CLINICAL HANDBOOK OF SCHIZOPHRENIA

50 I. CORE SCIENCE AND BACKGROUND INFORMATIONphrenia symptoms have been with temporal lobe structures. Symptom severity has beenassociated with reductions in bilateral temporal lobe volume, along with decreasedhippocampal and left STG volumes. The left anterior and left posterior STG have beenstrongly associated with the severity of both auditory hallucinations and thought disorder.Schneiderian symptom severity has been associated with volumes of the right posteriorcingulate gray matter and left anterior parahippocampal gyrus. Positive symptomsare not the only ones related to temporal lobe findings. Negative symptoms have beencorrelated with decreases in left medial temporal lobe volumes (as well as prefrontalwhite matter volume). Investigations specifically directed at white matter in patients withschizophrenia (discussed below) have noted an association between the organization andcoherence of white matter tracts in temporal lobe regions and impulsivity. Recently, theintegrity of white matter tracts in the medial temporal lobe has been determined to relateto the severity of positive, negative, and general psychopathology symptom domains.Parietal LobeRelatively few investigations have been directed at the parietal lobe in patients withschizophrenia, and most of those that have do not subdivide the parietal lobe into subregions.Nonetheless, the majority of studies directed at parietal lobe structures have shownsome volume reductions. More recently, subdivisions of the parietal lobe on imagingstudies have revealed reductions in the inferior parietal lobe and supramarginal gyrus.Perhaps most strikingly, correlations have been demonstrated between the inferior parietallobe, prefrontal cortex, and temporal cortex, supporting the idea that connectedbrain structures, and perhaps even the connecting tracts themselves, may be critical toour understanding of schizophrenia.CerebellumAlthough the cerebellum historically was relegated to the role of coordinating movement,recent evidence has suggested that it may play a role in higher cognitive functions. Thecerebellum is highly connected to cortical association areas and limbic regions, and thenotion has been put forth that the cerebellum may be associated with schizophrenia. Unfortunately,there have only been a handful of studies, and these studies have not yet consistentlyborne out any reliable findings. It should be noted, however, that these studieshave varied widely in methodology, and little attempt has been made to subdivide the cerebelluminto functionally discrete regions.ThalamusSUBCORTICAL FINDINGSThe thalamus is a relay station modulating input from cortical, limbic, and reticular activationareas, and it modulates sensory input and is involved in attention. The thalamus isalso intimately connected to the prefrontal cortex, including the orbitofrontal andDLPFC with reciprocal connections.The size of the thalamus has been demonstrated to be smaller in patients with schizophrenia.Subdivision of the thalamus in cytoarchitectural investigations seems particularlyappropriate given that the thalamus receives input and sends output to a variety ofcortical structures, each with potentially independent functions. The dorsomedial nucleus,which sends projections to the prefrontal cortex, has been shown to have a significantlydecreased number of axons. The coherence of this thalamocortical pathway has