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Executive and mnemonic impairments have been well documented in the high-risk states for development of psychosis and have been pinpointed as a possible core neuropsychological dysfunction. However, their neurofunctional correlates are still not clear.
fMRI was used in 17 patients at risk for developing psychosis (ARMS, “at risk mental state”), 10 patients with a first episode of psychosis (FEP) and 15 age-matched healthy comparison subjects to examine neural responses to increasing difficulty of mnemonic engagement in an object–location paired associate memory task. Groups were matched in terms of age, IQ, gender, and psychopathology ratings. Accuracy and reaction time were recorded during the scan.
As the mnemonic load increased, response latency increased and response accuracy decreased in an approximately linear fashion. No main effect for group was observed. However, a trend towards decreased accuracy in FEP subjects, as compared with controls, was evident. As the task difficulty increased, increased brain activity was observed in the medial frontal cortex and in the medial posterior parietal cortex. Between-groups differences in activation were observed in a cluster spanning the MFG, SFG and SMA and in the right precuneus. However, these neurofunctional abnormalities were more evident in the most demanding level of the task than in the easy level, with the ARMS groups showing less activation than controls and higher activation than FEP.
Abnormal neural activity in medial frontal cortex and posterior parietal cortex during paired associate learning task may represent a neurofunctional substrates of vulnerability to psychosis.
Object working memory performance is abnormal in the early stages of schizophrenia. Such tasks recruit frontal and temporal cortices, possible sites of progressive change over the early illness course. We wanted to clarify if functional changes can be detected in the early stages of schizophrenia, to identify their anatomical location and their relationship to the stage of illness using a functional object working memory task in which the length of memory delay was manipulated.
40 subjects contributed: 10 first episode psychosis (FEp) patients, 16 with an at risk mental state (ARMS) and 14 healthy controls. We collected functional MRI data while the subjects performed a version of the delayed matching to sample (DMTS) task from the Cambridge Automated Neuropsychological Test Battery (CANTAB).
Behaviourally there was a trend to a group by delay interaction, the two patient groups making more errors at longer memory delays. At successful recognition a main effect of group was detected in the medial temporal lobe bilaterally, while a main effect of delay was detected in the left medial temporal lobe. At each length of memory delay the patient groups showed consistently greater activation of medial temporal regions when performing the task accurately.
Both ARMS & FEp groups showed greater activation than controls in the medial temporal cortex across all lengths of memory delay. These differences were not related to poorer task performance, but suggest an inefficiency mechanism that may correlate with the vulnerability to psychosis rather than pychosis per se.
People with ‘prodromal’ symptoms have a very high risk of developing psychosis. We used functional MRI to examine the neurocognitive basis of this vulnerability.
Cross-sectional comparison of subjects with an ARMS (n=17), first episode schizophreniform psychosis (n=10) and healthy volunteers (n=15). Subjects were studied using functional MRI while they performed an overt verbal fluency task, a random movement generation paradigm and an N-Back working memory task.
During an N-Back task the ARMS group engaged inferior frontal and posterior parietal cortex less than controls but more than the first episode group. During a motor generation task, the ARMS group showed less activation in the left inferior parietal cortex than controls, but greater activation than the first episode group. During verbal fluency using ‘Easy’ letters, the ARMS group demonstrated intermediate activation in the left inferior frontal cortex, with first episode groups showing least, and controls most, activation. When processing ‘Hard’ letters, differential activation was evident in two left inferior frontal regions. In its dorsolateral portion, the ARMS group showed less activation than controls but more than the first episode group, while in the opercular part of the left inferior frontal gyrus / anterior insula activation was greatest in the first episode group, weakest in controls and intermediate in the ARMS group.
The ARMS is associated with abnormalities of regional brain function that are qualitatively similar to those in patients who have just developed psychosis but less severe.
Impaired spatial working memory (SWM) is a robust feature of schizophrenia and has been linked to the risk of developing psychosis in people with an at-risk mental state (ARMS). We used functional magnetic resonance imaging (fMRI) to examine the neural substrate of SWM in the ARMS and in patients who had just developed schizophrenia.
fMRI was used to study 17 patients with an ARMS, 10 patients with a first episode of psychosis and 15 age-matched healthy comparison subjects. The blood oxygen level-dependent (BOLD) response was measured while subjects performed an object–location paired-associate memory task, with experimental manipulation of mnemonic load.
In all groups, increasing mnemonic load was associated with activation in the medial frontal and medial posterior parietal cortex. Significant between-group differences in activation were evident in a cluster spanning the medial frontal cortex and right precuneus, with the ARMS groups showing less activation than controls but greater activation than first-episode psychosis (FEP) patients. These group differences were more evident at the most demanding levels of the task than at the easy level. In all groups, task performance improved with repetition of the conditions. However, there was a significant group difference in the response of the right precuneus across repeated trials, with an attenuation of activation in controls but increased activation in FEP and little change in the ARMS.
Abnormal neural activity in the medial frontal cortex and posterior parietal cortex during an SWM task may be a neural correlate of increased vulnerability to psychosis.
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