Stultification (from Latin stultus stupid) refers to the state of being or a situation or an action causing one to become

stupid or
foolish or
unsound
The silent implication of stultification in neurobiological terms is that certain external influences can have a lasting neural effect (reduction of the number of synapses, reduced number of interconnections between brain areas, less efficient signal transmission etc.). Such effects are studied by biopsychology and psychosomatic medicine.