Brain-derived neurotrophic factor Val66Met genotype and ovarian steroids interactively modulate working memory-related hippocampal function in women: a multimodal neuroimaging study.

Preclinical evidence suggests that the actions of ovarian steroid hormones and brain-derived neurotrophic factor (BDNF) are highly convergent on brain function. Studies in humanized mice document an interaction between estrus cycle-related changes in estradiol secretion and BDNF Val66Met genotype on measures of hippocampal function and anxiety-like behavior. We believe our multimodal imaging data provide the first demonstration in women that the effects of the BDNF Val/Met polymorphism on hippocampal function are selectively modulated by estradiol. In a 6-month pharmacological hormone manipulation protocol, healthy, regularly menstruating, asymptomatic women completed positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) scans while performing the n-back working memory task during three hormone conditions: ovarian suppression induced by the gonadotropin-releasing hormone agonist, leuprolide acetate; leuprolide plus estradiol; and leuprolide plus progesterone. For each of the three hormone conditions, a discovery data set was obtained with oxygen-15 water regional cerebral blood flow PET in 39 healthy women genotyped for BDNF Val66Met, and a confirmatory data set was obtained with fMRI in 27 women. Our results, in close agreement across the two imaging platforms, demonstrate an ovarian hormone-by-BDNF interaction on working memory-related hippocampal function (PET: F2,37=9.11, P=0.00026 uncorrected, P=0.05, familywise error corrected with small volume correction; fMRI: F2,25=5.43, P=0.01, uncorrected) that reflects differential hippocampal recruitment in Met carriers but only in the presence of estradiol. These findings have clinical relevance for understanding the neurobiological basis of individual differences in the cognitive and behavioral effects of ovarian steroids in women, and may provide a neurogenetic framework for understanding neuropsychiatric disorders related to reproductive hormones as well as illnesses with sex differences in disease expression and course.

Brain-derived neurotrophic factor (BDNF) Val(66)Met polymorphism differentially predicts hippocampal function in medication-free patients with schizophrenia.

A Val(66)Met single-nucleotide polymorphism (SNP) in the brain-derived neurotrophic factor (BDNF) gene impairs activity-dependent BDNF release in cultured hippocampal neurons and predicts impaired memory and exaggerated basal hippocampal activity in healthy humans. Several clinical genetic association studies along with multi-modal evidence for hippocampal dysfunction in schizophrenia indirectly suggest a relationship between schizophrenia and genetically determined BDNF function in the hippocampus. To directly test this hypothesized relationship, we studied 47 medication-free patients with schizophrenia or schizoaffective disorder and 74 healthy comparison individuals with genotyping for the Val(66)Met SNP and [(15)O]H(2)O positron emission tomography (PET) to measure resting and working memory-related hippocampal regional cerebral blood flow (rCBF). In patients, harboring a Met allele was associated with significantly less hippocampal rCBF. This finding was opposite to the genotype effect seen in healthy participants, resulting in a significant diagnosis-by-genotype interaction. Exploratory analyses of interregional resting rCBF covariation revealed a specific and significant diagnosis-by-genotype interaction effect on hippocampal-prefrontal coupling. A diagnosis-by-genotype interaction was also found for working memory-related hippocampal rCBF change, which was uniquely attenuated in Met allele-carrying patients. Thus, both task-independent and task-dependent hippocampal neurophysiology accommodates a Met allelic background differently in patients with schizophrenia than in control subjects. Potentially consistent with the hypothesis that cellular sequelae of the BDNF Val(66)Met SNP interface with aspects of schizophrenic hippocampal and frontotemporal dysfunction, these results warrant future investigation to understand the contributions of unique patient trait or state variables to these robust interactions.

Physiological dysfunction of dorsolateral prefrontal cortex in schizophrenia. III. A new cohort and evidence for a monoaminergic mechanism.

We previously reported that compared with normals, patients with chronic schizophrenia have reduced regional cerebral blood flow (rCBF) in dorsolateral prefrontal cortex (DLPFC) during performance of the Wisconsin Card Sort Test (WCS), a DLPFC-related cognitive task, but not during nonprefrontal tasks, such as a simple number-matching (NM) test. We also found that unlike normals, patients failed to activate DLPFC during the WCS over their own baseline (NM) level. To explore the reproducibility of these findings, a new cohort of 16 medication-free patients underwent a series of xenon 133 inhalation rCBF studies under the following conditions: at rest, while performing the WCS, and while performing NM. The results confirmed our earlier findings. In addition, the concentrations in cerebrospinal fluid of homovanillic acid and 5-hydroxyindoleacetic acid correlated with prefrontal rCBF during the WCS but not during the NM test or at rest. The results show that behavior-specific hypofunction of DLPFC in schizophrenia is reproducible, and they implicate a monoaminergic mechanism.

Physiological dysfunction of dorsolateral prefrontal cortex in schizophrenia. IV. Further evidence for regional and behavioral specificity.

In previous studies we found that patients with chronic schizophrenia had lower regional cerebral blood flow (rCBF) in dorsolateral prefrontal cortex (DLPFC) than did normal subjects during performance of the Wisconsin Card Sort Test, an abstract reasoning task linked to DLPFC function. This was not the case during less complex tasks. To examine further whether this finding represented regionally circumscribed pathophysiology or a more general correlate of abstract cognition, 24 medication-free patients and 25 age- and sex-matched normal control subjects underwent rCBF measurements with the xenon 133 technique while they performed two tasks: Raven's Progressive Matrices (RPM) and an active baseline control task. While performing RPM, normal subjects activated posterior cortical areas over baseline, but did not activate DLPFC, as had been seen during the Wisconsin Card Sort Test. Like normal subjects, patients showed maximal rCBF elevations posteriorly and, moreover, they had no significant DLPFC or other cortical deficit while performing RPM. These results suggest that DLPFC dysfunction in schizophrenia is linked to pathophysiology of a regionally specific neural system rather than to global cortical dysfunction, and that this pathophysiology is most apparent under prefrontally specific cognitive demand.

Physiologic dysfunction of dorsolateral prefrontal cortex in schizophrenia. II. Role of neuroleptic treatment, attention, and mental effort.

We conducted two xenon Xe 133 inhalation regional cerebral blood flow (rCBF) studies to clarify earlier findings of dorsolateral prefrontal cortex (DLPFC) dysfunction in medication-free patients with chronic schizophrenia. In the first study, 24 neuroleptic-treated patients and 25 normal controls underwent three rCBF procedures, first while at rest, then during the Wisconsin Card Sort (WCS), which tests DLPFC cognitive function, and during a number-matching task that controlled for aspects of the WCS-rCBF experience not specifically related to DLPFC. The results were qualitatively identical to those previously reported for medication-free patients. In the second study, rCBF was determined while 18 medication-free patients and 17 normal control subjects each performed two versions of a visual continuous performance task (CPT). No differences in DLPFC blood flow between the two groups were found during either CPT condition. These data suggest that DLPFC dysfunction in schizophrenia is independent of medication status and not determined simply by state factors such as attention, mental effort, or severity of psychotic symptoms. Dysfunction of DLPFC appears to be a cognitively linked physiologic deficit in this illness.

Physiologic dysfunction of dorsolateral prefrontal cortex in schizophrenia. I. Regional cerebral blood flow evidence.

To evaluate dorsolateral prefrontal cortex (DLPFC) physiology and function simultaneously, 20 medication-free patients with chronic schizophrenia and 25 normal controls underwent three separate xenon Xe 133 inhalation procedures for determination of regional cerebral blood flow (rCBF): first at rest, then while performing an automated version of the Wisconsin Card Sort (WCS), a DLPFC-specific cognitive test, and while performing a simple number-matching (NM) test. During rest, patients had significantly reduced relative, but not absolute, rCBF to DLPFC. During NM, no specific region differentiated patients from controls. During WCS, however, both absolute and relative rCBF to DLPFC significantly distinguished patients from controls. While controls showed a clear increase in DLPFC rCBF, patients did not. The changes were regionally specific, involving only DLPFC. Furthermore, in patients, DLPFC rCBF correlated positively with WCS cognitive performance, suggesting that the better DLPFC was able to function, the better patients could perform. Autonomic arousal measures, the pattern of WCS errors, and results of complementary studies suggest that the DLPFC finding is linked to regionally specific cognitive function and is not a nonspecific epiphenomenon.

Regional cerebral blood flow in monozygotic twins discordant and concordant for schizophrenia.

We addressed several questions regarding hypofunction of the prefrontal cortex ("hypofrontality") in schizophrenia by measuring regional cerebral blood flow during three different cognitive conditions in monozygotic twins who were discordant or concordant for schizophrenia or who were both normal. These questions included the prevalence of hypofrontality, the importance of genetic predisposition, and the role of long-term neuroleptic treatment. Significant differences between affected and unaffected discordant twins were found only during a task linked to the prefrontal cortex, the Wisconsin Card Sorting Test. During this condition, all of the twins with schizophrenia were hypofrontal compared with their unaffected co-twins, suggesting that, if appropriate cognitive conditions and control groups are used, hypofrontality can be demonstrated in the majority of, if not all, patients with schizophrenia. When unaffected co-twins of patients with schizophrenia were compared with twins who were both normal, no differences were observed, suggesting that nongenetic factors are important in the cause of the prefrontal physiologic deficit that appears to characterize schizophrenia. When concordant twins with a high- vs a low-dose lifetime history of neuroleptic treatment were compared, the twin receiving the higher dose was more hyperfrontal in six of eight pairs, suggesting that long-term neuroleptic treatment does not play a major role in hypofrontality.

Further evidence for dementia of the prefrontal type in schizophrenia? A controlled study of teaching the Wisconsin Card Sorting Test.

Recent physiological and cognitive studies of schizophrenia have implicated dysfunction of prefrontal cortex as a possible explanation for some of the disabling intellectual and social aspects of the disorder. To investigate the potential reversibility of cognitive deficits and the role of state variables, eg, attention and motivation, three groups of patients with schizophrenia were administered the Wisconsin Card Sorting Test on six consecutive occasions. Two of the groups received incremental information on how to do the test, including explicit card-by-card instruction. The third group served as a control. Regardless of the degree of instruction, patients who could not do the test could not learn it. The deficit did not appear generalized, as patients were able to learn word lists on the Selective Reminding memory test and were not globally demented on the Mini-Mental State Examination. These data suggest that prefrontal-type cognitive deficits in schizophrenia may be more profound than is generally appreciated.

Anxiety and cerebral blood flow during behavioral challenge. Dissociation of central from peripheral and subjective measures.

To investigate the relationship between anxiety and regional cerebral blood flow, we administered behavioral challenges to 10 patients with obsessive-compulsive disorder while measuring regional cerebral blood flow with the xenon 133 inhalation technique. Each patient was studied under three conditions: relaxation, imaginal flooding, and in vivo (actual) exposure to the phobic stimulus. Subjective anxiety, obsessive-compulsive ratings, and autonomic measures (heart rate, blood pressure) increased significantly, but respiratory rate and PCO2 did not change across the three conditions. Regional cerebral blood flow increased slightly (in the temporal region) during imaginal flooding, but decreased markedly in several cortical regions during in vivo exposure, when anxiety was highest by subjective and peripheral autonomic measures. These results demonstrate that intense anxiety can be associated with decreased rather than increased cortical perfusion and that ostensibly related states of anxiety (eg, anticipatory and obsessional anxiety) may be associated with opposite effects on regional cerebral blood flow.

Variation in the Williams syndrome GTF2I gene and anxiety proneness interactively affect prefrontal cortical response to aversive stimuli.

Characterizing the molecular mechanisms underlying the heritability of complex behavioral traits such as human anxiety remains a challenging endeavor for behavioral neuroscience. Copy-number variation (CNV) in the general transcription factor gene, GTF2I, located in the 7q11.23 chromosomal region that is hemideleted in Williams syndrome and duplicated in the 7q11.23 duplication syndrome (Dup7), is associated with gene-dose-dependent anxiety in mouse models and in both Williams syndrome and Dup7. Because of this recent preclinical and clinical identification of a genetic influence on anxiety, we examined whether sequence variation in GTF2I, specifically the single-nucleotide polymorphism rs2527367, interacts with trait and state anxiety to collectively impact neural response to anxiety-laden social stimuli. Two hundred and sixty healthy adults completed the Tridimensional Personality Questionnaire Harm Avoidance (HA) subscale, a trait measure of anxiety proneness, and underwent functional magnetic resonance imaging (fMRI) while matching aversive (fearful or angry) facial identity. We found an interaction between GTF2I allelic variations and HA that affects brain response: in individuals homozygous for the major allele, there was no correlation between HA and whole-brain response to aversive cues, whereas in heterozygotes and individuals homozygous for the minor allele, there was a positive correlation between HA sub-scores and a selective dorsolateral prefrontal cortex (DLPFC) responsivity during the processing of aversive stimuli. These results demonstrate that sequence variation in the GTF2I gene influences the relationship between trait anxiety and brain response to aversive social cues in healthy individuals, supporting a role for this neurogenetic mechanism in anxiety.

Cortical "stress tests" in schizophrenia: regional cerebral blood flow studies.

A total of 261 regional cerebral blood flow (rCBF) studies were carried out on 34 medication-free patients with chronic schizophrenia and 50 normal subjects. rCBF, an indicator of local cortical metabolism and activity, was measured during the resting state and also during four cognitive activation tasks or "cortical stress tests." The latter included the Wisconsin Card Sort (WCS), a test of prefrontal lobe function; a simple numbers matching task, and two versions of a visual Continuous Performance Task (CPT). Multivariate comparisons of the two subject groups were performed for each of the five testing conditions, and discriminant function analyses for each condition were carried out to define mathematical models that differentiated normal subjects from medication-free patients. The best such model was determined and was then applied to another group of patients who had diagnoses other than schizophrenia or for whom the diagnosis was unclear. This group included two patients with clinical "frontal lobe syndrome" and radiological evidence of frontal lobe damage. The most robust differences between the groups were seen in frontal rCBF during the WCS. In the discriminant function analysis, rCBF during the WCS was the best discriminator between the two groups, retrospectively classifying 85% of the subjects correctly. rCBF during the resting state and one of the CPTs correctly classified subjects at a rate only marginally better than chance. When the model derived from WCS rCBF was applied to a second group of patients, the two patients with known frontal lobe disease were classified as "schizophrenic" with 100% certainty. Three other patients with psychotic illnesses were also assigned to this group with greater than 80% certainty, whereas a patient with character disorder (rule-out affective disorder) was classified as "normal" with a high level of confidence. These data suggest (1) that schizophrenia is characterized by a deficit in prefrontal function that is revealed when regionally specific demand exceeds the physiological capacity, and (2) that functional brain imaging studies, such as rCBF, can best identify brain abnormalities during "cortical stress tests."

Functional lateralization of the prefrontal cortex during traditional frontal lobe tasks.

We attempted to identify brain regions functionally lateralized during cognitive tasks traditionally linked to the prefrontal cortex (PFC) by measuring regional cerebral blood flow with H2(15)O positron emission tomography (PET). Fourteen normal subjects were scanned six times while performing six different cognitive conditions comprising three task paradigms putatively sensitive to PFC integrity: the Wisconsin Card Sort (WCS), Delayed Response Alternation (DA), and the Spatial Delayed Response (SDR) Tasks, and three matched sensorimotor control tasks. Multivariate and repeated measures analyses indicated that for all three cognitive paradigms there were no significant hemisphere, hemisphere-by-condition, or hemisphere-by-region effects. However, with more liberal statistical comparison (paired t tests), the superior frontal gyrus showed lateralization during both the WCS and SDR tasks (both R > L). These results suggest that, although some asymmetries may be found using liberal analyses, there is less evidence of lateralized brain function during performance of these tasks of PFC function, than in language and motor systems. Implications for testing PFC function in neuropsychiatric groups are discussed.

Regional cerebral blood flow in Down syndrome adults during the Wisconsin Card Sorting Test: exploring cognitive activation in the context of poor performance.

BACKGROUND: Prior studies have indicated abnormal frontal lobes in Down syndrome (DS). The Wisconsin Card Sorting Test (WCST) has been used during functional brain imaging studies to activate the prefrontal cortex. Whether this activation is dependent on successful performance remains unclear. To determine frontal lobe regional cerebral blood flow (rCBF) response in DS and to further understand the effect of performance on rCBF during the WCST, we studied DS adults who perform poorly on this task. METHODS: Initial slope (IS), an rCBF index, was measured with the 133Xe inhalation technique during a Numbers Matching Control Task and the WCST. Ten healthy DS subjects (mean age 28.3 years) and 20 sex-matched healthy volunteers (mean age 28.7 years) were examined. RESULTS: Performance of DS subjects was markedly impaired compared to controls. Both DS and control subjects significantly increased prefrontal IS indices compared to the control task during the WCST. CONCLUSIONS: Prefrontal activation in DS during the WCST was not related to performance of that task, but may reflect engagement of some components involved in the task, such as effort. Further, these results show that failure to activate prefrontal cortex during WCST in schizophrenia is unlikely to be due to poor performance alone.

Prefrontal neurons and the genetics of schizophrenia.

This article reviews prefrontal cortical biology as it relates to pathophysiology and genetic risk for schizophrenia. Studies of prefrontal neurocognition and functional neuroimaging of prefrontal information processing consistently reveal abnormalities in patients with schizophrenia. Abnormalities of prefrontal information processing also are found in unaffected individuals who are genetically at risk for schizophrenia, suggesting that genetic polymorphisms affecting prefrontal function may be susceptibility alleles for schizophrenia. One such candidate is a functional polymorphism in the catechol-o-methyl transferase (COMT) gene that markedly affects enzyme activity and that appears to uniquely impact prefrontal dopamine. The COMT genotype predicts performance on prefrontal executive cognition and working memory tasks. Functional magnetic resonance imaging confirms that COMT genotype affects prefrontal physiology during working memory. Family-based association studies have revealed excessive transmission to schizophrenic offspring of the allele (val) related to poorer prefrontal function. These various data provide convergent evidence that the COMT val allele increases risk for schizophrenia by virtue of its effect on dopamine-mediated prefrontal information processing-the first plausible mechanism for a genetic effect on normal human cognition and risk for mental illness.

Global cerebral blood flow decreases during pain.

Positron emission tomography studies have identified a common set of brain regions activated by pain. No studies, however, have quantitatively examined pain-induced CBF changes. To better characterize CBF during pain, 14 subjects received positron emission tomography scans during rest, during capsaicin-evoked pain (250 micrograms, intradermal injection), and during innocuous vibration. Using the H215O intravenous bolus method with arterial blood sampling, global CBF changes were assessed quantitatively. Painful stimulation produced a 22.8% decrease in global CBF from resting levels (P < 0.0005). This decrease was not accounted for by arterial PCO2 or heart rate changes. Although the exact mechanism remains to be determined, this pain-induced global decrease represents a previously unidentified response of CBF.

Functional mapping of human sensorimotor cortex with 3D BOLD fMRI correlates highly with H2(15)O PET rCBF.

Positron emission tomography (PET) functional imaging is based on changes in regional cerebral blood flow (rCBF). Functional magnetic resonance imaging (fMRI) is based on a variety of physiological parameters as well as rCBF. This study is aimed at the cross validation of three-dimensional (3D) fMRI, which is sensitive to changes in blood oxygenation, with oxygen-15-labeled water (H2(15)O) PET. Nine normal subjects repeatedly performed a simple finger opposition task during fMRI scans and during PET scans. Within-subject statistical analysis revealed significant ("activated") signal changes (p < 0.05, Bonferroni corrected for number of voxels) in contralateral primary sensorimotor cortex (PSM) in all subjects with fMRI and with PET. With both methods, 78% of all activated voxels were located in the PSM. Overlap of activated regions occurred in all subjects (mean 43%, SD 26%). The size of the activated regions in PSM with both methods was highly correlated (rho = 0.87, p < 0.01). The mean distance between centers of mass of the activated regions in the PSM for fMRI versus PET was 6.7 mm (SD 3.0 mm). Average magnitude of signal change in activated voxels in this region, expressed as z-values adapted to timeseries, zt, was similar (fMRI 5.5, PET 5.3). Results indicate that positive blood oxygen level-dependent (BOLD) signal changes obtained with 3D principles of echo shifting with a train of observations (PRESTO) fMRI are correlated with rCBF, and that sensitivity of fMRI can equal that of H2(15)O PET.

Evidence of dysfunction of a prefrontal-limbic network in schizophrenia: a magnetic resonance imaging and regional cerebral blood flow study of discordant monozygotic twins.

OBJECTIVE: The authors previously reported that in monozygotic twins discordant for schizophrenia the affected twin almost invariably had a smaller anterior pes hippocampus, measured with magnetic resonance imaging (MRI), and invariably had less regional cerebral blood flow (rCBF) in the dorsolateral prefrontal cortex during performance of the Wisconsin Card Sorting Test. The present study was an investigation of the relationship between hippocampal pathology and prefrontal hypofunction in the same twin pairs. METHOD: Nine pairs of monozygotic twins discordant for schizophrenia underwent MRI scanning for determination of anterior hippocampal volume and xenon-inhalation rCBF testing for determination of prefrontal physiological activation associated with the Wisconsin Card Sorting Test. RESULTS: The differences within twin pairs on the MRI and rCBF measures were strongly and selectively correlated. Specifically, the more an affected twin differed from the unaffected twin in left hippocampal volume, the more they differed in prefrontal physiological activation during the Wisconsin Card Sorting Test. In the affected twins as a group, prefrontal activation was strongly related to both left and right hippocampal volume. These relationships were not found in the group of unaffected twins. CONCLUSIONS: This finding is consistent with the notion that schizophrenia involves pathology of and dysfunction within a widely distributed neocortical-limbic neural network that has been implicated in, among other activities, the performance of cognitive tasks requiring working memory.

A relationship between anatomical and physiological brain pathology in schizophrenia: lateral cerebral ventricular size predicts cortical blood flow.

The authors studied the relationship between lateral cerebral ventricular size and regional cerebral blood flow during mental activation in 30 patients with schizophrenia. Patients with large ventricles had diffusely lower cortical gray matter blood flow than patients with small ventricles. In addition, an inverse correlation between ventricular size and prefrontal blood flow was observed while patients were attempting to solve a neuropsychological test specifically related to the prefrontal cortex. These data suggest that structural brain pathology impairs prefrontal physiology in schizophrenia, implicating a neural mechanism for the intellectual deficits characteristic of this disorder.