Theories of mental fatigue disagree on whether performance decrement is caused by motivational or functional alterations. We tested the assumption that keeping neural networks active for an extensive period of time entrains consequences at the subjective, objective and neurophysiological level – the defining characteristics of fatigue – when confounds such as motivation, boredom and level of skill are controlled. We reveal that passive visual stimulation affects visual gamma activity and the performance of a subsequent task when carried out in the same portion of visual space. This outcome was influenced by participants’ level of arousal, manipulated through variations in the difficulty of concurrent auditory tasks. Thus, repeated stimulation of neural networks leads to their altered functional performance and this mechanism seems to play a role in the development of mental fatigue.