Automated anatomical labeling of activations in SPM using a macroscopic anatomical parcellation of the MNI MRI single-subject brain

Lithium alters brain activation in bipolar disorder in a task- and state-dependent manner: an fMRI study

BACKGROUND

It is unknown if medications used to treat bipolar disorder have effects on brain activation, and whether or not any such changes are mood-independent.

METHODS

Patients with bipolar disorder who were depressed (n = 5) or euthymic (n = 5) were examined using fMRI before, and 14 days after, being started on lithium (as monotherapy in 6 of these patients). Patients were examined using a word generation task and verbal memory task, both of which have been shown to be sensitive to change in previous fMRI studies. Differences in blood oxygenated level dependent (BOLD) magnitude between the pre- and post-lithium results were determined in previously defined regions of interest. Severity of mood was determined by the Hamilton Depression Scale for Depression (HAM-D) and the Young mania rating scale (YMRS).

RESULTS

The mean HAM-D score at baseline in the depressed group was 15.4 +/- 0.7, and after 2 weeks of lithium it was 11.0 +/- 2.6. In the euthymic group it was 7.6 +/- 1.4 and 3.2 +/- 1.3 respectively. At baseline mean BOLD signal magnitude in the regions of interest for the euthymic and depressed patients were similar in both the word generation task (1.56 +/- 0.10 and 1.49 +/- 0.10 respectively) and working memory task (1.02 +/- 0.04 and 1.12 +/- 0.06 respectively). However, after lithium the mean BOLD signal decreased significantly in the euthymic group in the word generation task only (1.56 +/- 0.10 to 1.00 +/- 0.07, p < 0.001). Post-hoc analysis showed that these differences were statistically significant in Broca's area, the left pre-central gyrus, and the supplemental motor area.

CONCLUSION

This is the first study to examine the effects of lithium on brain activation in bipolar patients. The results suggest that lithium has an effect on euthymic patients very similar to that seen in healthy volunteers. The same effects are not seen in depressed bipolar patients, although it is uncertain if this lack of change is linked to the lack of major improvements in mood in this group of patients. In conclusion, this study suggests that lithium may have effects on brain activation that are task- and state-dependent. Given the small study size and the mildness of the patient's depression these results require replication.

Neural networks of information processing in posttraumatic stress disorder: a functional magnetic resonance imaging study

BACKGROUND

Neuroimaging studies report reduced medial prefrontal cortical (particularly anterior cingulate) but enhanced amygdala response to fear signals in posttraumatic Stress Disorder (PTSD). We investigated whether anterior cingulate-amygdala dysregulation in PTSD would generalize to salient, but nonthreat related signals.

METHODS

Individuals with PTSD (n = 14) and age and sex-matched nontraumatized controls (n = 14) completed an auditory oddball paradigm adapted to functional magnetic resonance imaging at a 1.5-T field strength.

RESULTS

Controls displayed bilateral activation in ventral anterior cingulate and amygdala networks, and PTSD subjects showed bilateral dorsal anterior cingulate and amygdala activation to targets relative to nontargets. Compared to controls, PTSD subjects showed enhanced responses to targets in the dorsal and rostral anterior cingulate, and left amygdala. Whole-brain analyses confirmed the expected pattern of distributed prefrontal-parietal responses to targets in the oddball task. Greater activity in posterior parietal somatosensory regions was observed in PTSD.

CONCLUSIONS

Our findings of enhanced anterior cingulate responses in PTSD contrast with reports of reduced activity for threat stimuli, suggesting that the latter may be specific to processing of threat-related content. Activation in rostral and dorsal anterior cingulate, left amygdala and posterior parietal networks in response to salient, nonthreatening stimuli may reflect generalized hypervigilance.

Automated cortical projection of head-surface locations for transcranial functional brain mapping

Recent advancements in two noninvasive transcranial neuroimaging techniques, near-infrared spectroscopy (NIRS) and transcranial magnetic stimulation (TMS), signify the increasing importance of establishing structural compatibility between transcranial methods and conventional tomographic methods, such as functional magnetic resonance imaging (fMRI) and positron emission tomography (PET). The transcranial data obtained from the head surface should be projected onto the cortical surface to present the transcranial brain-mapping data on the same platform as tomographic methods. Thus, we developed two transcranial projection algorithms that project given head-surface points onto the cortical surface in structural images, and computer programs based on them. The convex-hull algorithm features geometric handling of the cortical surface, while the balloon-inflation algorithm is faster, and better reflects the local cortical structure. The automatic cortical projection methods proved to be as effective as the manual projection method described in our previous study. These methods achieved perfect correspondence between any given point on the head surface or a related nearby point in space, and its cortical projection point. Moreover, we developed a neighbor-reference method that enables transcranial cortical projection of a given head-surface point in reference to three neighboring points and one additional standard point, even when no structural image of the subject is available. We also calculated an error factor associated with these probabilistic estimations. The current study presents a close topological link between transcranial and tomographic brain-mapping modalities, which could contribute to inter-modal data standardization.

Differential activation of pre-SMA and SMA proper during action observation: Effects of instructions

Many neurophysiological studies give evidence for a matching system between action observation and imitation. We used functional MRI to investigate the effects of different instructions for observing identical stimuli of whole-body gymnastics movements. The imitative-like observation mode asked normal human participants to observe the sequence containing repetitive parts and to subsequently imagine the observed movements in the first-person perspective. The evaluative observation mode asked the participants to carefully observe and judge movement accuracy and consistency in the repetitive sequence. We hypothesized that the supplementary motor area would be specifically involved in performing the observational tasks. Results indicate that the SMA proper is generally activated during observation of whole-body gymnastic movements and shows pronounced activation in imitative-like observation mode. Pre-SMA activity can be differentially modulated by instructions related to the observation task.

Distinct fMRI responses to laughter, speech, and sounds along the human peri-sylvian cortex

In this event-related fMRI study, 12 right-handed volunteers heard human laughter, sentential speech, and nonvocal sounds in which global temporal and harmonic information were varied whilst they were performing a simple auditory target detection. This study aimed to delineate distinct peri-auditory regions which preferentially respond to laughter, speech, and nonvocal sounds. Results show that all three types of stimuli evoked blood-oxygen-level-dependent responses along the left and right peri-sylvian cortex. However, we observed differences in regional strength and lateralization in that (i) hearing human laughter preferentially involves auditory and somatosensory fields primarily in the right hemisphere, (ii) hearing spoken sentences activates left anterior and posterior lateral temporal regions, (iii) hearing nonvocal sounds recruits bilateral areas in the medial portion of Heschl's gyrus and at the medial wall of the posterior Sylvian Fissure (planum parietale and parietal operculum). Generally, the data imply a differential regional sensitivity of peri-sylvian areas to different auditory stimuli with the left hemisphere responding more strongly to speech and with the right hemisphere being more amenable to nonspeech stimuli. Interestingly, passive perception of human laughter activates brain regions which control motor (larynx) functions. This observation may speak to the issue of a dense intertwining of expressive and receptive mechanisms in the auditory domain. Furthermore, the present study provides evidence for a functional role of inferior parietal areas in auditory processing. Finally, a post hoc conjunction analysis meant to reveal the neural substrates of human vocal timbre demonstrates a particular preference of left and right lateral parts of the superior temporal lobes for stimuli which are made up of human voices relative to nonvocal sounds.

Functional MRI of galvanic vestibular stimulation with alternating currents at different frequencies

Functional MRI was performed in 28 healthy volunteers to study the effects of galvanic vestibular stimulation with alternating currents (AC-GVS) of different frequencies on brain activation patterns. The aims of this study were (1) to identify specific areas within the vestibular cortical network that are involved in the processing of frequency-specific aspects by correlation analyses, (2) to determine the optimal frequency for stimulation of the vestibular system with respect to perception, and (3) to analyze whether different frequencies of AC-GVS are mediated in different cortical areas or different sites within the vestibular cortex. AC-GVS was performed using sinusoidal stimulation currents with an amplitude of +/-2.5 mA, and frequencies of 0.1 Hz, 0.3 Hz, 0.8 Hz, 1.0 Hz, 2.0 Hz, and 5.0 Hz were applied. Regardless of the applied stimulation frequency, AC-GVS elicited activations within a network of multisensory areas similar to those described in earlier studies using direct currents. No mapping of different stimulation frequencies to different cortical locations was observed. Additional activations of somatosensory cortex areas were observed during stimulation with 5 Hz only. The strongest vestibular sensations were reported during stimulation with 1 Hz and 2 Hz. Correlation analyses between blood oxygenation level dependent (BOLD) signal changes and stimulation frequency revealed a positive dependency in areas of the supramarginal gyrus, posterolateral thalamus, cerebellar vermis, posterior insula, and in the hippocampal region/uncus. These regions represent areas involved in the processing of vestibular information for head and body orientation in space.

Adaptive cortical plasticity in higher visual areas after acute optic neuritis

The ability to distinguish adaptive cortical reorganization may help to target future therapeutic strategies after neurological insult. We investigated cortical plasticity by prospectively applying visual functional magnetic resonance imaging (fMRI) and optic nerve MRI to 20 patients with acute optic neuritis at baseline, 1, 3, 6, and 12 months. We performed three types of correlation analyses to investigate the relationships between fMRI activity, clinical function, and optic nerve structure. The first analysis directly correlated the fMRI response to clinical function or optic nerve structure and found dynamic relations especially within the first 3 months. The second analysis used a novel technique that modeled the fMRI response and optic nerve structure together with clinical function, to determine the contribution fMRI made to clinical function after accounting for structural factors. Significant effects were found at baseline only, within the right peristriate cortex, and bilaterally in the lateral occipital complexes, which are normally involved in higher order visual processing. The third analysis investigated the relation between the modeled visual recovery rate and fMRI response but found no significant effects. The key findings of this study are from the second analysis and suggest a genuine adaptive role for cortical reorganization within extrastriate visual areas early after optic neuritis.

Mining for associations between text and brain activation in a functional neuroimaging database

We describe a method for mining a neuroimaging database for associations between text and brain locations. The objective is to discover association rules between words indicative of cognitive function as described in abstracts of neuroscience papers and sets of reported stereotactic Talairach coordinates. We invoke a simple probabilistic framework in which kernel density estimates are used to model distributions of brain activation foci conditioned on words in a given abstract. The principal associations are found in the joint probability density between words and voxels. We show that the statistically motivated associations are well aligned with general neuroscientific knowledge.

Serotonergic modulation of prefrontal cortex during negative feedback in probabilistic reversal learning

This study used functional magnetic resonance imaging to examine the effects of acute tryptophan (TRP) depletion (ATD), a well-recognized method for inducing transient cerebral serotonin depletion, on brain activity during probabilistic reversal learning. Twelve healthy male volunteers received a TRP-depleting drink or a balanced amino-acid drink (placebo) in a double-blind crossover design. At 5 h after drink ingestion, subjects were scanned while performing a probabilistic reversal learning task and while viewing a flashing checkerboard. The probabilistic reversal learning task enabled the separate examination of the effects of ATD on behavioral reversal following negative feedback and negative feedback per se that was not followed by behavioral adaptation. Consistent with previous findings, behavioral reversal was accompanied by significant signal change in the right ventrolateral prefrontal cortex (PFC) and the dorsomedial prefrontal cortex. ATD enhanced reversal-related signal change in the dorsomedial PFC, but did not modulate the ventrolateral PFC response. The ATD-induced signal change in the dorsomedial PFC during behavioral reversal learning extended to trials where subjects received negative feedback but did not change their behavior. These data suggest that ATD affects reversal learning and the processing of aversive signals by modulation of the dorsomedial PFC.

Development of Korean standard brain templates

We developed age, gender and ethnic specific brain templates based on MR and Positron-Emission Tomography (PET) images of Korean normal volunteers. Seventy-eight normal right-handed volunteers (M/F=49/29) underwent 3D T1-weighted SPGR MR and F-18-FDG PET scans. For the generation of standard templates, an optimal target brain that has the average global hemispheric shape was selected for each gender. MR images were then spatially normalized by linear transformation to the target brains, and normalization parameters were reapplied to PET images. Subjects were subdivided into 2 groups for each gender: the young/midlife (<55 yr) and the elderly groups. Young and elderly MRI/PET templates were composed by averaging the spatially normalized images. Korean templates showed different shapes and sizes (mean length, width, and height of the brains were 16.5, 14.3 and 12.1 cm for man, and 15.6, 13.5 and 11.4 cm for woman) from the template based on Caucasian (18.3, 14.2, and 13.3 cm). MRI and PET templates developed in this study will provide the framework for more accurate stereotactic standardization and anatomical localization.

Undirected graphs of frequency-dependent functional connectivity in whole brain networks

We explored properties of whole brain networks based on multivariate spectral analysis of human functional magnetic resonance imaging (fMRI) time-series measured in 90 cortical and subcortical subregions in each of five healthy volunteers studied in the (no-task) resting state. We note that undirected graphs representing conditional independence between multivariate time-series can be more readily approached in the frequency domain than the time domain. Estimators of partial coherency and normalized partial mutual information phi, an integrated measure of partial coherence over an arbitrary frequency band, are applied. Using these tools, we replicate the prior observations that bilaterally homologous brain regions tend to be strongly connected and functional connectivity is generally greater at low frequencies [0.0004, 0.1518 Hz]. We also show that long-distance intrahemispheric connections between regions of prefrontal and parietal cortex were more salient at low frequencies than at frequencies greater than 0.3 Hz, whereas many local or short-distance connections, such as those comprising segregated dorsal and ventral paths in posterior cortex, were also represented in the graph of high-frequency connectivity. We conclude that the partial coherency spectrum between a pair of human brain regional fMRI time-series depends on the anatomical distance between regions: long-distance (greater than 7 cm) edges represent conditional dependence between bilaterally symmetric neocortical regions, and between regions of prefrontal and parietal association cortex in the same hemisphere, are predominantly subtended by low-frequency components.

Functional connectivity during working memory maintenance

Neurophysiological experiments with monkeys have demonstrated that working memory (WM) is associated with persistent neural activity in multiple brain regions, such as the prefrontal cortex (PFC), the parietal cortex, and posterior unimodal association areas. WM maintenance is believed to require the coordination of these brain regions, which do not function in isolation but, rather, interact to maintain visual percepts that are no longer present in the environment. However, single-unit physiology studies and traditional univariate analyses of functional brain imaging data cannot evaluate interactions between distant brain regions, and so evidence of regional integration during WM maintenance is largely indirect. In this study, we utilized a recently developed multivariate analysis method that allows us to explore functional connectivity between brain regions during the distinct stages of a delayed face recognition task. To characterize the neural network mediating the on-line maintenance of faces, the fusiform face area (FFA) was defined as a seed and was then used to generate whole-brain correlation maps. A random effects analysis of the correlation data revealed a network of brain regions exhibiting significant correlations with the FFA seed during the WM delay period. This maintenance network included the dorsolateral and ventrolateral PFC, the premotor cortex, the intraparietal sulcus, the caudate nucleus, the thalamus, the hippocampus, and occipitotemporal regions. These findings support the notion that the coordinated functional interaction between nodes of a widely distributed network underlies the active maintenance of a perceptual representation.

Activity and connectivity of brain mood regulating circuit in depression: a functional magnetic resonance study

BACKGROUND

Functional imaging studies indicate that imbalances in cortico-limbic activity and connectivity may underlie the pathophysiology of MDD. In this study, using functional Magnetic Resonance Imaging (fMRI), we investigated differences in cortico-limbic activity and connectivity between depressed patients and healthy controls.

METHODS

Fifteen unmedicated unipolar depressed patients and 15 matched healthy subjects underwent fMRI during which they first completed a conventional block-design activation experiment in which they were exposed to negative and neutral pictures. Next, low frequency blood oxygenation dependent (BOLD) related fluctuations (LFBF) data were acquired at rest and during steady-state exposure to neutral, positive and negative pictures. LFBF correlations were calculated between anterior cingulate cortex (ACC) and limbic regions--amygdala (AMYG), pallidostriatum (PST) and medial thalamus (MTHAL) and used as a measure of cortico-limbic connectivity.

RESULTS

Depressed patients had increased activation of cortical and limbic regions. At rest and during exposure to neutral, positive, and negative pictures cortico-limbic LFBF correlations were decreased in depressed patients compared to healthy subjects.

CONCLUSIONS

The finding of increased activation of limbic regions and decreased LFBF correlations between ACC and limbic regions is consistent with the hypothesis that decreased cortical regulation of limbic activation in response to negative stimuli may be present in depression.

A new SPM toolbox for combining probabilistic cytoarchitectonic maps and functional imaging data

Correlating the activation foci identified in functional imaging studies of the human brain with structural (e.g., cytoarchitectonic) information on the activated areas is a major methodological challenge for neuroscience research. We here present a new approach to make use of three-dimensional probabilistic cytoarchitectonic maps, as obtained from the analysis of human post-mortem brains, for correlating microscopical, anatomical and functional imaging data of the cerebral cortex. We introduce a new, MATLAB based toolbox for the SPM2 software package which enables the integration of probabilistic cytoarchitectonic maps and results of functional imaging studies. The toolbox includes the functionality for the construction of summary maps combining probability of several cortical areas by finding the most probable assignment of each voxel to one of these areas. Its main feature is to provide several measures defining the degree of correspondence between architectonic areas and functional foci. The software, together with the presently available probability maps, is available as open source software to the neuroimaging community. This new toolbox provides an easy-to-use tool for the integrated analysis of functional and anatomical data in a common reference space.

Pathways for fear perception: modulation of amygdala activity by thalamo-cortical systems

Effective perception of fear signals is crucial for human survival and the importance of the amygdala in this process is well documented. Animal, lesion and neuroimaging studies indicate that incoming sensory signals of fear travel from thalamus to amygdala via two neural pathways: a direct subcortical route and an indirect pathway via the sensory cortex. Other lines of research have demonstrated prefrontal modulation of the amygdala. However, no study to date has examined the prefrontal modulation of the thalamo-cortico-amygdala pathways in vivo. We used psychophysiological and physiophysiological interactions to examine the functional connectivity within thalamus, amygdala and sensory (inferior occipital, fusiform) cortices, and the modulation of these networks by the anterior cingulate cortex (ACC). Functional magnetic resonance imaging (fMRI) data were acquired for 28 healthy control subjects during a fear perception task, with neutral as the 'baseline' control condition. Main effect analysis, using a region of interest (ROI) approach, confirmed that these regions are part of a distributed neural system for fear perception. Psychophysiological interactions revealed an inverse functional connectivity between occipito-temporal visual regions and the left amygdala, but a positive connectivity between these visual region and the right amygdala, suggesting that there is a hemispheric specialization in the transfer of fear signals from sensory cortices to amygdala. Physiophysiological interactions revealed a dorsal-ventral division in ACC modulation of the thalamus-sensory cortex pathway. While the dorsal ACC showed a positive modulation of this pathway, the ventral ACC exhibited an inverse relationship. In addition, both the dorsal and ventral ACC showed an inverse interaction with the direct thalamus-amygdala pathway. These findings suggest that thalamo-amygdala and cortical regions are involved in a dynamic interplay, with functional differentiation in both lateralized and ventral/dorsal gradients. Breakdowns in these interactions may give rise to affect-related symptoms seen in a range of neuropsychiatric disorders.

Atypical hemispheric specialization for language in right-handed schizophrenia patients

BACKGROUND

The literature suggests that schizophrenia could be related to a failure in the setting up of left hemisphere dominance for language. We sought to determine hemispheric specialization for language in schizophrenic patients, using functional magnetic resonance imaging.

METHODS

Twenty-one right-handed patients with DSM-IV schizophrenia and 21 right-handed control subjects matched by age, gender, and level of education were recruited. Fractional blood oxygen level dependent (BOLD) signal variations in anatomic regions of interest were compared between groups. Functional asymmetry indices (FAIs) were calculated in a region (LANG) resulting from the merging of activated regions showing a Group x Hemisphere interaction. The FAI difference between each patient and their matched control subject was computed.

RESULTS

We found lower BOLD signal changes in patients as compared with their control subjects in a network comprising areas of the left middle temporal gyrus, the left angular gyrus, and the pars triangularis of the left inferior frontal gyrus, merged to constitute LANG. The intra-pair differences of FAIs in this area showed that 76% of the patients exhibited less leftward functional asymmetry than their matched control subjects, including six patients with a rightward asymmetry.

CONCLUSIONS

These results demonstrated the existence of an anomaly in left hemisphere specialization for language in schizophrenic subjects.

Functional disconnectivity of the medial temporal lobe in Asperger's syndrome

BACKGROUND

Autistic spectrum disorders (ASD) are neurodevelopmental conditions that may be caused by abnormal connectivity between brain regions constituting neurocognitive networks for specific aspects of social cognition.

METHODS

We used three-way multidimensional scaling of regionally parcellated functional magnetic resonance imaging (fMRI) data to explore the hypothesis of abnormal functional connectivity in people with ASD. Thirteen high-functioning individuals with Asperger's syndrome and 13 healthy volunteers were scanned during incidental processing of fearful facial expressions.

RESULTS

Using permutation tests for inference, we found evidence for significant abnormality of functional integration of amygdala and parahippocampal gyrus (p < .05, false discovery rate [FDR] corrected) in people with Asperger's syndrome. There were less salient abnormalities in functional connectivity of anterior cingulate, inferior occipital, and inferior frontal cortex, but there was no significant difference between groups in whole brain functional connectivity.

CONCLUSIONS

We conclude there is evidence that functional connectivity of medial temporal lobe structures specifically is abnormal in people with Asperger's syndrome during fearful face processing.

Relationship between disgust sensitivity, trait anxiety and brain activity during disgust induction

We examined the influence of disgust sensitivity and trait anxiety on disgust processing via functional magnetic resonance imaging. Data of 63 healthy females were combined across four studies, where the same disgusting and affectively neutral pictures had been presented. The disgust pictures, rated as highly repulsive, provoked activation in the occipital cortex, the left prefrontal cortex and both amygdalae. Disgust sensitivity and trait anxiety were positively, and independently from each other, correlated with the activation of the right amygdala. This points to the role of the amygdala as an integrative brain structure, whose activation can be modulated by different affective styles.

Influences of disgust sensitivity on hemodynamic responses towards a disgust-inducing film clip

The major goal of the present functional magnetic resonance imaging study was to investigate the influence of disgust sensitivity on hemodynamic responses during disgust induction. Fifteen subjects viewed three different film excerpts (duration: 135 s each) with disgust-evoking, threatening and neutral content. The films were presented in a block design with four repetitions of each condition. Afterwards, subjects gave affective ratings for the films and answered the questionnaire for the assessment of disgust sensitivity (QADS, []). The subjects' overall disgust sensitivity was positively related to their experienced disgust, as well as to their prefrontal cortex activation during the disgust condition. Further, there was a positive correlation between subjects' scores on the QADS subscale spoilage/decay and their amygdala activation (r=0.76). This was reasonable since the disgust film clip depicted a cockroach-invasion and the subscale spoilage/decay contains, among others, an item asking for disgust towards cockroaches. The study stresses, in accordance to previous studies, the importance of considering personality traits when studying affective responses in fMRI studies.

Neural responses of OCD patients towards disorder-relevant, generally disgust-inducing and fear-inducing pictures

This functional magnetic resonance imaging study investigated the disgust- and fear-reactivity of patients suffering from obsessive-compulsive disorder (OCD). Ten OCD patients were scanned while viewing blocks of pictures showing OCD triggers from their personal environment and OCD-irrelevant disgust-inducing, fear-inducing and neutral scenes. Afterwards, the patients rated the intensity of the induced disgust, fear and OCD symptoms. The responses were compared with those of 10 healthy control subjects. The disorder-relevant pictures provoked intense OCD symptoms in the clinical group associated with increased activation in the bilateral prefrontal cortex, the left insula, the right supramarginal gyrus, the left caudate nucleus and the right thalamus. The patients gave higher disgust and fear ratings than the controls for all aversive picture categories. Neural responses towards the disorder-irrelevant disgusting and fear-inducing material included more pronounced insula activation in patients than controls. Summarizing, photos of individual OCD-triggers are an effective means of symptom provocation and activation of the fronto-striato-thalamo-parietal network. The increased insular reactivity of OCD patients during all aversive picture conditions might mirror their susceptibility to experience negative somatic states.

Morphometric analysis of gray matter volume in demented older adults: exploratory analysis of the cardiovascular health study brain MRI database

We tested the feasibility of a fully automated brain MRI voxel count technique--automated labeling pathway (ALP)--in a sample of 15 demented and 13 cognitively normal women (age 75-85 years) participating to the Cardiovascular Health Study (CHS). We hypothesized that ALP would replicate well-established findings of the anatomical correlates of dementia. In particular, we hypothesized that ALP volumetric measures would: (1) significantly differ between cognitively normal and demented women in those brain areas that are established markers for diagnosis of dementia (temporal and medial temporal lobes, hippocampus, amygdala and parahippocampus) but not in other brain areas (e.g., occipital lobe, visual cortex, motor cortex) and (2) correlate with visual ratings of brain disease which have been previously collected as part of the CHS. ALP required minimal operator intervention (input of brain images and verification of misalignments) and employed computer time of about 1 h per brain. ALP detected significant focal volumetric differences in the limbic system (p values between groups for hippocampus and parahippocampus: 0.002 and 0.005, respectively), temporal lobe (p < 0.0001) and caudate (p = 0.009), but not in other brain areas (e.g. occipital lobe, visual or motor cortex). Furthermore, ALP measures of medial temporal lobe atrophy strongly correlated with CHS visual ratings of ventricular enlargement (r(2) = 0.6, p = 0.002 for medial temporal lobe). In conclusion, ALP-detected focal brain atrophy was strongly associated with dementia. Because of its fully automated design, ALP technique is an ideal candidate to assess whether volumetric measures of specific areas can discriminate dementia better than currently available measures of global brain atrophy in large epidemiological studies.

The effect of encoding strategies on medial temporal lobe activations during the recognition of words: an event-related fMRI study

It is known that manipulation of the encoding strategy affects behavioral and activation data during later retrieval. In the present fMRI study, we examined brain activity during the recognition of words encoded using three different strategies formed by the combination of two factors of relational and self-performed processes. The first encoding strategy involved subjects learning words using both relational and self-performed processes (R+S+). In the second, subjects learned words using only a relational process (R+S-). In the third, subjects learned words without using either process (R-S-). During fMRI after encoding, subjects were randomly presented with words encoded previously and with new words (New) and were required to judge whether or not the word presented had been previously encoded. The fMRI experiment was performed with the event-related design. Compared to New, activation of the left medial temporal lobe (MTL) occurred during the recognition of words encoded using R+S+ and R+S-, whereas right MTL activations only occurred with the R+S+ strategy. ROI analysis for the bilateral hippocampus and parahippocampal gyrus showed a linear increase in left MTL activity (hippocampus and parahippocampal gyrus) during the recognition of words encoded with the R-S-, R+S-, to R+S+, whereas right MTL activity (parahippocampal gyrus) was only increased with the R+S+ strategy. The findings suggest that the left and right MTL structures may contribute differentially to the processes involved in the recognition of stimuli and that these differential activities may depend on the encoding strategies formed by the two factors of relational and self-performed processes.

The appreciation of wine by sommeliers: a functional magnetic resonance study of sensory integration

We set out to investigate how the expertise of a sommelier is embodied in neural circuitry by comparing brain activity elicited by wine tasting with that found in naive drinkers of wine. We used fMRI to study 7 sommeliers and 7 age- and sex-matched control subjects to test the hypothesis that any difference in brain activity would reflect a learned ability to integrate information from gustatory and olfactory senses with past experience. A group analysis showed activation of a cerebral network involving the left insula and adjoining orbito-frontal cortex in sommeliers. Both these areas have been implicated in gustatory/olfactory integration in primates. In addition, activation was found bilaterally in the dorsolateral prefrontal cortex, which is implicated in high-level cognitive processes such as working memory and selection of behavioral strategies. Naive individuals activated the primary gustatory cortex and brain areas, including the amygdala, implicated in emotional processing.

Event-related functional magnetic resonance imaging investigation of executive control in very old individuals with mild cognitive impairment

BACKGROUND

Attentional control of executive cognitive function (ECF) decreases in older individuals with Alzheimer Disease (AD). In order to examine early AD-related changes in the neural substrates of ECF attentional control, we measured activation dorsolateral prefrontal (dLPFC), posterior parietal (PPC), and anterior cingulate cortex (ACC) in adults with mild cognitively impairment (MCI) and in cognitively normal (CN) adults.

METHODS

Functional magnetic resonance imaging analysis of brain activation in MCI (n = 8, mean age 79.5) and CN (n = 8 mean age 81.5) during increasing loads of attentional demands.

RESULTS

MCI and CN older adults performed with similar accuracy and reaction time. MCI had greater activation than CN in PPC (right p = .03 and left p = .05) and dlPFC areas (right p = .002 and left p = .004), while activation in ACC was similar in the two groups. Response to increasing loads of the task differed by group: MCI selectively engaged bilateral PPC (right p = .03, left p = .04), while CN subjects increased bilateral dlPFC activation (right p = .005 and left p = .02) and ACC activation (p = .04). Among MCI, greater load-related changes in PPC activity were associated with smaller load-related changes in accuracy rates (r = -.85, p = .07) and greater increases in reaction times (r = .97, p = .01). In CN subjects, load-related change in PPC activation was associated with load-related change in reaction time (r = .76, p = .02) but not with changes in accuracy rates.

CONCLUSIONS

PPC and dlPFC may show early functional changes associated with MCI.

Summarizing complexity in high dimensions

High-dimensional, multispectral data on complex physical systems are increasingly common. As the amount of information in data sets increases, the difficulty of effectively utilizing it also increases. For such data, summary information is required for understanding and modeling the underlying dynamics. It is here proposed to use an extension of computational mechanics [C. R. Shalizi and J. P. Crutchfield, J. Stat. Phys. 104, 817 (2001)] to arbitrary spatiotemporal and spectral dimension, for providing such summary information. An example of the use of these tools to identify state evolution in the brain, an archetypal, complex biophysical system, serves as an illustration.

NEURAL SYNCHRONY AND GRAY MATTER VARIATION IN HUMAN MALES AND FEMALES: AN INTEGRATION OF 40 HZ GAMMA SYNCHRONY AND MRI MEASURES

Coherent cognition requires activity to be brought together across diverse brain networks. Synchronous, in-phase oscillations in the high-frequency (40 Hz) Gamma range are thought to be one mechanism underlying the functional integration of brain networks. While sex differences have been observed across a range of cognitive functions, their role in normal cortical synchronization has not been elucidated. We recorded Gamma phase synchrony in 500 male and 500 female subjects during an auditory oddball task, which taps discrimination of task-relevant signals. Results revealed a marked sex-linked dissociation in the spatio-temporal pattern of cortical synchronization. Females showed increased Gamma synchrony in the frontal brain, while males showed enhanced synchrony in the parieto-occipital region. These differences were not accounted for by sex differences in whole brain MRI volume. However, there were positive associations between Gamma synchrony and gray matter for females, while these relationships were negative for males. Sex differences in the profile of cortical synchronization may reflect distinct aspects of evolutionary advantage.

Differential time courses and specificity of amygdala activity in posttraumatic stress disorder subjects and normal control subjects

BACKGROUND

Previous neuroimaging studies have demonstrated exaggerated amygdala responses to negative stimuli in posttraumatic stress disorder (PTSD). The time course of this amygdala response is largely unstudied and is relevant to questions of habituation and sensitization in PTSD exposure therapy.

METHODS

We applied blood oxygen level dependent functional magnetic resonance imaging and statistical parametric mapping to study amygdala responses to trauma-related and nontrauma-related emotional words in sexual/physical abuse PTSD and normal control subjects. We examined the time course of this response by separate analysis of early and late epochs.

RESULTS

PTSD versus normal control subjects have a relatively increased initial amygdala response to trauma-related negative, but not nontrauma-related negative, versus neutral stimuli. Patients also fail to show the normal patterns of sensitization and habituation to different categories of negative stimuli. These findings correlate with measured PTSD symptom severity.

CONCLUSIONS

Our results demonstrate differential time courses and specificity of amygdala response to emotional and control stimuli in PTSD and normal control subjects. This has implications for pathophysiologic models of PTSD and treatment response. The results also extend previous neuroimaging studies demonstrating relatively increased amygdala response in PTSD and expand these results to a largely female patient population probed with emotionally valenced words.

Lithium and valproate attenuate dextroamphetamine-induced changes in brain activation

BACKGROUND

Previous studies have suggested that both lithium and valproate may decrease phosphoinositol second messenger system (PI-cycle) activity. There is also evidence that dextroamphetamine may increase PI cycle activity. It was previously demonstrated that dextroamphetamine administration in volunteers causes a region and task dependent decrease in brain activation in healthy volunteers. The current study assessed the effect of 14 days pretreatment with lithium and valproate on these dextroamphetamine-induced changes in regional brain activity in healthy volunteers.

METHODS

This was a double-blind, placebo-controlled, study in which volunteers received either 1000 mg sodium valproate (n = 12), 900 mg lithium (n = 9) or placebo (n = 12). Functional images were acquired using functional magnetic resonance imaging (fMRI) while subjects performed three cognitive tasks, a word generation paradigm, a spatial attention task and a working memory task. fMRI was carried out both before and after administration of dextroamphetamine (25 mg). Changes in the number of activated pixels and changes in the magnitude of the blood-oxygen-level-dependent (BOLD) signal after dextroamphetamine administration were then determined.

RESULTS

In keeping with previous findings dextroamphetamine administration decreased regional brain activation in all three tasks. Pretreatment with lithium attenuated changes in the word generation paradigm and the spatial attention task, while pretreatment with valproate attenuated the changes in the working memory task.

CONCLUSIONS

These results suggest that both lithium and valproate can significantly attenuate dextroamphetamine-induced changes in brain activity in a task dependent and region specific manner. This is the first human evidence to suggest that both lithium and valproate may have a similar effect on regional brain activation, conceivably via similar effects on PI-cycle activity.

Sign and speech: amodal commonality in left hemisphere dominance for comprehension of sentences

The neural basis of functional lateralization in language processing is a fundamental issue in systems neuroscience. We used functional MRI (fMRI) to examine hemispheric dominance during the processing of signed and spoken sentences. By using tasks involving comprehension of sentences (Sc) and sentential non-word detection (Sn), we compared different groups and stimulus conditions. Under the sign condition with sentence stimuli in Japanese Sign Language (JSL), we tested two groups of subjects: Deaf signers (Deaf) of JSL, and hearing bilinguals (children of Deaf adults, CODA) of JSL and Japanese (JPN). Under the speech condition, we tested hearing monolinguals (Mono) of JPN with auditory JPN stimuli alone (AUD), or with an audiovisual presentation of JPN and JSL stimuli (A&V). We found that the overall bilateral activation patterns under the four experimental conditions of Deaf, CODA, AUD and A&V were almost identical, despite differences in stimuli (JSL and JPN) and groups (Deaf, CODA and Mono). Moreover, consistently left-dominant activations involving frontal and temporo-parietal regions were observed across all four conditions. Furthermore, irrespective of the modalities of sign and speech, the main effects of task (Sc-Sn) were found primarily in the left regions: the ventral part of the inferior frontal gyrus (F3t/F3O), the precentral sulcus, the superior frontal gyrus, the middle temporal gyrus, the angular gyrus and the inferior parietal gyrus. Among these regions, only the left F3t/F3O showed no main effects of modality condition. These results demonstrate amodal commonality in the functional dominance of the left cortical regions for comprehension of sentences, as well as the essential and universal role of the left F3t/F3O in processing linguistic information from both signed and spoken sentences.

Working memory and FDG–PET dissociate early and late onset Alzheimer disease patients

The aims of this study were to determine the influence of the onset of Alzheimer's disease (AD) on 1) memory and cerebral glucose metabolism, 2) the relationships between cognitive performance and cerebral glucose metabolism. Brain metabolism was measured by 18FDG-PET in 12 early onset AD patients (age < 65 years) and 26 late onset ones (> 65), with comparable mean MMSE scores. Working memory, semantic memory and episodic memory were assessed. Cognitivo-metabolic correlations (CMC) and complementary interregional correlations were performed in order to identify specific neurocognitive processes within each group. Both AD groups performed poorly on all tasks, except digit span in the late onset group. The early onset group performed more poorly than the late onset one on both the digit span and Brown-Peterson Paradigm (BPP) tasks. Temporo-parietal hypometabolism was found in both groups, the left hemisphere being more affected than the right, especially in the early onset patients, who also showed specific left frontal hypometabolism. For the BPP task, the CMC principally involved left frontal areas in the early onset group, and the cerebellum in the late onset one. For the digit span task, they involved cerebellar and occipital regions in the latter. Regarding the digit span, the occipital and cerebellar involvement may have reflected an effective compensatory mechanism in the late onset patients, while high left supramarginal gyrus hypometabolism in the early onset patients may have explained their failure in this task. In the BPP task, the lower performance of the early onset group may have been due to a frontal lobe dysfunction, as suggested by 1) the hypometabolism of this region, 2) the CMC results, 3) the interregional correlations, which indicated greater disruption of the antero- posterior loop.

Cortical Control of Visually Guided Reaching: Evidence from Patients with Optic Ataxia

The dorsal stream of visual information processing connecting V1 to the parietal cortex is thought to provide a fast control of visually guided reaching. Important for this assumption was the observation that in both the monkey and the human, parietal lesions may provoke disturbance of visually goal-directed hand movements. In the human, severe misreaching termed 'optic ataxia' has been ascribed to lesions of the superior parietal lobule (SPL) and/or the intraparietal sulcus. Using new tools for lesion analysis, here we re-evaluated this view investigating the typical lesion location in a large group of unilateral stroke patients with optic ataxia, collected over a time period of 15 years. We found no evidence for the assumption that disruption of visually guided reaching in humans is associated with a lesion typically centering on the SPL on the convexity. In both left and right hemispheres, we found optic ataxia associated with a lesion overlap that affected the lateral cortical convexity at the occipito-parietal junction, i.e. the junction between the inferior parietal lobule (IPL) and superior occipital cortex and--in the left hemisphere even more posteriorly--also the junction between occipital cortex and the SPL. Via the underlying parietal white matter, the lesion overlap extended in both hemispheres to the medial cortical aspect, where it affected the precuneus close to the occipito-parietal junction. These lateral and medial structures seem to be integral to the fast control of visually guided reaching in humans.

An evaluation of the use of passive shimming to improve frontal sensitivity in fMRI

The presence of the head in an MRI scanner leads to inhomogeneities in the magnetic field. These cause the 'susceptibility artifacts' of image distortion and signal dropout. In this paper, we evaluate a technique called passive shimming, which has the potential to reduce field inhomogeneities and the resultant artifacts. A piece of a magnetically active material (pyrolytic graphite) is held on the roof of the participant's mouth by a plastic mouth mould. We evaluate the effects in several different ways. We show that the presence of a shim reduces field inhomogeneity across much of the brain. From field maps, we generate simulations of EPI image intensity and BOLD sensitivity. Both of these are mainly improved by the presence of shim, although there were small reductions in some regions. Measured EPI image intensity also mostly increased. Finally, we ran a reward-punishment task in our subjects, and found that the presence of a shim increased functional sensitivity in the orbitofrontal cortex. Using the BOLD sensitivity measure, we provide estimates of the improvement to be expected in functional studies for a range of neural structures. Passive shims are quick to make and reasonably comfortable to wear, and have substantial potential for researchers investigating inferior frontal brain regions using MRI.

Attentional functions of parietal and frontal cortex

A model of normal attentional function, based on the concept of competitive parallel processing, is used to compare attentional deficits following parietal and frontal lobe lesions. Measurements are obtained for visual processing speed, capacity of visual short-term memory (VSTM), spatial bias (bias to left or right hemifield) and top-down control (selective attention based on task relevance). The results show important differences, but also surprising similarities, in parietal and frontal lobe patients. For processing speed and VSTM, deficits are selectively associated with parietal lesions, in particular lesions of the temporoparietal junction. We discuss explanations based on either grey matter or white matter lesions. In striking contrast, measures of attentional weighting (spatial bias and top-down control) are predicted by simple lesion volume. We suggest that attentional weights reflect competition between broadly distributed object representations. Parietal and frontal mechanisms work together, both in weighting by location and weighting by task context.

Visually cued motor synchronization: modulation of fMRI activation patterns by baseline condition

A well-known issue in functional neuroimaging studies, regarding motor synchronization, is to design suitable control tasks able to discriminate between the brain structures involved in primary time-keeper functions and those related to other processes such as attentional effort. The aim of this work was to investigate how the predictability of stimulus onsets in the baseline condition modulates the activity in brain structures related to processes involved in time-keeper functions during the performance of a visually cued motor synchronization task (VM). The rational behind this choice derives from the notion that using different stimulus predictability can vary the subject's attention and the consequently neural activity. For this purpose, baseline levels of BOLD activity were obtained from 12 subjects during a conventional-baseline condition: maintained fixation of the visual rhythmic stimuli presented in the VM task, and a random-baseline condition: maintained fixation of visual stimuli occurring randomly. fMRI analysis demonstrated that while brain areas with a documented role in basic time processing are detected independent of the baseline condition (right cerebellum, bilateral putamen, left thalamus, left superior temporal gyrus, left sensorimotor cortex, left dorsal premotor cortex and supplementary motor area), the ventral premotor cortex, caudate nucleus, insula and inferior frontal gyrus exhibited a baseline-dependent activation. We conclude that maintained fixation of unpredictable visual stimuli can be employed in order to reduce or eliminate neural activity related to attentional components present in the synchronization task.

Brain activity underlying emotional valence and arousal: a response-related fMRI study

Emotional behavior is organized along two psychophysiologic dimensions: (1) valence, varying from negative to positive, and (2) arousal, varying from low to high. Behavioral responses along these dimensions are assumed to be mediated by different brain circuits. We recorded startle reflex modulation and skin conductance responses in healthy volunteers during functional magnetic resonance imaging (fMRI) while they viewed a set of emotional pictures and took verbal ratings of the emotional valence and arousal of each picture after scanning. Response-related multiple correlation analysis revealed differential brain activity in five brain regions. Startle reflex changes, associated with the valence of a stimulus, correlated with activity in the amygdala, while verbal reports of negative emotional valence varied with insular activity. Peripheral physiologic and verbal responses along the arousal dimension varied with thalamic and frontomedial activity. Peripheral physiologic responses along both dimensions correlated with activity in somatosensory association areas in the anterior parietal cortex. In the valence dimension, activity in the left anterior parietal cortex was associated with highly correlating peripheral physiologic and verbal responses, suggesting that verbal reports of emotional valence might depend partly on brain circuits representing peripheral physiologic changes. Our data provide direct evidence for a functional segregation of brain structures underlying peripheral physiologic responses and verbal ratings along the emotional dimensions of valence and arousal.

Neurophysiological Architecture of Functional Magnetic Resonance Images of Human Brain

We investigated large-scale systems organization of the whole human brain using functional magnetic resonance imaging (fMRI) data acquired from healthy volunteers in a no-task or 'resting' state. Images were parcellated using a prior anatomical template, yielding regional mean time series for each of 90 regions (major cortical gyri and subcortical nuclei) in each subject. Significant pairwise functional connections, defined by the group mean inter-regional partial correlation matrix, were mostly either local and intrahemispheric or symmetrically interhemispheric. Low-frequency components in the time series subtended stronger inter-regional correlations than high-frequency components. Intrahemispheric connectivity was generally related to anatomical distance by an inverse square law; many symmetrical interhemispheric connections were stronger than predicted by the anatomical distance between bilaterally homologous regions. Strong interhemispheric connectivity was notably absent in data acquired from a single patient, minimally conscious following a brainstem lesion. Multivariate analysis by hierarchical clustering and multidimensional scaling consistently defined six major systems in healthy volunteers-- corresponding approximately to four neocortical lobes, medial temporal lobe and subcortical nuclei- - that could be further decomposed into anatomically and functionally plausible subsystems, e.g. dorsal and ventral divisions of occipital cortex. An undirected graph derived by thresholding the healthy group mean partial correlation matrix demonstrated local clustering or cliquishness of connectivity and short mean path length compatible with prior data on small world characteristics of non-human cortical anatomy. Functional MRI demonstrates a neurophysiological architecture of the normal human brain that is anatomically sensible, strongly symmetrical, disrupted by acute brain injury, subtended predominantly by low frequencies and consistent with a small world network topology.

Cerebral Haemodynamic Disturbances in Patients with Moderate Carotid Artery Stenosis

OBJECTIVE

Dynamic MR perfusion imaging can detect cerebral perfusion deficits resulting from severe internal carotid artery (ICA) stenosis. It is unknown, however, whether moderate ICA stenosis (50-69%) also causes haemodynamic disturbance. We investigated whether cerebral perfusion deficits were detectable in patients with moderate ICA stenosis.

METHODS

Eighteen patients underwent T2* weighted cerebral MR perfusion imaging with a gadolinium based contrast agent. Differences in mean time to peak (mTTP) and relative cerebral blood volume (rCBV) between cerebral hemispheres were calculated for middle cerebral artery territory regions by a reader blinded to the angiographic and clinical findings.

RESULTS

There were significant differences in mTTP between cerebral hemispheres in 15 patients with a mean inter-hemispheric delay in mTTP of 0.49 s (95% confidence intervals, 0.25 and 0.72 s) which was statistically significant ( p <0.001). In 1 patient with bilateral moderate stenosis there was no difference in mTTP.

CONCLUSIONS

Moderate ICA stenosis results in significant ipsilateral cerebral perfusion delays detectable by dynamic susceptibility MRI. Follow-up studies might reveal whether these delays improve following carotid endarterectomy.

Is there a functional neural correlate of individual differences in cardiovascular reactivity?

OBJECTIVE

The present study tested whether individuals who differ in the magnitude of their blood pressure reactions to a behavioral stressor also differ in their stressor-induced patterns of functional neural activation.

METHODS

Sixteen participants (7 men, 9 women aged 47 to 72 years) were classified as high (n = 8) or low (n = 8) blood pressure reactors by the magnitude and temporal consistency of their systolic blood pressure (SBP) reaction to a Stroop color-word interference stressor. Both high and low SBP reactors completed this Stroop stressor while their task-related changes in blood pressure and functional neural activity were assessed in a blocked functional magnetic resonance imaging design.

RESULTS

In both high and low SBP reactors, the Stroop-stressor engaged the anterior cingulate, orbitofrontal, insular, posterior parietal, and the dorsolateral prefrontal regions of the cortex, the thalamus, and the cerebellum. Compared with low reactors, however, high reactors not only showed a larger magnitude increase in SBP to the Stroop stressor, but also an increased activation of the posterior cingulate cortex.

CONCLUSION

A behavioral stressor that is used widely in cardiovascular reactivity research, the Stroop stressor, engages brain systems that are thought to support both stressor processing and cardiovascular reactivity. Increased activation of the posterior cingulate, a brain region implicated in vigilance to the environment and evaluative emotional processes, may be a functional neural correlate of an individual's tendency to show large-magnitude (exaggerated) blood pressure reactions to behavioral stressors.

A direct brainstem–amygdala–cortical ‘alarm’ system for subliminal signals of fear

We examined whether consciously undetected fear signals engage a collateral brainstem pathway to the amygdala and prefrontal cortex in the intact human brain, using functional neuroimaging. 'Blindsight' lesion patients can respond to visual fear signals independently from conscious experience, suggesting that these signals reach the amygdala via a direct pathway that bypasses the primary visual cortex. Electrophysiological evidence points to concomitant involvement of prefrontal regions in automatic orienting to subliminal signals of fear, which may reflect innervation arising from brainstem arousal systems. To approximate blindsight in 22 healthy subjects, facial signals of fear were presented briefly (16.7 ms) and masked such that conscious detection was prevented. Results revealed that subliminal fear signals elicited activity in the brainstem region encompassing the superior colliculus and locus coeruleus, pulvinar and amygdala, and in fronto-temporal regions associated with orienting. These findings suggest that crude sensory input from the superior colliculo-pulvinar visual pathway to the amygdala may allow for sufficient appraisal of fear signals to innervate the locus coeruleus. The engagement of the locus coeruleus could explain the observation of diffuse fronto-temporal cortical activity, given its role in evoking collateral ascending noradrenergic efferents to the subcortical amygdala and prefrontal cortex. This network may represent an evolutionary adaptive neural 'alarm' system for rapid alerting to sources of threat, without the need for conscious appraisal.

Evaluating fMRI methods for assessing hemispheric language dominance in healthy subjects

We evaluated two methods for quantifying the hemispheric language dominance in healthy subjects, by using a rhyme detection (deciding whether couple of words rhyme) and a word fluency (generating words starting with a given letter) task. One of methods called "flip method" (FM) was based on the direct statistical comparison between hemispheres' activity. The second one, the classical lateralization indices method (LIM), was based on calculating lateralization indices by taking into account the number of activated pixels within hemispheres. The main difference between methods is the statistical assessment of the inter-hemispheric difference: while FM shows if the difference between hemispheres' activity is statistically significant, LIM shows only that if there is a difference between hemispheres. The robustness of LIM and FM was assessed by calculating correlation coefficients between LIs obtained with each of these methods and manual lateralization indices MLI obtained with Edinburgh inventory. Our results showed significant correlation between LIs provided by each method and the MIL, suggesting that both methods are robust for quantifying hemispheric dominance for language in healthy subjects. In the present study we also evaluated the effect of spatial normalization, smoothing and "clustering" (NSC) on the intra-hemispheric location of activated regions and inter-hemispheric asymmetry of the activation. Our results have shown that NSC did not affect the hemispheric specialization but increased the value of the inter-hemispheric difference.

No epsilon4 gene dose effect on hippocampal atrophy in a large MRI database of healthy elderly subjects

The effect of ApoE genotype on grey matter (GM) atrophy was studied on a cohort of 750 healthy elderly volunteers (age range 63-75 years). High-resolution T1-weighted MR images were processed using both voxel-based morphometry and region of interest analysis for hippocampal volume estimation. Significant decrease of grey matter in epsilon(4) homozygous subjects (n = 12), as compared both to epsilon(4) heterozygous subjects (n = 175) and to noncarrier (n = 563) subjects, was found bilaterally in the medial temporal lobe, including the hippocampus, and extending over the superior temporal gyrus. By contrast, no significant difference was observed between epsilon(4) heterozygous subjects and noncarriers at the level of the medial temporal lobe. Follow-up of the cohort cognitive performances over 4 years after their MRI exam revealed that, as compared to noncarrier subjects, the relative risk of cognitive impairment was 5.9 for epsilon(4) homozygous subjects (P = 0.03), while it was not different from 1 for epsilon(4) heterozygous subjects (P = 0.92). These findings indicate that, in the age range of this cohort, ApoE-4 effects on cortical atrophy and cognitive performances of healthy elderly are limited to epsilon(4) homozygous subjects.

Processing of a simple aversive conditioned stimulus in a divided visual field paradigm: an fMRI study

A left visual hemifield advantage for the processing of negative facial expressions has been demonstrated in a variety of studies. We tested whether the same effect is found for a neutral facial expression that had acquired a negative meaning through pairing with an aversive event. Startle reflex amplitudes, skin-conductance responses (SCR), and two verbal measures of affect (negative valence and arousal) were significantly increased after pairing, but no stimulation side by pairing interaction was observed. Functional magnetic resonance imaging (fMRI) revealed a significant increase of BOLD (blood oxygen level dependent) activity in the medial prefrontal cortex (MPFC), and the right frontal opercular region (RFOP). MPFC activity was correlated with psychophysiological and verbal emotional responses across subjects and, like these responses, was independent of the stimulation side. In contrast, RFOP activity was significantly stronger during left than during right hemifield stimulation but did not correlate with psychophysiological or verbal measures of negative affect. These results suggest that emotional responses to an aversive conditioned expressively neutral face are similar in both visual hemifields. MPFC activity seems to be closely linked to the strength of these responses.

Hippocampal gray matter reduction associates with memory deficits in adolescents with history of prematurity

Using optimized voxel-based morphometry (VBM), we compared the relationship between hippocampal and thalamic gray matter loss and memory impairment in 22 adolescents with history of prematurity (HP) and 22 normal controls. We observed significant differences between groups in verbal learning and verbal recognition, but not in visual memory. VBM analysis showed significant left hippocampal and bilateral thalamic reductions in HP subjects. Using stereological methods, we also observed a reduction in hippocampal volume, with left posterior predominance. We found correlations between left hippocampal gray matter reductions (assessed by VBM) and verbal memory (learning and percentage of memory loss) in the premature group. The stereological analysis showed a correlation between verbal learning and the left posterior hippocampus. Our results suggest that left hippocampal tissue loss may be responsible for memory impairment and is probably related to the learning disabilities that HP subjects present during schooling.

Reference Frames for Spatial Cognition: Different Brain Areas are Involved in Viewer-, Object-, and Landmark-Centered Judgments About Object Location

Functional magnetic resonance imaging was used to compare the neural correlates of three different types of spatial coding, which are implicated in crucial cognitive functions of our everyday life, such as visuomotor coordination and orientation in topographical space. By manipulating the requested spatial reference during a task of relative distance estimation, we directly compared viewer-centered, object-centered, and landmark-centered spatial coding of the same realistic 3-D information. Common activation was found in bilateral parietal, occipital, and right frontal premotor regions.

The retrosplenial and ventromedial occipital–temporal cortex (and parts of the parietal and occipital cortex) were significantly more activated during the landmark-centered condition. The ventrolateral occipital–temporal cortex was particularly involved in object-centered coding. Results strongly demonstrate that viewer-centered (egocentric) coding is restricted to the dorsal stream and connected frontal regions, whereas a coding centered on external references requires both dorsal and ventral regions, depending on the reference being a movable object or a landmark.

Functional MRI during sleep: BOLD signal decreases and their electrophysiological correlates

Prominent local decreases in blood oxygenation level (BOLD) can be observed by functional magnetic resonance imaging (fMRI) upon acoustic stimulation during sleep. The goal of this study was to further characterize this BOLD signal decrease with respect to corresponding neurophysiological phenomena using a simultaneous electroencephalography (EEG)/fMRI approach in sleeping human subjects. Healthy volunteers were subjected to acoustic stimulation during non-rapid eye movement (NREM) sleep. On the basis of statistical parametric maps, the correlations between the fMRI response (both amplitude and extent of the BOLD response) and the concomittant changes in the EEG (delta power and K-complexes) were calculated. Amplitude and extent of the stimulus-induced negative BOLD effect correlated positively with measures of EEG synchronization, namely an increase in the number of K-complexes and EEG delta power. Stimulus-induced BOLD decreases were most prominent during light (stage 2) NREM sleep and disappeared during slow wave sleep, indicating an influence of the baseline degree of hyperpolarization. Our observations provide first evidence that 'negative' BOLD signal changes during human sleep are associated with electrophysiological indicators of altered neuronal activity. Increased number of K-complexes and delta power reflecting hyperpolarization suggests true cortical deactivation upon stimulus presentation. This sleep stage-dependent deactivation might serve to protect the brain from arousing stimuli, particularly during the light phases of sleep shortly after sleep onset.

Standardized whole brain mapping of tubers and subependymal nodules in tuberous sclerosis complex

Tuberous sclerosis complex is associated with radiologically visible abnormalities of brain structure, principally tubers and subependymal nodules. We reviewed the literature on neuroimaging of tubers and subependymal nodules and found qualitative evidence of bilateral, predominantly frontal distribution of tubers and bilateral, predominantly subcortical distribution of subependymal nodules in prior studies of pediatric samples. We studied 25 high-functioning adults with tuberous sclerosis complex and normal IQ, acquiring both dual spin-echo and fluid-attenuated inversion recovery magnetic resonance imaging sequences to optimize radiologic diagnosis of tubers and nodules. Individual lesion maps were then coregistered in a standard stereotactic space to facilitate construction of lesion density maps and estimation of lesion density in cortical and subcortical regions reliably defined by a parcellated template image. We found the highest frequency of tubers in frontal lobes and the highest density of tubers in parietal regions. There was significant regional variation in tuber density but no significant lateralization of frequently bilateral tubers. Nodules were located predominantly in the caudate nucleus and were not significantly lateralized. Tuber and nodule volumes were significantly positively correlated. Tuber volume was larger, on average, in patients with a lifetime history of epilepsy, but there was no correlation between IQ and these measures of lesion load. Contemporary image processing tools can be used to enhance quantitative, whole brain analysis of lesion load in patients with tuberous sclerosis complex.

Dextroamphetamine causes a change in regional brain activity in vivo during cognitive tasks: a functional magnetic resonance imaging study of blood oxygen level-dependent response

BACKGROUND

Dextroamphetamine is known to have profound effects on both subjective and physiologic measurements, but it is unclear to what extent these behavioral changes are a direct result of altered regional brain activation. One method to measure this is to use functional magnetic resonance imaging (fMRI).

METHODS

In the present study, fMRI was used to measure both the spatial extent of changes (the number of pixels activated) and the magnitude of the blood oxygen level-dependent (BOLD) response. We examined the effects of motor, verbal, memory, and spatial attention task during fMRI in 18 healthy volunteers. Functional MRI measurements were obtained at baseline and again 75 min after an oral dose of 25 mg dextroamphetamine.

RESULTS

Dextroamphetamine caused a decrease in the number of activated pixels and the magnitude of the BOLD response during the three cognitive tasks tested but not during the motor task. These changes were region and task specific.

CONCLUSIONS

This is the first study to examine the effect of dextroamphetamine on the number of activated pixels and the BOLD response during the performance of a range of cognitive and motor tasks. Our results suggest that dextroamphetamine causes measurable decreases in brain activity in a variety of regions during cognitive tasks. These changes might be linked to behavioral changes observed after dextroamphetamine administration and could possibly be mediated by alterations in dopaminergic activation.

The BOLD hemodynamic response in healthy aging

Several previous studies have compared the blood oxygen level-dependent (BOLD) hemodynamic response (HDR) in healthy elderly subjects to the HDR in young subjects. Some studies have found a relative decreased amplitude in the elderly in the visual cortex, whereas other studies have found the elderly HDR amplitude in the visual cortex to be nearly identical to that in young subjects. A possible explanation for the different findings is that the peak voxel HDR is similar between the groups, but that the HDR in the group-averaged region-of-interest (ROI) is "washed out" by the inclusion of less significant voxels (due to a smaller extent of activation in the elderly) or by the inclusion of negative-peaking voxels. We tested this hypothesis using event-related functional magnetic resonance imaging (fMRI ). While undergoing fMRI, subjects performed a simple visual and motor task, pressing with their index fingers in response to visual presentation of the word tap. Data from 18 subjects, 8 young and 10 elderly, were analyzed. For each subject, a visual and a motor ROI was selected by choosing the most significant positive voxels within the anatomically defined ROI. This individual subject approach excluded both low-significance and negative-peaking voxels. Similar peaks were found for the elderly and the young subjects in both motor and visual regions and a more sustained BOLD response was found for the elderly in both regions. Additionally, as predicted, a greater percentage of voxels with a negative HDR was found for the elderly in the visual region; this finding was also replicated in our reanalysis of an independent fMRI and aging study from the fMRI Data Center. Functional neuroimaging observations of negative HDRs in visual areas have been interpreted as the effect of unconstrained processing during rest. Our results suggest that the elderly may have more unconstrained visual processing during the rest condition in the scanner. The observation that the group differences in the BOLD response are sensitive to voxel selection (e.g., inclusion of low-significance and/or negative voxels) underscores the importance of ROI selection criteria in the interpretation of fMRI studies using elderly populations.

Semiautomatic brain region extraction: a method of parcellating brain regions from structural magnetic resonance images

Structural MR imaging has become essential to the evaluation of regional brain changes in both healthy aging and disease-related processes. Several methods have been developed to measure structure size and regional brain volumes, but many of these methods involve substantial manual tracing and/or landmark identification. We present a new technique, semiautomatic brain region extraction (SABRE), for the rapid and reliable parcellation of cortical and subcortical brain regions. We combine the SABRE parcellation with tissue compartment segmentation [NeuroImage 17 (2002) 1087] to produce measures of gray matter (GM), white matter (WM), ventricular CSF, and sulcal CSF for 26 brain regions. Because SABRE restricts user input to a few easily identified landmarks, inter-rater reliability is high for all volumes, with all coefficients between 0.91 and 0.99. To assess construct validity, we contrasted SABRE-derived volumetric data from healthy young and older adults. Results from the SABRE parcellation and tissue segmentation showed significant differences in multiple brain regions in keeping with regional atrophy described in the literature by researchers using lengthy manual tracing methods. Our findings show that SABRE is a reliable semiautomatic method for assessing regional tissue volumes that provides significant timesavings over purely manual methods, yet maintains information about individual cortical landmarks.

Central type benzodiazepine receptors in Gulf War veterans with posttraumatic stress disorder

BACKGROUND

A previous single photon emission computed tomography study showed decreased central type benzodiazepine receptors in the prefrontal cortex in Vietnam War veterans with posttraumatic stress disorder. To assess the generalizability of this finding to patients with more recent history, we studied central type benzodiazepine receptors in Gulf War veterans with posttraumatic stress disorder.

METHODS

Nineteen Gulf War veterans with posttraumatic stress disorder and 19 age-matched, healthy, nondeployed veterans participated in a single photon emission computed tomography study using [(123)I]iomazenil. Regional total distribution volume (V(T)') was compared between two groups using Statistical Parametric Mapping 99 (Wellcome Department of Imaging Neuroscience, London, United Kingdom) and volumes of interest analysis.

RESULTS

Benzodiazepine receptor levels did not show regional differences between the two groups, either with or without global normalization. Average difference in V(T)' was 2% across brain areas; however, by applying global normalization, V(T)' in the patient group showed significant negative correlation with childhood trauma scores in the right superior temporal gyrus.

CONCLUSIONS

Less severe symptoms and shorter duration of the illness in the current group than the prior one may be the source of the difference in the results of the two studies.