Which of the following is a biological cause of emotional disturbance?

A biological cause of emotional disturbance specifically includes conditions that are rooted in the physiological or anatomical structure of the brain and body, which can lead to emotional and behavioral challenges. Brain disorders, such as traumatic brain injuries, neurological conditions, or genetic disorders affecting brain chemistry, can significantly influence a person's emotional responses and regulation. These disorders can manifest in various ways, impacting mood, behavior, and social interactions.

In contrast, options like adverse early rearing environments and social rejection by peers focus more on environmental, social, and relational factors that can contribute to emotional disturbances but are not inherently biological in nature. Aggressive behavior patterns are generally more reflective of learned behaviors or responses to one's environment rather than direct biological causes. Therefore, brain disorders stand out as the correct answer since they are explicitly linked to the biological underpinnings of emotional disturbances.