Dharma Sindhu":
After Pranayama as above, then Gayatri Avahana Sankalpa ...
This is from Rigved. I find this enthralling and motivating especially when I listen to it here after reading its meaning.
संगच्छध्वम् संवद्धवम् संवोमनाँसि जानताम् ।
देवाभागम् यथापूर्वे सञ्जानानम् उपासते ।।
May we march forward with a common goal.
May we be open-minded and work together in harmony.
May we share our thoughts for integrated wisdom.
May we ...
To answer the bounty question:
Can someone re-upload the files in the accepted answer? They have been deleted.
You can view/download the Ṛgveda Anukramaṇī from here:
Source: The Rigveda: 3-Volume Set by Stephanie W. Jamison and Joel P. Brereton