do occur in the brains of people with schizophrenia. a 2006 meta-analysis of mri studies found that whole brain and hippocampal volume are reduced and that ventricular volume is increased in those with a first psychotic episode relative to healthy controls. the average volumetric changes in these studies are however close to the limit of detection by mri methods, so it remains to be determined whether schizophrenia is a neurodegenerative process that begins at about the time of symptom onset, or whether it is better characterised as a neurodevelopmental process that produces abnormal brain volumes at an early age. in first episode psychosis typical antipsychotics like haloperidol were associated with significant reductions in gray matter volume, whereas atypical antipsychotics like olanzapine were not. studies in non-human primates found gray and white matter reductions for both typical and atypical antipsychotics. abnormal findings in the prefrontal cortex, temporal cortex and anterior cingulate cortex are found before the first onset of schizophrenia symptoms. these regions are the regions of structural deficits found in schizophrenia and first-episode subjects. positive symptoms, such as thoughts of being persecuted, were found to be related to the medial prefrontal cortex, amygdala, and hippocampus region. negative symptoms were found to be related to the ventrolateral prefrontal cortex and ventral striatum. ventricular and third ventricle enlargement, abnormal functioning of the amygdala, hippocampus, parahippocampal gyrus, neocortical temporal lobe regions, frontal lobe, prefrontal gray matter, orbitofrontal areas, parietal lobs abnormalities and subcortical abnormalities including the cavum septi pellucidi, basal ganglia, corpus callosum, thalamus and cerebellar abnormalities. such abnormalities usually present in the form of loss of volume. most schizophrenia studies have found average reduced volume of the left medial temporal lobe and left superior temporal gyrus, and half of studies have revealed deficits in certain areas of the frontal gyrus, parahippocampal gyrus and temporal gyrus. however, at variance with some findings in individuals with chronic schizophrenia significant group differences of temporal lobe and amygdala volumes are not shown in first-episode people on average. finally, mri studies utilizing modern cortical surface reconstruction techniques have shown widespread reduction in cerebral cortical thickness (i.e., "cortical thinning") in frontal and temporal regions and somewhat less widespread cortical thinning in occipital and parietal regions in people with schizophrenia, relative to healthy control subjects. moreover, one study decomposed cortical volume into its constituent parts, cortical surface area and cortical thickness, and reported widespread cortical volume reduction in schizophrenia, mainly driven by cortical thinning, but also reduced cortical surface area in smaller frontal, temporal, parietal and occipital cortical regions. ct scans of the brains of people with schizophrenia show several pathologies. the brain ventricles are enlarged as compared to normal brains. the ventricles hold cerebrospinal fluid (csf) and enlarged ventricles indicate a loss of brain volume. additionally, the brains have widened sulci as compared to normal brains, also with increased csf volumes and reduced brain volume. using machine learning, two neuroanatomical subtypes of schizophrenia have been described. subtype 1 shows widespread low grey matter volumes, particularly in the thalamus, nucleus accumbens, medial temporal, medial prefrontal, frontal, and insular cortices. subtype 2 shows increased volume in the basal ganglia and internal capsule, with otherwise normal brain volume. white matter diffusion tensor imaging (dti) allows for the investigation of white matter more closely than traditional mri. over 300 dti imaging studies have been published examining white matter abnormalities in schizophrenia. although quite some variation has been found pertaining to the specific regions affected, the general consensus states a reduced fractional anisotropy in brains from people with schizophrenia versus controls. importantly, these differences between subjects and controls could potentially be attributed to lifestyle effects, medication effects etc. other studies have looked at people with first-episode schizophrenia that have never received any medication, so-called medication-naive subjects. these studies, although few in number, also found reduced fractional anisotropy in subject brains compared to control brains. as with earlier findings, abnormalities can be found throughout the brain, although the corpus callosum seemed to be most commonly effected. functional abnormalities during executive function tasks in people with schizophrenia, studies using functional magnetic resonance imaging (fmri) demonstrated decreased activity relative to controls in the bilateral dorsolateral prefrontal cortex (dlpfc), right anterior cingulate cortex (acc), and left mediodorsal nucleus of the thalamus. increased activation was observed in the left acc and left inferior parietal lobe. during emotional processing tasks, reduced activations have been observed in the medial prefrontal cortex, acc, dlpfc and amygdala. a meta-analysis of facial emotional processing observed decreased activation in the amygdala, parahippocampus, lentiform nuclei, fusiform gyrus and right superior frontal gyrus, as well as increased activation in the left insula. one meta-analysis of fmri during acute auditory verbal hallucinations has reported increased activations in areas implicated in language, including the bilateral inferior frontal and post central gyri, as well as the left parietal operculum. another meta analysis during both visual and auditory verbal hallucinations, replicated the findings in the inferior frontal and postcentral gyri during auditory verbal hallucinations, and also observed hippocampal, superior temporal, insular and medial prefrontal activations. visual hallucinations were reported to be associated with increased activations in the secondary and associate visual cortices. pet data from a pet study suggests that the less the frontal lobes are activated (red) during a working memory task, the greater the increase in abnormal dopamine activity in the striatum (green), thought to be related to the neurocognitive deficits in schizophrenia. pet scan findings in people with schizophrenia indicate cerebral blood flow decreases in the left parahippocampal region. a reduced ability to metabolize glucose in the thalamus and frontal cortex is also shown. pet scans show developmental abnormality in the medial part of the left temporal lobe, and the limbic, and frontal systems. pet scans show that thought disorders stem from increased blood flow in the frontal and temporal regions while delusions and hallucinations were associated with reduced flow in the cingulate, left frontal, and temporal areas. pet scans carried out during active auditory hallucinations revealed increased blood flow in the thalamus, left hippocampus, right striatum, parahippocampus, orbitofrontal, and cingulate areas. in addition, a decrease in naa uptake has been reported in the hippocampus and both the grey and white matter of the prefrontal cortex. naa may be an indicator of neural activity of number of viable neurons. however, given methodological limitations and variance it is not possible to use this as a diagnostic method. decreased prefrontal cortex connectivity has also been observed. dopa pet studies have confirmed an altered synthesis capacity of dopamine in the nigrostriatal system demonstrating a dopaminergic dysregulation.