fMRI changes over time and reproducibility in unmedicated subjects at high genetic risk of schizophrenia

BACKGROUND

Functional brain abnormalities have been repeatedly demonstrated in schizophrenia but there is little data concerning their progression. For such studies to have credibility it is first important to establish the reproducibility of functional imaging techniques. The current study aimed to examine these factors in healthy controls and in unmedicated subjects at high genetic risk of the disorder: (i) to examine the reproducibility of task-related activation patterns, (ii) to determine if there were any progressive functional changes in high-risk subjects versus controls reflecting inheritance of the schizophrenic trait, and (iii) to examine changes over time in relation to fluctuating positive psychotic symptoms (i.e. state effects).

METHOD

Subjects were scanned performing the Hayling sentence completion test on two occasions 18 months apart. Changes in activation were examined in controls and high-risk subjects (n=16, n=63). Reproducibility was assessed for controls and high-risk subjects who remained asymptomatic at both time points (n=16, n=32).

RESULTS

Intra-class correlation values indicated good agreement between scanning sessions. No significant differences over time were seen between the high-risk and control group; however, comparison of high-risk subjects who developed symptoms versus those who remained asymptomatic revealed activation increases in the left middle temporal gyrus (p=0.026).

CONCLUSIONS

The current results suggest that functional changes over time occur in the lateral temporal cortex as high genetic risk subjects become symptomatic, further, they indicate the usefulness of functional imaging tools for investigating progressive changes associated with state and trait effects in schizophrenia.

Limbic over-activity in depression during preserved performance on the n-back task

The profile of cognitive dysfunction observed in patients with major depressive disorder (MDD) may be partially attributed to a deficit in the central executive component of working memory (WM). This could be the consequence of a functional deficit in regions of cortex that are associated with WM function in healthy adults. In order to investigate this assertion, ten patients with a diagnosis of MDD and ten matched healthy controls undertook a parametric WM task (i.e. the n-back task) during the acquisition of blood oxygen level dependent echo planar magnetic resonance images (BOLD EPI fMRI). There was no significant difference in the behavioral performance of depressed patients and controls. This was true for both accuracy and reaction time on the n-back task. Random effects analysis of the functional imaging data (using SPM99) revealed a significant difference in load-dependent activation in the medial orbitofrontal cortex/rostral anterior cingulate between patients and controls (cluster size (K(E))/volume = 128/1024 mm3, P(corrected) = 0.025). While both participant groups exhibited a significant decrease in activation in this region with increased task difficulty, the magnitude of this decrease was smaller in patients with MDD than in controls. Therefore, this study implies that the performance of WM tasks is associated with a dysfunctional activation of the medial orbitofrontal and rostral anterior cingulate cortex in MDD. The study thus offers a rationale for explaining depressive cognitive impairment by the abnormal fronto-limbic activation found in clinical depression.

Episodic and semantic memory tasks activate different brain regions in Alzheimer disease

OBJECTIVE

To compare brain activity identified by fMRI in subjects with Alzheimer disease (AD) and older healthy controls (HCs) performing an episodic/working memory (EWM) and semantic memory (SM) task.

METHODS

Nine AD (mean age 73.6) and 10 HC (mean age 71.8) subjects underwent an fMRI memory paradigm. Tasks comprised 1) baseline (recognizing a single digit presented for 1 second), 2) SM (addition of two single digits, always producing a single digit answer), and 3) EWM (recall of the previous single digit on the stimulus of the next digit). Each condition was presented in 2-minute blocks with a shorter and longer time interval for the first and second minute within blocks.

RESULTS

Comparing AD and HC subjects, there were no activated brain regions in common for EWM > SM, but left anterior cingulate (Brodmann area [BA] 24, 0, 31, 4) and left medial frontal lobe gyrus (BA 25, -6, 23, -15) were activated by both groups for SM > EWM. Key differences were that for EWM > SM, HC subjects activated the right parahippocampal gyrus, whereas subjects with AD activated the right superior frontal gyrus and left uncus.

CONCLUSIONS

Subjects with Alzheimer disease (AD) recruited brain regions for easier episodic/working memory (EWM) tasks used by healthy controls (HCs) for more difficult EWM tasks. AD subjects recruited brain regions for semantic memory tasks used by HCs for more difficult EWM tasks. The authors propose a functional "memory reserve" model of compensatory recruitment according to task difficulty and underlying neuropathology.

fMRI correlates of state and trait effects in subjects at genetically enhanced risk of schizophrenia

Schizophrenia is a highly heritable disorder that typically develops in early adult life. Structural imaging studies have indicated that patients with the illness, and to some extent their unaffected relatives, have subtle deficits in several brain regions, including prefrontal and temporal lobes. It is, however, not known how this inherited vulnerability leads to psychosis. This study used a covert verbal initiation fMRI task previously shown to elicit frontal and temporal activity (the Hayling sentence completion task) to examine this issue. A large (n = 69) number of young participants at high risk of developing schizophrenia for genetic reasons took part, together with a matched group of healthy controls (n = 21). At the time of investigation, none had any psychotic disorder, but on detailed interview some of the high-risk participants (n = 27) reported isolated psychotic symptoms. The study aimed to determine: (i) whether there were activation differences that occurred in all subjects with a genetic risk of schizophrenia (i.e. 'trait' effects); and (ii) whether there were activation differences that only occurred in those at high risk who had isolated psychotic symptoms ('state' effects). No activation differences were found in regions commonly reported to be abnormal in the established illness, namely the dorsolateral prefrontal cortex or in the temporal lobes, but group differences of apparent genetic cause were evident in medial prefrontal, thalamic and cerebellar regions. In addition, differences in activation in those with symptoms were found in the intraparietal sulcus. No significant differences in performance were found between the groups, and all subjects were antipsychotic naïve. These findings therefore suggest that vulnerability to schizophrenia may be inherited as a disruption in a fronto-thalamic-cerebellar network, and the earliest changes specific to the psychotic state may be related to hyperactivation in the parietal lobe.