Theoretical limit to the use of mental faculty of the brain A lot of articles stress the importance of having to train the brain (By training the brain, I mean the cognitive faculty of the brain for learning things and not brain's normal functions) since the brain is a muscle and training it would improve its cognitive abilities.

Since using anything beyond a limit is detrimental to it, is there a theoretical limit to the use of brain beyond which it would be detrimental to the brain?
Intensive stimuli may trigger epileptic shocks in some individuals. At least prolonged epileptic shocks may damage neurons, I'm not sure about short epileptic shocks. So the answer is yes, using your brain eg. your extended visual system to process excessively intensive visual stimuli may cause epileptic shocks and thus be detrimental to the brain.

However, as far as I know, visual stimuli are not able to cause epileptic shocks to everyone (susceptibility to epilepsy is a requirement), so I'm not sure if there is any proven way how by you could cause brain damage only by brain function (without aid of any voluntary motoric movements) in any individual. 

As intensive visual and auditory stimuli are a part of our natural environment - whereas lack of stimuli (sensory deprivation) is an unnatural state - I think triggering epileptic shocks by intensive stimuli can not be considered only as a self-caused way of damaging the brain.