Single voxel proton magnetic resonance spectroscopy in women with and without intimate partner violence-related posttraumatic stress disorder

Psychiatry Research: Neuroimaging 139 (2005) 249 – 258 www.elsevier.com/locate/psychresns

Single voxel proton magnetic resonance spectroscopy in women with and without intimate partner violence-related posttraumatic stress disorder Soraya Seedat a,*, John S. Videen b,c, Colleen M. Kennedy b, Murray B. Stein b,d a

MRC Unit on Anxiety and Stress Disorders, Department of Psychiatry, University of Stellenbosch, P.O. Box 19063, Tygerberg, 7505 Cape Town, South Africa b Veterans Affairs Medical Center, San Diego, CA, USA c Department of Medicine, University of California at San Diego, San Diego, CA 92161, USA d Anxiety and Traumatic Stress Program, Department of Psychiatry (0985), University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0985, USA Received 4 November 2004; accepted 4 June 2005

Abstract Preliminary in vivo proton magnetic spectroscopic (1H-MRS) studies of N-acetylaspartate (a putative marker of neuronal viability and function) in combat veterans and maltreated children with posttraumatic stress disorder (PTSD) suggest altered neuronal integrity in anterior cingulate and medial temporal lobe structures. In this study, 1H-MRS was used to measure N-acetylaspartate (NAA), choline (Cho) and myo-inositol (mI) relative to creatine (Cr) in the anterior cingulate of 16 women with histories of intimate partner violence (7 with a DSM-IV diagnosis of PTSD, 9 without PTSD) and 11 healthy, non-abused comparison subjects. The relationship between anterior cingulate chemistry and performance on the Stroop Color-Word task and Part B of the Trail Making Test was also examined. There were no significant differences in anterior cingulate or occipital gray matter metabolite ratios of NAA/Cr and Cho/Cr between intimate partner violence and healthy comparison subjects. Intimate partner violence subjects with PTSD had significantly higher anterior cingulate Cho/Cr than intimate partner violence subjects without PTSD. There was evidence that the subjects with PTSD suffered more severe intimate partner violence as measured by the Conflict Tactics Scale-Revised. Metabolite ratios were not significantly correlated with performance on the Stroop or Trails B. Our findings, in agreement with earlier studies, showed significant alterations in anterior cingulate chemistry in women with PTSD. In contrast to other studies, we found an increase in Cho/Cr rather than a decrease in NAA/Cr, indicating alterations in glia, instead of neuronal dropout. D 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Anterior cingulate chemistry; Domestic violence; Posttraumatic stress; Cognition

* Corresponding author. Tel.: +27 21 938 9374; fax: +27 21 933 5790. E-mail address: [email protected] (S. Seedat). 0925-4927/$ - see front matter D 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.pscychresns.2005.06.001

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1. Introduction Several neuronal markers can be detected and quantified using proton magnetic resonance spectroscopy (1H-MRS) including N-acetylaspartate (NAA), choline (Cho), lactate, creatine (Cr), myo-inositol (mI), glutamine and glutamate (Bottomley, 1989; Miller, 1991; Barker et al., 1994). In studies of physiologic anxiety, healthy subjects were documented to have elevated levels of NAA in the orbitofrontal cortex (Grachev and Apkarian, 2000; Grachev et al., 2001a). Concentrations of NAA in the orbitofrontal cortex were highly correlated with state-trait anxiety, with high-anxious individuals demonstrating higher overall concentrations compared with low-anxious individuals, suggesting an association between abnormal neuronal activity and high anxiety. In contrast, reduced brain NAA concentrations have been documented in pathologic anxiety states (Davidson et al., 1993; Tupler et al., 1997; Dager et al., 1997, 1999; Ebert et al., 1997; Ohara et al., 1999; Fitzgerald et al., 2000), schizophrenia (Keshavan et al., 1997; Keshavan and Pettegrew, 1997), alcohol- and drug-related disorders (Chang et al., 1999; Schweinsburg et al., 2001), Alzheimer’s disease and AIDS (Passe et al., 1995; Pfefferbaum et al., 1999), suggesting degeneration or loss of neurons in these disorders (Prichard, 1996, Brand et al., 1993; Tsai and Coyle, 1995). While functional imaging studies indicate dysfunction in anterior limbic, paralimbic, orbitofrontal and anterior cingulate regions in persons with anxiety disorders (Krystal et al., 2001), until recently, relatively little was known about the relationship between these regional deficits and brain chemistry. 1H-MRS studies have provided insights into the neurochemical abnormalities that occur in persons with posttraumatic stress disorder (PTSD). Previous positron emission tomography and functional magnetic resonance imaging studies have documented alterations in regional cerebral metabolism in limbic (Semple et al., 1993; Rauch et al., 1996) and anterior cingulate cortices (Shin et al., 1997; Bremner et al., 1999), while structural imaging studies have been discrepant in findings of reduced hippocampal volumes (Gurvits et al., 1996; Bremner et al., 1997; Stein et al., 1997; De Bellis et al., 1999, 2001; Bonne et al., 2001). In contrast to MRI studies that have reported smaller volumes of the hippocampus in participants with PTSD, Fennema-

Notestine et al. (2002) did not demonstrate any differences in bilateral, left or right hippocampal volumes in adult victims of intimate partner violence (IPV) with PTSD when compared with healthy adult volunteers (NC) without histories of IPV. In the first reported MRS study in PTSD, Freeman et al. (1998) used 1H-MRS to measure medial temporal lobe neuronal density in male Vietnam veterans (n = 21). They reported significantly reduced NAA/Cr ratios in the right medial temporal lobes in the PTSD group compared with a control group (matched for handedness, age and educational status) and compared with left temporal structures. Other studies have found greater reduction in left hippocampal NAA and Cr in patients with PTSD (Villarreal et al., 2002; Mohanakrishnan Menon et al., 2003). Despite the inconsistency of hippocampal findings, these studies support the hypothesis that PTSD is associated with structural hippocampal damage. Furthermore, it has been suggested that such hippocampal lateralization may relate to specific symptom patterns in PTSD and that this may be underpinned by abnormal neuronal activity and an altered endocrine milieu (Nutt and Malizia, 2004). Altered neuronal integrity has also been implicated in other brain regions in PTSD, for example, the anterior cingulate and basal ganglia, suggesting neuronal loss in these regions. In maltreated children and adolescents with PTSD (n = 11), De Bellis et al. (2000) documented significantly lower ratios of NAA to Cr in the anterior cingulate compared with healthy matched subjects (n = 11), suggesting neuronal loss in this region in children with PTSD, while Lim et al. (2003) noted a decreased NAA/Cr ratio in the basal ganglia in adult patients with acute fire-related PTSD. We report here on single voxel 1H-MRS findings of NAA, Cho, and mI (relative to Cr) in the anterior cingulate in women with IPV with and without PTSD, compared with a healthy group without IPV exposure. We chose to study this group in view of the fact that IPV is a highly prevalent and often repetitive form of trauma in women and posttraumatic stress disorder is one of its most prevalent concomitants (Campbell, 2002). Based on functional imaging (PET) studies of women with childhood sexual abuse that have demonstrated failure of activation of the anterior cingulate in women with PTSD (Bremner et al., 1999; Shin et al., 1999), we predicted significantly reduced

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anterior cingulate concentrations of metabolites, in particular, reduced NAA, in subjects with PTSD. We also predicted that reduced metabolites in subjects with PTSD would be correlated with deficits on a cognitive task (e.g. the Stroop) (Stroop, 1995), in keeping with empirical data which suggest that anterior cingulate dysfunction may mediate some of the core symptoms of PTSD (for example, difficulty prioritizing stimuli and heightened fear conditioning) (Shin et al., 1997; Hamner et al., 1999). In a previous study of neuropsychological function in subjects with IPV, cognitive deficits were confined to measures of working memory, visuo-construction and executive function, and were independent of PTSD status (Stein et al., 2002).

2. Methods 2.1. Subjects Subjects were recruited via community services for abused women (YWCA, Center for Community Solutions, Women’s Resource Center) as participants in a

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study of neuropsychiatric function and brain morphometry in victims of intimate partner violence. The total sample that participated in the proton-MRS component of the study comprised 16 women with histories of intimate partner violence (7 with a diagnosis of PTSD, 9 with no PTSD diagnosis) and 11 healthy, non-abused comparison subjects. A diagnosis of PTSD was based on current DSM-IV criteria using the Structured Clinical Interview for DSM-IV (SCID) (First et al., 1997). The Conflict Tactics Scale-Revised (CTS-2) (Straus et al., 1996) was used to ascertain the nature and severity of IPV. To qualify for inclusion, IPV subjects had to be out of a physically and/or sexually abusive relationship for at least 4 months but not longer than 2 years. Control subjects had no lifetime history of exposure to a dstressorT as defined by dcriterion AT (DSM-IV) for PTSD (American Psychiatric Association, 1994). IPV subjects were matched with control subjects for age (mean = 32.3 years F 9.9 for IPV subjects and mean = 34.9 years F 9.3 for control subjects), race and handedness (see Table 1). All subjects were English-speaking and were able to read and write English at the 8th grade level. As differences were noted in the level of edu-

Table 1 Demographic and abuse characteristics of intimate partner violence (IPV) subjects (with/without PTSD) and non-abused healthy controls

N Age in years Mean (S.D.) Range Race: Caucasian Handedness: right Years of education Mean (S.D.) Range SES Hollingshead Mean (S.D.) Range CTS-2 Physical assault Injury Psychological aggression Sexual coercion Negotiation

IPV subjects

Healthy controls

IPV vs. control subjects: P

IPV PTSD+

IPV PTSD

PTSD+ vs. PTSD subjects: P

16

11

–

7

9

–

32.3 (9.9) 20.0–49.0 8/16 13/15

34.9 (9.3) 19.0–44.0 9/11 9/11

0.49

30.1 (10.9) 20.0–49.0 4/7 6/7

35.9 (9.1) 21.0–48.0 4/9 7/9

0.29

12.1 (1.8) 8.0–16.0

14.7 (2.2) 12.0–18.0

0.004*

12.3 (2.1) 9.0–16.0

11.7 (1.8) 8.0–14.0

0.54

30.9 (12.3) 11.0–53.0

47.6 (10.8) 35.0–66.0

0.001*

33.9 (13.5) 11.0–53.0

30.0 (12.4) 11.0–45.0

0.57

77.0 26.6 81.4 24.0 49.0

0.9 (0.3) 0.0 (0.0) 7.6 (17.9) 0.2 (0.6) 64.9 (61.8)

0.002* 0.009* 0.000* 0.05 0.45

103.0 (91.3) 41.1 (47.0) 111.6 (47.0) 50.2 (58.9) 43.6 (29.7)

56.8 (73.1) 15.2 (19.5) 57.9 (61.8) 6.6 (15.9) 53.2 (39.2)

0.29 0.21 0.06 0.13 0.58

(82.1) (35.5) (60.7) (43.3) (34.6)

0.11 0.66

0.50 0.83

SES: socio-economic status as measured on the Hollingshead scale (Hollingshead, 1975). CTS-2: Revised Conflict Tactics Scale (higher scores indicate more severe abuse, with the exception of the negotiation subscale, where higher scores represent better conflict resolution). * P b 0.05.

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cation (years) and socio-economic status between IPV subjects and controls (see Table 1), these were included as covariates in multivariate analysis. Written informed consent was obtained prior to administration of study procedures. Subjects with a lifetime history of a psychotic or bipolar disorder were excluded. Use of any psychotropic medication within 6 weeks of participation was also an exclusion criterion. Additionally, subjects with histories of substance use disorders within a year of screening or with histories of more than 2 years of alcohol abuse (determined on the Addiction Severity Index) (McLellan et al., 1992) were excluded. Other exclusion criteria were (1) history of neurological disorder or head injury associated with cognitive dysfunction, (2) history of seizure disorder, (3) history consistent with attention deficit disorder or learning disability in childhood, (4) pregnancy and (5) HIV+ or AIDS diagnosis. 2.2. Clinical measures A modified version of the Structured Clinical Interview for DSM-IV disorders (SCID-P) (First et al., 1997) was used to establish PTSD caseness and to screen for other Axis I disorders (panic disorder, generalized anxiety disorder, major depressive disorder). A battery of neurocognitive measures was administered (Stein et al., 2002). Relevant to this report, included among these were two measures of executive functioning: Part B of the Trail Making Test (Reitan, 1992), a test of executive function involving cognitive set shifting, and the Stroop Color-Word Interference task (Stroop, 1995), a measure thought to rely on intact functioning of the anterior cingulate (Pardo et al., 1990; Bench et al., 1993; MacDonald et al., 2000). 2.3. MRI acquisition Structural magnetic resonance imaging (MRI) was conducted at the San Diego Veterans Administration Medical Center using a 1.5 T superconducting magnet (General Electric [GE], Signa software, Milwaukee, Wisconsin). The high-resolution protocol involved collecting three whole-brain image series. The first was a gradient-echo (SPGR) T1-weighted series: repetition time (TR) = 24 ms, echo time (TE) = 5 ms,

number of excitations (ET) = 2, flip angle = 458, field of view (FOV) = 24 cm2, section thickness = 1.2 mm and no gaps. Images for this series were collected in the parasagittal plane to reduce the number of sections needed and to avoid wrap-around artefact from the nose into the occipital sections of the dataset. The second and third series were fast spin-echo acquisition (FSE) yielding two separate image sets in the coronal plane: TR = 3000 ms, TE = 17 ms, ET = 4 and TR = 3800 ms, TE = 102 ms, ET = 8, FOV = 24 cm, section thickness = 4 mm, no gaps (interleaved). Since the image matrix was 256  256 pixels, the voxel size for the SPGR series was 0.9375  0.9375 1.2 mm; for the spin-echo series, the voxel size was 0.9375  0.9375  4 mm. Registration of high-resolution T1-weighted and spin-echo datasets was accomplished with registered sections from both datasets available to operators for resolution of tissue-type ambiguities and anatomic details. The primary anatomic region of interest for correlation with spectroscopic data was the anterior cingulate, with the occipital cortex serving as a dcontrolT region (i.e. a region not expected to be different in PTSD). Conversion to absolute units was accomplished by comparing the signal obtained from a phantom of known concentration of creatine and adjusting for coil loading indicated by relative transmitter gains. 2.4. Proton MR spectroscopy After imaging sequences were obtained, the anterior cingulate was selected for single voxel PRESS spectroscopy (Point RESolved Spectroscopy) (Bottomley, 1987) using an echo time of 135 ms and a repetition time of 1.5 s. Chemical-shift artifact was minimized utilizing multi-lobed transmitter pulses. The 3.0-ml dorsal prefrontal gray matter localized in the anterior cingulate (1.0  1.0  3.0cm) was chosen as the region of interest from axial localizer images by a trained operator. Water suppression was performed by a CHESS (CHEmical-Shift-Selective) (Haase et al., 1985) pulse sequence with fixed flip angles to optimally minimize water signal and provide a measure of coil loading. Two hundred and fifty-six acquisitions were obtained using an eight-step phasecycling sequence, with four equilibration (dummy) scans obtained in approximately 7 min. A similar

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sequence was performed in a 3.0-ml left occipital gray matter region. Spectral processing conformed to a multisite protocol devised by General Electric (SAGE, Mountain View, CA) for use in an automated spectral software application (Schweinsburg et al., 2001). The 2048 collected points were apodized using a Lorentz– Gauss transformation and was zero-filled to 8k points. The spectra were baseline-corrected using an average of the spectral region from 0 to 2 parts per million (ppm). N-Acetylaspartate (NAA), creatine (Cr) and choline (Cho) were quantitated by fitting the peaks to a Gaussian Lineshape using the central 50% of the resonance at 2.02 ppm. Using this technique, resonances are overlapped among other resonances that lie at the feet of the resonance of interest. The line shapes are presumed Gaussian. (Using data from the points making up the central portion of the resonance avoids unnecessary lineshape deformation and broadening. While arbitrary, the technique does not introduce any bias.) (See Figs. 1 and 2.)

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Real NAA

Cho

4

Cr

3

2

1

0

Frequency (ppm)

Fig. 2. Representative 1H-MR spectrum for the anterior cingulate showing the three largest peaks: NAA, Cr and Cho. The spectrum was collected using a PRESS-CHESS sequence. Chemical shifts are indicated in parts per million (ppm).

2.5. Data analysis Independent t-tests were used to compare metabolite ratios in IPV subjects and controls. Correlations of Real NAA

Cr Cho

metabolite ratios and scores on the Stroop Test and the Trail Making Test Part B were conducted using Pearson correlations. One-way analysis of variance (ANOVA) was used to compare differences in metabolite concentrations and scores among the three groups (IPV with PTSD, IPV with no PTSD and controls) with Bonferroni corrections used to control for multiple comparisons. A multivariate general linear model, controlling for education, socio-economic status and IQ, was also used to assess for differences in metabolite ratios and executive function performance between IPV subjects and controls. The a level for all statistical analyses was set at 0.05, and all tests were two-tailed. Values are expressed as mean F S.D.

3. Results 4

3

2

1

0

3.1. Anterior cingulate metabolites

Frequency (ppm) 1

Fig. 1. Representative H-MR spectrum for the anterior cingulate showing the three largest peaks: NAA, Cr and Cho. The spectrum was collected using a PRESS-CHESS sequence. Chemical shifts are indicated in parts per million (ppm).

Contrary to prediction, there were no statistically significant differences bilaterally in anterior cingulate metabolites relative to creatine (NAA/Cr, Cho/Cr) between IPV subjects and control subjects (see

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S. Seedat et al. / Psychiatry Research: Neuroimaging 139 (2005) 249–258 Table 3 Correlation between anterior cingulate metabolites and executive function in intimate partner violence (IPV) subjects and non-abused healthy controls

Table 2). Anterior cingulate Cho/Cr (1.06 F 0.08 vs. 0.93 F 0.12, t = 2.24, df = 14, P = 0.034) and mI/Cr (0.84 F 0.08 vs. 0.76 F 0.06, t = 2.22, df = 14, P = 0.049) ratios were significantly higher in subjects with IPV and PTSD vs. those with IPV but without PTSD. As anticipated, there were no significant differences in NAA/Cr and Cho/Cr in occipital gray matter between subjects with and without PTSD.

Anterior cingulate

IPV subjects (n = 16)

Healthy controls (n = 11)

NAA/Cr Cho/Cr mI/Cr NAA/Cr Cho/Cr mI/Cr

Executive function, Trail Making Test Part B (s) 0.04 0.17 0.19 Total errors 0.04 0.13 0.18 Stroop Color-Word Interference Test Color 0.34 0.004 0.11 Word 0.11 0.18 0.09 Interference 0.25 0.22 0.19

3.2. Executive function IPV subjects compared with control subjects had significantly lower scores on the Stroop Color-Word task, suggestive of greater cognitive interference: (i) Stroop mean total score: 41.7 F 8.3 in IPV subjects vs. 54.3 F .0 in controls, t = 3.91, P = 0.001; (ii) Stroop mean Word score: 96.3 F 14.1 in IPV subjects vs. 111.1 F14.4 in controls, t = 2.6, df = 24, P = 0.016; and (iii) Stroop mean Color score: 71.8 F 9.7 in IPV subjects vs. 88.9 F 12.5 in controls, t = 3. 78, df = 24, P = 0.001. IPV subjects also performed significantly worse than healthy controls on the set shifting, Trail Making Test Part B (Trails B time to complete: 77.2 F 35.2 in IPV subjects vs. 46.4 F 14.5, df = 24, P = 0.012).

0.15 0.13

0.12 0.11

0.01 0.02

0.67* 0.28 0.41 0.09 0.15 0.19

0.42 0.17 0.13

Values are Pearson correlation coefficients. * P b 0.05.

and socio-economic status as covariates, we did not find any significant differences in association between metabolite levels in the anterior cingulate and performance on these measures. Subjects in both the IPV and control groups spanned a relatively large age range (approximately 30 years), so we considered whether age-related variations of metabolites might have obscured effects. However, there were no significant age-related differences in metabolites in either group.

3.3. Relationship between metabolites and anterior cingulate function

4. Discussion These findings do not suggest the presence of significant differences in metabolites in the anterior cingulate (an integral component of the PTSD neural circuit) in IPV subjects (with or without PTSD) compared with healthy matched controls (Shin et al., 1997, 2001; Hamner et al., 1999; Shin et al., 2001). PTSD+ subjects had significantly higher anterior cin-

Anterior cingulate metabolite ratios were not significantly correlated with performance on the Stroop or Trail Making Test Part B in IPV subjects (see Table 3). Using a multivariate general linear model with group (control, current PTSD, no lifetime or current PTSD) as the between-subjects factor and educational

Table 2 Metabolite ratios in intimate partner violence (IPV) subjects and non-abused healthy controls

N Anterior cingulate NAA/Cr Anterior cingulate Cho/Cr Anterior cingulate mI/Cr Occipital gray matter NAA/Cr Occipital gray matter Cho/Cr Occipital gray matter mI/Cr

IPV subjects

Healthy controls

IPV vs. control subjects P

IPV PTSD+

IPV PTSD

PTSD+ vs. PTSD subjects: P

16 1.35 F 0.08 0.99 F 0.11 0.79 F 0.08 1.51 F 0.11 0.66 F 0.04 0.71 F 0.07

11 1.39 F 0.09 0.99 F 0.09 0.78 F 0.09 1.54 F 0.07 0.65 F 0.04 0.71 F 0.03

– 0.20 0.92 0.89 0.40 0.57 0.87

7 1.34 F 0.10 1.06 F 0.08 0.84 F 0.08 1.54 F 0.12 0.67 F 0.05 0.72 F 0.09

9 1.36 F 0.06 0.93 F 0.12 0.76 F 0.06 1.49 F 0.09 0.66 F 0.04 0.71 F 0.03

– 0.71 0.03* 0.049* 0.44 0.68 0.74

Relative concentrations of N-acetylaspartate (NAA), choline (Cho) and myo-inositol (mI) expressed in relation to the concentration of creatine (Cr) (internal standard).

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gulate Cho/Cr and mI/Cr ratios compared with subjects without PTSD. Notably, no significant differences were noted in the severity of IPV (as measured on CTS-2 subscales) between abused women with and without PTSD (see Table 1), suggesting that elevated Cho and mI levels in the anterior cingulate may represent a marker for PTSD rather than for abuse, per se. To date, the only other study of anterior cingulate NAA in PTSD found reduced NAA/Cr in maltreated children and adolescents with the disorder as compared with traumatized subjects without PTSD and healthy controls (De Bellis et al., 2000). It remains to be seen whether or not these findings reflect a unique abnormality in pediatric PTSD. High levels of choline (a metabolite occurring in high concentrations in white matter and glia) in the presence of low levels of NAA usually occur where there is a proliferation of neuroglia at the expense of neuronal number (Michaelis et al., 1993; Soher et al., 1996; Fitzgerald et al., 2000). It may be hypothesized that grey matter atrophy in PTSD, disproportionately increasing white matter volume, may be contributing to higher Cho/Cr ratios in subjects with PTSD. Similarly, a high concentration of myo-inositol in astrocytes, a putative glial cell marker, may be associated with cell proliferation (Brand et al., 1993; Schweinsburg et al., 2001). In contrast, a reduction in NAA, a metabolite localized primarily within neurons (Urenjak et al., 1992), is suggestive of neuronal/axonal loss and function (Miller, 1991; Urenjak et al., 1993; VionDury et al., 1995; Hugg et al., 1996) and is dependent on factors both affecting the neuronal composition of tissue sampled as well as the viability of neurons, in particular, glutamatergic neurons where NAA occurs in high concentrations. The significance of these findings with respect to the neurobiology of PTSD has yet to be determined. It might be hypothesised that an elevation in choline in women with established PTSD may simply precede a decline in NAA. This is, in part, supported by studies that have shown a temporal relationship between cognitive dysfunction and decline in NAA over a number of years (Ross and Sachdev, 2004, review). However, this will need confirmation in prospective longitudinal studies of trauma-exposed subjects. Our data also do not support, in women exposed to IPV, significant associations between regional NAA, Cho and mI (relative to creatine), and perfor-

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mance on a task (Stroop) that relies, at least in part, on anterior cingulate functioning. Although PTSD subjects demonstrated significantly greater cognitive interference on the Stroop, cognitive deficits were not associated with significantly altered anterior cingulate chemistry. Some studies have fairly consistently documented correlations between NAA in the frontal lobe and executive function, and between NAA in the medial temporal lobe and verbal memory (for review, see Ross and Sachdev, 2004). The interrelationship between cognitive interference and NAA concentration was examined in a recent 1HMRS study using the Stroop Color-Word task in a sample of normal subjects (Grachev et al., 2001b). The authors reported a significant correlation between high cognitive interference and reduced NAA levels in the anterior cingulate. An abnormal response on the Stroop test (PTSD-specific Stroop) has also been documented in combat veterans with PTSD (McNally et al., 1993) consistent with PET and fMRI imaging studies that have used classic and modified Stroop paradigms as probes of executive anterior cingulate function (Pardo et al., 1990; Leung et al., 2000). In conclusion, it is important to note that this was a small sample study in which few subjects (n = 7) met criteria for PTSD. Quantification of metabolites was done using a 1.5 T magnet. A higher field strength would have improved spectral resolution and improved the precision of quantification of metabolites. In addition, we have reported metabolites as ratios rather than as absolute concentrations and this may explain the negative findings, since simultaneous change in metabolites (e.g. reduction of both NAA and Cr) may yield no net change in ratios. However, this study supports the work by other authors who found metabolite alterations in general in PTSD caused by stressors other than IPV. To definitively address differences between subjects with and without PTSD, future studies will need to consider a larger sample, multi-voxel MRS methods and more precise quantification of brain metabolites.

Acknowledgments This study was supported by a VA Merit Review grant to Dr. Stein. The authors are grateful to the San

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Diego YWCA and the San Diego Center for Community Solutions for their assistance with the project. The authors are grateful to Michael W. Weiner, M.D., for his generous provision of advice and encouragement during the early stages of development and implementation of this protocol.

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