Being under stimulated refers to not receiving enough appropriate sensory experiences or stimulation during a particular developmental stage. In Freud's oral stage, under stimulation can lead to frustration and aggression in adulthood.
Related terms
Frustration-aggression hypothesis: The theory that frustration leads to aggression as individuals try to relieve their pent-up energy or achieve their desired goals.
Sensory deprivation: A condition where an individual lacks normal patterns of sensory input, leading to cognitive and perceptual disturbances.