Descriptive Psychopathology: The Signs and Symptoms of ...

66 Section 1: Present, past, and futureThe thalamus is considered functionally to be a complex that includes thegeniculate bodies and the pulvinar. All sensory information is processed throughthis complex. Thalamic function includes: (1) relaying somatosensory informationto the appropriate area of the parietal cortex, maintaining body image;(2) synchronizing visual and auditory information with other perceptual modalities;(3) organizing all sensory information from a kaleidoscopic into a synchronizedset of perceptions; (4) integrating sensory information in conjunction witha special multimodal sensory cortical area in the temporal lobes near theinsula; and (5) providing tone to frontal circuitry and modulating attentiveness,wakefulness, and sleep.The thalamus also links the cerebellum to the frontal circuitry and is involvedin motor behavior as well as perception. Thalamic disease is associated withfrontal lobe syndromes (disinhibited or avolitional depending on the lesion sitein the thalamus), depression-like syndromes, dementia (when the lesion is extensive),amnestic syndromes, speech and language problems (subcortical aphasiaand “formal thought disorder” seen in some psychotic patients), pain syndromes,body image disturbances, parietal lobe syndromes, abnormal emotional regulation,balance and coordination difficulties, and perceptual disturbances of disintegration(including hallucinations). 68 Thalamic neglect (the patient failing torespond to stimuli from one side) is also reported. 69To be useful, the complex perceptions generated by the sensory integratingsystem require identification. Thus, the system is linked to stored information(i.e. memory) that permits the recognition of objects, their function and names, themeaning of the perception, and the enrichment of the perception from linkage toautobiographic and other memory. The storage of information (encoding) and itsretrieval is subserved by the hippocampus and its extensions, the mammillarybodies, and the entorhinal and the parahippocampal cortices. Alzheimer’s diseaseinitially disrupts the linkage between memory and perception leaving sufferersunable to identify familiar objects, places, and persons, and unable to understandthe full meaning of what is happening around them.Hemisphere differences and psychopathologyUnderstanding hemisphere functional specialization helps identify the neurologyof psychopathological phenomena and psychiatric syndromes secondary to definableneurologic disease. For example, depressive-like syndromes are commonfollowing left-sided strokes in frontal circuitry and early in the course of neurodegenerativedisease involving the basal ganglia (e.g. Parkinson’s and Huntington’sdiseases). 70 These depressions are less likely to respond to antidepressant treatments,but may respond to stimulants. 71 Strokes in the right hemisphere areless likely to be associated with depressive syndromes, and when these occur the