In prefrontal damage, the frontal lobe syndrome occurs with unilateral or bilateral damage (personality changes, irritability, euphoria, apathy, depression, impulsivity, social inappropriateness). Do not mistake this for depression or mania. Intelligence is usually unimpaired in unilateral damage, although memory can be affected. Symptoms are milder if only one side is involved. If the premotor area is involved (on the left), apraxia of the left hand and Broca (expressive) aphasia also may be present. Do not confuse with psychosis.

The hippocampal complex of the temporal lobe mediates recent (anterograde) memory and learning (left side is primarily verbal; right side, primarily visual); the amygdala mediates emotionladen memories; the temporal poles and inferotemporal regions coordinate retrograde memory. Stimulation or lesions may produce auditory or visual hallucinations or emotions such as fear, anxiety, and perhaps OCD. Bilateral lesions may result in the amnesia of Korsakoff and the Kluver-Bucy syndrome (placidity and hypersexuality).

Dominant lobe lesions may produce language difficulties (e.g., inability to express or understand spoken words, perform simple
tasks, read or write or both), tactile agnosia, apraxia, and intellectual deterioration. Nondominant lobe lesions may produce anosognosia.

Some lesions produce crude visual illusions (distortions) and hallucinations.

Effects are diverse but usually involve primitive and emotional behavior (e.g., emotional lability, fear, rage, impulsivity, irritability, depression, memory loss). Also, amnestic syndrome is seen when mammillary bodies are involved (Korsakoff syndrome).

Neurologic disorders can produce a variety of psychiatric symptoms. Consult a comprehensive source for detailed descriptions of specific conditions. Some major diseases include the following: