Chapter 16: Emotional Disorders in Neurological Disease

Emotional Disorders in Neurological Disease explores hemispheric specialization, noting that the right hemisphere plays a dominant role in interpreting and producing non-verbal cues, such as emotional facial expressions and the melodic intonation of speech known as prosody. While right-sided damage often leads to emotional indifference or inappropriate euphoria, left-hemisphere injuries are frequently linked to "catastrophic reactions" and clinical depression, particularly when language centers are compromised. The authors evaluate various theories of emotional experience, ranging from peripheral feedback models involving facial and visceral responses to central models focusing on the diencephalon and the limbic system. A contemporary modular theory is presented, suggesting that emotional experience is a result of integrated networks managing valence, arousal, and motor intention, with the right hemisphere exerting significant control over physiological activation. The role of the limbic system—specifically the amygdala—is emphasized in relation to fear conditioning and the processing of social signals. Furthermore, the text details how neurological conditions like temporal lobe epilepsy can produce intense emotional phenomena during seizures or contribute to distinctive interictal personality changes, such as hypergraphia and increased religious preoccupation. Movement disorders involving the basal ganglia, including Parkinson’s and Huntington’s diseases, are shown to be highly comorbid with mood disturbances like apathy and depression due to specific neurochemical and structural disruptions. Lastly, the chapter identifies the pseudobulbar state, a condition where involuntary laughing or crying occurs as a motor release phenomenon, highlighting a clear dissociation between outward emotional expression and inward emotional experience.