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Positron emission tomography

What is positron emission tomography? 

Positron emission tomography (PET) is a nuclear based imaging technique that utilises a radioactive tracer to visualise functional brain activity. PET imaging is frequently used in combination with anatomical imaging such as computed tomography (CT) or structural magnetic resonance imaging (MRI). The radioisotopes tracers are coupled with a biological molecule such as glucose, which is used during cellular metabolism and can be used to highlight areas with changes in metabolic activity. Using PET, functional brain activity has been investigated in people with schizophrenia compared to people without schizophrenia to identify regions of increased or decreased metabolic function or blood flow.

What is the evidence for PET brain functioning?

During executive functioning and working memory tasks, moderate quality evidence suggests significant decreases in functional activation in the frontal lobe, including the dorsolateral prefrontal cortex, and in neocortical regions, including the parietal and occipital cortices and bilateral claustrum, fusiform gyrus, and cerebellum, and in subcortical regions, including the right putamen, hippocampus and left mediodorsal thalamus. Moderate to low quality evidence suggests significant increases in functional activation in the anterior cingulate cortex, temporal lobe, parietal cortex, lingual gyri, insula and the amygdala.

During memory encoding tasks, moderate quality evidence suggests significant decreases in functional activation in the medial frontal gyri and the hippocampus. During memory retrieval tasks, decreased activation is seen in the medial and inferior frontal gyri, the cerebellum, hippocampus, and the fusiform gyrus, with increases in the anterior cingulate cortex and the medial temporal gyrus.

During emotion processing tasks, moderate and moderate to low quality evidence suggests decreased activation in the amygdala, parahippocampus, superior frontal gyrus and middle occipital gyrus. There is also lower magnitude of activation in the fusiform gyrus, lentiform nucleus, and parahippocampal gyrus. During explicit (effortful) emotion tasks, there is decreased activation in the fusiform gyrus, while during implicit (automatic) emotion tasks, there are decreases in the superior frontal and middle occipital gyri.

During auditory hallucinations, moderate and moderate to low quality evidence suggests increased activation in Broca’s area of the temporal lobe, insula, hippocampus, left parietal operculum, left and right postcentral gyrus, and left inferior frontal gyrus, and decreased activation of Broca’s area, the left middle temporal gyrus, left premotor cortex, anterior cingulate cortex, and left superior temporal gyrus during external auditory stimulation.

During cognitive tasks and rest periods, moderate to high quality evidence shows a medium to large effect of reduced functional activity in bilateral frontal lobes in people with schizophrenia. Moderate quality evidence suggests increased functional activity in the left temporal lobe during cognitive tasks, but no differences between patients and controls during rest periods.

Moderate to high quality evidence finds a large increase in striatal presynaptic dopamine function, particularly in associative and sensorimotor regions, and a small increase in striatal receptor availability in people with schizophrenia compared to controls. Moderate quality evidence finds greatest D2 receptor occupancy with haloperidol (92%), then risperidone, olanzapine, clozapine, quetiapine, aripiprazole, ziprasidone, and then amisulpride (85%). There may be an association between dopamine receptor occupancy and clinical improvement following treatment with antipsychotic medications.

There is also reduced translocator protein in the frontal cortex, temporal cortex, and the hippocampus of people with schizophrenia, with no moderating effects of antipsychotic medication; both drug free and medicated patients showed similar reductions.

December 2019

Last updated at: 4:57 am, 13th January 2020
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