Descriptive Psychopathology: The Signs and Symptoms of ...

64 Section 1: Present, past, and futureThe left hemisphere (by convention referred to as “dominant”) in about 98% ofthe population is on macro- and micro-architectural levels structurally organizedto most efficiently process high-frequency (dense) information, particularlylanguage-related information. Discrete areas such as Broca’s and Wernicke’s areas,the Planum Temporale, and the arcuate fasiculus are identified in the dominanthemisphere. 54 Subcortical structures also subserve language, and patients withformal thought disorder are reported to have abnormal metabolic activity inleft basal ganglia and thalamic nuclei. 55 Verbal memory and other dominanthemisphere functions are discussed below.The right hemisphere (referred to as “non-dominant”) is structurally organizedto most efficiently process low-frequency information, particularly informationthat is visual–spatial. Lexical information in the images of words is high frequency.The low-frequency aspects of stimuli (e.g. their shape), the spatialrelationships of objects within the environment, and the emotions of others aremost efficiently processed by the right hemisphere. The right hemisphere functionsholographically (it has more white matter and dendritic arborization thanthe left), and small lesions in the right hemisphere can go unnoticed. Correspondingly,environmental sounds are mostly low frequency, while speech soundsare mostly high frequency. 56 In normal persons, these different specializations areintegrated through the corpus callosum. 57The right hemisphere is also more involved in arousal and the processingof emotion-related information. Right posterior regions subserve perception ofemotion-related stimuli (receptive prosody) while anterior regions subserve theexpression of emotion (motor prosody). 58The right hemisphere is also seen as processing “negative” avoidance-relatedemotion, while the left hemisphere processes “positive” approach-related emotions.59 This laterality is also said to be more robust in women. 60 Some reports,however, find that while negative emotion stimuli are processed best by the righthemisphere, the processing of positive emotion occurs bilaterally. 61 The uncertainsupport for valence asymmetry reflects lack of attention to factors other than theemotional valence of the stimuli (e.g. physical aspects) and the laboratory settingin which stimuli are presented. 62Patients with right hemisphere lesions and the functional imaging studies ofnormal persons processing various aspects of language and conversation identifythe right hemisphere as also having a specific function in understanding humor,sarcasm, metaphor, the non-literal meaning of statements, and the primarytheme of a conversation. Subcortical and right hemisphere language-relatedstructures are particularly relevant to the speech and language problems ofpsychiatric patients. 63